When a mild-steel specimen fails in a torsion test fracture looks like

Q. Consider the following statements:
P. Volume of specimen under uniaxial compression remain constant upto elastic limit.
Q. Brittle materials fails perpendicular to the axis of the bar under torsion.
R. Proportional limit, yield point and fracture point can be assumed same for mild steel specimen.
The correct option for above statements is:

Q. Assertion (A): A mild steel tension specimen subjected to an axial load fails along a surface at 45° to its axis.
Reason (R): Mild steel is weaker in shear than in tension and the place of maximum shear is at 45° to its axis

Q. Assertion (A): The failure surface of a mild steel torsion specimen subject to a torque about its axis is along a surface perpendicular to its axis.
Reason (R): Mild steel is relatively weaker in shear than in tension and the plane of maximum shear is perpendicular to its axis.

Q. In mild steel specimens subjected to tensile test cycle, the elastic limit in tension is raised and the elastic limit in compression is lowered. This is called

Q. Statement (I): The failure of a mild steel specimen of circular cross-section, subjected to a torque occurs along its cross-section.
Statement (II): The failure occurs on a plane of the specimen subjected to maximum shear stress; and mild steel is relatively weak in shear.