1.2 Types of torsion failures
Torsion failures are different from tension failures and normally provide little deformation or
elongation. The characteristic of the fracture surface is related to the state of stress at the point on the
bar surface, which can be described as shown in figure 8. It can be seen that the maximum shear
stresses exist along two planes, which are perpendicular to each other. One is perpendicular to the
longitudinal axis (yy) and another is aligned parallel to the longitudinal axis (xx). The principleperpendicular to the
longitudinal axis (yy) and another is aligned parallel to the longitudinal axis (xx). The principle stresses σ1 and σ3 are inclined at 45o to the longitudinal axis and have their magnitudes equal to those
of the shear stresses. The principle stress σ1 is tensile while the principle stress σ3 is compressive.
The intermediate stress σ2 is zero under torsion.