Analytical and experimental investigation of transverse loading on grid stiffened composite panels

This paper investigates the behavior of grid stiffened composite panel (GSCP) subjected to transverse loading by analytical and experimental approach. An improved analytical model is proposed on the basis of smeared method to compute an equivalent stiffness matrix for the isogrid lattice of the GSCP. Hence, the panel can be considered as a laminate with different layers of specific stiffness. In this manner, the global deformation of GSCPs is studied in three types of transverse loading: three-point bending, quasi-static indentation and low-velocity impact. The model is verified by the same experimental tests on some fabricated glass/epoxy GSCPs. The results indicate the good compatibility of analytical model with experiments. Moreover, energy absorbing characterization and damage mechanisms of the tested GSCPs are studied experimentally. Observations indicate that if the skin and the lattice structure are fabricated simultaneously, debonding of ribs and facing would not happen until the main damage (central rib fracture) occurs. Also, micro buckling of skin laminas would not affect the global response significantly. So, the progressive damage and degradation of overall stiffness of the GSCPs have not considerable effect and the prediction of global response on the basis of equivalent stiffness matrix would be a high precision tool to design grid stiffened structures. Finally, based on the analytical model, a parametric study is performed to investigate the effect of changing some panel's variables and some optimum point is concluded.