|Politecnico di Torino|
|Academic Year 2016/17|
Jet Engine Mechanical Design
Master of science-level of the Bologna process in Aerospace Engineering - Torino
Machine Design prepares engineering students to identify how a device consisting of fixed and moving parts – the machine – can transmit mechanical energy in the ways which are best suited for a specific application. By the end of the semester the student will be able to deal with functional requirements and design specifications, to use a variety of existing mechanical components and systems and their most appropriate domain of application, to determine the shape and size of the machine components and to predict component strength and life, to choose materials best suited for the application, to take into account up-to-date standards or codes of practice and technological constraints, to employ the appropriate analytical models and numerical tools, to deploy all the appropriate arguments to assess and approve a design, and, in summary, to be able to take a responsible decision based on best current practice.
Expected learning outcomes
Foreword: Machine Design engineers/analysts are typically tasked with designing structural and mechanical components of machines (bolted connections, transmissions, bearings, shafts, couplings, springs, etc.) and the assembled systems which these components are part of. At the threshold professional level the Machine Design engineers/analysts must be able to analyse an existing machine component or design modification to meet given requirements: they apply methods and use existing software according to given specifications and under the supervision of a senior engineer. At the standard professional level the Machine Design engineers/analysts must be able to produce new designs for machine components or systems to meet specified requirements: they choose the appropriate analytical or numerical methods and use them under their own responsibility.
As a consequence this Subject Module aims at competences at the threshold level through the study of a selection of representative and complementary classes of problems each requiring a specific treatment (Contents 1 to 5), and introduces students to the standard level by exposure to a semester-long project where an assembled machine is examined and design alternatives are proposed and compared.
In order to develop the required competences applicable to any type of mechanical structure or machine, students are required, by the end of this course module, to show achievement of the following main points of knowledge:
know the theory, and the experimental evidence in support, which underpin the mathematical models of mechanical components
identify the critical weak points for strength, according to all possible failure mechanisms, evaluate uncertainties and apply the appropriate safety coefficients, assess whether the stresses are admissible
- analyse an existing machine component to check whether it meets given requirements
- identify the governing parameters in a component design, define the shape and size of machine components, know how to introduce appropriate design modifications to improve strength and life or to upgrade specifications; this may extend, in some selected cases, to propose new designs for machine components or systems while taking full responsibility to that
- analyze the mechanical performance of interacting components assembled in a machine, i.e. kinematics, exchanged loads and stresses by means of analytical methods and modelling techniques, whether analytical or numerical
- know the theoretical background of the relevant standards, codes and regulations which are used in a professional context
- correctly read the mechanical drawing of a machine or its subsystem, identify parts and their assembly, understand constraints taking account of mechanical and thermal stress conditions, functional requirements, material strength
- be able to propose more ways to assemble components into a mechanical system to achieve the same function
- be able to apply the theory and the mathematical models to component and machine designs
- identify which data are needed to a design, and where they can be found
- deploy the appropriate reasoning to approve a design, and be able to take a responsible decision based on evidence
- know how theoretical or numerical predictions or models can be checked with appropriate experimental tests
- be able to present, in both oral and written forms, a clear and well-structured set of relevant considerations on design assumptions, methods employed and results
- be able to read, understand and comment technical material from books, manuals and any other source.
Prerequisites / Assumed knowledge
Attendance of this module requires fluent spoken and written English as a necessary pre-requisite: all lectures and tutorials, and all study material will be in English. Standard mathematics for engineers is sufficient. It is assumed that students taking this course-module already have knowledge and understanding of the strength of materials principles; in detail, they know and use strain and stress tensors and their principal properties, preferably in matrix notation, their graphical representation through Mohr circles, the two and three dimensional behaviour of elastic materials, the constant force design criteria of brittle and ductile materials (maximum normal stress, maximum shear stress or Tresca, maximum distortion energy or Von Mises). Moreover they master the mechanics of forces and the dynamic of rigid bodies; as to deformable bodies, they master bar and beam problems for tension, bending and torsion, and know ensuing the cross section stress distribution. It would be an advantage if students would have a prior knowledge of basic machine design elements, technical drafting and elements of mechanical machining technologies.
