Abstract
The paper presents the results of experimental studies using the acoustic emission method of samples made of fiberglass, the design feature of which is the presence of both base fibers and weft fibers. The test data are presented in relative units and the concept of staged damage accumulation is used, which allows one to recognize subtle phenomena of the nature of the destruction of fiberglass. Tests of the samples with a transverse arrangement of fibers with respect to the applied load showed that the fracture process both in the strain parameters and in the parameters of the total acoustic emission has two stages of damage accumulation: the stage of proportional change of these parameters from stress and the stage of intensive increment of these parameters. In this case, the parameter of the total acoustic emission shows that this process of destruction begins earlier by 5–6% than the strain parameter shows. The proposed methodology and equipment allows us to identify the nature of fracture and assess the tensile strength of such a “staged” composition, and also to solve the problem of what affected the structural unity violations, which may be due to the presence of a set of cracks formed during manufacturing or under the influence of stresses and the external environment during the process of loading.
Highlights
The use of fibrous composite materials in aircraft construction is treated with great caution because of the need to ensure a high level of object reliability
For example, metal-based composites reinforced with ceramic fibres have high heat resistance and comparatively low specific weight, and they have higher fatigue strength when compared to traditional alloys
When testing samples with a transverse arrangement of the base fibers with respect to tensile strength (Figure 3), a twostage nature of the composite deformation was revealed both in the deformation parameters and in the parameters of the total acoustic emission (I1 and II1): the stage of proportional change of these parameters from voltage and the stage of their intensive increment, characterizing the beginning of the process of irreversible destruction of the composite (II and II1)
Summary
The use of fibrous composite materials in aircraft construction is treated with great caution because of the need to ensure a high level of object reliability. This task was first considered by Parratt (1960) who assumed that the failure of a composition occurs at the moment when the accumulating failure of the fibres leads to a shear failure of the matrix and a further increase of load cannot be transferred to other fibres because the ultimate shear strength of the matrix has been reached Both technical and economic efficiency of using composite materials largely depend on their strength, rigidity and integrity under specified operating conditions throughout the entire service life. The method of acoustic emission is characterized by high detection sensitivity and can be used to monitor the state of material structure in real time This method allows detecting and tracking the development of damage to both the reinforcement and matrix of the composite, taking into account the state of the boundary layer between its components. The article presents the results of experimental studies of samples made of fiberglass (Figure 1), the design feature of which is the presence in them of both base and weft fibers
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