Question

A structural component in the shape of a flat plate 24.2 mm thick is to be fabricated from a metal alloy for which the yield strength and plane strain fracture toughness values are 545 MPa and 20.0 MPa-m1/2, respectively. For this particular geometry, the value of Y is 1.0. Assuming a design stress of 0.2 times the yield strength, calculate the critical length of a surface flaw.

Answer 1

Answer:

ac = 0.01071 m = 10.71 mm

Explanation:

Given:-

- The thickness of plate,    t = 24.2 mm

- The yield strength of metal alloy,   σy = 545 MPa

- The fracture toughness,   Kic = 20.0 MPa-√m

- The geometrical criticality,  Y = 1.0

- Factor of design,  nd = 0.2

Find:-

Calculate the critical length of a surface flaw

Solution:-

- We are to determine the minimum critical length ( ac ) for the design stress ( σd ) that leads to failure of the plate with thickness ( t ).

- The relation for the critical length ( ac ) depends on the material intrinsic properties i.e Fracture toughness - ( Energy required for the material to fracture ) and the design yield strength ( σd =  nd*σy  ).

- The relation is given below:

                         

                          ac = [ Kic / Y*σd ] ^2 * ( 1 / π )

                          ac = [ Kic / Y*σy*nd ] ^2 * ( 1 / π )

                          ac = [ 20.0*5 / 1*545 ] ^2 * ( 1 / π )

                          ac = 0.01071 m = 10.71 mm

Answer: The minimum critical length ( ac ) for the metal alloy subjected to the given  design stress is ( 10.71 mm ) for fracture.