l01 Bulk Metal Forming 1
Transcript of l01 Bulk Metal Forming 1
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Bulk Metal Forming ISimulation Techniques in Manufacturing Technology
Lecture 1
Laboratory for Machine Tools and Production Engineering
Chair of Manufacturing Technology
Prof. Dr.-Ing. Dr.-Ing. E.h. Dr. h.c. Dr. h.c. F. Klocke
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Lecture objectives
Basic knowledge in metallurgy for a better understandingof the mechanisms during metal forming
Elastic and plastic material behaviour and its influence onthe process results in forming technology
Mathematical models for a description of the elastic andplastic material behaviour
Introduction of processes in cold and warm bulk formingas well as in forging
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Forging8
Warm Forming7
Cold Forming6
Recrystallisation5
Flow Stress4
Plastic Deformation3
Elastic Deformation2
Metallurgical Basics1
Outline
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Metallurgical Basics
4 Basic Chemical Bonds
+ + + + + + + + + +
+ + + + + + + + + +
+ + + + + + + + + +
+ + + + + + + + + +electron gas (e-)
positive chargedmetal ions
ionic bond
metal bond
+
-
-
--
-
-
--
---
-
-
-+
+
+
+
+
++
+
+
+
+
+
+
metal bond
ionic bond
covalent bond
Van-der-Waals bond
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Metallurgical Basics
The Metal Bond
metal atoms basically emit electronspositive charged ions
in pure metals no electron-absorbing atoms do existun-combined electrons (outer electrons) form an electron gas
outer electrons in metals can freely movegood electrical and thermal conductivity
in absolute pure metals all atoms are totally equalplastic deformation
+ + + + + + + + + +
+ + + + + + + + + +
+ + + + + + + + + +
+ + + + + + + + + +
electron gas (e-)
positive chargedmetal ions
metal bond
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Metallurgical Basics
Lattice Types of an Unit Cell
face-centredcubic(fcc)
body-centredcubic(bcc)
hexagonal(hex)
examples:
sliding planes:
sliding directions:sliding systems:
formability:
γ-Fe, Al, Cu
4
312
very good
α-Fe, Cr, Mo
6
212
good
Mg, Zn, Be
1
33
poor
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Metallurgical Basics
Atomic and Macroscopic View of Metal Structures
idealcrystal
structure
special agglomeration of crystals
section plane
a
crystal latticeunit cell
2D – Cutof the microstructure
microstructure
schematically photograph
realcrystal
structure
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Forging8
Warm Forming7
Cold Forming6
Recrystallisation5
Flow Stress4
Plastic Deformation3
Elastic Deformation2
Metallurgical Basics1
Outline
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Elastic Deformation
Tensile Test – Load-Displacement Diagram
specimen 1
specimen 2
A1 = 2 • A2
follows:F1 = 2 • F2
relate force to cross section surface
tensile specimen
l o a d
displacement
F1
F2
l1l1 = l2
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Elastic Deformation
Stress-Strain Curve of Elastic Behaviour
00
01
l
l 00 l
∆l
l
ll
l
dl ε
l
dl d
1
0
=−
==⇒= ∫ε
A
F
0
=σ
tanel
el
ε
σ α =
s t r e s s
strain
F
F
Re
σel
eel
l0
∆l
l
A0
A
engineering strain:
engineering stress:
α
For elastic behaviour:
Eel
el
ε
σ =
σ ≤ Re
E = Young‘s Modulus
specimenno. 1≙ no. 2
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tensile test compression test shear test
F
F
l 0
A0
l 1
A1
A0
F
F
A1
l 1
l 0
0A
F =σ
0A
F −=σ
Elastic Deformation
Stress Determination Depending on Load
0A
F
=τ
F
Fa
l
q
A0
tensile stress compression stress shear stress
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unloaded tensile-loaded
σ - nominal stress
ε - strainE - Young‘s Modulus
l0 l1
s
s
Elastic Deformation
Atomic Representation of Pure Elastic-Tensile Deformation
00
01el
l∆l
lll ε =−= E
el
el
ε σ =
elastic strain based on tensile load
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τ
γ
τ
unloaded shear-loaded
γ - shear angle
τ - shear stressG - shear modulus
ν - Poisson‘s ratio
E - Young‘s modulus
Elastic Deformation
Atomic Representation of Pure Elastic-Shear Deformation
)2(1
Gel µ γ
τ
+== E
elastic shearing based on shear load
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Forging8
Warm Forming7
Cold Forming6
Recrystallisation5
Flow Stress4
Plastic Deformation3
Elastic Deformation2
Metallurgical Basics1
Outline
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Plastic Deformation
Stress-Strain Curve up to the Uniform Elongation
AF
0
=σ
s t
r e s s
strain
engineering stress:(related to starting section)
F
F
Rm
Re ,se
eelepl
l0
∆l
l
A0
A
loadrelieving reload
A
F =′σ
true tensile stress:(related to real section)
σ‘σ
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Plastic Deformation
Strain Determination of an Idealized Upsetting Process
00
01
00
1
0
l
l
l
l l
l
dl
l
dl d
l
l
x x
∆=
−==⇒= ∫ε ε
0
1
0
1
0
1 ln ;ln ;lnh h
b b
l l z y x === ϕ ϕ ϕ
0
1ln1
0l
l
l
dl
l
dl d
l
l
