Abstract
Plastic energy dissipation is inevitable during fatigue crack growth. There have been previous attempts reported in literature to correlate the plastic dissipated energy (dW/dN) to fatigue crack growth rate (da/dN). However, at a given dW/dN, the da/dN changes with the ratio of minimum and maximum loads, known as the stress ratio. This paper describes an experimental study carried out on 2024-T3 central crack tension specimens to quantify the relation between dW/dN and da/dN. By selecting different stress ratios in the individual tests, the experiments reveal the influence of the stress ratio on this relationship. It is evident that dW/dN has no unique relationship with da/dN valid for the tested stress ratios. Instead, the relationship for each stress ratio is different. This is illustrated with the value of plastic dissipation per unit of fatigue crack growth (dW/da), representing the effective resistance to the crack increment. This value is not a constant, but changes with the stress ratios and da/dN values. Hence the plastic energy dissipation cannot be used directly for predicting crack growth.
Highlights
IntroductionFatigue failure is a major failure type in aerospace engineering, so it is important to have a deep understanding of this failure type, in order to mitigate it
Fatigue failure is a major failure type in aerospace engineering, so it is important to have a deep understanding of this failure type, in order to mitigate it. Linear Elastic Fracture Mechanics (LEFM) has been applied successfully to practical engineering fatigue problems through the use of the Paris relation, LEFM still fails in explaining the physical nature of fatigue phenomena in metallic materials
The experiment shows that plastic dissipation per unit of fatigue crack growth does not stay constant for different load cases
Summary
Fatigue failure is a major failure type in aerospace engineering, so it is important to have a deep understanding of this failure type, in order to mitigate it. Linear Elastic Fracture Mechanics (LEFM) has been applied successfully to practical engineering fatigue problems through the use of the Paris relation, LEFM still fails in explaining the physical nature of fatigue phenomena in metallic materials. This is because metallic materials are ductile, and the plasticity phenomena strongly influences the fatigue crack growth rate (da/dN). If a deeper understanding of the nature of fatigue is needed, it has to be answered how plasticity influences fatigue crack propagation in metallic materials. An energy approach is chosen because the energy approach shows the universality among various materials and the plasticity itself represents a typical type of energy dissipation
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