Indentation cracking under sharp-pointed indenters is analyzed using compliance-based, nonlinear, fracture mechanics, The stress intensity factor, K, in linear elastic fracture mechanics is well known to be proportion...
详细信息
Indentation cracking under sharp-pointed indenters is analyzed using compliance-based, nonlinear, fracture mechanics, The stress intensity factor, K, in linear elastic fracture mechanics is well known to be proportional to the load, P;in this nonlinear analysis K is proportional to P-3/4. The observed relation between indenter load-point displacement and crack length is based on similitude of crack lengths with load-point displacements as a strain-controlled fracture. The equations that relate load and a function of the crack length to the crack driving force, J, have been found for Vickers indentations. Analysis of the nonlinear load vs displacement assumes an equilibrium crack in the elastic material surrounding the indent, The hardness that describes the load vs load-point displacement during cracking is derived on a constant J line in load-displacement space. The crack length is shown experimentally to be proportional to the load-point displacement after crack initiation for several different indenters in ZnS. The measured loading curves are nonlinear and display crack initiation during loading, The K-Ic expressions found here are very similar to correlations that have been applied to indentation cracks.
A finite element algorithm to simulate two dimensional flows of viscous and inviscid compressible fluids for a wide range of Mach numbers is presented in this work. This model is coupled to immersed deformable structu...
详细信息
A finite element algorithm to simulate two dimensional flows of viscous and inviscid compressible fluids for a wide range of Mach numbers is presented in this work. This model is coupled to immersed deformable structures through equilibrium and compatibility conditions in order to analyze its dynamic behavior. For the fluid, time integration is performed by a two-step Taylor-Galerkin explicit scheme and Newmark’s method is used to obtain the dynamic response of the structure. An arbitrary mixed Euler-Lagrange description is used to re-define a new finite element mesh in the presence of the immersed structure displacements. Finally, several examples are included showing the model behavior and possibilities for future expansions.
The elevated temperature phase transformations occurring in investment cast and hot-isostatically pressed near-gamma Ti-48Al-2Nb-2Mn containing 0, 0.5, 1, 2 and 7 vol.% TiB2 have been investigated utilizing in situ th...
详细信息
The elevated temperature phase transformations occurring in investment cast and hot-isostatically pressed near-gamma Ti-48Al-2Nb-2Mn containing 0, 0.5, 1, 2 and 7 vol.% TiB2 have been investigated utilizing in situ thermal analysis, high temperature X-rays and optical and transmission electron microscopies. A series of reversible transformations were observed during heating and cooling: alpha2 + gamma --> alpha + gamma --> alpha + beta + gamma --> beta + gamma --> beta + L where, on heating, the low temperature eutectoid transformation alpha2 + gamma --> alpha was followed by beta precipitation and gamma dissolution, a high temperature reverse peritectoid reaction, alpha --> beta + gamma, and, finally, an inverse peritectic reaction, gamma --> beta + L. Furthermore, the variable TiB2 morphologies observed suggest that TiB2 redissolves during XD(TM) processing, reprecipitating during subsequent solidification. Its morphology then evolves from lacey to plate- or needle-like, to blocky as the B content increases or the solidification rate decreases. Finally, it was shown that, rather than the TiB2 content per se, the elemental B content and, by extension, the total interstitial content were the primary factors controlling the differences in the phase transitions temperatures observed in these materials. As the interstitial content increased, the eutectoid transformation temperature increased, while the peritectoid transformation temperature was not affected and the peritectic transformation temperature decreased.
Incramute Cu-Mn alloys were dealloyed to remove Mn by selective electrolytic separation. The porous dealloyed specimens were compressed at 0.17-14 GPa, resulting in densities of 55-88% of the density of pure copper. S...
详细信息
Incramute Cu-Mn alloys were dealloyed to remove Mn by selective electrolytic separation. The porous dealloyed specimens were compressed at 0.17-14 GPa, resulting in densities of 55-88% of the density of pure copper. Some porous copper specimens before compression were soaked in a mixture of monomer (MMA) and the initiator (AIBN), compressed, and then polymerized by heating. Young's moduli of both the dealloyed porous copper and its PMMA composite were found to decrease exponentially with porosity and volume fraction of PMMA, respectively. The apparent activation energy for damping of Cu-PMMA composite near the glass transition temperature of PMMA was found to increase with decreasing volume fraction of PMMA.
