Tatsuhiko Yoshimura

Three-Dimensional Crack Detection Method for Structures Using Simulated Strain Gages and the Body Force Method

A method for estimating the stress field of an observed domain by considering the surface of a 3-dimensional object as a pseudo3-dimensional object has been proposed in a previous report by the present authors. In this method, some strain gages and the body force method are used. In this paper, the method is applied to crack detection in notched structures. A characteristic stress field attributable to the crack can be expected in the observed domain. Crack detection is then tried by showing the characteristic stress field. Detection of an ideal crack, which is a through crack or a quarter-circular crack on the hidden side, is studied using the finite-element method (FEM). Moreover, the stress fields are estimated using the present method from the FEMs stress values instead of actual stress values. In both a through crack and a quarter-circular hidden crack, the characteristic stress field can be shown; the characteristic stress field means that two stress concentrations exist along the notch. Finally, the application limits of the present method are shown.

Laser welding conditions to improve tensile strength and fatigue strength of a lap joint in aluminum alloys

This research shows a procedure for seeking a domain of conditions under which the tensile strength and fatigue strength are improved in lap joints of aluminum alloys made by laser welding. Laser welding parameters involve the following three factors: gap width, welding speed, and laser power. The following conditions were obtained in this research. (a) When searching for favorable welding conditions, the required work involves only observing the states around the weld-zone. (b) In order to improved the fatigue strength, it is necessary to prevent the generation of lack of fusion by the shortage of heat input and a crack near the toe of the weld due to the excess heat input. Using the results, the above-mentioned simple method is shown.

Estimation of Stress Field Near a Notch Root of 3-D Structures with a Few Strain Data and the Body Force Method

A method is proposed for estimating stress fields using a few surface strain data, obtained either from strain gages or from finite-element analysis (FEA), and the body force method (BFM). A notch in a three-dimensional structural surface is considered to be an observed domain. The observed domain is treated as a pseudo-3-D plate, not a part of a 3-D body. In other words, the body force is distributed in the observed domain to add a 3-D influence to a plane stress problem. In this paper, the results by elastic finite-element method (FEM) analysis are used instead of the strain gage outputs on actual structures to investigate the application limit of the present method. It is possible to obtain the maximum stress value within 10% error by self-assessment of the result with the present method.

Influence of welding parameters on fatigue strength of spot-welded joint considering nugget size

Electrode force, welding current and time are welding parameters in determining the nugget size and the strength of spot-welded joint. The purpose of this study is, first, to evaluate the range of welding parameters under which the strength is robust and, second, to evaluate the relationship between welding parameters and the fatigue life. To achieve these purposes, two kinds of evaluations are made: ( i ) evaluation of the relationship between welding parameters and the nugget size using the heat transfer model; (ii) evaluation of the relationship between the nugget size and the fatigue strength considering the nominal stress at the nugget.

Application of fracture mechanics on Japanese automotive industry

Abstract The purpose of this paper is to survey the history of strength evaluation in the field of Japanese Automotive Industry and to discuss the present condition and the subjects of the application of fracture mechanics.