PSI - Issue 50

V.G. Degtiar et al. / Procedia Structural Integrity 50 (2023) 40–49 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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hexagon inscribed of a circle (Fig. 2). One of directions of reinforcing elements (carbon rods) of composites of the 4KMS-L type is oriented along an axis of the C-C composite cylindrical sample, 3 other directions are perpendicular to the axial direction and oriented at 120° relative to each other. If a TPS C -C composite element axis aligns with the FV axis, then with no misalignment of the C-C composite frame structure relative to the FV axis and even distribution of density over volume, this results in symmetrical ablated shapes. If there is a misalignment of the frame relative to the FV axis, sectors, where structures outcrop, ablate asymmetrically and cause a lateral moment. A composite of the 4KMS-L type has sectors with the same-type structures equal approximately to 1/6th of the whole frontal area, meanwhile in materials of the 4KMS, 4KMS-R types the sectors occupy 1/3rd, 1/4th of the frontal area. As a result, a misalignment of structure in applied composites of the 4KMS, 4KMS-R types manifests to a greater extent than in applied composites of the 4KMS-L type. The MKU-4M-7 composite has the structure geometry analog to the 4KMS-L composite, while the typical lateral diameter of rods of the composite is approximately 0.6 of the diameter of rods of the 4KMS-L composite, thus, the composite has finer structure and lower equivalent sandy-grained roughness, Degtiar et al. (2018), lower gains of heat exchange and lower lateral moments. A misalignment in the structure of a TPS C-C composite element frame relative to the FV axis is composed of a misalignment of a C-C composite element axis relative to its piece axis in the FV manufacturing and a misalignment in the element seating during the FV assembly with a tolerance stated in provisioned documents. Nonuniformity and asymmetry of the distribution of density over volume of a C-C sample with the tolerance (stated in provisioned documents) from the average value for a sample is resulted from the nonuniformity in the frame impregnation with coal tar and its carbonization in phases of saturation up to the sample average density, stated in provisioned documents. Planes of maximum asymmetry of the density distribution and maximum misalignment of the structure of a TPS C-C composite element frame are randomly positioned relative to each other. Depending on the relative position of planes of maximum misalignment of the frame structure relative to the FV longitudinal axis and a plane of maximum asymmetry of the distribution of density over volume of a TPS C-C composite element, the development of asymmetry of ablated shapes can be both worsened and compensated. In so doing, it is important to estimate maximum possible asymmetry of the FV ablated shapes. If the structure of a C-C composite sample frame is axisymmetric, then in deviation/misalignment of its structure there appears asymmetry of the distribution of roughness over an ablated surface. At small misalignments the height of physical roughness was supposed not to change, and asymmetry of shapes at misalignment in the structure of a composite of the 4KMS-L type and axisymmetric distribution of density for a cylindrical FV were assessed. Fig. 7 provides an example of the computation of an asymmetric shape of a nose part of a model FV made of the 4KMS-L C-C composite at a 5 degree misalignment in dimensionless coordinates. It can be seen that the misalignment gives considerable asymmetry to an ablated shape.

Fig. 7. Ablated dimensionless contours in plane of maximum asymmetry at 5-degree misalignment.