Indentation Bending Tests Research Articles

Numerical study of the mechanics of indentation bending tests of thin membranes and inverse materials parameters prediction

Indentation bending tests are an important testing method for thin rubber-like materials. The choice of material laws in finite element (FE) simulations of the test directly influences the accuracy of the numerical model and material properties predicted through inverse FE modelling. In this work, the effect of using a linear elastic or hyperelastic model on the material parameters predicted from indentation bending tests of a thin rubber sheet over a low strain range were studied. An inverse program has been developed based on the Kalman filter method to predict the material properties from experimental tests and to assess the uniqueness of the converged results for different material models. The predicted results were compared to standard tests carried out on the same material. Results showed that the Young’s modulus of the material with the linear elastic model can be accurately predicted while the converged parameters (C10 and C01) for the Mooney–Rivlin model were not unique; data analysis showed that parameters C10 and C01 of the converged data were associated with the shear modulus of the material.

Residual stresses around Vickers indents

The residual stresses generated by Vickers indentation in brittle materials and their changes due to annealing and surface removal were studied in 4 mol% yttria partially stabilized zirconia (4Y-PSZ). Three experimental methods to gain information about the residual stress field were applied: (i) crack profile measurements based on serial sectioning, (ii) controlled crack propagation in post indentation bending tests and (iii) double indentation tests with smaller secondary indents loccated around a larger primary impression. Three zones of different residual stress behavior are deduced from the experiments. Beneath the impression a crack free spherical zone of high hydrostatic streses exists. This “core” zone is followed by a transition regime where indentation cracks develop but still experience hydrostatic stresses. Finally, in an outward third zone, the crack contour is entirely governed by the tensile residual stress intensity (elastically deformed region). Annealing and surface removal reduce this crack driving stress intensity. The specific changes of the residual stresses due to the post indentation treatments are described and discussed in detail for the three zones.