Kohsoku Nagata

Transient Crack Growth Behavior Under Cycle/Time-Dependent Step Loading for Pb-Containing and Pb-Free Solders

In the present study, fatigue crack growth tests of Pb-containing [Sn-37Pb (wt.%)] and Pb-free [Sn-3.0Ag-0.5Cu (wt.%)] solders were performed under cycle/time-dependent step loading at a constant J-integral range (ΔJ). The C* parameter was also estimated for discussing time-dependent crack growth behavior. The experimental results indicated that acceleration of the crack growth rate at the beginning of the second loading step was induced when the C* value for the first loading step was high, regardless of time- or cycle-dependent crack growth and for both Sn-37Pb and Sn-3.0Ag-0.5Cu solders. The length of the acceleration region of the crack growth rate for both solders was in good agreement with the creep damage zone size estimated by the creep zone model proposed by Riedel and Rice.

Effect of Interface Shape of the Strength for Carbon Steel/PMMA Adhered Joint

The adhered joint composed of polymer and metal is a useful and practical method to take advantage of the both material properties. However, there are some basic problems for the material mismatch due to the different Youngs modulus. Inthis study, the stress singularity at the intersection between the free surface and the interface betweenpoly-methyl-methacrylate (PMMA) and structural carbon steel (JIS SS400) was analyzed to clarify the joint strength using a finite element method. As a result, the stress singularity was found above 130 degree of PMMA apex angle and between 35 and 41 degree of PMMA apex angle. In this experiment, it was confirmed that the no free-edge stress singularity was useful conditions to insure the reliability of bending strength for the adhered joint composed of SS400 and PMMA.

Fracture Toughness at High temperature of Tungsten-Rhenium Alloys.

Fracture toughness tests of tungsten and tungsten-rhenium alloy were carried out at elevated temperatures. The effect of rhenium content on fracture toughness and the temperature dependence of fracture toughness were investigated. Fracture surface were observed in detail. Although the fracture toughnesses of three kinds of materials with rhenium of 0, 5 and 10wt% were almost identical at room temperature, the materials with higher rhenium content had the higher fracture toughness at elevated temperatures. The brittle-ductile transition similar to that of steels and the ductile-brittle transition at which recrystallization occurred, were observed for all three kinds of materials. With an increase of rhenium content, the brittle-ductile transition temperature decreased and the ductile-brittle transition temperature increased. A significant grain growth in the temperature range higher than the recrystallizing temperature, which was observed in the tungsten material without rhenium, was not found in the tungsten-rhenium alloy materials.