Radial in-plane digital speckle pattern interferometer combined with instrumented indentation

• A compact device combining DSPI and instrumented indentation is presented.
• This device simultaneously measures the radial in-plane displacement field generated around the indentation and the force–penetration curve.
• Numerical simulations are performed for a free-stress material and for stressed material.
• Good agreement between measured and simulated displacements was achieved.

This paper presents a modular device based on digital speckle pattern interferometry (DSPI) which is combined with instrumented indentation. The interferometric module uses a diffractive optical element that confers radial in-plane sensitivity enabling the measurement of whole displacement field generated by the shallow indentation print on the surface of the material under testing. The indentation module uses a piezoelectric loading cell and an inductive transducer to simultaneously measure the loading applied on the ball indenter tip as well as its penetration on the material under testing. A mechanical/hydraulic scheme was developed to achieve a high loading capability with a compact indentation module, suitably sized with the interferometric module. A finite element simulation was carried out for a generic low carbon steel material without residual stresses and under a tensile external loading of 25%, 50% and 75% of its yielding stress. In the same way, a steel bar was experimentally indented by using the compact indenter module and the radial in-plane displacements around the indentation were measured with the measurement module. Good agreement was found between the simulated and measured displacement fields. In addition, the influence of the tensile load on the measured displacement fields was clearly observed by the measurement module.