Machine Design [MET 4501]

Module 2 - Failure Prevention

Chapter 6: Fatigue Failure

Chapter 6 Overview

Chapter 6 covers the following key concepts:

  • Exploration of material behavior under cyclic loading and its implications for design.
  • Introduction to fatigue life estimation techniques, including S-N curves and the Goodman line.
  • Discussion of factors influencing fatigue failure, such as surface finish, size, and environmental conditions.

Lecture 9: Introduction to Fatigue

Today, we're beginning our study of fatigue failures. Understanding this topic has been somewhat elusive, perhaps because it depends on a combination of many variables, with a high level of randomness. Nevertheless, there are models we can use to study this phenomenon, and (hopefully) prevent future catastrophes due to this insidious mode of failure.

  • Read
    • Sections 6.1-6.7 of Shigley's Mechanical Engineering Design

  • Watch
    • Incredible Footage of the Damage Endured by Aloha Airlines 243: Air Disasters | Smithsonian Channel: On April 28, 1988, a Boeing 737-297 serving the flight suffered extensive damage after an explosive decompression in flight, caused by part of the fuselage breaking due to poor maintenance and metal fatigue [according to the Wikipedia page]. Watch the linked video showing Aloha Airlines 243 shortly after its emergency landing on April 28, 1988, reveals a 737 with the front part of the cabin almost completely missing.
    • No Highway In The Sky 1951 Full Movie HD ( With English Subtitle): If you have time over the weekend, watch this movie which features James Stewart, Jack Hawkins, Maurice Denham, Marlene Dietrich, Wilferd Hyde White and a fatigue failure. This story was incredibly prescient to the metal fatigue issues encountered by the DeHavilland Comet jet airliner at the time, resulting in fatal crashes in the early 1950s, thus prompting the grounding of the entire fleet.

  • Practice
    • Problems 6-3 and 6-5 from Shigley's Mechanical Engineering Design, and then review the solutions posted. - Module 2 Homework Problems

Lecture 9 Notes

  • Lecture 9(A) Notes[pdf]
  • Lecture 9(B) Notes[pdf]

Lecture 10: Endurance Limit Modifying Factors

In this lecture, we will take a deeper look at endurance limit modifying factors, also known as Marin factors, which help refine fatigue life predictions by accounting for real-world influences on material strength. We'll explore how factors such as surface finish, size, loading, temperature, reliability, and manufacturing processes affect the endurance limit of a material.

Lecture 10 Notes

  • Lecture 10 Notes[pdf]
  • Lecture 10 Slides[pdf]

Lecture 11: Stress Concentration and Notch Sensitivity

In this lecture, we will explore stress concentration and notch sensitivity, two critical factors in fatigue failure analysis. Even small geometric features—like holes, fillets, and keyways—can create localized stress spikes that significantly reduce a component’s fatigue life. We’ll discuss how to quantify these effects and how materials respond to them.

Lecture 11 Notes

  • Lecture 11 Notes[pdf]
  • Lecture 11 Slides[pdf]

Lecture 12: In-Class Quiz #3

We will have In-Class Quiz #3 today.

In-Class Quiz 3

  • In-Class Quiz 3[pdf]
  • In-Class Quiz 3 Solution[pdf]

Lecture 13: Fatigue Failure Criteria

In this lecture, we will explore fatigue failure criteria, which allow us to predict failure in components that undergo combinations of mean and alternating stresses.

Lecture 13 Notes

  • Lecture 13 Notes[pdf]

Lecture 14: Combination of Loading Modes

In this lecture, we will explore combined loading modes, the final type of fatigue problem we will analyze in this class using the stress-life method. In contrast to the other two types of problems we've studied thus far, we will now look at problems where combined bending, torsion, and axial loading is allowed.

  • Read
    • Sections 6.16 and 6.19 of Shigley's Mechanical Engineering Design

  • Practice
    • Problem 6-47, 6-54, and 6-57 from Shigley's Mechanical Engineering Design, and then review the solutions posted. - Module 2 Homework Problems

  • Complete

Lecture 14 Notes

  • Lecture 14 Notes[pdf]

Lecture 15: Forensic Engineering - Guest Speaker

Mr. Steven Counts will be our guest speaker. He is a KSU alum and current Lab Director at Engineering Systems, Inc. As we’ve just wrapped up our section on failure analysis, this is a perfect opportunity to see how the concepts we’ve discussed apply in the real world.

  • Attend Thursday's class and turn in a paragraph describing your favorite part(s) of Mr. Counts' presentation to receive a 100% grade on your In-class Quiz 4.
  • Don't forget to submit the Lecture 14 Quiz, due Thursday night at 11:59 PM.
  • Practice the new material using the posted Practice In-Class Quiz 4 and then evaluate how you did with the posted Practice In-Class Quiz 4 Solutions.