B010668 - MECHANICAL BEHAVIOUR OF MATERIALS

Italian

- N.E.Dowling: Mechanical Behavior of Materials. Prentice Hall
- M.F.Ashby: Materials Selection in Mechanical Design (4ed). Butterworth-Heinemann
- G.E.Dieter: Mechanical Metallurgy. McGraw-Hill
- L.Vergani: Meccanica dei materiali. McGraw-Hill
- P.Davoli, A.Bernasconi, M.Filippini, S.Foletti: Comportamento meccanico dei materiali. McGraw-Hill

The design of reliable, economical and safe components depends on a sound understanding of different engineering materials and their responses to different loading conditions. Identifying the right materials to use influences the performance of engineered components. The course aims to introduce to students these important aspects in mechanical design.
In this course, the main notions concerning the behaviour of materials are presented, with particular reference to the mechanical properties. In particular, the course introduces basic concepts and principles behind material selection methodology, high temperature behaviour of materials, damage, creep, low-cycle fatigue, linear and plastic fracture mechanics, fatigue crack growth behaviour. Macro-mechanical properties and microscopic analysis will be correlated whenever possible.

The course aims to provide students with the ability to identify, formulate, and solve problems related to the mechanical behavior of engineering materials. Moreover, the course aims at giving the fundamental knowledge for selecting materials in mechanical applications, in order to guarantee the best performance.
On completion of this course, students are expected to acquire:
- Knowledge of the most common failure mechanisms in mechanical engineering and how these mechanisms relate to the mechanical properties of materials;
- ability to select a material in order to meet desired requirements of an engineering component;
- Knowledge and understanding of materials and their behaviour in the various loading conditions found in design practice. Methods for characterising material behaviour (CC5).
Students will prove:
- Applying knowledge and understanding related to the analysis and optimization of mechanical devices and systems, as well as to their innovation also through the development and improvement of design methods, constantly confronting with the rapid evolution of mechanical engineering (CA2).
- Applying adequate knowledge and understanding to understand English texts (CA12).

Knowledge of the main properties of the materials.
Knowledge of the phenomenon of fatigue in the elastic field.
Knowledge of the sizing methods of structures and components subjected to static and fatigue stresses.
Knowledge of the basics concepts concerning applied mechanics, structural strength of materials and processing technologies.

Classroom lectures and exercises

On completion of the course, students must show the ability to select, characterize and understand the behaviour of the main materials used in mechanical engineering.
The examination consist in an individual oral test, with specific questions posed in the form of theoretical questions or exercises.
The questions are selected in order to ascertain:
- a good level of the achievement of CC5 competence and CA2 capacity
- a sufficient level of achievement of CA12 capacity.

- Material selection in mechanical design.
Role of material in design; classifications of engineering materials; characteristics of metal alloys, ceramics and polymers; material selection methodologies; material property charts; material performance indices; selection of material and shape; penalty functions, multicriteria methods.
- Tensile behaviour of materials
Tension test; tensile behaviour and links with the microstructure; effective stress-strain curve; effects of strain rate and temperature; mono-axial plastic deformation behaviour, stress-strain models for plastic strain; Ramberg-Osgood relation.
- Creep.
Fundamentals of crystal structures: phenomenology of high temperature behaviour of materials; time-dependent plasticity; creep test and creep curve; presentation of engineering creep data; deformation mechanisms, diffusional flow, dislocation creep; deformation mechanisms maps; relaxation; constitutive equations; models of linear viscoelasticity; extrapolation procedure for creep rupture data; time-temperature parameters.
- Low cycle fatigue
Strain-based approach to fatigue analyses; cyclic plastic stress-strain behaviour, strain-life equations, Manson-Coffin and Basquin relations; Morrow approach; Smith-Watson-Topper parameter; stress and strain concentrations, Neuber’s rule, Glinka’s rule, evaluation of life for notched components.
High temperature low cycle fatigue; effect of loading frequency; creep-fatigue interaction; life prediction methods; strain-range partitioning.
- Fracture mechanics.
Energy method; strain energy release rate; stable and unstable crack growth; Irwin approach; stress intensity factors; plastic zone at the crack tip; plane-stress and plane-strain conditions; fracture toughness; effect of temperature, microstructure, and loading rate on fracture toughness; fracture toughness measurement.
Elastic-plastic fracture mechanics; crack tip opening displacement (CTOD); J integral.
Fatigue crack growth, Paris’ law, Walker’s relation; Forman’s relation; life prediction under constant and variable amplitude loading conditions; limitations of linear elastic fracture mechanics; fatigue crack growth retardation.
- Damage
Applicability of damage concept; representative volume element; effective stress; definition of a representative variable; damage measurements; linear and non-linear accumulation; continuum damage models for fatigue life prediction; double linear damage rule for fatigue.
- Fundamentals of fretting and fretting-fatigue.