34313 - Machine Design

Course Unit Page

SDGs

This teaching activity contributes to the achievement of the Sustainable Development Goals of the UN 2030 Agenda.

Quality education Industry, innovation and infrastructure

Academic Year 2021/2022

Learning outcomes

The outcomes of the course are to provide the basic knowledge, the methods and the tools useful for the correct definition of the mechanical design activities. At the end of the course the students will be able to reproduce the representation of a simple mechanical system, to define the relationship between the elements, to calculate the constraints, to draw the stress diagrams and to compute the maximum tensile state of the components. Furthermore they will be able to verify the fatigue life of simple mechanical components and to calculate the strength of some basic bolted and welted structures. Finally they will be able to select the most appropriate rolling bearings to be positioned as constraints of shafts, pins and axes.

Course contents

Introduction to the study and to the analysis of a mechanical system.

Function analysis of a product; the kinematics and dynamic representation of a simple mechanical system and the relationships between the machine elements.

The rigid body equilibrium.

Work and power. Motion and energy transmission between the machine elements. Morphologic characteristics and the load analysis of the mechanical systems. Structural models and tensile state analysis. Stress concentration factors. Residual stresses. The normal stress. The bending stress. The shear stress. The torsion stress. The failure of materials under static loads. The equivalent uniaxial stress in case of static load.

The dynamic failure of the metals. The fatigue stress. The S-N (Wlöer) curves and the Haigh diagrams. The surface, gradient, dimension and load effects on the fatigue strength. The equivalent uniaxial stress in case of dynamic load. The medium stress effects on the fatigue strength.

The gear design. The tooth stress: the bending and the pitting strength. The cylindrical gears straight-toothed and helical-toothed. The conical gears. The loads produced by the gears on the shafts.

Fundamentals of bolted and welded structures: the static calculation.

The rolling bearings selection and their life prediction.

Readings/Bibliography

Texts references

Dario Croccolo, Nicolò Vincenzi - Lezioni di fondamenti e tecnica della progettazione meccanica - Società Editrice Esulapio - Bologna - 2011

Dario Croccolo, Massimiliano De Agostinis, Giorgio Olmi - Esercizi di Coportamento meccanico dei materiali ed Elementi delle macchine - Società Editrice Esulapio - Bologna - 2013

Dario Croccolo, Massimiliano De Agostinis, Giorgio Olmi - Esercizi di Costruzione di macchine e Tecnica delle costruzioni meccaniche - Società Editrice Esulapio - Bologna - 2013


Recommended reading

R. Giovannozzi

“Costruzione di macchine” vol I e II

Patron, Bologna



Niemann/Winter

“Elementi di macchine” vol I

EST Springer–Verlag Berlin, Heidelberg, New York

Teaching methods

The lectures concern the fundamentals problems of the mechanical design of products and systems. The practicing are collective and concern the application and practical solutions of theoretical problems proposed during the lectures.

Assessment methods

The assessment of learning is performed through a written test and an oral test, both in presence.

The written test lasts three hours and consists of the solution of three numerical exercises, on the following topics.

  1. Resolution of an isostatic structure and its verification with calculation of the safety coefficient.
  2. Selection and verification of a bolted, welded or roller bearing connection.
  3. Fatigue verification of a structure with the presence of notches.

During the written test it is possible to consult the exercise and theory books suggested in class. It is not possible to use notes or consult previous solved exercises.

Each exercise is assigned the maximum score of 10 points out of 30.

The test is passed if the following two conditions are met at the same time.

  1. Having achieved a grade of at least 6 (six) points on the first exercise (Isostatic Structure). In fact, this exercise focuses on knowledge deemed necessary to achieve the minimum learning objectives.
  2. Having achieved an overall grade (given by the sum of the partial scores) of at least 18/30.

The oral exam aims to verify the learning of the theoretical topics covered in class and must be carried out within the three sessions scheduled for the exam session in which the written exam was taken (summer or autumn period). Taking the first available oral exam is recommended in order to be able, if necessary, to repeat the written exam.

In accordance with Art. 16, paragraph 5 of the Didactic Regulations, the grade obtained in the written test can be refused only once.

Teaching tools

PC projector. Overhead projector. Blackboard.

Office hours

See the website of Dario Croccolo

See the website of Giorgio Olmi