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Compared with the mechanical properties obtained from free-standing three-point bending tests, plate-shaped structures would exhibit different bending properties when subjected to tensile preloads. In this paper, elastic-plastic bending properties and fracture modes of an extruded AZ31B magnesium alloy based on tensile preloads varying from 0 N (Mg alloy specimen is double clamped) to 350 N are investigated. Bending load-deflection curves with various tensile preloads are obtained, the maximum bending deflection, residual deflection and the ratio of residual deflection to maximum bending deflection all gradually decrease as the preload increases. The preload is verified to improve the resistance capacity to bending deformation of the alloy specimens. Progressive linearization trend and obvious nonlinearities of the loading and unloading load-deflection curves are explained, respectively. The tensile preloads promote the directional movement of neutral layer, and the increased preloads would cause more inhomogeneous stress distribution when the bending deflection reaches its maximum. Moreover, regarding the fracture modes, as the preload increases, the proportions of shear dimples and equiaxed dimples decreases, and the proportion of tear dimples gradually increases.

Differences in surface mechanical properties of Zr55Cu30Al10Ni5 bulk metallic glass (BMG) was revealed through indentation tests. Inhomogeneous stress condition was constructed through fabricating asymmetrical double V-notches. Indentation responses at various locations along with and perpendicular to the connection line between the notch tips indicated a significant difference in surface hardness with range from 1.012 GPa to 1.463 GPa, corresponding to a tensile stress ranging from 11.8 MPa to 246.3 MPa. The stress gradients induced by prefabricted notches cased the anisotropy of residual indentation morphologies. Furthermore, selected area electron diffraction analysis adjacent to the notch tip exhibited typical halo ring and amorphous state, which indicated that the morphological anisotropy and differences in indentation responses were mainly caused by inhomogeneous stress and Poisson effect rather than local crystallization behaviors.

Crystallization behaviors of bulk metallic glass (BMG) have been obtaining widespread concern, especially under service conditions including elevated temperature, electrical pulse, mechanical stress and high pressure. In this paper, cyclic stress was considered as typical service condition and applied on a Zr55Cu30Al10Ni5 BMG specimen with prefabricated double V-notches. Through indentation tests on fatigue-fractured specimen along with the connection line between notch tips, diversities in indentation serrated flow behaviors and morphological anisotropies were directly observed. Through transmission electron microscopy (TEM) characterization and selected area electron diffraction (SAED) analysis of thinned BMG specimen adjacent to indentation edge, direct experimental evidence of local crystallization at room temperature (RT) was verified. Meanwhile, the distance-dependent crystallization behavior was investigated in terms of gradually increased quantity of diffraction spots and precipitated nanocrystalline adjacent to indentation edge. Furthermore, high resolution transmission electron microscopy (HRTEM) images and SAED patterns at identical indentation microregion of tensile-fractured BMG specimen did not exhibit obvious nanocrystalline and diffraction spots, which indicated that the cyclic stress rather than static stress induced surface crystallization adjacent to indentation edge at RT.