Processing of Composite Laminates The processing of polymer matrix composite laminates has been the subject of considerable research during the last two decades [1-11].Multiple physical and chemical phenomena must occur simultaneously and in the proper sequence to achieve desired laminate properties.There are several routes to achieve full consolidation and minimize void content of a polymeric matrix with a reinforcing fiber in volume fractions(50 to 60%)appropriate for structural applications.The most widely accepted approach is by impregna- tion of unidirectional fibers or textile fabrics to create a thin sheet or tape.If the polymer is a thermoset,it is often advanced in its curing state to the B stage(a state of cure of the matrix that is incomplete,but provides high room temperature viscosity of the prepreg).Known as prepreg in this form, it may be stored at low temperature (below freezing)to greatly reduce the rate of cure and thus increase the storage life.After being warmed to room temperature,these prepreg sheets or tapes may then be assembled into a laminate and subjected to a cure cycle. It is also possible to assemble dry fibers into an appropriate geometric form,and then impregnate the entire laminate in a single step.This approach is known as resin transfer molding (RTM),and there are several variations. The weaving of a fabric from reinforcing fibers is a widely accepted approach to creating the fiber preform,although there are other techniques designed to avoid fiber crimp and develop microstructures typical of that achieved with prepreg tape. For prepreg,heat and pressure are first applied to the laminate to reduce the viscosity of the polymer matrix,and achieve full densification of the laminate and coalescence of the laminae through matrix flow.The application of heat to the laminate is governed by the laws of heat transfer and is therefore a time-dependent phenomenon.Further,the pressure in the lami- nate is shared by the polymeric matrix and the fibers.For thermosetting polymers,the kinetic process to achieve gelation and vitrification is a themo- chemical process that is often exothermic.The decrease in polymer viscosity with temperature and its increase with degree of cure for theromsets requires that the necessary flow be achieved prior to gelation or vitrification.For thermoplastic polymers the process involves both viscosity changes and changes in the polymer morphology(degree of crystallinity).Thermoplastic ©2003 by CRC Press LLC3 Processing of Composite Laminates The processing of polymer matrix composite laminates has been the subject of considerable research during the last two decades [1–11]. Multiple physical and chemical phenomena must occur simultaneously and in the proper sequence to achieve desired laminate properties. There are several routes to achieve full consolidation and minimize void content of a polymeric matrix with a reinforcing fiber in volume fractions (50 to 60%) appropriate for structural applications. The most widely accepted approach is by impregna￾tion of unidirectional fibers or textile fabrics to create a thin sheet or tape. If the polymer is a thermoset, it is often advanced in its curing state to the B stage (a state of cure of the matrix that is incomplete, but provides high room temperature viscosity of the prepreg). Known as prepreg in this form, it may be stored at low temperature (below freezing) to greatly reduce the rate of cure and thus increase the storage life. After being warmed to room temperature, these prepreg sheets or tapes may then be assembled into a laminate and subjected to a cure cycle. It is also possible to assemble dry fibers into an appropriate geometric form, and then impregnate the entire laminate in a single step. This approach is known as resin transfer molding (RTM), and there are several variations. The weaving of a fabric from reinforcing fibers is a widely accepted approach to creating the fiber preform, although there are other techniques designed to avoid fiber crimp and develop microstructures typical of that achieved with prepreg tape. For prepreg, heat and pressure are first applied to the laminate to reduce the viscosity of the polymer matrix, and achieve full densification of the laminate and coalescence of the laminae through matrix flow. The application of heat to the laminate is governed by the laws of heat transfer and is therefore a time-dependent phenomenon. Further, the pressure in the lami￾nate is shared by the polymeric matrix and the fibers. For thermosetting polymers, the kinetic process to achieve gelation and vitrification is a themo￾chemical process that is often exothermic. The decrease in polymer viscosity with temperature and its increase with degree of cure for theromsets requires that the necessary flow be achieved prior to gelation or vitrification. For thermoplastic polymers the process involves both viscosity changes and changes in the polymer morphology (degree of crystallinity). Thermoplastic TX001_ch03_Frame Page 37 Saturday, September 21, 2002 4:51 AM © 2003 by CRC Press LLC