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A micromachined specimen with a test section only 150-μm thick was developed for investigating subcritical crack growth in silicon. Crack growth rates in the range 10−4–10−10 m/s were measured as a function of applied stress intensity (v–K curves) during tests in humid air and dry nitrogen lasting up to 24 h. The fracture toughness, KIc of {110} silicon was also measured at 1.15 ± 0.08 MPa m1/2. While some evidence MPa-m1/2 of subcritical crack growth appeared to occur in the region 0.9 KIc < K > 0.98 KIc, the extremely high crack growth exponent (n 100) and the high ratio of the apparent stress corrosion threshold, KIscc, to the fracture toughness, KIscc/KIc > 0.9, suggests that no clear evidence exists for a stress corrosion process in silicon exposed to humid air.

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