The course aims to give to the students the knowledge about the design and assessment of a component/system with specific regard to structural mechanics. In particular the main objective is to understand how to prevent the failure of a component subjected to external boundaries and under both static and fatigue loads. The main topics of the course are: static and fatigue assessment, design criteria; notch effect; state of stress; critical choice of materials; structural components: relevant examples.
The course is organised in lectures and tutorials. Theoretical concepts will be applied during the course for the design and assessment of actual components (shaft, pressure vessels, bolted and welded joints, hip replacement, gears, etc).
Internal forces: definition of slender members, definition of internal forces and equations of equilibrium, reticular structures;
Axial and bending problem in beams: hypotheses and basic assumptions for the Euler-Bernoulli beam; state of stress due to normal force and bending moment;
Shear in beams: relationship between bending moment and shear force; shear stress distribution in case of solid section; torsion in beam: distribution of torsional stresses for a circular solid beam;
State of stress: definition of equilibrium for deformable bodies; Cauchy tetrahedron; principal stresses and directions; stress invariants; hydrostatic stress tensor and stress deviator tensor; Mohr’s circles for plane stress; three-dimensional description of Mohr’s circles;
Material behaviour: tensile test devices and specimens; engineering stress-strain curve; true stress-strain curve; ductile and brittle failure mechanisms; ideal material models;
Influence of notch for ductile and brittle materials: phenomenological aspects; definition of Kt and Ks parameters.
Stress-strain relations: general expression of the elastic tensor; elastic tensor for isotropic materials; derivation of the generalised Hooke’s law; stress-strain relationships for plane stress and plane strain.
Failure criteria for isotropic materials: Galileo-Leibniz-Rankine-Navier criterion for brittle materials; Guest-Saint Venant-Tresca criterion for ductile materials; Huber-Hencky-von Mises criterion for ductile materials; general considerations about the definition of the safety factor;
Fatigue: fatigue phenomena; fatigue testing; definition of fatigue cycles; Wöhler diagram; finite and infinite life regime; relationship between fatigue limit and tensile strength; influence of mean stress with Haigh diagrams; notch effect on fatigue; influence of surface finishing; size effect and influence of stress gradient; damage accumulation with Miner-Palmgren rule; Gough-Pollard criterion for multi-axial loading condition.