Basic principles for material selection and design, Slides of Design

Download Basic principles for material selection and design and more Slides Design in PDF only on Docsity! BASIC PRINCIPLES FOR MATERIAL SELECTION AND DESIGN ผูส้อน รองศาสตราจารย์ ดร.ยุพาพร รกัสกุลพวิฒัน์ From Textbook: Ashby, Michael F.. (2005). Materials Selection in Mechanical Design (3rd Edition). Elsevier. Materials Selectton—The Basics Light, stiff beam: : Ep Light, strong tie: o,/p , Light, stiff panel: Light, strong column: E'ip oO, Cheap strong tie: Cheap stiff panel: O! Cp EC, mp Cheap strong beam: me! Materials Selection in Mechanical Design. DOI: 10.1016/B978-1-8561 7-663-7.00005-9 © 2011 Michael F. Ashby. Published by Elsevier Lid. All rights reserved  โจทย์คือการระบุสมบัตต่ิางๆทีต้่องการ แล้วน าไปเปรียบเทียบ กบัวสัดุวศิวกรรมทีม่ีเพ่ือหาวสัดุทีเ่หมาะสมทีสุ่ด  วธีิการ คือ 1. การคดัเลือกและการจดัล าดบั (screening and ranking) วสัดุต่างๆเป็นรายการ (shortlist) 2. หาข้อมูลรายละเอยีดสนับสนุนวสัดุแต่ละชนิด เพ่ือใช้ในการ ตดัสินใจขั้นสุดท้าย  ส่ิงทีส่ าคญั คือการเร่ิมด้วยตวัเลือกของวสัดุให้มากทีสุ่ด เพ่ือ หลกีเลีย่งการเสียโอกาสในการได้วสัดุทีเ่หมาะสมทีสุ่ด การลดตัวเลือก  ตัวเลือกทีม่ีจ านวนมากนั้นสามารถลดลงได้โดย - ขั้นแรก การใช้ property limits ซ่ึงจะช่วยคดัวสัดุทีไ่ม่ได้ตามความต้องการในการออกแบบ - ขั้นที่สอง การจดัล าดบัความสามารถของวสัดุทีจ่ะให้ได้ ประสิทธิภาพสูงทีสุ่ด (maximize performance)  โดยทัว่ไป Performance จะจ ากดัโดยสมบัติหลายอย่างรวมกนั ไม่ใช่ สมบัติอย่างเดียว  ตัวอย่างเช่น - วสัดุทีเ่หมะสมทีสุ่ดส าหรับการออกแบบเป็น light stiff tie-rod ได้แก่ วสัดุทีมี่ค่า specific stiffness สูงทีสุ่ด specific stiffness = E/  โดยที่ E = Young's modulus  = density The selection strategy  Material attributes The Kingdom of Materials can be subdivided into families, classes, subclasses and members. Each member is characterized by a set of attrributes: its properties. Material attributes Universe Family * Ceramics / * Metals / Materials /\ * Polymers \ \ * Elastomers \ * Hybrids / «Glasses f Cuwalloys / f / Subclass , Steels 7 1000 / 2000 / 3000 Al-alloys /( 4000 Tialloys \ 5000 \, Ni-alloys * Zn-alloys Member Attributes Alu 6067 Density Mechanical properties Thermal properties Electrical properties Optical properties Corrosion properties Documentation — specific — general Material records The taxonomy of the universe of materials and their attributes. Computer-based selection software stores data in a hierarchical structure like this. Material attributes  As an example, the materials universe contains the family “metals,” which in turn contains the class “aluminum alloys,” the subclass “6000 series,” and finally the particular member “Alloy 6061.”  It, and every other member of the universe, is characterized by a set of attributes that include its mechanical, thermal, electrical, optical, and chemical properties; its processing characteristics; its cost and availability; and the environmental consequences of its use.  We call this its property profile. —— Desired features \ data expressed as recorded as nstraints ° Features Family car ® Mid-sized family sedan Selection “engine” ® 4-door * Screening ® Gas tuel « Ranking © 750+ horsepower * Documentation Final selection Choosing @ cat—an example of the selection strategy. Required features are constraints; they are used to screen out unsuitable cars. The survivors are ranked by cost of ownership. The selection strategy  The requirements of four-door family sedan and gas power are simple constraints; a car must have these to be a candidate.  The requirement of at least 150 hp places a lower limit but no upper limit on power  it is a limit constraint; any car with 150 hp or more is acceptable. The selection strategy  The wish for minimum cost of ownership is an objective, a criterion of excellence.  The most desirable cars, from among those that meet the constraints, are those that minimize this objective.  Selecting materials involves seeking the best match between design requirementsand the properties of the materials that might be used to make the design.  Figure 5.4 shows the strategy of the last section applied to selecting materials for the protective visor of a safety helmet. On the left are requirements that the material must meet, expressed as constraints and objectives. Design requirements Materials data expressed as recorded as e Constraints e Material attributes ® Objectives ® Documentation LN Selection “engine” ® Screening e Ranking « Documentation Final selection FIGURE 5.4 Choosing a material. Design requirements are first expressed as constraints and objectives. The constraints are used for screening. The survivors are ranked by the objective, expressed as a material index.  The constraints: ability to be molded and, of course, transparency.  