1、Basic Knowledge of Steel and Plastic Mechanics,基础钢和塑性变形知识,2,Contents,1. Steel Mechanical properties Worldwide steel grades Advanced high strength steel (AHSS)2. Plastic mechanics Sheet deformation modes Forming limits Yield criteria,3,Introduction to elasticity and plasticity,固体材料受外力作用产生变形，从变形开始到破坏一
2、般要经历两个阶段：弹性变形(elastic deformation)和塑性变形(plastic deformation)。 外力卸载后，弹性变形能够完全消失，而塑性变形不能消失。 弹性变形和塑性变形的机理：材料原子之间的作用力平衡。 位错(dislocation)理论。 强化机制(work hardening mechanism)。,Dislocation movement,4,Uniaxial tensile test,GB/T228 金属材料室温拉伸试验方法 EN10002-1 Metallic materials - Tensile test - Part 1 : test method
3、 (in ambient temperature),Typical tensile test piece,5,Engineering stress-strain curve,6,Engineering stress-strain curve,7,Strength and Ductility,Strength parameters,Engineering stress,Engineering strain,Elongation,Reduction of area,Ductility,8,True stress-strain curve,True stress,True strain,9,Work
4、ing hardening (strain hardening),Strain hardening exponent (n-value),10,Influence of strain-hardening exponent,n3,n2,n1,11,Anisotropy (R-value),Width strain: w=ln(w/w0)Thickness strain: t=ln(t/t0)R= w/t,Planar anisotropy ratio,Normal plastic anisotropy ratio,12,Strain rate sensitivity,Strain rate,St
5、rain rate sensitivity exponent,Strain rate sensitivity has a crucial influence on the research of crash resistance and high-speed stamping formability.,13,Worldwide steel grades,14,Worldwide steel grades,15,Common steel types and evolving AHSS types,Interstitial free (IF) steels Mild steels Bake har
6、denable (BH) steels Isotropic (IS) steels Carbon-manganese (CM) steels High-strength low-alloy (HSLA) steels Dual phase (DP) steels Transformation induced plasticity (TRIP) steels Complex phase (CP) steels Martensitic (Mart) steels,16,Strengthening mechanism,17,HSLA steel,18,Grades of HSLA steel in
7、EU,19,Application of HSLA steel,20,Dual phase (DP) steel,21,EU steel grades,Comparison European steel grades (Mild steel, HSLA, Dual-Phase),Legend: Cold Rolled Hot Rolled Dual Phase cold rolled (values from ARCELOR),Not for new products,!: Availibility to be clarified,From Claus Unruh,22,Dimension a
8、vailability,Availability check materials Europe versus US update Nov 2006 (only acc. my information; must be checked and confirmed by Purchasing department),Material availibility of standard materials is given. Material availibility of S460 MC is decreasing even in Europe. Material availibility of D
9、ual Phase and other special grades must checked for each dimensions,From Claus Unruh,23,Dimension availability,Availability check materials Europe versus China update Nov 2006 (only acc. my information; must be checked and confirmed by Purchasing department),Material availibility of standard materia
10、ls is given. Material availibility of S460 MC is decreasing even Europe. Material availibility of Dual Phase and other special grades must checked for each dimensions,From Claus Unruh,24,Standard thickness China vs. Japan,China,Japan,25,HSLA steel grades overview,Overview steel grades: HSLA (high st
11、rength low alloyed),Steel family,cold rolled,hot rolled,Legend:,Existing grades after standardisation,Use only standard HSLA steel (worldwide available) H240 LA and S460 MC was cancelled caused by sourcing problems worldwide !,From Claus Unruh,26,Mild steel grades overview,Overview steel grades: Mil
12、d steel,Steel family,cold rolled,hot rolled,Legend:,Existing grades before standardisation,Existing grades after standardisation,Only 2 grades are allowed: DC01/ CS: soft steel for simple low strength press parts DC04/ DDS: soft steel with good deep drawing properties; for complex low strength press
13、 parts Brand names and other material designations will not be accepted.,From Claus Unruh,27,DP steel grades overview,Overview steel grades: Dual-Phase steel,Steel family,cold rolled,hot rolled,Legend:,(*) Japanese grades not exactly comparable,DP400 and DP 500 are not relevant for seat structures.
