Thermographic methodology for rapid determination of the fatigue limit of materials and mechanical components

Simple procedures are presented for treating cumulative fatigue damage under complex loading history using either the Damage Curve concept or the Double Linear Damage Rule. A single equation is provided for use with the Damage Curve approach; each loading event providing a fraction of damage until failure is presumed to occur when the damage sum becomes unity. For the Double Linear Damage Rule, analytical expressions are provided for determining the two phases of life. The procedure involves two steps, each similar to the conventional application of the commonly used Linear Damage Rule. When the sum of cycle ratios based on Phase I lives reaches unity, Phase I is presumed complete, and further loadings are summed as cycle ratios based on Phase II lives. When the Phase II sum reaches unity, failure is presumed to occur. No other physical properties or material constants than those normally used in a conventional Linear Damage Rule analysis are required for application of either of the two cumulative damage methods described. Illustrations and comparisons of both methods are discussed.

/pdf/practical-implementation-of-the-double-linear-damage-rule-1p4l1u7l85.pdf

Practical implementation of the double linear damage rule and damage curve approach for treating cumulative fatigue damage

https://ntrs.nasa.gov/api/citations/19860018208/downloads/19860018208.pdf

Re-examination of cumulative fatigue damage analysis—an engineering perspective

Effect of surface finish on fatigue strength

An engineering approach for the prediction of wear in mixed lubricated contacts

Bending fatigue in the low cyclic life range differs from axial fatigue due to the plastic flow which alters the linear stress-strain relation normally used to determine the nominal stresses. An approach is presented to take into account the plastic flow in calculating nominal bending stress (S sub bending) based on true surface stress. These functions are derived in closed form for rectangular and circular cross sections. The nominal bending stress and the axial fatigue stress are plotted as a function of life (N sub S) and these curves are shown for several materials of engineering interest.

/pdf/fatigue-life-prediction-in-bending-from-axial-fatigue-1yceb0kkiy.pdf

Fatigue life prediction in bending from axial fatigue information

The paper presents closed-form solutions (collocation method and spline-function method) for the constants of the cyclic fatigue life equation so that they can be easily incorporated into cumulative damage analysis. The collocation method involves conformity with the experimental curve at specific life values. The spline-function method is such that the basic life relation is expressed as a two-part function, one applicable at strains above the transition strain (strain at intersection of elastic and plastic lines), the other below. An illustrative example is treated by both methods. It is shown that while the collocation representation has the advantage of simplicity of form, the spline-function representation can be made more accurate over a wider life range, and is simpler to use.

Inversion of the strain-life and strain-stress relationships for use in metal fatigue analysis

Starting with the basic fatigue lift formula, an inversion formula is derived. The inversion formula is valid over the entire life range of engineering interest for all materials examined. Conformity between the two equations is extremely close, suitable for all engineering problems. The approach used to invert the life relation is also suitable for the inversion of other formulas involving the sum of two power-law terms.

/pdf/a-single-expression-formula-for-inverting-strain-life-and-yvll70zh2w.pdf

S. S. Manson

Papers

Fatigue life prediction in bending from axial fatigue information

Inversion of the strain-life and strain-stress relationships for use in metal fatigue analysis

A Single-Expression Formula for Inverting Strain-Life and Stress-Strain Relationships