Non-local stress gradient approach for multiaxial fatigue of defective material

The prediction of the fatigue resistance of additively manufactured parts is a current issue for the materials and process qualification in aerospace industry. Despite a continuous improvement of AM process, the presence of defects cannot yet be completely avoided, and the latter are still one of the main causes of fatigue damage in AM materials. In this framework, the present work focused on the influence of defects on the uniaxial fatigue behavior of AlSi7Mg0.6 alloy produced by Selective Laser Melting (SLM). Uniaxial fatigue tests have been performed. Fatigue specimens were subjected to a T6 treatment, and then machined in order to avoid the influence of surface roughness. Besides, for some specimens, artificial defects were directly introduced through CAD. The introduction of artificial defects, whose sizes and positions are precisely controlled, aims to provide a proper assessment of defect sensitivity. X-ray tomography was used to characterize both natural and artificial defects. Finite-element calculations of the local stress fields in the vicinity of defects were conducted, accounting for the real defect geometries obtained with CT scans. The application of a non-local multiaxial fatigue criterion then allowed to analyze defect criticity.

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Comparison of different one-parameter damage laws and local stress-strain approaches in multiaxial fatigue life assessment of notched components

International Journal of Fatigue ◽

10.1016/j.ijfatigue.2021.106405 ◽

2021 ◽

pp. 106405

Author(s):

R. Branco ◽

J.D. Costa ◽

L.P. Borrego ◽

F. Berto ◽

S.M.J. Razavi ◽

...

Keyword(s):

Fatigue Life ◽

Local Stress ◽

Multiaxial Fatigue ◽

Life Assessment ◽

Stress Strain ◽

Fatigue Life Assessment ◽

Notched Components

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A new non-local criterion in high-cycle multiaxial fatigue for non-proportional loadings

International Journal of Fatigue ◽

10.1016/j.ijfatigue.2006.10.033 ◽

2007 ◽

Vol 29 (8) ◽

pp. 1465-1474 ◽

Cited By ~ 15

Author(s):

A CHAMAT ◽

M ABBADI ◽

J GILGERT ◽

F COCHETEUX ◽

Z AZARI

Keyword(s):

Multiaxial Fatigue ◽

Local Criterion ◽

Non Local

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UV-Induced non-local stress relaxation in bimaterial systems

Bragg Gratings, Photosensitivity, and Poling in Glass Waveguides ◽

10.1364/bgpp.2003.md25 ◽

2003 ◽

Author(s):

H.N.J. Fernando ◽

L. Wosinski ◽

B. Jaskorzynska ◽

M. Dainese ◽

J. Canning

Keyword(s):

Stress Relaxation ◽

Local Stress ◽

Non Local

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Studies on the Residual Stress and Strain Gradients in Poly-SiGe Nanocantilevers

FUOYE Journal of Engineering and Technology ◽

10.46792/fuoyejet.v4i1.303 ◽

2019 ◽

Vol 4 (1) ◽

Author(s):

Tesleem B Asafa

Keyword(s):

Strain Gradient ◽

Stress Gradient ◽

Local Stress ◽

Stress And Strain ◽

Fast Method ◽

Stress Evolution ◽

Strain Gradients ◽

Study Results ◽

Evolution Study ◽

Gradient Measurement

One of the fundamental structural requirements for Micro/Nano-ElectroMechanical (M/NEM) devices is low strain gradient. Measurement of strain gradients is time consuming, therefore finding a simple and fast method is necessary. In this paper, a comparative study of the strain gradients in poly-SiGe nanocantilevers measured experimentally and obtained using finite element modelling (FEM) approach is reported. Arrays of nanocantilevers were fabricated from 100 nm thick poly-SiGe films via lithography. Then, strain gradients were calculated from the tip deflections and cantilevers’ lengths. In the modelling study, similar cantilevers were modelled with COMSOL Multiphysics as superposition of smaller layers in which each layer sustained local stress obtained from stress evolution study. Results showed that the average strain gradients obtained from the experimental and FEM studies differ by ~5% and ~6% for film A and B, respectively with standard deviations lying between ±0.004 and ±0.009/µm. While this study established that stress gradient is responsible for the calculated strain gradient, it also emphasises that both parameters are proportional. Key words: Poly-SiGe, Strain gradient, FEM, COMSOL.

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Ability of multiaxial fatigue criteria accounting for stress gradient effect for surface defective material

MATEC Web of Conferences ◽

10.1051/matecconf/201816522032 ◽

2018 ◽

Vol 165 ◽

pp. 22032

Author(s):

Wichian Niamchaona ◽

Fabienne Pennec ◽

Kévin Tihay ◽

Michel Duchet ◽

Bastien Weber ◽

...

Keyword(s):

Fatigue Strength ◽

Surface Defects ◽

Stress Gradient ◽

High Stress ◽

High Strength Steels ◽

Fatigue Behaviour ◽

Multiaxial Fatigue ◽

Integral Approach ◽

Manufacturing Defects ◽

Material Fatigue

New high strength steels are widely used nowadays in many industrial areas as in automotive industry. These steels are more resistant and provide higher fatigue limits than latter ones but they are also more sensible to small defects. Natural defects that outcome from metallurgy (as shrinkage, inclusion, void) are not considered in this study. We focus on small manufacturing defects such as cutting edge defects generated by punching or other surface defects due to stamping. These defects are harmful on the material fatigue behaviour due to high stress concentration at defects root. They also generate stress gradient that is beneficial from the fatigue strength point of view. This study focusses on the stress gradient (it does not account for the size effect) from cylindrical defect on specimen edge. Practically a normal stress gradient is added in multiaxial fatigue criteria formulation. Both critical plane approach and integral approach are involved in the present study. This gradient is calculated from stress states at defects root by using FEM. Criteria fatigue function at N cycles is used to assess the material fatigue strength. Obviously multiaxial fatigue criteria accounting for stress gradient give more precise fatigue functions than criteria that do not consider the gradient influence.

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