Thermal Stress Research Papers - Academia.edu (original) (raw)

Adhesive bonding technique is used successfully for joining the carbon fibre reinforced plastics to metals or composite structures. A good design of adhesive joint with either simple or more complex geometry requires its stress and... more

Adhesive bonding technique is used successfully for joining the carbon fibre reinforced plastics to metals or composite structures. A good design of adhesive joint with either simple or more complex geometry requires its stress and deformation states to be known for different boundary conditions. In case the adhesive joint is subjected to thermal loads, the thermal and mechanical mismatches of the adhesive and adherends cause thermal stresses. The plate-end conditions may also result in the adhesive joint to undergo large displacements and rotations whereas the adhesive and adherends deform elastically (small strain). In this study, the thermal and geometrically non-linear stress analyses of an adhesively bonded composite tee joint with single support plus an angled reinforcement made of unidirectional CFRPs were carried out using the non-linear finite element method. In the stress analysis, the effects of the large displacements were considered using the small displacement -large displacement theory. The stress states in the plates and the adhesive layer of the tee joint configurations bonded to a rigid base and a composite plate were investigated. An initial uniform temperature distribution was attributed to the adhesive joint for a stress free state, and then variable thermal boundary conditions, i.e. air flows with different velocity and temperature were specified along the outer surfaces of the tee joints. The thermal analysis showed that a non-uniform temperature distribution occurred in the tee joints, and high heat fluxes took place along the free surfaces of the adhesive fillets at the adhesive free ends. Later, the geometrical non-linear thermal-stress analysis of the tee joint was carried out for the final temperature distribution and two edge conditions applied to the edges of the vertical and horizontal plates (HP). High stress concentrations occurred around the rounded adherend corners inside the adhesive fillets at the adhesive free ends, and along the adhesive -composite adherend interfaces due to their thermal -mechanical mismatches. The most critical joint regions were adhesive fillets subjected to high thermal gradients, the middle region of HP, the region of the vertical plate corresponding to the free end of the vertical adhesive layer -left support interface. In addition, the support length had a small effect of reducing the peak stresses at the critical adherend and adhesive locations. q

2-O-␤-Mannosylglycerate, a solute that accumulates in some (hyper)thermophilic organisms, was purified from Pyrococcus furiosus cells, and its effect on enzyme stabilization in vitro was assessed. Enzymes from hyperthermophilic,... more

2-O-␤-Mannosylglycerate, a solute that accumulates in some (hyper)thermophilic organisms, was purified from Pyrococcus furiosus cells, and its effect on enzyme stabilization in vitro was assessed. Enzymes from hyperthermophilic, thermophilic, and mesophilic sources were examined. The thermostabilities of alcohol dehydrogenases from P. furiosus and Bacillus stearothermophilus and of glutamate dehydrogenases from Thermotoga maritima and Clostridium difficile were improved to a significant extent when enzyme solutions were incubated at supraoptimal temperatures in the presence of 2-O-␤-mannosylglycerate, but no effect on the thermostability of glutamate dehydrogenase from P. furiosus was detected. On the other hand, there was a remarkable effect on the thermal stabilities of rabbit muscle lactate dehydrogenase, baker's yeast alcohol dehydrogenase, and bovine liver glutamate dehydrogenase, which were used as model systems to evaluate stabilization of enzymes of mesophilic origin. For all of the enzymes examined and at the highest temperatures tested, 2-O-␤-mannosylglycerate was a better thermoprotectant than trehalose. The stabilizing effect exerted by 2-O-␤-mannosylglycerate on enzymes suggests a role for this compound as a protein thermostabilizer under physiological conditions. 2-O-␤-Mannosylglycerate was also effective in the protection of enzymes against stress imposed by freeze-drying, with its protecting effect being similar to or better than that exerted by trehalose. The data show 2-O-␤-mannosylglycerate to be a potential enzyme stabilizer in biotechnological applications.

The aim of this work was to study, using the finite element method (FEM), the distribution of thermal residual stresses arising in metal-ceramic dental restorations after cooling from the processing temperature. Three different interface... more

The aim of this work was to study, using the finite element method (FEM), the distribution of thermal residual stresses arising in metal-ceramic dental restorations after cooling from the processing temperature. Three different interface configurations were studied: with conventional sharp transition; one with a 50% metal-50% ceramic interlayer; and one with a compositionally functionally gradated material (FGM) interlayer. The FE analysis was performed based on experimental data obtained from Dynamic Mechanical Analysis (DMA) and Dilatometry (DIL) studies of the monolithic materials and metal/ceramic composites. Results have shown significant benefits of using the 50% metal-50% ceramic interlayer and the FGM interlayer over the conventional sharp transition interface configuration in reduction of the thermal residual stress and improvement of stress profiles. Maximum stresses magnitudes were reduced by 10% for the crowns with 50% metal-50% ceramic interlayer and by 20% with FGM int...

Thermal preconditioning protocols for cardiac cells were identified which produce elevated HSP70 levels while maintaining high cell viability. Bovine aortic endothelial cells were heated with a water bath at temperatures ranging from 44... more

Thermal preconditioning protocols for cardiac cells were identified which produce elevated HSP70 levels while maintaining high cell viability. Bovine aortic endothelial cells were heated with a water bath at temperatures ranging from 44 to 50°C for periods of 1 -30 min. Thermal stimulation protocols were determined which induce HSP70 expression levels ranging from 2.3 to 3.6 times the control while maintaining cell viabilities greater than 90%. An Arrhenius injury model fit to the cell damage data yielded values of A = 1.4ϫ 10 66 s −1 and E a = 4.1ϫ 10 5 J / mol. Knowledge of the injury parameters and HSP70 kinetics will enhance dosimetry guideline development for thermal stimulation of heat shock proteins expression in cardiac tissue.

The fundamentals of the theory of consolidation and thermoelasticity are recast into the formulation of a phenomenon called thermohydroelasticity. Subsequently, a variational principle and Galerkin formulation are combined with the finite... more

The fundamentals of the theory of consolidation and thermoelasticity are recast into the formulation of a phenomenon called thermohydroelasticity. Subsequently, a variational principle and Galerkin formulation are combined with the finite element method to develop a new technique to investigate coupled thermal-hydraulic-mechanical behavior of liquid-saturated, fractured porous rocks. A code-to-code verification of the method is performed. Finally, the environment of a heater emplaced in hard rock is simulated. The effects of the coupled thermal stresses in the fractured rock are evident from the dramatic reduction of permeability due to the deformation of the fractures. These results can improve the understanding of observations and displacement measurements made in the in situ experiments at the Stripa mine in Sweden.

