A compressive split-Hopkinson pressure bar and transmission electron microscope (TEM) are used to investigate the mechanical behavior and microstructural evolution of biomedical Ti alloy deformed at strain rates ranging from 8 · 10 2 s -1 to 8 · 10 3 s -1 at temperatures between 25°C and 900°C. In general, the results indicate that the mechanical behavior and microstructural evolution of the alloy are highly sensitive to both the strain rate and the temperature conditions. The flow-stress curves are found to include both a work-hardening region and a work-softening region. The strain-rate-sensitivity parameter, b, increases with increasing strain and strain rate but decreases with increasing temperature. The activation energy varies inversely with the flow stress and has a low value at high deformation strain rates and low temperatures. Microstructural observations reveal that the strengthening effect evident in the deformed alloy is a result primarily of dislocations and the formation of a phase. The dislocation density increases with increasing strain rate but decreases with increasing temperature. Additionally, the square root of the dislocation density varies linearly with the flow stress. Correlating the mechanical properties of the biomedical Ti alloy with the TEM observations, it is inferred that the precipitation of a phase dominates the fracture strain. Transmission electron microscope observations reveal that the amount of a phase increases with increasing temperature below the b-transus temperature. The maximum amount of a phase is formed at a temperature of 700°C and results in the minimum fracture strain observed under the current loading conditions.

This study investigates the multiwalled carbon nanotube as potential mechanical reinforcement in epoxy polymer. It is found that, by adding various concentrations of nanotube, both flow stress and fracture strain increased. Furthermore, the presences of the multiwalled carbon nanotubes are found to nucleate crystallization in the epoxy. This crystal growth is thought to enhance the strength of composite. The fracture surface analysis of the composite reinforced by carbon nanotube is used the scanning electron microscopy.

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In this study, the high strain rate deformation behavior and the microstructure evolution of Zr-Cu-Al-Ni metallic glasses under various strain rates were investigated. The influence of strain and strain rate on the mechanical properties and fracture behavior, as well as microstructural properties was also investigated. Before mechanical testing, the structure and thermal stability of the Zr-Cu-Al-Ni metallic glasses were studied with X-ray diffraction (XRD) and differential scanning calorimeter. The mechanical property experiments and microstructural observations of Zr-Cu-Al-Ni metallic glasses under different strain rates ranging from 10−3 to 5.1 × 103 s−1 and at temperatures of 25 °C were investigated using compressive split-Hopkinson bar (SHPB) and an MTS tester. An in situ transmission electron microscope (TEM) nanoindenter was used to carry out compression tests and investigate the deformation behavior arising at nanopillars of the Zr-based metallic glass. The formation and interaction of shear band during the plastic deformation were investigated. Moreover, it was clearly apparent that the mechanical strength and ductility could be enhanced by impeding the penetration of shear bands with reinforced particles.

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The dynamic mechanical properties of high strength aluminum-scandium (Al-Sc) alloy are investigated using a compression split Hopkinson bar. Dynamic impact testing is carried out at nominal strain rates (abbreviated to strain rate hereafter) ranging from 1:2 Â 10 3 to 5:8 Â 10 3 s À1 at room temperature. The effects of strain rate on the mechanical properties, microstructural evolution and fracture characteristics are investigated and the relationship between the mechanical properties of the alloy and its microstructure is explored. The measured strainstress curves reveal that the dynamic mechanical behaviour of Al-Sc alloy is highly dependent on the strain rate. The flow stress, work hardening rate and strain rate sensitivity increase with increasing strain rate, but the fracture strain and activation volume decrease. The Zerilli-Armstrong fcc constitutive law is used to model the shear flow response of the Al-Sc alloy. A good agreement is found between the predicted and measured shear flow responses. The Al-Sc alloy specimens fracture as a result of shear band formation and crack propagation within the shear band. SEM observations indicate that the fracture features are dominated by a transgranular dimple-like structure. The density and depth of the dimples decrease with increasing strain rate. TEM microstructural observations reveal that the presence of Al 3 Sc precipitated particles in the matrix and at the grain boundaries prevents dislocation motion and leads to a significant strengthening effect. An analysis of the dislocation substructure indicates that a higher strain rate increases the dislocation density, thereby reducing the size of the dislocation cells. The variations of the dislocation cell structure reflect different degrees of strain rate sensitivity and activation volume, and correlate well with the impact flow stressstrain response.

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