14、DP1400 in development.Standardisation of Dual Phase grades is difficult, caused by missing European standard. Availability has to be clarified for each grade and dimension.Purchasing department must support the process.,From Claus Unruh,28,Products from Bao Steel for automobile structures,Mild steel
15、s,29,Products from Bao Steel for automobile structures,DP steels,Hot rolled mild & HSLA steels,30,Products from Bao Steel for automobile structures,Cold rolled HSLA steels,Hot rolled HSLA steels,31,VHSS category at Arcelor,32,Metallurgy of VHSS at Arcelor,33,Application of VHSS,34,Application of VHS
16、S,35,Engineering stress-strain curve of DP steel,Higher tensile strength of DP steel (larger n-value) Better stamping formability and crash resistance performance of DP steel,36,n-value of DP steel,37,Application of DP steel,38,FEA results of DP steel,39,FEA results of DP steel,40,Sheet metal formin
17、g processes,blanking & piercing,bending,Bending in a folding machine Bending in a vee-die Section of a set of rolls in a roll former Wiping down a flange,41,Sheet metal forming processes,flanging,stretching,A shrink flange with buckling A stretch flange with cracking Flanging a curved sheet,Section
18、bending,Stretching a dome in a sheet A domed punch and die set for stretching a sheet,42,Sheet metal forming processes,hole-extrusion,stamping (drawing),Typical part formed in a stamping or draw die showing the die ring, but not the punch or blankholder Section of tooling in a draw die showing the p
19、unch and blankholder,43,Sheet metal forming processes,Tooling for deep drawing a cylindrical cup,Tooling for forward redrawing a cylindrical cup,Tube forming,Expanding the end of a tube with a flaring tool Reducing the diameter of a tube by pressing it through a sinking die,44,Sheet metal forming pr
20、ocesses,Hydroforming a shallow part,Expanding a round tube to a square section by hydroforming,Using combined axial force and fluid pressure to form a T-joint,Thinning a sheet locally using a coining tool,45,Sheet metal deformation modes - stretching,stretching,塑性变形局限在某一固定区域内。成形依靠材料表面积增大实现，因此变形区域材料厚
21、度变薄。 变形区域的应力状态是双向拉伸。材料不起皱，变形区域表面质量好。,Strain status: biaxial tension,试验方法：杯突 评估指标：IE,试验方法：极限拱顶高 评估指标：LDH0,46,Sheet metal deformation modes - drawing,drawing (cup drawing),坯料外部环形区域是变形区，坯料内部圆形区域不变形。 在径向的应力是拉应力，在切向的应力是压应力。因此，坯料在径向可能出现破裂（拉裂），在切向可能出现起皱（压缩）。,Strain status Radial: tension Tangential: compre
22、ssion,试验方法：圆筒拉深 评估指标：LDR,47,Sheet metal deformation modes - bending,bending,曲率发生变化的区域是变形区。 坯料圆角和直边部分参与变形，变形过程和卸载过程很复杂。 卸载后零件容易发生回弹，导致达不到尺寸精度。,试验方法：V形弯曲 评估指标：Rmin/t,48,Sheet metal deformation modes - flanging,Shrink flanging Stretch flanging,试验方法：扩孔 评估指标：,圆锥冲头 平底冲头,49,Principal strain status during d
23、eformation,drawing,plane strain,stretching,50,Forming limits,Test procedure of material forming limits (forming limit curve, FLC),Forming limit diagram (FLD),51,Application of FLD,Analysis of sheet metal forming process based on FLD,52,Yielding in plane stress,Plane stress,1, 20, 3=0,Maximum shear s
24、tress and maximum shear stress planes,There are on shear stresses on the faces of the principal element. On a face inclined at any other angle, both normal and shear stresses will act. On faces of different orientation it is found that the shear stresses will locally reach a maximum for three partic
25、ular directions. They are inclined at 45 to the principal directions.,53,Yielding in plane stress,Yielding condition can be expressed as,Mohr circle of stress,54,Tresca yield criterion,The Tresca yield criterion in plane stress,Hypothesis: yielding would occur when the greatest maximum shear stress
26、reaches a critical value.,1=2, 1=3, 3=0 max=1 If 20, min= 3=0 If 20, min= 2,In plane stress,Note: Application only to isotropic materials. Not considering material work hardening.,55,Von Mises yield criterion,The von Mises yield criterion in plane stress,Note: Application only to isotropic materials. Not considering material work hardening.,Hypothesis: yielding would occur when the root-mean-square value of the maximum shear stresses reaches a critical value,In plane stress,56,Thank you!,
