17395 - Reliability and Safety of Mechanical Constructions

Learning outcomes

The aim of the course is to provide basic information to face reliability problems concerned to many mechanical industrial applications. The reliability of a mechanical system depends on the reliability of each single component or subsystem, on their functionality, on how they contribute to the system main functions. The reliability properties of each component or, more generally, the final result of an industrial process may be due to several factors, such as the material, the layout or shape, the operative conditions… The main topics related to Design of Experiment are studied, so that the students can be able to plan an experimental campaign, to investigate which factors are significant and which other have a negligible impact. Some items related to safety are then studied: FMEA analysis (Failure Mode and Effect Analysis), to ensure that all the possible failure modes have been considered during the design process. The FTA (Fault Tree Analysis) is used to search causes of failures: reference is made to a posteriori investigations after really happened incidents in the fields of transports and nuclear industry. Finally, The “Direttiva Macchine” is presented in details, with reference to the machines it is applied to, to the people involved, to some applicative cases. Then, the procedure of certification and CE marking is presented, with particular emphasis on the importance of the technical attachment and of the instruction manual and of their careful composition. All the subjects are presented from the theoretical and practical points of view, with several numerical exercises and cases studied.

Course contents

Design for reliability:

What is reliability: how it is defined and how is computed. MTTF (Mean Time To Failure), MTBF (Mean Time Between Failures), failure rate. Probability and probability density functions. Conditioned failure probability. Series and parallel (full redundancy systems): calculation of reliability properties. Binomial probabilistic distribution, k/n redundancy systems: calculation of reliability properties. Stand-by redundancy systems. Complex systems: generalities, decomposition (or “of the key-item”) and enumeration methods: application to a case study: minimal path sets and minimal cut sets definitions and their application for determining reliability upper and lower bounds. Logic trees in the reliability analyses. Fault tree Analysis (FTA): generalities, logical connectors, symbols. Real applications of FTA to investigate the causes of great incidents. The relationship between the FTA and the determination of the minimal cut sets. The event tree (ET). Hishikawa schemes. Exercises.

The Failure Mode and Effect Analysis (FMEA): definition, generalities, goals, working team composition. Determination of the Risk Priority Number (RPN).

 

Design of Experiment (DOE):

One factor Design: Statistic model and Sum of Squares, Analysis of Variance. Hypotheses of significance and of not significance, the Fisher probability density function, F-test, p-value (definition and calculation). Significance level. Examples and practical applications.

Two factor Design: interaction, Statistic model and Sum of Squares, Analysis of Variance for two factors. Hypotheses of significance and of not significance, the F-test. Examples and practical applications.

Full factorial Design (2 levels, k factors). Yates notation, treatment combinations. Computation of main and interactive effects: graphical approach and sign tables. Examples and practical applications.

Fractional factorial Design: generalities, confounded effects, alias pairs and groups, treatment combination blocks, effect determination.

The Taguhi method: generalities, the magic squares, interactions according to Taguchi. Magic squares L4, L8 and L16 and their application for experimental planning and further data processing for effect calculation. Control factors and noise actors : robust design. How to maximize the ratio signal/noise (S/N): meaning and calculation.

 

Design for Safety: Direttiva Macchine and CE marking:

European Community Standards, and Italian laws related to safety in the working environment. The Direttiva Macchine (DM) 98/37/CE and the DPR n.459/96. Definition of “machine”: machines the DM is applied to, people involved in the DM, some applicative cases. The Appendix IV of DM: dangerous machines. The technical attachment: Appendices V ad VI. Certification procedures for dangerous and not dangerous machines: comparison among procedures. Declaration of certification (Appendix II). CE mark (Appendix III). The “almost machines” (quasi macchine): generalities, examples, “Declaration of incorporation” according to Appendix II. Differences between DM 98/37/CE and DM 2006/42/CE.

Readings/Bibliography

A. Freddi, Imparare a progettare. Principi e metodi del progetto concettuale per lo sviluppo della creatività industriale, Pitagora Editrice, Bologna, 2005, ISBN: 8837115121

S. Beretta, Affidabilità delle costruzioni meccaniche, Springer, Milano, 2008, ISBN: 978-88-470-1078-9

Berger, P.D., Maurer, R.E., Experimental design with applications in management, engineering and the sciences, Duxbury Press, Belmont, CA, 2002, ISBN: 0-534-35822-5

E. Grassani, La Direttiva Macchine - 98/37/CE (DPR 459/96) e la nuova 2006/42/CE, Editoriale Delfino, Milano, 2007, ISBN: 9788889518403

Teaching methods

Use of the blackboard, projection of slides

Assessment methods

Oral exam with resolution of numerical exercises and theoretical questions.

Teaching tools

Handouts by the professor

Links to further information

http://diem1.ing.unibo.it/personale/olmi/index.htm

Office hours

See the website of Giorgio Olmi