Three-point bend tests

FIG. 20-75 Fluid-bed erosion or wear rate as a function of granule material properties. Kq is fracture toughness and H is hardness as measured hy three-point bend tests. [Ennis [Pg.1888]

Fig. 18. Yield strengths in three-point bend tests of highly filled composites of polyfvinyl butyral) and silica particles treated with methylsilane and octylsilane coupling agents to varying degrees of surface coverage vs. work of adhesion measured independently using IGC. Redrawn from ref. [90].

Tensile and flexural properties were studied with an Instron 4204 testing machine. Tensile tests were performed on the drawn strands at a test speed of 3 mm/ min, while three-point-bending tests (ISO 178) at a speed of 5 mm/min were applied to the injection molded specimens. Charpy impact strength was measured of the unnotched samples with a Zwick 5102 pendulum-type testing machine using a span of 70 mm. The specimens (4 X 10 X 112 mm) used for three-point-bending tests were also used for the impact tests. It should be noted that neither the tensile tests for the strands nor the impact tests were standard tests. The samples were conditioned for 88 h at 23°C (50% r.h,) before testing. 

Flexural strength is determined using beam-shaped specimens that are supported longways between two rollers. The load is then applied by either one or two rollers. These variants are called the three-point bend test and the four-point bend test, respectively. The stresses set up in the beam are complex and include compressive, shear and tensile forces. However, at the convex surface of the beam, where maximum tension exists, the material is in a state of pure tension (Berenbaum Brodie, 1959). The disadvantage of the method appears to be one of sensitivity to the condition of the surface, which is not surprising since the maximum tensile forces occur in the convex surface layer. 

Boukhili, B., Hubert, P. and Gauvin, R. (1991). Loading rate effect as a function of the span-to-depth ratio in three-point bend testing of unidirectional pultruded composites. Composites 22, 39-45. 

Fig. 9.34 Four- and three-point bending test of a ceramic object.

The general formula for the three point bending test is... 

Photo 14.1 / 14.2 Optical micro-photograph of a SiC/SiCf composite, made by means of CVI before and after a three point bending test (source Ube Industries Co Ltd Japan). 

The cement rods were subjected to a three point bending test. The breaking strength and the E modulus were calculated using the following formulas ... 

Most of the time, the three-point bending test (Fig. 12.2c) induces fracture without exhibiting yielding. The stress calculated here is a maximum stress due to the inhomogeneity of the stress field along the thickness ... 

Figure 12.2 Schematic representations of (a) pure shear test (b) plane strain compression test and (c) three-point bending test.

D = span length of sample in three-point bending test, m dL = length variation of a sample in a tensile test, m E = Young s modulus, Pa (GPa)... 

Figure 7. Three-point-bending tests of 2D C-C specimens 1 and 2 in as-received condition 3 and 4 treatment at 2480°C for 1 hr.

Instron Three-Point Bending Failure. Three-point bending tests have also been conducted on notched Izod specimens at crosshead rates of 0.02-20 inches/min (Figure 5). Plots of work to break obtained from the areas under the Instron force-displacement traces show abrupt ductile-brittle transitions these are displaced to lower temperatures as the test rate is decreased. However the temperature interval between ductile-brittle transitions of the two materials remains about the same. The force-displacement trace for each specimen shows a yield point with a ductile failure but a sharp termination when the sample breaks in a brittle fashion. 

Figure 7, Temperature dependence of failure stresses in Instron three-point bend tests on Vs inch notched Izod bars cut from (a) extruded polycarbonate sheet and (b) compression molded block polymer B. Crosshead rate = 0,02 inch /min. Span = 2 inches, o = net section stress = force/net cross-section at notch root, O, Craze initiation , ductile failure X, brittle failure ...

Block polymer B differs substantially in its failure characteristics from BP A polycarbonate. For the block polymer a mixed failure mode predominates in three-point bend tests of notched specimens from —100°-90°C. In the mixed mode craze breakdown and plane strain fracture occur first inside the specimen subsequently shear failure occurs in the surface regions of the specimen. Shear lips (11) are formed as a result. Shear lips are also found on the notched Izod impact fracture surfaces of block polymer B, implying that the same mixed mode of failure occurs under high speed loading conditions. 

Creep of chemically modified woods along the grain was measured in three-point bending tests at 30°C using humidity cycles between 29% RH and 86%RH. The initial load was adjusted to specimen dimensions after chemical modification to obtain a stress level of 10 MPa in the dry state. The following procedure was imposed on all specimens loaded at 29% RH, kept 10 min, moved to 86% RH for 24 h, returned to 29% RH for 24 h, unloaded at 29% RH, kept 10 min, moved to 89% RH for 24 h, and, finally, returned to 29% RH for 24 h. A small fraction of the initial load remained on the specimen after unloading. 

Another important large deformation measurement is the three point bending test (Figure 17.19). Here a mold of the solid fat is plaeed on two beams and a third beam applies an external force between the other two beams. The Young s modulus ( ) and yield force may be determined depending on the cross-section as (rectangular Equation (17.18) or circular Equation (17.19)) ... 

The experiments were performed on commercially available samples of HOPE, PP, PA 6, PA 66, PBT, POM, and PEEK. Their trade namra are listed in Table 1. The dimensions and shape of the test samples, as shown in Fig. 1, were chosen to maintain a state of plane strain. A round notch of 0.5 mm radius was introduced in the center of one edge of the sample by machining. The samples were loaded in the three-point bending test using an Instron-type testing machine. For microscopic observations. 

To investigate the influence of self-organization on the mechanical properties of the composites, the compacts were cut into test pieces 5 x 3 x 20 nun in size with a diamond saw for a three-point bending test. The three-point bending tests were performed at a crosshead speed of 500 pm/min and a span of 15 nun with... 

A rectangular bar of polymer of thickness B = S mm and width = 20 mm has a central notch of length a = 10 mm. The bar is loaded in a three-point bending test with an 80 mm span, S, at room temperature. The bar fractures when the force applied is 300 N. Calculate (a) Kjc for the polymer and (b) the force needed to fracture in a compact tension test a specimen of dimensions IT = 50 mm, J = 10 mm, having a single-edge sharp crack of = 25 mm. 

The table shows the force needed to fracture single-edge bars of several polymers at room temperature in a three-point bending test. Bar dimensions are IT = 10 mm, B = 6 mm, a = 5 mm the test span S is 80 mm. The second column in the table gives the corresponding yield stress. Calculate Kic for each polymer, and indicate in which cases valid plane strain conditions exist. 

The critical stress intensity factor, Kc, at fracture initiation was measured by single-edge notched three-point bending tests carried out at low (lOmm/min) and high (Im/s) load point displacement rate under different environmental conditions (temperature and moisture). 

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