Silicon bending strength test

Figure 12.8 Bending strength test results for a silicon nitride ceramic. Plotted is the probability of failure versus the strength. The straight lines represent Weibull distributions. The measured Weibull distribution has a mod ulus of m = 15.5, and the characteristic strength is 844 MPa. Also...

Fig. 1 a) Strength data of a silicon nitride ceramic tested in four point bending (4PB) in a Weibull plot and b) the relative frequency distribution of flaw sizes. The data points were determined by fracture experiments. 

The density was measured by Archimedes method. The flexure strength were tested by three point bending way using an INSTRON 5566 test machine (Canton, MA, USA) with a span of 24 mm and a crosshead speed of 0.5 mm/min. The work of fracture was obtained from the characteristic area under the stress-displacement curve divided by the cross section of the specimen. In order to determine the work of fracture effectively, we defined the characteristic area which started from initial point to the 60% drop of the curve. After the test, the silicon volume content was calculated... 

From the performance in bending of present polymer systems usable for cured-in-place sealants, a polyurethane and a noncrystallizing silicone appear to be most suitable as cryogenic sealants. They must be reinforced with a woven glass fabric to provide the strength necessary for expected service conditions on launch vehicles. Tests are underway to determine if they will also remain serviceable down to 20°K. 

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