《纺织复合材料》课程参考文献（Fiber-Reinforced Composites，THIRD EDITION）05 Manufacturing

5 Manufacturing A key ingredient in the successful production application of a material or a component is a cost-effective and reliable manufacturing method.Cost- effectiveness depends largely on the rate of production,and reliability requires a uniform quality from part to part. The early manufacturing method for fiber-reinforced composite structural parts used a hand layup technique.Although hand layup is a reliable process,it is by nature very slow and labor-intensive.In recent years,particularly due to the interest generated in the automotive industry,there is more emphasis on the development of manufacturing methods that can support mass production rates.Compression molding,pultrusion,and filament winding represent three such manufacturing processes.Although they have existed for many years, investigations on their basic characteristics and process optimization started mostly in the mid-1970s.Resin transfer molding(RTM)is another manufac- turing process that has received significant attention in both aerospace and automotive industries for its ability to produce composite parts with complex shapes at relatively high production rates.With the introduction of automa- tion,fast-curing resins,new fiber forms,high-resolution quality control tools, and so on,the manufacturing technology for fiber-reinforced polymer compos- ites has advanced at a remarkably rapid pace. This chapter describes the basic characteristics of major manufacturing methods used in the fiber-reinforced polymer industry.Emphasis is given to process parameters and their relation to product quality.Quality inspection methods and cost issues are also discussed in this chapter. 5.1 FUNDAMENTALS Transformation of uncured or partially cured fiber-reinforced thermoset poly- mers into composite parts or structures involves curing the material at elevated temperatures and pressures for a predetermined length of time.High cure temperatures are required to initiate and sustain the chemical reaction that transforms the uncured or partially cured material into a fully cured solid.High pressures are used to provide the force needed for the flow of the highly viscous resin or fiber-resin mixture in the mold,as well as for the consolidation of individual unbonded plies into a bonded laminate.The magnitude of these two important process parameters,as well as their duration,significantly affects the 2007 by Taylor&Francis Group.LLC

5 Manufacturing A key ingredient in the successful production application of a material or a component is a cost-effective and reliable manufacturing method. Cost￾effectiveness depends largely on the rate of production, and reliability requires a uniform quality from part to part. The early manufacturing method for fiber-reinforced composite structural parts used a hand layup technique. Although hand layup is a reliable process, it is by nature very slow and labor-intensive. In recent years, particularly due to the interest generated in the automotive industry, there is more emphasis on the development of manufacturing methods that can support mass production rates. Compression molding, pultrusion, and filament winding represent three such manufacturing processes. Although they have existed for many years, investigations on their basic characteristics and process optimization started mostly in the mid-1970s. Resin transfer molding (RTM) is another manufac￾turing process that has received significant attention in both aerospace and automotive industries for its ability to produce composite parts with complex shapes at relatively high production rates. With the introduction of automa￾tion, fast-curing resins, new fiber forms, high-resolution quality control tools, and so on, the manufacturing technology for fiber-reinforced polymer compos￾ites has advanced at a remarkably rapid pace. This chapter describes the basic characteristics of major manufacturing methods used in the fiber-reinforced polymer industry. Emphasis is given to process parameters and their relation to product quality. Quality inspection methods and cost issues are also discussed in this chapter. 5.1 FUNDAMENTALS Transformation of uncured or partially cured fiber-reinforced thermoset poly￾mers into composite parts or structures involves curing the material at elevated temperatures and pressures for a predetermined length of time. High cure temperatures are required to initiate and sustain the chemical reaction that transforms the uncured or partially cured material into a fully cured solid. High pressures are used to provide the force needed for the flow of the highly viscous resin or fiber–resin mixture in the mold, as well as for the consolidation of individual unbonded plies into a bonded laminate. The magnitude of these two important process parameters, as well as their duration, significantly affects the
