Scaling and Curvature Effects on the Damage Tolerance of Impacted Composite Sandwich Panels

Abstract

An experimental program was conducted to investigate the effects of specimen width and specimen curvature on the residual compression strength of composite sandwich panels after low-energy impact. Flat and curved (1.1 m radius) specimens of three widths (83, 152, and 305 mm) were manufactured from thin-gage (four plies) graphite/epoxy facesheets and 25.4-mm-thick Nomex core. A drop mechanism was used to create barely visible impact damage on one facesheet of the panels (convex face of the curved panels) maintaining the energy level as constant in all cases. All specimens were then loaded axially in compression to failure. Above a certain panel width, the panel width and curvature had no effect on the ultimate strength of the panel. Although width and curvature increased the size of the damage caused by an identical energy impact, the indentation growth was delayed with respect to farfield strain (stress). Because indentation growth is chiefly a local phenomenon, the delay was probably due to the variations in the damage state. The baseline specimen (flat, 83 mm in width) serves as an adequate coupon-level test even though it is conservative when compared to wider plates.

On residual compressive strength prediction of composite sandwich panels after low-velocity impact damage

“…While along the longitudinal direction (y-axis), indentation propagation is arrested at locations near the edges of initially crushed core after the stroke ΔD exceeds 0.1 mm. These indentation propagation behaviors are exactly the same as what were observed in the SCAI tests [8] . In general, the deformation profile along x-axis is in the shape of a 'W' with a small bubble in the middle of residual indentation, while the one along y-axis is in a shape of letter 'V'.…”

“…SCAI tests conducted at the Composite Research Laboratory (CORE) at University of Maryland at College Park successfully revealed the damage propagation behavior of low-velocity impacted composite sandwich panels under in-plane uniaxial compression [8] . Sandwich panels, comprising of two thin laminated facesheets and honeycomb core, were manufactured with dimensions of 356 mm in length, 82 mm in width, and 25.6 mm in thickness.…”

“…Fig. 4 Cross section through the damage region (indentation, initially crushed core and delamination) [8] .…”

“…SCAI Tests were performed as an experimental approach to obtain the residual compressive strength of composite sandwich panels subjected to low-velocity impact damage [4,5,7,8] .…”

Compression strength of sandwich panels with sub-interface damage in the foam core

“…A number of new studies appeared later, e.g. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], but mainly dealing with experimental and finite-element (FE) results; only [11,15] present analytical failure models.…”