A comparison was made between thermal stresses occurring in radiant tubes used in regenerative and recuperative systems. It was found that higher temperatures close to the annealing temperatures lead to stress relieving. The only stresses... more

A comparison was made between thermal stresses occurring in radiant tubes used in regenerative and recuperative systems. It was found that higher temperatures close to the annealing temperatures lead to stress relieving. The only stresses occurring were due to the non-linear axial temperature gradients along the length of the radiant tube in a recuperative system, whereas the radiant tube in a regenerative system remained essentially stress free due to a comparatively linear axial temperature gradient.

The present study demonstrates the comparative thermal, conformational and kinetic stabilities of the three closely related enzymes; the mesophilic yeast alcohol dehydrogenase (YADH), horse liver alcohol dehydrogenase (HLADH), and the... more

The present study demonstrates the comparative thermal, conformational and kinetic stabilities of the three closely related enzymes; the mesophilic yeast alcohol dehydrogenase (YADH), horse liver alcohol dehydrogenase (HLADH), and the extreme-thermophilic Thermoanaerobacter brockii alcohol dehydrogenase (TBADH). The mid-point unfolding temperatures for TBADH and HLADH were at least 10 • C and 6 • C higher, respectively, than that of YADH. When YADH was completely inactivated by thermal stress, the residual activities of HLADH and TBADH were 70% and 100%, respectively. The optimum temperature (T opt ) activities of HLADH and TBADH were at least 40 • C and 55 • C higher, respectively, than that of YADH. Due to the higher rigidity of HLADH and TBADH, the enzymatic activation energies of HLADH and TBADH were higher than that of YADH. Geometric X-ray analysis indicated a comparatively higher coil (turn and loop) percentage in TBADH and HLADH than in YADH. Pairwise alignment for TBADH/HLADH exhibited a similarity score approximately 2.5-fold greater than that of the TBADH/YADH pair. Multiple alignments made with ClustalW revealed a higher number of conserved proline residues in the two most stable enzymes (HLADH/TBADH). These extra prolines tend to occur in surface loops and are likely to be responsible for the increased stability of TBADH and HLADH, by loop rigidification.

The authors present a predictive model for the negative bias temperature instability (NBTI) of PMOS under both short term and long term operation. On the basis of the reaction-diffusion mechanism, this model accurately captures the... more

The authors present a predictive model for the negative bias temperature instability (NBTI) of PMOS under both short term and long term operation. On the basis of the reaction-diffusion mechanism, this model accurately captures the dependence of NBTI on the oxide thickness (t ox), the diffusing species (H or H 2) and other key transistor and design parameters. In addition, a closed form expression for the threshold voltage change (DV th) under multiple cycle dynamic operation is derived. Model accuracy and efficiency were verified with 180, 130 and 90 nm silicon data. The impact of NBTI on the delay degradation of a ring oscillator and the various metrics of the SRAM such as its data retention voltage, read and hold margins, as well as read and write delay, is also investigated.

Birefringence induced by thermal stress in bow-tie optical fibers is studied in detail by the use of the finite-element method. Results of computer modeling show that a higher degree of birefringence can be obtained with the use of a... more

Birefringence induced by thermal stress in bow-tie optical fibers is studied in detail by the use of the finite-element method. Results of computer modeling show that a higher degree of birefringence can be obtained with the use of a larger cladding and larger stress-applying zones in the fiber.

The thermal degradation of Au/Ni 2 Si/n-SiC ohmic contact was investigated after long-time aging in air at 400 • C or rapid thermal annealing in Ar up to 700 • C. Current-voltage characteristics, sheet resistance measurements, Rutherford... more

The thermal degradation of Au/Ni 2 Si/n-SiC ohmic contact was investigated after long-time aging in air at 400 • C or rapid thermal annealing in Ar up to 700 • C. Current-voltage characteristics, sheet resistance measurements, Rutherford backscattering spectrometry, X-ray diffraction and scanning electron microscopy were used to characterize the contacts before and after heat treatments. Thermal stress at different conditions shows different influence on the properties degradation of Au/Ni 2 Si/n-SiC ohmic contacts. It is shown that aging of the contacts in air at 400 • C resulted in complete degradation due to both oxygen penetration and inter-diffusion/reaction processes at the metal/SiC interface. In contrast, only a small change in contact morphology was detected on the contacts annealed in Ar at 700 • C. * The error of rc determined from the spread of the experimental data over the area of the substrate did not exceed 10%. ** Hs peak-to-valley height measured on the 50 m surface scan length by the TENCOR ␣-Step 200 profiler.

Analyses and evaluation of the life cycle number and crack propagation rate were performed on oxygen-free high-conductivity copper X-ray beamline components based on data available in the literature . Recommendations are made with respect... more

Analyses and evaluation of the life cycle number and crack propagation rate were performed on oxygen-free high-conductivity copper X-ray beamline components based on data available in the literature . Recommendations are made with respect to the safe use of materials in high-heat-load beamline component design . The available literature is critically reviewed for low-cycle fatigue properties at the elevated temperatures typically found in synchrotron operations .

Water temperature plays a key role in determining the persistence of shovelnose sturgeon Scaphirhynchus platorynchus in the wild and is a primary factor affecting growth both in the hatchery and in natural waters. We exposed juvenile... more

Water temperature plays a key role in determining the persistence of shovelnose sturgeon Scaphirhynchus platorynchus in the wild and is a primary factor affecting growth both in the hatchery and in natural waters. We exposed juvenile shovelnose sturgeon to temperatures from 88C to 308C for 87 d to determine the effect of temperature on growth, condition, feed efficiency, and survival. Growth occurred at temperatures from 128C to 308C; the optimal temperature predicted by regression analysis was 22.48C, and the minimum temperature needed for growth was greater than 10.08C. The maximum feed efficiency predicted by regression analysis was 24.5% at 21.78C, and condition factor was highest in the 188C treatment. Mortality was significantly higher at 288C and 308C than at lower temperatures but less than 10% across the thermal regimes tested and 0% at 14-188C. Mortality was observed at and below 128C, suggesting that extended periods of low temperature may deplete energy reserves and lead to higher mortality. Rearing juvenile shovelnose sturgeon at temperatures above 248C reduced the growth rate and feed efficiency and increased mortality. Temperatures in the range 18-208C appeared to maximize the combination of condition, growth, and feed efficiency while not increasing thermal stress. This study corroborates field studies suggesting that altered temperature regimes in the upper Missouri River reduce the growth of shovelnose sturgeon. This information may help protect the thermal habitat critical to the species and guide restoration efforts by delineating temperature regime standards for regulated rivers and those affected by hydroelectric facilities and suggesting new criteria for conservation propagation.

