Stress Evolution Mechanism Research Articles

Investigation of Stress Evolution Induced by Electromigration in Sn-Ag-Cu Solder Joints Based on an X-Ray Diffraction Technique

The critical current density and temperature endured by solder joints are identified as the two most important parameters that determine the occurrence of electromigration (EM). It is well known that movement of metal atoms/ions during current stressing can induce obvious stress concentrations at the anode and cathode interfaces of the solder joint. Therefore, the global average effects of EM on stress evolution at both the anode and cathode interfaces were investigated with different current densities by employing a nondestructive x-ray diffraction technique. The ultimate results indicated that the compressive stress increased gradually at the anode side under low current density. However, stress fluctuation could be observed under high current density due to an obvious Joule heating effect. For further understanding of the mechanism of stress evolution in the solder joint during current stressing, a four-stage model is considered. First, Cu expansion led to increase of the compressive stress at both electrodes. Second, stress relaxation compensated the compressive stress and caused it to decrease. Third, the EM effect promoted compressive stress and tensile stress at the anode and cathode, respectively. Finally, a steady state of stress was achieved at the anode, while the state of tensile stress at the cathode remained transient.

1161 膝関節モデルを用いた衝撃荷重解析(S10 インパクトバイオメカニクス)

Human joints are subjected to dynamic or impact loading in life. However, conventional biomechanical research of human joints have been concerned principally to static loading condition. The purpose of this study was to investigate the mechanism of stress evolution through cancellous bone in knee joint. In this study, the human knee joint FE models which were consisted of hexahedoral finite elements were prepared and were applied impact loading. As the result, the number of element by the hexahedral meshing is less than a quarter of that by the tetrahedral one.

Method and Mechanism of Beneficial Residual Stresses in Tubes

It is shown in this paper that residual stresses in a tube could be created in such a way that they are in tension in the middle region of the wall and in compression throughout the entire inside and outside surfaces of the tube. The method of treatment consists of applying an internal pressure and some appropriate alternating hot and cold thermal shocks to the tube. The mechanism of stress evolution in tube wall is demonstrated using elastic-perfectly plastic analysis of a generalized plane strain ID model subjected to a primary tension load σm, and an alternating linear temperature difference ΔT across the thickness. Theoretical combinations of loads (σm, ΔT) which give such residual stress configurations and formulas for predicted residual stresses are developed. A possible application of this treatment is for prolonging the life of U-bend region of heat exchanger tubes against stress corrosion cracking.