Porous copper was produced by electrolytic dealloying of a Cu-Mn alloy (Incramute: Cu, 40-48 wt. % Mn, 1.4-2.3 wt. % Al) conducted in a 0.3 N-NaCl solution at a potential of -0.2 V (SCE). The dealloying time needed fo...
详细信息
Porous copper was produced by electrolytic dealloying of a Cu-Mn alloy (Incramute: Cu, 40-48 wt. % Mn, 1.4-2.3 wt. % Al) conducted in a 0.3 N-NaCl solution at a potential of -0.2 V (SCE). The dealloying time needed for the as-received cold-rolled specimen (50 h) is shorter than that of the annealed specimen (850 degrees C for 2 h). The pore size, about 1 mu m, of the dealloyed cold-rolled specimen is bigger than that, about 0.1 mu m, of the dealloyed specimen after annealing. This is probably because annealing reduced the phase inhomogeneity and removed the rolling effects.
The impression creep behavior of lead was investigated using a 100 mum diameter punch at ambient and elevated temperatures (433 K-563 K) under punching stresses of 6-70 MPa. The results were compared with the data obt...
详细信息
The impression creep behavior of lead was investigated using a 100 mum diameter punch at ambient and elevated temperatures (433 K-563 K) under punching stresses of 6-70 MPa. The results were compared with the data obtained from conventional creep tests reported in the literature. Unlike the indentation creep test, the impression creep test showed a steady-state velocity after a short transient period when the flat-end cylindrical punch was pushed against the lead surface by a constant load. Both the temperature and stress dependences were comparable to those of the constant stress tensile creep tests under similar conditions. A master curve for lead was established by collecting data from the impression creep tests and the constant stress tensile creep tests. The indentation creep measurements for lead were included also. However, the indentation data depend on the load applied.
Monolithic molybdenum disilicide (MoSi2) powder and MoSi2 powders blended with ductile and brittle reinforcements were consolidated by hot isostatic pressing (HIP). The extent of densification of the consolidated samp...
详细信息
Monolithic molybdenum disilicide (MoSi2) powder and MoSi2 powders blended with ductile and brittle reinforcements were consolidated by hot isostatic pressing (HIP). The extent of densification of the consolidated samples as a function of temperature, pressure and time was determined by precision density measurements. HIP diagrams were constructed based on theoretical models. Material properties, required as input for the HIP map software, were compiled or extrapolated from published literature, experimentally determined and in some cases were estimated from the rule of mixtures. The model predictions were compared with experimental data and dominant mechanisms of densification were identified.
The influence of hot isostatic pressing (HIP) consolidation parameters on the mechanical properties of molybdenum disilicide (MoSi2) and MoSi2 reinforced with ductile and brittle reinforcements was studied. MoSi2, MoS...
详细信息
The influence of hot isostatic pressing (HIP) consolidation parameters on the mechanical properties of molybdenum disilicide (MoSi2) and MoSi2 reinforced with ductile and brittle reinforcements was studied. MoSi2, MoSi2-20 vol.% coarse and fine niobium powder and MoSi2-20 vol.% silicon carbide whiskers consolidated by HIP at 1200-1400-degrees-C, 207 MPa, for 1 and 4 h were tested in compression for elevated temperature strength and creep resistance. Single-edge-notched specimens of the three materials were tested in a three-point bend configuration for fracture toughness. mechanical properties were related with consolidation parameters and post-HIP microstructures.
Dynamic material modeling (DMM) has been applied to the analysis of the mechanical behavior of a (Widmanstatten + primary alpha2 + beta) Ti-25Al-11Nb alloy to establish the flow stress-strain rate-temperature-strain c...
详细信息
Dynamic material modeling (DMM) has been applied to the analysis of the mechanical behavior of a (Widmanstatten + primary alpha2 + beta) Ti-25Al-11Nb alloy to establish the flow stress-strain rate-temperature-strain criteria for stable flow. Unstable and stable flow regimes predicted by DMM were correlated to microstructural observations. Unstable flow zones were related to transformation of orthorhombic O --> alpha2, kinking of the alpha2 lamellae, shear band formation and coarsening of the dynamically recrystallized gram structure;stable flow regimes were shown to be associated with dissolution of the Widmanstatten alpha2, coarsening of primary alpha2 and dynamic spheroidization of the lamellar alpha2 microconstituents.
暂无评论