Based on human-biometeorological measurements at two different sites within a street canyon in the city of Freiburg (southwest Germany), the shading influence of the canopy of street trees on human thermal comfort was investigated for a... more

Based on human-biometeorological measurements at two different sites within a street canyon in the city of Freiburg (southwest Germany), the shading influence of the canopy of street trees on human thermal comfort was investigated for a typical Central European summer day ...

All electric equipment in a power system has to be designed to withstand the mechanical and thermal stresses of potential short-circuit currents. Any reduction of these currents can lead to significant cost savings. Among all current... more

All electric equipment in a power system has to be designed to withstand the mechanical and thermal stresses of potential short-circuit currents. Any reduction of these currents can lead to significant cost savings. Among all current limiting devices, superconducting fault current ...

We used the instantaneous growth rate method to determine the effects of food, temperature, krill length, sex, and maturity stage on in situ summer growth of krill across the southwest Atlantic sector of the Southern Ocean. The main aims... more

We used the instantaneous growth rate method to determine the effects of food, temperature, krill length, sex, and maturity stage on in situ summer growth of krill across the southwest Atlantic sector of the Southern Ocean. The main aims were to examine the separate effects of each variable and to generate a predictive model of growth based on satellite-derivable environmental data. Both growth increments in length on moulting (GIs) and daily growth rates (DGRs, mm d Ϫ1 ) ranged greatly among the 59 swarms, from 0.58-15% and 0.013-0.32 mm d Ϫ1 . However, all swarms maintained positive mean growth, even those in the low chlorophyll a (Chl a) zone of the central Scotia Sea. Among a suite of indices of food quantity and quality, large-scale monthly Chl a values from SeaWiFS predicted krill growth the best. Across our study area, the great contrast between bloom and nonbloom regions was a major factor driving variation in growth rates, obscuring more subtle effects of food quality. GIs and DGRs decreased with increasing krill length and decreased above a temperature optimum of 0.5ЊC. This probably reflects the onset of thermal stress at the northern limit of krill's range. Thus, growth rates were fastest in the ice edge blooms of the southern Scotia Sea and not at South Georgia as previously suggested. This reflects both the smaller size of the krill and the colder water in the south being optimum for growth. Males tended to have higher GIs than females but longer intermoult periods, leading to similar DGRs between sexes. DGRs of equivalent-size krill tended to decrease with maturity stage, suggesting the progressive allocation of energy toward reproduction rather than somatic growth. Our maximum DGRs are higher than most literature values, equating to a 5.7% increase in mass per day. This value fits within a realistic energy budget, suggesting a maximum carbon ration of ϳ20% d Ϫ1 . Over the whole Scotia Sea/South Georgia area, the gross turnover of krill biomass was ϳ1% d Ϫ1 .

Wear of ceramics under dry sliding conditions is, besides mechanical overload, often governed by frictional heating. On the basis of this study a new thermal severity parameter is introduced and applied to an existing wear map as a... more

Wear of ceramics under dry sliding conditions is, besides mechanical overload, often governed by frictional heating. On the basis of this study a new thermal severity parameter is introduced and applied to an existing wear map as a function of mechanical and thermal loading introduced by Adachi et al. [Wear 203/204 (1997) 291]. The new map is valid for a wide range of material properties and operating conditions. In this paper, a method is presented to predict the boundary between the mild wear regime and the severe wear regime due to frictional heating. To obtain this, the work of Bos [Frictional heating of tribological contacts, Ph.D. Thesis, University of Twente, Enschede, The Netherlands, 1995] was used to calculate contact temperatures. This model is essentially a fit on numerical calculations, making it possible to include heat partitioning between dissimilar materials while retaining closed form expressions. The stress resulting from the contact temperature can be compared with material properties to obtain the thermal severity of a contact. A new dimensionless thermal severity number, TS, is introduced to determine the thermal severity of a contact. The model has been experimentally justified using measurements of pins of different materials sliding against two types of tetragonal zirconia polycrystal discs. In these experiments it was observed that if the specific wear rate exceeds the value of 3 × 10 −6 mm 3 /N m, the sliding surfaces were rough and the wear was regarded as severe. This criterion is closely related to the criterion based on the ratio of process surface roughness over mean grain size Adachi et al. [Wear 203/204 (1997) 291].

Maintaining insulative fat stores is vital for homeothermic marine mammals foraging in cold polar waters. To accomplish this, animals must balance acquisition and expenditure of energy. If this balance is shifted, body condition can... more

Maintaining insulative fat stores is vital for homeothermic marine mammals foraging in cold polar waters. To accomplish this, animals must balance acquisition and expenditure of energy. If this balance is shifted, body condition can decrease, challenging thermal homeostasis and further affecting energy balance. Prior studies of temperature regulation in sea lions have neither quantified basic all-inclusive heat flux values for animals swimming in cold water, nor determined whether they exhibit consistent spatial patterns of heat flux. Heat flux and skin temperature data were thus collected from four captive Steller sea lions using heat flux sensors (HFSs) with embedded thermistors. Optimal sensor placement was established using infrared thermography to locate the major areas of heat flux along the surface of the animals. Experiments were conducted on swimming animals in a large habitat tank with and without a drag harness, and on stationary animals in a temperature-and currentcontrolled swim flume. All heat flux measurements were corrected by a previously determined correction factor of 3.42 to account for insulative effects of the HFSs and attachment mechanism. Heat flux from shoulders and hips was consistently greater than from mid-trunk and axillary areas in both swimming and stationary animals, suggesting that certain areas of the body are preferentially used to offload excess heat. Mean heat flux for animals swimming with a drag harness was significantly greater than for unencumbered animals, indicating a likely increase in heat production beyond minimum heat loss. Thus, thermal stress does not appear to constitute significant costs for Steller sea lions swimming under conditions of increased drag at speeds of approximately 1 m/s in water temperatures of approximately 8.0 8C. D 2004 Elsevier B.V. All rights reserved.

