Temperature-based determination of the onset of yielding using a new clip-on device for tensile tests

摘要

The phenomenon springback strongly depends on the materials’ elastic behavior. It is crucial to determine the elasticity of a material precisely to be able to model and predict springback appropriately. The elastic-plastic transition describes the beginning of additional plastic deformation. In the state of the art, Rp0.2yield strength is commonly used to describe the onset of plastic yielding. The non-linear elastic behavior influences the determination of the Young’s modulus. Since Rp0.2yield strength depends on Young’s modulus, high deviations in characterizing the elastic behavior and hence the determination of the onset of yielding are possible.The Joule-Thompson effect for gases is also applicable for metal materials and describes the temperature changes induced by changes of volume. Hence, during elastic loading the temperature decreases. Assuming constant volume during plastic deformation, the Joule-Thompson effect does not contribute to the temperature, but the dissipating energy, which leads to an increasing temperature. The temperature signal shows a minimum and hence can be taken to define the onset of plastic deformation. This determination of the onset of plastic yielding is based on a physical effect and independent of the stress-strain curve. Within this study a clip-on device with PT1000 sensor is developed for uniaxial tensile tests to determine a temperature-based onset of yielding. This onset of yielding is investigated for different materials and experimental settings. Furthermore, cyclic tensile tests are performed to show the evolution of the onset of plastic yielding until uniform elongation and Young’s modulus is determined using this temperature-based evaluation method.