Impact behaviour of an innovative trapezoidal composite corrugated core sandwich structure under low-velocity impact: an experimental and numerical study

Impact behaviour of an innovative trapezoidal composite corrugated core sandwich structure under low-velocity impact: an experimental and numerical study

Composite core sandwich structures have been extensively used in aerospace, marine and automotive applications. A few configurations of composite cores have been used in manufacturing sandwich structures for many years. The usual configurations for a corrugated shape are sinusoidal, triangular and trapezoidal shapes. Unfortunately, until now there only has been limited research on the development of trapezoidal composite corrugated cores.

This is significant because sandwich structures in general are often subjected to compression loads and low-velocity impacts during their service life. Failure in composite core sandwiches can be internal and thus not easily noticed. Hence, the mechanical behaviour and failure mechanism of these structures under compression and low-velocity impact loads need to be clearly understood before being used for critical structural applications.

This project intends to fill the gap in the knowledge based on the trapezoidal composite corrugated core sandwich (TCS) structures by investigating the mechanical behaviours and failure mechanism of innovative TCS structure through a well planned experimental framework: quasi-static compression and low-velocity impact loading conditions. The initial experimental tests were limited to a single-cell of a trapezoidal composite corrugated core; later a few multi-cell specimens were experimentally investigated.

Under a quasi-static compression load, results showed that TCS structures are highly anisotropic, as anticipated, and possess superior mechanical behaviour compared to traditional foam, composite honeycomb, and a composite lattice core sandwich. The impact behaviours of TCS structure designs were investigated under low-velocity impact at the visible damage threshold energy of the composite parent materials and at roughly 30% greater than this. The damage mechanisms were scrutinized using high-speed video recordings. During the single-cell investigations, changes in design parameters of the core structure were also thoroughly investigated. TCS structure designs have shown superior impact performances and high resistance in comparison with monolithic composite plate. They also absorbed more impact energy than the visible damage threshold energy of composite parent materials, without a noticeable core fracture.

Where the impact energy exceeded the composite parent materials’ visible damage threshold energy, the impact response of the TCS structure performed significantly different depending on the core thickness and the core height. The core thickness was found the most critical influence on single-cell impact performance. The major damage mechanism was identified as starting when the core fails at the upper core angle, followed by a flattening deformation of the lower core angle.

In addition to experimental studies, comprehensive 3D finite element (FE) modelling was undertaken to analyse TCS structures under static and impact/dynamic loading using ANSYS software. Both implicit and explicit dynamic 3-D FE models demonstrated an excellent correlation with the experimental results. Interestingly, predicted mechanical properties under quasi-static compression load, damage area, and energy absorption capacity of the TCS structure correlate exactly with the experimental findings. After successful FE modelling regimes, an effective approach to optimizing the trapezoidal composite corrugated core of the sandwich structure was developed.

Finally, two case studies of multi-cell TCS structures were performed to prove the superior performances of optimized TCS structures. The first case involved the full-scale multi-cell TCS structures fabricated from woven E-glass fibre reinforced epoxy composite material. As anticipated, these structures showed the highest impact resistance, the highest energy absorption and superior impact performance. Furthermore, in full-scale TCS structures, the optimal core design eliminated core fracture damage and TCS structure penetration.

The second case was for a multi-cell TCS structure of hybrid composite core configuration, fabricated from high-performance fibre: kevlar and zaylon. These showed superior impact resistant performances: and severe core failure was eliminated and damage on the upper face sheet could easily be repaired. Furthermore, the hybrid TCS structures provided a high specific energy absorption (SEA) rate with the same structural weight as traditional core materials. In addition, the residual strength and stiffness of the hybrid TCS structures exceeded those of the E-glass fibre composite TCS structure.Finally, the optimized design was extended to a reasonably configured full-scale sample and hybrid core that experimentally proved its superior performances in terms of high impact resistance, high residual strength and core damage prevention.