A key issue in nonvolatile storage is long-term data retention. This aspect is even more important in innovative storage technologies such as phase-change memory (PCM), which promises better performance and easier scalability with respect... more

A key issue in nonvolatile storage is long-term data retention. This aspect is even more important in innovative storage technologies such as phase-change memory (PCM), which promises better performance and easier scalability with respect to traditional Flash memory and potential for multilevel storage. In this respect, we experimentally investigated the stability of intermediate states obtained by means of partial-SET programming. To this end, we analyzed the effects of the width and the amplitude of the programming pulses on the degradation of intermediate programmed resistance levels over time in PCM cells. Our study was carried out by considering the average behavior of an array of PCM cells, showing that data-retention properties degrade as the programming thermal stress increases.

ISO 7243 considers the WBGT (Wet Bulb Globe Temperature) index as an index of thermal stress in hot environments. It can be evaluated directly by measuring the globe temperature, the natural wet bulb temperature, and the air temperature... more

ISO 7243 considers the WBGT (Wet Bulb Globe Temperature) index as an index of thermal stress in hot environments. It can be evaluated directly by measuring the globe temperature, the natural wet bulb temperature, and the air temperature (only outside in the presence of solar radiation) or, indirectly, by measuring the air temperature, the air velocity, the humidity and the mean radiant temperature. The globe and natural wet bulb temperatures can only be estimated empirically, because they are not thermodynamic properties. The direct method, thus, permits neither very accurate measurements nor direct traceability. The aim of this study is to compare the above-mentioned methodologies experimentally. This analysis was carried out by varying the thermal and fluid dynamic parameters for transversal flow in the common measurement range.

Residual stress is lower in friction stir welding (FSW) compared with other melting weldment processes. This is due to being solid-state process in its nature. There are several advantages in utilizing stir welding process. Lower... more

Residual stress is lower in friction stir welding (FSW) compared with other melting weldment processes. This is due to being solid-state process in its nature. There are several advantages in utilizing stir welding process. Lower fluctuation and shrinkage in weldment metalenhanced mechanical characteristics, less defects, and ability to weld certain metals otherwise impractical by other welding processes are to name just a few of these advantages. These have caused an ever increasing attention by the concerned to the process of FSW. In this investigation, three-dimensional numerical simulation of friction stir welding was concerned to study the impact of tool moving speed in relation with heat distribution as well as residual stress. Simulation was composed of two stages. Firstly, thermal behavior of the piece while undergoing the welding process was studied. Heat is generated due to the friction between tool and the piece being welded. In the second stage, attained thermal behavior of the piece from previous stage is considered as inlet heat of an elasto-plastic, thermomechanical model for the prediction of residual stress. Also, in the second stage, tool is eliminated and residual stress distribution is found after complete cooling of the piece and disassembly of the clamp. Material characteristic are introduced into the proposed model as temperaturedependent parameters. Obtained residual indicate that heat distribution along thickness varies and is asymmetrical enormously. Moreover, longitudinal residual stress in the weld which increases as speed of process and tool movement ascends. In the prediction of results of residual stress, only heat impact was studied. This was recognized as the main element causing minor difference in results obtained for simulation in comparison with that of actual experiment.

Thermally induced stresses in growing shaped sapphire crystals are modelled using transient finite element simulations. Boundary conditions and mass changes are fixed on an expanding remeshed and updated grid. The actual stresses are... more

Thermally induced stresses in growing shaped sapphire crystals are modelled using transient finite element simulations. Boundary conditions and mass changes are fixed on an expanding remeshed and updated grid. The actual stresses are obtained taking into account plastic relaxation through dislocation glide along basal, prismatic and pyramidal slip planes. For this purpose, phenomenological creep laws available for this material are implemented in the frame of thermally activated plasticity. The model is calibrated by comparison with directional mechanical tests, and validation is performed by growth simulations and dislocation density measurements on as-grown crystals.

Baudoinia compniacensis is a microfungus recently described as the principal agent of fouling known as ''warehouse staining'', affecting building exteriors, fixtures and vegetation surfaces in areas proximate to distillery aging... more

Baudoinia compniacensis is a microfungus recently described as the principal agent of fouling known as ''warehouse staining'', affecting building exteriors, fixtures and vegetation surfaces in areas proximate to distillery aging warehouses, commercial bakeries and other areas subject to low-level ethanol vapour exposure. The surfaces most affected tend to be highly exposed and undergo extreme diurnal temperature fluctuations. In previous work, we have demonstrated the existence of heat-inducible putative chaperone proteins that may also be induced by low-level exposures to ethanol vapour (e.g., <10 ppm). The present study investigated the cellular accumulation of trehalose, a disaccharide identified in some microorganisms to be important in the protection of cell components during adverse stress conditions, such as thermal stress. Following heat shock at 45 C, we observed a 2.5-fold accumulation of trehalose relative to unheated controls maintained at 26 C. Peak trehalose concentrations of 10 mg g À1 dry wt were seen at 90 min after heat treatment, followed by a gradual return to post-treatment by 150 min. Exposure of B. compniacensis cells to ethanol resulted in a similar increased accumulation of trehalose compared to unexposed controls. These findings imply that trehalose may be important in the tolerance of this fungus to abiotic stresses, such as heat and solvent exposure, and suggest future research directions for the control and prevention of warehouse staining.

Rotating disks have many applications in the aerospace industry such as gas turbines and gears. These disks normally work under thermo mechanical loads. Minimizing the weight of such components can help reduce the overall payload in... more

Rotating disks have many applications in the aerospace industry such as gas turbines and gears. These disks normally work under thermo mechanical loads. Minimizing the weight of such components can help reduce the overall payload in aerospace industry. For this purpose, a rotating functionally graded (FG) disk with variable thickness under a steady temperature field is considered in this paper. Thermo elastic solutions and the weight of the disk are related to the material grading index and the geometry of the disk. It is found that a disk with parabolic or hyperbolic convergent thickness profile has smaller stresses and displacements compared to a uniform thickness disk. Maximum radial stress due to centrifugal load in the solid disk with parabolic thickness profile may not be at the center unlike uniform thickness disk. Functionally graded disk with variable thickness has smaller stresses due to thermal load compared to those with uniform thickness. It is seen that for a given value of grading index, the FG disk having concave thickness profile is the lightest in weight whereas the FG disk with uniform thickness profile is the heaviest. Also for any given thickness profile, the weight of the FG disk lies in between the weights of the all-metal and the all-ceramic disks.

