ABSOLUTE STRESS DETERMINATION IN ORTHOTROPIC MATERIALS FROM ANGULAR DEPENDENCES OF ULTRASONIC VELOCITIES

In this paper we describe a method to determine absolute plane stresse s in orthotropic materials from the angular dependence of ultrasonic v elocities. No prior information on material anisotropy (texture) is re quired since the stress dependent elastic constants and stresses are f ound simultaneously from velocity data using least-squares optimizatio n. In the optimization algorithm no relation between the stress depend ent elastic constants and stresses is assumed and therefore they are c onsidered as uncoupled variables, but it is shown that the iteration p rocess converges to the correct (coupled) values. The method is applic able for stress measurements in materials which have undergone a compl icated (possibly plastic) history of loading and unloading; thus it ca n be used to determine both applied and residual stresses. To check th e proposed technique we use synthetic sets of experimental data for di fferent degrees of anisotropy and stress levels. Calculations using th ese synthetic data show that when the principal stress directions coin cide with the symmetry axes the angular velocity data in the plane per pendicular to the stress plane may be used for reconstruction of both stress components. When the stress is off the symmetry axis, the shear and the difference of the normal stress components may be determined from the angular dependence of the velocities in the plane of stresses . In both cases the stress determination accuracy depends only on the accuracy of velocity measurements and is independent of stress level a nd material anisotropy. (C) 1995 American Institute of Physics.