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quality and performance of the molded product.The length of time required to properly cure a part is called the cure cycle.Since the cure cycle determines the production rate for a part,it is desirable to achieve the proper cure in the shortest amount of time.It should be noted that the cure cycle depends on a number of factors,including resin chemistry,catalyst reactivity,cure tempera- ture,and the presence of inhibitors or accelerators. 5.1.1 DEGREE OF CURE A number of investigators [1-3]have experimentally measured the heat evolved in a curing reaction and related it to the degree of cure achieved at any time during the curing process.Experiments are performed in a differential scanning calorimeter (DSC)in which a small sample,weighing a few milligrams,is heated either isothermally (i.e.,at constant temperature)or dynamically (i.e., with uniformly increasing temperature).The instrumentation in DSC monitors the rate of heat generation as a function of time and records it.Figure 5.1 schematically illustrates the rate of heat generation curves for isothermal and dynamic heating. The total heat generation to complete a curing reaction (i.e.,100%degree of cure)is equal to the area under the rate of heat generation-time curve obtained in a dynamic heating experiment.It is expressed as dt. (5.1) where HR heat of reaction (do/dt)d rate of heat generation in a dynamic experiment le =time required to complete the reaction H 0 Time Time (a) (b) FIGURE 5.1 Schematic representation of the rate of heat generation in (a)dynamic and (b)isothermal heating of a thermoset polymer in a differential scanning calorimeter(DSC). 2007 by Taylor Francis Group,LLC

quality and performance of the molded product. The length of time required to properly cure a part is called the cure cycle. Since the cure cycle determines the production rate for a part, it is desirable to achieve the proper cure in the shortest amount of time. It should be noted that the cure cycle depends on a number of factors, including resin chemistry, catalyst reactivity, cure tempera￾ture, and the presence of inhibitors or accelerators. 5.1.1 DEGREE OF CURE A number of investigators [1–3] have experimentally measured the heat evolved in a curing reaction and related it to the degree of cure achieved at any time during the curing process. Experiments are performed in a differential scanning calorimeter (DSC) in which a small sample, weighing a few milligrams, is heated either isothermally (i.e., at constant temperature) or dynamically (i.e., with uniformly increasing temperature). The instrumentation in DSC monitors the rate of heat generation as a function of time and records it. Figure 5.1 schematically illustrates the rate of heat generation curves for isothermal and dynamic heating. The total heat generation to complete a curing reaction (i.e., 100% degree of cure) is equal to the area under the rate of heat generation–time curve obtained in a dynamic heating experiment. It is expressed as HR ¼ ðtf 0 dQ dt d dt, (5:1) where HR ¼ heat of reaction (dQ=dt)d ¼ rate of heat generation in a dynamic experiment tf ¼ time required to complete the reaction HR Rate of heat generation Rate of heat generation 0 H (b) t Time 0 tf (a) Time FIGURE 5.1 Schematic representation of the rate of heat generation in (a) dynamic and (b) isothermal heating of a thermoset polymer in a differential scanning calorimeter (DSC).
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The amount of heat released in time t at a constant curing temperature T is determined from isothermal experiments.The area under the rate of heat generation-time curve obtained in an isothermal experiment is expressed as H=a} (5.2) where H is the amount of heat released in time t and (do/dt);is the rate of heat generation in an isothermal experiment conducted at a constant temperature T. The degree of cure ac at any time t is defined as H dc= (5.3) HR Figure 5.2 shows a number of curves relating the degree of cure ac to cure time for a vinyl ester resin at various cure temperatures.From this figure,it can be seen that ac increases with both time and temperature;however,the rate of cure,dac/dt,is decreased as the degree of cure attains asymptotically a max- imum value.If the cure temperature is too low,the degree of cure may not reach a 100%level for any reasonable length of time.The rate of cure dac/dt, obtained from the slope of ac vs.t curve and plotted in Figure 5.3,exhibits 0.8 65℃ 0.6 5✉回SD 6 0.4 4AA△△△bP50C 1 35C 0.2 000 00 0 .1 1 10 100 Cure time(min) FIGURE 5.2 Degree of cure for a vinyl ester resin at various cure temperatures.(After Han,C.D.and Lem,K.W.,J.Appl.Polym.Sci.,29,1878,1984.) 2007 by Taylor&Francis Group.LLC

The amount of heat released in time t at a constant curing temperature T is determined from isothermal experiments. The area under the rate of heat generation–time curve obtained in an isothermal experiment is expressed as H ¼ ðt 0 dQ dt i dt, (5:2) where H is the amount of heat released in time t and (dQ=dt)i is the rate of heat generation in an isothermal experiment conducted at a constant temperature T. The degree of cure ac at any time t is defined as ac ¼ H HR : (5:3) Figure 5.2 shows a number of curves relating the degree of cure ac to cure time for a vinyl ester resin at various cure temperatures. From this figure, it can be seen that ac increases with both time and temperature; however, the rate of cure, dac=dt, is decreased as the degree of cure attains asymptotically a max￾imum value. If the cure temperature is too low, the degree of cure may not reach a 100% level for any reasonable length of time. The rate of cure dac=dt, obtained from the slope of ac vs. t curve and plotted in Figure 5.3, exhibits 65C 60C 50C 45C 40C 35C 0 0 .2 0 .4 0 .6 0 .8 Degree of cure Cure time (min) 0.1 1 10 100 FIGURE 5.2 Degree of cure for a vinyl ester resin at various cure temperatures. (After Han, C.D. and Lem, K.W., J. Appl. Polym. Sci., 29, 1878, 1984.)
