Comparative evaluation of GFRP laminate panels manufactured by VARI and RTM methods
Mateusz Kozioł, Michał Bator, Henryk Rydarowski, Bartosz Hekner
Quarterly No. 4, 2015 pages 196-202
DOI:
keywords: laminate, resin transfer moulding (RTM), vacuum assisted resin infusion (VARI), repeatability of properties
abstract The aim of the study is a comparative evaluation of panels made of GFRP laminate (10 layers of plain-woven 0/90 glass fabric) by RTM and VARI methods. The evaluation was performed on the basis of the analysis of the laminate thickness, fibre volume fraction and flexural strength. An essential element of the evaluation is the repeatability of the analyzed properties, which is estimated by the standard deviation and coefficient of variation of respectively numerous result series. Comparison of the two mentioned technologies may be significant information concerning their alternative applicability. The range of the study covers: preparation of four reinforcement lay-ups (preforms) of plain-woven glass fabric, manufacturing four laminate panels using the preforms - two by RTM and two by VARI, cutting specimens from the panels, evaluation of the thickness and fibre volume fraction of the specimens, and evaluation of the flexural strength of the specimens in 3-point bending tests. Laminates manufactured by the RTM and VARI methods showed a relatively high reinforcing fibre volume fraction. A slightly higher volume fraction and, at the same time, a significantly smaller thickness were observed in the VARI laminates. The laminates manufactured by RTM showed about a 10% higher flexural strength in comparison with the VARI ones. The laminates manufactured by VARI showed a higher volume fraction but it is probably due to gas voids present in areas near the reinforcing fibre strands. The presence of voids was also proved in the structure of the RTM laminates, but they are of a different nature - they are bigger and are located within the resin-rich areas between the reinforcing layers. The quality of the specimen surface (two-side smoothness in the case of the RTM laminates, one-side smoothness in the case of the VARI ones) could also have some effect on the flexural strength. In the case of both the VARI and the RTM laminates as well, a visible thickness "gradient", directed the from outlet to inlet, was observed. It is caused by "relaxation" of the underpressure after passing of the resin flow front during the impregnation process. The "gradient" is bigger and less uniform in the case of the VARI laminates than in case of the RTM ones. The RTM method occurred to be minimally better than the VARI in terms of repeatability of the fibre volume fraction and flexural strength, measured as the variance coefficient of the results of a specimen series. The worse repeatability of the laminates manufactured by the VARI method results from the bigger laminate thickness "gradient".