Many studies have been carried out to relate K-I and K-II at fracture in bi
axial loading. In the present investigation, the Mohr type of stress intens
ity factor (SIF) circles in uniaxial and pure shear type of loading are pre
sented and discussed for the 'no fracture' relation between K-I and K-II fo
r inclined cracks in biaxial loading. This 'no fracture' relation forms the
lower bound for the fracture toughness relation between K-I and K-II. The
experimental data points are seen to lie outside this lower bound for diffe
rent materials.