The objective: If the visor is to protect the face, it must be as shatterproof as possible, meaning it must have as high a fracture toughness as possible. Translation  How are the design requirements for a component (defining what it must do) translated into a prescription for a material?  Any engineering component has one or more functions: to support a load, to contain a pressure, to transmit heat, and so on.  This must be achieved subject to constraints: that certain dimensions are fixed, that the component must carry the design loads or pressures without failure, that it insulates or conducts, Translation  or it can function in a certain range of temperature and in a given environment, and many more.  In designing the component, the designer has an objective: to make it as cheap as possible, perhaps, or as light, or as safe, or perhaps some combination of these.  Certain parameters can be adjusted to optimize the objective; the designer is free to vary dimensions that have not been constrained by design requirements and, most importanty, free to choose the material for the component.  We refer to these as free variables. Translation  Function, constraints, objectives, and free variables (Table 5.1) define the boundary conditions for selecting a material and—in the case of load-bearing components—a shape for its cross section.  The first step in relating design requirements to material properties is a clear statement of function, constraints, objectives, and free variables. BASIC PRINCIPLES FOR MATERIAL SELECTION AND DESIGN ผูส้อน รองศาสตราจารย์ ดร.ยุพาพร รกัสกุลพวิฒัน์ From Textbook: Ashby, Michael F.. (2005). Materials Selection in Mechanical Design (3rd Edition). Elsevier. Materials Selectton—The Basics Light, stiff beam: : Ep Light, strong tie: o,/p , Light, stiff panel: Light, strong column: E'ip oO, Cheap strong tie: Cheap stiff panel: O! Cp EC, mp Cheap strong beam: me! Materials Selection in Mechanical Design. DOI: 10.1016/B978-1-8561 7-663-7.00005-9 © 2011 Michael F. Ashby. Published by Elsevier Lid. All rights reserved  โจทย์คือการระบุสมบัตต่ิางๆทีต้่องการ แล้วน าไปเปรียบเทียบ กบัวสัดุวศิวกรรมทีม่ีเพ่ือหาวสัดุทีเ่หมาะสมทีสุ่ด  วธีิการ คือ 1. การคดัเลือกและการจดัล าดบั (screening and ranking) วสัดุต่างๆเป็นรายการ (shortlist) 2. หาข้อมูลรายละเอยีดสนับสนุนวสัดุแต่ละชนิด เพ่ือใช้ในการ ตดัสินใจขั้นสุดท้าย  ส่ิงทีส่ าคญั คือการเร่ิมด้วยตวัเลือกของวสัดุให้มากทีสุ่ด เพ่ือ หลกีเลีย่งการเสียโอกาสในการได้วสัดุทีเ่หมาะสมทีสุ่ด การลดตัวเลือก  ตัวเลือกทีม่ีจ านวนมากนั้นสามารถลดลงได้โดย - ขั้นแรก การใช้ property limits ซ่ึงจะช่วยคดัวสัดุทีไ่ม่ได้ตามความต้องการในการออกแบบ - ขั้นที่สอง การจดัล าดบัความสามารถของวสัดุทีจ่ะให้ได้ ประสิทธิภาพสูงทีสุ่ด (maximize performance)  โดยทัว่ไป Performance จะจ ากดัโดยสมบัติหลายอย่างรวมกนั ไม่ใช่ สมบัติอย่างเดียว  ตัวอย่างเช่น - วสัดุทีเ่หมะสมทีสุ่ดส าหรับการออกแบบเป็น light stiff tie-rod ได้แก่ วสัดุทีมี่ค่า specific stiffness สูงทีสุ่ด specific stiffness = E/  โดยที่ E = Young's modulus  = density The selection strategy  Material attributes The Kingdom of Materials can be subdivided into families, classes, subclasses and members. Each member is characterized by a set of attrributes: its properties. Material attributes Universe Family * Ceramics / * Metals / Materials /\ * Polymers \ \ * Elastomers \ * Hybrids / «Glasses f Cuwalloys / f / Subclass , Steels 7 1000 / 2000 / 3000 Al-alloys /( 4000 Tialloys \ 5000 \, Ni-alloys * Zn-alloys Member Attributes Alu 6067 Density Mechanical properties Thermal properties Electrical properties Optical properties Corrosion properties Documentation — specific — general Material records The taxonomy of the universe of materials and their attributes. Computer-based selection software stores data in a hierarchical structure like this. Material attributes  As an example, the materials universe contains the family “metals,” which in turn contains the class “aluminum alloys,” the subclass “6000 series,” and finally the particular member “Alloy 6061.”  It, and every other member of the universe, is characterized by a set of attributes that include its mechanical, thermal, electrical, optical, and chemical properties; its processing characteristics; its cost and availability; and the environmental consequences of its use.  We call this its property profile. —— Desired features \ data expressed as recorded as nstraints ° Features Family car ® Mid-sized family sedan Selection “engine” ® 4-door * Screening ® Gas tuel « Ranking © 750+ horsepower * Documentation Final selection Choosing @ cat—an example of the selection strategy. Required features are constraints; they are used to screen out unsuitable cars. The survivors are ranked by cost of ownership. The selection strategy  The requirements of four-door family sedan and gas power are simple constraints; a car must have these to be a candidate.  