Effects of forming techniques on residual stresses in stiffening ribs of sandwich panels

This study investigates residual stresses in stiffening ribs of composite materials formed by stamping in a punch-die system. Using two-dimensional X-ray diffraction (XRD), we measured residual stresses on both the anterior and posterior sides. Three LITECOR^® composite types, with core thicknesses of 0.8, 1.25, and 1.6 mm, were examined. Results indicate that as core thickness increases, residual stress values decrease on both sides. Notably, anterior side stresses on the y-axis are relatively higher (1027–1199 MPa) compared to the x-axis, exceeding posterior side values (998–1083 MPa) at 0.8 mm core thickness. Moreover, the study compares these values with Single Point Incremental Forming (SPIF) and finds that SPIF generally yields lower stress values for all core thicknesses. These findings suggest that SPIF is favourable for achieving minimal residual stress in LITECOR^® composites. Addressing residual stresses is crucial for enhancing structural integrity and extending the service life of sandwich panels and composite materials.