Shangli Dong

An analytical study of the influence of thermal residual stresses on the elastic and yield behaviors of short fiber-reinforced metal matrix composites

Abstract An analytical model was developed to study the influence of thermal residual stresses on the elastic and yield behaviors of aligned short fiber-reinforced metal matrix composites. Three-dimensional solutions of elastic stress field in the matrix of a circular cylindrical unit cell were first obtained based on the theory of elasticity. On this basis, an alternative analysis of the stress transfers between the matrix and the fiber was given by using the shear lag analysis, which provides the expressions for the stress distributions in the matrix and the fiber. The thermal residual stresses and the distributions of the stresses under tensile and compressive loadings as a function of the material parameters, such as fiber volume fraction, fiber aspect ratio and matrix yield stress, were calculated. Furthermore, simple expressions for the composite elastic modulus and yield strength under tensile and compressive loadings were derived. These expressions were used to study the influence of the thermal residual stresses and the material parameters on the elastic moduli and yield strengths under tensile and compressive loadings. Finally, the model predictions were compared with the experimental results on the SiC w /Al–Li T6 composite and several SiC w /Al T6 composites in literature and also with the other theoretical models.

Influence of Atomic Oxygen Exposure on Friction Behavior of 321 Stainless Steel

Atomic oxygen (AO) exposure testing has been conducted on a 321 stainless steel rolled 1 mm thick sheet to simulate the effect of AO environment on steel in low Earth orbit (LEO). An atomic oxygen exposure facility was employed to carry out AO experiments with the fluence up to ~1021 atom/cm2. The AO exposed specimens were evaluated in air at room temperature using a nanoindenter and a tribological system. The exposed surfaces were analyzed usign XPS technique.

Interaction between hydrogen and gallium vacancies in β-Ga2O3

In this paper, the revised Heyd-Scuseria-Ernzerhof screened hybrid functional (HSE06) is used to investigate the interaction between hydrogen with different concentrations and gallium vacancies in β-Ga2O3. The hydrogen can compensate a gallium vacancy by forming hydrogen-vacancy complex. A gallium vacancy can bind up to four hydrogen atoms, and formation energies decrease as the number of hydrogen atoms increases. Hydrogen prefers to bind with three coordinated oxygen. The bonding energy and annealing temperatures of complexes containing more than two hydrogen atoms are computed, and show relatively high stability. In addition, vacancy concentrations increase with the increasing vapor pressures. This paper can effectively explain the hydrogen impact in β-Ga2O3.

Effects of Atomic Oxygen Exposure on Tribological Property of Zirconium Alloy

ZrTiAlV alloy has potential applications in space mechanisms. The change of wear and the friction coefficient of the ZrTiAlV alloy subjected to atomic oxygen (AO) exposure were investigated aiming to evaluate the tribological properties influenced by the atomic oxygen (AO) environment of the low Earth orbit (LEO). The AO testing employing a 5 eV AO beam was performed under various AO fluencies. The mass loss and roughness of the exposed to AO surfaces were measured. The exposed surfaces and the worn surfaces were analyzed using scanning electron microscopy (SEM) and X-ray photoelectron spectrometry (XPS) to explore the mechanism of AO effect.

Effects of Thermal-Mechanical Cycling on Tension Properties of AZ31 Magnesium Alloy

Effects of thermal-mechanical cycling on tension properties of an extruded AZ31 alloy are studied. The results show that the strength of the examined AZ31 alloy samples varies with thermal cycles, increasing from non-cycle to 50 cycles and then decreasing to 380 cycles. The plastic elongation exhibits out of steps tendency which has maximum at 100 cycles and decreases after that. Microstructure development indicates that dislocation and twinning induced by accumulated internal stress vary with thermal cycling. And the tension fracture surface of the thermal cycled samples shows that fracture of cycled samples transits from cleavages and facets into dimple and second phase crack dominated feature. It is believed that dislocation and twinning evolution during thermal cycling are responsible for the observed tension deformation and fracture behaviors.

Influence of SiC whisker on planar slip in Al-Li based alloys

The tensile deformation microstructure characteristics of silicon carbide whisker (SiCw) reinforced Al-Li and Al-Li-Cu-Mg-Zr composites prepared by squeeze casting technique were studied by means of transmission electron microscopy (TEM), in order to evaluate the influence of SiC whisker on planar slip in Al-Li based alloys. For the purpose of comparison, the microstructural features of the unreinforced matrix alloys with the identical fabrication, thermal processing and tensile deformation history were also investigated. Dislocation pairs and intense slip bands originated from cutting of δ′ (Al3Li) phases by moving dislocations, could be found in the specimens of Al-Li and Al-Li-Cu-Mg-Zr alloys, whereas absent in either SiCw/Al-Li or SiCw/Al-Li-Cu-Mg-Zr composites. The results demonstrate that the addition of SiC whisker to Al-Li based alloys, has a considerable effect on suppressing planar slip which is a general phenomenon in Al-Li based alloys resulting from the interaction between δ′ phase and dislocations.