The paper considers the thermo-mechanical mechanism of interaction between the damage agents and armor protection made of polymer fabrics. A simplified mathematical model is proposed to describe the deceleration of a damage agent within an armor fabric due to the dissipation of energy expended on irreversible stretching deformations of fabric fibers, as well as fiber slipping friction and material heating. Woven fabric layers are replaced by solid layers characterized by averaged stiffness and viscosity. A discrete numerical model of a solid material is proposed to reduce a problem with a finite number of degrees of freedom; motion equations are obtained on the basis of the Lagrange equations of the second kind, and for their integration, a stable non-conservative difference scheme is used. The software implementation is based on a functional-object paradigm which allows the modeling of conjugated processes. The parameters of governing equations are identified by using the experimental data. Some illustrative examples of interaction between damage agents and armor barriers with different arrangement of fibers are presented. The proposed model can be used to predict the quality of armor protection with the changing number and location of fibers, as well as to test the armor protection by applying the technique of infrared thermography.

Analysis of internal defects in the structure of composite objects can be based on the study of dynamic temperature fields, the patterns of variation of which reflect the location of heat sources. For example, acoustic ones, under external influences, determination of the location of thermal field sources (internal defects) – thermal tomography – presents in this approach, in general, the problem of identifying the model of heat propagation in a plate. This paper describes a method and technical means for determining the depth of occurrence of internal defects in composite structures by analyzing the temperature fields on two surfaces of a product to be created by an internal heat source, which is a defect, and by formed mechanical action on it, for example, ultrasonic mechanical vibrations (ultrasonic thermotomography). Experimental studies of the previously theoretically proved method of thermal tomography in the presence of an internal heat source have been carried out. As a research object, a plate of composite material – pressed fabric-based laminate- was considered. To simplify the experimental studies and increase the reliability of the results, the internal heat source was modeled with a nickel-chromium spiral to be heated by an electric current. The nickel-chromium spiral was laid in the plates when their pressing (manufacturing) at various occurence depths relative to surfaces of the plates. The experimental investigation technique is described. It is experimentally shown that the proposed method allows the occurence depth of defects in a composite material to be determined. Fault in the depth determining of the defects occurrence depends on the depth value and does not exceed 10 % of the thickness of the controlled article that is acceptable for the practical use.

The paper presents the results of integrating of the fiber optic sensors (FOS) into the material of a metal-composite tank. It has been established, that FOS remain operable after all cycles of the technological processing. It was carry out technological development alternative technique for FOS location on end product and configuration output sensor on various segment of tank. It is shown that the integration of the FOS into the material of the structure makes it possible to analyze the changes of the structure deformations depending on the location of the FOS. Comparison of data display for FOS, located on outside surface and inside material of tank, to show possibility estimate evolution of defomation on time along depth tank. It was found that the readings of the FOS based on Rayleigh scattering and fiber-optic Bragg gratings (FBG) correlate well with each other, in case that the readings of the FOS are thermally compensated.

This paper describes research in the field of fiber optic nondestructive testing and structural health monitoring (SHM) of carbon fiber reinforced polymers (CFRP) by the use of integrated optical fiber sensors (OFS) based on fiber Bragg gratings (FBG). Basic mathematical expressions that represent optical SHM of composites are presented. Some new relationships are derived by considering the non-linear character of the FBG-sensor response and the combined effect of temperature and deformation. Both linear and non-linear coefficients of the sensor elements, as well as combined strain-temperature coefficients before and after the sensors are embedded into the composite panels, have been obtained. Experimental results on the strain state of CFRP under static and dynamic loads demonstrate the effectiveness of the proposed non-linear model for evaluating deformation in composites. It is shown that integrated OFS's allow SHM of composite parts when mechanically loaded to failure, and that they can provide the actual level of strain in the composite parts in real time. SHM improves the operational safety of highly loaded and/or critical aerospace structures by providing real-time stress data, which would permit data-based decisions on overload conditions or imminent failure. Additionally, actual stress data from CFRP samples, or from real parts in use, could show whether the design of the parts should be changed to improve safety margins or to reduce weight. KeywordsStructural health monitoring • Nondestructive testing • Carbon composite • Optical fiber sensor • Fiber Bragg grating • Deformation • Strain and temperature measurement B Marina Kuimova

The problem of assessing operational stability and, accordingly, assessing the storage and safe operation periods of objects (for example, load-bearing structural structures made of polymer composite materials (PCM)) has always been one of the most important. At present, this prediction problem is mainly solved on the basis of product testing, as well as a detailed study of the regularities of the physicochemical aging processes occurring in PCM and changes in the physical and mechanical characteristics of products, and the creation on this basis of appropriate test methods and mathematical prediction models. The paper considers the problem of increasing the reliability of assessing the maximum service life of multicomponent structures by constructing predictive models using the results of optical-thermal and electrical non-destructive testing of the state of objects by temperature fields and the value of internal deformation of the material under force on the structure as input information. It is shown that in the case of using logical approaches as a software tool for predicting the ultimate resource of structures made of polymer composite materials, part of the knowledge should be used for reasoning that provides an explanation of the conclusions drawn, since formal logic is of limited applicability, especially in conditions of incomplete or uncertain information. In this case, the solution to the problem becomes the identification and establishment of cause-and-effect relationships. For the tasks of technical assessment of the quality of structures and their service life, the use of such logical conclusions as inductive, deductive and analogous conclusions is impossible, since for their work, they require all information about the diagnosed structure. The use of the proposed method for assessing the service life will allow timely stopping the loading of products with loads and, thus, preventing structural destruction. It should be borne in mind that in order to reliably predict the ultimate service life of complex structures made of composite materials using the proposed method, a set of various input instrumental and subjective information about the structural and operational characteristics of the product is required, including information on intermediate tests, non-destructive testing data. at various stages of manufacturing, design features, stability of parameters during the development process, subjective opinions of specialists, changes in the properties of materials from time to time and loads, etc. Implementation of the proposed approach will allow creating a new generation of test methods and predicting operational stability with an assessment of the limiting service life of elements and structures, which, ultimately, will provide an additional opportunity for developing practical recommendations for confirming or extending the warranty periods of operation and increasing the reliability and safety of operation of structures.