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Silicone rubber sheet heater-aided vacuum-assisted resin infusion molding was developed in order to shorten curing cycle time. Three kinds of cooling methods, including air cooling, air water cooling, and water cooling, were employed; the effects of cooling process on processing time, residual strains, and mechanical properties were experimentally studied. The residual strains generated in cooling stage were monitored by embedded strain gauges. The results showed that in order to avoid serious residual strains and lower mechanical properties, the cooling rate of the silicone rubber sheet heater-aided vacuum-assisted resin infusion molding process should be designed carefully. Slow cooling rate before glass transition temperature of the composites and rapid cooling rate after it might be a practical method to maintain both high processing efficiency and acceptable mechanical properties.

This article investigated the effect of cellulose microcrystal (CMC) and low molecular polyamide (PA650) on the mechanical and water absorption properties of ramie fiber‐reinforced epoxy composites. Results showed that coating mixture of CMC and PA650 (CMC/PA650) on the surface of ramie fiber improved the interfacial adhesion strength of ramie fiber/epoxy composites. As a result, the flexural strength, flexural modulus, and interlaminar shear strength of PA650/CMC‐coated ramie fabric‐reinforced epoxy composites (CPRFC) were 10.6%, 8.1%, and 7.4% higher than those of ramie fabric without coating reinforced epoxy composites (RFC). Additionally, saturated water absorption of CPRFC was reduced by 40.5% and 31.5% than that of RFC and PRFC, it seems that a water‐resistant interphase exists in the CPRFC and it is more efficient at the early stage of water immersion. However, without filling of CMC in PA650, lowest flexural modulus and highest flexural strain of the composites were found. POLYM. COMPOS., 39:E2207–E2216, 2018. © 2017 Society of Plastics Engineers

This paper designs two kinds of rapid heating methods for vacuum assisted resin infusion moulding (VARIM) process aiming to reduce the cycle time of carbon fibre/rapid curing epoxy composite fabrication. One utilizes the silicone rubber heating sheet containing thin resistance wires, and the other takes advantage of carbon fibre conductivity to produce internal resistive heating. Conventional oven heating VARIM was performed as a reference. The heating rates and temperature distributions in carbon fibre preform heated by the three heating methods with and without epoxy resin injection were investigated and compared. The curing degree and glass transition temperature of laminates fabricated by different VARIM processes were determined. The heating rate of silicone rubber heating sheet was 26 °C/min, while the carbon fibre internal resistive heating reached 30 °C/ min, which was much higher than the heating rate of 2 °C/min in oven. Unlike the highly uniform temperature distribution in the oven heating process, there was a slight temperature gradient within 5 °C in the silicone rubber heating process and a relatively large gradient within 13 °C in internal resistive heating process for dry fibre preform. When epoxy resin was injected, the temperature gradients obviously increased along the resin flowing direction especially for the rapid heating methods. However, the temperature gradient seemed not to affect the curing degree and its uniformity of laminates for all studied VARIM processes. The cycle time of composite fabrication by the rapid heating VARIM processes was reduced by over 40% compared to oven heating VARIM.

The present article focused on the residual strains and deformation of the laminates fabricated by rapid hot press process using prepreg. Strain gauges and laser tracker were utilized to measure the residual strains and deformation of the laminates. By studying the effects of curing time and de-molding temperature on residual strains and deformation of composite laminates, the efficient curing conditions were proposed and good processing quality was ensured. The results indicate that the laminates with low curing degree incline to generate high residual stresses during curing and cooling processes. The effects of cure duration and de-molding temperature on the deformation degree and type of laminates are significant. In order to ensure both curing efficiency and low deformation, the curing time of the resin and de-molding temperature should be designed cautiously. The experimental results suggest that the curing duration longer than 12 min is needed, and the de-molding temperature should be no less than 40°C lower than glass transition temperature of the cured matrix.