Issue 78

V. Pisarev et alii, Fracture and Structural Integrity, 78 (2026) 96-117; DOI: 10.3221/IGF-ESIS.78.06

The distributions of the residual stress components over the thickness of the conventional coupon Sp_75+Sp_75-Back, which are constructed using linear approximation as the first step, are shown in Fig. 13a, 13b and 13c for points P1 (P1A), P5 (P5A) and P6 (P6A), respectively. The maximum compressive component of the residual stresses in the center of the dimple 1  retains its negative sign on the opposite side of the sample, but decreases in absolute value by almost five times. Another situation is observed at point P1 for the component 2  , namely, the compressive stresses in the center of the dimple become tensile on the opposite side (Fig. 13a). At point P5, both components of the residual stresses have the same signs on both surfaces of the coupon. Naturally, the maximum absolute values of the stress components occur on the impact side (Fig. 13b). The tensile component 1  at point P6 retains its positive sign on the opposite surface of the plate. At the same time, its value changes only by (145.6–137.5)/145.6 = 0.056. The compressive component 2  at the boundary of the contact dimple changes its initial sign to negative, while maintaining its absolute value (Fig. 13c). It should also be noted that the studied samples already contain technological residual stresses. The values of these stresses, obtained by the approach mentioned in work [22], averaging the results of 5 measurement points, equal to 1 σ = +10.1 MPa; 2 σ = + 42.3 MPa.

Figure 14: Typical distribution of residual stress over a thickness of thin plate. An analysis of the distributions of the residual stress components over the specimen thickness would be incomplete without discussing a very important feature. The matter is that macro residual stresses must be self-balanced stresses that exist in engineering components, even though they are not subjected to external loads. Fig. 14 illustrates this fact [25]. It is quite obvious that the requirement for a self-balanced dependence leads to uneven distributions of the residual stress components over the thickness of the specimen. This raises the question of the deformation response of the composite plate to drilling a through hole, which is caused by the release of residual stress energy. The paper [24] shows that in the case of a residual stress field evenly distributed over the front surface of the plate, processing interference fringe patterns gives values of the residual stress components that are equal to the difference between the stress values on the outer surface and in the middle plane of the thin plate. The validity of this statement is proved by numerical modeling of reference fringe patterns and their comparison with real interferograms. In addition, the values of residual stresses were determined for plates of three various thicknesses [24]. There is every reason to believe that this is not true in the case of impact damage. As a first approximation, it can be assumed that the residual stress components obtained by drilling a through hole in the contact interaction area relate to the surface of the drill entrance. But even in this case, only 2  component distributions, taking into account the rejection of linear approximation, can be represented in a self-balanced form for points P1 and P6. The remaining four dependences reveal the same signs of the residual stress components on opposite coupon surfaces. The reason for this, first of all, is that at point P5 both components of in-plane displacements have the same signs on opposite sides of the sample. The positive sign of u component detected on the side of the contact dimple at point P6 will remain on the opposite surface. Changing the sign of v component from negative (impact side) to positive (back side) while maintaining the negative sign of u component on both sides of the sample does not lead to a change in the sign of the residual stress component 1 σ at point P1. Thus, it can be argued that the signs of the residual stress components on the opposite sides of the specimen are

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