Elsevier

Composite Structures

Volume 158, 15 December 2016, Pages 30-43
Composite Structures

Experimental and numerical research on the low velocity impact behavior of hybrid corrugated core sandwich structures

https://doi.org/10.1016/j.compstruct.2016.09.009Get rights and content

Abstract

Corrugated core sandwich structures are fabricated with carbon fiber reinforced polymer (CFRP) face sheets and aluminum alloy cores. This lightweight design concept enables sandwich structures to maximize the specific bending stiffness/strength and improve the energy absorption capability. The low velocity impact behavior of such structures is investigated by experimentally and numerically. A range of low velocity impact tests are conducted to study the impact resistance, considering the effects of impact energy, core thickness and impact site on the impact load, absorbed energy and failure modes. A user subroutine VUMAT is developed to model the composite face sheet behavior, in which a progressive damage model based on the Hashin failure criteria and Yeh delamination failure criteria is implemented in ABAQUS/Explicit. There is a generally good agreement between the experimental and predicted results in terms of impact force, absorbed energy, and failure modes of sandwich structures. These studies reveal that fiber damage, matrix damage and delamination of face sheets as well as buckling of core members occur under varied impact energies. The results provide insight into the low velocity impact behavior of such structures, and the knowledge of failure mechanisms could be useful for the development of novel lightweight multifunctional structures.

Introduction

Sandwich structures are increasingly being applied to a number of critical industrial sectors such as aerospace, marine and automobile engineering, as they provide outstanding structural performance with limited weight [1], [2], [3]. Typically, a sandwich structure is composed of thin but stiff face sheets bonded to a lightweight core, such as closed cell foam, honeycomb, prismatic or truss core [2], [3], [4], [5]. More recently, corrugated core composite panels have received increasing attention for the potential applications in the design and manufacture of morphing wing, yacht hull and other energy-absorbing components due to their extremely anisotropic behavior [6], [7]. It is a common sense that sandwich structures are vulnerable to impact which may cause severe damage to degrade the integrity [8], [9], [10], [11]. Therefore, the low velocity impact behavior of such structures has attracted much more attention recently.

Numerous investigations have so far been reported in literatures on the mechanical properties of corrugated core sandwich structures, and most are focused on metallic structures. The mechanical properties of metallic corrugated sandwich structures under quasi-static or dynamic/impact loading have been studied by experimental and numerical method. For example, Tilbrook et al. [12] investigated the dynamic out-of-plane compression behavior of stainless steel corrugated core sandwich structure under impact loading. The failure mechanisms and energy absorption capacity of aluminum sandwich structures also have been investigated under impact loading, and their influencing factors have been discussed [13], [14]. Radford et al. [15] made a comparison among the corrugated, pyramidal and aluminum foam core sandwich structures subjected to impact loading. The results showed that corrugated and metal foam core sandwich structures had the best impact resistance performance. In addition, the quasi-static crushing of metal corrugated sandwich structures under the off-plane compression, longitudinal shear and bending are studied both experimentally and numerically [16], [17]. As a result, corrugated sandwich structures offered significant potential for applications demanding high level of through-thickness stiffness while lightweight, since they exhibited outstanding longitudinal shear strength and energy absorption capacity. To raise rigidity, corrugated sandwich panels with low density foam-filled have been developed to stabilize core members against bulking [18], [19]. Furthermore, metallic multi-layered corrugated sandwich panels were developed to disperse the high-intensity impulses [20], [21]. However, it is reported that composites structures have many remarkable benefits over traditional metallic structures, including higher stiffness and strength, better fatigue resistance, and lower lifecycle cost [1], [22].

More recently, some investigations have attempted to replace all-metallic corrugated core structures with face sheets and corrugated core of composite materials. As a potential energy absorbing component, Mamalis et al. [23] carried out numerical modeling of square tubes with corrugated core under axial compressive loading. Schneider et al. [24] developed a fully recyclable corrugated core sandwich structure made from self-reinforced polymer composites (SrP), and its dynamic out-of-plane compression properties were investigated. The results showed that SrP corrugated cores had more significant advantages than commercial polymeric foams. Kazemahvazi et al. [25] investigated the dynamic compressive response of corrugated cores sandwich structures made from carbon fiber reinforced epoxy, and discussed the effects of the impact velocity and slenderness ratio on the strengthening of inclined struts. In addition, the compressive response and transverse shear behaviors under quasi-static conditions have been investigated, respectively [26], [27], [28]. Rejab and Cantwell [28] investigated the compressive responses and failure modes of corrugated core sandwich panels. The results showed that composite corrugated core structures had superior compression properties than ones with polymer and metal foam cores. To improve the weight specific strength, Kazemahvazi et al. [29], [30] developed a novel hierarchical corrugated composite core, and the compressive and shear response of this structure was investigated. The result showed that the hierarchical structures had more than 7 times higher weight specific strength over their monolithic counterpart. In order to improve resistance of the bulking, Malcom et al. [31] inserted Divinycell PVC foam core into the glass fiber corrugated structure to explore a foam-filled corrugated core sandwich structure. However, the investigations revealed that premature brittle fracture and delamination of composite corrugated core members occurred in the compression tests [28], and the similar failure modes emerged in tensile tests of composite corrugated core [32].

