Shear geometry

Fig. 1 At the level of the approximation we use in this chapter, all experimental shear geometries are equivalent to a simple steady shear. We choose our system of coordinates such that the normal to the plates points along the z-axis and the plates are located at z = j. Between two parallel plates we assume a defect-free well aligned lamellar phase. The upper plate moves with the velocity in positive x direction, the lower plate moves with the same velocity in negative A direction. The y-direction points into the xz-plane. We call the plane of the plates Cry-plane) the shear plane, the x-direction the flow direction, and the y-direction the vortidty direction...

FIGURE 16.3 Typical bond durability data for Ti-6 Al-4 V adherends bonded with an epoxy adhesive and aged at 60°C and 100 percent RH. (a) Crack propagation versus time for the wedge crack propagation test. (b) Applied stress versus time to failure for the lap shear geometry. PF—phosphate fluoride MPF—modified phosphate fluoride DP—PasaJell 109 dry hone LP—PasaJell 107 liquid hone CAA-5—-5% solution CAA-10—10% solution TU—Turco 5578 etch DA—Dapcotreat.50... 

Fig. 18. The simple shear geometry used to characterise the interfacial friction the fluid thickness is e. The top plate limiting the sample is translated at the velocity and transmits this velocity to the fluid. The bottom plate is immobile, and the local velocity of the fluid at the bottom interface is Vs. The fluid is submitted to a simple shear, with a shear rate y = (Vt-VsYe. The velocity profile extrapolates to zero at a distance b below the interface, with...

The only observation of a stick-slip transition in a simple shear geometry is the unique experimental study of Laun [39]. This controlled stress experiment not only observed a stick-slip transition but also explicitly recorded the time scale (a few milliseconds) on which the boundary condition (BC) evolved from... 

A first step in the validation of this approach is to test simple specimens under controlled conditions and to compare predictions with measured failure load values. First lap shear geometries were examined, then an L-geometry was studied in more detail. The bond-line in these small specimens was very similar to that in the quasi-unidirectional fracture specimens as the small dimensions allow panels to be pressed uniformly after assembly (which is not the case for industrial top-hat stiffeners). 

Creep tests can be performed with steady rotating viscometers. Conventional forced-oscillation measurements can also be performed with ordinary shear geometries such as plate-plate or plate-cone systems in rotating rheometers. 

Punch shear geometry is relatively popular for plastics to measure shear strength, although it can be used for any material. The approximation to pure shear conditions are achieved by a punch bearing on a sheet of material supported by a die. The smaller the difference between the internal diameter of the die and the external diameter of the punch, the nearer the approximation. 

Figure 4 Standard lap shear geometries (a) simple lap joint test, ASTM D-1002 (b) laminated lap shear joint test, ASTM D-3165 (c) double lap joint test, ASTM D-3528.

The shear strengths of the composites were measured in a double notch shear geometry, loaded in compression with an anti-buckling fixture. Compression testing was done on test coupons with dimensions as shown in Figure 3, using an anti-buckling fixture. 

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. 

Work on the effect of flow on block copolymer melts has been reviewed [1,5,39,40]. Due to the convenience and well defined nature of the shear geometry most model studies have exploited this type of flow. The application of shear leads to orientation of block copolymer microstmctures at sufficiently high shear rates and/or strain amplitudes (in the case of oscillatory shear). Depending on shear conditions... 

FIGURE 15. Typical bond durability data for Ti-6A1-4V adherends bonded with epoxy adhesives. Abbreviations are given in the text (a) crack propagation vs. time for the double cantilever beam geometry (from Reference 55) and (b) applied stress vs. time-to-failure for the lap-shear geometry (From Reference 66). 

Figure 1. Schematic illustration of the x-ray shearing cell setup. The exploded view depicts the shearing geometry and window design which allows a 1mm diameter x-ray beam to pass through the sample during shear. Reproduced with permission from Reference 15. Copyright 1998 American Chemical Society.

The standard ASTM D4680 Standard Test Method for Creep and Time to Failure of Adhesives in Static Shear by Compression Loading (Wood-to-Wood) also applies a compressive force to shear specimens to monitor the creep properties of wood adhesives in lap shear geometry. 

Most rheological measurements are performed in one of the following four shear geometries capillary flow, parallel-plate and cone-plate torsional flow, and Couette flow. Excellent books on this topic to find more detailed information are [40] and [8]. 

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