习 ￥ 3 20. 60. 695-862 178-227-232. 855.861. delamination.Composites Science and Technology (special issue),66(6). Allix,O.and Johnson,A.eds.2006.Advances in statics and dynamics of failures of three-dimensionally braided composite I-beams. Yau,S.-S.,Chou,T.-W.,and Ko,F.K.1986.Flexural and axial compressive Part A Applied Science and Manufacturing;30A(7),859-870. Philadelphia,PA toughness properties of advanced textile fiberglass composites.Composites Mouritz,A.P.,Baini,C.,and Herszberg,I.1999.Mode I interlaminar fracture carbon fibre reinforced laminates.Composites Science and Technology,66(6) Cartie,D.D.R.,Troulis,M.,and Partridge,I.K.2006.Delamination of z-pinned test.Composites Part B Engineering,37(4-5),365-378. ination of co-cured composite joints on the example of a double cantilever Byrd,L.W.and Birman,V.2006.Effectiveness of z-pins in preventing delam- V08031061481-3499 delamination toughness of z-pinned laminates.Composites Science and Tech- Yan,W.,Liu,H.-Y.,and Mai,Y.-W.2003.Numerical study on the Mode I ogy333-378 composites with interface control- Materials,Philadelphia PA. -a review.Composites Science and Tech- Kim,J.K.and Mai,Y.W.1991.High stretch,high fracture toughness fibre posites,ASTM STP 937,pp.397-412.American Society for Testing and ments through hybridized composites,in Johnston,N.J.ed.,Toughened Com- Garcia,R.,Evans,R.E.,and Palmer,R.J.1987.Structural property improve- for Testing and Materials,Philadelphia,PA. and Debonding of Materials,ASTM STP 876,Pp.371-385.American Society delamination in laminated composites,in Johnson,W.S.ed.,Delamination Mignery,L.A.Tan,T.M.,and Sun,C.T.1985.The use of stitching to suppress Testing and Materials,Philadelphia,PA. (Seventh Conference),ASTM STP 893,Pp.256-265.American Society for .Browning,C.E.and Schwartz,H.S.1986.Delamination resistant composite concepts,in Whithey,J.M.ed.,Composite Materials:Testing and Design ASTM STP 937,Pp.150-178.American Society for Testing and Materials, fracture toughness of composites,in Johnston,N.J.ed.,Toughened Composites Schwartz,H.S.and Hartness,T.1987.Effect of fiber coatings on interlaminar Science,14(8),581-588. an interfacial layer on the properties of composites.Polymer Engineering and Broutman,L.J.and Agarwal,B.D.1974.A theoretical study of the effect of Principles of Composite Material Mechanics Composites, piled mainly in ASTM Volume 15.01 [2].The emphasis in this chapter will ites and their constituents are compiled mainly in ASTM Volume 15.03 [11,while the standards for testing ceramic matrix composites are com- tional,formerly the American Society for Testing and Materials.The ASTM standards for testing of polymer matrix and metal matrix compos- have evolved into standards that have been adopted by ASTM Interna- with the corresponding analytical methods.Many of these test methods ics community.The technology associated with composite test methods and test equipment has become just as sophisticated as that associated been,and continues to be,a major challenge for the experimental mechan- development and evaluation of new test methods for composites have found that the mechanical test methods that are used for conventional metallic materials are usually not applicable to composites.Thus,the coupling effects,and the variety of possible failure modes,it has been Due to the special characteristics of composites,such as anisotropy, rials and structures. erties is also an important element of the quality control and quality assurance processes associated with the manufacture of composite mate- edge about the special nature of composite behavior has been derived from experimental observations.The measurement of mechanical prop mental approach may be the only acceptable solution.Much of our knowl- feasibility of proper analytical modeling is questionable,and the experi- sured intrinsic mechanical property data to use as input.In addition,some aspects of mechanical behavior of composites are so complex that the usefulness of such models depends heavily on the availability of mea- of analytical models for mechanical behavior of composite materials.The uents.In previous chapters,the emphasis has been on the development methods for mechanical testing of composite materials and their constit- The purpose of this chapter is to review briefly the most widely used 10.1 Introduction and Their Constituents Mechanical Testing of Composites
ngt FIGURE 10.1 3 C1557-03.Copyright ASTM International.Reprinted with permission.) Different ways of mounting fiber specimens on backing strip.(From ASTM Standard Overall length men is clamped in the grips of the tensile testing machine,the backing backing strip that has a central longitudinal slot or hole.Once the speci- specimen is adhesively bonded to a thin paper,compliant metal,or plastic C1557.031 standard test method [6].As shown in figure 10.1,the fiber under static longitudinal loading may be determined by the ASTM D The tensile strength and Young's modulus of individual reinforcing fibers 10.2.1 Fiber Tests of fiber and matrix materials. with the test methods that are used to measure the mechanical properties new materials before composites are made from them.This section deals matrix materials,constituent material tests are often used for screening composites depends so heavily on the development of new fiber and ties are required as input to these models.Since the development of new be obvious that experimentally determined constituent material proper- From the earlier discussion of various micromechanical models,it should 10.2 Measurement of Constituent Material Properties Standard Guide for Testing Polymer Matrix Composite Materials [5]. polymer matrix composites are conveniently listed in the ASTM D4762-04 have been published [3,4],and all of the ASTM standards for testing books that are devoted to experimental characterization of composites be on mechanical testing of polymer matrix composites.Several useful Principles of Composite Material Mechanics bottom end.The weight was set into oscillation as a torsional pendulum vertically suspended from one end and a weight was attached at the shear modulus of single fibers.The fiber specimen was clamped and [11]used a torsional pendulum to indirectly measure the longitudinal even greater anisotropy than did the inferred properties.Tsai and Daniel ments.Kawabata's measurements on graphite and aramid fibers showed as a curve-fitting parameter to match the predictions with the measure- to the model is the transverse Young's modulus of the fiber,which is used retical model of the fiber under transverse compression.One of the inputs is compared with the corresponding load-deflection curve from a theo- the apparatus shown in figure 10.3.The resulting load-deflection curve Kawabata [10]has tested fibers in transverse diametral compression using and composite test data,but direct measurement is possible.For example, the transverse Young's modulus of fibers may also be inferred from matrix tests will be discussed later in this chapter.As mentioned in chapter 3, may be inferred from matrix and composite test data,however,and these loading or longitudinal shear loading is very difficult.Such properties Direct measurement of fiber properties under longitudinal compressive dinal coefficient of thermal expansion of fibers. fiber at midspan.The same apparatus was used to measure the longitu- span as small incremental weights were suspended transversely from the end and optically measured the transverse deflection of the fiber at mid- sured by Tsai and Daniel [91,who clamped the fiber specimen on each The longitudinal modulus of single fibers has also been directly mea- failure mode,particularly any atypical failure modes(fig.10.2). the resin-impregnated strand.It is important to observe and record the modulus are calculated on the basis of the fiber stress,not the stress in is similar to that used in C1557.03,except that the tensile strength and uniform loading of the fibers in the bundle.The specimen test procedure to handle and test than a loose bundle of yarn and that should ensure The impregnating resin is used to produce a rigid specimen that is easier of carbon and graphite fibers may be tested by using ASTM D4018-99 [8] Resin-impregnated and consolidated yarns,strands,rovings,and tows tudinal tensile properties have been evaluated by McMahon [7]. and other techniques for the measurement of single graphite fiber,longi- ing to zero gage length is assumed to be the system compliance [61.This extrapolating the curves to zero gage length.The compliance correspond- different gage lengths,plotting the compliance versus gage length,and ance.The system compliance can be determined by testing specimens of correct the measured compliance by subtracting out the system compli- the usual formulas.For such small specimens,however,it is important to are recorded,and the tensile strength and modulus are calculated from tensile load.The specimen is pulled to failure,the load and elongation strip is burned or cut away,so that the filament transmits all the applied Mechanical Testing of Composites and Their Constituents
FIGURE 10.2 Other Explosive (fiber pullout) Lateral Grip/tab Failure type GAT 日 molding the resin to the desired shape.For example,the Specimen Types by machining or die cutting from sheets or plates of the material or by whether the material is rigid or nonrigid.Specimens may be fabricated standard,depending on the thickness of the available material and Several types of "dogbone-shaped"specimens are specified under this using the ASTM D638-03 method for tensile properties of plastics [12]. and elongation of neat resin matrix specimens may be determined by The tensile yield strength,tensile strength at break,modulus of elasticity, 10.2.2 Neat Resin Matrix Tests of vibration will be discussed later in this chapter. mechanical properties of fibers.Dynamic test methods involving the use Long splitting Most of the methods described above are used to determine static of the fiber specimen. equation for the pendulum to solve for the longitudinal shear modulus and the measured frequency of oscillation was used in the frequency D4018-99.Copyright ASTM International.Reprinted with permission.) Different failure modes for resin-impregnated strand test specimens.(From ASTM Standard First character GPT Unknown Various Tab pullout <1W from grip/tab At grip/tab Inside grip/tab Code Failure area 日 日 Second character LGM 日 Unknown Various Middle Top Bottom Code Failure location Third character Principles of Composite Material Mechanics socket arrangement is used (fig.10.7). FIGURE 10.3 of the specimen (fig.10.6).In order to generate true axial loading on the specimen without bending,a special compression fixture with a ball-and- by using a very short specimen(fig.10.5)and a support jig on each side of neat resin matrix materials.Out-of-plane buckling failures are avoided pressive yield strength,compressive strength,and modulus of elasticity and procedures are also given in the standard. The ASTM D695-02a test method [14]can be used to determine com- plastics are also strain-rate sensitive,so the speed of testing should be consistent,as specified in D638-03.The details of the other test conditions relative humidity is specified in the ASTM standard D618-05 [13].Some so-called "standard laboratory atmosphere"of 23C (73.4F)and 50% may be sensitive to temperature and relative humidity,the procedure used to condition specimens should be consistent from one test to another.The I-V for rigid or semirigid plastics are shown in figure 10.4.Since plastics Kawabata,S.1989.In Vinson,J.R.ed.,Proceedings of the Japan-U.S.Conference on Composite Materials,Pp.253-262.CRC Press,Boca Raton,FL.With permission.) Diametral compression of fiber for measurement of fiber transverse Young's modulus.(From Mechanical Testing of Composites and Their Constituents 7-30Mm Fiber diameter 器
