Authors: Jong Woong Kim, Sun Kyu Park, Seung Boo Jung
Abstract: Ball shear test was investigated in terms of effects of important test parameters, i.e. shear height and shear speed, with an experimental and non-linear finite element analysis for evaluating the solder joint integrity of area array packages. A Pb-free solder composition was examined in this work: Sn-3Ag-6Bi-2In. The substrate was a common SMD (Solder Mask Defined) type with solder bond pad openings of 460㎛ in diameter. It could be observed that increasing shear height, at fixed shear
speed, has the effect of decreasing shear force, while the shear force increased with increasing shear speed at fixed shear height. Too high shear height could cause some bad effects on the test results such as unexpected high standard deviation values or shear tip sliding from the solder ball surface. The low shear height conditions were favorable for screening the type of brittle interfacial failures or the degraded layers in the interfaces.
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Authors: Yoshifumi Iwasaki, Yuji Nakasone
Abstract: The present study has investigated plasticity-induced martensitic phase transformation in fatigue of unnotched SUS304 plates. Martensitic phase transformation occurred in uunotched SUS304 plate specimens fatigued at room temperature in air. Volume fraction Va’ of a’ martensite in the uunotched portion of fatigued specimens was measured by ferrite scope. The relations between the maximum value of Va’, Va’max, and the number of load cycles N were represented by reverse sigmoidal curves for all the applied stress range Ds levels tested in this study. For the most portion of fatigue life, the value of Va’max remained almost constant. This value was increased with increase in the value of Ds. The spatial distribution of Va’ in the specimens varied with N: i.e., continued cycling of stress made a’ transformation localized near the central portion of specimens where the Va’ value reached as high as 35-40%. This value is more than doubled compared to the highest Va’ value found in the tensile tests of SUS304 at room temperature in air. Invisible cracks of 200µm in length were found in
the high Va’ value region. These results imply that the measurement of Va’ in fatigued SUS304 components may detect crack initiation sites and may predict residual fatigue life.
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Abstract: Equal Channel Angular Extrusion (ECAE) has become a very popular tool for studying the evolution of microstructure and properties under severe plastic deformation. It is believed that the stress-strain characteristics are uniform in a cross-section of the billet and this uniformity of the stress-strain distribution ensures the uniformity of microstructure and mechanical properties in ECAE processed billet. However, some experimental data such as the fracture of the extruded billet, which is initiated at the inner surface of the sample, has caused doubts about uniformity of stress-strain distribution. This non-uniformity has been proved recently by Finite Element Simulation.
In this paper the studies of the positive role of the applied back-pressure during ECAE are reviewed and the influence of a back-pressure on the uniformity of the stress-strain distribution, strain localisation, die corner filing, and the prevention of fracture is shown. The effect of back-pressure on grain refinement and improvement in mechanical properties is emphasized. The paper summarises our results from over seven years of work using a unique machine for ECAE with computer-controlled back-pressure and velocity of the backward punch.
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Authors: Zhen Yin, Hua Li, Bang Fu Wang, Ke Feng Song
Abstract: Based on FEM, a new type of ultrasonic elliptic vibrator design method was proposed, the ultrasonic elliptic vibration was achieved by the structural curve of the longitudinal and torsional vibrations. The impedance and vibration characteristics of the new longitudinal-torsional composite ultrasonic elliptic vibrator prototype were tested. It provides an important basis for impedance matching and longitudinal-torsional composite ultrasonic elliptical vibration application.
341
Authors: Xiao Jing Tan, Bin Wu
Abstract: Pseudo-dynamic testing using force- mixed control strategy is presented for structures with large stiffness. In this proposed method, the displacement response of the specimen measured by a linear variable displacement transducer with higher resolution than that in the actuator is fed back. A proportional-integral controller is adopted in the outer displacement control loop, and a coefficient CF is employed to convert the displacement to force command. Numerical and experimental validations show that this method exhibits excellent performance in terms of stability and accuracy if proper controller parameters are adopted and is superior to the conventional displacement control method for large-stiffness structures.
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