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Learn about the criteria for selecting materials based on properties and strength limits for different classifications, including low, medium, high, and super high strength. Explore stress concentration, stiffness, reliability, and toughness in structural materials. Discover how materials are tested for tensile and compression strength, as well as factors influencing lifetime and corrosion resistance.
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Application of Materials Part II, Engineering materials
Structural strength Strenth of Materials Stiffness Reliability Lifetime
Strength of materials Properties determined at tensile/compression tests Permanent elongation Total elongation
Criteria for materials selection • plastic materials – yield strength (yield limit) – Re, Rp (Rec, Rpc) • brittle materials – strength limit – Rm (Rmc), Rm/ Classification of materials (Re, Rp0,2) • low strength < 250 N/mm2 • medium strength 250...750 N/mm2 • high strength 750...1500 N/mm2 • super high strength > 1500 N/mm2
Stiffness Stiffness D = Ex K(geometric characteristic of cross-section) At tension K = S (cross-section area) At bending K = I (moment of inertia) I = bh3/3 Modulus of elasticity Normal Shear Volume
Reliability (1) Toughness – notch impact energy KU or KV, J – fracture toughness KC, N/mm2 m1/2 Ductile fracture % TDBT T’DBT TDBT T KU, KV – cold brittleness TDBT – ductile-to-brittle transition
Reliability (2) Influence of C, ordinary and alloying elements to KU TDBT TDBT TDBT el steel normal cold worked cold worked TDBTC TDBTC
Reliability (3) Ductile-to-brittle transition T50, C % of alloying elements
Reliability (4) Dependence of M toughness of A-grain size KU, J Dependence of KU/KV on temperature low strength KU, KV high strength Grain no. T
Fine and coarse grain steels 1 – killed steel 2 – rimmed steel
Influence of microalloying elements V Grain size of ferrite, m2 Ti Nb Alloying elements, %
Plane strain fracture toughness K1c At tension K1c Coefficient of stress intensity [MPam1/2]
Low-alloyed highly tempered steels Relationship between K1c and yield strength Superplastic steels Fracture toughness K1c, MPa m1/2 Maraging steels Precipitation hardened stainless steels Yield strength, MPa
Life time (1) R (R = min/max) -1 – symmetric loading Fatigue Impactors: - surface roughness - stress state - stress concentrations Steels N = 107 Nonferrous alloys N = 108
Life time (3) Creep = f(, T, t) • low temperature T/Tm < 0.5 • high temperature T/Tm > 0.5 Impactors • structure • alloying (super creep alloys) – • TMT
Corrosion Modes of corrosion in dry gases in organic liquids Chemical in water containing environments in melt electrolytes Electrochemical Biochemical
Types of corrosion Types of corrosion: a – uniform b – nonuniform c – selective d – spotted e – pitting f – dotted g – under surface h – intercrystal i - stress
Chemical corrosion of metals (1) 2 Mg + O2 = 2 MgO 2 Fe + 3 O2 = Fe2O3 For protection Voxide > Vmetal Kui Voxide/Vmetal> 1 – Cd, Al, Ti, Zr, Zn, Ni, Cr, Fe At high Voks / Vmet (1,2…2,0) cracking High temperature corrosion T 1000 C – oxide layer electroconductive
Chemical corrosion of metals (2) Corrosion influencing parameters • structure • surface treatment materials parameters • internal stresses • T • gas composition • velocity environmental parameters • heating parameters
Chemical corrosion of metals (3) Protection • alloying ( ) • coatings • protective atmosphere (at heat treatment) (H2 + N2 + H2O; CO + CO2 + N2; etc.)
Electrochemical corrosion of metals (1) Moisture + H2S, Co2, So2, NaCl electrolyte metals galvanic pair
Electrochemical corrosion of metals (2) Microgalvanic pairs at steels Atmosphere Moisture film Metal
Electrochemical corrosion of metals (3) Protection (1) • Selection of materials Table: Allowed contacts of metals
Protection (2) • Protective coatings - metallic (less active metals (Cu, Ni, Sn, Ag) – up to coating must be undamage; active (Zn, Co) – protection up to end) - paints, lubricants • other - cathodic protection - protector protection - anodic protection - corrosion inhibitors (high molecular matters)
Wear Modes of wear Mechanical Corrosive-mechanical Adhesive -abrasion -oxidizing wear -erosion -fretting corrosive wear -cavitation -fatigue wear
Method for wear protection • hardening, thermo-chemical treatment • overwelding • surface alloying • coating (chemical, thermo-chemical, thermally sprayed, PVD, CVD, mechanical) • selection of pairs (by adhesion)
Material groups Metals Cermets MCM Ceramics CCM Glass-ceramics Composites GCCM PCM FRG Polymers Glass MCM Metal composite materials CCM Ceramic composite material PCM Polymeric composite material GCCM Glass-ceramic composite material FRG Fiber-reinforced glass
Basic physical and mechanical properties of construction materials (1)
Basic physical and mechanical properties of construction materials (2)
Thank you for attention priit.kulu@ttu.ee