EVALUATION OF THE ELASTIC COMPLIANCE OF THE HARDNESS TESTER IN KINETIC INDENTATION TESTS

When determining the mechanical properties of materials in kinetic indentation tests using indentation diagrams, careful consideration of the elastic compliance of the device, i.e., the hardness tester, is required. The determined values of the Young's modulus of the tested material substantially depend on the reliability of the method of evaluation and accounting for the elastic compliance. Therefore, verification of the test techniques based on kinetic indentation should be carried out using the materials with the known, but rather different values of the Young's modulus. Successful experience has been gained to date in the evaluating and accounting for the elastic compliance of the device upon kinetic indentation of the materials by a diamond pyramid which is reflected in the relevant standards. However, there is no way of transferring this experience to the kinetic indentation by a steel or carbide ball without additional research and experimental verification. We proposes a technique for estimating the elastic compliance of a hardness tester using a kinetic ball indentation diagram based on the G. Hertz equation for the case of elastic contact of a ball with a plane. A linear correlation has been determined between the additional elastic deformations of the device and indentation load, which is characteristic of each device and independent on the ball diameter. The obtained dependence allows for correct consideration of the elastic compliance of the device using software applications in recording and processing the ball indentation diagrams. Experiments have been carried out to determine the hardness and the Young's modulus through ball instrumented indentation of different materials (steel, aluminum alloy, magnesium alloy, and titanium alloy) using the existing and developed methods of taking into account the elastic compliance of the device. The coincidence or proximity of the values of the Young's modulus of the same material determined from the ball indentation diagrams and sample tensile tests is considered the main criterion proving the accuracy of the technique. The advantages and shortcomings of the known and proposed procedures are discussed along with practical recommendations for their applications.