Development of the heat treatment system for the 40 T hybrid magnet superconducting outsert Rev. Sci. Instrum. 82, 105106 (2011) Coaxial cable Bragg grating Appl. Phys. Lett. 99, 113517 (2011) Design and performance of a pulse transformer... more

Development of the heat treatment system for the 40 T hybrid magnet superconducting outsert Rev. Sci. Instrum. 82, 105106 (2011) Coaxial cable Bragg grating Appl. Phys. Lett. 99, 113517 (2011) Design and performance of a pulse transformer based on Fe-based nanocrystalline core Rev. Sci. Instrum. 82, 084703 (2011) Effect of surrounding air region size on finite element modeling for permanent magnetic solenoids Abstract. Continual scaling of on-chip wiring structures has brought significant challenges for materials and processes beyond the 32 nm technology node in microelectronics. Recently threedimensional (3-D) integration with through-silicon-vias (TSVs) has emerged as an effective solution to meet the future interconnect requirement. Among others, thermo-mechanical reliability is a key concern for the development of TSV structures used in die stacking as 3-D interconnects. This paper examines the effects of thermally induced stresses on interfacial reliability of TSV structures. First, three-dimensional distribution of the thermal stress near the TSV and the wafer surface is analyzed. Using a linear superposition method, a semi-analytic solution is developed for a simplified structure consisting of a single TSV embedded in a silicon (Si) wafer. The solution is verified for relatively thick wafers by comparing to numerical results from finite element analysis (FEA). The stress analysis suggests interfacial delamination as a potential failure mechanism for the TSV structure. An analytical solution is then obtained for the steady-state energy release rate as the upper bound for the interfacial fracture driving force, while the effect of crack length is evaluated numerically by FEA. With these results, the effects of the TSV dimensions (e.g., via diameter and wafer thickness) on the interfacial reliability are elucidated. Furthermore, the effects of via material properties are discussed.

Finite element analysis (FEA) AISI 316L stainless steel grade type High temperature fatigue a b s t r a c t Cracks have nucleated and propagated through the exhaust systems of naval gas turbines. The main cracks have propagated, along the... more

Finite element analysis (FEA) AISI 316L stainless steel grade type High temperature fatigue a b s t r a c t Cracks have nucleated and propagated through the exhaust systems of naval gas turbines. The main cracks have propagated, along the circumferential direction, from the weld toe of some butt and fillet welded joints located near the lower supporting ring, where the temperature measured with a Cu-Ni thermocouple was about 350°C. The exhaust system studied has more than 8 m long and the dimensions of the cross sections varies from 1.5 m  1 m at the inlet section to 2.6 m  2 m at the outlet section. The structure is thermally insulated and is made of AISI 316L stainless steel grade type plates, with a wall thickness of about 4 mm, which were bent in roll machines and mainly butt welded by MIG/ MAG welding process. This paper presents finite element analyses (FEA) of the exhaust system outlined before. Several elastic boundary conditions were simulated and the nominal stresses induced by the relative pressure, the thermal stresses, the inertial loads and the self-weight were determined. Moreover, the theoretical stress concentration factors of the critical butt and fillet welds were also calculated. The first frequencies and modes of vibration were determined. Design changes to the original exhaust system were then analysed in order to diminish the stresses and prevent further failures.

Microstructural physical based constitutive models are developed in this work in order to characterize the deforma-11 tion behavior of body centered cubic (bcc) and face centered cubic (fcc) metals under different strain rates and... more

Microstructural physical based constitutive models are developed in this work in order to characterize the deforma-11 tion behavior of body centered cubic (bcc) and face centered cubic (fcc) metals under different strain rates and temper-12 atures. The concept of thermal activation energy as well as the dislocations interaction mechanisms is used in the 13 derivation procedure taking into consideration the effect of the mobile dislocation density evolution on the flow stress 14 of the deformed material. The derivation of the Zerilli-Armstrong (Z-A) physical based model for both (bcc) and (fcc) 15 metals is investigated and a number of modifications are incorporated such as the evolution of mobile dislocation den-16 sity. The authors conclude that in spite of the physical basis used in the derivation of the Z-A model, its parameters can 17 not be interpreted physically since the approximation ln(1 + x) % x is used in the final step of the derivation. This expan-18 sion, however, is valid only for values x ( 1.0 which is not the case at high strain rates and temperatures. New bcc and 19 fcc relations for the flow stress are therefore suggested and derived using the exact results of the expansion of ln(1 + x). 20 Several experimental data obtained by different authors for tantalum (Ta), niobium (Nb), molybdenum, (Mo), vana-21 dium (V) (bcc metals) and Oxygen Free High Conductivity (OFHC) Copper (Cu) (an fcc metal) are used in evaluating 22 the proposed models. A good agreement between the experimental results and the proposed models are obtained. More-23 over, the predicted results show that the assumption of ignoring the generation of dislocation density during the plastic 24 deformation is not appropriate particularly in the case of high strain rates and temperatures. This causes the values of 25 the thermal stresses to be overestimated. Numerical identification for the physical quantities used in the definition of the 26 model parameters is also presented. 27

Exposure of superalloy surfaces to jet fuel at elevated temperatures leads to the formation of carbonaceous deposits and metal sulfides. The formation of stable oxide layers on alloy surfaces can reduce the activity of the constituent... more

Exposure of superalloy surfaces to jet fuel at elevated temperatures leads to the formation of carbonaceous deposits and metal sulfides. The formation of stable oxide layers on alloy surfaces can reduce the activity of the constituent transition metals that catalyze the dehydrogenation of hydrocarbons and the subsequent carbon deposit growth. The metals Ni, Cr, Fe, Mn, Al, Ti and Nb + Ta

