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Mechanical Testing of Composites and their Constituents 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)

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American Society for Testing and Materials (ASTM) Standards Test standards for polymer matrix and metal matrix composites - ASTM Vol Space Simulation; Aerospace and Aircraft; Composite Materials Test standards for ceramic matrix composites – ASTM Vol – Refractories; Activated Carbon; Advanced Ceramics

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HI-NICALON TM Type S CERAMIC FIBER

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Direct measurement of fiber longitudinal properties E f1 and S f1 (+) Different ways of mounting fiber specimens on backing strip. (From ASTM Standard C R08. Copyright ASTM International. With permission.)

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Different failure modes for resin-impregnated strand test specimens. (From ASTM Standard D (2008). Copyright ASTM International. Reprinted with permission.)

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P = load Δ = deflection P Δ Diametral compression of fiber for measurement of fiber transverse Young’s modulus. (From Kawabata, S In Vinson, J.R. ed., Proceedings of the 4 th Japan–U.S. Conference on Composite Materials, pp. 253–262. CRC Press, Boca Raton, FL. With permission.) Indirect measurement of fiber transverse modulus E f2 Experimental data Prediction

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Tensile measurement of neat resin properties E m and S m1 (+) ASTM D Type I, II, III, IV and V neat resin tensile specimen geometries. (From ASTM Standard D Copyright ASTM International. Reprinted with permission).

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ASTM Conditioning Plastics and Electrical Insulating Materials for Testing Standard Laboratory Atmosphere: Temperature of 23C (73.4F) and relative humidity of 50%

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Specimen for measurement of neat resin compressive properties E m and S m1 (-) Neat resin compressive test specimen. (From ASTM Standard D Copyright ASTM International. Reprinted with permission.)

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Neat resin compression specimen support jig Support jig for D compressive test specimen. (From ASTM Standard D695-02a. Copyright ASTM International. Reprinted with permission.)

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Compression test fixture for neat resin specimen Compression fixture with ball-and-socket joint to minimize bending. (From ASTM Standard D Copyright ASTM International. Reprinted with permission.)

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Three-point bending specimen for flexural properties of neat resin or composite. (From ASTM Standard D Copyright ASTM International. Reprinted with permission.) M Bending moment diagram

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Constituent Volume Fraction Measurement Removal of resin matrix from composite sample by either chemical digestion with acids or other chemicals (carbon fiber composites), or resin burn-off in a furnace (glass fiber composites) according to ASTM Standard D Computer-aided image analysis of digital photomicrographs to determine fiber area fractions of polished composite specimens

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Composite tensile specimen for measurement of longitudinal properties E 1 and S L (+) Specimen geometry for ASTM D3039/D3039M-08 standard tensile test. (Dimensions from ASTM D3039/D3039M-08. Copyright ASTM International. Reprinted with permission.)

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Typical stress-strain curves from D3039 specimen Longitudinal and transverse strain data at different stresses for [0] 8 graphite/epoxy tensile specimen. (From Carlsson, L.A. and Pipes, R.B Experimental Characterization of Advanced Composite Materials. Prentice-Hall, Inc., Englewood Cliffs, NJ. Reprinted by permission of Prentice-Hall, Englewood Cliffs, NJ.)

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End constraints can cause bending of off-axis tensile specimens due to shear coupling Effect of end conditions on deformation of an off-axis tensile specimen exhibiting shear coupling. (From Pagano, N.J. and Halpin, J.C Journal of Composite Materials, 2, 18–31. With permission.)

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Importance of specimen length-to-width ratio

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Variation of “apparent moduli” and with fiber orientation for off-axis tensile test of a unidirectional T300/934 carbon/epoxy lamina. Lamina engineering constants are taken from Table 2.2. Conclusion: except at

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Lamina tensile strength can be “backed out” from laminate tensile test data “Backed out” tensile strength data from seven different laminates of IM7G/ graphite/epoxy. (From Rawlinson, R.A Proceedings of the 36th International SAMPE Symposium and Exhibition, Book 1, pp. 1058–1068. Reprinted by permission of the Society for the Advancement of Material and Process Engineering.)

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Compression test specimen for ASTM D3410/D3410M-03 D3410 fixtures produce side-loading rather than end-loading as in D695 Geometry for tabbed compression test specimen. (From ASTM Standard D3410/D3410M-03 (Reapproved 2008). Copyright ASTM International. Reprinted with permission.)

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Cutaway view of compression test fixture for ASTM D3410/D3410M-03 Cross-section view of ASTM D3410/D3410M-03 (Reapproved 2008) compression test fixture. (From ASTM Standard D3410/D3410M-03 (Reapproved 2008). Copyright ASTM International. Reprinted with permission.)

