Shear properties

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). 

Extensional Viscosity. In addition to the shear viscosity Tj, two other rheological constants can be defined for fluids the bulk viscosity, iC, and the extensional or elongational viscosity, Tj (34,49,100—107). The bulk viscosity relates the hydrostatic pressure to the rate of deformation of volume, whereas the extensional viscosity relates the tensile stress to the rate of extensional deformation of the fluid. Extensional viscosity is important in a number of industrial processes and problems (34,100,108—110). Shear properties alone are insufficient for the characterization of many fluids, particularly polymer melts (101,107,111,112). 

In designing the eon-rod, we wish to ensure that the pin will fail, in the ease of an overload, in preferenee to the eon-rod. To realize this, the mean values of their individual strength distributions are to be set apart by a margin to ensure this requirement. In this way, the probability of eon-rod failure will beeome insignifieant to that of the pin. The foree to shear the pin in an overload situation is a funetion of the ultimate shear strength, t, of the material. The relationship between the ultimate tensile and shear properties for steel is (Green, 1992) ... 

The viscous shear properties at any given shear rate are primarily determined by two factors, the free volume within the molten polymer mass and the amount of entanglement between the molecules. An increase in the former decreases the viscosity whilst an increase in the latter, i.e. the entanglement, increases viscosity. The effects of temperature, pressure, average molecular weight, branching and so on can largely be explained in the these terms. 

The continuing search to determine the shear modulus and shear strength consists of a collection of tests. Several tests are discussed because each has faults, as will be seen, and because, to some extent, there is no universal agreement on the best way to measure the shear properties. 

Unlike the methods for tensile, flexural, or compressive testing, the typical procedure used for determining shear properties is intended only to determine the shear strength. It is not the shear modulus of a material that will be subjected to the usual type of... 

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. 

To date, the melt state linear dynamic oscillatory shear properties of various kinds of nanocomposites have been examined for a wide range of polymer matrices including Nylon 6 with various matrix molecular weights [34], polystyrene (PS) [35], PS-polyisoprene (PI) block copolymers [36,37], poly(e-caprolactone) (PCL) [38], PLA [39,40], PBS [30,41], and so on [42],... 

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. 

The stress due to the shear properties of the material at that residence time and range of rates. 

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,... 

Sullivan, J.L., Kao, B.G. and van Oene, H. (1984). Shear properties and a stress analysis obtained from vinyl-ester losipescu specimens. Exper. Mech. 24, 223-232. 

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 main property that distinguishes a pressure-sensitive adhesive from other types of adhesives is that it exhibits a permanent and controlled tack. This tackiness is what causes the adhesive to adhere instantly when it is pressed against a substrate. After it adheres, the PSA should exhibit tack, peel, and shear properties, which are reproducible within... 

Benjamins, J., van Voorst Vader, F. (1992). The determination of the surface shear properties of adsorbed protein layers. Colloids and Surfaces, 65, 161-174. 

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... 

To increase the vertical stiffness of any load-bearing component, multiple layers of steel plates can be inserted into the molding. This will increase the vertical stiffness while having no influence on the shear properties. There will be more bulges of smaller magnitude than if a single unit is poured. 

Adhesives by the Thick Adherend Tensile Lap Specimen D 4027 Test Method for Measuring Shear Properties of Structural Adhesive by the... 

---