ABSTRACT
This chapter considers static loads, where the load is gradually applied and equilibrium is reached in a relatively short time. Under static loads, a machine element may often fail at sites of local stress concentration caused by geometrical or microstructural discontinuities. Calculation of stress concentration factors is examined in detail in Section 6.2, and the mechanics are explained through a flow analogy. Another failure mode that is often encountered is fracture, whereby cracks within a microstructure grow or propagate in an uncontrolled fashion, leading to failure. Fracture mechanics is a technique used to determine the stress level at which preexisting cracks of known size will propagate, or the largest allowable crack for a given stress and material can be estimated. Geometric factors and a material property called fracture toughness are used in the theory. The chapter ends with failure criteria for both uniaxial and multiaxial stress states. The most common failure criteria in engineering practice are presented, and their applicability to different materials is discussed.
