Cyclic Buckling Tests Under Combined Loading on Predamaged Composite Stiffened Boxes

Abstract

The results obtained on two predamaged closed boxes composed of four graphite-epoxy curved stiffened panels are presented. One panel of each box is predamaged, using Teflon inserts between three stringers and the skin to reproduce skin-stringer disbonding. The boxes are tested under axial compression and torque, applied individually and in combination, both statically and cyclically. The tests allow the investigation of the effect of static and cyclic postbuckling combined loads in terms of structural behaviors, of collapse modalities and of damage propagation. The boxes do not suffer any loss of structural performances or any predamage propagation for combined loading under small compression and torsion up to 275% of the buckling torque, which corresponds to 85% of the collapse torque

Experimental study of post-buckled single-stringer composite specimens under fatigue loads with different load levels and load ratios

“…However, in the case of composite stiffened panels most research focused on the effect of the load ratio and their fatigue life has been studied solely from the numerical approach [16], where the use of numerical tools as cohesive-zone model methods [17] or the virtual crack-closure technique [18] have proved crucial to accurately evaluate local fracture parameters in non-linear three-dimensional structural cases. A few authors have experimentally investigated and reported the buckling and post-buckling behavior of composite stiffened structures under quasi-static and fatigue compressive loads [19][20][21], although these test campaigns only consider one combination of load level and load ratio. Recent experimental works include research on the propagation of an artificial delamination or impact damage in post-buckling conditions of hat-stiffened [22], T-stiffened [23], I-stiffened [24], and J-stiffened panels [25]; highlighting the strive for gaining further knowledge on this topic to increase the component structural efficiency.…”

Experimental Study on Post-Buckled Composite Single-Stringer Specimens With Initial Delamination Under Fatigue Loads

“…Despite the large number of studies on this topic, the prediction of fatigue-driven delamination in aerospace composite structures represents still an open issue, since the applicability of the available numerical techniques is mainly limited to coupon specimens [3][4][5][6]. Furthermore, only few experimental tests are reported in literature on stiffened composite structures in post-buckling regime, due to the high costs for the manufacturing and the difficulties in terms of time and complexity in performing this type of test [7][8][9].…”

Fatigue life and damage tolerance of postbuckled composite stiffened structures with indentation damage

“…The phenomenon is even more complex when fatigue loads are considered in the postbuckling regime and when defects such as impact damage are present. However, few experimental studies that consider the postbuckling behavior of composite stiffened panels with impact damage under static and fatigue loads 1 – 10 are available in the literature, mostly because these tests are complex and expensive to conduct.…”