The requirement of at least 150 hp places a lower limit but no upper limit on power  it is a limit constraint; any car with 150 hp or more is acceptable. The selection strategy  The wish for minimum cost of ownership is an objective, a criterion of excellence.  The most desirable cars, from among those that meet the constraints, are those that minimize this objective.  Selecting materials involves seeking the best match between design requirementsand the properties of the materials that might be used to make the design.  Figure 5.4 shows the strategy of the last section applied to selecting materials for the protective visor of a safety helmet. On the left are requirements that the material must meet, expressed as constraints and objectives. Design requirements Materials data expressed as recorded as e Constraints e Material attributes ® Objectives ® Documentation LN Selection “engine” ® Screening e Ranking « Documentation Final selection FIGURE 5.4 Choosing a material. Design requirements are first expressed as constraints and objectives. The constraints are used for screening. The survivors are ranked by the objective, expressed as a material index.  The constraints: ability to be molded and, of course, transparency.  The objective: If the visor is to protect the face, it must be as shatterproof as possible, meaning it must have as high a fracture toughness as possible. Translation  How are the design requirements for a component (defining what it must do) translated into a prescription for a material?  Any engineering component has one or more functions: to support a load, to contain a pressure, to transmit heat, and so on.  This must be achieved subject to constraints: that certain dimensions are fixed, that the component must carry the design loads or pressures without failure, that it insulates or conducts, Translation  or it can function in a certain range of temperature and in a given environment, and many more.  In designing the component, the designer has an objective: to make it as cheap as possible, perhaps, or as light, or as safe, or perhaps some combination of these.  Certain parameters can be adjusted to optimize the objective; the designer is free to vary dimensions that have not been constrained by design requirements and, most importanty, free to choose the material for the component.  We refer to these as free variables. Translation  Function, constraints, objectives, and free variables (Table 5.1) define the boundary conditions for selecting a material and—in the case of load-bearing components—a shape for its cross section.  The first step in relating design requirements to material properties is a clear statement of function, constraints, objectives, and free variables. Screening and ranking  Unbiased selection requires that all materials are considered to be candidates until shown to be otherwise.  Screening, eliminates candidates which cannot do the job at all because one or more of their attributes lies outside the limits imposed by the design. Example  The requirement that ‘the component must function at 250oC’, or that ‘the component must be transparent to light’ imposes obvious limits on the attributes of maximum service temperature and optical transparency which successful candidates must meet.  We refer to these as property limits. Property limits  Property limits do not, however, help with ordering the candidates that remain.  To do this we need optimization criteria. They are found in the material indices, developed below, which measure how well a candidate which has passed the limits can do the job. Screening and ranking for the helmet visor @ following list. T acture toughness values can Average Fracture Toughness Documentation or Supporting information  The outcome of the steps so far is a ranked short-list of candidates that meet the constraints and that maximize or minimize the criterion of excellence  whichever is required. You could just choose the top-ranked candidate, but what secret vices might it have? What are its strengths and weaknesses? Documentation  Does it have a good reputation? What, in a word, is its credit rating?  To proceed further we seek a detailed profile of each candidate: its documentation Local conditions  The final choice between competing candidates will often depend on local conditions: on the existing in-house expertise or equipment, on the availability of local suppliers, and so forth.  The decision must be based on local knowledge. Deriving property limits and material indices How are the design requirements for a component (which define what it must do) translated into a prescription for a material? Ans: We must look at the function of the component, the constraints it must meet, and the objectives the designer has selected to optimize its performance. Function, objectives and constraints  Any engineering component has one or more functions: to support a load, to contain a pressure, to transmit heat, and so forth.  