Brittleness Research Papers - Academia.edu (original) (raw)

One key failure root cause during wafer production is the electrical test by probing all interconnects of each die of the wafer. The probing process can result in excessive damage of the back end of line (BEOL) wafer layers underneath the probe pad, especially if brittle low-k dielectrics are used. The industry is trying to reduce design limitations for these under pad areas. A 3D sub-modeling simulation approach has been used to investigate stress states in layers below the probe pad. The dynamic behavior of the needle is determined by modal analysis. Its representation and calculation is done by an analytical model using the modal superposition method. These small, specialized simulation models help to distribute the simulation effort, by handling specific aspects of the real process, such as the contact problem, needle dynamics and homogenization of fine structures. The results showed that the needle dynamics can be neglected during further studies. The static load due to the max...

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- Production, Stress, Modal Analysis, Failure Analysis

The increasing interest in resilience engineering (RE) has led to a demand for frameworks that undertake safety assessments from such a standpoint. However, the few existing frameworks have drawbacks, such as not analyzing the sources of resilience (SRs) and the sources of brittleness (SBs) side-by-side. Moreover, they limit themselves to investigating resilience in predetermined units of analysis (e.g., teams), neglecting the fact that resilience might be in any element of a socio-technical system. This article introduces a framework for identifying and analyzing SRs and SBs jointly, which do not constrain the identification process to any specific unit of analysis within the investigated system. The sources should be identified and analyzed across five categories: the opposite SR or SB; the risk from the SB; the effectiveness of the SR; those originating from either internal processes or the external environment; those arising from formal or informal practices. A case study of two air taxi carriers illustrates the application of the framework. Relevance to industry: Resilience engineering (RE) is an emerging safety management paradigm concerned with normal work, rather than emphasizing learning from incidents. The proposed framework allows the identification and analysis of the most salient sources of resilience and brittleness. It can be applied for investigating resilience at any unit of analysis within a socio-technical system, supporting the identification of strengths and weaknesses from the RE perspective.

It is desirable to verify the structural performance based on a multi-hazard approach, taking into account the critical actions the structure in question could be subjected to during its lifetime. This study presents a proposal for a probabilistic model for multi-hazard risk associated with the limit state of collapse for a reinforced concrete (RC) structure subjected to blast threats in the presence of seismic risk. The annual risk of structural collapse is calculated taking into account both the collapse caused by an earthquake event and the blast-induced progressive collapse. The blast fragility is calculated using a simulation procedure for generating possible blast configurations, and verifying the structural stability under gravity loading of the damaged structure, using a kinematic plastic limit analysis. As a case study, the blast and seismic fragilities of a generic four-storey RC building located in seismic zone are calculated and implemented in the framework of a multi-hazard procedure, leading to the evaluation of the annual risk of collapse.

- by Gaetano Manfredi
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- Civil Engineering, Monte Carlo Simulation, Risk assessment, Structural Stability

Predicting tunnel boring machine (TBM) performance is a crucial issue for the accomplishment of a mechanical tunnel project, excavating via full face tunneling machine. Many models and equations have previously been introduced to estimate TBM performance based on properties of both rock and machine employing various statistical analysis techniques. However, considering the nature of the problem, it is relatively difficult to estimate tunnel boring machine performance by linear prediction models. Artificial neural networks (ANNs) and non-linear multiple regression models have great potential for establishing such prediction models. The purpose of the present study is the construction of non-linear multivariable prediction models to estimate TBM performance as a function of rock properties. For this purpose, rock properties and machine data were collected from recently completed TBM tunnel project in the City of New York, USA and consequently the database was established to develop performance prediction models utilizing the ANN and the non-linear multiple regression methods. This paper presents the results of study into the application of the non-linear prediction approaches providing the acceptable precise performance estimations.

- by Saffet Yagiz
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- Civil Engineering, Density, Quantitative analysis, Compressive Strength

The demand for representative rock property parameters related to planning of underground excavations is increasing, as these parameters constitute fundamental input for obtaining the most reliable cost and time estimates. The Brittleness Value (S20), Sievers’ J-Value (SJ), Abrasion Value (AV) and Abrasion Value Cutter Steel (AVS) have been used extensively at NTNU/SINTEF since the 1960s in connection with drillability testing

- by Filip Dahl and +1
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- Civil Engineering, Rock Mechanics, Statistical Analysis, Cost Estimation

Hydrogen embrittlement of austenitic steels is of high interest because of the potential use of these materials in hydrogen-energy related infrastructures. In order to elucidate the associated hydrogen embrittlement mechanisms, the mapping of heterogeneities in strain, damage (crack/void), and hydrogen and their relation to the underlying microstructures is a key assignment in this field.
Specifically mapping the connection between microstructure heterogeneity
and the associated hydrogen trapping at similar spatial resolution opens a novel pathway to identify hydrogen embrittlement mechanisms in complex alloys.
One of the materials classes that is expected to be applied for energy-related structure parts are austenitic steels with high Mn content. In particular, twinning-induced plasticity (TWIP) high Mn austenitic steels are well known for an exceptional balance of ductility and strength with less hydrogen susceptibility compared to ferritic steels with a similar strength.
The hydrogen embrittlement phenomenon has been observed under severe mechanical deformation and hydrogen charging conditions such as delayed fracture testing in a deep drawn cup or tensile testing during hydrogen charging at a high current density. Fracture was in such cases caused by various metallurgical factors e.g. by the formation and failure of deformation twins. The importance of deformation twins on hydrogen embrittlement of austenitic steels has been recently studied. It was found that they can act as crack initiation sites and enable crack propagation. Microstructure-sensitive hydrogen mapping in a TWIP steel has been conducted by using microprinting experiments, which enable visualization of hydrogen emission from a sample through reduction of silver ions in gelatin-based AgBr emulsion. The microprinting technique demonstrated that hydrogen is indeed localized at deformation twins, hence, promoting the initiation of hydrogen embrittlement. Also, from our previous experiments we suggested that the hydrogen localization at/near deformation twins requires local plastic straining at/before deformation twins. These facts indicate that the hydrogen-assisted twin boundary cracking of TWIP steels is a complex phenomenon including both, local plastic straining and local hydrogenation. To better understand the influence of deformation twins on the hydrogen embrittlement phenomenon, it is thus essential to map the spatial hydrogen distribution through a high resolution detection approach that is sufficiently microstructure and concentration sensitive. It should be noted here that the microprinting technique is only sensitive to hydrogen at relatively
high concentration levels, or more precisely at relatively high emission rates. It has, therefore, to be applied directly after a sample is charged with hydrogen. It will be shown here that hydrogen is critical for prolonged times after charging. Hence, the findings obtained by microprinting needed to be confirmed also for longer times after charging by a more sensitive technique. In the last years several promising novel approaches have been reported for the localized resolved and sensitive detection of hydrogen.
One is a direct electrochemical detection via a capillary cell, developed by Suter et al. which, however, does not provide the resolution required here. Another approach is the use of Kelvin probe techniques, which allow detection of hydrogen in a material by means of the change ofwork function caused by the hydrogen entering the oxide at the surface. Studies at quite high resolution have been carried out with Scanning Kelvin Probe ForceMicroscopy (SKPFM), where diffusion profiles of hydrogen have been mapped successfully at relatively high
resolution at cross section of samples after hydrogen charging.
However, a direct quantification is not possible by this method, due to the complex dependence of the work function of oxide on different defect states in the oxides. For the same reason this approach is not suitable to provide reliable information on hydrogen at different features of the microstructure, because different oxides show a different dependence on hydrogen. A new approach by applying a thin palladium layer eliminates this problem. More specifically, the SKPFM with a thin palladium layer is a novel and efficient method to very sensitively analyze local hydrogen concentrations down to levels well below 0.01 atom ppm at spatial resolutions as small as several tens of nanometers. The SKPFM can hence be used for detecting the hydrogen distribution with high sensitivity, since the potential measured by the SKPFM on the palladium that has been deposited as a thin layer on the hydrogen charged sample surface correlates logarithmically with the hydrogen content in the palladium. Because of this Nernstian-like behavior, which is similar to a hydrogen electrode, as also reported for immersed palladium metal, we also refer to the work function as electrode potential. In fact, as discussed previously, the surface of the palladium is, even in dry nitrogen atmosphere, still covered by an ultrathin water layer, which together with the hydrogen in the palladium leads to the formation of an hydrogen electrode “in the dry”. By exploiting this effect, SKPFM was successfully applied to the spatially resolved detection of hydrogen in ferrite/austenite duplex stainless steels. More specific in this project the hydrogen distribution in a hydrogen-charged Fe-18Mn-1.2C (wt%) twinning-induced plasticity austenitic steel was studied by Scanning Kelvin Probe Force Microscopy (SKPFM). We observed that 1–2 days after the hydrogen-charging, hydrogen showed a higher activity at twin boundaries than inside the matrix. This result indicates that hydrogen at the twin boundaries is diffusible at room temperature, although the twin boundaries act as deeper trap sites compared to typical diffusible hydrogen trap sites such as dislocations. After about 2 weeks the hydrogen activity in the twin boundaries dropped and was indistinguishable from that in the matrix. These SKPFM results were supported by thermal desorption spectrometry and scanning electron microscopic observations
of deformation-induced surface cracking parallel to deformation twin boundaries. With this joint approach, two main challenges in the field of hydrogen embrittlement research can be overcome, namely, the detection of hydrogen with high local and chemical sensitivity and the microstructure-dependent and spatially resolved observation of the kinetics of hydrogen desorption.

- by Asif Bashir and +1
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- Hydrogen, Corrosion Science, Fracture, Mechanics of Fracture and damage

A C-L-C E k Approved for public release; distribution 2b'ac FI ~SCATI'O-RIJ iLt 1 unlimited. d PIRFORING ORGANIZATION O NUMBER * The work carried out during the 1985186 contract year is summrized: Markov Monte Carlo methods are generalized to include inhomogeneous Markov processes. Two new sampling techniques allow the treatment of reliability problems which include time-dependent failure rates and preventive maintenance. Incorporation of periodic testing and repair allows classes of revealed and unrevealed failures to be combined in problems with wear, periodic maintenance and component dependencies. 20. DISTRlUTION/AVAILASILITY OF ABSTRACT 21. ABSTRACT SECURITY CLASSIFICATION UNCLASISIPI9D/UNLIMITEO M[ SAME AS APT. 0: OTIC USERS C] UNCLASSIFIED 22a. NAME OP RESPONSIBLE INDIVIDUAL 22b. TELEPHONE NUMBER 22c. OFF ICE SYMBOL r(Incude Ann Codo) , (0)767-1 KM DO FORM 1473,83 APR EDITION OF iJ AN 73 IS OSOLrET.

- by Elmer Lewis
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- Systems Analysis, Markov Processes, Simulation, Sampling

The purposes of banding and sealing of hard gelatin capsules are well known; however, the effects of these processes on shell fragility have not been documented. In this study the effect of banding and fluid sealing (both water and a 50 : 50 water/ethanol mixture) on shell mechanical strength was evaluated using a modified capsule plug hardness tester. Banded capsules were prepared using an Elanco laboratory model banding machine. Fluid sealed capsules were prepared by a manual sealing process. Failure force data were collected for natural and white opaque size 0 Elanco capsules and natural size 0 Capsugel capsules. Fluid sealed capsules were found to fail at lower applied crushing forces than banded capsules. The effect of banding on shell fragility was found to be slight and the forces of failure were comparable to those of unsealed capsules. In some cases, visual observations of fragility during the crushing event correlate well with low failure forces. Work of failure was also assessed and found less discriminating than the force of failure.

