Machine Elements in Mechanical Design FIFTH EDITION CHAPTER

Machine Elements in Mechanical Design FIFTH EDITION CHAPTER 5 Design for Different Types of Loading Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Types of Loading and Stress Ratio • Stress Variations Key Values § § Maximum stress Minimum stress Mean (average) stress Alternating stress • Static Stress § When part is subjected to load applied slowly, without shock, and held at a constant value Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Types of Loading and Stress Ratio • Stresses § Stress reversal: element of loadcarrying member subjected to level of tensile stress followed by same level of compressive stress § Repeated and reversed or pure oscillation: stress cycle repeated many thousands of times Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Types of Loading and Stress Ratio • Stresses § Fluctuating (pulsating) stress: loadcarrying member subjected to alternating stress with nonzero mean Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Types of Loading and Stress Ratio • Loading § Loads applied suddenly and rapidly cause shock or impact. § Random: varying loads are applied that are not regular in their amplitude. Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Endurance Strength and Mechanisms of Fatigue Failure • Fatigue Failures § Low-cycle fatigue (LCF) or high-cycle fatigue (HCF) • Endurance Strength, Fatigue Strength or Limit § Stress level reached where virtually unlimited number of cycles of stress can be applied without fatigue failure Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Estimated Actual Endurance Strength • Factors Affecting Endurance Strength § § § Surface finish Material factor Type-of-stress factor Reliability factor Size factor Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Table 5 -3 Size Factors Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Estimated Actual Endurance Strength • Other Factors § § § § Flaws Temperature Nonuniform material properties Residual stresses Corrosion and environmental factors Nitriding Effect of stress ratio Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Design Philosophy • General Considerations § § Application Environment Loads Types of stresses Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Design Philosophy • General Considerations § Material § Confidence • Design Factor § Measure of relative safety of loadcarrying component Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Predictions of Failure and Design Analysis Methods • Design Methods § Maximum Normal Stress Method for Uniaxial Static Stress on Brittle Materials § Yield Strength Method for Uniaxial Static Normal Stresses on Ductile Materials § Maximum Shear Stress Method for Static Shear Stress on Ductile Materials Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Predictions of Failure and Design Analysis Methods • Design Methods § Endurance Strength Method for Repeated and Reversed Normal or Shear Stresses on Ductile Material § Goodman Method for Fluctuating Stresses on Ductile Materials • Checking for early cycle yielding Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

General Design Procedure • General Design Requirements § Objectives and limitations on size, shape, weight, desired precision § Nature of loads to be carried § Types of stresses produced by loads § Type of material from which element to be made Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

General Design Procedure • General Design Requirements § General description of manufacturing process to be used, particularly surface finish § Desired reliability Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Additional Design Analysis Methods • Modified Mohr Method for Biaxial Static Stress on Brittle Materials • Distortion Energy Method for Static Stress on Ductile Materials Using von Mises Stress • Fluctuating Combined Stresses— Maximum Shear Stress Method Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Additional Design Analysis Methods • Fluctuating Combined Stresses— Distortion Energy Method • Gerber Method for Fluctuating Stresses on Ductile Materials • Smith Diagram for Showing the Effect of Mean Stress on Fatigue Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Statistical Approaches to Design • Samples of Statistical Terminology and Tools § § Statistical and stochastic methods Data sets Inferences Linear regression Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Statistical Approaches to Design • Samples of Statistical Terminology and Tools § Distributions for applied loads and stresses compared with distribution for strength of material § Reliability of component quantified § Optimum assignment of tolerances Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Finite Life and Damage Accumulation Method • Finite Life and Varying Stress Amplitude Examples § Bicycle brake lever § Lawn mower height-adjustment mechanism § Automotive lift in a service station § Parts feeding device Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Finite Life and Damage Accumulation Method • Finite Life and Varying Stress Amplitude Examples § Automotive suspension member § Machine tool drive system § Cranes, power shovels, bulldozers, construction equipment Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved

Finite Life and Damage Accumulation Method • Damage Accumulation Method § Principle: assumption any given level of stress applied for one cycle of loading contributes to a certain amount of damage to a component. § Failure predicted using Miner linear cumulative-damage rule or Miner's rule Machine Elements in Mechanical Design , Fifth Edition Robert L. Mott Copyright © 2014 by Pearson Education, Inc. All Rights Reserved