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INTRODUCTION TO DESIGNSKMM 1512

Semester 2 Session 2014/2015

INTRODUCTION TO

DESIGNSKMM 1512

Week 2Engineering Design

MR. KHAIRUL ANWAR BIN HANAFIAHSenior Lecturer,

Applied Mechanics and Design Department

Faculty of Mechanical Engieering. UTM. Skudai.

Engineering Design

6 Fatigue Failure Resulting from Variable Loading

Chapter Outline

6-1 Introduction to Fatigue in Metals

6-2 Approach to Fatigue Failure in Analysis and Design

6-3 Fatigue-Life Methods

6-4 The Stress-Life Method

6-5 The Strain-Life Method

6-6 The Linear-Elastic Fracture Mechanics Method

6-7 The Endurance Limit

6-8 Fatigue Strength

6-9 Endurance Limit Modifying Factors

6-10 Stress Concentration and Notch Sensitivity

6-11 Characterizing Fluctuating Stresses

6-12 Fatigue Failure Criteria for Fluctuating Stress

6-13 Torsional Fatigue Strength under Fluctuating Stresses

6-14 Combinations of Loading Modes

6-15 Varying, Fluctuating Stresses; Cumulative Fatigue Damage

6-16 Surface Fatigue Strength

6-17 Stochastic Analysis

6-18 Road Maps and Important Design Equations for the Stress-Life Method

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!

END OF SLIDE

THANKS

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