- by larry augsburger
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- Pharmaceutics, Dosage Form, Ethanol, Sorption

This paper presents the results of a numerical study on the influence of structural passive supplemental damping systems on structural and nonstructural seismic fragilities of a steel framed building. Hysteretic and viscous bracing systems were used to retrofit a four-storey steel framed building containing generic rigidly anchored and vibration isolated secondary nonstructural components located at various floor levels in the building. The Incremental Dynamic Analysis (IDA) procedure was utilized with an ensemble of 44 scaled historical ground motions to construct structural and nonstructural fragility curves for various performance objectives. The results obtained indicate that both supplemental damping systems improved the seismic behaviour of the original building by increasing the median values of the structural fragility curves and reducing the probabilities of exceedence at the Design Basis Earthquake (DBE) and Maximum Credible Earthquake (MCE) levels. The nonstructural components mounted on vibration isolation systems exhibited reduced seismic fragilities compared to that of rigidly anchored nonstructural components. Retrofitting the building with viscous dampers reduced the seismic fragility of nonstructural components mounted to the roof of the building. Retrofitting the building with hysteretic dampers, on the other hand, was detrimental to the seismic fragility of acceleration sensitive rigidly anchored nonstructural components at the roof level.

- by Assawin Wanitkorkul
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- Civil Engineering, Earthquake Engineering, Modeling, Steel Structure

The problems posed by mission-critical legacy systemse.g., brittleness, inflexibility, isolation, nonextensibility, lack of opennessare well known, but practical solutions have been slow to emerge. Generally, organisations attempt to keep their legacy systems operational, while developing mechanisms which allow the legacy systems to interoperate with new, modem systems which provide additional functionality. The most mature approach employs gateways to provide this interoperability.

- by Deirdre Lawless
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- Information Systems, Engineering, Computer Science, Documentation

As production of hydrocarbons from tight reservoirs becomes more prevalent, the need to understand fracture density and what can affect fracture density has become the goal of new research. In this study, fracture density is defined as the fracture surface area per volume (m-1), and is derived from strain energies and material properties of the rock. Brittleness is defined as the fracture density at a particular strain state.
One purpose of the study is to use the dimensionless geomechanical equation, ("F" _"d" "U" _"a" )/"μ" " = A" "ν" /"1-2ν" " + B" , to test whether the strain conditions were constant from layer to layer. If they were, the data will plot as a straight line with a positive slope where A and B are related to the strain invariants. Fracture density measurements were taken in Millsap, TX, Baird and Clyde, TX and Midlothian, TX on outcrops using scan lines. Samples were collected and brought back to the Geomechanics Lab at UTA to measure material properties using P and S wave velocities. Density and porosity were measured via Mercury Injection at the Geology Lab at UTA. Weatherford Laboratories measured mineralogical percentages of the samples using XRD. These mineralogical percentages were used for fracture toughness estimates and for comparisons of the fracture density brittleness with the commonly used brittleness index derived from the Jarvie (2007) equation.
Using the dimensionless equation above, the data from Millsap, TX plotted as a straight line with a correlation coefficient > 0.9 showing that the strain was constant from layer to layer in that area. The Baird and Clyde and Midlothian, TX data plotted as a line with a negative slope and poor correlation coefficients suggesting that the strain was not constant from layer to layer in those areas.
Another goal of the study was to compare the fracture density brittleness using "F" _"d " "= " "μ" /"U" _"a" ("A " "ν" /"1-2ν" " + B" ), with Jarvie’s (2007) mineralogical brittleness index. In general, the two methods predict different layers to be the most brittle. The advantage of the geomechanical equation is that it produces results in fracture surface area per cubic meter compared to the XRD brittleness index, which is a dimensionless number. Knowing fracture density at a particular strain state may permit better hydraulic fracturing designs. Results show that the brittleness predicted by the two methods are significantly different, but accuracy of the two methods is not well constrained.

- by Brett Zastoupil
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- Geomechanics, Fracture Density, Brittleness

A model that predicts the osmotic fragility curve of a red cell population is developed by relating the critical osmotic pressure to the size distribution of the cells, determined by resistive pulse spectroscopy. Two of the parameters involved, namely the normalized osmotic volume correction, B, and the swelling index, k, are previously determined from the experimental average properties of the population. From these values the critical volume of the cell is obtained, and is shown to be 6-12% larger than the first spherical volume, obtained from an independent experiment. A new parameter, n, a measure of the surface area distribution of the cells, is incorporated through a simple function that relates the critical volume to the size of the cells, and is theoretically shown to be linked to parameters k and B. The model is used to fit and interpret fragility data obtained in this laboratory for normal and sickle cell samples. From the values of n obtained for normal samples, the model predicts an essentially constant surface-to-volume ratio within an individual's cell population. For sickle cell samples, instead, the value of index n is negative, thereby supporting an increase in excess surface area as cell size decreases. Both findings are in agreement with direct observations reported in the literature. It is concluded that this set of parameters may be used to develop an index classification of blood disorders.

- by Hugo Massaldi
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- Mathematics, Kinetics, Sickle Cell Anemia, Biophysical Chemistry

The present review is intended to revisit the advances and debates in the comprehension of the mechanisms of subcritical crack propagation in silicate glasses almost a century after its initial developments. Glass has inspired the initial insights of Griffith into the origin of brittleness and the ensuing development of modern fracture mechanics. Yet, through the decades the real nature of the fundamental mechanisms of crack propagation in glass has escaped a clear comprehension which could gather general agreement on subtle problems such as the role of plasticity, the role of the glass composition, the environmental condition at the crack tip and its relation to the complex mechanisms of corrosion and leaching. The different processes are analysed here with a special focus on their relevant space and time scales in order to question their domain of action and their contribution in both the kinetic laws and the energetic aspects.

