A large, thin $($plane stress$),$ plate with a central crack of length $2a=50mm$ is loaded by

a remote tensile stress $$; at an experiment the crack started to propagate when

$=150$MPa. For the material we have $E=210$GPa and ${}_Y=500$MPa.

a$)($Problem $34)$ Verify that it is appropriate to use linear elasticiry to analyse the problem.

and determine $K_{Ic}.$

b$)$ Assume that the thickness is so small that LEFM is not valid. and use Irwin correction

to determine the fracture toughness. Is the result on the safe side $($conservative esti$-$

mate$)?$