Forging new generations of engineers Stress Principles of EngineeringTM Lesson 5.2 – Strength of Materials Forging new generations of engineers Project Lead The Way, Inc. Copyright 2007

Stress

STRESS Stress in a structure is a quantity that’s calculated once you know the applied forces and the shape or geometry of a part. The stresses in a part should be below the allowable stress of the material. The allowable stress in a part depends on several factors which will be shown later in this lesson.

Types of Stresses  Before After Axial   Shear Axial and shear stresses are deforming a small element of material   

Types of Loading Formula Axial  = P / A where: A is the cross section area Shear  = P / A Formulas shown can be used to calculate average stress on the cross section P

Pure Bending Compression M M Tension M is a moment or torque. M creates axial compressive (-) stress on the top surface and axial tensile (+) stress on the bottom surface. The axial stress crosses through zero at the location of the centroid of the cross section, this location is called the neutral axis.

Neutral Axis Compression Tension Location of centroid & Neutral Axis

Fiber Distance C C Note the stress changes with location. To find the stress at a point you need to know the distance from the neutral axis (NA). The maximum stress is at the point furthest from the NA.

Bending Stress or Use one of the two formulas shown below: Where: M = moment C = maximum fiber distance I = moment of inertia of cross section S= section modulus= I / C or