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Introduction to Composites: Materials Science Presentation
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C CINEC CAMPUS Beyond A Graduate ME4327 - Product Realisation & Materials Introduction to Composites T.S.Peiris. 1 Do we know these? McDonnell Douglas F-15 Eagle Early 1970s 2% Composites Boeing F/A-18E/F Super Hornet Late 1990s 21% Composites McDonnell Douglas F/A-18 Hornet Mid 1970s 10% Composites Lockheed Martin F-22 Raptor 2005 24% Composites McDonnell Douglas AV-8B Harrier Early 1980s 27% Composites Lockheed Martin F-35 Lightning II 2015 2 35% Composites Do we know these? Boeing 787 Dreamliner 50% Composites Airbus A350-900 52% Composites 3 Marine/Offshore Applications Tubulars in oil & gas industry Wind turbines - Siemens SG-14-222 DD 4 Transportation & Motor Sport Applications Mercedes F1 W06 Hybrid (900 hp & 700kg) 5 Sporting Applications Space Applications 6 Outline • Introduction • Classification • Particle-Reinforced Composites • Fiber-Reinforced Composites 7 Introduction to Composites • Combination of two or more materials – results in better properties than those of the individual components used alone • Unlike metallic alloys, each material retains its separate chemical, physical, and mechanical properties • The two constituents • Matrix • Reinforcement • Main advantages • high strength and stiffness • low density 8 Introduction to Composites – Cont. • In general - reinforcement is harder, stronger, and stiffer than the matrix • In general - reinforcement • Fiber • Particulate • Particulate Composites • weaker and less stiff than continuous fiber composites • usually much less expensive • Particulate reinforced composites usually contain less reinforcement (up to 40 to 50 volume percent) due to processing difficulties and brittleness 9 Terminology/Classification woven fibers • Matrix: -- Purposes are to: - transfer stress to reinforcement - protect reinforcement from environment 0.5 mm -- Types: MMC, CMC, PMC metal ceramic polymer cross section view • Reinforcement : -- Purpose: MMC: increase sy, TS, creep resist. CMC: increase KIc PMC: increase E, sy, TS, creep resist. -- Types: particle, fiber, structural 0.5 mm Reprinted with permission from D. Hull and T.W. Clyne, An Introduction to Composite Materials, 2nd ed., Cambridge University Press, New York, 1996, Fig. 3.6, p. 47. 10 Classification of Composites Composites Particle-reinforced Largeparticle Dispersionstrengthened Fiber-reinforced Continuous (aligned) Structural Discontinuous (short) Aligned Randomly oriented Laminates Sandwich panels Adapted from Fig. 16.2, Callister & Rethwisch 8e. 11 Classification: Particle-Reinforced Particle-reinforced • Examples: - Spheroidite matrix: ferrite () steel Fiber-reinforced (ductile) 60 m - WC/Co cemented carbide matrix: cobalt (ductile, toug: h) Structural particles: cementite (Fe C) 3 (brittle) particles: WC (brittle, hard) 600 m - Automobile matrix: tire rubber rubber (compliant) 0.75 m particles: carbon black (stiff) Adapted from Fig. 10.19, Callister & Rethwisch 8e. (Fig. 10.19 is copyright United States Steel Corporation, 1971.) Adapted from Fig. 16.4, Callister & Rethwisch 8e. (Fig. 16.4 is courtesy Carboloy Systems, Department, General Electric Company.) Adapted from Fig. 16.5, Callister & Rethwisch 8e. (Fig. 16.5 is courtesy Goodyear Tire and Rubber Company.) 