1. ENGR 225 Section 2.1

2. Review ~ Force per Area Normal Stress –The average normal stress can be determined from σ = P / A, where P is the internal axial load. Shear Stress –The average shear stress can be determined from τ = V / A, where V is the resultant shear force.

3. Strain Deformation due to a stress is specified using the concept of normal and shear strain.

4. Normal Strain Elongation or contraction of a line segment per unit of length.

5. Shear Strain The change in angle the occurs between two line segments that were originally perpendicular.

6. Volume and shape deformations

7. Strain Normal strain causes a change in volume Shear strain causes a change in shape

8. Positive and Negative strain Normal strain : Initial line elongates :  L positive, strain positive Initial line contracts :  L negative, strain negative Shear strain :  ’ <  /2 : Strain positive  ’ >  /2 : Strain negative

9. Small strain Analysis Deformations very small Normal strain  < < 1 sin  ≈  tan  ≈  cos  ≈ 1

10. Problem 2-4: Find the normal strain developed in each wire if the force P cause point A to be displaced 2mm horizontally.

11. 2.8 Part of a control linkage for an airplane consists of a rigid member CBD and a flexible cable AB. If a force applied to the end D causes CBD to rotate by 0.3 , determine the normal strain in the cable. Originally the cable is un-stretched.