Evaluation of the Residual Strength of Composite Products Based on the Structural-Phenomenological Concept of Damage and Acoustic Emission Diagnostics

A structural-phenomenological concept of monitoring the residual strength of composite materials is proposed. The structural-phenomenological concept was developed taking into account the kinetics of damage and destruction of polymer composite material (PCM) at the micro-, meso-, and macroscale levels, which generate acoustic emission pulses (AE) recorded by the receiving transducers of the antenna array. A correspondence between the ongoing destruction of the composite material structure at the micro-, meso-, and macroscale level and the AE pulses recorded at the same time and their weight content provides the possibility of monitoring of the damage kinetics in the loading mode at all structural levels and, consequently, the possibility of control of the residual strength of the product. An algorithm and software have been developed that made it possible to divide the recorded AE signals into clusters of lower, middle, and upper energy levels corresponding to micro-, meso-, and macroscale disruptions of the structure of a composite material and calculate the AE activity and the weight content of location pulses in energy clusters, thus displaying the dynamics of their changes every second. Comparison of the current values of the most informative parameters of the weight content of location pulses in energy clusters with the threshold values recorded during the destruction of the material provides monitoring of the residual strength of the product in the loading mode. The validity of the developed concept, algorithm and software was proved during tests of elementary and structurally similar samples of PCM under different loading conditions. An example of using the developed technique for revealing the areas of the most intense damage accumulation in a MS-21 fuselage panel at a stepwise increase in the compressive load is presented. In addition to the possibility of identification of the area of intense accumulation of damage and failure of the structure of the composite material, the structural-phenomenological concept of the AE diagnostics provides also the possibility of tracing the damage kinetics at different scale-structural levels, controlling the level of the residual strength of the panel upon the stepwise compression.