12 Classification: Particle-Reinforced Particle-reinforced Fiber-reinforced Structural Concrete – gravel + sand + cement + water - Why sand and gravel? Sand fills voids between gravel particles Reinforced concrete – Reinforce with steel rebar or remesh - increases strength - even if cement matrix is cracked Prestressed concrete - Rebar/remesh placed under tension during setting of concrete - Release of tension after setting places concrete in a state of compression - To fracture concrete, applied tensile stress must exceed this compressive stress Posttensioning – tighten nuts to place concrete under compression threaded rod nut 13 Classification: Particle-Reinforced Particle-reinforced Fiber-reinforced Structural • Elastic modulus, Ec, of composites: -- two “rule of mixture” extremes: upper limit: Ec = VmEm + VpEp E(GPa) 350 Data: Cu matrix 30 0 w/tungsten 250 particles 20 0 150 0 lower limit: 1 Vm Vp = + Ec Em Ep 20 40 60 80 (Cu) Adapted from Fig. 16.3, Callister & Rethwisch 8e. (Fig. 16.3 is from R.H. Krock, ASTM Proc, Vol. 63, 1963.) 10 0 vol% tungsten (W) • Application to other properties: -- Electrical conductivity, e: Replace E’s in equations with e’s. -- Thermal conductivity, k: Replace E’s in equations with k’s. 14 Example upper limit: E c = Vm E m + Vp E p E(GPa) 350 Data: 30 0 Cu matrix w/tungsten 250 particles 20 0 150 lower limit: 1 Vm Vp = + Ec Em Ep 0 (Cu) 20 4 0 6 0 8 0 10 0 vol% tungsten (W) 15 Classification: Fiber-Reinforced Particle-reinforced • Fiber-reinforced Structural Fibers very strong in tension – Provide significant strength improvement to the composite – Ex: fiber-glass - continuous glass filaments in a polymer matrix • Glass fibers – strength and stiffness • Polymer matrix – holds fibers in place – protects fiber surfaces – transfers load to fibers 16 Classification: Fiber-Reinforced Particle-reinforced • Fiber-reinforced Structural Fiber Types – Whiskers - thin single crystals - large length to diameter ratios • graphite, silicon nitride, silicon carbide • high crystal perfection – extremely strong, strongest known • very expensive and difficult to disperse – Fibers • polycrystalline or amorphous • generally polymers or ceramics • Ex: alumina, aramid (/Kevlar®), E-glass, boron, UHMWPE – Wires • metals – steel, molybdenum, tungsten 17 Longitudinal direction Fiber Alignment Adapted from Fig. 16.8, Callister & Rethwisch 8e. Transverse direction aligned continuous aligned random discontinuous 18 Classification: Fiber-Reinforced Particle-reinforced • Aligned Continuous fibers • Examples: Fiber-reinforced Structural -- Metal: g'(Ni3Al)-a(Mo) -- Ceramic: Glass w/SiC fibers matrix: a (Mo-Molybdenum) (ductile) formed by glass slurry Eglass = 76 GPa; ESiC = 400 GPa. by eutectic solidification. (a) 2 mm fibers: g ’ (Ni3Al – Nickel Aluminide) (brittle) From W. Funk and E. Blank, “Creep deformation of Ni3Al-Mo in-situ composites", Metall. Trans. A Vol. 19(4), pp. 987-998, 1988. Used with permission. (b) fracture surface From F.L. Matthews and R.L. Rawlings, Composite Materials; Engineering and Science, Reprint ed., CRC Press, Boca Raton, FL, 2000. (a) Fig. 4.22, p. 145 (photo by J. Davies); (b) Fig. 11.20, p. 349 (micrograph by H.S. Kim, P.S. Rodgers, and R.D. Rawlings). Used with permission of CRC Press, Boca Raton, FL. 19 Classification: Fiber-Reinforced Particle-reinforced Fiber-reinforced • Discontinuous fibers, random in 2 dimensions • Example: Carbon-Carbon -- fabrication process: - carbon fibers embedded in polymer resin matrix, - polymer resin pyrolyzed at up to 2500ºC. -- uses: disk brakes, gas turbine exhaust flaps, missile nose cones. (b) 500 m view onto plane (a) Structural C fibers: very stiff very strong C matrix: less stiff less strong fibers lie in plane • Other possibilities: -- Discontinuous, random 3D -- Discontinuous, aligned Adapted from F.L. Matthews and R.L. Rawlings, Composite Materials; Engineering and Science, Reprint ed., CRC Press, Boca Raton, FL, 2000. (a) Fig. 4.24(a), p. 151; (b) Fig. 4.24(b) p. 151. (Courtesy I.J. Davies) Reproduced with permission of CRC Press, Boca Raton, FL. 20 Classification: Fiber-Reinforced Influence of Fiber Length • The mechanical characteristics depend