| Popis: |
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. |
