摘要：Strength and fracture parameters are very impor-tant in fracture mechanics. Hereupon when at crack tipexists stress concentration complex stress state is obtained.Here is not enough to determine highest stresses whilestrength and fracture are governed by equivalent effect.This effect also depends on material properties: elasticityand plasticity. In various studies [1-2] mostly brittle frac-ture is researched and plastic fracture studies are muchmore rare [3]. Fracture depend on crack size as well [4, 5].Considering defect like round hole strength can be com-puted according theory of elasticity [6] and especially forfracture of brittle materials Griffiths criteria shall be ap-plied [4]. But using this criteria it is complicated to deter-mine crack growth and its area size. This task requires ad-ditional studies.
