Size effects in material strength due to crack growth and material non-linearity

Failure by strength and fracture collapse tend to compete with one another when the specimen sizes are varied. Material testing dealing with the determination of tensile strength and hardening is usually carried out with small specimens while the evaluation of fracture mechanics parameters such as critical stress-intensity factor or strain energy density factor requires specimens that are larger in size. The formation of cracks in small specimens does not appreciably affect failure by strength collapse. On the other hand, the fracture process is not disturbed by the development of plastic hinges in the unbroken ligament of the larger specimens.