Lecture Prof Martina Zimmermann.pdf

Fraunhofer IWS

BRT: WP2013_1.ppt Lehrstuhl fr Werkstoffprfung und -charakterisierung

Prof. Dr.-Ing. M. Zimmermann

Jrgen Klinsmann Silvia Neid Henry Maske

Jens Weiflog Mats Wilander Michelle Obama

Rumul-Symposium 17-19th September 2014

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Next time we might get into business

I want that chair and expresso machine included in the offer!

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BRT: WP2013_3.ppt

Competences at Fraunhofer IWS, Dresden

Material, component and process characterization

Chemical surface and reaction

technology

PVD- and Nanotechnology

Joining

Surface Technology

Thermal coating and additive

manufacturing

Ablation and cutting

Laser material processing Surface and coating technology

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Prof. Dr.-Ing. Martina Zimmermann

Professur fr Werkstoffprfung und

-charakterisierung

Institut fr Werkstoffwissenschaft

TU Dresden

Fraunhofer Institut fr

Werkstoff- und Strahltechnik, Dresden

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Material Characterization at Fraunhofer IWS, Dresden

Mechanical behavior

under application

relevant loads

Characterization

of macro to nano

layers

Failure analysis

e.g. laser hardening e.g. windscreen

wipers

e.g. x-ray mirrors z. B. Schaufelabriss

an Turbolader

1m 2 nm

Microstructure

on demand

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(micro)

structure

mechanical

properties

Process &

design

optimization

Material Characterization at Fraunhofer IWS, Dresden

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Challenges in the experimental characterization of the fatigue behavior in the VHCF regime

and its significance for the identification of failure-relevant defects

regular grain boundary

twin boundary

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Me, when I started working in

the field of VHCF!

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Outline

Introduction

Damage Mechanisms in VHCF

Challenges for Testing Strategies

Conclusion

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Fatigue crack growth

lg d

a/d

N

lg D K

Loading conditions

Load collective

Fatigue Properties

Material

S-N-curve (directives, component tests)

Damage accumulation

(& numerical integration)

lg s

A

lg N

s

lg n

Fatigue Life

Geometry Processing

Relevant fatigue property = classical durability?

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ICE-wheels:

daily performance 1425 km

= daily about N =

0,5x106

= total life N = 7x108

aus Internetseiten des LBF, Darmstadt und Bhmer et.

al.: Dynamik u. Festigkeit von gummi-gefederten

Radreifen

Fatigue strength up to N = 107 no longer sufficient?

S

iem

en

s

Steam turbine:

rotations: 3000/min or 1500/min

Product life ~ 25.000 h

= N = 4,5x109 resp.

N = 2,25x109

WE-powertrain:

Slow rotation: 18-50/min Transformator: 1500/min = daily N=2,1x106 (under full-

loading conditions)

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Damage Mechanisms: Basic Assumption

Mu

gh

rab

i (2

00

2, 2

00

4, 2

00

6):

Material Type I

pure, annealed and ductile with no

(extrinsic) interior defects

roughening of the surface through

irreversibility of heterogeneous plastic

deformation

Material Type II

with inclusions, dispersoids, pores

etc.

size, position and distribution of the

inclusion, hardness (acc. to Murakami)

Damage mechanism dominated by:

Damage Mechanisms in the VHCF-Range

Inclusion

Facet

Specimen

surface

AISI 304, N > 107

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Damage Mechanisms and S-N-curves

M. Zimmermann: Int. Mater. Review, 2012

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Influence of microscopic notches becomes the fatigue life dominating parameter

Fatigue crack initiation and crack growth

in 1.4301 at non-metallic inclusion, failure

at N = 1,49 x 108

Change in damage mechanism is possible

Damage Mechanisms and S-N-curves

Crack initiation changes from surface to subsurface region

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Microstructural Inhomogeneity

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microcracks at Ds/289.5MPa and N=6x108

formation of dislocation cell structure at

Ds/294MPa and N=1.2x1010.