In designing the component, the designer has an objective: to make it as cheap as possible, perhaps, or as light, or as safe, or perhaps some combination of these. Examples  In the case of load-bearing components - a shape for its cross-section.  The loading on a component can generally be decomposed into some combination of axial tension or compression, bending, and torsion. Almost always, one mode dominates. ‘@) Compression : Colum (a) pre umn Area Moment fe Fig. 5.4 A cylindrical tie-rod loaded (a)in tension, (b) in bending, (c)in torsion and (d) axially, as a column. The best choice of materials depends on the mode of loading and on the design goal; it is found by deriving the appropriate material index.  Section area A Force F . Deflection é =i — +——_—___ _, ————_> Square section area A—b2 T section area A AF Ww Generic components: (a) a tie, a tensile component; (b) a panel, loaded in bending; (c) and (dq) beams, loaded in bending.  The first step in relating design requirements to material properties is a clear statement of function, objectives and constraints. Stiffness Objectives specified Minimize cost Failure load specified Ps ; { Minimize mass |° Fatigue life specified Minimize environmental impact Geometry specified Mechanical, Maximize energy thermal, storage electrical ... FIGURE 5.7 The specification of function, objective, and constraint leads to a materials index. The combination in the highlighted boxes leads to the index E''*/p.  Some constraints translate directly into simple limits on material properties.  If the component must operate at 250°C then all materials with a maximum service temperature less than this are eliminated.  If it must be electrically insulating, then all material with a resistivity below 1020 m are rejected. Property limits  The three groups of parameters in previous equation are said to be separable. ** the optimum choice of material becomes independent of the details of the design; it is the same for all geometries, G, and for all the values of the functional requirement, F .  Then the optimum subset of materials can be identified without solving the complete design problem, or even knowing all the details of F and G.  This enables enormous simplification: the performance for all F and G is maximized by maximizing f 3 ( M ) , which is called the material efficiency coefficient, or material index.  The remaining bit, fl(F), f2(G), is related to the structural efficiency coeflcient, or structural index. Example 1: The material index for a light, strong, tie  A design calls for a cylindrical tie-rod of specified length l, to carry a tensile force F without failure; it is to be of minimum mass.  ‘maximizing performance’ means ‘minimizing the mass while still carrying the load F safely’.  The lightest tie which will carry F safely is that made of the material with the smallest value of  It is more natural to ask what must be maximized in order to maximize performance; we therefore invert the material properties define the material index M as: calculation for ; (one f strength oy is : ) leads to the index Minimizing Mass: A light, stiff panel A panel is a flat slab, like a table top. Its length L and width b are specified but its thickness Is free. It is loaded in bending by a central load F (see Figure 5.6(b)). The stiffness con- straint requires that it must not deflect more than 6. The objective is to achieve this with minimum mass, m. Table 5.3 summarizes the design requirements. Design Requirements for a Light, Stiff Panel Function Panel Constraints Bending stiffness S* specified (functional constraint) Length L and width 6 specified (geometric constraints) Objective Minimize mass m of the panel Free variables Panel thickness fh Choice of maternal From Appendix B rid 4) mT 4 Ay qu (ry X -— (Ip -F ° gio") ap 2% = art e2nrt zat =2prt (3-4) 2t(n+b) lias?) atbPn 4 ty Trtci4a®) | tpn 22 (nosat) | 6 h n h (nab) | 3 abi 20) 4nfabp!?t Fa? 11.25) 2nt(a’p) 2 nabt(2+3) 4 a 4 a b t(a+b)t m(a+b) (a+ b?) (b>a) (ab >>t) biMo- hj) b 3 13 D2 2 — (h3- ni 2 (n2-h =2bt &hg ) gito-) (h,b>>t) = bth, = bthy 2t(h+b) n That 43% (hb>>t) 3 n 2t(h+b) 2t (b-2t (h,b>>t) 3 ae } We can reduce the mass by reducing h, but only so far that the stiffness constraint is still met. Using the last two equations to eliminate h in the objective function gives fo og Wh3 fa m=| 12S (bL?) | P —«— Material properties | C\b / \ Eu | \, ‘, Functional constraint _4 tL Geometric constraints The quantities $*, L, b, and C, are all specified; the only freedom of choice left is that of the material. The index is the group of material properties, which we invert such