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0.7 0.6 65℃ 0.5 ⊙ ⊙ 60C 0.4 50℃ 0.3 ⊙ 0.2 45C 40C 0.1 35C A 0.0 0 0.2 0.40.6 0.8 1.0 Degree of cure (ac) FIGURE 5.3 Rate of cure for a vinyl ester resin at various cure temperatures.(After Han,C.D.and Lem,K.W.,J.Appl.Polym.Sci.,29,1878,1984.) a maximum value at 10%-40%of the total cure achieved.Higher cure temperatures increase the rate of cure and produce the maximum degree of cure in shorter periods of time.On the other hand,the addition of a low-profile agent,such as a thermoplastic polymer,to a polyester or a vinyl ester resin decreases the cure rate. Kamal and Sourour [4]have proposed the following expression for the isothermal cure rate of a thermoset resin: dae=(k+kzae)(1-ae)", (5.4) dt where k and k2 are reaction rate constants and m and n are constants describ- ing the order of reaction.The parameters m and n do not vary significantly with the cure temperature,but k and k2 depend strongly on the cure temperature. With the assumption of a second-order reaction (i.e.,m+n=2),Equation 5.4 has been used to describe the isothermal cure kinetics of epoxy,unsaturated polyester,and vinyl ester resins.The values of k1,k2,m,and n are determined by nonlinear least-squares curve fit to the dac/dt vs.ac data.Typical values of these constants for a number of resins are listed in Table 5.1. 2007 by Taylor Francis Group,LLC

a maximum value at 10%–40% of the total cure achieved. Higher cure temperatures increase the rate of cure and produce the maximum degree of cure in shorter periods of time. On the other hand, the addition of a low-profile agent, such as a thermoplastic polymer, to a polyester or a vinyl ester resin decreases the cure rate. Kamal and Sourour [4] have proposed the following expression for the isothermal cure rate of a thermoset resin: dac dt ¼ (k1 þ k2am c )(1 ac) n , (5:4) where k1 and k2 are reaction rate constants and m and n are constants describ￾ing the order of reaction. The parameters m and n do not vary significantly with the cure temperature, but k1 and k2 depend strongly on the cure temperature. With the assumption of a second-order reaction (i.e., m þ n ¼ 2), Equation 5.4 has been used to describe the isothermal cure kinetics of epoxy, unsaturated polyester, and vinyl ester resins. The values of k1, k2, m, and n are determined by nonlinear least-squares curve fit to the dac=dt vs. ac data. Typical values of these constants for a number of resins are listed in Table 5.1. 65C 60C 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 0.2 0.4 0.6 Degree of cure (ac) 0.8 1.0 50C 45C 40C 35C Rate of cure ( ac) (per minute) FIGURE 5.3 Rate of cure for a vinyl ester resin at various cure temperatures. (After Han, C.D. and Lem, K.W., J. Appl. Polym. Sci., 29, 1878, 1984.)