on: • properties of the fiber • degree to which an applied load is transmitted to the fibers by the matrix phase • interfacial bond between the fiber and matrix phases 21 Classification: Fiber-Reinforced Influence of Fiber Length • Deformation pattern in the matrix surrounding the fiber • Critical fiber length is necessary for effective strengthening and stiffening of the composite • Critical length is dependent on • fiber diameter d • fiber ultimate (or tensile) strength • fiber–matrix bond strength (or the shear yield strength of the matrix, whichever is smaller) 22 Classification: Fiber-Reinforced Influence of Fiber Length • Critical fiber length for effective stiffening & strengthening: fiber ultimate tensile strength d fiber length f2c fiber diameter shear strength of fiber-matrix interface • Critical length is on the order of 1 mm, which ranges between 20 and 150 times the fiber diameter 23 Classification: Fiber-Reinforced Influence of Fiber Length • Ex: For fiberglass, common fiber length > 15 mm needed • For longer fibers, stress transference from matrix is more efficient Short, thick fibers: Long, thin fibers: f f fiber length fiber length Low fiber efficiency d2c d2c High fiber efficiency 24 When fiber length is equal to the critical length 25 When fiber length is greater than the critical length 26 When fiber length is less than the critical length 27 Classification: Fiber-Reinforced Influence of Fiber Orientation and Concentration • With respect to orientation – two extremes (1) a parallel alignment of the longitudinal axis of the fibers in a single direction (2) a totally random alignment • Continuous fibers are normally aligned (𝑙 > 15��� ) • Discontinuous fibers may be aligned, randomly oriented or partially oriented (a) Continuous and aligned, (b) Discontinuous and aligned, and (c) Discontinuous and randomly oriented fiber-reinforced composites 28 Classification: Fiber-Reinforced Stress-strain Behaviour of Fiber and Matrix brittle ductile 29 Classification: Fiber-Reinforced Stress-strain Behaviour of Aligned Fiber Composite 30 Question: Explain why composite failure is not catastrophic? • Not all fibers fracture at the same time, since there will always be considerable variations in the fracture strength of brittle fiber materials • Even after fiber failure, the matrix is still in plastic region • Fractured fibers, which are shorter than the original ones, are still embedded within the intact matrix, and are capable of carrying a load (lower than previous) as the matrix continues to plastically deform 31 Classification: Fiber-Reinforced Elastic Behaviour of continuous fiber reinforced composites – Longitudinal Loading • Assumption – bond between the fiber and matrix is good • Hence, deformation of both matrix and fibers is the same (an isostrain situation i.e., �� ��� = ��� = 𝜀𝑓 = ) �� = load sustained by the �� composite �� = load sustained by the matrix �𝑓 = load sustained by the fiber �� = �� + 32 Classification: Fiber-Reinforced Elastic Behaviour of continuous fiber reinforced composites – Longitudinal Loading 𝐴� , 𝐴� , and 𝐴𝑓 = respective cross sectional area 𝜎� , 𝜎� , and 𝜎𝑓 = respective � stresses � � � 𝜎� 𝐴� = 𝜎� 𝐴� + 𝜎𝑓 𝐴𝑐 𝐴𝑐 𝐴𝑓 𝐴 � 𝐴𝑓 𝜎� = 𝐴 𝜎� + 𝐴 𝜎𝑓 • and are respective area fractions for the matrix Classification: Fiber-Reinforced Elastic Behaviour of continuous fiber reinforced composites – Longitudinal Loading • Since ��� = ��� = 𝜀𝑓 � � � where, 𝑓 � � 𝜎� 𝑉 𝜀𝑓 + 𝜎� = � � � �� � � = 𝑉� �� + 𝑉 𝜎𝑓 𝑉 𝑓 �𝑓 ��� = Elastic modulus of the composite in the longitudial direction 𝑉� + = 𝑉𝑓 = 1 • It also could be shown that 34 Classification: Fiber-Reinforced Elastic Behaviour of continuous fiber reinforced composites – Longitudinal Loading Example 1 A continuous and aligned glass fiber-reinforced composite consists of 40 vol% of glass fibers having a modulus of elasticity of 69 GPa and 60 vol% of a polyester resin that, when hardened, displays a modulus of 3.4 GPa. (a) Compute the modulus of elasticity of this composite in the longitudinal direction. (b) If the cross-sectional area is 250 mm2 and a stress of 50 MPa is applied in this longitudinal direction, compute the magnitude of the load carried by each of the fiber and matrix phases. (c) Determine the strain that is sustained by each phase when the stress in part (b) is applied. 