The cos α method for X-ray residual stress measurement using two-dimensional detector

Abstract

X-ray stress measurement is widely used as one of the most powerful nondestructive tools to measure residual stresses in polycrystalline solids. In most cases, the sin 2  method has been used to determine the stress. In recent years, however, the cos method has attracted engineers as a new method to measure the stress using two-dimensional detectors, such as imaging plates. The present article is the review of the state of the art of the cosmethod. For biaxial stress cases, the cos method utilizes the whole Debye-Scherrer ring recorded on a two-dimensional detector taken by single exposure of X-rays, and normal and shear stresses are determined simultaneously. The accuracy of the stress measurement of the cos method has been confirmed to be equivalent to that of the sin 2  method for various metals. The simple optical system of the cos method makes stress analyzers smaller, lighter and more convenient to use for on-site or field measurements. A recent portable stress analyzer adopting the cos method shortens the measurement time to 60 s. The method has been further developed to analyze triaxial residual stresses. Various advantages of the cos method are highlighted in comparison with the other methods of X-ray stress determination. Applications of the cos method to machines and engineering structures are presented, together with future perspectives of the method.