Metal tensile test by using miniaturised test pieces 2016 ... · −Material without upper and lower yield strength −Material is very strain rate sensitive, therefore application

(1) 2016-10-12 Johannes Aegerter, Stefan Keller, Heike Berk 25th International Forum for Materials Testing Ulm

Metal Tensile Test Using Miniaturized Test Pieces

Johannes Aegerter,

Stefan Keller,

Heike Berk

2016-10-12


Objective

Development and Optimisation of the testing technique for testing ofminiaturised test tensile test pieces for the determination of localstrength properties and flow curves from deformed component areas fore. g. the following applications:

● Verification of component specifications and optimisation of the production of components

● Validation of FE-forming simulations

● Determination of input data for crash and service life calculation

● Characterisation of local properties of weldings

● Evaluation of cases of damage


Problem definition and boundary conditions

Problem definition

● Clamping of the test piece without bending and shearing forces

● Warranty of uniaxial stress

● Dimensionally accurate machining of the test pieces without workhardening and heat input

● Realisation of small gauge length and accurate measurement of very small extensions

● Largely compliance of normative specifications acc. to ISO 6892-1:2009

Boundary conditions

● Applicable in the normal industrial environment, this means by using mainly standard equipment

● Largely comparability with standard tensile test properties


Investigated test piece geometries

Form Lt(mm)

B(mm)

bo(mm)

Lc(mm)

Le(mm)

C(mm)

D(mm)

E(mm)

r(mm)

Lc───────

bo

Le───────

bo

Form 1 250 30 20 120 80 35 - - 20 6 4

Form 2 165 20 12.5 75 50 30 - - 20 6 4

Form 3 35 6.5 2.5 15 10 8 3 3 2 6 4

Form 4 32 6.0 2.0 12 10 8 3 3 2 6 5

Form 5 23 4.0 1.25 7.5 5 6 2 2 2 6 4

Form

3

Form

4

Form

5Le = Extensometer gauge length

Form

2

Form

1

Source: ISO 6892-2:2011-02


Influence of the gauge length on elongation after fracture

Nearly equal elongations after fracture for different test piece geometries only if:

– Equal coefficient of proportionality k of the test pieces (Standard: 5.65)Non proportional test pieces (A50mm, A80mm): Nearly equal thicknesses are necessary.

“Comparisons of percentage elongation are possible only when the gauge length or extensometer gauge length, the shape and area of the cross-section are the same or when the coefficient of proportionality, k, is the same.” (ISO 6892-1:2009)

11.3

5.65

Source: W. Domke


Coefficient of proportionality of the investigated test piece geometries

Form Lt B bo Lc Le rLc

───────

bo

Le───────

bo

k1,0mm

k0,29mm

Form 1 250 30 20 120 80 20 6 4 17.89 33.22

Form 2 165 20 12.5 75 50 20 6 4 14.14 26.26

Form 3 35 6.5 2.5 15 10 2 6 4 6.32 11.74

Form 4 32 6.0 2.0 12 10 2 6 5 7.07 13.13

Form 5 23 4.0 1.25 7.5 5 2 6 4 4.47 8.30

Form

3

Form

4

Form

5Le = Extensometer gauge length

Form

2

Form

1

Source: ISO 6892-2:2011-02


Testing machine, clamping system and force measurement

● 250 kN load cell● Hydraulic clamping system● Extensometer class 0.5

● 2.5 kN load cell● Bending and shear force free clamping

by using bolts● Extensometer class 0.5


Modification of the extensometer

● Extensometer class 0.5− By using standard edges smallest possible

gauge length 10 mm− Reduction of the gauge length to 5 mm: − Spacer, t = 2.5 mm (b)− between edge holder (c)− and edge (a)

− Problem: Machine calculates extensions with “set”-gauge length Le = 10 mm− Conversion of extensions to real gauge

length necessary:− Multiplication of extensions or the measured

length change by the factor:Le(set)/Le(real), here: Factor 2 Extensometer with

5 mm gauge length

c)

b)

a)


Materials, test piece preparation and testing rates

● AA6016 (AlMg0,4Si1,2), condition T4, 1.0mm thickness

● AA6016 (AlMg0,4Si1,2), condition T6, 1.0mm thickness

● AA5182 (AlMg4,5Mn0,4), condition H111, 1.0 mm thickness

● AA3104 (AlMn1Mg1Cu), condition H19, 0.29 mm thickness

● Test piece preparation by using CNC-milling machine

● Testing rates according to ISO 6892-1:2009, Method A (open loop)


Elastic range for different test piece geometries,material AA 6016-T6

0

50

100

150

200

250

0,0 0,1 0,2 0,3 0,4 0,5 0,6

Span

nung

in M

Pa

Dehnung in %

Form 1: m E = 67,5 GPaForm 2: m E = 67,4 GPaForm 3: m E = 66,8 GPaForm 4: m E = 65,5 GPaForm 5: m E = 66,9 GPa

