1. 4 Constituent Properties properties of the constituent materials. As a starting point, the basic propertiesthe The mechanical properties of a composite material are determined by commonly used constituents in composite material construction are discussed 1.4.1 MATRIX PROPERTIES The matrix represents the binding material of the composite, which supports and protects the fibers. It also provides a mechanism for the transfer of loads in the event of fiber breakage. Typically, the matrix has a lower density, stiffness and strength than the fibers. The response characteristics for polymeric matrix materials are usually viscoelastic or viscoplastic and therefore the matrix is affected by time, temperature and moisture. Indeed, the stress-strain response of polymeric matrices is influenced by all these factors. A summary tabulation of the properties of typical polymeric matrices is included in Table 1.2 below, and Table 13 provides properties of some structural matrix materlals TABLE 1.2 Typical Matrix Properties Material Density E. Ec or (GPa)(GPa) (MPa) (MPa) (106/C) Polyester 1200.2.5-40 45901002500.37-100-200 1400 0.40 Epoxy 1100.3.0-5.5 40-1001002000.38-45-65 1350 0.40 NARMCO238712103.3838629158 1400 Polyethelene 960 120 In Table 1.2, Er and Ec are the tensile and compressive moduli of elasticity respectively, or and oc are the ultimate strengths, v is the Poissons ratio and a is the coefficient of thermal expansion
8 1.4 Constituent Properties The mechanical properties of a composite material are determined by the properties of the constituent materials. As a starting point, the basic properties of commonly used constituents in composite material construction are discussed. 1.4.1 MATRIX PROPERTIES The matrix represents the binding material of the composite, which supports and protects the fibers. It also provides a mechanism for the transfer of loads in the event of fiber breakage. Typically, the matrix has a lower density, stiffness and strength than the fibers. The response characteristics for polymeric matrix materials are usually viscoelastic or viscoplastic and therefore the matrix is affected by time, temperature and moisture. Indeed, the stress-strain response of polymeric matrices is influenced by all these factors. A summary tabulation of the properties of typical polymeric matrices is included in Table 1.2 below, and Table 1.3 provides properties of some structural matrix materials. In Table 1.2, and are the tensile and compressive moduli of elasticity respectively, and are the ultimate strengths, is the Poisson’s ratio and is the coefficient of thermal expansion
TABLE 1.3. Typical Structural Matrix Resins Tensile Strength Tensile Modulus T(K)* (GPa) Thermosets Epoxy (TSMDa) 4.1 Bismaleimide 4.1 547 4.8 Thermoplastics Polyhenylene sulfide 65.5 4.3 366(555mp) Polyetheretherketone Glass Transition Temperature 1.4.2 FIBER PROPERTIES Reinforcement of the matrix, to provide the majority of the stren of a composite is accomplished by the fibers, which carry the majority of the loading and which inherently have superior properties to the bulk fiber material. The fiber can be of one of the following ty Metallic Mineral Fibers, as used for reinforcement, can also be classified according to their geometrical properties. For reinforcement in a composite, characteristic fiber dimensions are seen below. Fibers Whiskers Length 5 mm (20)inches >100×dia 10×dia. Cross Sectional Area 1975×103mm2 (3.6×10in2) Diameter 5 mm A typical demand curve for carbon fibres is shown in Figure 1.5[1] Numbers in brackets refer to references at the end of the Chapter
9 1.4.2 FIBER PROPERTIES Reinforcement of the matrix, to provide the majority of the strength and stiffness of a composite is accomplished by the fibers, which carry the majority of the loading and which inherently have superior properties to the bulk fiber material. The fiber can be of one of the following types: Organic Metallic Synthetic Mineral Fibers, as used for reinforcement, can also be classified according to their geometrical properties. For reinforcement in a composite, characteristic fiber dimensions are seen below: * Numbers in brackets refer to references at the end of the Chapter. A typical demand curve for carbon fibres is shown in Figure 1.5[1]*
CF Demand 21D5m神pPdc的 ” aze Cited PAN De CF adopted at pimary c继m电(198 5 ben Fbe sh。 5时; 96019551970195198019851991995200。2005 183 C给? he intAn献Exp1 ch Adjs! Tne S:Ma! FIGURE 1.5. Demand for Carbon Fiber 1971-2005
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1.5 Composite Manufacturing, Fabrication and Processing Composite fabrication can be considered to be related to three ba nanufacturing techniques shown in Table 1. 4 TABLE 14. Basic Manufacturing Techniqe Description Limitations Laminating Material, usually in form of reinforcing cloth, High tool and die paper, foil, metal, wood, glass fiber, plastic, costs. Limited to etc,preimpregnated or coated with thermoset simple shapes and resin(sometimes a thermoplastic) is molded cross section under pressure greater than 6895 kPa into sheet, rod, tube or other simple shapes Excellent dimensional stability of finished product; very economical in large production of parts. Pultrusion This process is similar to profile extrusion, Close tolerance however, it does not provide flexibility and control requires uniformity of product control, and automation Used for continuous production of simple Unidirectional shapes(rods, tubes and angles) principally ength usually incorporating fiberglass or other reinforcement. the rule High output possible. Filament Excellent strength-to-weight ratio. Continuous, Limited to shapes of windIn reinforced filaments, usually glass, in the form positive curvature; of roving are saturated with resin and machine openings and wound onto mandrels having shape of desired holes can reduce finished part. Once winding is completed, part strength if not and mandrel are cured; mandrel can then be properly designed removed through porthole at end of wound into molding oriented precisely in direction where strength is operat part. High strength reinforcements can be required. Good uniformity of resin distribution in finished part; mainly circular objects such as ressure bottles, pipes and rocket cases. Comparisons of various composite manufacturing processes are shown in Table 1.5(a) and (b)
11 1.5 Composite Manufacturing, Fabrication and Processing Composite fabrication can be considered to be related to three basic manufacturing techniques shown in Table 1.4. Comparisons of various composite manufacturing processes are shown in Table 1.5(a) and (b)
TABLE 1.5(a). Comparison of FRP Composite Manufacturing Processes, Production Factors (adapted from Wittman and Shook, 198 Hand L LHH M LHH LRO Tape Lay-up(Manual) Tape Lay-up(Automated)HH Vacuum Bag Moulding(Wet L M M HHLR Autoclave Moulding(Tape M M H Filament Winding Compression MouldingHHH MHHRC Resin Transfer Moulding MH RC ng MouldingHH LHH Stitched/ Thermoform MM Preforms Random Fibre Preforms 3-D Woven/Braided Preforms IHMIHHTHHIC Legend: H-high
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