Daiko Takamatsu

In Situ Stress Measurements during Welding Process

Welding technologies are indispensable for fabricating various industrial structures and must be highly reliable. Since tensile residual stresses at surface after welding cause crack progress, it is important to understand how stresses built up during the welding process in order to optimize final residual stresses as reduced tensile or introduced compressive stresses. Therefore, we conducted in-situ measurements of phase transformations, stresses and temperatures during tungsten inert gas (TIG) welding to understand how stresses built up. X-ray diffraction rings were detected per 0.1 sec during TIG welding by using a large-area two-dimensional detector and the accuracy of the stress analysis was estimated to be 8 MPa using the sin2ψ technique. In this paper, we described the phase transformations of ferrite low-carbon rolled steel and the changes in stresses during TIG welding.

Analysis of Residual Stresses in Pistons of Motor Vehicle Engines Using Neutron Diffraction at J-PARC

Internal residual stresses in the pistons of motor vehicle engines were measured to verify the accuracy of residual stresses estimated by thermal simulations. Coarse crystal grains in aluminum casting alloys frequently make it difficult to measure neutron diffraction profiles if a conventional diffractometer is used for steady reactors [1]. Therefore, the Takumi diffractometer installed at the Japan Proton Accelerator Research Complex (J-PARC), which is a pulse neutron source, was applied to measure them. Residual stresses in pistons determined by the method of neutron diffraction were in good agreement with those estimated through thermal simulations. We concluded from these results that the thermal simulations could be applied to designing and producing pistons. Moreover, Youngs modulus and Poissons ratio for aluminum-silicon casting alloy were determined by using neutron diffraction. We also verified that internal residual stresses could be measured with a tensile sample holder by using the Takumi diffractometer.