Numerical and experimental research of the evaluation of the mechanical behavior of carbon fiber reinforced polymerspecimens with an embedded smart-layer

Currently, scientists have paid special attention to the possibility of creating so-called Smart-structures that are capable of real-time self-diagnostics and/or functional changes. Within the framework of this work, the possibility of creating structures capable of diagnosing the deformation state in real-time is considered. When creating such Smart-structures, fiber-optic, piezo-, and strain-gauge sensors are usually used as control sensors. The use of such sensors is due to a number of their advantages, such as small size, the ability to integrate into a single measuring network, ease of use, a wide range of measured values, the ability to transmit data over long distances. However, when such sensors are embedded into the structure, several difficulties arise in installation/dismantling or implementation due to the fragility of the fiber, the difficulty of locating the sensitive element, ensuring the integrity of the fiber-optic sensors at the exit from the polymer structure. The team of the Scientific and Educational Center of Aviation Composite Technologies, PNRPU, has developed a prototype of a Smart-layer based on 3D-printing technology, capable of solving the problems described above. However, the influence of such an embedding on the structure of structures made of carbon fiber reinforced polymer (CFRP) remains open. Thus, this work aims to carry out computational and experimental studies to assess the mechanical behavior of CFRP samples with an embedded Smart-layer. Within the framework of this work, the technology and scheme for manufacturing a Smart-layer with embedded fiber-optic sensors, as well as a scheme for laying a Smart-layer into CFRP samples, are described. Since the properties of molded plastic specimens differ from those of printed specimens, mechanical tensile tests of printed specimens were carried out. The obtained values of the strength limit and the modulus of elasticity were used to identify the mathematical model. Within the framework of the experimental part, mechanical tests for tension, compression, and interlayer shear of CFRP samples with an embedded Smart-layer were carried out. When analyzing the obtained experimental results, it was found that the maximum percentage deviation of the physical and mechanical characteristics (PMC) is no more than 15 %, which lies within the spread of the PMC of carbon fiber in a prepreg roll. As a result, we can conclude that the embedded of such Smart-layers does not significantly affect the PMC of the final CFRP structure. According to the results of mathematical modeling of the tensile strength of a CFRP sample with an embedded Smart-layer, it was found that the maximum value of normal stresses in the sample reaches 540,28 MPa, which is 1,46 % higher than the maximum value for the statistical ultimate strength of the sample. The maximum values of the Mises stress for the Smart-layer do not exceed the ultimate strength, while for the epoxy binder there is a significant excess of the ultimate strength, on the basis of which one can make an assumption about its destruction during deformation.