Issue 78

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

sufficiently reliably established. These facts mean only one thing, namely, changes in the sign of the corresponding components of the residual stresses, which are necessary to obtain self-balanced thickness distributions, occur in the inner layers of the sample. In turn, this also means that linear approximation cannot be used to correctly describe the distribution of residual stresses over the specimen thickness. However, the ways of experimental confirmation of the assumption that residual stress components change its sign in the inner layers of the coupon are not yet clear. Modeling of reference fringe patterns in the contact interaction zone, which is characterized by significant stress gradients in all directions, is practically impossible. C ONCLUSIONS he dependences connecting the values of the residual stress components in the contact interaction zone of the steel indenter and the surface of the composite plate with the impact energy are presented. The studied impact energies are 55, 65 and 75 J. It is established that the maximum values of the residual stress components occur at three points on the surface of the contact interaction. The first one (P1) is located in the center of the contact dimple, where biaxial compression is observed. With an increase in the impact energy from 55 to 75 J, the increase in the absolute magnitude of the transverse 1 σ and longitudinal 2 σ component is 47 and 39%, respectively. The maximum values for the impact energy of 75 J are 1 σ = -267.4 MPa and 2 σ = -194.1 MPa. The second and third points are located at the intersection of the horizontal (P5) and vertical axes (P6) of symmetry of the sample. Tangential tensile components of residual stresses are observed at these points, namely, 2 σ at point P5 and 1 σ at point P6. The increase in the tangential component is 26% in both cases. The maximum values for the impact energy of 75 J are 2 σ =+137.0 MPa and 1 σ =+145.6 MPa. These quantitative data are first obtained on the basis of an original experimental method developed earlier by the authors of this article [1, 2]. Interference fringe patterns of high quality are obtained for contact interaction area caused by impact energy of 65 and 75 J for the first time. All these facts mean that the upper limit of applicability of the developed approach to residual stress quantifying has been expanded to the impact energy of 75 J. New results are obtained that make it possible to estimate the distribution of the residual stress components over the thickness of the composite plate. The required data for 75 J energy are obtained by drilling probe holes from the side opposite to the contact dimple. The maximum compressive component of the residual stresses in the center of the dimple 1 σ = –267.4 MPa retains its negative sign on the opposite side of the sample, but decreases in absolute value up to 1 σ = –56.1 MPa. Another situation takes place at the same point for the component 2 σ , namely, the compressive stress ( 2 σ = –194.1 MPa) in the center of the dimple become tensile ( 2 σ = +72.8 MPa) on the opposite side. The same trend occurs for 2 σ -component at point P6 only. All other residual stress components retain its signs on both faces. Thus, two side data, which are obtained for the first time, clearly show that linear approximation can not be used for quantitative description of self-balanced residual stress distribution over specimen thickness. Solving this important problem needs additional studies. In any case presented research is the first essential step in this way. All presented data are essential to create a methodology for assessing the residual strength of composite plates with impact damage based on the use of residual stress values as a design parameter. T

D ECLARATION OF COMPETING INTEREST

T A

he authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

A CKNOWLEDGEMENTS uthors thank the Russian Science Foundation for providing support in the frame of the 24-19-00117 project (https://rscf.ru/en/project/24-19-00117).

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