罕 International.Reprinted with permission.) FIGURE 10.5 FIGURE 10.4 Neat resin compressive test specimen.(From ASTM Standard D695-02a.Copyright ASTM 1.90cm 5 Types 1,II,III &V (1.5 in) 3.81cm radius (3.13 in) 7.94 cm 050mm 127cm 381cm Standard D638-03.Copyright ASTM International.Reprinted with permission). ASTM D638-03 Type I,II,III,IV and V neat resin tensile specimen geometries.(From ASTM Principles of Composite Material Mechanics FIGURE 10.7 FIGURE 10.6 D695-02a.Copyright ASTM International.Reprinted with permission.) Compression fixture with ball-and-socket joint to minimize bending.(Prom ASTM Standard Test specimen Hardened ball right ASTM International.Reprinted with permission.) Mechanical Testing of Composites and Their Constituents 0 之 and ground Hardened and lapped ground, Hardened Hardened Supportjig for D695-02a compressive test specimen.(From ASTM Standard D695-02a.Copy- 三器 0401mm 018754 0141 ·375 2.875 0.500 .500 0.1875 2250 222375 2250 0125 0.0156im Letter Metric system British system 品
of radii for the loading noses and recommended Ee=E and v:=Ve=v,equation (10.2)reduces to equation (10.1). Poisson's ratio from compressive test. ulus,G,can be expressed as be found from the isotropic relationship 2(1+v) specimen dimensions standard D6272-02 describes a four-point bending test.Allowable ranges This test method involves three-point bending (fig.10.8),and a separate of plastics may be determined by the ASTM D790-03 test method [16] The flexural yield strength,flexural strength,and modulus of elasticity tensile compressive values of E and v.It is easily shown that when E 0.】)出0。)was1 of of of was found to give much better agreement with directly measured values This equation,which involves both tensile and compressive properties from compressive test,V:the Poisson's ratio from tensile test,and,ve the where E is the Young's modulus from tensile test,E the Young's modulus in tension and compression,Novak and Bert showed that the shear mod- using the Hooke's law for an isotropic material with different properties ented at 45 to the x,y axes.By equating these strain energy terms and the corresponding biaxial tensile and compressive principal stresses ori- pure shear along the x,y axes is equal to the strain energy associated with to a rotation of coordinates,the strain energy for an isotropic material in was based on the premise that since the elastic strain energy is invariant ences between tensile and compressive values of E and v.Their approach accurate calculation of G could be obtained by taking into account differ- twist versus torque for solid rod torsion tests.It was found that a more Directly measured values of G were determined from a plot of angle of pressive tests differ substantially from directly measured values of G. values of G found from applying equation(10.1)to either tensile or com- However,Novak and Bert [15]have reported that for some epoxies the definitions of those parameters.If desired,the shear modulus,G,can also E,and the Poisson's ratio,v,can then be determined from the standard measure the longitudinal and transverse strains.The Young's modulus, material,biaxial strain gages can be attached to the specimen so as to In either the tensile test or the compressive test of the neat resin matrix Principles of Composite Material Mechanics 102 4o1 it can be calcnlated from 10.2.3 FIGURE 10.8 to determine the matrix volume fraction,If the void fraction is desired, the matrix density pm can be determined,then equation(3.6)can be used weight and volume measurements on a separate neat resin matrix sample, and the fiber volume fraction can be calculated from v=Vi/Ve.From then measuring the weight,Wi,and volume,Vi of fibers remaining after resin removal,the fiber weight fraction can be calculated from wr=W/W, weight,W and volume,Vo of a composite sample before resin removal, burn-off in a furnace,in cases where it is safe to assume that the fibers are unaffected by the resin removal process.For example,by measuring the either chemical digestion(with acids or other chemicals)or ignition and involves removal of the matrix resin from the composite sample using matrix composites,ASTM standard D3171-99 [17]covers two basic approaches to the measurement of constituent volume fractions.Method I and for quality control during manufacturing of composites.For polymer Knowledge of the volume fractions of fiber and matrix materials(and also void fractions,if possible)is essential for use in micromechanical analysis Constituent Volume Fraction Measurement sion,impact,creep,and fatigue response are also given in ref.[1]. mechanical properties of other constituents such as sandwich core mate- rials and other constituent properties such as coefficient of thermal expan- are provided in tables in D790-03 [161.Test methods for measurement of Three-point bending specimen for flexural properties of neat resin or composite.(Prom ASTM Standard D790-03.Copyright ASTM International.Reprinted with permission.) Support span Mechanical Testing of Composites and Their Constituents