Search

For Aurivillius phase Bi 4 Ti 3 − x W x O 12 + x + 0.2 wt.% Cr 2 O 3 (BTW x -C, x = 0–0.1) ceramics prepared by a conventional ceramic process, plate-like grains with random orientations are formed there. The aspect ratio of grains increases after the doping of W for ceramics, at the same time the bulk density of ceramics decreases. The change of Poisson's ratio may be related to the change of bulk density, whilst the change of bond strength could be responsible for the change of Young's modulus. The large-grained samples tend to possess a lower frequency constant but a higher elastic compliance, as well as a lower hardness. Especially, a larger grain size provides a higher fracture toughness for the sample at x = 0.05 due to the mechanism of crack deflection. The stress–strain curves of BTW x -C ceramics under a uniaxial compression load are characterized as three stages: linear elastic deformation, ferroelastic domain switch and microcrack propagation. The microcrack propagation along grain boundaries results in the final axial flerry of ceramics. Additionally, the fracture strength of ceramics may be largely influenced by the internal stress resulted from the paraelectric–ferroelectric phase transformation during sintering. [ABSTRACT FROM AUTHOR]

The effects of mechanical heterogeneity on the tensile and high cycle fatigue (10 4 –10 7 cycles) properties were investigated for laser-arc hybrid welded aluminium alloy joints. Tensile–tensile cyclic loading with a stress ratio of 0.1 was applied in a direction perpendicular to the weld direction for up to 10 7 cycles. The local mechanical properties in the tensile test and the accumulated plastic strain in the fatigue test throughout the weld’s different regions were characterized using a digital image correlation technique. The tensile results indicated heterogeneous tensile properties throughout the different regions of the aluminium welded joint, and the heat affected zone was the weakest region in which the strain localized. In the fatigue test, the accumulated plastic strain evolutions in different subzones of the weld were analyzed, and slip bands could be clearly observed in the heat affected zone. A transition of fatigue failure locations from the heat affected zone caused by accumulated plastic strain to the fusion zone induced by fatigue crack at pores could be observed under different cyclic stress levels. The welding porosity in the fusion zone significantly influences the high cycle fatigue behaviour. [ABSTRACT FROM AUTHOR]