Residual Stresses in a Damaged Area of a Composite Plate under Static and Dynamic Influences of a Steel Indenter

A novel approach is developed and implemented, which enables determining principal residual stress components arising as a result of both static and impact contact interactions of a spherical indenter and a plane surface of a cross-ply composite plate. The experimental technique employs the probe hole drilling and further measurements of the hole diameter increments in principal strain directions by the speckle-pattern interferometry. Interference fringe patterns of high quality, which are essential for a successful realization of the created procedure, are visualized both inside and outside the contact dimple, which is located on the long symmetry axis of the rectangular samples. In-plane displacement component values, derived from optical interferometric measurements, serve for the residual stress determination proceeding from an unequivocally solution of the correctly-posed inverse problem. This fact provides a minimal possible uncertainty in the final results. The key point of the developed approach is that the residual stresses are quantified based on the direct physical measurements of the increment of the diameters of the probing holes made in different zones of the contact interaction. On this basis, the presence of the significant principal components of residual stresses that occur in the contact zone of the steel indenter and the surface of the composite plate has been established. It is revealed that the distribution of the main components of residual stresses along the contour of the contact indentation in relation to its center has a radially symmetrical character. In this case, the tangential components are tensile stresses, and the radial stresses are compressive in both cases. In both cases, the largest compressive components occur in the center of the contact dent. We compare the values of the main components of the residual stresses arising from the static indentation of a spherical indenter and impact, which are characterized by an almost identical diameter of the contact indentation. The obtained data clearly evidence that the principal stress component values reveal the representative parameter, which can reliably connect the composite plate strength decrease, caused the impact influence, and quantitative characteristics of the residual stress field near the contact dimple.