==ϕ ⇒ =ϕ ∫
engineering strain (elastic)
true strain (plastic)
including of volume constancy
)1(ln l
l
l
l ln
l
ll ln
l
ul ln
l
l ln
0
0
00
0
0
x0
0
1 +=
+
∆=
∆+=
+=
= x x ε ϕ
const. 111000 =⋅⋅=⋅⋅ b h l b h l
0 =++ z y x ϕ ϕ ϕ
connection between true strain - engineering strain
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Plastic Deformation
Types of Plastic Deformation
dislocation movement
low energy required
sliding
high energy required
before
after
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Plastic Deformation
Sliding and Dislocation Movement
dislocation movementsliding
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Forging8
Warm Forming7
Cold Forming6
Recrystallisation5
Flow Stress4
Plastic Deformation3
Elastic Deformation2
Metallurgical Basics1
Outline
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Flow Stress
Flow Curve
f l o w
s t r e s s
effective strain
required stress to break
the strain hardening
required stress forplastic deformation
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Flow Stress
Strain Hardening Depends on Dislocations
schematic diagramdislocation movement
sliding planes
dislocation origingrain boundary
moving direction
grain boundary
piled up dislocations at boundary grainsdislocation structure of little-formed copper
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Forging8
Warm Forming7
Cold Forming6
Recrystallisation5
Flow Stress4
Plastic Deformation3
Elastic Deformation2
Metallurgical Basics1
Outline
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Recrystallisation
Static Recrystallisation
requirements:
- ϕϕϕϕv > 0
- T > TRecrystallisation
- impact time
Schematic course of recrystallisation of cold formed structure
d u
c t i l e y i e l d A 1 0 ,
t e n s
i l e s t r e n g t h R m
c r y s t a l
r e g e n e r a t i o n
large increase
of A10
small decreaseof Rm
temperature, °C
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Recrystallisation
Stress Curve of Cold Forming as a Result of Static Recrystallisation
f l o w
s t r e s s
effective strain
a n n e a l i n g f o r
r e c r y s
t a l l i s a t i o n
ϕϕϕϕvBr ϕϕϕϕvBr
ϕϕϕϕvBr - effective strainat time of fracture
annealing for recrystallisation increases effective strain and decreases flow stress
a n n e a l i n g f o r
r e c r y s
t a l l i s a t i o n
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Recrystallisation
Effective Strain and Temperature Influence the Grain Size
g r a i n
s i z e
effective strain
range ofrecrystallisation
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Recrystallisation
Forming Temperature and Velocity Influence the Flow Stress
forming temperature belowrecrystallisation temperature
high forming velocity
low forming velocity
forming temperature above
recrystallisation temperature
effective strain
f l o w
s t r e s s
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Forging8
Warm Forming7
Cold Forming6
Recrystallisation5
Flow Stress4
Plastic Deformation3
Elastic Deformation2
Metallurgical Basics1
Outline
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Bulk forming
massivesemi-finished material
component
Cold forming
What is Bulk Forming?
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semi-finished part component
Cutting
1,3 kg
Introduction
Advantages of Bulk Forming
Forming
0,4 kg
componentbasic workpiece
C
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fcc
bcc
Recrystallization
Cold forming
Iron-Carbon Phase Diagram
Carbon content in weight percent
Cermentite content in weight percent
δ-Fe
δ- + γ -Fe
T e m p e r a t u r e
i n ° C
Liquid + δ-Fe
Liquid
Fe3C(Cementite)
Liquid +
Fe3C
Liquid + γ -Fe
γ -Fe + Fe3C
γ -Fe(Austenite)
α-Fe (Ferrite)
γ - + α-Fe
α-Fe + Fe3C
C ld f i
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Workpiece temperature / °C
S t r a i n ϕ
F l o w
s t r e s
s k f / M P a
L a y e r o f s c a l e / µ m
Cold forming
Material Properties
high flow stresses and low achievable strains by classic steel materials
C ld f i
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Cold forming
Advantages and Disadvantages of Cold Forming
Cold Forming Advantages:
low tool material costs
low influence of forming velocity
no energy costs for heating no dimension faults caused by dwindling
high surface quality
increasing strength of the component
Disadvantages:
high forces
limited plastic strain
Cold forming
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Forming process IT-Grade according to DIN ISO 286
5 6 7 8 9 10 11 12 13 14 15 16
Cold extrusion
Warm extrusion
Hot extrusion
Centerline average Ra / µm
0,5 1 2 3 4 6 8 10 12 15 20 25 30
achievable with special proceedings achievable without special proceedings
Cold forming
Efficiency
small shape, dimension and position tolerances as well as
good surface qualities are possible
Cold forming
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forming cold warm hotworkpiece weight 0,001 – 30 kg 0,001 – 50 kg 0,05 – 1.
