296 LONG FIBER THERMOPLASTIC MATRIX COMPOSITES FIGURE 8.4 Photo of a roll of unidirectional tape made of carbon/PEKK. three dimensional fabrics are difficult to produce.Figure 8.4 shows a photograph of a roll of tape. The speed of production of the hot melt process(meters per minute) depends on the viscosity of the melt,the thickness of the prepregs to be made and the applied pressure.Darcy's law can be used to estimate the rate of production as illustrated in the example below. Example 8.1 A hot melt process is used to produce prepregs for carbon/PEEK 0.2 mm thick.The temperature of the process is 380C giving rise to the viscosity of the resin of 1000 Pa(sec.A pressure of 1 MPa is applied to induce the flow across the thickness of the prepreg.Determine the maximum rate of production,if the length of the die is 50 cm and the permeability of the fiber preform is assumed to be 10-12 m2. Solution The fastest rate of production occurs when the resin has sufficient time to flow across the thickness of the layer.Using Darcy's law,one has: u=-K4 μAx where, u=the flow velocity across the thickness of the prepreg K=the permeability of the fiber preform Ap the pressure gradient across the thickness of the prepreg Ax=thickness of the laminatethree dimensional fabrics are difficult to produce. Figure 8.4 shows a photograph of a roll of tape. The speed of production of the hot melt process (meters per minute) depends on the viscosity of the melt, the thickness of the prepregs to be made and the applied pressure. Darcy’s law can be used to estimate the rate of production as illustrated in the example below. 296 LONG FIBER THERMOPLASTIC MATRIX COMPOSITES FIGURE 8.4 Photo of a roll of unidirectional tape made of carbon/PEKK. Example 8.1 A hot melt process is used to produce prepregs for carbon/PEEK 0.2 mm thick. The temperature of the process is 380°C giving rise to the viscosity of the resin of 1000 Pa(sec. A pressure of 1 MPa is applied to induce the flow across the thickness of the prepreg. Determine the maximum rate of production, if the length of the die is 50 cm and the permeability of the fiber preform is assumed to be 10−12 m2. Solution The fastest rate of production occurs when the resin has sufficient time to flow across the thickness of the layer. Using Darcy’s law, one has: u K p x = − µ ∆ ∆ where, u = the flow velocity across the thickness of the prepreg K = the permeability of the fiber preform ∆p = the pressure gradient across the thickness of the prepreg ∆x = thickness of the laminate