چكيده به لاتين
Over the past decades, polymer composites have been used prominently in various industrial applications due to their high-strength, low thermal expansion coefficient, low weight, corrosion resistance and high fatigue resistance. Due to destructive effects that residual stresses have on the composite during construction, calculating residual stress in composites is very important. Due to the fact that destructive methods lead to the loss of performance of components, the use of non-destructive methods has been more widely used in the industry.
For many years, infrared thermography has been used as a non-destructive technique, which has a very great potential for rapid scanning of large surface areas and also it can be applied some distance away from the test surface. The main goal of this project is to propose a non-destructive method for investigating the possibility of stress detection in composites using Pulse thermography method. For this purpose, an 8-layer carbon epoxy unidirectional composite sample is provided. At first the residual stress in composite sample is modeled by Finite element method and behavior of heat transfer in the sample under thermal excitation and different kinds of stress will be studied. The results of this modeling have helped to determine the test parameters. In the test, the stress was applied by a constant load with the aid of a tensile machine. pulsed thermography test was first carried out on a CFRP specimen without applying any stress, then the different tensile loads were applied to the specimen, and the thermography test was also repeated for every tensile load. Finally, the possibility of detecting stress in the composite is evaluated by checking the temperature variations of the surface of the sample (at the moment of stopping the heat and reaching maximum temperature) in the case of no tensile load and with different tensile loads. The experimental results revealed that with increasing tensile loading, surface temperature changes have increased. The results of finite element modelling indicated these changes have an almost linear relationship with tensile loading.
Keywords: Residual Stress, Carbon/Epoxy, Pulse Thermography, Finite Element Modeling.