Prediction of the fatigue life of a notched body by the local stress-strain state. Part 2. Determination of a parameter representing the fatigue life of bodies with stress concentrators

Substantiation of the predicted fatigue curve for structural elements of aluminum alloy

“…The expression (19) is valid because the residual strain amplitude in the stress concentrator in low-ductility materials is essentially equal to half of the plastic strain amplitude [3]. Upon substitution of (15) into (19) in view of (4) and subsequent manipulations, we have The quantity B depends on the loads that act on the specimen with a stress concentrator and varies from 0.15-0.16 in the low fatigue life range to 2 in the field of almost elastic deformation.…”

“…The solution of nonlinear equation (3) in view of (2) yields the maximum stress in the notch, which corresponds to s n max .…”

“…The exponent in (23) is the slope ratio of the fatigue curve. For aluminum alloys the cyclic deformation diagram parameter m can be load-dependent [2,3]. We take an averaged value of the exponent in (23), which is numerically equal to M in relation (24).…”

“…The systems include the units for analog and digital processing of signals proportional to stresses and strains, the dedicated add-on strain gages, and the required software [10]. As applied to as-delivered D16AT and AMtsM alloys, and 30KhGSA steel, the numerical values of the parameters for the fatigue life calculation by the local SSS were provided earlier in [2][3][4].…”

“…The tests are performed until the specimen fails, and a relation between the number of cycles and the maximum nominal stress is found. The fatigue curves are approximated by exponential equations.The method of the fatigue life calculation by a local stress-strain state (SSS), which is based on the energy criterion for fatigue failure [2][3][4], makes it possible to theoretically predict the fatigue life till the formation of microcracks on the hole surface and macrocracks in the stress concentrator. For input data on the material properties this method uses cyclic deformation and fatigue characteristics as determined from the test results for smooth specimens.…”