Rapid estimation of the fatigue limit of polymer composite materials using infrared thermography

To ensure the reliability of structural elements made of polymer composite materials operating under vibration conditions, it is necessary to have data on their resistance to destruction for a reason of high-cycle fatigue. The traditional approach to determining the fatigue strength characteristics of materials involves long-term expensive tests. The infrared thermography method for express estimation of the fatigue limit was actively developed in recent years. The method is based on the use of self-heating of the material under cyclic loads exceeding the fatigue limit. The purpose of this work is to develop, within the framework of the infrared thermography method, a technique for experimental rapid assessment of the fatigue limit of polymer composite materials using the example of laminated carbon fiber, substantiation of the choice of controlled parameters of the thermal state of samples and processing of the results. The technique was developed using the example of laminated carbon fiber. Standard samples were subjected to block cyclic loading in the «tension-tension» cycle on the resonance testing machine. The surface temperature of the samples was recorded during loading using a precision infrared camera. Four variants of processing the test results were compared. The first two options are based on the use of the maximum and averaged stabilization temperature over the sample surface in the loading blocks. The third and fourth options are based on the use of increase of the maximum and averaged temperature at the beginning of the loading block. The estimates of the fatigue limit obtained by named four variants of the thermogram processing method are in agree with each other and with the results of standard fatigue tests. The use of the infrared thermography method makes it possible to significantly reduce the number of tested samples, the labor intensity and duration of work compared with standard fatigue tests. This allows us to recommend the described methodology for obtaining an express estimation of the fatigue limit at the stage of development of products made of composite materials when choosing design and technological solutions.