Shear frame test

The standard test for measuring the shear behavior of fabrics is the shear-frame test, also known as trellis-frame test, or the picture-frame test, as shown in Fig. 6.12. In this test, a fabric specimen is clamped with the yams typically directed perpendicular and parallel to the four clamping bars. Shear deformation is developed by fixing one corner and applying a tensile load on the opposing corner. The deformation of the fabric in the shear-frame test is shown in Fig. 6.13. 

Deformation of shear-frame test (a) before deformation and (b) after deformation. 

The shear-frame test assumes there is only in-plane pure-shear deformation of the fabric before any out-of-plane buckling occurs. This assumption has been verified using digital image correlation (DIC). Figure 6.15 shows a shear-frame test of a plain-weave fabric where DIC has been used to map the state of shear over the surface if the fabric. There is some variation in the shear angle across the surface, but the variation is in the order of 1°, which can be assumed to be essentially uniform. 

In a manner similar to that shown for the shear-frame test, DIC can be used to capture the shear-angle contours developed in the fabric during a bias-extension test, which can be compared to the shear angles predicted by the finite element model (Fig. 6.30). It is noted that the boundaries for the three different theoretical zones as viewed in the experiment (DIC image) do not exhibit as sharp a transition as is shown for the boundaries in the simulations. The sharp transitions observed in the model are due to the pin-jointed connections between the elements whereas in reality, the yams are continuous and are allowed to bend along a smooth curve (Fig. 6.31). 

Lebrun G, Bureau MN, Denault J. Evaluation of bias-extension and picture-frame test methods for the measurement of intraply shear properties of PP/glass commingled fabrics. Compos Stmct 2003 61 341-52. 

Figure 18 shows a widely used test configuration where the matrix is a sphere of resin deposited as a liquid onto the fiber and allowed to solidify. The top end of the fiber is attached to a load-sensing device, and the matrix is contacted by load points affixed to the crosshcad of a load frame or another tensioning apparatus. When the load points are made to move downward, the interface experiences a shear stress that ultimately causes debonding of the fiber from the matrix. 

Because high fluxes and the abdity to process streams containing suspended solids and fibers are often wanted in the pulp and paper industry, high-shear modules have been developed. Currently existing high-shear modules, excluding tubular modules, are modified plate and frame constructions. Both a cross-rotational module from Metso Paper and a vibration enhanced module (VSEP) from New Logic Inc. have been industrially used or tested in pulp and paper industry applications [48-51]. 

The tests were also performed on computer-generated data in which additional uniform or non-uniform motion was added, to study how far the CG algorithm could be pushed beyond its original design parameters. For uniform motion, CG tracking was as successful as in the quiescent case for small drifts but failed for drifts of the order of half the particle-particle separation. For non-uniform (linear shear) flows with small strains between frames the identification worked correctly, but large non-uniform displacements caused major tracking errors. 

While a static load test is the commonly accepted procedure, in practice many variations in areas and weights are used, to compensate for the various qualities of adhesive evaluated, so that the test results will fall into a similar time frame, so it becomes difficult to compare different adhesive systems from accumulated data. It has the disadvantage of giving variable results for the same adhesive system, and is essentially a pass/ fail test, as many products remain in place at the end of the test period. Experience has shown that the shear properties of pressure-sensitive adhesives to porous and nonporous substrates can be quite different, and each must be judged on its own merits. 

In order to predict the deformations in a simple statically loaded portal frame by means of frame analysis, it is necessary to know the stiffness of the beam and columns. These stiffnesses may be determined by measuring the material properties of coupons cut from the WF-section and combining them with nominal values of the section cross-sectional area and second moment of area. Accordingly, a series of tension, compression and shear tests on coupons cut from the flanges and web of the WF-section material was carried out. 

It is important to check the extensometer knife edges for damage and to ensure that no additional load is applied by the weight of the extensometer cable, which is best supported with a magnetic clip attached to the metal frame of the testing machine. If wedge action grips are used, make certain that the shear pins are intact. 

Column and beam end rotations were measured by LVDTs installed at the member ends of the first and second stories. Load cells were located between actuators and test frame to measure story forces. Shear deformation of infill walls were monitored by diagonally positioned LVDTs on infill walls of the first and second stories. Reactions (bending moment, axial force and shear force) at the base of external columns were measured using two special force transducers (Canbay et al. 2004). These transducers were manufactured, calibrated, and placed between the base of external columns and the foundation. Longitudinal reinforcements of external columns were welded to base plates that were connected to transducers. Transducers were fixed to the fomidation block by using bolts. 

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