Void formation as a result of prepreg moisture content and processing pressure during cure was experimentally investigated in thermosetting composite laminates. This was achieved by determining the void contents of eight-ply laminates fabricated from TenCate V R BT250/7781 E-glass/epoxy prepreg at processing pressures of 1.7, 3.0, 4.4, and 5.8 atm. At each processing pressure, three types of laminates were fabricated using: (i) unconditioned prepregs (direct from the storage bag); (ii) prepregs conditioned at 25% relative humidity; and (iii) 99% relative humidity. Dynamics of prepreg moisture uptake during conditioning was measured using a moisture analyzer and was shown to exhibit Fickian diffusion behavior. The void contents of the cured laminates were found to vary from 1.6% to 5.0% depending on humidity environment the prepregs were exposed and the pressure applied during fabrication. The void contents of all laminates were observed to approach an asymptotic value of $1.6% as pressure was increased. The experimental results indicated the processing pressure applied during fabrication was increasingly carried by the fiber bed, reducing resin pressure during cure. Therefore, an enhanced void formation model was proposed through the addition of a pressure reduction factor and an asymptotic void content term. The proposed model was found to accurately predict the void content of laminates made of prepregs exposed to constant/varying humidity environments and fabricated at a wide range of processing pressures. POLYM. COMPOS., 36:376-384, 2015.

An innovative manufacturing method, bladder assisted composite manufacturing (BACM), to fabricate geometrically complex, hollow parts made of polymeric composite materials is presented. Unlike the conventional bladder or diaphragm assisted curing processes, BACM uses an internally heated bladder to provide the consolidation pressure at the required cure temperature. The feasibility of this manufacturing method is demonstrated by fabricating laminated composite cylinders using multiple cure pressures and number of plies. The elastic moduli, failure strength, fiber volume fraction, and void contents of the cylinders were found to be comparable to the values obtained fi-om fiat laminates produced by hot plate molding of the same material. Compared to conventional bladder manufacturing methods, the BACM process reduced the energy required to cure the cylinders by almost 50% due to internal heating and insulatedmold.

No abstract

No abstract

Bladder Assisted Composite Manufacturing (BACM) is a recently developed out-of-autoclave process designed to fabricate geometrically complex, hollow composite parts. This paper assesses the ability of three new BACM process variations to fabricate parts with high fiber and low void contents. This was achieved by fabricating 4-ply cylinders from a carbon/ epoxy prepreg at cure pressures of 207 and 483 kPa. The fiber/void content, mechanical properties, and energy consumed during the curing of the cylinders are investigated and compared to the original BACM process. The fiber content of the cylinders were observed to be dependent on both bladder pressure and BACM variation used, reaching a maximum fiber content of 66% which is 5% greater than that obtained by the original BACM process. The elastic moduli and failure strength results for the cylinders were found to increase with fiber content and showed no preference to any of the studied BACM process variations. In addition, the void content of the cylinders were reduced by 94% with the utilization of a porous bleeder fabric when compared to the original BACM process. POLYM. COMPOS., 37:561-572, 2016.