Shear properties composites

Those stmctural variables most important to the tensile properties are polymer composition, density, and cell shape. Variation with use temperature has also been characterized (157). Flexural strength and modulus of rigid foams both increase with increasing density in the same manner as the compressive and tensile properties. More specific data on particular foams are available from manufacturers Hterature and in References 22,59,60,131 and 156. Shear strength and modulus of rigid foams depend on the polymer composition and state, density, and cell shape. The shear properties increase with increasing density and with decreasing temperature (157). 

Yanez-Flores et al. have studied the shear properties of blends of PE with polyisoprene rubber (Guayule mbber) [50]. The blends were prepared using a cam-type mixer at 50 rpm for 10 min at 140°C. The blend compositions ranged from 10% to 70% mbber content. 

Experimental results are presented that show that high doses of electron radiation combined with thermal cycling can significantly change the mechanical and physical properties of graphite fiber-reinforced polymer-matrix composites. Polymeric materials examined have included 121 °C and 177°C cure epoxies, polyimide, amorphous thermoplastic, and semicrystalline thermoplastics. Composite panels fabricated and tested included four-ply unidirectional, four-ply [0,90, 90,0] and eight-ply quasi-isotropic [0/ 45/90]s. Test specimens with fiber orientations of [10] and [45] were cut from the unidirectional panels to determine shear properties. Mechanical and physical property tests were conducted at cold (-157°C), room (24°C) and elevated (121°C) temperatures. 

Apart from the short beam shear test, which measures the interlaminar shear properties, many different specimen geometry and loading configurations are available in the literature for the translaminar or in-plane strength measurements. These include the losipescu shear test, the 45°]5 tensile test, the [10°] off-axis tensile test, the rail-shear tests, the cross-beam sandwich test and the thin-walled tube torsion test. Since the state of shear stress in the test areas of the specimens is seldom pure or uniform in most of these techniques, the results obtained are likely to be inconsistent. In addition to the above shear tests, the transverse tension test is another simple popular method to assess the bond quality of bulk composites. Some of these methods are more widely used than others due to their simplicity in specimen preparation and data reduction methodology. 

Adams, D.F. and Walrath, D.E. (1982). losipescu shear properties of SMC composite materials. In Composite Materials Testing and Design (Sixth Conf ), ASTM STP 787 (I.M. Daniel ed.), ASTM, Philadelphia, PA, pp. 19-33. 

ASTM D 4255 (1983). Guide for testing in plane shear properties of composite laminates. 

Chamis, C.C. and Sinclair, J.H. (1977). 10° off-axis test for shear properties in fiber composites. Exper. Mech. 17, 339-346,... 

Mayadas, A. Pastore. C, Ko, F.K. (1985). Tensile and shear properties of composites by various reinforcement concepts. In Proc. 30th Int. SAMPE Symp. pp. 1284 1293. 

Table 5.8 Selected Compressive and Shear Properties of Various SMC Composites...

In-Plane Shear Properties. The basic lamina in-plane shear stiffness and strength is characterized using a unidirectional hoop-wound (90°) 0.1 -m nominal internal diameter tube that is loaded in torsion. The test method has been standardized under the ASTM D5448 test method for in-plane shear properties of unidirectional fiber-resin composite cylinders. D5448 provides the specimen and hardware geometry necessary to conduct the test. The lamina in-plane shear curve is typically very nonlinear [51]. The test yields the lamina s in-plane shear strength, t12, in-plane shear strain at failure, y12, and in-plane chord shear modulus, G12. 

The increase in ILSS for the epoxy-sized fibers over the bare fibers is 12.4%, approximately 50% of the increase observed in the interfacial shear strength as measured by ITS testing. Changes in the failure mode at the fiber-matrix interface may account for the differences. The sized fibers produced large matrix cracks that grew quickly to catastrophic size under load. This would tend to limit the increase in composite shear properties if at every fiber break in the tensile surface of the coupon a matrix crack was created. The presence of these matrix cracks... 

Figure 5. Torsional shear properties of two 3D composites subjected to similar processing.

Shear strength and modulus of rigid foams depend on the polymer composition and state, density, and cell shape. Shear properties increase with increasing density and decreasing temperature [30]. 

ASTM D 5379. Shear properties of composite materials by the V-notched beam method. 

The compressive properties of a composite under aU loading conditions are strongly affected by moisture absorption because of the reduction in shear properties of the matrix polymer. The design of artefacts with polymer matrix composites needs to reflect the limitations of these materials in compression, especially in service where environmental conditioning is likely. 

TABLE 5. Interlaminar Shear Properties of 0/90° Nicalon/BN/SiC/BSAS Composites at Various Temperatures inAir Vf = 0.38-0.40... 

Shear Properties - Double notch shear testing is preferred to short-beam shear, because of the multiple stress condition for the short beam shear geometry. In the double notch shear (DNS) test, the compression load translates into an interlaminar shear stress along the midplane connecting the two notches in the composite (See Figure 3). Table 3 lists the ultimate double notch shear strengths for the two sets of composite test bars. 

Pering, G.A., Farrell, P.V., and Springer, G.S. (1980) Degradation of tensile and shear properties of composites exposed to fire or high temperatures. J. Compos. Mater., 14, 54-68. 

Table 2.30 Shear Properties of Composites of Kevlar 49 Fiber in Epoxy Resins (8) ...

Figure 17.51 Schematic diagram of 10° off-axis shear test. Source Reprinted from Chamis CC, Sinclair JM, Ten-degree off-axis test for shear properties in fibre composites, Exp Mech, 17, 339-346,1977.

Lee S, Munroe M, In-plane shear properties of graphite/epoxy composites for aerospace applications evaluation of test methods by the decision analysis method, Aeronautical Note NAE-AS22, NRC No.23778, Mechanical Engineering Department, University of Ottawa, Canada, Oct 1984. 

Lee, B.L., Holl, M.W. Effects of moisture and thermal cycling on in-plane shear properties of graphite fibre-reinforced cyanale estta- resin composites. Compos. A Appl. Sci. Manuf. 27, 1015-1022 (1996)... 

JL Thomason, GE Schoolenberg. An investigation of glass fibre/polypropylene interface strength and its effect on composite properties. Composites 25 197-203,1994. MJ Folkes, WK Wong. Determination of interfacial shear strength in fibre-rein-forced thermoplastic composites. Polymer 28 1309-1314, 1987. 

Lebrun, G., Bureau, M. N. and Denault, J. (2003), Evaluation of bias-extension and picture-frame test methods for the measurements of intraply shear properties of PP/Glass commingled fabrics . Composite Structures, 61, 341-352. 

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