Disc brakes are exposed to large thermal stresses during routine braking and extraordinary thermal stresses during hard braking. High-g decelerations typical of passenger vehicles are known to generate temperatures as high as 900 C in a... more

Disc brakes are exposed to large thermal stresses during routine braking and extraordinary thermal stresses during hard braking. High-g decelerations typical of passenger vehicles are known to generate temperatures as high as 900 C in a fraction of a second. These large temperature excursions have two possible outcomes: thermal shock that generates surface cracks; and/or large amounts of plastic deformation in the brake rotor. In the absence of thermal shock, a relatively small number of high-g braking cycles are found to generate macroscopic cracks running through the rotor thickness and along the radius of the disc brake. The analysis herein shows that rotor failure is a consequence of low cycle thermo-mechanical fatigue. An analysis of the vehicle dynamics was used to ®nd a heat¯ux equation related to braking forces. The heat¯ux equation was then used in a ®nite element analysis to determine the temperature pro®le in the brake. Once the brake temperature was obtained, a simpli®ed shrink ®t analysis was used to estimate the stresses that arise during hard braking. This approach shows that plastic deformation occurs due to the large thermal strains associated with high-g braking. The calculated strain amplitude was then used in a ConÀManson law to predict the number of high-g braking cycles to failure. Good agreement was obtained between reported braking cycles to failure and the proposed theoretical approach #

In this study, a systematic experimental work was performed to evaluate the reliability of the anisotropic conductive adhesive film (ACF) joint at high temperature for flip-chip-on-flex (FCOF) assemblies. A four-point probe method was... more

In this study, a systematic experimental work was performed to evaluate the reliability of the anisotropic conductive adhesive film (ACF) joint at high temperature for flip-chip-on-flex (FCOF) assemblies. A four-point probe method was developed to measure the contact resistance at high temperature. Measurement was also conducted along the length of the chip. The correlation between the increased resistance and the failure mechanism was investigated using scanning electron microscopy (SEM). Initially, the contact resistance increased linearly with rising temperature, but later, it increased abruptly. This changeover was related to the glass-transition temperature (T g ) of the ACF matrix. The coefficient of thermal expansion (CTE) is very high at temperatures above T g ; thus, the ACF swells too much, reducing the mechanical contact of the particles with the bump and/or pad. Again, as the adhesive strength becomes weaker at temperatures above the glass transition, it is unable to resist the thermal stress of the flex. The cumulative thermal stress at the edges dislodges the particles from the interconnection. Even below T g , the thermal stress at the edges is higher than the middle point. Thus, the contact resistance varied from the middle joint of the chip to that of the corner at the same high temperature. To reduce the contact resistance at the corner joint of the FCOF packages bonded by ACF, a square-shaped chip instead of a chip with a higher aspect ratio should be used. It was also suggested to use an adhesive with a higher glass-transition temperature and lower CTE.

This paper presents a comparative study of three-and two-dimensional axisymmetric finite element (FE) analyses of a welded pipe-flange joint for residual stresses and deformations in order to identify their merits or demerits.... more

This paper presents a comparative study of three-and two-dimensional axisymmetric finite element (FE) analyses of a welded pipe-flange joint for residual stresses and deformations in order to identify their merits or demerits. Sequentially coupled thermal stress analysis is performed to simulate single pass metal inert gas welding. Butt weld geometry with a single 'V' for a 100 mm nominal diameter pipe and same sized weld neck type ANSI class #300 flange is used. The heat input is modelled by using the Goldak double ellipsoidal heat source model. Temperature dependent material properties are used and deposition of filler metal is obtained by element birth and death feature. Both thermal and structural FE models are validated with experimental measurements. Residual stresses predicted by two-dimensional model are generally on the higher side and hence more conservative. However, we conclude that the three-dimensional FE model is preferable for the prediction of flange face distortion since it is a vital parameter for flange joint performance.

Twenty single male Assaf lambs were divided into two groups and housed in semi-open barns. Air temperature averaged 35°C. For 9 weeks after parturation, one group was cooled by fan between 1000 and 1600 hours and the other group was not... more

Twenty single male Assaf lambs were divided into two groups and housed in semi-open barns. Air temperature averaged 35°C. For 9 weeks after parturation, one group was cooled by fan between 1000 and 1600 hours and the other group was not cooled. Rectal and skin (head and testis) temperatures, respiration rate, and pulse rate were recorded twice daily. Lambs were weighed individually every week and levels of T3 and thyroxin were determined. Differences in rectal, head, and testis temperatures (P < 0.05) and respiration rates (P < 0.01) between the two groups were significant. Growth was affected positively by fan treatment, live weight increased by 15%, and cooled lambs had higher thyroxin levels.

For almost half a century the catastrophic failure of direct chill (DC) cast high strength aluminum alloys has been challenging the production of sound ingots. To overcome this problem, a criterion is required that can assist the... more

For almost half a century the catastrophic failure of direct chill (DC) cast high strength aluminum alloys has been challenging the production of sound ingots. To overcome this problem, a criterion is required that can assist the researchers in predicting the critical conditions which facilitate the catastrophic failure of the ingots. This could be achieved at first glance by application of computer simulations to assess the level and distribution of residual thermal stresses. However, the simulation results are only able to show the critical locations and conditions where and when high stresses may appear in the ingots. The prediction of critical void/crack size requires simultaneous application of fracture mechanics. In this paper, we present the thermo-mechanical simulation results that indicate the critical crack size distribution in several DCcast billets cast at various casting conditions. The simulation results were validated upon experimental DC-casting trials and revealed that the existence of voids/cracks with a considerable size is required for cold cracking to occur.

