  We report a combined experimental and theoretical study of boron carbide
under stress/deformation. A special rotating anvil press, the rotating
tomography Paris Edinburgh cell (RotoPEC), has been used to apply torsional
deformation to boron carbide under a pressure of 5~GPa at ambient temperature.
Subsequent damages and point defects have been analysed at ambient pressure by
energy dispersive X-ray microdiffraction at the synchrotron and by Raman
spectroscopy, combined with calculations based on the density functional theory
(DFT). We show that apart from the signals due to B$_4$C, new peaks appear in
both characterisation methods. The DFT calculations of atomic structures and
phonon frequencies enable us to attribute most of the new peaks to boron
vacancies in the intericosahedral chains of boron carbide. Some of the Raman
spectra also show three peaks that have been attributed to amorphous boron
carbide in the literature. Deformed boron carbide thus shows small inclusions
of clusters of boron carbide with chain vacancies, and/or small zones
interpreted as amorphous zones.
