Material Properties Mark Sullivan September 25, 2008
Agenda • Review of Material Properties • Strength, Stiffness, Wear • Material Parameters • Table of Material Properties (SI, English) • Figures of Merit • Property Map, Groups, & Profiles
Acknowledgements • Text and figures in these lecture notes are taken from the following sources: • Slocum, A. H., FUNdaMENTALs of Design, MIT, 2008. • Hale, L. C., “Principles and Techniques for Designing Precision Machines,” UCRL-LR-133066, Lawrence Livermore National Laboratory, 1999. (http://www.llnl.gov/tid/lof/documents/pdf/235415.pdf) • Smith, S. T., Chetwynd, D. G., Foundations of Ultraprecision Mechanism Design, Taylor & Francis, 1994. • Belt, R. T., “Optimum Precision Engineering Material,” 2007.
Review of Material Properties • Materials • Structural • Rigid • Compliant or Resilient • Aesthetic • Hybrid • Hooke’s Law • F = k x • σ = E ε • Generalized: • Linear • Isotropic Text from “FUNdaMENTALs of Design,” Slocum
Review of Material Properties (2) • Ultimate Strength = Stress at which the material breaks • Tensile Strength = Stress at which the materials sufferspermanent deformation • Fatigue Strength (Endurance Limit) = Stress at which material can be subjected for many cycles • Tensile, Flexural (Bending), & Compressive Strengths are about the same for metals, but vary for plastics, rubbers, woods • Brittle materials (glass, ceramics, concrete) are much stronger in compression than tension • Ductility = resistance to fracture • Fracture Toughness = resistance to crack growth • Brittle-to-Ductile Transition Temperature = temperature where a marked increase in toughness occurs Text from “FUNdaMENTALs of Design,” Slocum
Strength & Stiffness Chart from “FUNdaMENTALs of Design,” Slocum
Strength & Wear • Strength – determined by complex interaction of metalurgical properties • Wear – determined by the distribution of particles on the surface of the material • Example: • Al 7075-T6: Syt = 462 MPa • A36 Steel: Syt = 250 MPa • But if rubbed together, steel would win! • Friction and wear properties of materials are highly dependent on which two materials are paired together and the type of lubricant between them. • In general, dissimilar materials wear best • e.g., nylon on steel is better than nylon on nylon • aluminum on aluminum is perhaps the worst! Text from “FUNdaMENTALs of Design,” Slocum
Wear • Wear-resistant Materials • Often have hard carbide, nitride, or oxide layer on their surfaces • Hardened steels, ceramics, thickly anodized aluminum all have good wear properties • Wear-resistant Material Pairs • Brass, cast iron, and most plastics wear well when used in conjunction with a hard material • Inherent lubricity of softer materials Text from “FUNdaMENTALs of Design,” Slocum
Material Selection Chart from “FUNdaMENTALs of Design,” Slocum
Material Properties needed for design • Materials Aluminum Steel Adhesive Beryllium Titanium Glass (Vis, NIR, MWIR) Copper Plastic Miscellaneous • Properties Density CTE Moduli (Tensile, Shear) Melting Temperature Specific Heat Poisson’s Ratio Thermal Conductivity Resistivity Strength (Tensile, Ultimate) • Figures of Merit Specific Stiffness Thermal Diffusivity Specific Strength Figures of merit allow material selection using normalized metrics.
Figures of merit aid material selection • Materials Selection • Separate geometry effects from the materials’ effects. • Use geometry first. Materials properties cannot substitute for proper scaling and best use of form. • Employ material figures of merit • Specific stiffness: a measure of stiffness efficiency (maximize) • Specific strength: a measure of strength efficiency (maximize) • Thermal diffusivity: a measure of heat transfer efficiency (maximize)
Material Properties- Optical - • Materials Crown Glasses Low Expansion Ceramics Flint Glasses Optical Plastics Fused Silica Vis and IR • Properties Indices of refraction: nd, nF, nC Abbé number, nd Principle dispersion , nF – nC Relative partial dispersion ratio, Pd,C Stress optic coefficient, KS Change in index with temperature, dn/dT Change in focus of lens with temperature, Mechanical properties from previous page • Figures of Merit Use material properties to help solve your design problem.
Application of optical material properties • Athermalization • Stress Birefringence Optothermal Coefficient Stress Optical Coefficient
Property Maps,Groups, and Profiles • Governing equations to optimize • e.g., Axial beam deflection: • Determine performance parameter • Property Maps (Ashby) • Property Profiles (Chetwynd) • Property Groups • Mechanical • Thermal • Optical • Material Types • Metals • Ceramics & Glasses • Polymers & Composites • Non-conventional Materials See Chapter 8, “Foundations of Ultraprecision Mechanism Design,” Smith & Chetwynd
Optimum Precision Engineering Material Primary mirror from the XLT. Its diameter is 0.63 m Chart from “Optimum Precision Engineering Material,” Belt
General Viability Categories Performance Machinability Cost Chart from “Optimum Precision Engineering Material,” Belt
Performance Parameters Static elastic structural deformation : E/r, Specific Stiffness Dynamic elastic structural deformation: (E/r)1/2, Specific 1st Modal Frequency Hertzian contact elastic deformation: (E/r)2/3, Point Specific Stiffness Static thermal structural deformation : 1/a, Steady State Thermal Expansion Dynamic thermal structural deformation: Dt ≡ k/rcp, Thermal Diffusivity Chart from “Optimum Precision Engineering Material,” Belt
Summed Performanceusing Performance Parameters Chart from “Optimum Precision Engineering Material,” Belt
Histogram of Metals Performanceusing Performance Parameters Chart from “Optimum Precision Engineering Material,” Belt
Histogram of Best Material Performance Chart from “Optimum Precision Engineering Material,” Belt
Best Parameter Distributions. Not Including Diamond and Composites. 1.2 Be 1.0 WC 0.8 Steel, 440C Ti-6Al-4V Normalized Value (0-1) 0.6 Ag (99.999Ag), annealed 0.4 Si3N4, Hot Pressed BeO 0.2 SiC, Sintered Alpha 0.0 Alumina Ceramic, Al203 E/r v [E/r] E2/3 sut/r 1/a DT = k/(r·cp) a-Alumina, Al203, para to C Normalized Performance Parameters ULE (92.5% SiO2, 7.5% TiO2) Property Group Profile Chart from “Optimum Precision Engineering Material,” Belt