- by Matteo Ciccotti
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- Engineering, Physics, Materials Science, Plasticity

The concepts of disaster resilience and its quantitative evaluation are presented and a unified terminology for a common reference framework is proposed and implemented for evaluation of health care facilities subjected to earthquakes. The evaluation of disaster resilience is based on dimensionless analytical functions related to the variation of functionality during a period of interest, including the losses in the disaster and the recovery path. This evolution in time including recovery differentiates the resilience approach from the other approaches addressing the loss estimation and their momentary effects. The recovery process usually depends on available technical and human resources, societal preparedness, public policies and may take different forms, which can be estimated using simplified recovery functions or using more complex organizational and socio-political models. Losses are described as functions of fragility of systems that are determined using multidimensional performance limit thresholds. The proposed framework is formulated and exemplified for a typical Californian Hospital building using a simplified recovery model, considering direct and indirect losses in its physical system and in the population served by the system. A hospital network is also analyzed to exemplify the resilience framework. Resilience function captures the effect of the disaster, but also the results of response and recovery, the effects of restoration and preparedness. Therefore, such a function becomes an important tool in the decision process for both the policy makers and the engineering professionals.

- by Andrei Reinhorn
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- Civil Engineering, Resilience, Health Care, Structures and Fire Engineering
- by Chandra Nath
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- Mechanical Engineering, Manufacturing, Modeling, Ultrasound

Ca and Sr-based oxynitride glasses with very high nitrogen content have been synthesized using metal hydrides as primary precursors. Values of Young's modulus, shear modulus, bulk modulus and Poisson's ratio were determined by means of ultrasonic echography. Vickers micro-indentation has been used to characterize hardness and indentation fracture toughness behaviour. Elastic moduli were found to increase linearly with nitrogen content, with the highest value of Young's modulus at 135 GPa, for a Ca-glass with 58 e/o of nitrogen. The Sr-glasses exhibit lower elastic moduli than Ca glasses. Poisson's ratio, hardness, indentation fracture toughness, crack initiation load and surface damage resistance were found to increase with increasing nitrogen content for both glass series.

- by Saeid Esmaeilzadeh
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- Materials Engineering, Glass, Non crystalline solids, Nitrogen

This paper proposes a probabilistic formulation to assess the effectiveness of the fiber reinforced polymer (FRP) retrofit schemes in enhancing the structural performance of reinforced concrete (RC) bridge columns. Two probabilistic models are proposed to predict the deformation capacities of retrofitted columns. One deformation model corresponds to the flexural failure and the other considers the bond failure in the lap-splice region. A Markov Chain Monte Carlo (MCMC) simulation method is used to estimate unknown model parameters in the context of a Bayesian updating approach. The probabilistic capacity models are used to estimate the fragility curves of three example columns. In this paper, fragility is defined as the conditional probability of failure for given deformation demand. The results compare the column fragilities before and after the application of the retrofit measure. The results from the example columns indicate that the use of FRP composites considerably reduced the fragility for the bond failure mode and is also beneficial but with a moderate impact when considering the flexural failure.

- by Qindan Huang
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- Engineering, Mechanical Engineering, Civil Engineering, Engineering Mechanics

The malfunctioning of acceleration-sensitive equipment in wind turbines has the potential to affect their annual failure rates during normal operating conditions. Current protective measures for wind turbines are triggered by wind speed. However, this option neglects the structural response of the wind turbines, and limits the possibility of effectively controlling accelerations at the top of the wind towers. In this study, a dynamic model of the wind tower/rotor blade system is used to estimate the acceleration response at the top of the towers. This model is coupled with a probabilistic description of the dynamic properties of the wind turbines, and an annual distribution of the wind hazard to obtain a distribution of the acceleration response for various levels of wind speed. This distribution is used to develop wind-induced acceleration fragility curves for typical wind turbines. Acceleration thresholds of 10, 15, and 20 m/s 2 are likely to be exceeded at the onset of protective cut out wind speeds of 25 m/s, with probabilities as high as 64%, 48%, and 37%, respectively. Several wind turbine subcomponents are sensitive to these levels of acceleration. Some examples, in decreasing order of acceleration susceptibility, include generators, brakes, yaw systems, inverters, mechanical controls, electrical controls, hydraulic systems, gearboxes, shafts, and physical/electrical connections to the power grid. By weighting the fragility curves with the likelihood of observing specific wind speeds during any given year, this study provides unconditional probabilities of failure that represent annual unavailability rates for wind turbines. Exceeding any of the acceleration levels between 10 m/s 2 and 20 m/s 2 has probabilities of 47% and 49% at two locations with different wind regimens: Western Texas, USA, and Northern Ireland. This annual unavailability rate indicates that almost half the units of a wind farm at either location are likely to experience abnormal operation owing to the demands on acceleration-sensitive equipment. The use of fragility curves and the risk of unavailability for wind turbines will continue to grow because they allow performance assessment of future systems which favor larger, more flexible, more massive, and more complex wind turbine units. These new generation units will be able to operate at higher wind speeds and more demanding environmental conditions. A short-term option to reduce acceleration-induced failures in built systems is to establish shutdown criteria based on acceleration, rather than just wind speed. However, longterm handling of acceleration-sensitive equipment requires fragility and reliability analysis at the design stage, and the use of actively controlled protective devices. (L. Dueñas-Osorio).

- by Biswajit Basu
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- Civil Engineering, Structural Reliability, Modeling, Aerodynamics
- by Seong-Hoon Jeong
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- Civil Engineering, Mathematics, Failure Analysis, Reinforced concrete

A study has been made of the conditions which lead to intergranular brittle fracture in 4340-type steels at an ultra high yield strength level '(200 ksi, 380 MPa) in both an ambient environment and gaseous hydrogen. By means of Charpy impact tests on commercial and high purity steels, and by Auger electron spectroscopy of fracture surfaces, it is concluded that one-step temper embrittlement (OSTE or "500~ embrittlement"), and low K intergranular cracking in gaseous hydrogen are primarily the result of segregation of P to prior austenite grain boundaries. Segregation of N may also contribute to OSTE. Most, if not all, segregation apparently occurs during austenitization, rather than during tempering. Elimination of impurity effects by use of a high purity NiCrMoC steel results in an increase in Kth for hydrogen-induced cracking by about a factor of five (to the range 130 to 140 MNm-3/2). These observations are discussed in terms of our understanding of the mechanisms of OSTE and hydrogen-assisted cracking.

