Effect of machining coolant on integrity of FRP composites

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.