With permission. FIGURE 10.11 FIGURE 10.10 coupling.(From Pagano,N.J.and Halpin,J.C 1968.Journal of Composite Materials,2,18-31. Effect of end conditions on deformation of an off-axis tensile specimen exhibiting shear Stress,MPa 500 2500 (a)Ends unconstrained Pagano and Halpin found that the distortion shown in figure 10.11(b) and the usual definitions.of the engineering constants are not valid the latter case,the specimen is no longer under a uniform state of stress, moments that distort the specimen,as shown in figure 10.11(b).Thus,in sion of Prentice-Hall,Englewood Cliffs,N].) vanced Composite Materials.Prentice-Hall,Inc.Englewood Cliffs,N.Reprinted by permis- specimen.(From Carlsson,L.A.and Pipes,R.B.1989.Experimental Characterization of Ad- Longitudinal and transverse strain data at different stresses for [O]graphite/epoxy tensile 02 Strain, 0.60.8 1 (b)Ends clamped -0.29 1214 1V-14 E1=126 GPa Graphite/epoxy (0)8 Principles of Composite Material Mechanics When these strain conditions are substituted in equation(2.35),the result- ing stress condition in the gage length of the short,wide specimen is found to be in the gage length to be approximately FIGURE 10.12 611810 clamped ends.However,in a short,wide specimen (fig.10.12[b1),the proximity of the clamped ends to the gage length will cause the strains because the gage length is sufficiently far removed from the effects of the oy=txy=0 and ox=Exex off-axis specimens under a uniaxial stress,as shown in figure 10.12(a),the state of stress in the gage section of the specimen would be approximately mens was proposed by Jones [211.Jones suggested that for long,slender tion of the ends of the specimen could be used with off-axis specimens. A similar conclusion regarding end constraint effects in off-axis speci- instead of off-axis specimens,or that a test fixture that allowed free rota- in order to minimize such effects,angle-ply laminates could be used decreases with decreasing shear-coupling ratio,(recalleq.[2.401)and increasing length-to-width ratio of the specimen.They also suggested that Tensile specimens of different length showing relationship of gage length to specimen length Strain gage (a)Long,slender specimen Clamps (b)Short,wide specimen Mechanical Testing of Composites and Their Constituents Strain gage Specin 4o0 (10.3)