Introduction to Engineering-Solid Mechanics 2.Stress and Strain Stress -The rod is formed of a solid continuous material Instead of concentrated at a point,the internal force spreads out over the cross section - Tensile stress,is the applied force per unit of original cross- sectional area F A (c) When the stress tends to lengthen the rod,it is called tension, and o >0. When the rod tends to be shortened,the stress is called compression.and o 0. Introduction to Engineering 10 H.ShaoIntroduction to Engineering Introduction to Engineering —— Solid Mechanics Solid Mechanics Introduction to Engineering Introduction to Engineering H. Shao 10 2. Stress and Strain Stress – The rod is formed of a solid continuous material – Instead of concentrated at a point, the internal force spreads out over the cross section – Tensile stress, is the applied force per unit of original cross￾sectional area  When the stress tends to lengthen the rod, it is called tension, and σ >0.  When the rod tends to be shortened, the stress is called compression. and σ < 0. σ (c) F A F  