Numerical Model of Tubular Composite Sandwich Structures Under Low-Velocity Impact

Numerical Model of Tubular Composite Sandwich Structures under Low-Velocity Impact

Chao Zhang^*, K.T. Tan

Department of Mechanical Engineering, The University of Akron, Akron, OH44325, USA

*Corresponding Author: cz39@zips.uakron.edu

ABSTRACT

       This study aims to investigate the dynamic impact response of tubular composite structures with/without honeycomb sandwich core under transverse low-velocity impact (LVI) test. We establish a simulation model of composite sandwich structures, then compare simulation results with the experimental results to verify the correctness of the model and analysis method. This model can accurately predict the impact-induced damage response of composite sandwich structure in test experiments and address the major failure modes in the numerical model. It is also able to link numerical results with microscopic experimental observations of composite sandwich structures after impact.

       In order to understand different impact scenarios that could occur in a non-flat tubular composite structure, LVI experiments are conducted utilizing hemispherical and cylindrical impact striker to enact both point and line impact. Damage mechanisms, such as matrix cracking, delamination and fiber breakage/rupture in face sheets as well as honeycomb crushing and buckling in the core, are characterized by X-ray micro-computed tomography (µCT) to understand failure processes and their relationship with core material and impactor shapes. Hemispherical impactor induces localized damage failure, while cylindrical impactor creates global damage phenomena. Compared to carbon fiber reinforced plastic (CFRP) tubes, composite sandwich (SAN) tubes have more varied types of failure mechanisms, but with fewer localized damage. It is found that sandwich core material helps to absorb impact energy and resist localized damage formation. The benefit of core material includes greater energy absorption capability. Furthermore, the multiple damage mechanisms dissipate more energy instead of only damage on face sheet itself. On the other hand, the tube can still be considered as light weight structure after addition of core, due to the small mass of honeycomb material.

       Dynamic response of tubular composite structures is further investigated by using finite element analysis. A three-dimensional damage model based on the Hashin’s failure initiation criteria and cohesive zone method is developed to analyze tensile and compressive damage on matrix and fiber. The combination of experimental and numerical results illustrates the effect of various impactor, facesheet and core material on failure mechanisms. Results show the main contribution of CFRP layer for the energy absorption during low-velocity impact (LVI) is deformation. However, for the whole sandwich structure, the majority of the energy absorption is devoted by the plastic strain energy of the core. After confirming that the finite element model and analysis method are effective, we study effect of dimensions like diameters of impactor, thickness of facesheet and core material which can improve the structural design of the existing tubular structures for good impact resistance.