A two part research study has been completed on the topic of compression after impact (CAI) of thin facesheet honeycomb core sandwich panels. The research has focused on both experiments and analysis in an effort to establish and validate a new understanding of the damage tolerance of these materials. Part one, the subject of the current paper, is focused on the experimental testing. Of interest are sandwich panels, with aerospace applications, which consist of very thin, woven S2-fiberglass (with MTM45-1 epoxy) facesheets adhered to a Nomex honeycomb core. Two sets of specimens, which were identical with the exception of the density of the honeycomb core, were tested. Static indentation and low velocity impact using a drop tower are used to study damage formation in these materials. A series of highly instrumented CAI tests was then completed. New techniques used to observe CAI response and failure include high speed video photography, as well as digital image correlation (DIC) for full-field deformation measurement. Two CAI failure modes, indentation propagation, and crack propagation, were observed. From the results, it can be concluded that the CAI failure mode of these panels depends solely on the honeycomb core density.

No abstract

A two part research study has been completed on the topic of compression after impact (CAI) of thin facesheet honeycomb core sandwich panels. The research has focused on both experiments and analysis in an effort to establish and validate a new understanding of the damage tolerance of these materials. Part 2, the subject of the current paper, is focused on the analysis, which corresponds to the CAI testings de-

No abstract

A research study has been conducted on compression after impact of thin facesheet honeycomb core sandwich panels. This paper is focused on the modeling and analysis used to simulate the tests described in a companion paper. Of interest are composite sandwich panels with aerospace applications, which contain either a 3 or 6 lb∕ft 3 honeycomb core. It was found that compression after impact testing of these coupons resulted in either an indentation propagation failure for the lower density core or a crack propagation failure mode for the higher density core. An analysis model is developed to account for both modes through the inclusion of progressive failure analysis of the facesheets and a homogenized, nonlinear material model for the honeycomb core. In addition, significant impact damage detail is included in the model based on experimental observation. Analysis results are compared with the experimental results for each of the 24 sandwich panel specimens tested. Good agreement of failure mode predictions with test results demonstrates the importance of considering both facesheet and core failure, as well as the initial damage severity. Finally, a parametric study highlights the strength benefits compared with mass penalty for various core densities.Young's modulus G = shear modulus h max = maximum dent depth I = stress invariant i = subscript indicator W = waviness coefficient x = global coordinate or axis, coupon width direction y = global coordinate or axis, coupon load direction z = global coordinate or axis, coupon through the thickness direction ϵ = strain σ = stress υ = Poisson's ratio ϕ f = fiber volume fraction ϕ m = matrix volume fraction