that a maximum is sought: The best materials for a light, stiff panel are those with the greatest values of Mp =  The quantities $*, L, and C) are all specified or constant; the best materials for a light, stiff beam are those with the largest values of index M,, where My, = 5.15) n= (5.15) Repeating the calculation with a constraint of strength rather than stiffness leads to the index (5.16)  Minimizing material cost: Cheap ties, panels, and beams When the objective is to minimize cost rather than mass, the indices change again. If the material price is C,, $/kg, the cost of the material to make a component of mass m is just mC,,. The objective function for the material cost C of the tie, panel or beam then becomes C=mC,,=ALC,, p — i _ ~~] — Proceeding as before leads to indices that have the form of Equations (5.4), (5.5), (5.9), (5.10), (5.15), and (5.16), with p replaced by C,,, o. Thus the index guiding material choice for a tie of specified strength and minimum material cost is where C,, is the material price per kg. The index for a cheap stiff panel is EY3 =— 5.19) Cn Pp ( ) and so forth (It must be remembered that the material cost is only part of the cost of a shaped component; there is also the manufacturing cost—the cost to shape, join, and finish it.) The Selection Procedure  Property limits: go no-go conditions and geometric restrictions Any design imposes certain non- negotiable demands on the material of which it is made.  Temperature : วสัดุท่ีใชง้านท่ีอุณหภูมิท่ี 500°C ไม่สามารถ ท าจากพอลิเมอร์ได ้เน่ืองจากพอลิเมอร์จะเส่ือมสภาพท่ีอุณหภูมิท่ีต ่ากวา่น้ี  Electrical conductivity : วสัดุท่ีตอ้งการใชง้านเป็นฉนวน ไม่สามารถท าจากโลหะไดเ้น่ืองจากโลหะมีการน าไฟฟ้าท่ีดี  Corrosion resistance  Cost Property limits  One way of applying the limits is illustrated in next Figure.  It shows a schematic E - chart with a pair of limits for E and  plotted on it.  The optimizing search is restricted to the window between the limits within which the next steps of the procedure operate. Performance maximizing criteria  The next step is to seek, from the subset of materials which meet the property limits, those which maximize the performance of the component.  We will use the design of light, stiff components as an example; the other material indices are used in a similar way. A design of light, stiff components E/p=C or taking logs log F = log p+ loge (5,25) isa family of straight parallel lines of slope | on a plot of log £ against log p; each line corresponds to a value of the constant C, The condition (5.24) gives another get, this time with a slope of 2; and Eips (5.25) [=E'p — My=E*?/p } Modulus — Density __ _|. Coramics Guide lines for _| minimum mass |, design = a 5 a g Wy 0 2 3 3B QO E 2 Dp € 3 9 > Density p (kg/m?) A schematic F — » chart showing guide lines for the three material indices for stiff, lightweight design. The structural index  The efficiency of material usage in mechanically loaded components depends on the product of three factors: - the material index - a factor describing section shape - a structural index , which contains elements of the F and G of this equation. The structural index  Consider, as an example, the development of the index for a cheap, stiff column.  The objective was that of minimizing cost.  The mechanical efficiency is a measure of the load carried divided by the ‘objective’ - in this case, cost per unit length.  the efficiency of the column is given by CONSTANT MATERIAL INDEX STRUCTURAL INDEX STRUCTURAL INDEX has the dimensions of stress; it is a measure of the intensity of loading. Materials for oars Materials for oars Spoon FIGURE 6.1 An oar. Oars are designed on stiffness, measured in the way shown in the Jower figure, and they must be light. Materials for oars  an oar is a beam, loaded in bending.  It must be strong enough to carry the bending moment exerted by the oarsman without breaking.  It must have just the right stiffness to match the rower’s own characteristics and give the right ‘feel’,  And - very important - it must be as light as possible. Materials for oars  A soft oar will deflect nearly.50mm; a hard one only 30.  A rower, ordering an oar, will specify how hard it should be.  The oar must also be light; extra weight increases the wetted area of the hull and the drag that goes with it. Materials for oars  So there we have it: an oar is a beam of specified stiffness and minimum weight.  The material index for a light, stiff beam: Materials for oars  There are other obvious constraints.  Oars are dropped, and blades sometimes clash. The material must be tough enough to survive this, so brittle materials (those with a toughness less than 1 kJ/m2) are unacceptable.  And, while sportsmen will pay a great deal for the ultimate in equipment, there are limits on cost.