- by Charles McMahon and +1
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- Materials Engineering, Mechanical Engineering, High Pressure, Fracture Mechanics

The effect of milk origin on the physicochemical characteristics, microstructure and texture of Lighvan cheese was investigated over a 90-day ripening period. Besides fat, other physicochemical properties of Lighvan cheese were affected... more

- by zahra emam-djomeh
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- Engineering, Biological Sciences, Hardness, Dairy Technology

Kernel density, test weight, Stein and Wisconsin breakage susceptibility was primarily influenced by hardness, whereas Wisconsin breakage bilities, stress cracking, and Stenvert hardness were determined for three susceptibility was correlated with stress cracking. Milling quality, as meacorn hybrids that were classified as soft, hard, and of intermediate hardsured by a milling evaluation factor (MEF), decreased linearly with inness. A stress crack index was developed for quantifying degree of stress creasing drying temperature. For all drying temperatures, the hard hybrid cracking. Severity of stress cracking was directly related to hardness with had the highest MEF and the soft hybrid had the lowest MEF. Kernel the hardest hybrid showing the most severe cracking. Surprisingly, stress density was the best single predictor of MEF (R 2 = 0.773). A two-variable cracking was most severe at the intermediate (600C) drying temperature. model that combined test weight and kernel density improved the predic-Stein breakage was greatest for the soft hybrid and least for the hard tion of MEF (R 2 = 0.907). Incorporation of additional variables into hybrid, whereas Wisconsin breakage was greatest for the hard hybrid the model did not significantly improve the two-variable MEF prediction and least for the hybrid of intermediate hardness. Stein breakage susceptimodel.

- by Richard Stroshine
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- Prediction, Density, Drying, Temperature

Physical ageing of amorphous polymers well below their glass transition temperature leads to changes in almost all physical properties. Of particular interest is the increase in yield stress and post-yield strain softening that accompanies ageing of these materials. Moreover, at larger strain polymers seem to rejuvenate, i.e. aged and non-aged samples have identical stress-strain responses. Also, plastically deforming an aged sample seems to rejuvenate the polymer. In this work we use molecular dynamic simulations with a detailed force field suitable for macromolecular ensembles to simulate and understand the effects of ageing on the mechanical response of these materials. We show that within the timescales of these simulations it is possible to simulate both ageing and rejuvenation. The short range potentials play an important role in ageing and rejuvenation. A typical yield drop exhibited by glassy polymers is a manifestation of a sudden relaxation in the short range structure of an aged polymer. Moreover, the aged polymers are known to be brittle. We show that this is intimately related to its typical stress-strain response which allows it to carry arbitrarily large mean stresses ahead of a notch.

- by Dhiraj Kumar Mahajan
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- Engineering, Molecular Dynamics, Mathematical Sciences, Physical sciences

Structures in locations susceptible to severe seismic disturbances should be designed properly in order to resist lateral forces induced by earthquake motions. Steel offshore platforms are some of those structures which are built to withstand environmental and accidental loads during oil exploitation operation. Particular attention is being paid to earthquake loads in seismic active areas because it directly influences the capacity of the offshore installations. In this paper, a small-scaled planar platform has been modelled analytically using nonlinear finite element program, based on an experimental test, conducted simultaneously in order to assess the local and global behavior of pile-leg interaction in Jacket Type Offshore Platforms (JTOPs). A combination of nonlinear beam column elements and fatigue affected elements are used to capture the inelastic cyclic behavior of planar frame as accurately as possible. Results of analytical tests are to be compared with experiments and it is concluded that an analytical approach can be best used for modelling JTOPs with reasonable accuracy regardless of the type and scale of the structure. Moreover, a special study on joints has been carried out and the best model has been selected to simulate brittle behavior of joints resulting from heat affected zone.

- by Behrouz Asgarian
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- Civil Engineering, Oceanography, Finite Element, Offshore

The sensitivity of the empirical exponent of Bazant's size-effect scaling law on structural geometry is clarified through numerical experiments. For large centre-cracked tension panels, made of a linearly softening material, the best-fitting exponent is 0.90, whereas for large edge-cracked panels it is 0.75. For edge-cracked panels, the value of the exponent increases as a function of increasing crack-length-to-width-ratio. The results indicate that with structures of brittleness numbers below unity, reliable predictions of strength require the sizeeffect scaling law to be fitted for any particular structural geometry.

- by S. Östlund
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- Materials Engineering, Mechanical Engineering, Civil Engineering, Fracture

Two aluminium titanate (AT) ceramics containing magnesium and iron were sintered to study their high-temperature mechanical property and thermal stability. Both materials exhibited a pronounced inelastic stress-strain behaviour which is caused by extensive microcracks. The microcracking also led to an increasing R-curve behaviour which was measured in the Mg-AT material in the as-sintered state. At 1000°C, crack healing took place which led to an increase in the strength and Young's modulus. At 1100°C, the glassy phase started to soften which resulted in a reduction of the strength and Young's modulus. Thermal stability was assessed after annealing at 1000, 1100 and 1200°C for 250 and 1000 h in air. Although the FeAT material did not show any significant decomposition and degradation in mechanical properties, the Mg-AT material annealed at 1000 and 1100°C showed pronounced decomposition into corundum and rutile. The decomposition led to a brittle fracture, but increased the strength and Young's modulus. Both materials showed a lower coefficient of thermal expansion ((0.2;10\6 K\1) than that of stoichiometric aluminium titanate. The results are discussed with respect to the microstructure and phase relationship.

- by Dan Perera
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- Engineering, Materials Science, Microstructure, Ceramics

A Bayesian methodology to construct probabilistic seismic demand models for the components of a structural system is developed. Existing deterministic models and observational data are used. The demand models are combined with previously developed capacity models for reinforced concrete (RC) bridge columns to estimate the seismic fragilities of bridge components and systems. The approach properly accounts for all relevant uncertainties, including model error. Application to two bridge examples typical of modern California practice is presented.

