A 1-cm thick plate will be fabricated from one of the three materials listed bel

Question

A 1-cm thick plate will be fabricated from one of the three materials listed below. The material can be non-destructively inspected with dye penetrant testing for surface flaws and radiography for internal flaws. Assuming that the detection limit of dye penetrant is 0.05 mm and that of radiography is 2% of the plate thickness, what design stress would you use for each of the materials? You may assume Y=1.

Material A has Yield Strength of 500 MPa and a K of 20 (MPa*m^0.5)

Material B has Yield Strength of 750 MPa and a K of 12 (MPa*m^0.5)

Material C has Yield Strength of 1000 MPa and a K of 8 (MPa*m^0.5)

Explanation / Answer

Material A

500 * sqrt(a)   = 20        ( a is the crack length)

a = 0.0016 m or 1.6 mm

sigma * sqrt(0.00005) = 20

Material B

750 * sqrt(a)   = 12       ( a is the crack length)

a = 0.000256 m or 0.256 mm

Material C

1000 * sqrt(a)   = 8        ( a is the crack length)

a = 0.000064 m or 0.064 mm

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