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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 K I and K II 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. 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.

In this study, the cyclic crack growth behavior of biaxially loaded cruciform specimens is investigated and compared with an uniaxially loaded cruciform specimen together with the Paris law to detect differences between uniaxial and multiaxial experiments and to understand the occuring mechanisms. The tests are performed on a planar‐biaxial test system and a stress ratio of R = 0.1. Biaxial loading takes place both in‐phase as well as out‐of‐phase, after an initial technical crack is generated, whereby the phase shift loading leads to a constantly changing biaxial force ratio . The crack path curved after changing from in‐phase to out‐of‐phase loading and subsequently the cracks grow straight again. Both cracks of each specimen have an almost identical crack path indicating a symmetrical stress distribution on the specimen. The calculation of the stress intensity factor range for the curved crack path is done by FE‐calculations.

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