- by Jinquan Zhong
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- Mechanical Engineering, Civil Engineering, Statistics, Engineering Mechanics

- by Gian Paolo Cimellaro
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- Civil Engineering, Resilience, Health Care, Structures and Fire Engineering

- by Qindan Huang
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- Mechanical Engineering, Civil Engineering, Statistics, Engineering Mechanics

An advanced high strength steel (0.08 %C, 1.79 %Mn, 0.23 %Si) was subjected to different post-weld heat treatments by quenching & tempering treatments (Q&T) after laser welding to reduce the risk of martensite formation in a few seconds based on an idea of quench and partitioning (Q&P), mechanism. The thermal stability of retained austenite, microstructure development and mechanical properties have been studied at 2 tempering temperatures of 440°C (Ms) and 636°C (Bs), both for 15 minutes, by means of electron microscopy, dilatometry, hardness profile and tensile tests. Dilatometer study unveiled that redistribution of carbon atoms and precipitation of transition carbides occur around 150°C and austenite decomposition occur at 600°C. Tempering at 636°C resulted in notable effect on the mechanical properties, while no significant difference was detected at 440°C, except a slight hardness drop. The strength increased up to 12% for the different specimens without significant loss in ductility for all specimens tempered at 636°C, which may be caused by precipitation hardening and recrystallization of martensite lath boundaries during tempering around 600°C.

- by Esa Vuorinen
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- Engineering, Materials Engineering, Mechanical Engineering, Microstructure

Abrasive waterjet (AWJ) cutting is a versatile technique which has been effectively applied to rock cutting since the late 1980s. The complexity of the interaction between the waterjet and the rocks complicates the thorough understanding of the phenomena involved in AWJ rock cutting. On one hand, rocks are complex materials which are generated through different processes in an uncontrolled environment without human interference. On the other hand, the AWJ acts with high velocity and turbulence, complicating direct observation and the perception of details. In this respect, the present research aims to contribute to the study of AWJ cutting applied to rocks, including the analysis of qualitative and quantitative information, both of great importance regarding the study of complex materials. Concerning quantitative data, special attention is given to the investigation of the cutting efficiency, which can be analyzed by observing conditions in which the higher cutting rate is associated with the minimum energy provided by the AWJ machine per removed volume of rock. Moreover, the real efficiency can be analyzed through the investigation of the conditions in which the major part of the energy provided by the AWJ machine is used effectively for rock cutting, deducting dissipation losses. The effects of varying traverse velocity and pump pressure on cutting parameters were also investigated, in addition to the influence of rock properties on the effective energy of cutting. The effective energy was calculated based both on the specific energy and specific destruction work of the materials. With respect to the qualitative investigation, petrographic and scanning electron microscopy (SEM) analyses were conducted in order to visualize and better understand the different effects of cutting on the studied rocks. Cutting tests with a traverse velocity of 200 mm/min and a pump pressure of 400 MPa presented the most efficient rock cutting regarding both methods of efficiency analysis. Dry density and tensile strength presented fair correlations with the effective cutting energy, while the modulus ratio presented the best correlations. It was observed that brittleness plays a key role in the understanding of the phenomena involved in AWJ rock cutting.

- by Paola B Arab
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- Abrasive Waterjet Cutting, Petrography, Brittleness, Hard Rocks

Poly(lactic acid) (PLA) and starch copolymers are obtained by reactive blending -varying the starch compositions from 0 to 60%. PLA is functionalized with maleic anhydride (MA), obtaining PLA-g-MA copolymers using dicumyl peroxide as an initiator of grafting in order to improve the compatibility and interfacial adhesion between the constituents. PLA þ starch blends without a compatibilizer do not have sufficient interfacial adhesion. Decomposition temperature of PLA is not affected by grafting. Glass transition temperatures and dynamic mechanical properties are affected since MA has a plasticizing effect. Along with an increasing starch content friction decreases while wear loss volume in pin-on-disk tribometry has a minimum at nominal 15% wt. starch but increases at higher starch concentrations. The residual depth in scratching and sliding wear testing has a maximum at 15% starch; there is a minimum of storage modulus E 0 determined in dynamic mechanical testing at the same concentration. Microhardness results also reflect the plasticization by MA.

- by victor orozco
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- Morphology, Tribology, Polymer Blends, Grafting

Fracture of glass seals in metallic hermetic electronic packaging is a significant failure mode because it may lead to moisture ingress and also to loss of load carrying capacity of the glass seal. Seal glasses are intrinsically brittle and their fracture is governed by the stresses generated. This study investigates stresses in lead seals caused by handling, testing, mechanical vibration, and thermal excursions. Loads considered are axial tension, bending, and twisting of the lead. More general loading can be handled by superposition of these results. Factorial techniques, commonly used in multi-variable Design of Experiments (DoE), are used in conjunction with finite element parametric simulations, to formulate closed-form regression models which relate the maximum principal stress within the glass seal to the type of loading and geometry. The accuracy of the proposed closed-form equations are verified through analysis of residuals. The analysis reveals the sensitivity of the magn...

- by Abhijit Dasgupta
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- Design, Manufacturing, Glass, Stress

Analytical probabilistic fragility studies require extensive computer simulations to account for the randomness in both input motion and response characteristics. In this study, an approach whereby a set of fragility relationships with known reliability is derived based on the fundamental response quantities of stiffness, strength and ductility is presented. An exact solution for a generalized single degree of freedom system is developed and employed to construct a Response Database of coefficients describing commonly used log-normal fragility relationships. Once the fundamental response quantities of a wide range of structural systems are defined, the fragility relationships for various limit states can be constructed without recourse to further simulation. The uncertainty associated with modeling simplifications is quantified by conducting comparisons between the proposed approach and detailed multi-degree of freedom (MDOF) systems. Application examples are given to demonstrate the efficiency of the proposed approach.

