Learning objectives
Knowledge and understanding:
At the end of this course the student should know the basics of machine design. He should gain understanding of the many factors affecting the design of mechanical parts with special regards to safety and reliability. He should be familiar with design schemes and checks required to analyze machine parts.
Applying knowledge and understanding:
He should be able to design a mechanical part on the basis of suitable material and process selection, load analysis and functional requirements. He should be able to select from catalogues the main mechanical components found in machines. He should be able to draw and dimension the part for production.
Making judgments:
By the end of the course the student should be able to critically analyze machines and mechanical components and to their functions and requisites.
Communication skills:
The student should be able to clearly present the functioning of mechanical devices and the design issues involved.
Prerequisites
Physics
Mechanical drawing
Strength of materials
Machine theory
Course unit content
The course is divided in two parts: the design criteria against the main causes of failure and damage of mechanical parts are presented in the first part, the selection criteria and design check of mechanical elements are presented in the second part of the course.
Full programme
Introduction to structural design, safety, safety factor, Technical
Standards
Mechanical tests on materials, tensile, hardness, impact, fatigue,
fracture, metallic materials (steel, cast iron, aluminum alloys,
magnesium, titanium, non-metallic materials (polymers and ceramics),
Manufacturing technology , Selection criteria.
Load analysis, statics, application of the beam model in mechanics, axial
load, bending load, shear load torsion. Stress and strain. Mohr circles.
Principal stresses, Strength criteria (Tresca, Von Mises, Rankine), ductility
and brittleness. Compression instability and Eulerian load. Stiffness.
Notches and stress concentration, nominal stress and local stress, stress
concentration factor Kt, Conforming and non-conforming contacts,
specific contact pressure, Hertzian theory, Contact stresses. Thermal
expansion.
Fatigue of metallic materials, characteristics of the phenomenon, fatigue
experiments , fatigue limit, S / N curves , fatigue parameter estimates,
influencing factors, mean stress effect, fatigue damage accumulation,
multiaxial stress effect, notch sensitivity, notch factor Kf . Contact
fatigue, pitting, fretting.
Fixed connections , welding and bonding, technical standards, welded
joint design, weld types.
Non permanent connections, screws, bolts, rivets and nails, rules for
threaded connections, load transmission in shear or by friction, bolted
connections, preload, stiffness of the parts and load distribution, Fatigue
loading , self-locking devices.
Mechanical power transmission: axes and shafts, materials, construction
details, sizing and verification, shaft-hub connections, gears, pulleys.
Rolling bearings, types (rolls, balls) and load capacity, mounting, bearing
selection from the catalog. Bearings, examples, materials testing. Power
screws: Examples and thread types, checks.
Springs, fields of use, types, stiffness.
Bibliography
Lecture slides
Shigley Machine design
Manfredi De Paulis, Costruzione di macchine
Teaching methods
Course topics are presented through lectures and numerical exercises carried out in the classroom. Problems are proposed to be carried out at home with subsequent discussion in the classroom.
Groups of students are also stimulated to develop a project of a real mechanical device.
Assessment methods and criteria
The exam consists of a open-book written test and an oral.
The development of a project report, individually or in group, provides a bonus.