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TABLE 5.1 Kinetic Parameters for Various Resin Systems Kinetic Parameters in Equation 5.4 Temperature, Resin ℃(F) k (per min) k2 (per min) m n Polyester 45(113) 0.0131 0.351 0.23 1.77 60(140) 0.0924 1.57 0.40 1.60 Low-profile polyester 45(113) 0.0084 0.144 0.27 1.73 (with 20%polyvinyl 60(140) 0.0264 0.282 0.27 1.73 acetate) Vinyl ester 45(113) 0.0073 0.219 0.33 1.76 60(140) 0.0624 1.59 0.49 1.51 Source:Adapted from Lem,K.W.and Han,C.D.,Polym.Eng.Sci.,24,175,1984. 5.1.2 VisCOsITY Viscosity of a fluid is a measure of its resistance to flow under shear stresses. Low-molecular-weight fluids,such as water and motor oil,have low viscosities and flow readily.High-molecular-weight fluids,such as polymer melts,have high viscosities and flow only under high stresses. The two most important factors determining the viscosity of a fluid are the temperature and shear rate.For all fluids,the viscosity decreases with increas- ing temperature.Shear rate does not have any influence on the viscosity of low- molecular-weight fluids,whereas it tends to either increase (shear thickening) or decrease (shear thinning)the viscosity of a high-molecular-weight fluids (Figure 5.4).Polymer melts,in general,are shear-thinning fluids since their viscosity decreases with increasing intensity of shearing. The starting material for a thermoset resin is a low-viscosity fluid.However, its viscosity increases with curing and approaches a very large value as it transforms into a solid mass.Variation of viscosity during isothermal curing of an epoxy resin is shown in Figure 5.5.Similar viscosity-time curves are also observed for polyester [3]and vinyl ester [5]resins.In all cases,the viscosity increases with increasing cure time and temperature.The rate of viscosity increase is low at the early stage of curing.After a threshold degree of cure is achieved,the resin viscosity increases at a very rapid rate.The time at which this occurs is called the gel time.The gel time is an important molding parameter,since the flow of resin in the mold becomes increasingly difficult at the end of this time period. A number of important observations can be made from the viscosity data reported in the literature: 2007 by Taylor&Francis Group.LLC

5.1.2 VISCOSITY Viscosity of a fluid is a measure of its resistance to flow under shear stresses. Low-molecular-weight fluids, such as water and motor oil, have low viscosities and flow readily. High-molecular-weight fluids, such as polymer melts, have high viscosities and flow only under high stresses. The two most important factors determining the viscosity of a fluid are the temperature and shear rate. For all fluids, the viscosity decreases with increas￾ing temperature. Shear rate does not have any influence on the viscosity of low￾molecular-weight fluids, whereas it tends to either increase (shear thickening) or decrease (shear thinning) the viscosity of a high-molecular-weight fluids (Figure 5.4). Polymer melts, in general, are shear-thinning fluids since their viscosity decreases with increasing intensity of shearing. The starting material for a thermoset resin is a low-viscosity fluid. However, its viscosity increases with curing and approaches a very large value as it transforms into a solid mass. Variation of viscosity during isothermal curing of an epoxy resin is shown in Figure 5.5. Similar viscosity–time curves are also observed for polyester [3] and vinyl ester [5] resins. In all cases, the viscosity increases with increasing cure time and temperature. The rate of viscosity increase is low at the early stage of curing. After a threshold degree of cure is achieved, the resin viscosity increases at a very rapid rate. The time at which this occurs is called the gel time. The gel time is an important molding parameter, since the flow of resin in the mold becomes increasingly difficult at the end of this time period. A number of important observations can be made from the viscosity data reported in the literature: TABLE 5.1 Kinetic Parameters for Various Resin Systems Resin Temperature, 8C (8F) Kinetic Parameters in Equation 5.4 k1 (per min) k2 (per min) m n Polyester 45 (113) 0.0131 0.351 0.23 1.77 60 (140) 0.0924 1.57 0.40 1.60 Low-profile polyester (with 20% polyvinyl acetate) 45 (113) 0.0084 0.144 0.27 1.73 60 (140) 0.0264 0.282 0.27 1.73 Vinyl ester 45 (113) 0.0073 0.219 0.33 1.76 60 (140) 0.0624 1.59 0.49 1.51 Source: Adapted from Lem, K.W. and Han, C.D., Polym. Eng. Sci., 24, 175, 1984.
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