Katsuhiko Murase

Ultrasonic detection of spall damage induced by low-velocity repeated impact

This paper address the examination of spall damage in medium carbon steel subjected to a repeated impact testing. The experiments were performed well below the threshold spall-stress of 2.6 GPa and the damage introduced in the subsurface volume was investigated using the low frequency scanning acoustic microscopy. Based on B- and C-scan images (the images taken along and perpendicular to the impact surface) we made a qualitative and semi-quantitative evaluation of the damage type (voids in a ductile material or cracks in a brittle one) and its distribution. We found the spall damage development dependent on the amplitude and the duration of the stress pulses. In particular, we proved that the high, long stress pulses induce damage that resembles tensile failure of material, in which voids or cracks nucleate along the spall plane to form macro-cracks. This explains why spall-damage is not seen when the first impact is below the characteristic threshold spall-stress. However, when the tests consist of more than four impacts the spall damage is produced already under stress below the threshold-value.

Evaluation of Sliding Behavior of Simple Structures for Oblique Collision

When a simple structure collides with inclined barrier, behavior and deformation of the structure after impact are different in the case in which the structure slides on a contact surface or the case in which it does not slide. In order to investigate the structural collapse behavior for oblique collided structure, therefore, it is important to clarify the sliding behavior of the structure on the contact surface. The sliding behavior of the structure during collision was estimated according to theoretically obtained the equation considering the equilibrium of change in the momentum and the impulse before and after the collision. For evaluating the sliding behavior of the simple structure, the impact test by the drop type impact testing machine was carried out to collide with inclined barrier. In the impact test, the circular plate of 60 mm diameter and 10 mm thickness was used as the simple structure, and impacted with various collision velocities (range from 2 to 6 m/s). The sliding behavior of the simple structure at the collided surface was observed by high speed camera, and evaluated by the image analysis. The theoretical result was compared to evaluate with experimental results.

Characteristic Evaluation of the Enforcement Device for the Car

In this study, collision and braking behavior and braking distance of the enforcement device were investigated for characteristic evaluation. The basic theory for the braking distance was derived using the law of the energy conservation. In this basic theory, the braking distance was compared with difference collision speed and arm angles of enforcement device. And also, the collision experiment was carried out by simple model of the enforcement device and the car. The behavior of the enforcement device was examined by the simple model with 3 kinds of different arm angles. The braking distance by the experiment was well agreement with theoretical result. It is possible to optimize and improve the enforcement device by these evaluations of collision behavior.

Evaluation of dynamic collapse in thin-walled composite members

Many of steel thin wall closed section members are used by automobile industry. The local buckling of these elements that occur under compressive stress remains the main technological problem. To improve the performance of the members, the filling the inside of closed section with the low-density foaming material are usually used. In this study, we present the usefulness of axial compression and 3-point bending tests for the composite members filled with two kinds of epoxy resin. The difference between composite member and thin-walled member was investigated concerning their elastic and plastic collapse characteristics while tested with various deformation velocities. The adherent strength between thin-walled member and foaming material, and filling effect of the foaming material in the energy absorption characteristics was clarified.

Constitutive relations of thin-walled members for impact collapse

This study develops impact collapse problem of thin-walled members as follows: 1) A visco-plastic constitutive equation was expressed for characteristics after collapse of local buckling. 2) Experiments of impact collapse were done under eccentric compression load for square tubes. 3) Using the experimental data, the constitutive equation was shown to be practically useful.

Identification of the bending stiffnesses of an orthotropic lamina.

In this paper, the authors describe a method that identifies four bending stifnesses of an orthotropic plate. A circular plate is used to carry out the static test of three points bending. Its deformation is measured in several cases of supporting and loading conditions. Then, from the measured values and some initial set ones, four bending stiffnesses are determined by the least square method using a personal computer.