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PROCESSES: FORMING OF COMPOSITE MATERIALS
This area of CTM, which has been created recently, is structured within the Area of Processes. The area, in collaboration with Applus, MAPRO, AMADE and CD6 focuses its activities on the three following aspects:
1. Forming of fibers pre-impregnated with resin
The manufacturing of composite materials such as polymers strengthened with carbon fiber (CFRP) may require to stack ribbons (or layers) of prepreg with specific orientations for later forming products such as stringers or profiles in T, I, J, the shape of a hat or others. CTM has experience in advising companies in how to avoid, during the forming of prepreg stacks, the formation of ondulations, wrinkles, separations of fibers, elastic returns or other defects which cannot be corrected with the curing tools. The prepreg formation has to reach amost the final shape for the fibers to be tense and really act as a reinforcement in the final product. This is just one of the important aspects that should be taken care over when forming prepreg. CTM´s experience in the limits of the forming of prepreg has been useful for the design of machinery for automating a process that up to this day is still very manual.
2. Microtopographical inspection(confocal) of plastics strengthened with fibers.
CTM counts with a confocal microscopy unit for the inspection of sheets of plastics strengthened with Carbone fibre (Carbon Fibre Reinforced Polymer CFRP) or with glass (Graphite Fibre Reinforced Polymer). Confocal microscopy can detect defects near to the surface, even if it is the apparently flat surface what was in contact with the curing mould. Other inspection technologies such as ultrasounds can hardly see defects on the layers closer to the surface because the noise of the walls disguises the signal. On the other hand, the topographical images at a microscopic scale of the confocal unit complement the information previously obtained with an ultrasound unit. The digitalised images from the confocal unit make it possible to quantify the affected area. Even though the resins used in the manufacturing of CFRP or GFRP are usually translucent, the confocal unit is capable of getting images of the surface rugosity. On the other hand, if what we want is to have a register of the rugosity of the areas superior to 6 mm, CTM also counts with a linear perfilometer.
3. Mechanical characterisation of composite materials
CTM has carried out the mechanical characterisation of different polymers strengthened with glass or carbon fibers for several companies. CTM counts with working units for the determination of the elasticity modulus in traction or in flexion using gages or extensometric bands. The traction tests are carried out at different orientations of the plate. CTM also counts with precision scales for determining the density of the composite and after the percentage of fiber. The number of layers in the composite material and other microscopical characteristics are determined by metallographically preparing and observing in an optical microscope, a confocal microscope or a Field Emission Scanning Electron Microscope (FESEM). The later one is capable of observing polymers without covering them with a conductive layer because it uses a flow of nitrogen.
Determination of the effect that fatigue (a flexion on 4 points) has on the accoustic signal detected by the ultrasound unit
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