1. 1 INTRODUCTION TO DESIGN SKMM 1512 Semester 2 Session 2014/2015

2. INTRODUCTION TO DESIGN SKMM 1512 Week 2 Engineering Design MR. KHAIRUL ANWAR BIN HANAFIAH Senior Lecturer, Applied Mechanics and Design Department Faculty of Mechanical Engieering. UTM. Skudai.

3. Engineering Design

4. 6 Fatigue Failure Resulting from Variable Loading Chapter Outline 6-1Introduction to Fatigue in Metals 6-2Approach to Fatigue Failure in Analysis and Design 6-3Fatigue-Life Methods 6-4The Stress-Life Method 6-5The Strain-Life Method 6-6The Linear-Elastic Fracture Mechanics Method 6-7The Endurance Limit 6-8Fatigue Strength 6-9Endurance Limit Modifying Factors 6-10Stress Concentration and Notch Sensitivity 6-11Characterizing Fluctuating Stresses 6-12Fatigue Failure Criteria for Fluctuating Stress 6-13Torsional Fatigue Strength under Fluctuating Stresses 6-14Combinations of Loading Modes 6-15Varying, Fluctuating Stresses; Cumulative Fatigue Damage 6-16Surface Fatigue Strength 6-17Stochastic Analysis 6-18Road Maps and Important Design Equations for the Stress-Life Method

5. Introduction to Fatigue in Metals Static conditions : loads are applied gradually, to give sufficient time for the strain to fully develop. Variable conditions : stresses vary with time or fluctuate between different levels, also called repeated, alternating, or fluctuating stresses. When machine members are found to have failed under fluctuating stresses, the actual maximum stresses were well below the ultimate strength of the material, even below yielding strength. Since these failures are due to stresses repeating for a large number of times, they are called fatigue failures. When machine parts fails statically, the usually develop a very large deflection, thus visible warning can be observed in advance; a fatigue failure gives no warning!

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