A study of applicability of instrumented indentation method to determine the mechanical properties of thermoplastic

The article deals with the method of instrumental indentation as an effective tool for studying the mechanical properties of thermoplastics. The method allows to determine such material properties as hardness, modulus of elasticity, rheological characteristics. The paper presents a review of examples of using the method of instrumental indentation to solve research problems in studying the properties of various types of polymeric materials, describing the parameters that affect the results of measurements. Analyses and experimental studies of the method’s capabilities were carried out on the example of high-density polyethylene, which is used in the production of gas pipelines. The results showed the applicability of this method in studying the material properties of polyethylene (PE) gas pipeline pipes for diagnosing their technical condition. In this work, samples that have been in service for a long time and a sample of new pipe were investigated. It has been revealed that the hardness values of polyethylene samples of different service life as an indicator of resistance to plastic deformation under static loads are quite close, while the rheological properties differ significantly. This peculiarity should be taken into account when conducting various mechanical tests, since the rate of load increase during such tests will significantly affect their results. It was found that the values of hardness and modulus of elasticity decrease with increasing indenter dwell time under load due to stress relaxation in the deformed region under the indenter. The influence of polyethylene structure on its mechanical properties is considered. It is also revealed that the modulus of elasticity of polyethylene samples multiply increases when the degree of crystallinity changes from 48 to 56%. The article describes the prospectivity and efficiency of using the method of instrumental indentation to analyse the elastic-plastic and rheological properties of thermoplastics, as well as their relationship with the crystal structure.