Page 21 - Aircraft Stuctures for Engineering Student

6 Basic elasticity

Fig. 1.4 Components of stress at a point in a body.

We shall now define the directions of the stresses in Fig. 1.5 as positive. Thus,
normal stresses directed away from their related surfaces are tensile and positive,
opposite compressive stresses are negative. Shear stresses are positive when they act
in the positive direction of the relevant axis in a plane on which the direct tensile
stress is in the positive direction of the axis. If the tensile stress is in the opposite

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Fig. 1.5 Sign conventions and notation for stresses at a point in a body.