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.

Рассматривается однопараметрическая математическая модель деформирования слоистой среды, содержащей чередующиеся упругие и объемно несжимаемые слои. Используется регуляризация некорректной задачи по А.Н. Тихонову с параметром, обратным к модулю объемной сжимаемости. Численная схема на основе метода конечных элементов сводится к системе линейных алгебраических уравнений с матрицей коэффициентов, линейно зависящей от параметра, а искомые поля перемещений и напряжений вычисляются как предел решения регуляризованной задачи. Сеточная сходимость исследована на контрольном примере, допускающем аналитическое решение.

Dynamic temperature fields on the surface of a polymer composite material under the action of an internal heat source are considered. It is shown that the use of thermal control based on the measurement and analysis of the temperature field parameters allows detecting a defect (heat source) in the material and determining its depth and coordinates. The studies have shown the possibility of using thermal control to detect internal defects in products made of polymer composite materials when creating internal heat sources in the vicinity of defects with the use of modern thermograph systems that provide the registration of changing the temperature field of 0.1 deg and higher. The numerical solution using the finite element method and the time difference scheme is in good agreement with the analytical solution when choosing grid steps: the error is reduced to 2.4% already at a distance of three grid steps from the source. It is shown that on the basis of the measurement of the parameters of dynamic temperature fields, it is possible to determine the location of the depth of the defect (internal heating source) and its area coordinates that makes it possible significantly to extend the scope of application of thermal control.

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