  In this communication, the feasibility of the nonlocal strain gradient theory
for fields of applied mechanics is investigated. It is demonstrated that the
nonlocal strain gradient theory is physically incorrect. It is proved that each
of the nonlocal theory and the strain gradient theory can model, both,
hardening and softening behaviors of materials. Moreover, it is proved that the
nonlocal theory and the strain gradient theory describe the same physical
phenomena, and hence the strain gradient theory cannot be merged with the
nonlocal theory in a unified model. This short communication comments on a
series of papers in which the nonlocal strain gradient theory was utilized in
different areas of applied mechanics.