35 Classification: Fiber-Reinforced Elastic Behaviour of continuous fiber reinforced composites – Transverse Loading • Composite, matrix phase and the fiber phase are subjected to the same stress (isostress condition. i.e., 𝜎� = 𝜎� = 𝜎𝑓 = ) �� • Strain on the entire composite ��� ��� = ��� 𝑉� 𝐸 • Since 𝜀= 𝜎 + 𝜀𝑓 𝑉𝑓 � � �𝑡 � � 𝜎� = 𝜎� 𝑉 = + 𝜎𝑓 𝑉 � 𝑓 𝑓 + 36 Classification: Fiber-Reinforced Elastic Behaviour of continuous fiber reinforced composites – Transverse Loading 1 = 𝑉� + 𝑉𝑓 • This reduces to ���� �� ���� = � +𝑉 �𝑉 𝑓 � �� �𝑓 � 𝑓 37 Classification: Fiber-Reinforced Elastic Behaviour of continuous fiber reinforced composites – Transverse Loading Example 2 A continuous and aligned glass fiber-reinforced composite consists of 40 vol% of glass fibers having a modulus of elasticity of 69 GPa and 60 vol% of a polyester resin that, when hardened, displays a modulus of 3.4 GPa. Compute the modulus of elasticity of this composite assuming that the load is applied transversely. 38 Classification: Fiber-Reinforced Longitudinal tensile strength of continuous fiber reinforced composites (i.e., Fiber fails before matrix) • Usually, 𝜖𝑓 < ∗ ∗ �� brittle ductile • Once the fibers have fractured, the majority of the � load that was borne by the fibers is now transferred to the matrix 𝜎 � � ∗ ′ � =𝜎 𝑉 𝑓 𝑓 + 𝜎 ∗𝑉 � 39 Classification: Fiber-Reinforced Transverse tensile strength of continuous fiber reinforced composites • The strengths of continuous and unidirectional fibrous composites are highly anisotropic • Composites are normally designed to be loaded along the high strength, longitudinal direction • However, during in-service applications transverse tensile loads may also be present • Under these circumstances, premature failure may result inasmuch as transverse strength is usually extremely low—it sometimes lies below the tensile strength of the matrix • Longitudinal strength is dominated by fiber strength • Transverse strength depends on a few factors • Properties of both the fiber and matrix • Fiber-matrix bond strength • Presence of voids 40 Classification: Fiber-Reinforced Tensile strength of continuous fiber reinforced composites 41 Classification: Fiber-Reinforced Tensile strength of continuous fiber reinforced composites 42 Classification: Fiber-Reinforced Tensile strength of discontinuous and aligned fiber reinforced composites • Efficiency is lower for discontinuous than for continuous fibers • Discontinuous and aligned fiber composites are becoming increasingly more important • Short fiber composites could have • ~90% of modulus of elasticity • ~50% of tensile strength • For 𝑙 of their continuous fiber counterparts > ��� Longitudinal tensile strength, 𝜎�� = 𝜎𝑓 𝑉𝑓 ∗ • For 𝑙 < ��� ∗ 1 − 2� + 𝜎� (1 � 𝑐 ′ − 𝑉𝑓 ) Longitudinal tensile strength, 𝜎�� 𝑐 𝑓 + 𝜎� (1 − ∗ ′ =��𝜏 𝑉 𝑉𝑓 ) -fiber bond yield matrix (whichever the smallest) strength strength or matrix shear strength (whichever the where 𝜏� is either 43 Classification: Fiber-Reinforced Stiffness of discontinuous and random fiber reinforced composites • “rule-of-mixtures” expression for the elastic modulus can be used ��� = 𝑉� �� + �� 𝑉𝑓 �𝑓 where 𝐾 = fiber efficiency parameter � � , (2D isotropy) (3D isotropy) 44
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