


Politecnico di Torino  
Academic Year 2009/10  
07ALPDS Machine Design 

Master of sciencelevel of the Bologna process in Mechanical Engineering  Vercelli 





Objectives of the course
This course introduces students to theoretical and practical aspects of machine design failures.

Expected skills
By the end of this course students should have an understanding of the mechanical behaviour of materials. This will include the deformation behaviour of metals and the various failure modes. Students should have answers to the following questions: why do materials behave differently under low and high cyclic loads? Why do components fails at high temperatures? Why and how do components fail? Can we prevent failure?

Prerequisites
Solid mechanics, kinematics & dynamics engineering, materials engineering.

Syllabus
Fracture mechanics
Machine design and fracture mechanics, Energy principle, Griffith theory, stress fields at crack tip, Westergaard equations, fracture modes, Strain state at crack tip, plastic zone, Linear elastic fracture mechanics. Fracture toughness, Standard tests, Fracture criteria, Design methods. Crack propagation rate, Paris law, Crack propagation rate under variable amplitude loading, Retardation models, Random loads. Cycle counting methods,: level crossing, peak counting, simple range, rainflow, simplified rainflow. Fatigue. Fatigue life prediction methods, Stress life vs. Strain life, Low cycle fatigue, strain controlled tests, Stressstrain behaviour, cyclic stressstrain equation, 'o'nHysteresis loop equation, strain hardening e strain softening StrainLife Relationship , 'o'nFour parameter strainlife equation, Mean Stress effects, 'o'nMorrow Equation, 'o'nSmithWatsonTopper Equation, Linear damage rule (MinerPalmgren). Fatigue life under triaxial loading, Gough and Pollard hypothesis, Sines method. Creep. Generalized creep behaviour, Factors affecting creep, Stress and temperature effects, Creep curve, Stress rupture, life time behaviour, Creep mechanisms, Creep testing: Mechanical acceleration method, Thermal acceleration Methods, Abridged method, StressStrainTime, StressRupture Lifetime Behaviour, StressStrainTime, StressSteady State Creep Rate Behaviour, LarsonMiller parameter, Cumulative creep: time hardening, strain hardening and life fraction rules. Materials for high creep resistance. 
Laboratories and/or exercises
Example problems will be solved to help students understand how to use analytical knowledge to solve practical problems. Practical computer lab session will be dedicated to solve LEFM problems, experimental lab session will introduce students to creep analysis for simple elements.
A detailed report of the lab project must be turned in at the end of the course. 
Bibliography
Course notes.
A. Gugliotta, Introduzione alla meccanica della frattura lineare elastica, Levrotto&Bella J. A. Collins, Failure of materials in mechanical design, Wiley. H.O. Fuchs, R.I. Stephens, Metal fatigue in engineering, Wiley D. Broek, Elementary engineering fracture mechanics, Martinus Nijhoff Publishers, IV ed. S. T. Rolfe, J. M. Barsom, Fracture and fatigue control in structures, Prentice Hall 
Revisions / Exam
Oral examination will be related also to subjects developed in the computer and practical lab. No books or student notes are admitted.