Sta

nzl-Tsch

eg

g, S

ch

oe

nb

auer,

In

t. J

. F

atig

ue

, 2

01

0

isolated dipole bundles

in the VHCF regime

surface roughening at

N > 1010 cycles at 150 MPa

Sto

ecke

r e

t a

l.,

Int.

J.

Fatigu

e, 2

011

pure copper pure nickel

Damage evolution in the VHCF regime

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Nickel-base superalloys

Damage evolution in the VHCF regime M

iao

et a

l., A

cta

M

ate

r.,

20

09

J. Miao et al. (2009)

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Nickel-base superalloys Nimonic 80A


Be

an

spru

chun

gsrichtu

ng

/2 = 454 MPa; Nf=2,01106

/2 = 410 MPa; Nf=2,09107

regular grain boundary

twin boundary 360

380

400

420

440

460

480

500

0 10 1'000

stre

ss a

mp

litu

de

, MP

a

number of cycles to failure, 106

Hochgesezte Proben

Brche

Durchlufer

pre-fatigued

failure

run-out

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Aluminium alloy EN AW-6082


void formation at the crack initiation site in the vicinity of

primary MgSi-particles (due to size identified as primary

particles resulting from the initial casting process)

Cremer et al., submitted to Int. J. Fatigue, 2012

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Challenge in the characterization of damage evolution

Nickel-base superalloys Nimonic 80A

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Metastable austenitic steel

in the fully austenitic condition

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Challenges for test procedure

misalignment

unwanted heating

crack initiation at

surface flaws

Ma

ye

r e

t a

l.,I

nt.

J.

Fa

tig

ue

, 2

00

9

representative

microstructure &

sample volume true strain distribution

residual stresses

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Challenges for test procedure

What should be the new finite number of cycles to failure?

Sample preparation?

Tested volume fraction?

Statistical evaluation of the fatigue results (how to deal with run-outs)?

Defined testing conditions (temperature, air humidity etc.)

Defined reference testing for frequency influence?

Consideration of residual stresses?

Standardization of test procedure for the VHCF regime?

How to define the true loading condition on a microstructural basis?

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Characterization of

Inhomogeneity

Probability of

Occurance

Capability of Crack

Propagation

type and size

position

strength mismatch

anisotropy

distribution

damage relevance

crack growth threshold

influence of

- temperature

- strain rate

- air humidity

Life Prediction Curve including

Microstructural Notch Effect

+

Threshold for Crack Growth

Reliable Life Prediction

Microstructural

Notch Factor

Kf,micro

for da/dN < 10-10

? Microstructural Crack

Growth Threshold

DKVHCF- Thres

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Monte Carlo Simulation

Statistical Model

Stress distribution

Size distribution

of inclusions

Position of inclusion Position of inclusions

Distribution of inclusion

in the fatigue sample and

in the real component

Probabilistic Modelling & Reliable Life Prediction

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Early Crack Detection by indirect methods

Detection of crack initiation (also from sample interior)

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Early Crack Detection by indirect methods

N = 3107

2%

21C 95%

26 C 97%

41C 99%

85C 100%

98C

0.5 mm

1 mm

N = 2106

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Primal forming

e.g. casting

Forming

e.g. beding

Cutting

e.g. punching Joining

e.g. welding

Modifying

inherent

properties

Coating

Inhomogeneity through Processing

Even higher complexity in damage evolution to be expected!

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Very High Cycle Fatigue Behavior of Welded Structures

GW WEZ SN

Welding defects

Weld geometry

s

R

b

microstructure

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VHCF strength is dominated by weld defects

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Summary

Me (Us?) and the current state of the art in VHCF research!

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Many thanks

to the organizers of this colloquium for the invitation to give this lecture! to the audience for their interest in my talk! to my very ambitious and hard working PhD students Christian Stcker, Carsten Mller-Bollenhagen, Martin Cremer, Andrei

Grigorescu, Philipp Hilgendorff, Anton Kolyshkin!

to the german research foundation and the RWTV Stiftung for financial support

Prof. Dr.-Ing. Martina Zimmermann

Tel. 0172 1645855

E-Mail: [email protected]

[email protected]

Documents

Lecture Prof Martina Zimmermann.pdf