Influence of tensile overload on crack growth in 316L stainless-steel - including high strain & low stress interactions in 316l stainless steel, mild steel and aluminium alloy 6060-T5

Wheatley, H. Gregory (2001) Influence of tensile overload on crack growth in 316L stainless-steel - including high strain & low stress interactions in 316l stainless steel, mild steel and aluminium alloy 6060-T5. PhD thesis, University of Western Australia.

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Abstract

The fatigue crack growth behaviour of 316L stainless steel (Batch A} following a tensile overload has been observed. Micrographs and compliance measurements have also been taken. Results indicated that strain hardening may be the primary contributor toward retardation of crack growth. High strain - low stress interactions were observed in 316L stainless steel (Batch B and C), mild steel (C1020 and AS1214) and aluminium alloy (6060-T5). This was done as plasticity-induced crack closure is largely removed by using tensile specimens. Pre-training of 316L (Batch B) by low cycle fatigue (LCF) showed an increase in the fatigue life while pre-training of 316L (Batch C) showed a retardation of fatigue crack initiation and growth. Pre-training of the other materials showed little effect or a decrease in the fatigue life.

The conclusions of this thesis are as follows:

1. Fatigue crack growth occurs by a process of damage accumulation in the material in front of the crack tip.

2. Tensile overload creates a plastic deformation zone ahead of the crack tip. The material within this zone is strain hardened and also causes plasticity-induced crack closure (PICC). It has been found that retardation of post-overload fatigue crack growth is mainly a result of the increased fatigue resistance of the· strain-hardened material within the overload plastic zone.

3. A tensile overload enhances the fatigue damage ahead of the crack tip.· This results in a transient acceleration in the fatigue crack growth following overload.

4. 316L Stainless Steel (Batch B} displayed ail enhancement of fatigue life with LCF · pre-training. Crack initiation and propagation was retarded in 316L (Batch C) by similar LCF pre-training. This behaviour was not observed in mild steel (C1020 and AS1214) or aluminium alloy (6060-T5). A martensitic strain induced transformation was found to be not responsible for the observed behaviour of 316L (Batch B). It is suggested that this behaviour supports the findings of fatigue crack growth experiments of 316L stainless steel (Batch A), i.e. that strain hardening is primarily responsible for fatigue crack growth retardation following tensile overload.

Item ID: 58767
Item Type: Thesis (PhD)
Copyright Information: Copyright © 2001 H. Gregory Wheatley.
Date Deposited: 22 Jan 2020 04:37
FoR Codes: 09 ENGINEERING > 0912 Materials Engineering > 091207 Metals and Alloy Materials @ 50%
09 ENGINEERING > 0913 Mechanical Engineering > 091307 Numerical Modelling and Mechanical Characterisation @ 50%
SEO Codes: 86 MANUFACTURING > 8614 Machinery and Equipment > 861403 Industrial Machinery and Equipment @ 100%
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