Fine residual stress distribution measurement of steel materials by SOI pixel detector with synchrotron X-rays

TL;DR

This work extends the $cos \alpha$ method for residual-stress mapping to synchrotron X-rays using the INTPIX4 SOI detector, enabling rapid 2D stress distributions with high spatial resolution. It details the detector hardware, data-processing workflow, and Debye-ring elliptic fitting used to extract stress components from 2D diffraction images. Initial synchrotron measurements at 5.415 keV show feasibility but larger uncertainties and depth-dependent differences compared with laboratory Cr X-ray results, highlighting the impact of detector efficiency and setup stability. The study outlines concrete paths to improve accuracy, including better detector performance, more rigid instrumentation, and depth-resolved profiling via energy stepping or surface treatment.

Abstract

Residual stress is an important factor governing evaluating and controlling the quality of metal materials in industrial products. X-ray measurements provide one of the most effective means of evaluating residual stress without destruction. In such measurements, the effects of residual stress on the crystal structure can be observed through the Debye ring deformation. In previous studies, we developed a residual stress measurement system based on the $cos α$ method, using a two-dimensional (2D) silicon-on-insulator pixel (SOIPIX) detector known as INTPIX4. In a typical laboratory setup, this system requires only 1 second to measure a specified point. This is drastically faster than the conventional system based on the $sin^{2} ψ$ method, which requires more than 10 min, and the $cos α$-based system using an imaging plate, which requires 1 min. Compared to other systems, it can evaluate the 2D distribution of residual stress faster and provide more detailed information for evaluating materials. We first attempted to measure the 2D distribution in a laboratory setup with a Cr X-ray tube (Cr K$α$ 5.4 keV) and obtained satisfactory results. We subsequently took measurements using synchrotron monochromatic X-rays to determine the fine accuracy and fine sampling pitch distribution. In this paper, we report the results of the initial synchrotron experiment, including the residual stress distribution of the standard specimen obtained by the first prototype setup. Furthermore, we compare the synchrotron measurements with those from the laboratory.

Figures (10)

• Figure 1: Schematic of $cos \alpha$ method.
• Figure 2: Structure of SOI detector.
• Figure 3: Photograph of INTPIX4.
• Figure 4: Photograph of INTPIX4 two-chip board using wire bonding.
• Figure 5: Decision procedure for shape of Debye ring.