The three-point bending test by Kolsky-bar apparatus is a convenient technique to test the dynamic fracture properties of materials. This paper presents detailed three-dimensional finite element simulations of a silicon particle reinforced aluminum (SiCp/Al) experiment (Li et al., [Proceedings of the US Army Symposium on Solid Mechanics]. In the simulations, the interaction between the input bar and the specimen is modeled by coupled boundary conditions. The material model includes large plastic deformations, strain-hardening and strain-rate hardening mechanisms. Furthermore, crack initiation and propagation processes are simulated by a cohesive element model. The simulation results quantitatively agree with the experimental measurements on three fronts: (1) the structural response of the specimen, (2) the time of unstable crack propagation, and (3) the local deformations at the crack-tip zone. The simulations reveal crack propagation characteristics, including crack-tip plastic deformation, crack front curving, and crack velocity profile. The effectiveness of Kolsky-bar type fracture tests is verified. It is shown that a rate-independent cohesive model can describe the complicated dynamic elastic–plastic fracture process in the SiCp/Al material.

The mechanical response of a metal-matrix composite to dynamic shearing deformations has been measured, using a new design of the thin-walled tubular specimen for the torsional Kolsky bar experiment that allows working with these difficult-to-machine materials. The advantages of using the new specimen design are as follows: (i) the thickness of the thin wall along the axial direction is very uniform; (ii) specimen machining is extremely simple; (iii) the cost of specimen machining is greatly reduced. The approach has been used to characterize the high shear strain rate (103s−1) behavior of an A359/SiCp composite and its corresponding A359 monolithic alloy with the torsion Kolsky bar. The experimental results show that the flow stress of the composite in shear increases in the presence of SiC particles, whereas the failure strain is reduced. The shear failure strains of both the A359/SiCp composite and the A359 monolithic alloy appear to increase with increasing strain rate. Previous observations have shown that particle fracture develops during compressive deformations of this material. However, particle fracture is not a significant damage mode during the shearing deformations of the composite, and this is reflected in differences between the torsional and tension behaviors of the material.

Porcelain-fused-to-metal (PFM) is playing a very important role in prosthetics dentistry. The bond strengths in metal-ceramic system have been focused on, since the method of PFM was used to prosthetics. In this paper, the thermal residual stress effects on metal-ceramic bond were considered during cooling of porcelain-fused-to-metal restoration to analysis the metal-ceramic bond stresses. The ISO crack initiation test specimen (three-point flexure bond test) was simulated by finite element method. The analysis was implemented in two steps. In the first step, the porcelain was assumed as viscoelastic material (720℃-550℃), while in the second step the porcelain was as elastic body (550℃-25℃). The results show that the compressive stress caused by difference ofthermal expansion coefficients of two materials during cooling occurs in the ceramic. The shear stress induced by mechanical load is offset by thermal shear stress. The mechanical tensile stress and the thermal compressive stress normal to interface are concentrated at the end of the bond interface, but the tensile stress is much higher. It is clear that the thermal residual stresses are very important to metal-ceramic restorations, and it is greatly affected by the viscoelastic behavior of porcelain. This also indicates a higher probability of failure produced by the tensile stress rather than by shear stress.

The mechanical behaviors of an A359/SiCp metal

In this paper, the mechanical behavior of acrylic polymers at elevated temperature was investigated. Four acrylic polymers were tested at high strain rate by using compression Hopkinson bar and at quasi-static strain rate by using an Instron servo hydraulic axial testing machine with the testing temperature from 218K to 393K. The results show that the mechanical property of acrylic polymers depends heavily on the testing temperature. The yield stress and Young's modulus were found to decrease with increasing temperature at low strain rate. At very low temperature, the materials display typical brittle fracture; however their plasticity improves remarkably at high temperatures. The predictions of the mechanical behavior including the effect of temperature and strain rate using a proposed theoretical model have a good agreement with experimental results.