Applied Mechanics and Materials Vols. 217-219

Abstract: In this paper, the effect of laser parameters on fatigue life was investigated by laser irradiation for the undamaged and pre-damaged copper film specimens with thickness of 25μm. The results showed that the laser parameters have a great impact on the strengthening of original specimens and the healing of specimens with fatigue damage, and total fatigue life of the healed specimen with fatigue damage was longer than that of the strengthened original specimen. According to the obtained fatigue life results under different laser irradiation conditions, the optimal laser parameters were identified. The fracture morphology was observed by SEM. The results showed that, under the optimal laser parameters condition, a dense layer was found on the surface of specimen and the columnar grains were refined, which results in increasing the total fatigue life of the specimen.

Abstract: Safety valve is an important component of a boiler. The failure of its spring will bring hidden trouble to the boiler operation. The fracture failure of a drum safety valve spring of a power plant boiler was discussed based on chemical composition analysis, hardness test, metallurgical microstructure observation and SEM. Results showed that improper material selection and improper heat treatment process which led to temper brittleness contributes to the fracture. In addition, oxygen corrosion pit on the surface of the spring play an important role in promoting the cracking.

Abstract: Sand and fluid may both run into the wellbore during the production of loose sandstone reservoir, but cavities around the wellbore are prone to form when sand is produced, which makes the casing lost the protection of the formation and casing failure comes about. The limitation of thin cylindrical shell buckling model is analyzed and a mechanical model for casing under sand production is established by M.M.протодьяконоВ’ theory and the pressures of the casing where cavities exist are determined by numerical method. The research shows the cavity height and sand production volume are in a power relationship; the cavity height and axial force are in a linear relationship. With the increase of the overburden pressure, higher steel grade have to be used to keep the reliability of the casing. The research provides theoretical foundation for production casing design and casing strength verification with reasonable sanding.

Abstract: In this paper, the thermal fatigue damage phenomenon in the comprehensive temperature environment is studied by means of thermal fatigue damage mechanics and FEM technology, the thermal-stress analysis modal under the comprehensive thermodynamic boundary conditions is established, the regularities of distribution of temperature fields, thermal stress fields effected by the comprehensive coupled variables are investigated. According to the modify of material characteristics under the high-temperature alternating thermal impact conditions and the integrated influences of environment, mechanical parameter and material microstructure to the fatigue fracture, numerical modal of thermal fatigue crack initiation and propagation are developed, so the characteristics of thermal fatigue crack propagation are studied, which are verified by the experiments, it is very significant to study thermal damage question of working equipments in the similar conditions.

Abstract: The function characteristics of bending moment and torque were analyzed based on the principle of torque measurement and the adverse effect of bending moment to torque measurement was proved theoretically. By distributing the positions of resistance strain gauge on the transmission shaft and the relative positions in the bridge, an effective method of eliminating the adverse effect of bending moment was proposed base on the principle of superposition and counterbalance in the bridge, and the potential errors were analyzed and corrected. Then the proposed method was applied in measuring the torque of a motor shaft. The result shows that the effect of bending moment has been eliminated, and this method is feasible and effective.

Abstract: A 3D numerical model was developed to analyze the deformation and stress characteristics of HDPE material circular net cage exposed to waves, using the finite element method (FEM). The total wave forces acting on the structure were evaluated with method combining analytical and numerical, and served as boundary conditions during the simulation. Testing cases were performed eventually based on the actual conditions in Zhanjiang bay. The results show that wave height is an important factor that affects the dynamics response characteristics of net cages as well as the working conditions of the cages in sea environment, and the peak stress of the flotation structure always occurs at the mooring points. We also suggest that the net cages that constructed inside Zhanjiang Bay may not fail even during the storm process when in normal working condition.

Abstract: Plane strain compression were carried out for as-cast and pre-strained AZ31 alloy specimens at 210～330°C. The influence of initial grain on strengthening effect was analyzed by means of metallographic examination and mechanical testing. The results indicate the recrystallized grain of Mg alloy is sensitive to initial grain. With the deformation temperature increasing, the ultimate tensible strength decreases for as-cast and pre-strained alloy. With the deformation degree increasing, the tensile strength presents an increasing trend for as-cast alloy, but the tensile strength decreases on the whole for pre-strained alloy. The tensile strength increments of ～50% can be achieved under appropriate processing conditions.

Abstract: Based on the singular stress field near the V-notch tip and under the two basic assumptions in this paper, twin-shear yield criterion under mixed loading mode I and II is established and the numerical results of the crack angles are calculated by this criterion. In order to verity twin-shear yield criterion ,tension tests are carried out under mixed mode loading by tension testing machine using polymethyl methacrylate(PMMA). The experimental results coincide with the numerical prediction results, which suggests that the twin-shear yield criterion is valid for the V-notch brittle facture.

Abstract: The R-function theory and least square method are employed to solve the torsion problem of the bar with H-shaped cross-section. When the least square method is used to solve the elastic torsion problem alone, the stress function can be set to meet the boundary condition, only with the simple cross-section such as the rectangle and ellipse. For the H-shaped cross-section, it is hard to find a stress function to meet the boundary condition. The R-function theory can solve the problem, and it can be used to describe H-shaped cross-section by implicit function form. Introducing the R-function theory can be easy to construct the stress function that satisfied the boundary of H-shaped cross-section. A numerical example demonstrates the feasibility and efficiency of the present method.

Abstract: The copper wire has some advantages in thermal performance, mechanical performance, and low cost, which make it can provide the lowest cost flip-chip(FC) package for low I/O density device. The 2D Cu stud bump finite element model was set up by using ANSYS/LS-DYNA with LOLID162 element to dynamic simulate the Cu stud bump bonding shaping process. The stress distribution in the Cu stud bump and the pad during the bonding process were studied, and the influence of pad thickness on the stress distribution of Si chip was also analyzed. The results shows that under the bonding process the Cu bump height is mainly influenced by the bonding pressure and the top shape of the Cu bump is influenced by ultrasonic energy, the increase of pad thickness results in reducing stress concentration inside the Si chip.