X-Ray Stress Measurement by The Cos α Method Using Two-Dimensional Detector Part 1: Fundamentals of Measurements

Abstract

X-ray stress measurements are widely used as one of the most powerful nondestructive tools to measure residual stress in polycrystalline solids. In most cases, the sin²ψ method has been adapted to determine the stress. In recent years, the cos α method attracts engineers as a new method to measure the stress using two-dimensional detectors, such as imaging plates (IP). The present article is the part one of the review of state of the art of the cos α method. The principle of the method was originally proposed in Japan and has been developed in cooperative works in the Society of Materials Science, Japan. The strain is determined from the whole Debye-Scherrer ring recorded on IP by single exposure of X-rays as a function of the orientation angle α. In one measurement, the normal stress is determined by cos α diagrams and the shear stress by sin α diagrams, without knowing the exact value of stress-free diffraction angle. A commercial portable stress analyzer adapting the cos α method shortens the measurement time to about 1min. In the　present article, the history of the development of the cos α method is covered and fundamentals of the method are presented. The advantages of the cos α method are highlighted in comparison with the other methods of X-ray stress determination.