Koichiro Kihara

A study and evaluation of the shear strength of adhesive layers subjected to impact loads

Experimental equipment was developed in order to measure easily the shear strength of adhesive layers subjected to impact loads. The stress state of an adhesive joint was calculated with the finite element method (FEM). The results calculated from the FEM were compared with those from experiments conducted with the equipment. It was shown that the fracture behaviour of the joint depended on the level of the incident stress wave. When loading a comparatively high incident stress, the adhesive layer fractures mainly with the shear stress. It is considered that the maximum shear stress measured is the shear strength under impact loads. In order to confirm the validity of this evaluation method, the maximum shear stress was compared with the impact shear strength, which was measured using a cylindrical butt joint subjected to impact torsional loads. Both values accorded well. From this we were able to conclude that the shear strength of the adhesive layer subjected to impact loads could be evaluated with this equipment.

Effect of Strain Rate on Plastic Deformation Behavior of Austempered Spheroidal Graphite Cast Iron.

The effect of strain rate on the plastic deformation behavior of austempered spheroidal graphite cast iron was studied. The matrix of specimens consisted of mixed banitic ferrite together with retained austenite. Thin-walled tubular specimens were strained under tensile stresses or torsional stresses. It was found that the deformation of austempered spheroidal graphite cast iron under both tensile and torsional stresses did not depend much on strain rate in an elastic region. The results for maximum strain under tensile stresses were scattered because the specimens were thin-walled tubes which had numerous graphite nodules and a few defects. The results of tensile tests of thin-walled tubular specimens were greatly influenced by the shape of specimens and defects, whereas the results of torsional tests were hardly influenced. The ratio of transformed retained-austenite into martensite under torsional stresses did not vary with strain rate. It was presumed from this result that work hardening affected an increase of yield stress and torsional strength.