On the combination of the critical distance theory with a multiaxial fatigue criterion for predicting the fatigue strength of notched and plain shot-peened parts

This work applies Taylor's theory of critical distance to quantify the effect of defects on fatigue initiation in an additively manufactured metal. We focus on hollow pores that are ideal spherical, prolate, and oblate spheroids isolated in an otherwise homogeneous linear‐elastic material. These conditions support the development of exact solutions using the exterior Eshelby tensor for a pore in a remote, arbitrary stress field. For spheres, this solution process admits simple closed‐form solutions for principal stresses disturbed by the pore. For prolate and oblate spheroids, we present the solutions as graphical curves showing stress variations under uniaxial tension. This report then extends the analysis to determine the effect of defects on a parametric, power‐law stress range vs fatigue life model. By propagating the distributed stress fields through this model, this study demonstrates the effect of pore size, pore shape, stress, and parametric fatigue properties on the life reduction due to porosity. These results suggest several approaches to increasing fatigue lives in porous materials, eg, reducing the pore size, promoting spherical pores, and increasing the microstructural parameter (comparable to the El Haddad parameter). Results presented in this work may be useful to inform trends of fatigue strength and fatigue initiation lives in metallic alloys with limited porosity, eg, additively manufactured materials that have been HIP'ed.

Section: Introductionmentioning

confidence: 99%

Application of critical distances to fatigue at pores

Sobotka

Enright

McClung

2019

“…The theory of critical distance (TCD), developed by Taylor to study notched components in fatigue, has been applied to multiple axial criteria . Susmel gave a review regarding the development and application of TCD in fatigue.…”

Section: Introductionmentioning

confidence: 99%

Experimental and numerical investigation on crack initiation of fretting fatigue of dovetail

Chen

Liu

et al. 2018

The present study investigated the fretting fatigue crack initiation of dovetail structure based on experimental observation and multiple axial criteria. Two typical critical plane approaches of the Smith‐Watson‐Topper (SWT) and the Fatemi and Socie (FS) model were used to predict the crack initiation location, orientation angle, and fatigue life. The results indicate that both SWT and FS models predict consistent results with the experiment in crack initiation location. Regarding the crack initiation angle, FS model shows good agreement with the experimental observation, but SWT model exhibits a large difference. The two models give conservative results in fretting fatigue life. In view of this, the theory of critical distance (TCD) was incorporated into the SWT and the FS models. It shows that both the TCD‐SWT and the TCD‐FS predict fatigue lives within a scatter band of 2. It suggests that introducing the TCD into the critical plane model can greatly reduce the conservatism of the prediction. Furthermore, the prediction has less dependence on specific models.

Section: Introductionmentioning

confidence: 99%

“…In the practice, however, this is not the case when L is derived from notched geometries other than the cracked one, as shown in the following. Other averaging domains of higher geometrical complexity 5,6 have been proposed in the past, yet receiving much lesser attention than PM and LM, especially because of their complicated implementation. Despite providing satisfactory fatigue predictions in a wide variety of situations, [7][8][9] this conceptual framework of the TCD suffers from some limitations and drawbacks, which stimulated the scientific community to attempt further improvements: 1) In general, only under uniaxial loading the fatigue damage is controlled by the maximum principal stress range.…”

mentioning

confidence: 99%

Mean stress and plasticity effect prediction on notch fatigue and crack growth threshold, combining the theory of critical distances and multiaxial fatigue criteria

Benedetti

Santus

2018

In the present work, we propose a robust calibration of some bi‐parametric multiaxial fatigue criteria applied in conjunction with the theory of critical distances (TCD). This is based on least‐square fitting fatigue data generated using plain and sharp‐notched specimens tested at two different load ratios and allows for the estimation of the critical distance according to the point and line method formulation of TCD. It is shown that this combination permits to incorporate the mean stress effect into the fatigue strength calculation, which is not accounted for in the classical formulation of TCD based on the range of the maximum principal stress. It is also shown that for those materials exhibiting a low fatigue‐strength‐to‐yield‐stress ratio σfl,R = −1/σYS, such as 7075‐T6 (σfl,R = −1/σYS = 0.30), satisfactorily accurate predictions are obtained assuming a linear‐elastic stress distribution, even at the tip of sharp notches and cracks. Conversely, for any materials characterized by higher values of this ratio, as quenched and tempered 42CrMo4 (σfl,R = −1/σYS = 0.54), it is recommended to consider the stabilized elastic‐plastic stress/strain distribution, also for plain and blunt‐notched samples and even in the high cycle fatigue regime still with the application of the TCD.