Mechanical Testing of Composites and American Society for Testing and their Constituents Materials (ASTM) Standards • Tests done to determine intrinsic material • ASTM Standards and Literature References properties such as modulus and strength for use in for Composite Materials, 1987 design and analysis (major emphasis here) • ASTM Vol. 15.03 Space Simulation; • Tests done to determine quality or acceptability of Aerospace and Aircraft; Composite specific components during manufacturing (minor Materials, published annually emphasis here) Indirect measurement of fiber longitudinal Direct measurement of fiber properties E f1 and S L (+) longitudinal properties E f1 and S L (+) Note: strength and modulus values must be corrected to account for the portion of the load carried by resin (use micromechanics equations) Indirect measurement of fiber Tensile measurement of neat resin transverse modulus E f2 properties E m and S m1 (+) P P = load Prediction Experimental data ∆ ∆ = deflection Note: Experimental load-deflection curve compared with predicted curve (from finite element model) using E f2 as a curve-fitting parameter in prediction 1
Specimen for measurement of neat resin compressive properties E m and S m1 (-) ASTM 618-81 Conditioning Plastics and Electrical Insulating Materials for Testing Standard Laboratory Atmosphere: Temperature of 23C (73.4F) and relative humidity of 50% Neat resin compression specimen support jig Compression test fixture for neat resin specimen 3 point bending specimen for measurement of 4 point bending specimen for measurement of flexural properties of neat resin or composite flexural properties of neat resin or composite M M Bending moment diagram Bending moment diagram 2
Description of specimen from ASTM D3039-76 Composite tensile specimen for measurement of longitudinal properties E 1 and S L (+) Adhesively bonded load transfer tabs End constraints can cause bending of off-axis Typical stress-strain curves from D3039 specimen tensile specimens due to shear coupling Importance of specimen length-to-width ratio Q Difference between E x and for graphite/epoxy 11 E x Q ≈ 10 E ! ! ! ! ! x 11 “Modulus” ε = γ = 0 σ = τ = 0 y xy y xy σ = ε σ = ε Q E x x x x x 11 O 0 45 0 90 0 E ≠ Q ! ! ! ! ! x Fiber orientation, θ 11 3
Compression test specimen and fixture for Lamina tensile strength can be “backed out” ASTM D3410-87 Procedure A (Celanese fixture) from laminate tensile test data Note: D3410-87 fixtures produce side-loading rather than end-loading as in D695-90 Compression test specimen and fixture for Exploded view of compression test specimen and ASTM D3410-87 Procedure B (IITRI fixture) fixture for ASTM D3410-87 Procedure A Compression test specimen and fixture for Compression after impact (CAI) fixture ASTM D3410-87 Procedure C (sandwich beam) 4
Rail shear test, ASTM D4255-83 Methods A and B Measurement of shear properties G 12 , S LT • Rail shear test, ASTM D4255-83 • degree laminate test ± 45 • Off-axis tensile test • Iosipescu shear test, ASTM D5379 • Torsion tube • Sandwich cross-beam Off-axis tensile test for indirect ± Laminate test for in-plane shear modulus G 12 45 measurement of G 12 σ Young’s modulus, E x = E x x ε x σ ≠ σ = τ = 2 0 , 0 When y xy x σ 1 ∴ = = y x E (2.38) x σ σ S S τ = x Shear stress from applied stress: 11 11 x 12 2 or 1 x o o γ = ε x ε − Shear strain from measured normal strains: 1 y 12 = E x (2.39) τ σ 12 1 2 v 1 1 G = Shear modulus: γ + − + + 12 x c 4 12 c 2 s 2 s 4 12 E E G E 1 1 12 2 5
Iosipescu test specimen and fixture for Off-axis tensile test for indirect in-plane or through-thickness shear properties measurement of G 12 • Conduct off-axis tensile test to measure E x at some fiber orientation θ • Conduct longitudinal tension test to measure E 1 and υ 12 • Conduct transverse tension test to measure E 2 • Use above results in Eq. 2.39 to calculate G 12 ASTM D2344-76 Short beam shear test for interlaminar strength (parallel fibers only) Note: not recommended for measurement of design properties, only for quality control and specification 6
Exact stress distributions in short beam shear test specimen from theory of elasticity analysis Short beam shear test (from J. M. Whitney, Composites Science and Technology , Vol. 22, 1985, pp. 167-184) • Short beam fails due to interlaminar shear stress • Long beam fails due to either tensile or compressive normal stress on bottom or top of beam, respectively • Questions about accuracy of mechanics of materials beam theory equations for stresses in short beams where support effects may not be negligible (Whitney’s theory of elasticity analysis) Conclusion: Stress distributions from mechanics of materials beam theory are only accurate far away from loads and supports Microindenter test for fiber/matrix Single fiber fragmentation specimen for measurement of fiber/matrix interfacial interfacial shear strength shear strength Test procedure: Load specimen until fiber starts to break up into Test procedure: Load end of fiber in compression with fragments, then measure “critical lengths” of fragments, then microindenter probe until fiber slips with respect to matrix, calculate interfacial shear strength from theory of discontinuous then use finite element analysis of specimen to estimate fiber composites developed later in Chap. 6 fiber/matrix interfacial shear strength Microbond test for fiber/matrix interfacial shear strength fiber embedded in resin droplet resin droplet applied tensile force Problem: Difficult to reproduce the composite resin matrix cure condition in a small droplet. 7
Exploded view of test fixture for ASTM D2290-76 Split Disk Test for Rings 8
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