plasticity φ < 1,6 r<4 r<6
finishing effort less low high
semi-finished part cold forming
Cold forming
Efficiency
(for classic forming steels)
by the aid of cold forming processes a good workpiece quality can be reached
Cold forming
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extrusion full extrusion hollow extrusion cup extrusion
forwardextrusion
backwardextrusion
radialextrusion
before after
Cold forming
Forming Processes
a: punch, b: die, c: workpiece, d: ejector, e: counter punch, f: spike
Cold forming
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workpieceinsertion
compression extrusion ejection
punch
workpiece
cavity
ejector
die
Cold forming
Full Forward Extrusion: pin production
Cold forming
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workpieceinsertion
compression extrusion ejection
punch
workpiece
die
ejector
Cold forming
Cup Backward Extrusion: cup production
Cold forming
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workpieceinsertion
closing ofthe die
extrusion ejection
upper punch
workpiece
lower die
lower punch
upper die
Co d o g
Radial Extrusion of a Cardan Joint
Cold forming
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g
Mechanical Loads in Full Forward Extrusion Processes
mechanical surface loads in a range of several 1000 MPa
material: QST 32-3 effective strain: φ = 1,4
radial stresses σr / MPa axial stresses σz / MPa
angle of shoulder :
Cold forming
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g
Reinforcement of extrusion dies
without internal pressure
with internal pressurereinforcement creates compression stresses in the die, in order to reduce process-related
tensile stresses
compression
tensile
Cold forming
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Typical Cold Formed Components
gear shafts
tubes
denticulations
screws
Hirschvogel Hirschvogel
FuchsSchraubenwerk
Flow Stress
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Fracture as a result of Radial Extrusion
fractures depending on passing a critical deformation value
Cold forming
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Crack Reduction by Superposition of Compressive Stresses
punchgasket
die
workpiece
pressure mediumrelief pressure valve
tearing could effectively be shift to higher strains by superposition
of compressive stresses
(superposition of compressive stresses)
(conventional cold forming)
Crack
Crack
Cold forming
Ch C k b F ll F d E i
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Chevron Cracks by Full Forward Extrusion
Cold forming
Ch C k b F ll F d E t i
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3. forming step real workpiece
Chevron Cracks by Full Forward Extrusion
an unfavourable distribution of the interior material generates cracks
Chevrons
FEM-Simulation
DEFORM
Cold forming
Ph f P d ti f B l G
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bucking upsetting indirect
cup extrusion
cutting radial extrusion burr cutting calibration
recrystallization recrystallization recrystallization
Phases of Production of a Bevel Gear
achievable deformation can be increased by recrystallization
Outline
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Forging8
Warm Forming7
Cold Forming6
Recrystallisation5
Flow Stress4
Plastic Deformation3
Elastic Deformation2
Metallurgical Basics1
Outline
Warm forming
Iron Carbon Phase Diagram
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Iron-Carbon Phase Diagram
fcc
bcc
Recrystallization
Carbon content in weight percent
Cermentite content in weight percent
δ-Fe
δ- + γ -Fe
T e m p e r a t u r e i n ° C
Liquid + δ-Fe
Liquid
Fe3C(Cementite)
Liquid +
Fe3C
Liquid + γ -Fe
γ -Fe + Fe3C
γ -Fe(Austenite)
α-Fe (Ferrite)
γ - + α-Fe
α-Fe + Fe3C
Warm forming
Material properties
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Material properties
Workpiece
temperature / °C
reduction of flow stress and increase of the achievable strain
S t r a i n ϕ
F l o w
s t r e s s k f / M P a
L a y e r o f s
c a l e / µ m
Warm forming
Advantages and Disadvantages of Warm Forming
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Advantages and Disadvantages of Warm Forming
Warm forming Advantages:
strengthening of the workpiece
small range of tolerance caused by dwindling
good surface quality
Disadvantages:
energy input for heating
high flow stresses
Hirschvogel
Warm forming
Efficiency
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forming cold warm hotworkpiece weight 0,001 – 30 kg 0,001 – 50 kg 0,05 – 1.500 kg
plasticity φ < 1,6 φ < 4 j < 6
finishing effort less low high
semi-finished part coldforming
warmforming
Efficiency
Warm forming
Efficiency
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Forming process IT-Grade according to DIN ISO 286
5 6 7 8 9 10 11 12 13 14 15 16
Cold extrusion
Warm extrusion
Hot extrusion
Centerline average Ra / µm
0,5 1 2 3 4 6 8 10 12 15 20 25 30
achievable with special proceedings achievable without special proceedings
Efficiency