Compared with metallic cores, CFRP corrugated cores have higher specific stiffness and strength, while their energy-absorption is poor owing to the premature brittle fracture or delamination of core members [28], [32]. A wonderful combination could be face sheets of laminated composites bonded to metal cores. This kind of hybrid sandwich structures could maximize the specific bending stiffness/strength by using of composite face sheets, while improve energy absorption capacity by using of metal cores. The material combination has commonly employed in the aerospace industry, such as the sandwich structures with aluminum honeycomb cores and composite face sheets [33]. The impact properties of the hybrid sandwich structures, consisting of CFRP face sheets and aluminum alloy pyramidal truss core [22], [34] or carbon fiber face sheets and aluminum alloy honey core [5], [33], [35], have been studied by combining the experimental and numerical methods. However, to the best knowledge of the authors, only a few research efforts are devoted to the low velocity impact behavior of corrugated core sandwich structures [36], and no literature can be found related to hybrid sandwich structures with CFRP face sheets and aluminum corrugated cores.

This paper aims to investigate the low velocity impact behavior of hybrid sandwich structures consisting of CFRP face sheets and aluminum alloy corrugated cores by experimental and numerical method. Low velocity impact tests with three kinds of core thickness under various impact energy levels are carried out to investigate the impact resistance of such structures. Two representative impact sites are chosen to explore their influences on the impact behavior, which are located on the short span and the long span, respectively. In order to gain further insight into failure mechanisms of such structures, the finite element simulation is conducted. The composite face sheet behavior is modeled through a user subroutine VUMAT, in which a progressive damage model based on the Hashin failure criteria and Yeh delamination failure criteria is implemented in ABAQUS/Explicit. And then the comparisons between the numerical calculations and experimental measurements are discussed.

Section snippets

Materials and specimen

The hybrid sandwich structures with 3 unit cells are fabricated consisting of two CFRP face sheets and aluminum alloy corrugated core. The detailed manufacturing process of the sandwich structure is displayed in Fig. 1. The corrugated cores are fabricated from the 2A12-T4 aluminum alloy sheets by using folding technique, with the size of 96 mm × 96 mm. The basic forms of corrugated sandwich panel are depicted in Fig. 2(a). The relative density ρ¯ of the corrugated core is given byρ¯=2[(2cosω-1)L1+L2

Experimental methodology

An experimental investigation on corrugated core sandwich structures subjected to low velocity impact loading is carried out using an instrumented drop hammer impact test machine with adjustable rebound catchers, as shown in Fig. 4. During impact tests, the square specimens are clamped by the pneumatic clamping fixture with a 75 mm diameter circular test area. An appropriate clamping pressure of 0.02 MPa is imposed on the pneumatic clamps, which is well below the lowest compression strength of

Damage model for aluminum core

The aluminum alloy core is considered as an elastic-plastic material with isotropic hardening, and strain rate effects are neglected in the low velocity impact in the current study [22]. Built-in ductile damage model of ABAQUS is adopted to characterize the failure of corrugated core [37], in which the failure initiation and damage evolution are based on the equivalent fracture strain and fracture energy, respectively. The condition for damage initiation is satisfied when:ωD=dε¯plε¯Dpl(η,ε¯̇pl)

Results and discussions

The samples with three kinds of thickness are impacted on the short span under the impact energy of 10 J, 20 J and 50 J, respectively. Besides, these samples are impacted on the long span under the impact energy of 50 J for comparison. These tests are conducted to investigate the effects of impact energy, core thickness/relative density and impact site on the impact force, absorbed energy and failure modes. The mechanical response and failure modes about the damage process can be obtained according

Conclusions

In this paper, the low velocity impact characteristics and impact damage of hybrid sandwich structures consisting of CFRP face sheets and aluminum alloy corrugated cores are investigated by experimentally and numerically. A range of low velocity impact tests are conducted to study the impact resistance of such structures, considering the effects of impact energy, core thickness and impact site on the impact force, absorbed energy and failure modes. The results show that the slopes and peak

Acknowledgement

The present work is supported by National Natural Science Foundation of China (Grant Nos. 51579110, 51609089 and 51079059), the China Postdoctoral Science Foundation (Grant No. 2016M592338), the National High Technology Research and Development Program of China (863 Program, Grant No. 2012AA112601) and the Fund project Independent Innovation Research Fund of Huazhong University of Science and Technology (Grant No. 2015TS004). Moreover, Wuhan Rules and Research Institute of China Classification

References (40)

Cited by (0)

View full text