In Brazil, covered conductors must withstand an ageing test combining the stresses of heat, voltage to ground and corona. The observed failures indicate the necessity of complementary tests. In this paper Fourier transform infrared... more

In Brazil, covered conductors must withstand an ageing test combining the stresses of heat, voltage to ground and corona. The observed failures indicate the necessity of complementary tests. In this paper Fourier transform infrared spectroscopy (FTIR), electron spin resonance (ESR), thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), contact angle and scanning electron microscopy (SEM) measurements on artificially aged and unaged cross-linked polyethylene (XLPE) insulation of medium voltage covered conductors is reported. The ESR spectroscopy results show clear evidence of the presence of free radicals in all unaged and aged XLPE insulation cables suggesting inadequate manufacture and processing conditions. The FTIR showed the presence of carbonyl groups in both, unaged and aged XLPE insulation indicating that oxidation process occurred during the manufacturing process. The TGA analysis demonstrates that the decomposition temperature of XLPE insulation did not change significantly except for one of the manufactures. It was observed in DSC analysis that the ageing of the XLPE insulation causes a decrease in intensity and broadening of the peak corresponding to fusion heat, indicating the bond scission in the backbone of the XLPE. The contact angle measurements showed hydrophilic character for all unaged and aged XLPE insulation possibly due to some oxidation during cables manufacturing. After ageing the contact angle is about 23.1° and 52.4°, indicating a significant increasing in the hydrophilicity of the XLPE insulation. The increase in hydrophilicity of aged XLPE insulation appears to be due to the increase in oxygen functional groups and the results are consistent with the FTIR spectroscopy measurements. The defects observed in SEM analysis of unaged XLPE insulation indicate a nonuniform mechanical and thermal stresses during cables manufacturing.

We have investigated compositional variations of light hydrocarbons in crude oils from the Beryl and adjacent fields of the North Sea in combination with carbon isotopic ratios of light hydrocarbons and biomarker properties of oils.... more

We have investigated compositional variations of light hydrocarbons in crude oils from the Beryl and adjacent fields of the North Sea in combination with carbon isotopic ratios of light hydrocarbons and biomarker properties of oils. Although there appears to be a strong source influence on various light hydrocarbon maturity parameters, this is a consequence of the mixing of hydrocarbons derived from the Kimmeridge Clay Formation as well as from the Heather Formation and Brent coal at varying thermal maturity levels. Light hydrocarbon parameters based on Mango's reaction scheme involving 3-ring and 5-ring intermediates are supported by carbon isotopic ratios of light hydrocarbons. However, there also is evidence that iso-and cyclo-heptane precursors exist that contribute C7 light hydrocarbons independent of Mango's model. The ratio of 2,4-dimethylpentane to 2,3-dimethylpentane (2,4-DMP/2,3-DMP) and other related parameters appear to be reliable indicators of thermal stress, but must be interpreted within a complete understanding of the petroleum system under study.

The characteristics of plastic injection molding were considered using the theory of thermo-viscoelasticity by considering the effect of packing bulk strain during the cooling stage of the injection molding process. The mathematical model... more

The characteristics of plastic injection molding were considered using the theory of thermo-viscoelasticity by considering the effect of packing bulk strain during the cooling stage of the injection molding process. The mathematical model governing the development of residual stress in the amorphous polymer has been established. The residual stress model is solved with the ®nite difference method. Due to the rapid changes at the initial stage, a quasi-numerical procedure is adopted for evaluating the integral terms arising from the thermal residual stress model during the cooling stage. The results are discussed with an illustrative example. # 2000 Elsevier Science S.A. All rights reserved.

The future success of many electronics companies will depend to a large extent on their ability to initiate techniques that bring schedules, performance, tests, support, production, life-cycle-costs, reliability prediction and quality... more

The future success of many electronics companies will depend to a large extent on their ability to initiate techniques that bring schedules, performance, tests, support, production, life-cycle-costs, reliability prediction and quality control into the earliest stages of the product creation process. Earlier papers [1, 2] have discussed the benefits of an integrated analysis environment for system-level thermal, stress and EMC prediction. This paper focuses on developments made to the stress analysis module and presents results obtained for an SMT resistor. Lifetime predictions are made using the Coffin-Manson equation. Comparison with the creep strain energy based models of Darveaux [3] shows the shear strain based method to underestimate the solder joint life.

Ziel dieses Beitrags, der in zwei Teilen erfolgt, ist es, die Wirkungen des globalen Klimawandels auf einen Ballungsraum (Ruhrgebiet) zu untersuchen und Gegenmaßnahmen auf lokaler Ebene zu diskutieren. Im ersten Teil wird auf die... more

Ziel dieses Beitrags, der in zwei Teilen erfolgt, ist es, die Wirkungen des globalen Klimawandels auf einen Ballungsraum (Ruhrgebiet) zu untersuchen und Gegenmaßnahmen auf lokaler Ebene zu diskutieren. Im ersten Teil wird auf die Entstehung des natürlichen und anthropogenen Treibhauseffektes eingegangen und deren jeweilige Beiträge an der globalen Überwärmung herausgestellt. Exemplarisch wird auf die jüngere Klimaentwicklung in der Metropolregion Ruhr eingegangen. Zu den durch verschiedene numerische und statistische Modelle projizierten Klimaveränderungen zählen auch die Zunahme thermischer Belastungen für die Stadtbevölkerung sowie die Verstärkung sommerlicher konvektiver Niederschläge mit entsprechenden Abflussspitzen. Unter den Luftverunreinigungen wird es in erster Linie das bodennahe Spurengas Ozon sein, dass bei ansteigenden Temperaturen eindeutig höhere Konzentrationen erwarten lässt, wohingegen die atmosphärischen Feinstaubkonzentrationen (≤ PM 10 ) bislang keine enge Bindung an die Temperaturentwicklung erkennen lassen.

Numerous studies have confirmed that performance can be impaired when athletes are dehydrated. Endurance athletes should drink beverages containing carbohydrate and electrolyte during and after training or competition. Carbohydrates... more

Numerous studies have confirmed that performance can be impaired when athletes are dehydrated. Endurance athletes should drink beverages containing carbohydrate and electrolyte during and after training or competition. Carbohydrates (sugars) favor consumption and Na(+) favors retention of water. Drinking during competition is desirable compared with fluid ingestion after or before training or competition only. Athletes seldom replace fluids fully due to sweat loss. Proper hydration during training or competition will enhance performance, avoid ensuing thermal stress, maintain plasma volume, delay fatigue, and prevent injuries associated with dehydration and sweat loss. In contrast, hyperhydration or overdrinking before, during, and after endurance events may cause Na(+) depletion and may lead to hyponatremia. It is imperative that endurance athletes replace sweat loss via fluid intake containing about 4% to 8% of carbohydrate solution and electrolytes during training or competition....

