Response and Damage Tolerance of Composite Sandwich Structures under Low Velocity Impact

Abstract

The deformation and failure response of composite sandwich beams and panels under low velocity impact was reviewed and discussed. Sandwich facesheet materials discussed are unidirectional and woven carbon/ epoxy, and woven glass/vinylester composite laminates; sandwich core materials investigated include four types of closed cell PVC foams of various densities, and balsa wood. Sandwich beams were tested in an instrumented drop tower system under various energy levels, where load and strain histories and failure modes were recorded for the various types of beams. Peak loads predicted by springmass and energy balance models were in satisfactory agreement with experimental measurements. Failure patterns depend strongly on the impact energy levels and core properties. Failure modes observed include core indentation/ cracking, facesheet buckling, delamination within the facesheet, and debonding between the facesheet and core. In the case of sandwich panels, it was shown that static and impact loads of the same magnitude produce very similar far-field deformations. The induced damage is localized and is lower for impact loading than for an equivalent static loading. The load history, predicted by a model based on the sinusoidal shape of the impact load pulse, was in agreement with experimental results. A finite element model was implemented to capture the full response of the panel indentation. The investigation of post impact behavior of sandwich structures shows that, although impact damage may not be readily visible, its effects on the residual mechanical properties of the structure can be quite detrimental.

Hierarchical structural design for fracture resistance in the shell of the pteropod Clio pyramidata

“…First, the variation of the cross-sectional geometry of the fibres along the axial directions promotes crack deflection at the nanoscale (and discussed in detail below), further increasing resistance to crack propagation. Second, simple plywood composite materials suffer delamination failure through the weak in-plane interfaces 5,37 , which results in low resistance against out-of-plane impact 38 . The helical organization of fibrous building blocks can potentially minimize this problem by having 3D interfaces without the presence of large in-plane weak interfaces where delamination might occur.…”

Characterization of dynamic damage mechanisms in Palmetto wood as biological inspiration for impact resistant polymer composites

“…This assumption is similar to the 'quasistatic' assumption previously employed in impact testing of composite sandwich structure that exhibit similar mechanical behavior to Palmetto wood (Daniel et al, 2012). Furthermore, the approach of Ravichandran and Subhash (1994) for analyzing the critical strain rate that establishes equilibrium loading conditions yields a value of 1000/s for these types of materials and loading conditions.…”

Composite materiomics

“…Specifically, the integration of multiscale experimental and simulation tools has led to advances in appreciating the complex change of material properties across scales and hierarchy levels [29]. Specifically, the integration of multiscale experimental and simulation tools has led to advances in appreciating the complex change of material properties across scales and hierarchy levels [29].…”

“…In spite of their widespread commercial success, current structural fiberreinforced composites (FRCs) exhibit number of shortcomings [29][30][31]. Attempts have been made to circumvent these shortcomings by employing 3D fiber architecture [32] and by making their structure hierarchical to some extent by adding nanosized fillers to the micrometer-sized reinforcing fibers [33][34][35][36][37].…”