Papers by Author: Yong Shou Liu

Abstract: A reliability-based multidisciplinary design optimization (RBMDO) frame work for Centrifugal compressor was presented. Multidisciplinary feasible method was used to decouple the multidisciplinary analysis and the fourth moment method for reliability analysis was recommended systematically. Based on the approximation, the RBMDO framework was finished. The case study shows that optimization efforts could improve obviously the performance of centrifugal compressor under the requirements of reliability. This framework could make the design reach the best performance with a good reliability. It indicates that the proposed optimization method is available and feasible for the engineering application.

Abstract: In this paper, four axisymmetrical finite element models have been established to study effect of thinckness on residual stress fields of cold expansion hole, experiments were carried out to measure the residual stress of cold expansion hole and verify simulation results. The experiment results also show that cold expansion processing can decrease surface roughness of holes and improve surface quality. The FEM results show, at the top(bottom) surface, the volue of the radial residual stress varies with the plate’s thickness, and the regularities of distribution of the radial residual stress are identical. The volue and the regularities of distribution of the circumferential residual stress vary with the plate’s thickness. At the mid-thickness surface, the volue and the regularities of distribution of radial residual stress vary with the plate’s thickness. The volue of the circumferential residual stress varies with the plate’s thickness, and the regularities of distribution of the radial residual stress are identical.

Abstract: Two-dimensional (2D) finite element analyses have been carried out to study the crack opening displacement and stress intensity factor of a cracked centre-hole plate. With the different interference levels (2%, 4%, 6% and 8%) and acted by residual stress caused by cold expansion, the crack opening displacement, the stress intensity factor and J-integral around the crack tip is presented. With the different interference levels and acted by different applied loads , the crack opening displacement, the stress intensity and J-integral around the crack tip is also presented. The results of the 2D FEM analysis show, 1) with the different interference levels and acted by residual stress caused by cold expansion, the crack mouth is throughout closed and the middle part is open, but the opening displacement is constant; 2) under some applied loads, with the interference levels up, the stress intensity factor on the crack tip and J-integral, become weak gradually, then they keep constant values; 3) with the interference increases, the stress intensity factor and J-integral decreases. When the interference increases a certain value, the stress intensity factor and J-integral do not decrease and keep constant values.

Abstract: In this paper, an amendment method for stress and strain of double-curved laminated composite is proposed and studied. According to finite element analysis results of the same model with two different mesh size (coarse mesh size 120mm× 300mm and refined mesh size 30mm× 30mm ), stress and strain have been amended with modified formula in user material subroutine (UMAT) subprogram so that the corrected results of model with coarse mesh is similar to the results of model with refined mesh. Using this method, with coarse mesh, a satisfied accuracy results still can be obtained without refining mesh. It’s efficient for design and analysis of complex structures.

Abstract: A 2D cylindrical plate model has been established to study the distribution of residual stress of cold expansion hole under different interference values. In addition, the effects of material models on residual stress fields are considered also. Experiments are carried out to measure the residual stress of cold expansion hole and verify simulation results. FEM results show, with interference values increasing, the higher residual radial and circumferential stresses are obtained. At same interference value, the residual stress of Hardening Material( HM ) model is much larger than that of Elastic Perfectly Plastic Material( EPPM ) model.

Abstract: The fatigue testing of the specimen with a central open hole was carried out to investigate the influence of the surface roughness on the fatigue lifetime. Fracture morphology investigations were used by scanning electron microscope. The reliability analysis of the specimen was carried out by detail fatigue rating. The results revealed that the less the roughness is, the longer the fatigue life of open hole and the higher the value of DFR (Detail Fatigue Rating) is. Under the same technological conditions, the effect of corner crack on fatigue life of open holes is greater than the effect of internal crack. So, the effect of a decrease of roughness on the fatigue life of an open hole is similar to a change of crack type from a corner crack to an internal crack.

Abstract: A 2D rectangular plate model has been established to study the residual stress fields of cold expansion hole. Experiments were carried out to measure the residual stress of cold expansion hole and verify simulation results. The FEM results show, with interference values developing, the maximum values of circumferential residual compressive/tensile stress increase and higher positive stress values are obtained at the boundary of the rectangular plate. However, higher positive stresses at the boundary of plate are harmful to the capacity of fatigue resistance, the determinations of best interference value to a certain wide plate were proposed. Finally, the effect of the plate width on the residual stress distribution was analyzed.

Abstract: A 3D finite element model of bolt composite joint has been established to determine the stress distribution on the contact surface. The effects of clamping torque and friction on the contact stress and interlaminar normal stress are considered. From the analysis results, contact stress is bared mainly by the 0° layer. The distribution and magnitude of contact stress are conducted by friction. The effect of clamping torque on interlaminar normal stress is very strong. A 3D damage user subroutine is added to the FEM to simulate the damage of joint. By the means of damage simulation, the initiation and progression direction of three types damage are predicted. Matrix cracking and fiber-matrix shear occur at first, and fiber buckling is founded subsequently. The matrix cracking and fiber-matrix debonding initiate at circumferential angle 45°and 135°, and fiber buckling initiate at the 0° layer on the bearing plane. The friction and bolt clamping torque can restrain damage initiation and development.

Abstract: In this paper, a plate containing a central hole was used to simulate gas turbine blade with cooling hole
. Numerical calculations based on crystal plasticity theory have been performed to study the elastic-plastic stress field near the hole under tension. Two crystallographic orientations [001] and [111] were considered. The distributions of resolved shear stresses and strains of the octahedral slip systems {110}<112> were calculated. The results show that the crystallographic orientation has remarkable influence on both von Mises stress and resolved shear stress distributions. The resolved shear stress distributions around the hole are different between the two orientations, which lead to the different activated slip systems. So the deformed shape of the hole in [001] orientation differs from that in [111] orientation.

Abstract: Fracture along an interface between materials plays a major role in failure of material. In this investigation, finite element calculations with Kachanov–Rabotnov damage law were carried out to study the creep damage distribution near the interface cavity in bimaterial specimens. The specimens with central hole were divided into three types. The material parameters of K-R law used in this paper were chosen for a brittle material and ductile material. All calculations were performed under four load cases. Due to the difference between elastic moduli of the bounded materials, the elastic stress field as a function of the Young’s modulus ratio (R=E1/E2) was determined. At the same time, the influence of model type on elastic stress distribution near the cavity was considered. Under the same conditions, the material with larger modulus is subjected to larger stress. The creep damage calculations show that the location of the maximum damage is different for each model. The distributions of creep damage for all three models are dependent on the material properties and load cases.