The Wöhler Curve, also known as an S-N curve, is a graphical representation of the relationship between cyclic stress (S) and the number of cycles to failure (N) in a material. It is fundamental in fatigue analysis, helping engineers predict the lifespan of materials under repeated loading conditions.
Non-proportional loading refers to a scenario in material mechanics where the direction of the applied load changes during the deformation process, leading to complex stress-strain responses that are not directly proportional. This phenomenon is critical in understanding material behavior under multi-axial loading conditions, as it can significantly affect the fatigue life and failure mechanisms of materials.
High Cycle Fatigue refers to the phenomenon where materials fail after being subjected to a large number of stress cycles, typically in the range of 10^4 to 10^7 cycles, at stress levels below the material's ultimate tensile strength. This type of fatigue is critical in the design and analysis of components that undergo repeated loading, such as aircraft wings, automotive parts, and machinery, emphasizing the importance of understanding material endurance limits and the effects of cyclic stress.