Revisiting Classical Issues of Fatigue Crack Growth Using a Non-Linear Approach

Fatigue crack growth (FCG) has been studied for decades; however, several aspects are still objects of controversy. The objective here is to discuss different issues, using a numerical approach based on crack tip plastic strain, assuming that FCG is driven by crack tip deformation. DK was found to c...

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Main Authors:	Micael F. Borges, Diogo M. Neto, Fernando V. Antunes
Format:	Article
Language:	English
Published:	MDPI AG 2020-12-01
Series:	Materials
Subjects:	fatigue crack growth constant amplitude loading crack closure overload
Online Access:	https://www.mdpi.com/1996-1944/13/23/5544

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spelling	doaj-a9dbf06651044a9db49109aae05388fa2020-12-05T00:05:00ZengMDPI AGMaterials1996-19442020-12-01135544554410.3390/ma13235544Revisiting Classical Issues of Fatigue Crack Growth Using a Non-Linear ApproachMicael F. Borges0Diogo M. Neto1Fernando V. Antunes2Department of Mechanical Engineering, Centre for Mechanical Engineering, Materials and Processes (CEMMPRE), University of Coimbra, 3030-788 Coimbra, PortugalDepartment of Mechanical Engineering, Centre for Mechanical Engineering, Materials and Processes (CEMMPRE), University of Coimbra, 3030-788 Coimbra, PortugalDepartment of Mechanical Engineering, Centre for Mechanical Engineering, Materials and Processes (CEMMPRE), University of Coimbra, 3030-788 Coimbra, PortugalFatigue crack growth (FCG) has been studied for decades; however, several aspects are still objects of controversy. The objective here is to discuss different issues, using a numerical approach based on crack tip plastic strain, assuming that FCG is driven by crack tip deformation. DK was found to control cyclic plastic deformation at the crack tip, while <i>K</i><sub>max</sub> has no effect. Therefore, alternative mechanisms are required to justify models based on D<i>K</i> and <i>K</i><sub>max</sub>. The analysis of crack tip plastic deformation also showed that there is crack tip damage below crack closure. Therefore, the definition of an effective load range D<i>K</i><sub>eff</sub> = <i>K</i><sub>max</sub> − <i>K</i><sub>open</sub> is not correct, because the portion of load range below opening also contributes to FCG. Below crack closure, damage occurs during unloading while during loading the crack tip deformation is elastic. However, if the maximum load is decreased below the elastic limit, which corresponds to the transition between elastic and elasto–plastic regimes, there is no crack tip damage. Additionally, a significant effect of the crack ligament on crack closure was found in tests with different crack lengths and the same D<i>K</i>. Finally, the analysis of FCG after an overload with and without contact of crack flanks showed that the typical variation of <i>da/dN</i> observed is linked to crack closure variations, while the residual stresses ahead of crack tip are not affected by the contact of crack flanks.https://www.mdpi.com/1996-1944/13/23/5544fatigue crack growthconstant amplitude loadingcrack closureoverload
collection	DOAJ
language	English
format	Article
sources	DOAJ
author	Micael F. Borges Diogo M. Neto Fernando V. Antunes
spellingShingle	Micael F. Borges Diogo M. Neto Fernando V. Antunes Revisiting Classical Issues of Fatigue Crack Growth Using a Non-Linear Approach Materials fatigue crack growth constant amplitude loading crack closure overload
author_facet	Micael F. Borges Diogo M. Neto Fernando V. Antunes
author_sort	Micael F. Borges
title	Revisiting Classical Issues of Fatigue Crack Growth Using a Non-Linear Approach
title_short	Revisiting Classical Issues of Fatigue Crack Growth Using a Non-Linear Approach
title_full	Revisiting Classical Issues of Fatigue Crack Growth Using a Non-Linear Approach
title_fullStr	Revisiting Classical Issues of Fatigue Crack Growth Using a Non-Linear Approach
title_full_unstemmed	Revisiting Classical Issues of Fatigue Crack Growth Using a Non-Linear Approach
title_sort	revisiting classical issues of fatigue crack growth using a non-linear approach
publisher	MDPI AG
series	Materials
issn	1996-1944
publishDate	2020-12-01
description	Fatigue crack growth (FCG) has been studied for decades; however, several aspects are still objects of controversy. The objective here is to discuss different issues, using a numerical approach based on crack tip plastic strain, assuming that FCG is driven by crack tip deformation. DK was found to control cyclic plastic deformation at the crack tip, while <i>K</i><sub>max</sub> has no effect. Therefore, alternative mechanisms are required to justify models based on D<i>K</i> and <i>K</i><sub>max</sub>. The analysis of crack tip plastic deformation also showed that there is crack tip damage below crack closure. Therefore, the definition of an effective load range D<i>K</i><sub>eff</sub> = <i>K</i><sub>max</sub> − <i>K</i><sub>open</sub> is not correct, because the portion of load range below opening also contributes to FCG. Below crack closure, damage occurs during unloading while during loading the crack tip deformation is elastic. However, if the maximum load is decreased below the elastic limit, which corresponds to the transition between elastic and elasto–plastic regimes, there is no crack tip damage. Additionally, a significant effect of the crack ligament on crack closure was found in tests with different crack lengths and the same D<i>K</i>. Finally, the analysis of FCG after an overload with and without contact of crack flanks showed that the typical variation of <i>da/dN</i> observed is linked to crack closure variations, while the residual stresses ahead of crack tip are not affected by the contact of crack flanks.
topic	fatigue crack growth constant amplitude loading crack closure overload
url	https://www.mdpi.com/1996-1944/13/23/5544
work_keys_str_mv	AT micaelfborges revisitingclassicalissuesoffatiguecrackgrowthusinganonlinearapproach AT diogomneto revisitingclassicalissuesoffatiguecrackgrowthusinganonlinearapproach AT fernandovantunes revisitingclassicalissuesoffatiguecrackgrowthusinganonlinearapproach
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Revisiting Classical Issues of Fatigue Crack Growth Using a Non-Linear Approach

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