Crack Paths 2012

X - F E Mbasedmodellingof complexmixedm o d efatigue

crack propagation

H a n s Minnebo’, S i m o nAndréz, Marc Duflot’, T h o m a sPardoenz, Eric

Wyart1

1 Cenaero,Ruedes Freres Wright 29, 6041 Gosselies, Belgium

2 Université catholique de Louvain, 2, Place Ste Barbe, 1348 Louvain-la-Neuve,

Belgium

Contact: hans.minnebo@cenaero.be

A B S T R A C TT.his papers aims at describing the usage of the eXtended Finite Element

Methodand more widely the fracture mechanics in a general framework. First, the

numerical approach with its hypotheses is described. Then, an experimental procedure

is developed to validate some assumptions about crack orientation, the numerical tool

has been used to estimate an a priori crack propagation behavior. Finally, conclusions

are drawn aroundthe opportunity of using such predesign tool.

I N T R O D U C T I O N

Cost reduction in combination with performance improvement implies weight and

shape optimization, whithout forgetting safety aspects. Failure analysis can be carried

out with fail-safe, safe-life or damage tolerant approaches. While in the first two,

studied parts should undergo a given numberof cycles without cracking, as they could

not be changed or repaired when a crack occurs, the latter addresses the problem of

parts that are regularly inspected and can be changed or repaired if a detected crack

would grow to a critical size before the next inspection. More generally, damage

tolerance is used to define inspection intervals by considering an undetectable crack of

the biggest possible size located in the most critical area and determining the numberof

loading cycles until a critical configuration is reached. In aeronautics and other

industrial sectors, a linear elastic behavior is observed enabling the use of the Linear

Elastic Fracture Mechanics [1] assumptions where the eXtended Finite Element Method

[2] has shown to be a numerical method with very powerful possibilities in the last

years. This method has been thoroughly validated on multiple applications where L o w

Cycle and High Cycle Fatigue are considered. Still, the question remaining on the

physics of a crack propagation cannot be answered by a numerical tool. For that reason,

an experimental procedure has been developed. Using the X F E Mas a predimensionning

tool for the specimens and load cases, the experiments are built in several steps in order

to be able to test a mixed-modecrack propagation under varying load conditions.

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