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

Adhesive organs like arolia of insects allow these animals to climb on different substrates by creating high adhesion forces. According to the Dahlquist criterion, adhesive organs must be very soft, exhibiting an effective Young's... more

Adhesive organs like arolia of insects allow these animals to climb on different substrates by creating high adhesion forces. According to the Dahlquist criterion, adhesive organs must be very soft, exhibiting an effective Young's modulus of below 100 kPa to adhere well to substrates. Such a low effective Young's modulus allows the adhesive organs to make almost direct contact with the substrate and results in van der Waals forces along with capillary forces. In previous studies, the effective Young's moduli of adhesive organs were determined using indentation tests, revealing their structure to be very soft. However, adhesive organs show a layered structure, thus the measured values comprise the effective Young's moduli of several layers of the adhesive organs. In this study, a new approach is illustrated to measure the Young's modulus of the outermost layer of the arolium, i.e. of the epicuticle, of the stick insect Carausius morosus. As a result of the epicuti...

Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and... more

Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of ...

Needles with asymmetric bevel tips naturally bend when they are inserted into soft tissue. In this study, we present an analytical model for the loads developed at the bevel tip during needle-tissue interaction. The model calculates the... more

Needles with asymmetric bevel tips naturally bend when they are inserted into soft tissue. In this study, we present an analytical model for the loads developed at the bevel tip during needle-tissue interaction. The model calculates the loads based on the geometry of the bevel edge and gel material properties. The modeled transverse force developed at the tip is compared to forces measured experimentally. The analytical model explains the trends observed in the experiments. In addition to macroscopic studies, we also present microscopic observations of needle-tissue interactions. These results contribute to a mechanics-based model of robotic needle steering, extending previous work on kinematic models.

The importance of breakfast cereal flakes (BCF) in Western diets deserves an understanding of changes in their mechanical properties and microstructure that occur during soaking in a liquid (that is, milk or water) prior to consumption.... more

The importance of breakfast cereal flakes (BCF) in Western diets deserves an understanding of changes in their mechanical properties and microstructure that occur during soaking in a liquid (that is, milk or water) prior to consumption. The maximum rupture force (RF) of 2 types of breakfast flaked products (BFP)--corn flakes (CF) and quinoa flakes (QF)--were measured directly while immersed in milk with 2% of fat content (milk 2%) or distilled water for different periods of time between 5 and 300 s. Under similar soaking conditions, QF presented higher RF values than CF. Soaked flakes were freeze-dried and their cross section and surface examined by scanning electron microscopy. Three consecutive periods (fast, gradual, and slow reduction of RF) were associated with changes in the microstructure of flakes. These changes were more pronounced in distilled water than in milk 2%, probably because the fat and other solids in milk become deposited on the flakes' surface hindering liqu...

Summary of the doctoral dissertation The main purpose of this work was to recognize the technological construction of individual elements of hand-held firearms. The analysis of literature sources and conducted material science researches... more

Summary of the doctoral dissertation
The main purpose of this work was to recognize the technological construction of individual elements of hand-held firearms. The analysis of literature sources and conducted material science researches allowed us to broaden our knowledge of the processes of their production in specific chronological sections.

Torsion extrusion (TE) process was performed successfully for consolidation of commercially pure aluminum powder at 350 °C. It was shown by a specific mechanism that the shear strains applied during consolidation of aluminum powder by the... more

Torsion extrusion (TE) process was performed successfully for consolidation of commercially pure aluminum powder at 350 °C. It was shown by a specific mechanism that the shear strains applied during consolidation of aluminum powder by the TE process have a considerable effect on the micro-structural shape of the porosities and also their omission efficiency. Density measurements showed that in the TE process a better consolidation, with respect to hot forward extrusion, was accomplished. Tensile and hardness tests results showed superior values for the ultimate tensile strength (UTS) and hardness values in the specimens produced by the TE process.

To evaluate the radiopacity, ultimate tensile strength (UTS), microhardness (KHN), degree of conversion (DC), water sorption (WS) and solubility (SL) of experimental adhesives. Five experimental adhesives with different concentrations of... more

To evaluate the radiopacity, ultimate tensile strength (UTS), microhardness (KHN), degree of conversion (DC), water sorption (WS) and solubility (SL) of experimental adhesives. Five experimental adhesives with different concentrations of barium-borosilicate oxide microfillers [0% (R0), 30% (R30), 40% (R40), 50% (R50), 60% (R60)] were formulated based on the adhesive system Ambar (FGM). The adhesive Adper Single Bond 2 (SB, 3M ESPE) was used as commercial reference. For the radiopacity (n = 5), KHN (n = 5), WS (n = 10), and SL (n = 10) tests, adhesive disks were constructed (5.0 mm in diameter and 1.0 mm thick), while for UTS (n = 5), hourglass-shaped specimens with a cross-sectional area of 0.8 mm2 were used. The FTIR spectra of unpolymerized and polymerized adhesives were used to determine the DC. Data were submitted to a one-way ANOVA and Tukey's test (α = 0.05). All experimental adhesives showed radiopacity similar to enamel, except those of R0 and SB. Filler addition did not...

