1、材料成形力学材料成形力学（双语教学）（双语教学）Mechanics of Material Forming The Contents of the Subject1 Introduction (引言)2 Stress Analysis （应力分析）3 Strain Analysis （应变分析）4 Yield Criteria for Ductile Metals （塑性材料的屈服准则）5 Stress-Strain Relation （应力应变关系）6 Stress Evaluation Approch-Slab Method （工程法）7 Plain Strain Slip-line Fi
2、eld Theory（平面应变滑移线场理论）8 Extremum Principle for a Rigid Perfectly Plastic Material （刚塑性材料的极限分析原理）Chapter 1 Introduction1)Elastic and plastic deformation(弹性变形和塑性变形弹性变形和塑性变形)A)Elastic deformationForce(small)(力力)Stress State(应力状态应力状态)Deformation(strain)(变形或应变变形或应变)Stress-Strain:linear(线性的线性的)Deformation
3、:recoverable（变形）（变形）reversibleElastic deformationTheory of elasticity(elastic deformed body)(弹性理论)（弹性变形体）1.1 Definition and scope of the subjectB)Plastic deformationStress-Strain:non-linear(非线性的非线性的)Deformation:irrecoverable(不可恢复的不可恢复的)（变形）（变形）irreversiblePlastic deformationTheory of Plasticity (塑性理
4、论)2)Theory of Plasticity(塑性理论塑性理论)It is concerned with the mathematical study of stress and strain in a plastically deformed body.塑性理论主要考虑塑性变形体内应力应变的数学关系。Object （研究对象）（研究对象）Research method （研究方法）（研究方法）Ductile metal materials(塑性金属材料塑性金属材料)，independent of time.Experimental observationMacroscopic behav
5、iour.FormulizationIt is different from material science.Physical explanationMicroscope structureCombine Theory of plasticityMaterial scienceUnified theory of plasticityOur task 3)Nature of Engineering Plasticity(工程塑性理论的特性工程塑性理论的特性)Practice and application （实践和应用）（实践和应用）To construct relation between
6、stress and strain for metals and their alloysTo develop mathematical technique,determine stress distribution and predict plastic deformationTwo aimsFeaturesComplex stress stateNon-linearMath.difficultiesAssumptionsapproximations1864.Tresca Yield criterion1.2 Brief historical accountH.E.Tresca carrie
7、d out experiments of metal forming such as punching,extrusion and compression using some metals,and measured the relation between forming load and ram displacement.He presented a series of papers to the French Academy of Sciences,first in1864.In Fig.4 the cross-section of an extruded billed made of2
8、0 lead sheets is given.Tresca was interested in the metal flow as suggested by the title of his first paper,(On the flow of solid body subjected to high pressure),not yielding in material testing.Tresca assumed that the extrusion force P could be expressed in terms of the shear stress k,and estimate
9、d the value of k from the measured forming load of various processes.Because the values of shear stress k estimated from the forming loads dropped in a certain range,he concluded that the metal flow occurred under a constant maximum shear stress.Saint-Venant and Lvy1.2 Brief historical accountWhen T
10、resca presented his paper to the French Academy of Sciences,Barr de Saint-Venant(1797 1886)was the authority of mechanics in France who was elected a member of the Academy in 1868.After reading the experimental results of plastic flow by Tresca,his attention was drawn to the area of plasticity.In 18
11、71,he wrote a paper on elastic-plastic analysis of partly plastic problems,such as twisting of rod,bending of rectangular beam and pressurizing of hollow cylinder.Saint-Venant assumed that(1)the volume of material does not change during plastic deformation,(2)the directions of principal strains coin
12、cide with those of the principal stresses(now known as total strain theory),(3)the maximum shear stress at each point is equal to a specific constant in plastic region.1.2 Brief historical account1.2 Brief historical accountProgress of research in yield condition1.2 Brief historical account1.2 Brief
13、 historical account1920.Prandtl and Hencky.Theory of slip line field1.2 Brief historical accountLudwig Prandtl（1870 1953）received engineering education at the Munich TH.After graduating,he remained at the school as an assistant of A.Fppl,and carried out doctoral work on bending of circular plates.Af
14、ter working in the industry for a while,he was appointed as a professor of industrial mechanics of Hannover TH in 1900.There he proposed membrane analogy of torsion and boundary layer of fluid flow.In 1904 he was invited to the Institute of Mechanics in Gttingen University.Soon he began to study pla
15、sticity such as plastic buckling and bending.He was appointed the leader of the laboratory of aerodynamics,and studied wing theorem and other important works of fluid dynamics.In 1922 Prandtl established the society of applied mathematics and mechanics,“Gesellschaft fr Angewandte Mathematik und Mech
16、anik”,and led the area of applied mechanics.He is also famous as the teacher of many leaders in mechanics in the 20th century such as Th.von Krmn(California Institute of Technology),S.P.Timoshenko(Stanford University),A.Ndai(Westinghouse Laboratory),W.Prager(Brown University)and others.1.2 Brief his
17、torical account1.2 Brief historical account1.2 Brief historical account1.2 Brief historical account1.2 Brief historical account1925.Von-Karman.Slab method apply to rolling1.2 Brief historical account1.2 Brief historical account1.2 Brief historical accountChapter 1 Introduction1)According to the homo
18、logous temperature THthe homologous temperatureHMTT TTThe absolute test temperature(实验时的绝对温度实验时的绝对温度)MTThe absolute melting temperature(绝对熔点温度绝对熔点温度)0.5HT Hot metal forming processes（热加工）（热加工）0.5HT Cold metal forming processes（冷加工）（冷加工）Intermediate:Warm metal forming processes（温加工）（温加工）1.3 Classific
19、ation of metal forming processes2)According to the type of stress stateCompressive stress state(predominant)Squeezing group（压应力状态类）（压应力状态类）UpsettingClose dieforgingForging（锻造）（锻造）Extrusion（挤压）（挤压）ForwardBackwardPunch(冲头冲头)Work-piece(工件工件)Rolling（轧制）（轧制）Tensile stress state Drawing group（拉应力状态类）s1s2s
20、3Drawing of sheet,tube,bar and wire.Fs1s2s3Deep drawing.s1s2s3Dending group（弯曲类）（弯曲类）Tensile stress state on one side.Compression stress state on the another side.Stress gradientflangingStretch concave（拉伸弯曲）（拉伸弯曲）Shrink concave(压缩弯曲压缩弯曲)Straight (矫直矫直)Cutting group（切削类）（切削类）Machining,Drill,Turn,Mill
21、1.4 Forming Limts (成形极限成形极限)The condition of plastic deformationShear stressesThe extent of plastic deformation that can be achieved is highly dependent on the nature of the stress state induced.The limit of plastic deformation:a)necking（颈缩）（颈缩）b)Buckling（屈曲）（屈曲）c)fracture（断裂）（断裂）A limit to forming is imposed when uniform plastic flow ceases and forming limit is determined by whichever defect occurs first.The forming limits depend on the state of stress induced in the work-piece.
