Parametric Study of Three-Stringer Panel Compression-After-lmpact Strength

Abstract

Damage tolerance requirements for integrally stiffened composite wing skins are typically met using design allowables generated by testing impact-damaged subcomponents, such as three-stringer stiffened panels. To improve these structures, it is necessary to evaluate the critical design parameters associated with three-stringer stiffened-panel compressive behavior. During recent research and development programs, four structural parameters were identified as sources for strength variation: (a) material system, (b) stringer configuration, (c) skin layup, and (d) form of axial reinforcement (tape versus pultruded carbon rods). The relative effects of these parameters on damage resistance and damage tolerance were evaluated numerically and experimentally. Material system and geometric configuration had the largest influence on damage resistance; location and extent of the damage zone influenced the sublaminate buckling behavior, failure initiation site, and compressive ultimate strength. A practical global-local modeling technique captured observed experimental behavior and has the potential to identify critical damage sites and estimate failure loads prior to testing. More careful consideration should be given to accurate simulation of boundary conditions in numerical and experimental studies.

Impact on composite structures

“…In contrast, tensile tests on coupons can be expected to be generally relevant for structures, provided a similar damage is present and that the ratio of coupon width to damage width is sufficient to ignore finite width effects. Experimental studies of the failure mechanisms of stiffened panels have been presented by Wiggenraad, Zhang & Davies(1999), Rosseau, Baker & Hethcock(2000), Kong, Hong & Kim(2000), Wiggenraad, Greenhalgh & Olsson(2002) and Greenhalgh et al(2003). Impact damage seems to have a marginal influence on the buckling load of plain laminates with all sides supported, except when significant portions of the width are affected by fibre fracture, Olsson(1999), or when the boundary conditions are relaxed by impact close to edges with strong rotational constraint, Nilsson(1994).…”

Response of Damaged and Undamaged Tailored Extension-Shear-Coupled Composite Panels

“…Specimens TP-3 and TP-8 were subjected to low-speed impact at the thickness transition at the center stringer. Previous testing 4 on non-tailored panels with the same design indicated that the thickness transition area is a critical point and 500 in.-lbs of impact energy produced barely visible impact damage.…”

“…One specimen of a similar design with a balanced ± 45°skin stacking sequence, has been tested with a failure load of 22.7 kips/in. 4 The tailoring reduces the failure strength by approximately 10 percent. A plot of the specimen axial end shortening (solid lines) and transverse in-plane displacement (dashed lines) as a function of load are shown in Figure 10.…”