- by Seong-Hoon Jeong
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- Civil Engineering, Comparative Study, Failure Analysis, Damage Assessment

Generally, there are components loaded in a wide spectrum of loading rates, however most of design work is based on the data obtained using quasi-statical and uniaxial loading conditions. In case of inherently brittle materials the situation is all the more complicated because of their brittleness. There is a lack of experimental data and knowledge base of material response at loading in the range between quasi-static and ballistic loading rates. Cast basalt and soda-lime glass were the main experimental materials used in this investigation as a representative of natural based and structural brittle materials. These materials are widely used in civil industry as a building and decorative material, in chemical industry for transport of chemicals and in mining industry for transportation of powders (e.g. coal). Application in extreme conditions and safety requirements, in particular, raise an issue of fracture behaviour at higher loading rates. The main aim of the contribution is to investigate influence of strain rate on fracture resistance and to analyze response of the microstructure to high strain rate loading including the change of mechanical properties. The fractographic analysis of fracture surfaces was employed in the investigation with the aim to identify changes in fracture behaviour.

- by Ivo Dlouhy
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- Microstructure, Multidisciplinary, Strain Rate, Crack propagation

The fracture properties of different concrete-concrete interfaces are determined using the Bazant's size effect model. The size effect on fracture properties are analyzed using the boundary effect model proposed by Wittmann and his co-workers. The interface properties at micro-level are analyzed through depth sensing micro-indentation and scanning electron microscopy. Geometrically similar beam specimens of different sizes having a transverse interface between two different strengths of concrete are tested under three-point bending in a closed loop servo-controlled machine with crack mouth opening displacement control. The fracture properties such as, fracture energy (G f), length of process zone (c f), brittleness number (b), critical mode I stress intensity factor (K Ic), critical crack tip opening displacement CTOD c (d c), transitional ligament length to free boundary a Ã l À Á , crack growth resistance curve and micro-hardness are determined. It is seen that the above fracture properties decrease as the difference between the compressive strength of concrete on either side of the interface increases.

- by J. Chandra Kishen
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- Materials Engineering, Mechanical Engineering, Civil Engineering, Modeling

Pubic recofung burls" for trim collection of Information rs esntiated to average I nour Ofr 'ectonse. .indc iwan time tim e fo rviewingq ~insfJtIf1 ternn aiq aajuo q Amnl nd maintaining rie asta needed. and carnloirt~iq and revieswing te collection of information. Sena comments regarding tri.n burden enifflaten a, any outer asoect of ri,, c oflcin0 1nfom.Utn. including suggestion$ for reducing this burden. to Wasrni tngti i@acauarters sorvicm, osrectorate fo inomtitofifln 0oeiecion, anid fieboru 121 iSjefferon Oavfi'liqliwav. Suiote 204. Atlinglon. VA 22202-A302. and to the office Of Management and Budget. Pacetwofm ReduactionProject (* 7 04418S1.Wasiinqton 0Cc zSoj.

- by Waltraud M. Kriven
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- Crystallography, Microstructure, Kinetics, Glass

Three principal methods of failure prediction for brittle materials are analyzed statistically. Each method depends on fracture mechanics for its predictive value; hence the variance of the failure time depends on the scatter in the fracture mechanics data and the scatter in the estimate of the initial size of the strength-limiting crack. The variance is used to calculate confidence limits for the prediction of failure for glass and SIC. Procedures for the collection and analysis of data are discussed and the implications of the analysis for lifetime prediction are evaluated.

- by Edwin Fuller
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- Materials Engineering, Mechanical Engineering, Statistical Analysis, Glass

The risk of hydrogen embrittlement (HE) is currently one important factor impeding the use of medium Mn steels. However, knowledge about HE in these materials is sparse. Their multiphase microstructure with highly variable phase conditions (e.g. fraction, percolation and dislocation density) and the feature of deformation-driven phase transformation render systematic studies of HE mechanisms challenging. Here we investigate two austenite-ferrite medium Mn steel samples with very different phase characteristics. The first one has a ferritic matrix (~74 vol.% ferrite) with embedded austenite and a high dislo-cation density (~10 14 m −2) in ferrite. The second one has a well recrystallized microstructure consisting of an austenitic matrix (~59 vol.% austenite) and embedded ferrite. We observe that the two types of microstructures show very different response to HE, due to fundamental differences between the HE mi-cromechanisms acting in them. The influence of H in the first type of microstructure is explained by the H-enhanced local plastic flow in ferrite and the resulting increased strain incompatibility between fer-rite and the adjacent phase mixture of austenite and strain-induced α'-martensite. In the second type of microstructure, the dominant role of H lies in its decohesion effect on phase and grain boundaries, due to the initially trapped H at the interfaces and subsequent H migration driven by deformation-induced austenite-to-martensite transformation. The fundamental change in the prevalent HE mechanisms between these two microstructures is related to the spatial distribution of H within them. This observation provides significant insights for future microstructural design towards higher HE resistance of high-strength steels.

To control molecular mobility and study its effects on mechanical properties, we synthesized two series of poly(ester carbonate) and polycarbonate copolymers with different linkages: (B x t) n (x ϭ 3, 5, 7, 9) and (B x T) n (x ϭ 1, , where t represents the terephthalate, T represents the tetramethyl bisphenol A carbonate linkages, and B is the conventional bisphenol-A (BPA) carbonate. These two series of materials have distinct differences in their relaxation behaviors and chain mobility, as indicated by the -flip motion of the phenylene rings in the B x blocks. Uniaxial tensile tests of the copolymers indicate that the brittle-ductile transition (BDT) temperatures of the copolymers are correlated to whether the ␥-relaxation peaks due to the B x sequence is fully established. The materials possessing more fully established lowtemperature ␥ peaks give rise to a lower BDT. Also, the locations of the ␥ peaks are correlated to the ring flips of the B x blocks of polymer chains.

