Cruciform specimens used for determination of the influence of T-stress on fatigue crack growth with overloads on aluminum alloy Al 6061 T651

Sebastian Henkel,Meinhard Kuna,Carl Wolf,Horst Biermann,Andreas Burgold

doi:10.3221/igf-esis.48.16

Sebastian Henkel, Meinhard Kuna + Show 3 more

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https://doi.org/10.3221/igf-esis.48.16

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Abstract

The publication presents a cruciform specimen for the determination of cyclic crack growth data under biaxial loading. The design of the specimen with slotted loading arms allows good decoupling between the two loading directions. For different initial crack geometries, the solutions for the stress intensity factors KI and KII as well as the crack-parallel T-stress are calculated by linear elastic finite element analysis (FEA) with the program ABAQUS. For two specimens with the same geometry made of aluminum alloy 6061 T651, the crack growth behaviour is measured at different T-stresses at a stress ratio of R=0.7 and overloads. It is shown that the crack retardation after an overload with crack-parallel tensile stress is less than without it. The reason for this behaviour is considered to be the reduced plasticity at the crack tip due to the higher triaxiality of the stress state.

Highlights

Testing of cruciform specimens is useful in a transfer chain from small uniaxial laboratory samples to complex multiaxially loaded components, especially to understand the material behavior under biaxial stress state [1]
For different initial crack geometries, the solutions for the stress intensity factors KI and KII as well as the crack-parallel T-stress are calculated by linear elastic finite element analysis (FEA) with the program ABAQUS
For two specimens with the same geometry made of aluminium alloy 6061 T651, the crack growth behaviour is measured at different Tstresses at a stress ratio of R=0.7 and overloads

Summary

Introduction

Testing of cruciform specimens is useful in a transfer chain from small uniaxial laboratory samples to complex multiaxially loaded components, especially to understand the material behavior under biaxial stress state [1]. Such stress conditions occur, for example, in thin-walled structural components such as the aircraft's outer skin, pressure. For the uniaxial load case, simple specimens are tested often under standardized conditions. Multi-axial testing, on the other hand, uses complex specimens or components that are in many cases subjected to high load gradients and have so far only been standardized in very few cases. Possible stress gradients and coupling between the loading axes have to be taken into account in such samples

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