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Sandwich beam specimen for face sheet compression ASTM D5467/D5467M-97 (Reapproved 2004) sandwich beam specimen for face sheet compression. (From ASTM Standard D5467/D5467M-97 (Reapproved 2004). Copyright ASTM International. Reprinted with permission.)

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Test fixture for ASTM D 6641/D 6641M- 09 combined loading compression (CLC) test method Test fixture for ASTM D6641/D6641M-09 CLC test method. (From ASTM Standard D6641/D6641M-09. Copyright ASTM International. Reprinted with permission.)

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Test fixture for compressive residual strength of polymer composite plates. (From ASTM D 7137/D 7137M-07) Test fixture for compressive residual strength of polymer composite plates. (From ASTM D7137/D7137M-07. Copyright ASTM International. Reprinted with permission.)

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Comparison of shear test methods for composites. (From Adams, D.F., 2005 High Performance Composites, 13(5), pp. 9–10)

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Iosipescu test fixture for shear strength and stiffness in all three shear stress states (ASTM D5379)

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Test fixture for V-notched rail shear test Test fixture for V-notched rail shear test. (From ASTM Standard D7078/D7078M-05. Copyright ASTM International. Reprinted with permission.)

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Different test specimen arrangements for V-notched rail shear test. (From ASTM Standard D7078/D7078M-05. Copyright ASTM International. Reprinted with permission.)

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Rail shear test fixtures, ASTM D4255/D4255M-01 (Methods A and B) Rail shear test fixtures. (From ASTM Standard D4255/D4255M-01(2007). Copyright ASTM. Reprinted with permission.)

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Analysis of Rail Shear Test Procedure A (10.8) Shear stress along loading axes x,y) Strain transformation from normal strain along strain gage axis x’ oriented at 45 o from x to shear strain along (x,y) axes (10.10)

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Therefore the shear modulus along loading axes is where P, L, t, and ε x’ are all measured quantities. If the specimen is unidirectional, and (x,y) are aligned with (1,2), then and if this specimen is loaded to failure

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Laminate test for in-plane shear modulus G 12 Shear stress from applied stress: Shear strain from measured normal strains: Shear modulus:

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Off-axis tensile test for indirect measurement of G 12 Young’s modulus, E x 2 1 y x When or (2.39) (2.40)

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Off-axis tensile test for indirect 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 to calculate G 12

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ASTM D2344/D2344M-00 Short beam shear test for interlaminar strength (parallel fibers only) Note: not recommended for measurement of intrinsic properties, only for quality control and specification

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Short beam test specimen with shear and moment diagrams Shear stress Bending stress Mechanics of materials stresses

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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)

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Whitney’s conclusion: Stress distributions from mechanics of materials beam theory are only accurate far away from loads and supports Comparison of predicted interlaminar shear stress distributions from theory of elasticity (solid curves) and beam theory (dotted curve) for a 50 ply short beam shear specimen with length-to-depth ratio of 4. Differences are particularly large near loading point (section C) and support points (section A). (From Whitney, J. M Composites Science and Technology, 22, With permission)

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Interlaminar Fracture Tests

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DCB analysis – treat one half of DCB as cantilever beam (ASTM D (2007)e3) Mode I strain energy release rate (10.16)

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Mixed mode bending (MMB) test for Mode I and Mode II delamination testing (ASTM Standard D6671) Test fixture for MMB test. (From ASTM Standard D6671/D6671M-06. Copyright ASTM International. Reprinted with permission.)

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Single fiber fragmentation specimen for measurement of fiber/matrix 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 in Chap. 6 Single-fiber fragmentation specimen developed by Drzal et al. (From Drzal, L.T., Rich, M.J., and Lloyd, P.F Journal of Adhesion, 16, 1–30.; Drzal, L.T., Rich, M.J., Koenig, M.F., and Lloyd, P.F Journal of Adhesion 16, 133–152. With permission.)

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Microindenter test for fiber/matrix interfacial shear strength Test procedure: Load end of fiber in compression with microindenter probe until fiber slips with respect to matrix, then use finite element analysis of specimen to estimatefiber/matrix interfacial shear strength Microindenter test for fiber/matrix interfacial strength. (From Mandell, J.F., Grande, D.H., Tsiang, T.H., and McGarry, F.J Composite Materials: Testing and Design (Seventh Conference), ASTM STP 893, pp. 87–108. American Society for Testing and Materials, Philadelphia, PA. Copyright ASTM. Reprinted with permission.)

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Microbond test for fiber/matrix interfacial shear strength applied tensile force fiber embedded in resin droplet Problem: Difficult to reproduce the composite resin matrix cure condition in a small droplet.

