Composites Manufacturing - Materials, Product, and Process Engineering Part 11 pps

© 2002 by CRC Press LLC • The processed part should have the lowest possible void content. • In the case of thermoset composites, the resin should be cured uniformly and completely. Uneven curing generates residual stress in the part. Similarly, for thermoplastic composites, uniform cool- ing should take place to avoid residual stress build-up. • The finished part should have minimum residual stress to mini- mize part distortion. Part distortion or uneven shrinkage may cause the part to go out of tolerance. • The complete process should be achieved in the shortest possible time. A shorter process cycle time provides higher production rate and lower production cost. • During the curing process of thermoset composites, the excess resin must be squeezed out from every ply and resin distribution must be uniform. Methods of applying heat and pressure are different in each manufacturing process. In the autoclave process, heat is supplied with the help of hot air or hot nitrogen gas inside the autoclave, and pressure is applied by vacuum bagging and by pressurizing the chamber with air. In the RTM process, pressure is controlled by injection pressure and heat is supplied by heating the mold. In the thermoplastic tape winding process, heat is supplied by a laser or hot gas, and pressure is applied with the help of a compaction roller. In the pultrusion process, heat is supplied by a heated die and pressure is caused by narrowing the die opening. During the solidification or curing process, a number of physical and mechanical phenomena occur in the composite material, 1 including: • Formation of a polymer structure, change in physical and mechan- ical properties, change in degree of cure or crystallinity, relaxational transitions (gelation and vitrification) 2 • Chemical and temperature shrinkage 3–5 • Stress and strain development 4–7 • Formation of kogesive defects and adhesive debonding 6,7 • Release of volatiles and void growth 8 7.4 Process Models for Selected Thermosets and Thermoplastics Processing For composites processing, various analytical models have been developed to simulate the resin flow, degree of cure (for thermosets) or crystallinity (for thermoplastics), degree of compaction and consolidation, residual stress, etc. © 2002 by CRC Press LLC • The processed part should have the lowest possible void content. • In the case of thermoset composites, the resin should be cured uniformly and completely. Uneven curing generates residual stress in the part. Similarly, for thermoplastic composites, uniform cool- ing should take place to avoid residual stress build-up. • The finished part should have minimum residual stress to mini- mize part distortion. Part distortion or uneven shrinkage may cause the part to go out of tolerance. • The complete process should be achieved in the shortest possible time. A shorter process cycle time provides higher production rate and lower production cost. • During the curing process of thermoset composites, the excess resin must be squeezed out from every ply and resin distribution must be uniform. Methods of applying heat and pressure are different in each manufacturing process. In the autoclave process, heat is supplied with the help of hot air or hot nitrogen gas inside the autoclave, and pressure is applied by vacuum bagging and by pressurizing the chamber with air. In the RTM process, pressure is controlled by injection pressure and heat is supplied by heating the mold. In the thermoplastic tape winding process, heat is supplied by a laser or hot gas, and pressure is applied with the help of a compaction roller. In the pultrusion process, heat is supplied by a heated die and pressure is caused by narrowing the die opening. During the solidification or curing process, a number of physical and mechanical phenomena occur in the composite material, 1 including: • Formation of a polymer structure, change in physical and mechan- ical properties, change in degree of cure or crystallinity, relaxational transitions (gelation and vitrification) 2 • Chemical and temperature shrinkage 3–5 • Stress and strain development 4–7 • Formation of kogesive defects and adhesive debonding 6,7 • Release of volatiles and void growth 8 7.4 Process Models for Selected Thermosets and Thermoplastics Processing For composites processing, various analytical models have been developed to simulate the resin flow, degree of cure (for thermosets) or crystallinity (for thermoplastics), degree of compaction and consolidation, residual stress, etc. . the part. Similarly, for thermoplastic composites, uniform cool- ing should take place to avoid residual stress build-up. • The finished part should have minimum residual stress to mini- mize part. debonding 6,7 • Release of volatiles and void growth 8 7.4 Process Models for Selected Thermosets and Thermoplastics Processing For composites processing, various analytical models have. The finished part should have minimum residual stress to mini- mize part distortion. Part distortion or uneven shrinkage may cause the part to go out of tolerance. • The complete process should