American Society for Testing and Materials (ASTM) Standards. Mechanical Testing of Composites and their Constituents

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1 Mechanical Testing of Composites and their Constituents American Society for Testing and Materials (ASTM) Standards Tests done to determine intrinsic material properties such as modulus and strength for use in design and analysis (major emphasis here) Tests done to determine quality or acceptability of specific components during manufacturing (minor emphasis here) ASTM Standards and Literature References for Composite Materials, 1987 ASTM Vol Space Simulation; Aerospace and Aircraft; Composite Materials, published annually Direct measurement of fiber longitudinal properties E f1 and S L (+) Indirect measurement of fiber 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 transverse modulus E f2 P = load P Prediction Eperimental data Tensile measurement of neat resin properties E m and S m1 (+) = deflection Note: Eperimental load-deflection curve compared with predicted curve (from finite element model) using E f2 as a curve-fitting parameter in prediction

2 Specimen for measurement of neat resin compressive properties E m and S m1 (-) ASTM 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 fiture for neat resin specimen 3 point bending specimen for measurement of fleural properties of neat resin or composite 4 point bending specimen for measurement of fleural properties of neat resin or composite M Bending moment diagram M Bending moment diagram

3 Composite tensile specimen for measurement of longitudinal properties E 1 and S L (+) Description of specimen from ASTM D Adhesively bonded load transfer tabs Typical stress-strain curves from D3039 specimen End constraints can cause bending of off-ais tensile specimens due to shear coupling Importance of specimen length-to-width ratio Difference between E and Q 11 for graphite/epoy E Modulus Q 10E!!!!! 11 σ y = τy = 0 σ = E ε E Q!!!!! 11 ε y = γ y = 0 σ = Q ε 11 O Fiber orientation, θ

4 Lamina tensile strength can be backed out from laminate tensile test data Compression test specimen and fiture for ASTM D Procedure A (Celanese fiture) Note: D fitures produce side-loading rather than end-loading as in D Eploded view of compression test specimen and fiture for ASTM D Procedure A Compression test specimen and fiture for ASTM D Procedure B (IITRI fiture) Compression test specimen and fiture for ASTM D Procedure C (sandwich beam) Compression after impact (CAI) fiture

5 Measurement of shear properties G 12, S LT Rail shear test, ASTM D Methods A and B Rail shear test, ASTM D ±45 degree laminate test Off-ais tensile test Iosipescu shear test, ASTM D5379 Torsion tube Sandwich cross-beam ±45 Laminate test for in-plane shear modulus G 12 Shear stress from applied stress: τ = σ 12 2 o Shear strain from measured normal strains: γ ε o 12 = ε y τ Shear modulus: G = γ 12 Off-ais tensile test for indirect measurement of G 12 Young s modulus, E σ E = ε 2 When σ 0, σ y = τ y = 0 y σ 1 E = = S11σ S11 1 or 1 E = σ 1 4 2v c + c s s E E1 G 12 E2 (2.38) (2.39)

6 Off-ais tensile test for indirect measurement of G 12 Iosipescu test specimen and fiture for in-plane or through-thickness shear properties Conduct off-ais tensile test to measure E 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 to calculate G 12 ASTM D Short beam shear test for interlaminar strength (parallel fibers only) Note: not recommended for measurement of design properties, only for quality control and specification

7 Short beam shear test 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) Eact stress distributions in short beam shear test specimen from theory of elasticity analysis (from J. M. Whitney, Composites Science and Technology, Vol. 22, 1985, pp ) Conclusion: Stress distributions from mechanics of materials beam theory are only accurate far away from loads and supports Single fiber fragmentation specimen for measurement of fiber/matri interfacial shear strength Microindenter test for fiber/matri interfacial shear strength Test procedure: Load specimen until fiber starts to break up into fragments, then measure critical lengths of fragments, then calculate interfacial shear strength from theory of discontinuous fiber composites developed later in Chap. 6 Test procedure: Load end of fiber in compression with microindenter probe until fiber slips with respect to matri, then use finite element analysis of specimen to estimate fiber/matri interfacial shear strength Microbond test for fiber/matri interfacial shear strength resin droplet fiber embedded in resin droplet applied tensile force Problem: Difficult to reproduce the composite resin matri cure condition in a small droplet.

8 Eploded view of test fiture for ASTM D Split Disk Test for Rings