Norio Kawagoishi

Fatigue failure analyses on a Ti-45Al-8Nb-0.2W-0.2B-0.1Y alloy at different temperatures

The fatigue micro crack initiation and propagation tests of a TiAl alloy with 8% Nb content were carried out by using scanning electron microscopy in situ technology at room temperature and at 750 °C. These results indicated that the fatigue micro crack initiation was mainly caused by the stress concentration at room temperature, but at an elevated temperature (750 °C) the multi-cracks were caused by the coupled factors of both lamellar microstructure and stress concentration. Therefore, fatigue micro crack initiation behavior is much more dependent on the lamellar structure at an elevated temperature. One of the reasons is that the elevated temperature degrades the interface strength between the lamellar of the TiAl alloy with 8% Nb content. Therefore, the small fatigue crack propagation behavior of the alloy exhibited a mixture damage model of interlamellar and translamellar at a micro scale. The crack growth path and fracture characteristics provided a proof of crack deflection, branching and/or bridging induced either by interlamellar or by translamellar failure mode.

EFFECT OF LOADING TYPE ON FATIGUE CRACK GROWTH BEHAVIOR OF SOLDER JOINT IN ELECTRONIC PACKAGING

Fatigue cracking tests of a solder joint were carried out using in-situ scanning electron microscopy (SEM) technology under tensile and bending cyclic loadings. The method for predicting the fatigue life is provided based on the fatigue crack growth rate of the solder joint. The results show that the effect of the loading type on the fatigue crack growth behavior of a solder joint cannot be ignored. In addition, the finite element analysis results help quantitatively estimate the response relationship between solder joint structures. The fatigue crack initiation life of a solder joint is in good agreement with the fatigue life (N50%) of a totally electronic board with 36 solder joints.

Effects of Tool Wear on Surface Integrity of Aluminum Alloy Machined in Ultra-Precision Cutting Process (2nd Report)

Ultra-precision cutting of soft metals is mainly used for generating reflection surface of optical equipments. Accordingly roughness of machined surface is very important evaluation item in quality because the roughness affects performance of the optical equipments. Workpieces are actually machined with a worn diamond tool in machining shops whereas ultra-precision cutting with a single crystal diamond tool is well known as a machining method owing high quality finished surface to a sharp cutting edge of the tool. The purpose of this study is to find out the relation between tool wear and surface roughness machined with a worn tool in ultra-precision cutting process. Profile of a machined surface was measured at intervals of a fixed cutting distance, and profile curves in cutting and feed directions were investigated by using spectrum analysis. As a result of experiments and considerations, we reached the following results. (1) Cutting tool vibrations induced by tool flank wear increased roughness of machined surface in cutting direction and also increased roughness in feed direction. (2) Deterioration of copying of cutting edge shape decreased surface roughness in feed direction. (3) Surface roughness generated by tool vibrations exponentially increased with increase in flank wear of cutting edge generating finished surface.