CH 560 Engineering Material Selection PDF

Engineering Material Selection CH 560 Prof. Yehia M. Youssef Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 1 Material Selection ...

Engineering Material Selection CH 560 Prof. Yehia M. Youssef Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 1 Material Selection  The Design Process Design is an iterative process. The starting point is: a market need, an idea. The end point – a product which: fulfils the need, embodies the idea. Start → conceptual design → embodiment design → detailed design → production information, i.e. specifications – they define how the product will be made: Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 2 Material Selection  The Design Process Market Need Consider all options Determine function structure Concept Assess viability of technical system Model and analyse assemblies Optimisation of function Embodiment Approximate scale and layout Detailed analysis of components Selection of production route Detail Detailed technical specs/drawings Iterate Product Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 3 Material Selection  The Design Process Conceptual Design: – the designer considers the alternative working principles or schemes for the functions which make up the system. – the ways in which sub-functions are combined and separated. – the implications of each scheme for performance and cost. Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 4 Material Selection  The Design Process Embodiment Design: – takes a function structure and seeks to analyse its operation at an appropriate level. – sizing the components and selecting materials which will perform properly in the ranges of stress, temperature and environmental conditions suggested by the analysis. – the embodiment stage ends with a feasible layout which is passed to the detailed design stage. Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 5 Material Selection  The Design Process Detailed Design: – here specifications for each component are drawn up. – critical components may need precise mechanical and thermal analysis e.g. using finite element methods. – optimisation methods are applied to components (and groups of components) to maximize performance. – materials are chosen. – the production route is analysed. – the design is analysed in terms of cost. – the stage ends with a detailed production specification. Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 6 Material Selection  Design Tools and Materials Data The three mentioned design stages are achieved using design tools which are shown as inputs feeding in the main backbone of the design methodology. On the left are the tools of Engineering Science which allow the analysis, modelling and optimisation of the design. Increasingly, the routine aspects of design are made easier by: –The use of computer aided design (CAD) tools –The use of the databases which store information about standard components and configurations. Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 7 Material Selection  Design Tools and Materials Data Using these tools as the design evolves, we progress in the following manner: –Conceptual stage – approximate analysis and modelling –Embodiment stage – more sophisticated modelling and optimisation –Detailed design – “exact” analysis Materials Selection enters at each stage of the design process. The already large materials catalogue will increase further as better materials are developed. On the other hand, the increasing constraints as we progress through the three design stages will progressively limit the candidate materials. Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 8 Material Selection  Design Tools and Materials Data As the list of materials narrows the question is no longer “which material will do the job?” but “which material will do it best?”. Additionally, the materials with the most desirable properties is seldom the one which is cheapest to shape, join and finish. So, we have a trade-off between performance and overall cost. Detailed design can only proceed when the list of candidate materials for each component is reduced to one (or a very few). Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 9 Material Selection  Material Property Data Increasingly precise material property data is needed as we progress through the three stages of design: – Conceptual design stage – requires approximate data for a wide range of materials – Embodiment design stage – requires high level of precision and details found in handbooks or computer databases which list, plot and compare the properties of a single class of materials e.g. metals – allowing choice of material at a level of detail not possible from the broader compilations which include all materials. Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 10 Material Selection  The Design Flowchart – Detailed design stage – requires a high level of precision and detail but for only one or very few materials. Such information is usually found in the produces data sheets. The design flowchart shows how design tools and materials selection enter the procedure. Information about materials is needed at each stage, but at very different levels of breadth and precision. Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 11 Material Selection  The Design Flowchart Market Design Tools Need Materials Engineering Selection Materials Science All Materials Science Viability Concept Analysis (low precision data) Structure Mechanics Subset of Properties Thermo- Approximate Analysis Embodiment Materials dynamics (higher data Processing Optimisation precision) Fluid Flow Surface Methods Engineering Numerical One Material Methods Detailed Detail (best Joining Analysis: e.g. available data Technology etc inc FEA precision) etc Product Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 12 Material Selection  Material Property Data For some materials, e.g. polyethylene, we can get different properties in materials obtained from different producers. If the particular component is critical (i.e. a failure would be catastrophic), then we would be prudent to in-house test in order to measure the critical property. We must learn from failures in service, failure analysis prompting component redesign or material reselection. Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 13 Material Selection  Function, Material, Shape & Processing The selection of a material cannot be separated from the choice of shape. Shape includes: – External shape – external shape and size (the macroshape) – Internal shape – e.g. a honeycomb or cellular structure (the microshape) In order to achieve the final product shape, the material is subject to various processes which collectively we call manufacture. Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 14 Material Selection  Function, Material, Shape & Processing Component manufacture may include the following: – Forming processes e.g. casting, forging, rolling, extrusion, …etc. – Material removal processes e.g. machining operations (such as drilling, turning, milling). – Finishing processes e.g. grinding and polishing. – Joining processes e.g. welding. Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 15 Material Selection  Function, Material, Shape & Processing Function Transmit loads, heat, contain pressure, store energy, etc. At maximum weight, cost or maximum efficiency, Safety. Material Shape Process The central problem of materials selection in mechanical design is: the interaction between function, material, process and shape. Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 16 Material Selection  Design Function Design statement of functions which the product must perform and is made up of: 1. A basic function 2. Several secondary functions Take for example a pair of scissors: Basic function - to cut thin sheets of material Secondary functions: Function Material Property Required To stay sharp Wear resistance Resist plastic deformation Yield strength Resist corrosion Corrosion property data Resist elastic deflection High Modulus, E Minimise mass Density,  Permit processability into required shape Formability, castability Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 17 Material Selection  Function, Material, Shape & Processing They all interact as follows: Function – dictates the choice of material Shape – is chosen to perform the function using the material Processing – is influenced by: – Material properties such as formability, machinability, weldability, heat treatability Processing interacts with shape Processing determines the shape, the size, the precision and the cost. The interaction between function, material, shape and processing lies at the heart of the material selection process. Copyright © YM Youssef, 24-Oct-24 CH560 - Engineering 18 Material Selection