Anti-buckling device for biaxial testing with cruciform specimens

Abstract

The use of an anti-buckling device is proposed to avoid the appearance of undesired instabilities during biaxial testing with cruciform specimens in which the compressive loads are applied directly on the arms of the sample by means of compression plates. The device consists on a cross-shaped accessory that restricts out-of-plane displacements and a L-shaped support that forces the alignment of the fixture, the specimen and the testing machine. In addition, recommendations about the test methodology and the conditioning of the cruciform sample are given. For this purpose, analytical and numerical studies are developed to design the experiments and to describe both the global buckling of the cruciform specimen and the local instability of the central region subjected to biaxial loading. The risk of instability in the arms of the sample is reduced under tension-compression and compression-compression loading cases whenever the device is used, ensuring that the results are not affected by premature buckling of the specimen and favoring the appearance of appropriate failure modes.