Experimental setup for tests under biaxial tension of anisotropic cruciform specimen

Testing method for suitable measurement of the mechanical properties of materials is considered. Mutually perpendicular biaxial tension forces applied to the edges of a flat cruciform specimen produce in its thinnest part in-plane biaxial stresses. The problem of homogeneity of stresses is discussed in terms of the specimen shape design. The laminar specimen structure is necessary for testing the directional properties of materials with the induced anisotropy such as the fibre reinforced plastics usually fabricated in a sheet form or the rolled sheet-metals. The uniformity condition of the stress-strain field allowing the strain field measurement on the plane surface by means of the mechanical extensometer the idea of which is here pointed out. This paper highlights the problems arising in measuring, monitoring and control of strains in cruciform specimen. The testing machine and gripping system for inelastic tests at room and elevated temperatures are also described.