Two-point bending

The simplicity of the rigs used in the constant-strain tests is an advantage in the application of the corrosive solution. Thus, in the case of two-point bending (Fig. 8.89a) several specimens may be strained in the same rig which can be constructed of plastic and immersed in a tank containing the test solution. 

We perform flexural testing on polymer rods or beams in the same basic apparatus that we use for tensile or compressive testing. Figure 8.6 illustrates two of the most common flexural testing configurations. In two-point bending, shown in Fig. 8,6 a), we clamp the sample by one end and apply a flexural load to the other. In three-point bending, shown in Fig. 8.6 b), we place the sample across two parallel supports and apply a flexural load to its center. 

The fracture stress, ay corresponding to failure at 3% strain is 150 Mpa. By applying laminate theory and the working spreadsheet model described earlier, the deformation required to reproduce the fracture stress under a different geometry can be easily calculated. Thus for the same laminate sample, the solution for a two-point bend deformation is that a plate separation of 6.5 mm will apply a strain of 3% and develop fracture stress in the coating layer. 

Figure 7.12 shows the result of a fracture measurement using two-point bend geometry. The agreement between observed and predicted behavior is excellent -cracks began to develop in the coating layer at a plate separation between 6 and 7 mm and propagated across the width of the specimen. The point of maximum... 

Fig. 7.12. Experimental measure of fracture under two-point bend.

Fig. 9.11 (a) A graphene sample is placed in the middle part of a flexible substrate (b) two-point bending and (c) four-point bending [18]... 

Two-point bending test on trapezoidal (2PB-TR) or prismatic (2PB-PR) specimens... 

The two-point bending test on trapezoidal specimens (and later on prismatic specimens) was initially developed in Shell laboratories in Holland and soon adopted by LPC in France for determining the stiffness modulus and the asphalt fatigue performance (Moutier 1990). Today, this test is the recommended type of stiffness test in France. 

Figure lA Schematic representation of the two-point bending test on trapezoidal specimens (application of force in the horizontal direction). 

The specimens are produced and prepared the same way as specimens for the two point bending test. 

Two-point bending test on trapezoidal-shaped specimens... 

This test method determines the asphalt s behaviour under fatigue loading with controlled displacement by two-point bending using trapezoidal specimens. The method is used for asphalts with maximum aggregate size up to 20 mm. Eor asphalts with maximum aggregate size between 20 and 40 mm, the test can be performed with adapted specimen sizes. 

Because the probability of the presence of an extrinsic flaw increases with increase in volume or in total surface of test samples, intrinsic strength measurements require fiber samples of as small a diameter and as small a length as possible. The two-point bend technique (Matthewson et al., 1986) currently provides the simplest way of carrying out such experiments provided the fiber is not too thin (diameter > 50 p.m). This technique is routinely used for testing silica fibers (typical diameter of 125 p.m). For... 

The two-point bend test for glass fibers, (see figure 1)... 

FIGURE 1. Two-point Bend Testing of Glass Fiber... 

The layout of the piping systems has many important factors in pneumatic conveying. One should keep the flow path as the most direct between two points. Bends should be eliminated as much as possible. Care should be taken in the design that the distance after a feed point before the first bend is inserted in a minimum of 3 meters (10 feet) when two-phase conditions are present. If the flow is dilute or dense, this distance is not crucial. The two-phase condition tends to cause a sloshing of the solids in the bend in an unsteady condition. This sloshing behavior causes plugging and other upsets in the operation of the pneumatic conveying systems. As noted before, one should at all costs avoid more than two bends in quick succession. 

The two point bending test, schematieally represented in figure 6, has no clamping problems. A rectangular sample of the film (length 80 mm, width 15 mm) is plaeed between two parallel plates. At the loeation with the lowest curvature radius. 

The length of the ITO edges, tested in the two point bending test, is similar for the uniform ITO layer and the etched ITO line. The difference in crack density at the ITO edges is not responsible for the larger critical failure strain of the uniform ITO layer. 

Suhir E, Effect of the nonlinear stress-strain relationship on the maximum stress in silica fibers subjected to two-point bending , Appl. Optics, 1993,32(9), 1567-72. 

Fig. 4.23 a Schematic diagram of three-point bending test, b two- point bending test and c tipless multi-point bending test Re noduced from Refs. [236, 239, 241], respectively... 

---