Moduli of rupture

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. 

There are, of course, many more ceramics available than those listed here alumina is available in many densities, silicon carbide in many qualities. As before, the structure-insensitive properties (density, modulus and melting point) depend little on quality -they do not vary by more than 10%. But the structure-sensitive properties (fracture toughness, modulus of rupture and some thermal properties including expansion) are much more variable. For these, it is essential to consult manufacturers data sheets or conduct your own tests. 

Fig. 17.2. Tests which measure the fracture strengths of ceramics, (a) The tensile test measures the tensile strength, CTj. (b) The bend test measures the modulus of rupture, o , typically 1.7 x CTj. (<) The compression test measures the crushing strength, a, typically 15 x...

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... 

Modulus-of-rupture tests are carried out using the arrangement shown in Fig. 17.2. The specimens break at a load F of about 330 N. Find the modulus of rupture, given that I = 50 mm, and that b = d = 5 mm. 

Estimate the thermal shock resistance AT for the ceramics listed in Table 15.7. Use the data for Young s modulus E, modulus of rupture c, and thermal expansion coefficient a given in Table 15.7. How well do your calculated estimates of AT agree with the values given for AT in Table 15.7 ... 

Bnich-kupfer, n. scrap copper, -last, /. breaking load, -metall, n. broken metal, scrap metal, -modul, m. modulus of rupture, -probe, /. breaking test, breakdown test, -punkt, m. breaking point, -riss, m. (Meial.) failure crack, -silber, n. broken silver, scrap silver, -spaonung,/. breaking stress tensile strength, -stein, m. quarry stone broken stone, -stelle,/. broken place, place of fracture. -strich, m. (Math.) fraction stroke (between numerator and denominator), -stiick, n. fragment shred, -stiicke, pi. debris scrap, -teil, m. fraction, -zahl, /. fractional number. 

Body Tensile strength (MN/m ) Com- pressive strength (MN/m ) Modulus of rupture (MN/m ) Apparent porosity m Thermal Young s conductivity modulus (Wm- K- )(GN/m ) Thermal expansion coefficient 0-500°C (mm/mm°C)... 

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. 

Using these relationships, the flexural strength, also called the modulus of rupture,... 

Sugar maple was reacted with propylene and butylene oxide (Rowell etal., 1982). The modulus of elasticity (MOE) and modulus of rupture (MOR), fibre stress at proportional limit, and maximum crushing strength all exhibited a reduction, compared to unmodified samples. Nilsson and Rowell (1983) reacted ponderosa pine with butylene oxide and exposed the wood in an unsterile soil decay test. At low WPGs, severe surface decay due to soft rot and tunnelling bacteria was observed. Such attack was reduced at 15 % WPG,... 

Type PCEb Modulus of rupture, MPa Temp, °C Change, % at °C % at °C % Bulk density g/cm3 Porosity, %... 

Silica Brick. Under ASTM C416, types A and B silica bricks are classified according to chemical composition and strength. Silica brick must have an average modulus of rupture of 3.5 MPa (500 psi), <1.5% A O no more than 0.2% Ti02, <2.50% Fe203, and <4.00% CaO. Type A brick must have a flux factor <0.5. The flux factor is equal to the percent alumina plus twice the percent of alkalies. Type B are all other silica brick covered by the standard chemical and strength specifications. 

High temperature strength of refractory materials is determined on rectangular prisms 25 x 25 x 150 mm cut from the product being tested. The specimens are placed in a furnace, heated to a desired temperature, and the modulus of rupture is determined. A detailed description is given in ASTM C583. 

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