GENERAL RELATIONS OF STRAIN-GRADIENT STRESS-ANALYSIS

Some particular fields of stress gradients in plates are investigated analytically and experimentally. Carriers of empirical information are light beam deflections caused by stress or strain gradients in homoge neous beams subjected to a particular case of flexure with shear, This study is based on theories and techniques of the strain-gradient meth od that was recently introduced by the authors. This is a generalizati on of prior analytical-experimental examination of strain-gradient lig ht deflections produced in stressed plates, which had concentrated on the simplest case where information of interest is collected along a l ine of symmetry of the stress field and where both the information car rying light beams are deflected in the plane of symmetry only. The dev eloped relations were tested experimentally, by using an S-beam as rep resentative example of general plane stress field, The main purpose of the present investigation is to document the efficacy of the strain-g radient method in analysis of the general case of stress state and to test the ranges of applicability of the accepted mathematical models a nd of the subsequently derived relations. In this respect, the most in teresting stress state is that in a beam subjected to the Saint-Venant bending, where the transversal and longitudinal axes of the beam are in pure shear. The obtained results are compared, at each step, with t he predictions of the developed analytical models and with the predict ions of Filon's stress function. The results of comparison are satisfa ctory. The procedures of evaluating the photoelastic and material coef ficients using strain-gradient techniques were tested positively. The developed method can yield valuable information on the actual features of stress states in fracture mechanics. Part of the problems and firs t results of this investigation will be presented in the authors' pape r ''Strain-gradient stress analysis in Saint-Venant bending''.