An interpretation and modification of the SWT function

The influence of pre‐strain on the tensile and fatigue properties of a dual phase DP600 steel was studied. The material was pre‐strained by uni‐axial tension in rolling and transverse direction. Thereafter, specimens were cut from the deformed plates in parallel or orthogonal to pre‐strain direction. It was found that pre‐strain increases yield and tensile strength. Results suggested that strain path change primarily affects the elastic‐plastic transition during early stage of reloading. Pre‐strained specimens showed an increase in high cycle regimes as a consequence of yield strength increment, irrespective of imposed pre‐straining direction. A modified stress life equation that accounts for pre‐strain was proposed and showed good agreement with experimental data. Bake hardening enhanced both tensile and high cycle fatigue resistance. Walker equation was successfully fitted to account for tensile mean stress. In low cycle fatigue, negligible influence of pre‐strain was observed due to cyclic softening and residual stress relaxation.

R = σ_{m i n} false/ σ_{m a x} \leq - 1

, for which it has been shown to be non‐conservative.…”

Section: Overview Of Recent Developmentsmentioning

confidence: 99%

Influence of pre‐strain and bake hardening on the static and fatigue strength of a DP600 steel sheet

Kusch

Crivelli

Diviani

et al. 2023

“…Arora et al model for these paths. However, a large set of data points with larger compressive/tensile stresses [63][64][65][66] (not leading to ratcheting damage) are required to verify the capability of each CP model under loading paths with mean stress/strain components. The present analyses considered limited numbers of mean stress data points (34 in number) on three material grades out of total 708 data points on 17 material grades.…”

Section: Modelsmentioning

confidence: 99%

“…SWT model resulted in large numbers of data points crossing the material intrinsic bounds especially for pure torsion, non-proportional, loading with stress/strain effect, and asynchronous loading conditions (Figure 12C). Kujawski 63,64 and Ince 65,66 proposed deviatoric versions of SWT model for improved predictions of fatigue life under cyclic loading with mean stress. However, these models are strain energy density-based models which consider the state of stress at three mutually perpendicular planes unlike the present critical plane models considering the state of stress on one material plane.…”

Section: Inter-comparisons Of Models Based On Loading Categoriesmentioning

confidence: 99%

Comparing fatigue life prediction capability of critical plane models using multiaxial test database on 17 materials

Arora

Gupta

Samal

et al. 2023

The present study validates recent as well as extensively used critical plane (CP)‐based fatigue life assessment models for 10 ferrous and 7 non‐ferrous materials. Fourteen CP models, including recently reported in‐house developed model, have been analyzed. These models use resolved stresses, strains, strain energy density, and combinations of stresses and strains to identify critical plane and quantify fatigue damage. The loading conditions cover various proportional and non‐proportional axial‐torsion strain paths with different phase shift angles with (or without) mean stress/strain component(s), loading waveforms, and asynchronous axial‐torsion stain paths. The comparative study brought out the goodness of various models by quantifying the extent of scatter and computational time. Some of the strain energy density‐based models (including in‐house model) have been shortlisted, which produced accurate fatigue life assessments. Among the shortlisted models, in‐house model is free from the calculation subjectivities of resultant shear and performs faster fatigue damage calculations.

“…[49][50][51][52] Alternative approaches were introduced, such as Vasudévan et al, 53 proposing a two parameter damaging process controlled by ΔK and K max , and Kujawski 54 who proposed a driving force as a function of K max and the positive range of ΔK, ΔK + . Recently, Kujawski 55 proposed a modified Smith-Watson-Topper (SWT) function, which takes into account the sum of the strain energy density and the complementary energy density to define a damaging energy density. More recently Kujawski, 56 based on the previous study, re-wrote the modified SWT function based on a stress formulation.…”

Section: Alternative Crack Driving Parametermentioning

confidence: 99%

Effect of L‐T and S‐T orientations on fatigue crack growth in an aluminum 7050‐T7451 plate

Borges

Antunes

Jesús

et al. 2023

This study is focused on the anisotropic fatigue crack growth (FCG) behavior of an aluminum AA7050‐T7451 plate. L‐T and S‐T orientations were studied in M(T) samples with W = 50 mm, in mode I loading, with R‐ratio of +0.05. A numerical approach was used, assuming that crack tip plastic strain is the crack driving force. A purely kinematic elastic–plastic model was calibrated using experimental data from low cycle fatigue tests of smooth specimens in L and S orientations. The predicted FCG rates agree well with experimental trends in the Paris' regime, suggesting that cyclic plastic deformation is the main damage mechanism. The numerical model was used to estimate the stress ratio effect for both orientations, which was found to be linked with crack closure variations. However, the closure free predicted trends for both microstructural orientations at R = 0.05 are not overlapped, suggesting an effect of microstructure not linked to crack closure.