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91.
92.
In this article, the tensile and fracture properties of a discontinuously reinforced aluminum (DRA) alloy composite are modeled
to determine the influence of constituent parameters on material behavior. Comparison of the elastic-modulus calculations
to the experimental data suggest that the angular particles are more effective in load transfer than spherical particles,
and that a unit cylinder geometry is a good representation of the particles under elastic conditions. This same geometry is
used in the finite element-based elastic-plastic model of Bao et al., and reasonably good agreement is obtained between the experimental and predicted yield strengths. A fracture-mechanics model
is proposed for predicting the elongation to failure. The model assumes the existence of particle cracks, and criticality
is based on the strain required for matrix rupture between cracked particles. The damage criterion of Cockcroft and Latham
is utilized, and model predictions are compared to data from different investigations. It is shown that the volume fraction
of particles and the work-hardening coefficient of the matrix have a strong influence on the strain to failure. Fracture toughness
modeling once again exposes the limitations of existing zero-degree crack-propagation models, such as that of Hahn and Rosenfield,
which predict increased toughness with yield strength rather than a decrease, which is observed experimentally. A shear-failure
model along a 45-deg direction is proposed for the higher-strength conditions, where concentrated slip bands were observed.
The model exhibits the inverse toughness dependence on strength and better correlation to peak-aged (PA) data, but shows poorer
agreement with underaged (UA) data. Thus, a transition from zero-degree propagation to 45-deg propagation with increasing
strength is suggested. A simplified method for extracting particle stresses is illustrated and is used to estimate a Weibull
modulus of 4.9 and a Weibull strength of 2450 MPa for the SiC particles of an average diameter of 10 μm.
This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October
11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite Materials
Committee. 相似文献
93.
Among various coating systems for industrial and engineering applications, glass and glass-ceramic coatings have advantages
of chemical inertness, high temperature stability and superior mechanical properties such as abrasion, impact etc as compared
to other coating materials applied by thermal spraying in its different forms viz. PVD, CVD, plasma, etc. Besides imparting
required functional properties such as heat, abrasion and corrosion resistance to suit particular end use requirements, the
glass and glass-ceramic coatings in general also provide good adherence, defect free surface and refractoriness.
Systematic studies covering the basic science of glass and glass-ceramic coatings, the functional properties required for
a particular end-use along with the various fields of application have been reviewed in this paper. 相似文献
94.
Single crystals of MgO were subjected to plastic strain-controlled push-pull cyclic deformation at elevated temperatures. Below 400° C the crystals were very brittle and failed with a few fatigue cycles. At 470° C a large number of cycles could be obtained before failure, and the cyclic stress-strain response showed a period of rapid hardening followed by a period of decreasing hardening rate. TEM investigations of the lower temperature samples show structures of isolated dislocation dipoles, multipoles and debris. At 470° C dense bundles of dislocations were observed aligned perpendicular to the Burgers vector direction. The regions between the bundles were relatively dislocation free, but they contained a high density of debris. Bowed out screw dislocations are observed between the edge dislocation bundles, suggesting that screw dislocations were largely mobile. Comparisons are made with the cyclic deformation and structure of fcc metals and other NaCl structure single crystals. 相似文献
95.
We have studied the hydration of Secar 71 high alumina cement with added poly(vinyl alcohol-acetate). These materials are used in production of macro-defect-free cements. The polymer has considerable effects on the cement chemistry; the heat output profile measured by conduction calorimetry is significantly altered and few crystalline hydrates are produced. Where hydrate crystals do occur, the calcium-rich compounds are preferred. There are some differences in behaviour between pure polyvinyl alcohol and polymers containing acetate groups. Evidence is presented for polymer complexes in which metal ions from the cement crosslink the polymer chains. Such complexes are formed most readily by aluminium ions, so the cement grains are left with a relative surplus of calcium on their hydrating surfaces. 相似文献
96.
Steven Blake Samiul Amin Wei Qi Madhabi Majumdar E. Neil Lewis 《International journal of molecular sciences》2015,16(8):17719-17733
A detailed understanding of the mechanism of unfolding, aggregation, and associated rheological changes is developed in this study for β-Lactoglobulin at different pH values through concomitant measurements utilizing dynamic light scattering (DLS), optical microrheology, Raman spectroscopy, and differential scanning calorimetry (DSC). The diffusion interaction parameter kD emerges as an accurate predictor of colloidal stability for this protein consistent with observed aggregation trends and rheology. Drastic aggregation and gelation were observed at pH 5.5. Under this condition, the protein’s secondary and tertiary structures changed simultaneously. At higher pH (7.0 and 8.5), oligomerizaton with no gel formation occurred. For these solutions, tertiary structure and secondary structure transitions were sequential. The low frequency Raman data, which is a good indicator of hydrogen bonding and structuring in water, has been shown to exhibit a strong correlation with the rheological evolution with temperature. This study has, for the first time, demonstrated that this low frequency Raman data, in conjunction with the DSC endotherm, can be been utilized to deconvolve protein unfolding and aggregation/gelation. These findings can have important implications for the development of protein-based biotherapeutics, where the formulation viscosity, aggregation, and stability strongly affects efficacy or in foods where protein structuring is critical for functional and sensory performance. 相似文献
97.
