Impact resistance of Nomex honeycomb sandwich structures with thin fibre reinforced polymer facesheets

In order to investigate the impact resistance of the Nomex honeycomb sandwich structures skinned with thin fibre reinforced woven fabric composites, both drop-weight experimental work and meso-mechanical finite element modelling were conducted and the corresponding output was compared. Drop-weight impact tests with different impact parameters, including impact energy, impactor mass and facesheets, were carried out on Nomex honeycomb-cored sandwich structures. It was found that the impact resistance and the penetration depth of the Nomex honeycomb sandwich structures were significantly influenced by the impact energy. However, for impact energies that cause full perforation, the impact resistance is characterized with almost the same initial stiffness and peak force. The impactor mass has little influence on the impact response and the perforation force is primarily dependent on the thickness of the facesheet, which generally varies linearly with it. In the numerical simulation, a comprehensive finite element model was developed which considers all the constituent materials of the Nomex honeycomb, i.e. aramid paper, phenolic resin, and the micro-structure of the honeycomb wall. The model was validated against the corresponding experimental results and then further applied to study the effects of various impact angles on the response of the honeycomb. It was found that both the impact resistance and the perforation depth are significantly influenced by the impact angle. The former increases with the obliquity, while the latter decreases with it. The orientation of the Nomex core has little effect on the impact response, while the angle between the impact direction and the fibre direction of the facesheets has a great influence on the impact response. </jats:p

Experimental and numerical study on the mechanical response of Nomex honeycomb core under transverse loading

This paper presents an experimental and numerical investigation on the mechanical response of the Nomex honeycomb core subjected to transverse loading. Here, a series of tensile, stabilized compressive and step-by-step compressive tests were carried out, also a meso-scale finite element modelling method was developed to simulate the resin-paper-resin layered honeycomb cell walls by employing explicit shell elements. Through the analysis of the test results, the brittle fracture behaviour of the phenolic resin coating is recognised as a main reason of the honeycomb collapse. Both the strength and modulus of the honeycomb core in tension are higher than those in compression, due to the local buckling of the thin cell walls at a quite low level of compressive loading. From the numerical analysis, it was found that the volume of the resin coating has a positive effect on the collapse strength of the honeycomb core, however has no influence on the collapse strain. Moreover, the modulus of the resin coating has a positive effect on the collapse strength but a negative effect on the collapse strain. In addition, the strength of the resin coating has positive effects on both the collapse strength and strain of the honeycomb core

A Parametric Study of the Low-Impulse Blast Behaviour of Fibre-Metal Laminates Based on Different Aluminium Alloys

A parametric study has been undertaken in order to investigate the influence of the properties of the aluminium alloy on the blast response of fibre-metal laminates (FMLs). The finite element (FE) models have been developed and validated using experi-mental data from tests on FMLs based on a 2024-O aluminium alloy and a woven glass-fibre/polypropylene composite (GFPP). A vectorized user material subroutine (VUMAT) was employed to define Hashin’s 3D rate-dependant damage constitutive model of the GFPP. Using the validated models, a parametric study has been carried out to investigate the blast resistance of FML panels based on the four aluminium alloys, namely 2024-O, 2024-T3, 6061-T6 and 7075-T6. It has been shown that there is an approximation linear relationship between the dimensionless back face displacement and the dimensionless impulse for all aluminium alloys investigated here. It has also shown that the residual displacement of back surface of the FML panels and the internal debonding are dependent on the yield strength of the aluminium alloy