材料科学与工程导论总复习-课件.ppt
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- 材料科学 工程 导论 复习 课件
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1、About this course(contd)4.Course evaluation How to assess the learning quality?Final exam 70%weight(multiple choice,analysis and calculation,English/Chinese alternatively)In-class quiz 30%weight(1 quiz/Per 2 weeks,totally 6 quizzes)Homework By your choice,not a must 5.Textbook:D.R.Askeland and P.P.P
2、hule,Essentials of Materials Science and Engineering(材料科学与工程基础材料科学与工程基础),Tsinghua University Press,2005(影印本影印本).Evolution of materialsOur tasks,challenges and goalsCompositionStructures Processing Properties/performance Stronger Tougher Lighter Cheaper Safer Smarter Friendly Our tasks 4 components i
3、n materials research&the linear interrelationship Our challenges&goals:To make materialsMaterials scienceMaterials engineeringWhat is Materials Science&Engineering?Materials Science:Investigate the material structures Understand how the material behaves/works in a scientific way Underlie relationshi
4、ps among composition,processing,structures and properties/performance of materials.Materials engineering:Based on materials science How to translate or transform materials into useful devices or structures Making products using materials with a good cost-to-performance ratio (性价比性价比)and environment
5、friendly.Materials Science and Engineering:This subject is an interdisciplinary field concerned with inventing new materials and improving previously known materials by developing deeper understanding of the composition-processing-structure-property relationships.Materials family classification(by b
6、ond)X.P.Zhang(张新平张新平)X.Ma(马骁马骁)Z.M.Yang(杨中民杨中民)Hui He(何慧何慧)PE,PP,PCPA(Nylon)PolymersButyl rubberNeopreneGFRPCFRPCompositesKFRPPlywoodAluminaSi-CarbideInorganic mat./CeramicsSoda-glassPyrexFe,Cu,Al,Ni,Au,Metals&AlloysSteels,cast ironMaterials family classification(by use)MaterialsStructural materials
7、Functional materialsMagnetic materials Optical materials Electronic materials Superconductive materials:Metallic materials Plastic materials Wood structural materials Other structural materials :What is a metal?What is a ceramic?Natural&synthetic rock:hard,brittle&heat-resistantWhat is a polymer?The
8、 word polymer literally means many parts Better know as“plastics”by general public The great majority of elements in the periodic table are metals.A metal has a particular type of bonding known as metallic bonding(as distinct from ionic bonding and covalent bonding).Metals tend to be ductile strong
9、shiny materials that corrode easilyWhat is a composite material?An engineering material which consists of more than one material type1.Macrostructure(宏观结构宏观结构)We can see it by our eyes:100 m.2.Microstructure(微观结构微观结构)We can only see it by a microscope:0.01 1 m.3.Nano-structure(纳米结构纳米结构)Only see it b
10、y special tools (AFM&HRTEM):1000 nm.4.Short-&long range atomic arrangement(短程和长程有短程和长程有 序原子排列序原子排列)We can only see it by special tools:100 nm5.Atomic structure Nearly can not see it:2 N.Microhardness Hardness of materials typically measured using loads less than 2 N using such test as Knoop(HK).Nano
11、-hardness Hardness of materials measured at 110 nm length scale using extremely small(100 N)forces.Indenters for the Brinell&Rockwell hardness tests(a)Charpy&Izod tests;(b)dimensions of typical specimensImpact tests Fracture mechanics(断裂力学断裂力学)Fracture mechanics The study of a materials ability to w
12、ithstand stress in the presence of a flaw or a crack(裂纹)(裂纹).Fracture toughness(断裂韧性断裂韧性)The resistance of a material to failure in the presence of a flaw or a crack.It is totally different from conventional tensile test or impact test,and gives much more accurate evaluation of a materials propertie
