Effect of Injection Rate and Post-Fill Cure Pressure on Properties of Resin Transfer Molded Disks

The effects of flow rate andpost-fill cure pressure, i.e., packing pressure, on the mechanical properties of resin transfer molded disks are experimentally investigated. An experimental molding setup is constructed to fabricate fiber-reinforced, center-gated, disk-shaped composite parts. Disks are molded at different flow rates and packing pressures in order to observe the effects of these parameters on the mechanical properties andvoidcontent of the final parts. Specimens are cut from three different locations in the molded disks for testing. Specimens from the first two locations are tensile testedto obtain strength and stiffness properties, and the third location is usedfor microscopic analysis to determine void content and void properties. Increased injection rate is found to reduce both the strength and stiffness of the molded parts due to more voids induced by the faster moving fluidfront. Packing pressure is also foundto have a significant effect on specimen properties. At higher packing pressures fewer voids and improved strength andstiffness are observed. Mechanical properties are correlatedwith total void fraction for disks molded at different packing pressures. Exponential decrease in both tensile strength andelastic modulus is observedwith increasing voidfraction. Doubling the voidvolume fraction from 0.35 to 0.72% results in a 15% decrease in strength and a 14% decrease in stiffness. The results demonstrate that selection of suitable injection rate and addition of packing pressure to resin transfer molding (RTM) process can improve mechanical properties of molded parts considerably.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Effect of Preform Thickness and Volume Fraction on Injection Pressure and Mechanical Properties of Resin Transfer Molded Composites

An experimental study is performed to characterize the effect of the thickness of random preforms on injection pressure and mechanical properties of resin transfer molded (RTM) parts. Center-gated, disk-shaped parts are molded using two different chopped-strand glass fiber preforms. Both preforms have random microstructure but different planar densities (i.e., different uncompressed layer thicknesses). Tensile strength, short-beam shear strength, and elastic modulus are measured for parts molded with each preform type at three different fiber volume fractions of 6.84, 15.55, and 24.83%. Although mechanical properties are found to increase linearly with volume fraction, significant difference is not observed between disks containing thick and thin mats at equivalent fiber volume fraction.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Experimental Characterization of Orientation Formation in a Mold Cavity with Sudden Contraction

Orientation formation of short fibers suspended in a flow through a planar mold cavity is experimentally analyzed. The suspension of corn syrup mixed with short fibers is injected into the mold at constant flow rate through a narrow, planar inlet gate. The mold cavity contains a sudden expansion following the inlet gate, and a three-to-one sudden contraction downstream. Orientation data are obtained using computerized image analysis on photographs of thirteen zones of interest near the sudden contraction. The photographs are taken through the transparent top mold wall, thus collecting average planar orientation data through the mold thickness. Orientation distribution histograms are generated from the individual fiber orientations to graphically depict orientation microstructure. These histograms reveal bimodal fiber orientations in nearly all zones of interest. Experiments performed at different volume flow rates and viscosities also confirmed the bimodal orientation distribution observed through the top mold wall. Orientation results are observed to be more random compared to those predicted using Jeffery's theory (He et al., 1997). Fiber size or wall effects may contribute to the formation of a more random orientation field.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline