Material propertiesSetup for evaluation of fatigue crack growth in rubber: Pure shear sample geometries tested in tension-compression mode

A novel measurement setup is developed to determine fatigue crack growth and heat build-up in rubber. Loading conditions include tensile and compressional loads. Deviations in the crack shape are detected with special features (swivel arm and additional light sources) and provide the possibility of a subsequent manual correction of the shadow crack length. This results in improved reproducibility and a worst-case scenario is obtained.Flat pure shear (PS) samples with 2 mm and 4 mm thickness are compared with faint waist pure shear (FWPS) samples. Especially due to the waisted shape and the corresponding non-uniform strain distribution, FWPS samples show augmented in-plane crack growth, but the validity of the tearing energy concept is questionable. PS samples with 4 mm thickness can easily support compressional loads but they show larger heat build-up at comparable tearing energies due to increased thickness. Thus, advantages and disadvantages are identified for each geometry.