Under uniaxial tensile load why does ductile fail at 45 degr

Under uniaxial tensile load, why does ductile fail at 45 degrees with the loading direction?

mechanic of material

Solution

When we do ductility test under uniaxial tensile load, maximum shear plane will be at 45 deg to Principle stress or normal stress. That is why ductility fails at 45deg with loading direction.