Modulus of rupture in bending

Figure 21 Modulus of rupture in bending of surface-benzylated and self-bonded boards. BE21% (O) benzylated board with a 21 WPG BE38% (A) benzylated board with a 38 WPG BE51% ( ) benzylated board with a 51 WPG. PF ( ), conventional particleboard bonds using phenol-formaldehyde resin binder acted as a control. (From Ref. 32.)...

ASTM C-1025 Modulus of rupture in bending of electrode graphite... 

The value of the coefficient r is about two for the modulus of elasticity, and four for the modulus of rupture in static bending. The maximum value of about six applies to compressive strength parallel to the grain (42). 

Because of this, the data listed in Table 15.7 for ceramic materials differ in emphasis from those listed for metals. In particular, the Table shows the modulus of rupture (the maximum surface stress when a beam breaks in bending) and the thermal shoek resist-anee (the ability of the solid to withstand sudden changes in temperature). These, rather than the yield strength, tend to be the critical properties in any design exercise. 

The common tests are shown in Fig. 17.2. The obvious one is the simple tensile test (Fig. 17.2a). It measures the stress required to make the longest crack in the sample propagate unstably in the way shown in Fig. 17.3(a). But it is hard to do tensile tests on ceramics - they tend to break in the grips. It is much easier to measure the force required to break a beam in bending (Fig. 17.2b). The maximum tensile stress in the surface of the beam when it breaks is called the modulus of rupture, o for an elastic beam it is related to the maximum moment in the beam, M by... 

All ceramic materials are elastic, and hence show very little bending under load. They do not exhibit any creep under load. The modulus of rupture type of test is the routine test most commonly used in the ceramic industry, and gives the figure generally quoted for the strength of the material. It must be remembered that the value obtained for any particular body depends on the cross-sectional area of the test piece thus figures quoted from test results may be higher than those obtained on actual articles, which usually have a thicker section than the test piece. 

For members subjected to bending, the value of the modulus of rupture % rather than tensile splitting strength f is used in design. The modulus of rupture is measured by testing to failure, plain concrete beams 6 in. square in cross-section having a span of 18 in. and loaded at two points, each 16 in. equidistant from the end supports of the beam (ASTM C-78). 

Most of the mechanical properties of propylene oxide-modified wood are reduced (116). The modulus of elasticity is reduced 14%, modulus of rupture is reduced 17%, fiber stress at proportional limit is reduced 9%, and maximum crushing strength is reduced 10% (116). Ethylene oxide-modified wood showed no reduction in static bending tests (107). 

After conditioning the boards at 25 C and RH 65% for one month, bending specimens measuring 50 mm in width and 280 mm in length were cut. The three-point bending test was conducted according to the JIS (Japanese Industrial Standard) A 5908, and modulus of rupture (MOR) of each type of board were determined. 

X-ray analysis indicates that the fired material is amorphous silica. Translucent specimens prepared in this manner have a density of over 99% of the theoretical density of pure fused amorphous silica as calculated from the dimensions and weight of the sample. The modulus of rupture is 5000 p.s.i., as measured by the conventional transverse bend technique of applying a measured increasing load at the middle of the bar which is supported across a 1-inch span. 

The modulus of rupture (MOR), modulus of elasticity (MOE) in bending, and tensile strength (TS) parallel to the board surface are shown in Table 7.16 for fiberboards made from control and acetylated kenaf fiber. Acetylation results in a small decrease in MOR, but about... 

Modulus of rupture, MOR. was obtained on polished samples by four point bend tests (4 X 20 mm) with 1 mmmin deformation rate using Instron equipment. The elastic modulus, E, was measured at room temperature, by the acoustic resonance method using a self-assembled apparatus and, at high temperature, from the stress-strain curve obtained in the four point bend tests. 

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