Proportional Cyclic Loading Research Articles

Modeling of the effects of isotropic strengthening in nonproportional cyclic loading

On the basis of tests of the austenitic steel 03Kh21N32M3B with different programs of nonproportional loading including stages of various kinds of proportional cyclic loading and cyclic loading with constant strain intensity, the article analyzes the influence of the history of deformation on isotropic strengthening. It was established that in the material there exist several states of stabilization depending on the loading path, and to each of these states corresponds its own degree of isotropic strengthening. To express the experimentally observed effects, the article suggests determining equations in which isotropically kinematic strengthening is described on the basis of the evolution of a surface of “memory” in the space of plastic deformations. There is good agreement between the results of calculation and the experimental data.

Modified crack closure integral method with quarter point elements

The strain energy release rate is calculated numerically for cracks in shells from shell elements by using the modified crack closure integral. This enables the separation of individual strain energy release rates for the different crack opening modes and the calculation of the corresponding stress intensity factors for mixed mode loading situations. The presented formulas are validated by comparing numerical results for a 3d finite element model with results computed from a plane shell model. These formulas are then used to calculate the stress intensity factors for thirteen crack configurations measured on a notched hollow cylinder under proportional cyclic loading.

Estimates of the rupture life of structural components subjected to proportional cyclic loading

The process of creep in metals is associated with physical mechanisms which cause internal damage. This damage weakens the material; so that for a given stress level, the strain-rate increases with time. As a result of this behaviour, stress redistribution occurs which can greatly influence the ruptuie life of structural components. By use of the appropriate constitutive relations which model the tertiary portion of the creep curve, it is possible to estimate the life of a structural component by use of finite element methods. Unfortunately, the procedure is demanding on computer time; and, as a result, considerable attention has been given to the possibility of the use of bounding techniques which ease the computing problem and which are particularly useful at the early stage of design. Techniques have already been developed for bounding the rupture life of structural components subjected to constant loading and these are found to be useful. In this paper, bounding procedures are developed for structural components subjected to proportional cyclic loading. The results may be expressed in terms of a representative rupture stress, so that structural-component performance can readily be related to material behaviour.