For the lifetime designs there are two possible ways of strength verification: calculations and experiments. The experimental strength verification in the very high cycle regime is only in a few possible cases due to the long experiment time and high costs of testing. Due to these reasons there is only a limited number of test results available for the high cycle regime and experiments must carefully be monitored to gain the most possible information. The lifetime calculation verification is based on various lifetime calculation models and modifications. Nevertheless, the calculated lifetimes are varying up to a factor of 200 in lifetime for spectrum loads with maximum stresses just above the fatigue limit. Therefore for spectrum loading is a high uncertainty in the predicted lifetime of a component. Lifetime Calculation for Variable Amplitude Constant Amplitude Component Stress Analysis Lifetime prediction of components is based on stress analysis. These analyses are either base on nominal stress analysis, local stress analysis. In more complicated cases of complex components the finite element method (FEM) is used to determine the local stress distributions and to find the most claimed section of the component. A component, which shows no stress concentration, is considered a well-designed component because all sections of the component are equally stressed. The spots of stress maximums are called critical spots. These spots are considered the weakest spots of the design where the component is expected to fail. Figure 1: Elastic-Plastic Stress Analysis Compared to Strain Gauge Measurements The FEM-analysis of such stress distribution can be verified using strain gauges to analyse local strains and calculate elastic stresses. These stresses can be compared with the analytical calculated local stresses on these spots. The accuracy of a FEM-model can be evaluated by a comparison of the calculated stresses by FEM analysis to the observed experimental stresses for elastic deformations. Figure 2: Digital Video Test Observations of Multiple Surface Cracks
RkJQdWJsaXNoZXIy MjM0NDE=