A ferrofluid-cooled low power, single-phased electric transformer was designed and prototyped with the aim of investigating the performance that such an apparatus may exhibit. The nanometric, colloidal, super-paramagnetic fluid used as... more

A ferrofluid-cooled low power, single-phased electric transformer was designed and prototyped with the aim of investigating the performance that such an apparatus may exhibit. The nanometric, colloidal, super-paramagnetic fluid used as coolant has specific electric, magnetic, and thermal properties, and presents an overall better stability and capacity to withstanding electromagnetic and thermal stress. This paper addresses also the electromagnetic and heat transfer processes that occur. First, the physical, mathematical, and numerical models are introduced. Numerical simulation results suggest that the magnetization body forces may add to the thermal, buoyancy body forces in providing for better heat transfer. To outline this, several numerical models that may conveniently be treated numerically within the current hardware and software limits, while still providing for satisfactory accuracy were developed. The results may be utilized also in the design phase of the transformer.

There are several reasons for mechanical stresses in "globbed" assemblies. For example: cure shrinkage; thermal gradients; and moisture diffusion. Thermal mismatch between substrate, silicon die, and encapsulant represent a main reason... more

There are several reasons for mechanical stresses in "globbed" assemblies. For example: cure shrinkage; thermal gradients; and moisture diffusion. Thermal mismatch between substrate, silicon die, and encapsulant represent a main reason for thermally induced stresses and is investigated in detail. The filled polymers used have shown temperature, time, and moisture dependent mechanical characteristics. The viscoelastic properties of the encapsulant below the glass transition temperature (T g ) are represented by a Prony series sum of exponentials with three terms, while the temperature dependence is included by a temperature time shift formula. Finite element (FE)-simulations including the creep characteristics allow the evaluation of thermally induced stresses. The calculations show the major stress concentration to occur at the inner edge between die/adhesive/encapsulation and the ceramic board. Local stress concentrations arise at the upper interfacial edge die/encapsulation and at the outer border of the glob-top. Furthermore, the theoretical results are compared with observations of thermally cycled hybrids made by scanning acoustic microscopy (SAM) and metallographic investigations. In this way not only the influence of thermal cycling, but also humidity exposure on the glob-top's integrity was evaluated. The typical failures were shown to be delaminations at the epoxy encapsulant interface.

The paper estimates the technical risk associated with the operation of power machines. The sources of risk are presented with possible scenarios of failures. The risk involving the operation of steam turbine valves is discussed in more... more

The paper estimates the technical risk associated with the operation of power machines. The sources of risk are presented with possible scenarios of failures. The risk involving the operation of steam turbine valves is discussed in more detail. The point estimation technique for reliability analysis and the finite element analysis of thermal stresses are applied. Calculations of the probability of failure are made for random loads and random properties of materials. On the basis of the real data, mean values of stresses and strains under transient operating conditions were calculated, as well as the level of stresses under creep conditions. The calculated values were used for estimation of the probability of valve failure and the value of technical risk. q

Thermal expansion CVD Single crystal Dilatometry Strain a b s t r a c t Thermal expansion of CVD single crystal silicon was measured with a push-rod dilatometer up to 1100 • C for different crystallographic orientations of the specimen.... more

Thermal expansion CVD Single crystal Dilatometry Strain a b s t r a c t Thermal expansion of CVD single crystal silicon was measured with a push-rod dilatometer up to 1100 • C for different crystallographic orientations of the specimen. Thermal analysis, Laue analysis and X-ray diffraction were used to verify silicon crystal orientation and absence of possible phase transformations. Coefficients of technical thermal expansion have been calculated in this temperature range and their variations with temperature have been demonstrated. These differences might cause anisotropy in thermal stresses, which has been calculated and compared with experimental values of dry-oxidised silicon wafers.

Within the framework of the ‘Component Specific Analysis of Mechanical Behaviour’, the nuclear codes and standards, e.g. KTA Standard KTA 3201.2 on Components of the Reactor Coolant Pressure Boundary of Light Water Reactors (Design and... more

Within the framework of the ‘Component Specific Analysis of Mechanical Behaviour’, the nuclear codes and standards, e.g. KTA Standard KTA 3201.2 on Components of the Reactor Coolant Pressure Boundary of Light Water Reactors (Design and Analysis) allow a simplified stress and fatigue analysis for piping by applying the stress index method. The equations supplementary to present KTA Standard given in this context can be used for the consideration of the thermal loads arising from piston flow but not of those from thermal stratification. Thermal stratification occurs e.g. in the surge line of pressurised water reactors during start-up and shut-down processes. This phenomenon is explained and its effects are described. The equations supplementary to the present KTA Standard are derived which enable the consideration of the load case ‘thermal stratification’ in the simplified stress and fatigue analysis. Their applicability is demonstrated by a numeric example.

In this paper, the failure of a large Pelton turbine, arising immediately after receiving a quenching and tempering heat treatment, is analysed. The turbine was manufactured in ASTM CA-6NM soft martensitic stainless steel. A... more

In this paper, the failure of a large Pelton turbine, arising immediately after receiving a quenching and tempering heat treatment, is analysed. The turbine was manufactured in ASTM CA-6NM soft martensitic stainless steel. A thermo-mechanical finite elements model was developed to evaluate the homogeneity of the heat treatment; for this purpose, the thermal histories of internal and external points of the component were compared, and the possible existence of temper embrittlement was assessed. Moreover, the thermal stresses during heat treatment were obtained in order to perform a failure analysis. After analysing the fracture surface through visual inspection and scanning electron microscope fractography, the material properties were characterised all around the fracture surface including optical and transmission electron microscopy, chemical composition and Vickers and Charpy impact tests. All this experimental information allowed a satisfactory understanding of the phenomenon to be obtained and a failure analysis to be performed in order to justify the fracture of the component.

Flash-lamp annealing (FLA) on a millisecond time scale has been shown to be a promising tool in the preparation of high-quality semiconducting materials. The process imposes time varying through-thickness temperature profiles on the... more

Flash-lamp annealing (FLA) on a millisecond time scale has been shown to be a promising tool in the preparation of high-quality semiconducting materials. The process imposes time varying through-thickness temperature profiles on the substrates being processed, and consequently thermal stresses. A combined thermal and optical model has been developed to predict the substrate temperature distribution and this model has been linked to a structural model to compute stresses and deflections. The paper shows how these models can be used to explore process conditions in flash lamp annealing, with particular regard to the annealing of ion implants in silicon and the crystallization of amorphous silicon layers on glass substrates. r