Illinois MatSE 280 Introduction to Engineering Materials, Lecture 9: Mechanical Failures

By Duane Douglas Johnson1, Omar N Sobh2

1. Iowa State University (formerly University of Illinois Urbana-Champaign) 2. University of Illinois at Urbana-Champaign

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Mechanical Failure: temperature, stress, cyclic and loading effect


  • How do cracks that lead to failure form?
  • How is fracture resistance quantified? How do the fracture
    resistances of the different material classes compare?
  • How do we estimate the stress to fracture?
  • How do loading rate, loading history, and temperature
    affect the failure behavior of materials?


  • Fracture, Fatigue and Creep
  • Fracture mechanisms: Ductile vs Brittle Failure
  • Stress-Strain Behavior versus Temperature
  • Charpy Impact Testing
  • Charpy V-Notch Impact Data: Energy vs Temperature
  • Famous example failures: Liberty ships
  • Ductile Fracture: distinctive features on macro and micro levels
  • Fracture Surface under Tensile and Shear load
  • Brittle Fracture Surface
  • Brittleness of Ceramics
  • Porosity and Temperature Effects in Ceramics
  • Nucleation and Propagation Of Cracks in Ceramics
  • Crazing during Fracture of Thermoplastic Polymers
  • Ideal versus Real Behavior
  • Flaws are Stress Concentrators!
  • Concentration of Stress at Crack Tip
  • Modes of Fracture which Operate on Cracks
  • Griffith’s Criteria for Fracture and Failure
  • Fatigue: Failure from cyclic stress
  • S-N Curves Failure
  • Fatigue Behavior of Polymers
  • Fatigue Mechanisms
  • Improving Fatigue Life
  • Anelastic Effects
  • Creep Failure and Secondary Creep
  • Creep RECOVERY and Vacancy-assisted Climb
  • Major recover mechanism is non-conservative climb
  • Design Examples, Design Strategy, Case Studies

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Cite this work

Researchers should cite this work as follows:

  • Duane Douglas Johnson; Omar N Sobh (2009), "Illinois MatSE 280 Introduction to Engineering Materials, Lecture 9: Mechanical Failures,"

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