0 – Review of applied criteria for static strength of isotropic metallic materials (tutorials 3 hrs)
1 – Design against fatigue (lectures 9 hrs, tutorials 6 hrs):
- History and overview of fatigue problems
- Stress-life fatigue: basic material properties, specimen testing
- Stress-life fatigue: component fatigue
- Tutorial 1a: selection of overview exercises
- Semester Tutorial: Application to the design of gearbox shafts
2 – Bolted connections (lectures 6 hrs, tutorials 6 hrs):
- Prestressed single bolt connections (non gasketed)
- Refinements and special problems
- Elements of gasketed bolted connections
- Tutorial 2a: selection of overview exercises
- Tutorial 2b: application to an hydraulic piston or to a tie-rod connection
- Semester Tutorial: Application to the design of gearbox shafts - connections
3 – Hertz contact and rolling bearings (lectures 9 hrs, tutorials 9 hrs):
- Hertz theory and applications
- Rolling bearings: static loading
- Rolling bearings: fatigue
- Design of bearing arrangements
- Tutorial 3a: application of Hertz theory to strength of a selection of contact cases
- Tutorial 3b: application to loading and stresses in a high speed bearing
- Semester Tutorial: Application to the design of gearbox shafts – rolling bearings assembly and sizing
4 – Gears (lectures 9 hrs, tutorials 9 hrs):
- Summary of motion transmission, tooth shape
- Spur and helical gears with parallel axes: kinematics, geometry, forces
- Cutting techniques and profile displacement
- Criteria for strength assessment of gears: fatigue, hertz contact, wear, scuffing
- Tutorial 4a: selection of overview exercises
- Semester Tutorial: Application to the design of gearbox shafts - sizing of a set of gears in a gearbox
5 – Rotating discs (lectures 6 hrs, tutorials 6 hrs):
- Summary of plane elastic fields and elastic stresses in discs and thick-walled tubes
- Plastic stresses in thick-walled tubes
- Rotating discs: elastic and plastic solutions (fatigue, thermal stresses, burst)
- Tutorial 5: numerical calculation of elastic and plastic stresses in a rotating disc, strength assessment
6 – Seminars, visits, unplanned teaching and student support (lectures 3 hrs, tutorials 3 hrs).
Credits 8, 84 classroom hours (42 lecture hours, 42 tutorial hours). The total study load for this course-module is 200 to 240 total hours, i.e., 25 to 30 hours per credit. This includes classroom hours, self study, completion of tutorials at home and reporting.
Class hours are equally shared between theoretical lectures and application tutorials, in order to achieve a balance between knowledge and skills. The subject is organised to allow students to progress incrementally in the development of their knowledge and skills under expert supervision.
All lecture materials will be made available on the course unit website before the class activity. Students are urged to download or print them so to have them at hand to take notes.
Lectures on a section of the material will be followed by specific tutorials, where students are required to apply knowledge to working context problems. The tutor will provide organised materials and frames for solutions. However, the students will solve the proposed tasks themselves in small groups (max 3 students)
Moreover, there will be a semester-long project: in order to enhance problem solving capabilities, encourage independent thinking and develop professional reporting skills.
For each task each group will produce a final report; the set of all reports will be examined during the final exam. Students are asked to work cooperatively in a small group environment.
The tutor will assist the groups during the tutorial class hours, supporting students in their learning progression and clarifying their doubts. Attendance to both lectures AND tutorials is strongly recommended, this being vital to achieve the expected learning outcomes. The teacher and the tutor are available weekly during the teaching period in order to meet students for consultation; please contact them by e-mail.
Tutorials may benefit from using EXCEL or MATLAB. Writing reports with editing software is not required; handwritten reports in block letters are fully acceptable if tidy and properly organised. The group decides. Drawing instruments (compass, set squares, scale rulers) are necessary.
Texts, readings, handouts and other learning resources
Lectures: the subject is fully treated in the slides provided by the teacher. Reference textbooks of international standing are suggested.
Tutorials: texts of problems, datasheets of materials, extracts of standards and manuals will be provided by the tutor.
All lecture materials will be made available on the course website before the lecture starts. Students should either download or print the files before the lecture and use the copy to facilitate taking notes.
Assessment and grading criteria
Achieved learning outcomes will be assessed by means of a final exam. In order to properly assess achievement of the expected learning outcomes, the examination is composed of different sections:
a) written session, day 1: test, duration 2 hrs, closed book, composed of three questions, two on chapters or sections of the lectures to assess knowledge, one problem to assess skills; each question scores max 8 points;
b) oral session, day 2:
b1) preliminarily, each student is informed on the reasons for grading obtained, and may appeal with appropriate explanations
b2) students will defend a technical theory or argument proposed by the teacher, to prove achievement of understanding of the subject: max additional 4 points
b3) students will submit the full set of tutorial reports to the tutor, who will investigate effective personal achievement of know how: max additional 4 points
Programma definitivo per l'A.A.2016/17