E-Modul des Werkstoffs: 69 GPa

1,1 · E = 75,9 GPa

0,9 · E = 62,1 GPaE-Modulus of the material: 69 GPa

Stre

ss in

MPa

Strain in %

Form 1: mE = 67.5 GPaForm 2: mE = 67.4 GPaForm 3: mE = 66.8 GPaForm 4: mE = 65.5 GPaForm 5: mE = 66.9 GPa

1.1 · E = 75.9 GPa

0.9 · E = 62.1 GPa

0.0 0.1 0.2 0.3 0.4 0.5 0.6


Rp0,2 and Rm for different test piece geometries

0

50

100

150

200

250

300

350

AA6016-T4

AA6016-T6

AA5182-H111

AA3104-H19

AA6016-T4

AA6016-T6

AA5182-H111

AA3104-H19

Deh

ngre

nze

Rp0

,2un

d Zu

gfes

tigke

it R

m(M

Pa) Geo. 1 Geo. 2 Geo. 3 Geo. 4 Geo. 5

Zugfestigkeit RmDehngrenze Rp0,2

0

50

100

150

200

250

300

350

AA6016-T4

AA6016-T6

AA5182-H111

AA3104-H19

AA6016-T4

AA6016-T6

AA5182-H111

AA3104-H19

Deh

ngre

nze

Rp0

,2un

d Zu

gfes

tigke

it R

m(M

Pa) Form 1 Form 2 Form 3 Form 4 Form 5

Zugfestigkeit RmDehngrenze Rp0,2

Proo

f str

engt

h R

p0,2

and

tens

ile s

tren

gth

Rm

(MPa

)

Proof strength Rp0,2 Tensile strength Rm


Stress-strain curve for the material AA 6016-T41.0 mm thickness

0

50

100

150

200

250

300

0 5 10 15 20 25 30 35

Span

nung

in M

Pa

Dehnung in %

Form 1Form 2Form 3Form 4Form 5

Form bo Le K1.0mm

Form 1 20 80 17.89

Form 2 12.5 50 14.14

Form 3 2.5 10 6.32

Form 4 2.0 10 7.07

Form 5 1.25 5 4.47

Lo = k (ao bo)^0.5

k = Lo/(ao bo)^0.5

Stre

ss in

MPa

Strain in %


0

50

100

150

200

250

300

0 0.05 0.1 0.15 0.2

Wah

re S

pann

ung

in M

Pa

Wahre Dehnung

Form 1Form 2Form 3Form 4Form 5

Flow curve for the material AA 6016-T41.0 mm thickness

True

str

ess

in M

Pa

True strain


0

50

100

150

200

250

300

0 0,05 0,1 0,15 0,2

Wah

re S

pann

ung

im M

Pa

Wahre Dehnung

Form 1

Form 2

Form 3

Form 4

Form 5

Flow curve for the material AA 6016-T6 1.0 mm thickness

True

str

ess

in M

Pa

True strain0 0.05 0.1 0.15 0.2


0

50

100

150

200

250

300

350

400

0 0.05 0.1 0.15 0.2 0.25

Wah

re S

pann

ung

in M

Pa

Wahre Dehnung

Form 1

Form 2

Form 3

Form 4

Form 5

Flow curve for the material AA 5182-H1111.0 mm thickness

True

str

ess

in M

Pa

True strain

Typical strain marks for alloys of the series 5xxx


0

50

100

150

200

250

300

350

400

0 0.01 0.02 0.03 0.04 0.05 0.06

Wah

re S

pann

ung

in M

Pa

Wahre Dehnung

Form 1

Form 2

Form 3

Form 4

Form 5

Flow curve for the material AA 3104-H190.29 mm thickness

True

str

ess

in M

Pa

True strain


Is the testing technique used by Hydro useable for steel?

Frame conditions for the usability of the Hydro testing technique for steel● Available clamping system− Limitation of the maximum force soft and intermediate strength steels

● Available concept for test piece preparation for miniaturised test pieces− Was used up to now only for aluminium

● Modulus of Elasticity of steel three times higher than for aluminium− For equal stress level in the elastic range only approx. 1/3 of extension as for

aluminium

Test material DC04, soft, 1 mm thickness− Material without upper and lower yield strength− Material is very strain rate sensitive, therefore application of Method A of

ISO 6892-1:2009, open loop, (strain rates: for Rp0,2: 0.00025 s-1, then 0.0067 s-1)− Used test piece geometry: Form 1 and Form 3− Testing direction: parallel to rolling direction


Testing results for the test piece geometries 1 and 3 testing direction: Parallel to RD

Form No.Rp0,2

[MPa]Rm

[MPa]Ag

[%]A80mm

[%]n2-20

[-]r2-20

[-]

1

1 146.5 306.0 24.3 43.6 0.260 1.908

2 148.8 305.9 24.6 43.1 0.258 ---

3 146.1 305.5 25.0 43.1 0.260 1.996

Average 147.1 305.8 24.6 43.3 0.259 1.952Std.-Dev. 1.5 0.3 0.4 0.3 0.001 0.062

Form No.Rp0,2

[MPa]Rm

[MPa]Ag

[%]A10mm

[%]n2-20

[-]r2-20

[-]

