Experimental investigation of the local deformation processes in joints under cyclic loading by traditional methods of fatigue testing

The task of calculation of joints fatigue life and their optimum design should be solved based on the analysis of local elasto-plastic strains.So it is necessary to overcome severe difficulties, arising from the considering the nature of contact interrelation and redistribution of residual stresses.The first of them is connected with the fact that the relation between local strains and local netstresses is non-linear as a rule and sometimes, owing to physical and geometrical non-linearity of deforming process, it is expressed as hysteresis loops.Beside the local mechanical properties of a material in non-regular zones of joints change during loading and, generally, cannot be evaluated by tests of standard specimens.In this connection it can be concluded that the task of optimum design of joints cannot be solved without test data obtained by different methods of experimental mechanics.