Shrinkage studies were conducted on silane‐grafted moisture crosslinkable linear low‐density polyethylene (LLDPE) insulation stripped from extrusion‐coated copper conductors. The insulation, which possesses orientation imparted during melt processing, showed remarkable levels of shrinkage when heated above the melting point of the polymer, though the shrinkage can be greatly reduced by moisture crosslinking the insulation below the melting point of the LLDPE. Shrinkage along the direction of orientation was accompanied by swelling in the other dimensions. Differential scanning calorimetry (DSC) revealed several trends, including a decrease in both melting point and degree of crystallinity with increasing crosslinking. In the first heat after annealing, crosslinked samples exhibited a shoulder in the DSC endotherm several degrees below the normal melting point of the LLDPE. In agreement with prior studies in silane‐grafted HDPE, relaxation of orientation by annealing appeared to result in an increase in the enthalpy of melting. The degree of shrinkage was also found to be dependent on the insulation thickness, which is attributed to faster cooling in thinner insulation immediately following extrusion coating. The results highlight the extensive built in stresses that can be frozen into polymer layers in fabricated articles due to melt orientation. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
98.
Rongsong Li Zhi Ning Rohit Majumdar Jeffery Cui Wakako Takabe Nelson Jen Constantinos Sioutas Tzung Hsiai 《Particle and fibre toxicology》2010,7(1):1-12
Background
Nanometer silicon dioxide (nano-SiO2) has a wide variety of applications in material sciences, engineering and medicine; however, the potential cell biological and proteomic effects of nano-SiO2 exposure and the toxic mechanisms remain far from clear.Results
Here, we evaluated the effects of amorphous nano-SiO2 (15-nm, 30-nm SiO2). on cellular viability, cell cycle, apoptosis and protein expression in HaCaT cells by using biochemical and morphological analysis, two-dimensional differential gel electrophoresis (2D-DIGE) as well as mass spectrometry (MS). We found that the cellular viability of HaCaT cells was significantly decreased in a dose-dependent manner after the treatment of nano-SiO2 and micro-sized SiO2 particles. The IC50 value (50% concentration of inhibition) was associated with the size of SiO2 particles. Exposure to nano-SiO2 and micro-sized SiO2 particles also induced apoptosis in HaCaT cells in a dose-dependent manner. Furthermore, the smaller SiO2 particle size was, the higher apoptotic rate the cells underwent. The proteomic analysis revealed that 16 differentially expressed proteins were induced by SiO2 exposure, and that the expression levels of the differentially expressed proteins were associated with the particle size. The 16 proteins were identified by MALDI-TOF-TOF-MS analysis and could be classified into 5 categories according to their functions. They include oxidative stress-associated proteins; cytoskeleton-associated proteins; molecular chaperones; energy metabolism-associated proteins; apoptosis and tumor-associated proteins.Conclusions
These results showed that nano-SiO2 exposure exerted toxic effects and altered protein expression in HaCaT cells. The data indicated the alterations of the proteins, such as the proteins associated with oxidative stress and apoptosis, could be involved in the toxic mechanisms of nano-SiO2 exposure. 相似文献99.
Present work describes a kinetic analysis of various aspects of biohydrogen production in batch test using optimized conditions obtained previously. Monod model and Logistic equation have been used to find growth kinetic parameters in batch test under uncontrolled pH. The values of μm, Ks, and Xm were 0.64 h−1, 15.89 g-COD L−1, and 7.26 g-VSS L−1, respectively. Modified Leudeking-Piret and Michaelis–Menten equation corroborates a flux of energy to hydrogen production pathway and energy sufficiency in the system. Modified Gompertz equation illustrates that the overall rate and hydrogen yield at 15 g-COD L−1 was higher compared to a dark fermentation of other wastewaters. Besides, Andrew's equation also suggests that since the higher value of KI (19.95 g-COD L−1), k (255 mL h−1 L−1) was not inhibited at high S. The experimental results implied that the entire products during the fermentation process were growth and substrate degradation associated. The result also confirms that the acetate and butyrate were substantially used for hydrogen production in acidogenic metabolism under uncontrolled pH. 相似文献
100.