State of the art of nondestructive stress measuring techniques

Engineering structures for reliable function and safety have to be designed such that operational mechanical loads are compensated for by stresses in the components bearable by the materials used. What is bearable depends upon the properties of the chosen materials under the environmental situation, operational parameters, elapsed or remaining serviceable time of life and last but not least residual stresses in the components wherever they come from. Always the sum of load induced and residual stresses has to be considered. Therefore techniques are needed to measure as well load induced stresses under test loads or simulated operational resp. real operational loads as residual stresses in components or unloaded structures. Well approved elastomechanical finite element codes are available and used for calculating load induced stresses; redundancy and reliability engineers, however, need procedures and instrumentation for experimental checks. Residual stresses normally cannot be calculat ed. They always have to be measured. In both cases these measurements should be performed nondestructively as far as possible. In this key note lecture a rough surview will be given to the state of the art of stress measuring techniques with special emphasis to nondestructive techniques and residual stress states. Afterwards much more detail will be given by more than 25 oral and poster presentations. The following techniques will be covered: X-ray- and neutron diffraction; ultransonics; magnetics especially Barkhausen noise; optical ones including Raman spectroscopy; mechanical ones especially the well known stress release techniques by holes or notches. The contents of this key note lecture is described more extensively in a document of the commission V of the International Institute of Welding (V847/87)