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The work-hardening response of TRIP780 steel subjected to strain-path changes was investigated using two-stage tension experiments. Large specimens were prestrained and then sub-sized samples were subjected to tension along various directions. The influence of strain-path changes on flow stress and work hardening performance was discussed in detail. The specific plastic work was calculated to compare the kinematic hardening behaviour after strain-path changes. The results showed that transient hardening was observed for TRIP780 sheets subjected to orthogonal strain-path change. The strain-hardening exponent (n-value) was influenced by prestraining levels and the strain path. The n-value exhibited a greater decrease under an orthogonal strain-path change. Prestraining can delay the onset of high work hardenability of TRIP steels. It is meaningful for the safety design of vehicles.

Carbon Fiber Reinforced Plastic (CFRP) tube is an important material for the lightweight design of automotive structures. Simulation method of CFRP thin-walled tubes subjected to axial compression using MAT54 in LS-DYNA was investigated. Based on the two-layer shell model combined with MAT54, failure strategy and the parameters sensitivity of the model were discussed in detail. Then the simulation model was verified by using duplicate specimens comprised of carbon fiber/epoxy unidirectional prepreg tape. Furthermore, the modeling methods of crush trigger and different types of loading speed were analyzed. In addition, based on the method of equal energy absorption, energy absorption performance of thin-walled circular and square tubes made from four materials including mild steel, high strength steel, aluminum alloy and CFRP were also compared.

Based on the basic structure and operating function of engine throttle, according to the actual structure of throttle, a 3-dimensional air transient flow is simulated to realize throttle rotated from closed position to opened position by using CFD moving mesh technology and user defined program. By applying CFD and CAA coupling method, the influence of the movement of throttle on air flow and flow-induced noise process are studied, the transient opening process is studied and analyzed. The velocity field, pressure field and the principle of flow-induced noise are analyzed under different rotational angle velocity of throttle.

This study investigated the plastic deformation behavior of 304 stainless steel thin-walled tubes under axial compression by means of numerical calculation and theoretical analysis. It was found that the plastic deformation length of thin-walled tube determined the formability of folds and the work done in the whole axial compression process. To reveal the relation between the range of plastic deformation length and tube geometry parameters, regression equations were established using the quadratic regression orthogonal design method. Experiments were conducted to validate the equations. The process windows for forming a single fold and tube joining at ends had been printed ultimately. The results showed that the regression equations can accurately predict the range of plastic deformation length for forming a single fold.

The yield locus of a cold-rolled transformation-induced plasticity (TRIP780) steel sheet was investigated using a biaxial tensile test on a cruciform specimen. The effect of the key dimensions of the cruciform specimen on the calculation error and stress inhomogeneity was analyzed in detail using an orthogonal test combined with a finite element analysis. Scanning electron metallography (SEM) observations of the TRIP780 steel were performed. The yield curve of the TRIP780 steel was also calculated using the Von Mises, Hill '48, Hill '93, Barlat '89, Gotoh and Hosford yield criteria. The experimental results indicate that none of the selected yield criteria completely agree with the experimental curve. The Hill '48 and Hosford yield criteria have the largest error while the Hill '93 and Gotoh yield criteria have the smallest error.

Several failure criteria and stiffness degradation laws for composite materials are summarized and compared in terms of precision and convenience of use. The 2D/3D Hashin failure criteria are coupled with the stiffness degradation rules provided by Tan, Tserpes and Zinoviev. Three new failure models including 2D Hashin-Tan, 3D Hashin-Tser and 3D Hashin-Zin are presented for CFRP materials. The above three models were coded and incorporated into the ABAQUS software by user subroutines, among which model 2D Hashin-Tan and model 3D Hashin-Tser were programmed using the implicit algorithm VUSDFLD while model 3D Hashin-Zin was coded using the explicit algorithm VUMAT. Experiments of uniaxial tension and three-point bending were performed. A single element subjected to uniaxial tension and three-bending were simulated to check the function and precision of the new models.