Frame by frame

I have previously reported the emerging capabilities of Acrosoma, evolving from its roots as Composite Trailer through a number of key contracts in the aerospace and defence sector as business development intentions are becoming reality.

The company had originally configured itself to make large stiffened panels to meet a requirement for trailer structures for the road haulage market, but the engineering requirements and business dynamics of this have given it the capability to address other market sectors as well.

The most recent of these is in large tooling frames consistent with the requirements of moving Airbus A350 XWB composite wing components between and around various Airbus production facilities. These lifting frames therefore have implications not only in their mass for handling but also in transportation over considerable distances by air and surface means.

The critical design factor here was the ability to produce a tooling solution that was stiff but at a realistic weight. The traditional steel tooling would have weighed about three times as much, but the Acrosoma solution for a 33m by 9m frame weighed in at 3.5 tonnes for an increase in stiffness and negligible thermal expansion. Previous experience in constructing road haulage structures, which are exposed to in-service loadings of up to 20g, paved the way for a more relaxed requirement of 6g for the transport frames.

The skin of the panel structure material is a mix of woven glass and unidirectional carbon, with a PET foam core. The through-stitching is in aramid yarn and the matrix material is a thermoplastic vinyl ester.

The interesting point here is not that a composite solution can produce a higher mechanical performance for a given mass, compared to its metallic alternative. We've known this for years. The uniqueness of the Acrosoma panels is in the quasi-continuous production method which means a very cost-effective and low cost way of achieving the design requirements. It is the batching of the cure cycle through autoclave methods or dedicated tooling for example, which causes a discontinuous production cycle.

The failure mode for sandwich panels is generally in delamination of the interface joint between the skin and core components. The Acrosoma technique of through-stitching usually with aramid yarns, although adding an extra process to the production method greatly increases the performance of the structures and allows some design freedoms.

Structures are built up by cutting and joining sections from the panel, and can also incorporate filament winding where this adds to the structural integrity of the finished component. Acrosoma has demonstrated considerable success in the manufacture of box section components, which are finished in-house before delivery to the customer.

As this is the first application of its kind for this company, it is probably fair to say that other similar uses will become known in the coming months and years. The cost versus benefit advantage of these stiffened panels has also been used in demonstration for the US Department of Defence in a requirement for expeditionary airfield matting, where it outperformed the existing requirement by many times.

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