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The yield strength of a material is 200MPa when the grain size is 80 micron. If the frictional stress is 80MPa, find the strength when the grain diameter is 160 micron?

Correct Answer: 180 MPa
According to the hall-patch relationship: σo=σi+kD-1/2 -> 200=80+k(80)-1/2 -> k=1252 So at D=160 σo=80+1252(160)-1/2 σo=178.9 MPa.

Identify the correct statements from the following:
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Q. Von-Misses yield criterion implies that yielding occurs when the distortion energy reaches a critical value.
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S. Tresca's yield criterion gives a circular cylinderical surface in the space of the three principal stresses.

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