Core crush criterion to determine the strength of sandwich composite structures subjected to compression after impact

In this study a core crush criterion is proposed to determine the residual strength of impacted sandwich structures. The core of the sandwich is made of a Nomex Honeycomb core and the faces are laminated and remain thin. The mechanism of failure of this kind of structure under post-impact compressive loading is due to interaction between three mechanical behaviors: geometrical nonlinearity due to the skin’s neutral line off-set in the dent area, nonlinear response of the core and damages to the skins. For the type of sandwich analysed in this study, initially the core crushes at the apex of the damage. Using a finite element discrete modelling of the core previously proposed by the authors, the load corresponding to the crushing of the first cell can be computed and it gives the value of the residual strength for our criterion. Some geometric and material hypotheses are assumed in the damaged area mainly based on nondestructive inspection (NDI). The criterion is then applied to tests modelled by Lacy and Hwang [Lacy TE, Hwang Y. Numerical modelling of impact-damaged sandwich composites subjected to compression after impact loading. Compos Struct 2003;61:115–128]. It is shown that the criterion allows a good prediction of the tests except in the case of very small dents. Several sensitivity studies on the assumptions were made and it is shown that using this approach, the criterion is robust

Experimental study of energy absorption capability of metallic-palm fiber-metallic hybrid composite plate

An experimental campaign on metallic-palm fiber-metallic hybrid subjected to impact loading using spherical projectile has been carried out. High initial energy impact with projectile mass of 24 kg and speed of 1, 3 and 5 mm/s, has been set enabling to determine the energy absorption capability of hybrid composite panel. The influence of stacking sequences metallic-palm-fiber-metallic and metallic-palm fiber-metallic-palm fiber-metallic with different thickness of metallic and palm fiber, to the energy absorption were investigated. The effect of different striker radius; 10, 13 and 20 mm were carried out as well. The mechanism of failure and energy absorbed by the hybrid composite panel and its components; metallic alone and palm fiber alone, were carried out to understand the advantage of having hybrid structure. The optimum configuration of hybrid panel in term of stacking sequence to absorb the energy of impact is proposed. The methodology of this study can be used for designing the armor to absorb the energy of projectile using palm fiber composite panel

The study of impact behaviour of two types of glass fibre reinforced polymer (GFRP) subjected to low velocity impact

The aim of this work is to study the behaviour of two types of composite material when subjected to impacts at different energy levels under low velocity impact events. The composite material used in this study was Glass Fibre Reinforced Polymer (GFRP) which was C-type/600 g/m2 and E-type/600 g/m2. This material was fabricated to produce laminated plate specimens with a dimension of 100 mm 150 mm. Each specimen had 10 layers of GFRP woven roving plies. The low velocity impact test was performed using an IM10 Drop Weight Impact Tester with a 10 mm hemispherical striker cap. The impact energy was set to 14, 28, 42 and 56 joules with velocity ranging from 1.73 m/s to 3.52 m/s. The relationships of impact energy with impact force, displacement and energy absorbed are presented. The comparison and behaviour between the two types of GFRP are discussed

Modelling of low-energy/low-velocity impact on Nomex honeycomb sandwich structures with metallic skins

In the aircraft industry, manufacturers have to decide quickly whether an impacted sandwich needs repairing or not. Certain computation tools exist at present but they are very time-consuming and they also fail to perfectly model the physical phenomena involved in an impact. In a previous publication, the authors demonstrated the possibility of representing the NomexTM honeycomb core by a grid of nonlinear springs and have pointed out both the structural behaviour of the honeycomb and the influence of core-skin boundary conditions. This discrete approach accurately predicts the static indentation on honeycomb core alone and the indentation on sandwich structure with metal skins supported on rigid flat support. In this study, the domain of validity of this approach is investigated. It is found that the approach is not valid for sharp projectiles on thin skins. In any case, the spring elements used to model the honeycomb cannot take into account the transverse shear that occurs in the core during the bending of a sandwich. To overcome this strong limitation, a multi-level approach is proposed in the present article. In this approach, the sandwich structure is modelled by Mindlin plate elements and the computed static contact law is implemented in a nonlinear spring located between the impactor and the structure. Thus, it is possible to predict the dynamic structural response in the case of low-velocity/low-energy impact on metal-skinned sandwich structures. A good correlation with dynamic experimental tests is achieved

Experimental study of impact on carbon-fiber-epoxy composite wing leading edge structure

This paper works on the curvature composite structure for wing leading edge application using fabric carbon/epoxy material subjected to impact loading. At first stage, rigid spherical projectile and elliptical panel with were used. The impact testing has been carried out by varying the radius of curvature, the thickness of the panel and different stacking sequence. The experimental results show the trend of specific energy absorption capability of structure in function of the radius, thickness of panel and carbon fiber directions