3

1 148.3 313.8 26.7 56.9 0.259

2 146.9 313.2 26.8 57.3 0.261

3 150.6 314.4 26.3 59.9 0.255

4 150.2 312.9 27.2 57.5 0.259

5 147.4 314.4 26.7 61.0 0.260

Average 148.7 313.7 26.7 58.5 0.259Std.-Dev. 1.7 0.7 0.3 1.8 0.002

NOTE: The different elongations after fracture caused on different coefficients of proportionality, see table on page 6


Rp0,2 and Rm for the test piece geometry 1 and 3Material DC04

147,1

305,8

148,7

313,7

0

50

100

150

200

250

300

350

DC04 DC04

Deh

ngre

nze

Rp0

,2un

d Zu

gfes

tigke

it R

m(M

Pa) Form 1 Form 3

Zugfestigkeit Rm

Dehngrenze Rp0,2

Proo

f str

engt

h R

p0,2

and

tens

ile s

tren

gth

Rm

(MPa

)

Proof strength Rp0,2

Tensile strength Rm147.1

305.8

148.7

313.7


Stress-strain curves for the test piece geometry 1 und 3 Material DC04

0

50

100

150

200

250

300

350

0 10 20 30 40 50 60

Span

nung

im M

Pa

Dehnung in %

Form 1 Nr. 1 Form 1 Nr. 2 Form 1 Nr. 3

Form 3 Nr. 1 Form 3 Nr. 2 Form 3 Nr. 3

Form 3 Nr. 4 Form 3 Nr. 5

Form 1

Form 3

Rm = 8 MPa (2.7%)

Stre

ss in

MPa

Strain in %


Flow curves for the test piece geometries 1 und 3Material DC04

0

50

100

150

200

250

300

350

400

450

0,00 0,05 0,10 0,15 0,20 0,25

Wah

re S

pann

ung

im M

Pa

Wahre Dehnung

Form 1 Nr. 1 Form 1 Nr. 2 Form 1 Nr. 3Form 3 Nr. 1 Form 3 Nr. 2 Form 3 Nr. 3Form 3 Nr. 4 Form 3 Nr. 5

Form 1

Form 3

True

str

ess

in M

Pa

True strain0 0.05 0.1 0.15 0.2 0.25


What is the reason for lower tensile strength Rm of test piece geometry 1 for the material DC04?

Consideration

● The same strain rates were used for all materials and test piece geometries

● No differences were observed for the aluminium alloys

Temperature measurement with thermocouple

● Will a different temperature increase of the test piece during testing will be the cause?● Different heat conduction Al/Fe● Different ratio of surface/volume of

the two test piece geometries


20

30

40

50

60

70

80

90

0

50

100

150

200

250

300

350

0 10 20 30 40 50

Prob

ente

mpe

ratu

r in

°C

Span

nung

im M

Pa

Dehnung in %

Form 1 Nr. 2-1 Form 1 Nr. 2-2Form 1 Nr. 2-3 Form 1 Nr. 2-4

Stress-strain curves and temperature-strain curves for test piece geometry 1, material: DC04

Stress

Test piece temperature

ϑ / e ≈ 0.65 K / %

Stre

ss in

MPa

Strain in %

Test

pie

ce te

mpe

ratu

re in

°C


20

30

40

50

60

70

80

90

0

50

100

150

200

250

300

350

0 10 20 30 40 50 60

Prob

ente

mpe

ratu

r in

°C

Span

nung

im M

Pa

Dehnung in %

Form 3 Nr. 2-1Form 3 Nr. 2-2Form 3 Nr. 2-3

Stress-strain curves and temperature-strain curves for test piece geometry 3, material: DC04

Stress

Test piece temperature

ϑ / e ≈ 0.067 K / %

Stre

ss in

MPa

Strain in %

Test

pie

ce te

mpe

ratu

re in

°C


Summary (1/2)

The testing technique developed by Hydro for the determination of localstrength properties and flow curves from deformed component areas byusing miniaturised test pieces fulfils the defined requirements andprovide results, which are nearly identical with those of standard testpieces geometries.

This was verify for:● Various aluminium alloy types

(3xxx, 5xxx with strain marks and 6xxx)

● Various conditions(soft, artificial aged, as rolled)

● Two very different thicknesses(0.29 mm and 1.0 mm)

● Applicable in the normal industrial environment, this means by using mainly standard testing equipment.


Summary (2/2)

The presented testing technique is also applicable for soft andintermediate strength steels.

This was verified for the steel DC04.

● A slightly higher tensile strength Rm was determined for the steel DC04 by using miniaturised test pieces.This may be caused by the clearlysmaller temperature increase during testing for these test pieces.

● For high strength steels the clamping device has to be produced out of materials with higher strength.


Hydro Aluminium Rolled Products GmbH

Forschung & Entwicklung Bonn

Johannes Aegerter

Georg-von-Boeselager-Str. 21

53117 Bonn

T: +49 (0)228-552-2386

F: +49 (0)228-552-2017

E: [email protected]

www.hydro.com

Documents

Metal tensile test by using miniaturised test pieces 2016 ... · −Material without upper and lower yield strength −Material is very strain rate sensitive, therefore application