Composite materials perform extremely well in crash and impact scenarios, and are a key enabler in light-weighting structures that have high crashworthiness and certification requirements. Our work on crashworthiness and energy absorption of composite structures has been used in aircraft and automotive designs; recently for a Jetpack landing gear structure and previously helicopter sub-floor structures (see figure right) in the event of high energy crash landings. The representative sub-floor composite structure was developed with two main goals for crashworthiness certification, firstly to limit deceleration on occupants, and secondly to allow the safe evacuation of occupants by maintaining sufficient structural integrity.
Through testing and computer modelling composite materials show one of the highest specific energy absorption of any material. It can be seen (figures right) energy is absorbed by the composite structure through delamination, matrix cracking, fibre breakage and friction. During crushing, well designed composite structures fail by crushing, as such composite energy absorbers can exhibit ideal energy absorption behaviour, where a typical load-displacement response shows a small initial peak load followed by near constant crushing load (see right).
ACS Australia has over 25 years of experience in the design and analysis of composite structures, in particular working in collaboration with the DLR (German Aerospace Center) on crash and impact – see Composite Structure impact test video (below). This work successfully validated the advanced design tools we use today, namely the explicit FE software PAM-CRASH, which significantly reduces the need for costly physical testing.
If you are seeking crashworthiness design, impact testing and support in certification for your product please contact us today!
In this composite structure impact test video the sub-floor absorbs 5.1 kJ of energy (159 kg at 8 m/s) with near steady-state crushing. The crash test article represented the lower half of a helicopter frame (sub-floor). This was used to demonstrate energy absorbing concepts and to validate the high fidelity FE (Finite Element) modelling methods. The test article consisted of three components: an upper non-crushing structure; a lower sacrificial energy absorbing structure; and a skin. The overall dimensions of the structure were 450 mm (height) x 700 mm (width) x 200 mm (depth). The structure sub-components were bonded and the skin mechanically fastened and bonded to the energy absorbing structure and upper frame. As a result of the crashworthiness test program, excellent correlation between test and simulation was achieved – shown in crushing behaviour, energy absorption and acceleration response.
This was a collaborative project between CRC-ACS and DLR. The CRC-ACS participants were ACS Australia, UNSW, Australian Aerospace and Pacific ESI.