medium shape, dimension and position tolerances as well as
medium surface quality are possible
Warm forming
Typical Warm Formed Components
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Typical Warm Formed Components
slide hinge flange cylinder injector
Hirschvogel Hirschvogel
Audi
Outline
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Forging8
Warm Forming7
Cold Forming6
Recrystallisation5
Flow Stress4
Plastic Deformation3
Elastic Deformation2
Metallurgical Basics1
Outline
Forging
Iron-Carbon Diagram
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g
fcc
bcc
Recrystallization
Carbon content in weight percent
Cermentite content in weight percent
δ-Fe
δ- + γ -Fe
T e m p e r a t u r
e i n ° C
Liquid + δ-Fe
Liquid
Fe3C(Cementite)
Liquid +Fe
3C
Liquid + γ -Fe
γ -Fe + Fe3C
γ -Fe(Austenite)
α-Fe (Ferrite)
γ - + α-Fe
α-Fe + Fe3C
Forging
Material Properties
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p
Workpiece temperature / °C
low flow stress and high achievable strain
S t r a i n j
F l o w
s t r e s s k f / M P a
L a y e r o f s
c a l e / µ m
Forging
Advantages and Disadvantages of Forging
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g g g g
Forging Advantages:
less effort
high plasticity
Disadvantages:
high energy input for heating
high material costs for tools
dimension faults by shrinkage
material loss and finishing caused by tinder
Forging
Efficiency
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forming cold warm hotworkpiece weight 0,001 – 30 kg 0,001 – 50 kg 0,05 – 1.500 kgplasticity φ < 1,6 φ < 4 φ < 6finishing effort less low high
initial state coldforming warmforming forging
Forging
Efficiency
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Forming process IT-Grade according to DIN ISO 286
5 6 7 8 9 10 11 12 13 14 15 16
Cold extrusion
Warm extrusion
Hot extrusion
Centerline average Ra / µm
0,5 1 2 3 4 6 8 10 12 15 20 25 30
achievable with special proceedings achievable without special proceedings
low shape, dimension and position tolerances as well as
low surface quality possible
Forging
Heating Methods
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Heating in furnaces:
furnaces are heated by gas, oil or electricity
heat transmission to the workpiece by radiation andconvection
Heating by induction:
heat in the workpiece rim is generated byelectromagnetic induction by eddy current formation
Conductive heating:
heating by high-frequency current with direct workpiececontact
Furnace
Inductive heating facility
inductive and conductive heating reduces the production of primarytinder as a result of the heating rate
Forging
Tinder
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If iron-based materials are heated above 500 °C
under the influence of oxygen, iron oxide (Fe3O2)
will be generated on the surface, which is called
tinder. Tinder peels away off the workpiece during the
forming process.
This results in loss of material, surface marking
and tool wear.
Saarstahl
Forging
Processes – Open Die Forging
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upsetting
stretching
flat back gage acuminate back gage round back gage
Saarstahl
Saarstahl
simple tool geometries are used for open die forging processes
workpiece manipulator
upper die
lower die
work-
piece
Forging
Process cycle
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Freiformschmieden
simple tool geometries can produce complex workpiece geometries
round forging
upsetting
streching
upsetting
strechingforging
forging and shearingwastage
blank
forging a step
forging a step
Forging
Open Die Forging
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Saarstahl
Forging
Closed Die Forging
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Upper die
Lower die
Lower die
Upper die
Forging part
Forging part
Burr cavity
Forging without burr:
• low forming forces
• complete material utilization
• max. permitted volume fluctuation 0,5%
• exact workpiece positioning required
Forging with burr:
• less standards on workpiece volume
fluctuation
• no exact workpiece positioning required
• the removal of the burr needs an extra
process step
Forging
Die Wear
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1 - wear / abrasion
2 - thermal fatigue / crack formation
3 - mechanical fatigue / crack formation
4 - plastic deformation
2
1/3/4
1/4
1
3 1/41 2
the main reason for tool change is the abrasion on edges and cracks in cavitations
Forging
Stages of Closed Die forging
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crankshaft
connection rod
hinge bearing
an effective preform production is the key for short production chains
Summaryg
σ
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Influence of the metallurgical composion on the
formability of metals
Basic understanding of the elastic and plastic materialbehaviour and it‘s characterization
Introduction of processes in cold and warm bulk formingas well as in forging
tanelε∆
σ∆=α
Eelε
σ=
S p a n n u n g
Nenndehnung ε0,2 %
α
Rp0,2
∆εel
∆σ
ReS
εel εpl
εel