Multiaxial fatigue life assessment of welded structures

A rapid path‐length searching procedure for multi‐axial fatigue cycle counting

“…For simple loading, such as shown in Fig. 1, 8 the path length is calculated as for a half cycle in the equivalent stress space where σ and τ are normal stress and shear stress components, respectively; β is an equivalency factor, which can be interpreted as a ratio between the ranges of normal and shear stresses acting on a critical plane within a life range of interest 7,8 . One of the significant features of this new damage parameter is that any change in the load path length will be reflected in the value of the damage parameter as well as the estimated life; therefore, load path dependency of fatigue damage is explicitly included in the path‐length dependent multi‐axial cycle counting method.…”

“… Time‐history data with stress components σ ( t ) and τ ( t ) should be placed in certain order, for example, normal stress in the first column and the shear stress in the second column, in input data sheet. The value of β, which is defined as a fatigue equivalence ratio between cyclic normal stress and shear stress fatigue test data, 7,8 should be properly defined in input data sheet. Renumber data points properly. Setting an upper bound dimension for the arrays holding σ ( t ) and τ ( t ) may be required.…”

“…The value of β, which is defined as a fatigue equivalence ratio between cyclic normal stress and shear stress fatigue test data, 7,8 should be properly defined in input data sheet.…”

“…Various models have been introduced in the literature for performing multi‐axial fatigue analysis and most of them are limited to proportional or simple non‐proportional loadings 6 . Recently, a path‐length based multi‐axial cycle counting and fatigue life assessment procedure has been proposed 7, 8 . This method avoids the concepts ‘peak' and ‘valley' as used in traditional rainflow counting but instead works with the concept ‘distance'.…”

“…The S − N curve is usually obtained by curve fitting tested data using least square or maximum likelihood method, and it has been standardized for industry application, such as ASTM 10 . Recently, the standard practice, as adopted by ASTM and many other standards, for statistical analysis of linear or linearized stress‐life and strain‐life fatigue data has been critically reviewed and its limitation can be overcome by using a newly developed approach; 11 , 12 The effectiveness of the path‐length dependent multi‐axial cycle counting method 7,8 has been validated by its ability to correlate multi‐axial fatigue data available in the literature and it provides a reliable way to address items (2) and (3) above; Miner's linear damage rule, 3 that is, a component fails when the accumulated damage equals unity or other certain values, based on experimental data, is often well accepted and has been adopted in many engineering applications.…”