Abrasive wear is an important component in failure analyses in mining equipment. This work relates to a wear test for mill components after the occurrence of a failure in an iron ore pelletizing plant at Vale’s Tubarao Complex, Vitoria,... more

Abrasive wear is an important component in failure analyses in mining equipment. This work relates to a wear test for mill components after the occurrence of a failure in an iron ore pelletizing plant at Vale’s Tubarao Complex, Vitoria, Brazil. The equipment involved is a ball mill, which is used to grind the pellet feed into extremely fine powder for use in pelletizing process. Metallurgical components of this mill, such as screws, shell and mill head, are analyzed in a milling system simulation using iron ore slurry in order to correlate the components loss weight with running time. The analysis results and the tribology involved in this iron ore grinding process are presented in this paper. Finally, the value of the inspection process is evidenced as a key factor at the prevention of failures, at the prediction of the life cycle of the mill's components and at the reliability of the production assets.
Keywords: :Abrasive Wear; Iron Ore; Pelletizing; Grinding.

For heterogeneous integration in many More-than-Moore applications, surface preparation is the key step to realize well-bonded multiple substrates for electronics, photonics, fluidics and/or mechanical components without degradation in... more

For heterogeneous integration in many More-than-Moore applications, surface preparation is the key step to realize well-bonded multiple substrates for electronics, photonics, fluidics and/or mechanical components without degradation in performance. Therefore, it is critical to understand how various processing and environmental conditions affect their surface properties. In this paper, we investigated the effects of oxygen plasma and humidity on some key surface properties such as water contact angle, roughness and hardness of three materials – silicon (Si), silicon dioxide (SiO2) and glass, and their impact on bondability. The low surface roughness, high surface reactivity and high hydrophilicity of Si, SiO2 and glass at lower activation times can result in better bondability. Although, the surface reactivity of plasma-ambient-humidity-treated Si and SiO2 is considerably reduced, their reduction of roughness and increase of hydrophilicity may enable good bonding at low temperature heating due to augmented hydroxyl groups. The decrease of hardness of Si and SiO2 with increased activation time is attributed to higher surface roughness and formation of amorphous layers of Si. While contact angle and surface roughness results show correlation with bondability, the role of hardness on bondability requires further investigation.

Duplex stainless steel samples were aged at low temperatures of the 300ºC and 400ºC for 3000, 5000 and 7000 hours. The changes at the micro-structure were fol-lowed during the annealing time using an optical micro s-copy and measurements... more

Duplex stainless steel samples were aged at low temperatures of the 300ºC and 400ºC for 3000, 5000 and 7000 hours. The changes at the micro-structure were fol-lowed during the annealing time using an optical micro s-copy and measurements of phase percentages. Nano-hardness was used in order to identify the phase responsi-ble for the increasing in the global hardness. The G phase precipitation and alpha’ phase due to spinodal decomposition was identified by transmission electron microscopy. It was detected that the micro-structural changes affect the global properties, remarkably the global hardness. TEM results showed that the chromium rich precipitation occurs mainly in the ferrite phases. The results also showed a clear difference between the kinetics of precipitation of the lower chromium content sample and the higher chromium sam-ple. The phenomena of precipitation and coalescence ofchromium rich phases must be related to the increasing and decreasing tendencies of hardness, res...

The influence of ionic substituents in calcium phosphates intended for bone and tooth replacement biomedical applications is an important research topic, owing to the essential roles played by trace elements in biological processes. The... more

The influence of ionic substituents in calcium phosphates intended for bone and tooth replacement biomedical applications is an important research topic, owing to the essential roles played by trace elements in biological processes. The present study investigates the mechanical and biological evaluation of ionic doped hydroxyapatite/β-tricalcium phosphate mixtures which have been prepared by a simple aqueous precipitation method. Heat treating the resultant calcium phosphates in a carbonated atmosphere led to the formation of ionic doped carbonated hydroxyapatite/β-tricalcium phosphate mixtures containing the essential ions of biological apatite. The structural analysis determined by Rietveld refinement confirmed the presence of hydroxyapatite as the main phase, together with a considerable amount of β-tricalcium phosphate. Such phase assemblage is essentially due to the influence of substituted ions during synthesis. The results from mechanical tests proved that carbonate substitutions are detrimental for the mechanical properties of apatite-based ceramics. In vitro proliferation assays of osteoblastic-like cells (MC3T3-E1 cell line) to powders revealed that carbonate incorporation can either delay or accelerate MC3T3 proliferation, although reaching the same proliferation levels as control cells after 2 weeks in culture. Further, the powders enable pre-osteoblastic differentiation in a similar manner to control cells, as indirectly measured by ALP activity and Type-I collagen medium secretion.