- by Albert Fan Yee
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- Engineering, CHEMICAL SCIENCES, Tensile Stress, Brittleness

In hereditary pyropoikilocytosis (HPP) and one type of hereditary elliptocytosis (HE), spectrin self-association is abnormal . Spectrin extracted from normal erythrocyte membranes at 0°C is nearly all tetrameric, while in HPP and HE (type 1) a substantial amount of the extracted spectrin is dimeric. Abnormal reassociation of spectrin dimers to tetramers can also be demonstrated. We here report the case of a family in which the child has moderately severe hemolysis, with extreme microcytosis and poikilocytosis. The spectrin extracted at 0°C was predominately dimer. Parents had levels of dimer intermediate between patient and control values. The temperature dependence was normal for (a) erythrocyte fragmentation; (b) spectrin extractability; and (c) circular dichroism of purified spectrin. Neither the patient nor either parent had elliptocytic red cells as judged from smears and scanning electron microscopy. The presence of substantial amounts of dimeric spectrin in the parents is consistent with a model in which each parent is heterozygous for a different nonassociating mutant spectrin, while the child has inherited a nonassociating molecule from each parent. In each individual, the degree of mechanical stability of the erythrocyte membrane, determined by ektacytometry, was proportional to the amount of tetramer found in the membrane. The description of this case is consistent with either HPP or a form of homozygous HE which is asymptomatic in the carrier state.

A finite element model was developed to study adhesion of elastic-plastic microcontacts in a previous investigation. An interesting result was the identification of two distinct separation modes, i.e. brittle and ductile separation. In the current study, that model is used to conduct a series of simulations to determine the influence of four nondimensional parameters (including the maximum load parameter) on the contact and on the separation modes. The results show that the parameter S (the ratio of the theoretical stress to the hardness) and deltaf/deltac (representing the loading level) are the most important. Smaller S can only lead to brittle separation, while larger S can cause either separation mode depending on deltaf/deltac. Ductile separation is more likely to occur at smaller deltaf/deltac and brittle separation at greater deltaf/deltac. The transition between the two separation modes occurs at about S =1.2 (for deltaf/deltac=30) which corresponds to the theoretical stress for adhesion being 20% greater than the hardness. This result is qualitatively similar to the existing simplified analytical models, in that the adhesion energy, the hardness, and the loading level play important roles in the occurrence of ductile separation. However, there are important quantitative differences. Comparisons are also made with molecular dynamics simulations of a contact and with a fracture mechanics model of crack propagation.

- by Izhak Etsion
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- Engineering, Applied Physics, Adhesion, Finite Element Analysis

Existing models of brittle shear failure are unable to account for three-dimensional deformation involving the development of polymodal sets of fractures. Motivated by field observations of contemporaneous arrays of quadrimodal faults and deformation bands, we use an idealised micromechanical model to explain how brittle shear fractures can form oblique to all three remote principal stresses. We model tensile microcracks as finite ellipsoidal voids, subjected to small opening strains, in a linear isotropic elastic matrix. The geometry of the tensile stress lobes around the ends of an isolated microcrack promotes the en echelon interaction of neighbouring cracks with respect to the prescribed crack orientation. Coalescence of these interacting crack arrays into a through-going composite fracture surface leads to a brittle shear failure plane oriented obliquely to all three coordinate axes and all three remote principal stresses. Experimental evidence supports the idea that composite shear fractures can propagate in-plane through the coalescence of many constituent tensile microcracks. Our new model, based on the 3-D geometry of the elastic stress field around a mode I crack, can explain the oblique orientations of polymodal faults formed in a triaxially compressive stress field.

- by R. Holdsworth
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- Earth Sciences, Geology, Fracture, Interaction

Public reoortmc burden for this collection of information is estimated to average 1 hour oer resoor.se including the time for reviewing instructionssear, n,ng_existing oata sources gathering and maintaining the data needed, and comoletinq and reviewing the collection of information Sen,! comments regarding this burden es .mate o, an othe a oea of this ?ol ectio of information, including suggestions for reducing this burden to Washington Headauirters Services Directorate tor Information Oo*rat,ons and Reocrts. J215 Jefferson Davis Hiahwa-Suite 1204 Arlington i/A 22202-4302. and to the Office of Management and Budget. Paperwork Reduction Pr0)ect (0704-0186). Washington, DC 205C3.

- by Ajit Kelkar
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- Materials Science, Ceramic matrix composites, Brittleness

- by Ajit Kelkar
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- Materials Science, Ceramic matrix composites, Brittleness

- by Richard Stroshine
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- Prediction, Density, Drying, Temperature

- by Richard Stroshine
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- Prediction, Density, Drying, Temperature

The micromechanical damage mechanics formulated by Ashby and Sammis, 1990, “The Damage Mechanics of Brittle Solids in Compression,” Pure Appl. Geophys., 133(3), pp. 489–521, and generalized by Deshpande and Evans 2008, “Inelastic Deformation and Energy Dissipation in Ceramics: A Mechanism-Based Constitutive Model,” J. Mech. Phys. Solids, 56(10), pp. 3077–3100. has been extended to allow for a more generalized stress state and to incorporate an experimentally motivated new crack growth (damage evolution) law that is valid over a wide range of loading rates. This law is sensitive to both the crack tip stress field and its time derivative. Incorporating this feature produces additional strain-rate sensitivity in the constitutive response. The model is also experimentally verified by predicting the failure strength of Dionysus-Pentelicon marble over strain rates ranging from ∼10− 6to 103s− 1. Model parameters determined from quasi-static experiments were used to predict the failure stre...

- by Ares Rosakis
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- Mechanical Engineering, Civil Engineering, Aerospace Engineering, Stress

- by Rafael Estevez
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- Engineering, Molecular Dynamics, Mathematical Sciences, Physical sciences

This study aimed to investigate the machinability of zirconia blocks pre-sintered at four different temperatures (900 °C, 1000 °C, 1100 °C, and 1200 °C). Vickers hardness and fracture toughness were measured to obtain the brittleness index (BI) of the zirconia blocks. The shrinkage percentage of the blocks pre-sintered at different temperatures was also determined upon final sintering at 1500 °C. The blocks were then subjected to machining, and the machined surfaces were morphologically analyzed. Although the materials pre-sintered at 900 °C and 1000 °C could be machined, noticeable trace lines and grooves formed on the machined surface due to lack of strength prior to sintering. BI and surface morphology confirmed that the new zirconia block can be milled at a pre-sintering temperature of 1100 °C and can achieve an acceptable shrinkage value for machining upon final sintering. © 2019 Elsevier B.V.