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Source: From McDonough, W.G., Herrera-Franco, P.J., Wu, W.L., Drzal, L.T., and Hunston, D.L In Advanced Materials/Affordable Processes, Proceedings of 23rd International SAMPE Technical Conference, Kiamesha Lake, NY, pp. 247–258. Society for Advancement of Material and Process Engineering, Covina, CA. Reprinted by permission of the Society for the Advancement of Material and Process Engineering.

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ASTM D5766 open hole tension test – similar to ASTM D3039 tensile test, but with central hole Acceptable test failure modes for ASTM D 5766/D 5766M-07 standard test method for open hole tensile strength (a) failure mode codes (b) LGM (c) AGM (d) MGM. (From ASTM D5766/D5766M Copyright ASTM International. Reprinted with permission.)

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Fixture assembly for ASTM D5961/D5961M-08 (Procedure A) double shear test method for bearing response of polymer matrix composite laminates. (From ASTM D5961/D5961M Copyright ASTM International. Reprinted with permission.) ASTM D5961 bearing test – Procedure A

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Test fixture and specimen for ASTM standard test method for measuring the fastener pull-through resistance of a fiber-reinforced polymer matrix composite, Procedure B. (From ASTM D 7332/D 7332M-07e1. Copyright ASTM International. Reprinted with permission.) ASTM D7332 fastener pull-through test

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Measurement of Viscoelastic and Dynamic Properties

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Strain, ε Time, t Constant applied stress, σ o Initial elastic strain, ε o Creep strain, ε(t) Creep test parameters Elastic compliance = ε o / σ o Creep compliance = ε(t)/σ o Test specimen Total strain = ε o +ε(t) Strain gage

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Measurement of orthotropic creep compliances

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Empirical power law for creep compliance where S(t) is the creep compliance, S 0 the initial elastic compliance, and S 1 and n the empirically determined parameters

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Important modes of specimen deformation for vibration tests Flexural Torsional Longitudinal

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Response Frequency Flexural and torsional modes Longitudinal modes Range of typical excitation frequencies Natural frequencies of flexural and torsional modes of vibration are usually in the range of typical excitation frequencies, but longitudinal modes are usually well above this range. Automated Dynamic Mechanical Analyzers (DMA) typically operate in the flexural mode.

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Representation of automated DMA plot showing storage modulus, loss modulus and loss factor (tan δ) vs. temperature.

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Material Damping Energy dissipation within a material under cyclic or oscillatory stress Characterized by stress-strain hysteresis loop under steady-state vibration and decaying oscillation under free vibration Area enclosed by hysteresis loop and rate of decay are proportional to damping factor Damping is linear if it is independent of oscillation amplitude Hysteresis loop in steady state vibration Free vibration decay

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Complex modulus of linear viscoelastic material from stress- strain hysteresis loop ( assuming perfectly elliptical loop) Energy dissipated per cycle Energy stored at maximum displacement Loss factor Storage Modulus

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Free vibration decay method Logarithmic decrement Loss factor (for light damping)

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Impulse-frequency response apparatus for flexural vibration of cantilever beam specimens Impulse-frequency response method

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Modal frequencies and loss factors found by curve-fitting to frequency response curve at peak frequencies Modal frequencies

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Single Degree of Freedom Curve Fit to Peak in Frequency Response Curve by Half Power Bandwidth Method Damping Loss Factor Amplitude Frequency X X = natural frequency of nth mode = bandwidth at half power points Peak for nth mode (10.36)

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Measurement of Hygrothermal Properties

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ASTM D e1 test for determination of DMA T g from storage modulus vs. temperature plot Measurement of glass transition temperature, T g

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Measure thermal strain,, or the change in length,, of a specimen of original length which is subjected to a temperature change in an environmental chamber Measured coefficient of thermal expansion is ASTM test for measurement of coefficient of thermal expansion, CTE (10.37)

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Variation of measured longitudinal and transverse thermal strains for unidirectional Kevlar 49/epoxy and S-glass/epoxy with temperature. (From Adams, D.F., Carlsson, L.A., and Pipes, R.B., Experimental Characterization of Advanced Composite Materials. CRC Press, Boca Raton, FL. With permission.)

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Measured longitudinal CTE Measured CTEs for undirectional orthotropic lamina Measured transverse CTE

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ASTM D5229 test for measurement of moisture absorption properties Through-thickness Diffusivity (10.40)

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ASTM D2290 Split Disk Test for tensile strength of filamentwound composite rings Example of test done to determine quality or acceptability of specific components during manufacturing

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Exploded view of test fixture for ASTM D2290 Split Disk Test for Rings

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