At the heart of our vision for innovation in advanced composites is the provision of first rate experimental facilities in which ideas and novel concepts can be developed, tested and proven. Within the Engineering Faculty there has recently been a major investment in new, state of the art laboratories to form the £18 million Bristol Laboratories for Advanced Dynamic Engineering (BLADE). ACCIS makes use of this world class infrastructure to house composites-specific equipment and additionally has access to the broader range of laboratory equipment as and when required. Further facilities are available in other faculties across the University of Bristol.
A wide range of mechanical test machines are available with capacities from single fibre testing through to the MN range. Many of these machines are fatigue rated servohydraulic universal testers, and some of them are fitted with temperature cabinets allowing use at sub-zero or elevated temperatures. The hydraulic supply for these machines is taken from a high capacity ring main. Further testing machines can simultaneously apply tension and torsion to generate complex loadings and a four actuator load bed system can supply loading from simple uniaxial or biaxial cruciform loading to complex tension, bending torsion cases. Large scale bending rigs allow, for example, fatigue testing of composite reinforced concrete beams or bridge deck sections. Dynamic or high cycle testing can be carried out within the dynamics lab in BLADE using electromagnetic shakers and the associated control circuitry. Large scale testing can be carried out within the earthquake lab in BLADE which can accommodate very large specimens and very high loads.
As composite components are increasingly used in critical applications, understanding the properties under high strain rate conditions is becoming more important. A drop weight impact tower with a spring assist to increase the maximum energy is available. This machine has a impact capacity of up to 800J and can take large samples as well as simple laminates and is equipped with state of the art data capture. A tensile Hopkinson’s bar apparatus is also available for measuring the mechanical response of materials under very high strain rate conditions.
A high speed video camera is available to provide detailed visualisation of the impact testing at up to 200 000 frames per second. Video Gauge software can be used to extract deformation and strain data from any test, irrespective of scale, so long as a stream of images can be obtained. For low speed testing on conventional test machines this data can be extracted in real time up to at least 60Hz. It can also be used in conjunction with the high speed camera post-test. When coupled with a miniaturised test machine and a metallurgical microscope this gives us the capacity to carry out very fine scale studies of the strains within loaded composites at the meso and micro scales. A range of conventional, stereo and inverted microscopes linked to state of the art image capture and analysis capability are available. Access to further visualisation and surface analysis techniques, such as SEM, is available through the Interface Analysis Centre.
Facilities exist to manufacture laminates and components by industry-standard processes. In addition, glass fibres of complex cross sections can be made in-house and incorporated into conventional laminates to introduce additional functionality such as damage visualisation and self-healing. Processing starts with a walk-in freezer for storing temperature sensitive prepregs and resins. Ply cutting and honeycomb routing can be carried out on a computer controlled flat bed cutter, with manual ply cutting and lay-up in a 40m2 air conditioned lay-up room. Cutting edge processes such as fibre steering and preform stitching can be carried out on purpose built equipment and a vacuum former is available for diaphragm forming of prepreg or RTM preforms. Moulding is via a 1m diameter autoclave, by RTM or by compression moulding in a press rated for 500C to permit the handling of any polymers. A squeeze caster is available for metal matrix composites processing. Post moulding processes such as machining can be accommodated within ACCIS or in the central workshop facilities within BLADE.
Facilities exist for the measurement of process critical properties such as resin cure kinetics via state of the art DSC equipment, which can also be used to measure critical in-service parameters such as Tg and how this may be affected by the working environment. Other critical properties such as the viscosity profile during cure can be monitored by DMA, as can the changes in mechanical properties during cure and as a result of environmental changes after cure. Techniques have been developed within ACCIS to measure resin cure shrinkage, reinforcement drape and consolidation, ply to ply interactions, part/tool interactions and residual stresses and distortions where there are no standard tests using commercially available equipment. The Interface Analysis Centre, Chemistry and Physics Departments also have other methods of characterisation available.
The RMR facility is used by ACCIS for manufacturing research with advanced composite materials. The group uses the RMR hardware for both fully-automated and man-and-machine techniques, while the software is used in simulation of factory operations. ACCIS has further developed the facility by adding machining capability to the RMR, as well purchasing two highly novel robotic stand alone systems that work within the footprint to increase flexibility.