AAE 55400: Fatigue of Structures and Materials

Description

Development and application of methods for predicting the fatigue life of structural components. Characterization and response of materials to cyclic loading. Fatigue resistant design of aerospace structures. Both fatigue crack initiation and crack propagation concepts are discussed.

Format 3 hours of lecture per week
Credit hours 3
Status Elective, Structures
Offered Fall
Pre-requisite AAE 352 or a prior course in strength of materials
Co-requisite None
Course instructor Professor Grandt
Assessment method 2 midterm exams (50%), final exam (25%), homework (25%)

Course Objectives

  1. Develop methods to characterize the fatigue resistance of materials and predict cyclic lives of structural components
  2. Discuss approaches for preventing fatigue failures through materials selection, fatigue resistant design, and "fleet management" concepts

Both crack formation (stress or strain based) and crack propagation (fracture mechanics) approaches are developed and compared. While emphasis is on aerospace applications, class concepts are relevant to many other types of high performance structures.

Necessary Background

  1. Vector calculus and differential equations through PDE's
  2. Basic understanding of strength of materials (i.e. concepts of stress and strain, mechanical properties of materials)
  3. Ability to write a computer program to solve a system of equations

Topics (number of Lectures)

  1. Introduction (3 classes): course objectives, characteristics of fatigue failure mode, examples of service failures
  2. Fatigue crack formation (11 classes): stress-life concepts (S-N curves, mean stress models and "correction factors"), strain-life concepts (monotonic and cyclic stress-strain behavior, cyclic strain versus life, mean stress models), Miner's rule and load sequence effects, notch fatigue
  3. Fatigue crack growth (11 classes): overview of linear elastic fracture mechanics (crack tip stress intensity factors, da/dN versus DK, fatigue crack growth life calculations), crack tip plasticity, fracture toughness (3-D aspects of fracture, leak-before break, proof testing), fatigue crack retardation, variable amplitude fatigue crack growth analysis
  4. Advanced fatigue topics and applications (11 classes): total fatigue life concepts, residual stress effects, cycle counting, variability and statistical aspects of fatigue behavior, environmental effects, life extension concepts, surface cracks, widespread fatigue damage, small crack effects, fatigue crack closure
  5. Fatigue research topics (3 classes)
  6. Nondestructive evaluation (3 classes)
  7. Exams (3 classes)

Relationship of course to program objectives

This elective course deals with technical issues associated with designing and maintaining structures that resist failure from cyclic loading (Program Objective 1). Several homework assignments require the ability to formulate computational solutions to open-ended problems (Objective 2a). Several case studies discuss the role of fatigue testing and analysis in certifying structural integrity in order to protect public safety (Objective 4). Several classes emphasize the role of continued research in fatigue related areas (Objective 3).

Prepared by: A. F. Grandt, Jr.

Date: February 14, 2001