13、s.Charpy specimen:V-notch Less to see in practice A crack with the sharp tip More often to see in practiceSchematic of fracture toughness specimensEdge flaws(边裂纹)(边裂纹)Internal flaws(内部裂纹)(内部裂纹)afKStress intensity factor:(应力强度因子)(应力强度因子)Kc:Fracture toughness(断裂韧性断裂韧性)It is a materials property growth
14、crackNoKKC:Importance of fracture mechanics Selection of a material Design of a component Design of a manufacturing or testing method Brittle fracture(脆断脆断)&Griffith flaw(格里菲思微格里菲思微裂纹裂纹)A crack or flaw in a material that concentrates(集中)(集中)&magnifies(放大)(放大)the applied stress.Schematic diagram of a
15、 Griffith flaw in a ceramicraactual/2The actual stress at the crack tip:Micro-structural features of fracture in metallic materials Ductile fracture(韧韧/塑塑/延性断裂延性断裂)A metal fractures with good ductility and toughness.It normally occurs in a transgranular(穿晶断裂)(穿晶断裂)manner(through the grains),i.e.,the
16、 cracks would go thru the grains.Microvoids(微孔微孔)form in fracture process.Brittle fracture(脆性断裂脆性断裂)A metal or alloy fractures with poor ductility and toughness.It occurs without plastic deformation and takes an intergranular path(沿晶断裂)(沿晶断裂)(along the grain boundaries).Cleavage fracture(解理断裂)(解理断裂)
17、is often observed.Chevron pattern fracture(人字纹形断裂人字纹形断裂)A common fracture feature produced by separate crack fronts propagating(扩展)(扩展)at different levels in the material.Fatigue(疲劳)(疲劳)of materials oFatigue It means that the material is tired from the applied cyclic load(循环载荷)(循环载荷).It is the lower
18、ing of strength or failure of a material due to repetitive stress(反复应力)(反复应力)which may be above or below the yield strength.80%of failures of engineering parts&structures are related to fatigue,more or less!oCreep(蠕变)(蠕变)A time dependent,permanent deformation at high temperatures,occurring at consta
19、nt load(恒载荷)(恒载荷)or constant stress(恒应力)(恒应力).oBeach(海滩纹)(海滩纹)or clamshell(蛤壳纹)(蛤壳纹)marks Patterns often seen on a component subjected to fatigue.oRotating cantilever beam(悬臂梁)(悬臂梁)test An older test for fatigue testing(P.197).oS-N curve(also known as the Whler curve)A graph showing stress as a func
20、tion of number of cycles in fatigue.Creep(蠕变)(蠕变),stress rupture(应力断裂)(应力断裂)&stress corrosion(应力腐蚀)(应力腐蚀)oStress-rupture curve(应力断裂曲线应力断裂曲线)A method of reporting the results of a series of creep tests(蠕变(蠕变试验)试验)by plotting the applied stress versus the rupture time.oStress-corrosion A phenomenon in
21、 which materials react with corrosive(腐蚀性)(腐蚀性)chemicals in the environment leading to the formation of cracks and lowering of strength.o Creep(蠕变)(蠕变)A time dependent,permanent deformation at high temperatures,occurring at constant load(恒载荷)(恒载荷)or constant stress(恒应力)(恒应力).Strain Hardening and Ann
22、ealing(应变(应变/加工硬化与退火)加工硬化与退火)Strain hardening and annealing relationship of cold working(冷加工)(冷加工)to the stress-strain curve:Manufacturing processes that make use of cold working as well as hot working.Common metalworking methods轧制轧制 rolling挤出挤出 extrusion拉拔拉拔 wire drawing冲压冲压 stamp/punch锻造锻造 forging
23、Three stages of annealingoRecovery(回复)(回复)A low-temperature annealing heat treatment designed to eliminate residual stresses(残余应力)(残余应力)introduced during deformation without reducing the strength of the cold-worked material.oRecrystallization(再结晶)(再结晶)A medium-temperature annealing heat treatment de
24、signed to eliminate all of the effects of the strain hardening produced during cold working.oGrain growth(晶粒长大)(晶粒长大)Movement of grain boundaries by diffusion in order to reduce the amount of grain boundary area.An Introduction to Materials Science&Engineering Lecture 5(Chapters 9+10)Todays objectiv
25、es:What is solidification凝固?why solidification can occur?Solidification mechanism and theory;Solidification defects&how to prevent the defects;Some application(glass-making,joining metals etc);What is a phase相 and what is a phase diagram相图(PD)?Solid-solution strengthening 固溶强化and other;Typical solid
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