Mitsuo Obata

Stress dependence of leaky surface wave on PMMA by line-focus-beam acoustic microscope

The authors discuss a line-focus-beam (LFB) acoustic microscope as a system for evaluating local stresses in polymeric materials. The goal of this paper is to reveal the stress-dependence of the velocity of the leaky surface skimming-compressional wave (LSSCW), which is excited by the LFB acoustic microscope and propagates on the boundary of the water/specimen surface.

Fine-grid method for large-strain analysis near a notch Tip

The purpose of this paper is to develop a technique for a fine-grid method to analyze the large strains in a local region surrounding a notch tip. There is a region surrounding a notch tip where very large displacements take place. In such a region, the assumption of infinitesimal deformation does not apply. In this paper, the Lagrangian description was used as a strain-displacement relation. In-plane components of displacements,u andv were obtained directly from change of location of fine grids. Displacement in the thickness direction,w, was estimated by a relation betweenw and (∂v/∂y), decided in advance. It was confirmed that the fine-grid method described in this paper was very useful in measuring directly and continuously the large strains in a local region surrounding a notch tip.

Embedded fine-grid method applied to three-dimensional stress-intensity-factor analysis

The purpose of this paper is to extend the embedded fine-grid method to three-dimensional stress-intensity-factor analysis. The embedded crossed fine grids give two components of displacement and are capable of calculatingKI without the assumption of the plane-strain condition along a crack or a notch front. It is not valid to assume the plane-strain condition to calculateKI in the vicinity of a free surface, whereKI is influenced by a free surface (plane-stress condition).In this paper, a dyeing and bleaching process is considered to reproduce the crossed fine grids on an epoxy plate. By using these grids as embedded grids, the distributions ofKI along notch fronts in SEN specimens with various different thicknesses and side grooves are studied. The influences of a free surface and the side-groove effects on the distribution ofKI are discussed.