Forces are applied to produce stress tangential to the specimen surface.
Units of Stress
A force is measured in newtons (N). Therefore, if the stress is the force divided by the area to which it is applied (m2) then the units of stress are N/m2 (Nm-2). This is usually too small to be useful in engineering applications so the units most commonly used are mega newton per metre squared (MNm-2) also termed a mega pascal (MPa).