History and current status of X-ray stress analysis

X-ray stress analyses on crystalline or partially crystalline materials are based on the determination of elastic lattice strains from the appertaining shift of diffraction profiles by means of monochromatic X-rays. Then, the lattice strains are converted to stresses using theory of elasticity. The practical as well as the scientific importance of X-ray stress analysis have been increased enormously during the passed three decades. Today, it is a widely spread tool for materials science and materials engineering. This is even more remarkable since during the 1950s the state of development and practical acceptance of X-ray stress analysis did not justify optimism concerning future perspectives. The pinciples of the method were difficult to understand and the necessary experimental efforts seemed to be too high for technical application. The evaluation procedures were not free of individual personal influences, and doubts arised concerning the meaning and the assessment of the measured stress values. From the beginning of the 1960s, however, the situation was completely changed by the development of the sin(2) psi-method for X-ray stress analysis, by the development of experimental methods for the determination of precise X-ray elastic constants, and by the substitution of the classical X-ray film chambers for the registration of the interference lines by diffractometers using proportional counters. Since that time, many technical problems were investigated using X-ray stress analysis, and today it is worldwide the most widely applied method for residual stress determinations in several fields of research, engineering and quality control. Today, X-ray stress analyses are mainly performed using fully computer controlled four circle diffractometers and software packages allowing user friendly measurements and evaluations. However, the increasing knowledge about basic principles and difficulties in X-ray stress analysis opened a wide range of specific problems. Also the rapid development of materials science and materials technology concerning, e.g., single crystalline materials, ceramics, and coatings requires a large variety ofnew specific measuring and evaluation methods. Consequently, in the field of X-ray residual stress analysis, again a complex situation developed which is difficult to handle for many users in industry as well as in research. This paper sketches the historical development of X-ray stress analysis and gives a structured description of the actual state of the art.