RESIDUAL-STRESSES OF TYPE-II AND TYPE-III AND THEIR ESTIMATION

Residual stresses (RS) are induced in metallic materials by a variety of working and fabrication processes. They are generally classified in to three categories'(types I, II and III) depending upon their range o f influence. Separation of type I and II stresses often requires stres s measurements on thin specimens. Type III stresses are related closel y to grain fragmentation and micro-strains associated with plastic def ormation. Perhaps the oldest and the most rigorous method of estimatin g these stresses is still the Warren-Averbach analysis developed durin g the late forties/early fifties. Other techniques involving integral breadths and variance of the profiles have also been developed. In all these methods developed during the early stages, prior to seventies, a major requirement was well-separated non-overlapping profiles. The l ate sixties and early seventies saw a dramatic increase in computation al capabilities with the advent of powerful electronic computers. This led to the introduction of curve-fitting procedures into the field of X-ray diffraction. The most remarkable achievement of this period is the development of the Rietveld Method. Although this method was initi ally developed to tackle the neutron diffraction profiles, which are a s a rule nearly symmetric and Gaussian in nature, the method saw rapid developments during the eighties. At present, techniques based on con cepts developed by Rietveld could be applied to essentially asymmetric and non-Gaussian multiple spectral components of X-ray diffraction pr ofiles. Pattern decomposition techniques which separate composite-powd er diffraction profiles into individual profiles are now available. In combination with single line profile analysis techniques, this provid es a powerful tool in the hands of researchers. A typical example of s uch a single line profile analysis is given.