Solartron helps Cranfield to find cure

Citation

(1998), "Solartron helps Cranfield to find cure", Aircraft Engineering and Aerospace Technology, Vol. 70 No. 3. https://doi.org/10.1108/aeat.1998.12770caf.003

Solartron helps Cranfield to find cure

Solartron helps Cranfield to find cure

Keywords Adhesives, Aircraft industry, Cranfield University, Solartron

Manufacturers of aeronautical and marine components look set to benefit from research conducted by the School of Industrial and Manufacturing Science at Cranfield University, which relates to practical cure monitoring methods for industrial adhesives. Researchers hope that manufacturers can improve the control of processing in both glass and carbon fibre commercial laminates, using the dynamic dielectric analysis (DDA) cure monitoring technique.

Cranfield has used equipment from Solartron, one of the leading world-wide suppliers of measurement instrumentation, in its application of the DDA technique. Organisations such as British Aerospace, Short Brothers plc, Defence Research Agency (DRA), and IFREMER, the French Research Institute for the Exploitation of the Sea, are also using dielectric methods as a result of this research.

Dynamic dielectric analysis (DDA), is a technique which monitors the cure reaction of industrial adhesives. In the manufacture of aerospace components, for example, these adhesives are used for the wing boxes, engine cases, under-carriage doors for luggage, and in some cases the fuselage.

In carrying out the DDA technique, researchers at Cranfield use mould-mounted and embedded sensors placed at various points along the composite layers of carbon or glass fibres. The layers are pre-impregnated with wet resin, put in a vacuum bag to compress the layers, and then placed in an autoclave where the sensors are connected to the Solartron 1260 impedance analyser.

The 1260 applies voltage and measures the current that returns, giving the frequency dependency of the dielectric properties. Analysis of this data is formulated by software which has been developed in-house at Cranfield. The properties monitored can be related to the resin viscosity, degree of cure and the point at which the material reaches its optimum cure state. These properties determine the mechanical performance of the material when taken out of the autoclave.

The main advantage of using the DDA technique is its ability to relate, in situ and in real time, the state of resin cure to temperature and viscosity. It also allows quality control of the manufacturing cycle for carbon fibre reinforced composites, and real time detection of moisture in-take of components which may be used in marine manufacturing.

Dr George Maistros, research officer at Cranfield University, explains the importance of using Solartron's equipment:

Solartron's 1260 frequency response analyser is the heart of our monitoring system. We prefer it to other bridges because of its wide frequency range. In our set-up, the sensors which monitor the materials under investigation are in an autoclave. This means we need to have long cables to connect the sensors to the instrumentation. To minimise the effect of cabling we use the 1260 in conjunction with the 1287 Electrochemical Interface, The 1287 uses driven shield technology, which minimises the effects of cables on the measured results. This combination also gives us the best current sensitivity over the entire frequency range of interest. Using this system we measure the dielectric properties of the material close to the sensor; the frequency dependence of these properties is then used to optimise process conditions of the material with the aid of thermoanalytical models.

Although the DDA process has been used for many years, the technique has now been developed into a monitoring process which is industrially viable. Solartron's modern dielectric equipment provides the technique with major advantages. The 1260 allows fast frequency sweeps, is portable, and allows real time data acquisition. This means that the DDA technique may be used as a process control tool on the production shopfloor, or as a component health monitoring process at a parts servicing site.

Details from Dr Nigel Evans at Solarton, UK. Tel: +44 (0)1252 376666.