Page 19 - Aircraft Stuctures for Engineering Student

4 Basic elasticity

Fig. 1.1 Internal force at a point in an arbitrarily shaped body.
Generally, the direction of SP is not normal to the area SA, in which case it is usual
to resolve SP into two components: one, SP,, normal to the plane, the other SPs,
acting in the plane itself (see Fig. 1.2). The stresses associated with these components
are a normal or direct stress defined as

and a shear stress deiined as
SPs
T= lim -
6A-0 SA
The resultant stress is computed from its components by the normal rules of vector
addition, namely
Resultant stress = d m

n

p3
Fig. 1.2 Internal force Components at the point 0.