Corrosion and Durability of Engineering Materials

Lecturer(s)

Dr. P. Schmutz, EMPA (Part I), Dr. M. Diener (Part II)

Hour(s) of lecture(s), exercise(s) and credit points

2L
2E
4CP

Teaching goals

The course will be an introduction in the fundamental aspects of the degradation mechanisms induced by (electro)chemical and mechanical interaction on materials. The students should then know the possibilities and limitations of the use of “standard” materials as well as get an idea of the new innovative development to prevent failure problems. It is also an introduction to the field of fracture mechanics, an engineering discipline that draws upon the principles of applied mechanics and materials science. Cracks and crack-like defects are evaluated with a view to understanding and predicting the cracks' growth tendencies. Such growth may be either stable (relatively slow and safe) or unstable (instantaneous and catastrophic). The course gives the tools to a successful application of fracture mechanics concepts to failure analysis.

Summary and outline

Part I:
Surface physico - chemical und bulk mechanical processes will be discussed during this course. In a first part, the surface degradation as a result of corrosion processes will be described. This includes a detailed description of the electrochemical reactions (thermodynamic and kinetic aspects). The aqueous oxidation and condition for stable passivation will then be reviewed. Uniform and localized Corrosion types/mechanisms will be presented illustrated by examples of new research fields in the corrosion domain. Corrosion protection strategies and criteria for selection of materials for use in aggressive environments should help the students make the right choice in his future engineering work.

Part II:
Crack-flaws cannot be neglected in engineering analysis. Even microscopic crack flaws can grow over time, ultimately resulting in fractured components. Structures that may have been blindly deemed "safe" could fail disastrously, causing injuries to its users, or the loss of life. Fracture mechanics can be used to:

• Determine how large a crack can be in a structure before it leads to catastrophic failure
• Predict the rate at which a crack can approach a critical size due to fatigue loads or aggressive environmental conditions

The topics covered are

• Introduction to Linear Elastic Fracture Mechanics (LEFM): crack tip stress, strain and displacement fields in linear elastic materials (Modes I, II and III); the stress-intensity factor, K; the fracture toughness KIc and their determination; fracture criterion
• Estimates of crack plastic zones in ductile materials
• The compliance method; experimental determination of compliance
• Introduction to fracture mechanics of nonlinear materials: the J-integral; the JIc fracture criterion; JIc testing
• Application of fracture mechanics concepts in the analysis of subcritical crack growth (fatigue, stress corrosion cracking, creep and their combinations)
• Lifetime determination and prediction; failure analysis.

Literature

T.L. Anderson, Fracture Mechanics, Fundamentals and Applications, CRC Press

K.H. Schwalbe, Bruchmechanik, Carl Hanser Verlag