Alumina bending tests

Figure 12.7 Fracture origins, (a) In a silicon nitride bending test specimen (b) In a barium titanate (PTC ceramic) bending test specimen (c) In an alumina bending test specimen. The origins are an agglomeration of coarse.

The Youngs moduli of the support has been measured with four point bending tests, Poisson s ratio is taken to be equal to that of dense alumina. Values of Eg and Vg are 65 4 GPa and 0.23 respectively. To obtain measurable values of 5, dg is taken about 0.4 mm, while df is in the range of 1-10 pm. The values of 5 range from 0.05-0.15 mm. 

A commercially available polycrystalline alumina is tested using three different methods three-point bend, four-point bend, and uniaxial tension. The resulting MOR values are 550, 410, and 175 MPa, respectively. What conclusions can you make about the material from these data ... 

Figure 12.16 Bending tests at room temperature on an alumina ceramic [99]. Plotted is the cumulative frequency (a) versus time to failure for constant loading (0 = 270 MPa) and (b) versus strength for tests...

Figure 12.17 (Mean) strength versus stress rate for constant stress rate bending tests performed on alumina (same material as described above). For details, see Ref [99]. The SCCC exponent determined using this data is n = 33. Each datum point results from seven...

A recent use of equation (5.73) to determine K,c values as a function of grain size for alumina compares results to notched beam tests. The broken arms of the beams were used for the indentation-strength in bending test (ISB). Thus a good comparative study was possible. Figure 5.16 shows the close correspondence between the ISB results and the earlier results of Rice et using a double cantilever beam method. 

A typical rack employed for installation of specimens in pilot plants is shown in Fig. 6. Both corrosion coupons, 2 X 1 X 0.35 in. thick, and bend specimens intended to determine stress-corrosion cracking susceptibility, are included in the installation for aqueous corrosion testing. Specimens are separated by high density alumina spacers to eliminate electrochemical effects. During exposure, the racks are welded to existing components in the pilot plant equipment. 

Table 1. Four point bending strength, fracture toughness measured by single edge pre cracked beam (SEPB) method, and Vickers hardness of the tested alumina specimens. Standard deviations are in brackets.

Pett,T, and Munz,D, Prediction of time to failure of alumina under constant loading as deduced from bending streogth tests,Cfi/Ber.DKG 4/5-84, 190-197. 

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