A Study on the influence of indenter shape for small punch test of non-metallic materials

Abstract Small punch test (SPT) is a type of advanced method for material mechanical property obtain with small-invasive test, which has a good application prospect for judging the mechanical properties of materials at the local position of service components. However, at present, there is a lack of data and engineering basis for the applicability of the two commonly used ball shaped and hemisphere shaped indenters of the SPT method to flexible non-metallic materials, resulting in the lack of universal adaptability standards for the SPT method of non-metallic materials, which is one of the core shackles of the current engineering application of this method. Therefore, based on the results of the traditional uniaxial tensile test, the SPT of polyamide (PA) was carried out by using two shapes of indenters, ball shaped and hemisphere shaped indenter, and the differences between material deformation and fracture caused by the two shapes of indenters were analyzed by the methods of material mechanical properties, macro and micro fracture morphology and numerical simulation. The experimental results show that the top of the indenter has obvious friction with the material during the small punch test, and the maximum deformation position of the material occurs at the diameter of the indenter rounding. Due to the viscoelastic characteristics of high flexibility and large deformation of PA, the shaped part of the indenter is bonded due to plastic deformation rebound during the fracture process. For the spherical indenter, the maximum deformation of the material can wrap the gap formed between the spherical indenter and the punch platform, which will cause the maximum deformation position of the specimen to change during continuous loading, which will affect the authenticity of the data. The maximum deformation position of the hemisphere shaped indenter remains stable, which has a more accurate positioning for evaluating the performance of the material. The test results screen out the SPT indenter shape suitable for flexible non-metallic materials, which provides theoretical guidance and basis for the formulation of SPT test method standards.