No abstract

It is well known that carbon fibre-reinforced polymer/plastic (CFRP) composites are sensitive to moisture, and so there is a reluctance to use cutting/machining fluids within the composites industry. In this work, the influence of a selection of machining fluids on the integrity of CFRP's and their final mechanical properties was studied. Six sets of CFRP specimens were exposed to air, water and four machining coolants at an elevated temperature of 60°C for 7 days. Swell tests were performed to observe the specimen weight gain due to moisture absorption during soaking. The specimens were subsequently bonded to produce lap shear test specimens. Bond strength test and short-beam shear test were performed to assess the degradation in mechanical properties due to exposure to the various lubricants. Out of the five fluid soaking media (water and four coolants), it was found that only one media (called Cindolube V30ML) did not cause the specimens to absorb moisture and it also had the lowest detrimental effect on the mechanical properties of composite.

The work presented here focusses on the developments in the stabilising and trimming of 3D woven preforms. Dry fibre preforms are notoriously difficult to trim; once a fabric is cut, it loses its edge stability and consequently the fabric frays. The result is an unstable fabric which can easily be displaced/ distorted prior to composite manufacturing. In this work, three stabilisation and three trimming techniques were investigated. Of the stabilisation techniques these included powder binder, thermoplastic binder yarn (activated to give fabric stabilization); and polyester stitching. The stabilised fabrics were trimmed to near-net-shape using different trimming techniques. The trimming techniques investigated were laser, clicker press and ultrasonic knife. Each stabilisation method was trialled with each trimming method to assess the most suitable combination. The assessment of quality and suitability was made by observing the level of stabilisation, amount of fraying fibres, quality of the cut, ease of application and repeatability of the process. This paper details the assessments made for each combination alongside practical application conclusions. The key findings were; cutting by means of a laser is capable of sealing the fabric edges, producing high edge quality. Stitching as a method of stabilising is not sufficient in preventing fibres from moving during the cutting process, hence producing an unclean cut.