304 LONG FIBER THERMOPLASTIC MATRIX COMPOSITES form).For PMC in the form of tapes,the resin has already wetted the fi- bers.As such the need for the resin to be liquid during the final fabrica- tion stage is not essential as far as fiber wetting is concerned (liquefaction is still necessary to fill up all empty space inside the material to prevent voids). For PMC in other forms,melting of the resin is necessary to wet the fibers.In order to determine the temperature and the energy required for melting the resin,differential scanning calorimeter(DSC)tests can be used.Figure 8.12 shows the DSC curve for amorphous PEEK.Fig- ure 8.13 shows a typical DSC scan for a thermoplastic composite (PEKK). The DSC curve contains a few features. First the ordinate shows the energy,positive is up and negative is down.Negative(endothermic)means that energy is entered into the material system,and positive(exothermic)means energy is released from the system.Along the curve,the positive and negative peaks can be interpreted along this way. Figure 8.13 contains two curves.The lower curve represents the heating and the upper curve represents the subsequent cooling. 04 221.78℃ 1.0.g 02 26985℃ 3427的 (B/M)MOL 2OH 23571℃ 00 02 50100 150 200 250300 350 Temperature ("C) FIGURE 8.12 DSC curve for PEEK (DS)resin
form). For PMC in the form of tapes, the resin has already wetted the fibers. As such the need for the resin to be liquid during the final fabrication stage is not essential as far as fiber wetting is concerned (liquefaction is still necessary to fill up all empty space inside the material to prevent voids). For PMC in other forms, melting of the resin is necessary to wet the fibers. In order to determine the temperature and the energy required for melting the resin, differential scanning calorimeter (DSC) tests can be used. Figure 8.12 shows the DSC curve for amorphous PEEK. Figure 8.13 shows a typical DSC scan for a thermoplastic composite (PEKK). The DSC curve contains a few features. • First the ordinate shows the energy, positive is up and negative is down. Negative (endothermic) means that energy is entered into the material system, and positive (exothermic) means energy is released from the system. Along the curve, the positive and negative peaks can be interpreted along this way. • Figure 8.13 contains two curves. The lower curve represents the heating and the upper curve represents the subsequent cooling. 304 LONG FIBER THERMOPLASTIC MATRIX COMPOSITES FIGURE 8.12 DSC curve for PEEK (DS) resin
Fabrication of the Final Product 305 0.2 248.16C 0.1 61已 4057 2356话0 0.0 150.770 27花39℃ 15314GH0 0.1 41.D6g27170℃ 155.51*G 32.7g 222.02℃ 3450 07 304C 297.49r℃ 0.3 50 100 150 200 250 300 350 Temoeralue C FIGURE 8.13 Typical DSC scan for carbon/PEKK composite. For the heating curve,as the temperature of the test is increased, there is some change in the slope of the curve indicating that energy is needed to be entered into the system to increase the temperature of the material.This is due to the heat capacity of the material according to the equation:O=mC AT where m is the mass of the material,C is the heat capacity of the material and AT is the temperature change. There is a jump in the curve and a change in the slope of the curve at about 150C.This change indicates a change in microstructure of the materials.The jump indicates that additional energy was entered into the system to make the change.The change in slope indicates that the heat capacity of the material has changed at that temperature.This temperature is called the glass transition temperature T,because upon heating past that temperature,the material changes from a glassy state to a viscous state.Each of these states has a different heat capacity.In this case,the glass transition temperature is determined to be 153C. The material becomes soft above the glass transition temperature, and it is usually recommended to use the material at a temperature of about T-30C
• For the heating curve, as the temperature of the test is increased, there is some change in the slope of the curve indicating that energy is needed to be entered into the system to increase the temperature of the material. This is due to the heat capacity of the material according to the equation: Q = mCp T where m is the mass of the material, Cp is the heat capacity of the material and ∆T is the temperature change. • There is a jump in the curve and a change in the slope of the curve at about 150°C. This change indicates a change in microstructure of the materials. The jump indicates that additional energy was entered into the system to make the change. The change in slope indicates that the heat capacity of the material has changed at that temperature. This temperature is called the glass transition temperature Tg, because upon heating past that temperature, the material changes from a glassy state to a viscous state. Each of these states has a different heat capacity. In this case, the glass transition temperature is determined to be 153°C. The material becomes soft above the glass transition temperature, and it is usually recommended to use the material at a temperature of about Tg –30°C. FIGURE 8.13 Typical DSC scan for carbon/PEKK composite. Fabrication of the Final Product 305