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12/11/20
Institute for Ship Structural Design and Analysis
Sören EhlersProf. DSc. (Tech) / Institutsleiter
M-10
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Institute for Ship Structural Design and Analysis (M-10)
212/11/20
Sören Ehlers: Design and analysis of ships and offshore structures
Teaching• Fundamentals of engineering
design• Ship structural design I, II and III• Introduction to ship structural
analysis• Arctic technology
Research• Analytical, numerical and experimental
structural analysis• Structural analysis and design under extreme
conditions• Fatigue of Ships and Offshore structures• Design of Ships and Structures for polar regions• Structural optimisation
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Marine Technology Students at TUHH
Teaching in the current situation:§ Teaching is primarily online with live or
pre-recorded presentations
312/11/20
Registered students 2020:§ Quite a drop in recent years§ New Master students: 8§ New Bachelor students: 18§ Total registered students: 71
§ General trend is a decreasing amount of students in mechanical engineering§ Especially for Marine Technology I feel that we fail to communicate the
diversity and cutting-edge technology we deal with. Often the one associates naval architecture with steel and iron work of heavy labor at a yard alone
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Research Areas
412/11/20
Fatigue/fracture mechanics• Detail design• New cutting and welding methods• New materials• Production and in-service
influences on fatigue and fracture behavior
Ice loads• Ice-structure interaction • Ice-pressure-distribution• Thin sections• Friction testing
Nonlinear Waves under Solid Ice• Nonlinear wave propagation• Dispersion of waves• Swell conditions• Ice breakup mechanism
Numerical Simulations• Component design• Structural optimization• Fatigue assessment• Material models• Simulation of collision and
grounding
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Research Areas
512/11/20
Residual stresses and laser scanning• Hole-drilling rosette method• Weld surface geometry scanning• Plate deformation
Ship structural design for ice loads• Ice-structure interaction • Ice-pressure-distribution• Thin sections• Friction testing
Structural behavior• Design of ships and equipment• Collision and grounding• Production and in-service
influences on structural strength• Influence of corrosion
Ship acoustics• Sound sources• Sound propagation through
structures• Sound radiation into water
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Fatigue strength andresidual stresses
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Motivation§ Vielseitige Schadensfälle für Schiffe und
Offshore Strukturen 1
§ Oft kombinierte Schäden 2
§ Ein Großteil der Schäden sind auf schlechtes design und operative Fehler zurückzuführen 2
§ Materialwahl kann Schäden beeinflussen 3
11.12.20 7
Ref.: 1 A. Dehghani, F. Aslani, A review on defects in steel offshore structures and developed strengthening techniques. Structures, 20 (2019) 635-657. https://doi.org/10.1016/j.istruc.2019.06.0022 S.J. Price, R.B. Figueira, Corrosion Protection Systems and Fatigue Corrosion in Offshore Wind Structures: Current Status and Future Perspectives. Coatings, 7 (2017). https://doi.org/10.3390/coatings70200253 V. Igwemezie, A. Mehmanparast, A. Kolios, Materials selection for XL wind turbine support structures: A corrosion-fatigue perspective. Marine Structures, 61 (2018) 381-397. https://doi.org/10.1016/j.marstruc.2018.06.008
Image © Structural Integrity Associates, Inc.
Dokumentierte Schäden in Offshore Strukturen 1
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Post-weld improvement and retrofitting§ TIG-dressing as a repair
method up to 2.3 mm crack depth without reduction in fatigue strength 1
§ Recent results on TIG-dressing and grinding support and assessment based on a slope m = 4 2,3
§ Higher fatigue strength improvement for weld profiling than for burr grinding and disc grinding 2
§ Highest improvement for combination of grinding and peening 3
11.12.20 8
0 5 10 15 20 25Numbers of specimens in data series n
0
5
10
15
20
Slop
e m
r = -0.02 p = 0.92
S700 R=0.1 (Pedersen et al., 2009 )A36 R=0 (Mendez et al., 2017)A36 R=0 (Mendez et al., 2017)Low carbon micro alloyed R=0.1(Haagensen, 1993)S420 R=0 (Miki et al., 1999)S355 R=0.5 A (Huther et al., 2001)S355 R=0.5 B (Huther et al., 2001)S355 R=0.5 C (Huther et al., 2001)S355 R=0.5 D (Huther et al., 2001)DH36 R=0.1 (Polezhayeva et al., 2009)DH36 R=0.1 (Gao et al., 2015)S355 R=0.1 (Zhang and Maddox, 2009)Grade A R=0.1 (Rutherford et al., 2006)S700 R=0.2 (Lieurade et al., 2005)S275 R=0 (Hansen et al., 2007)304L R=0.1 (Baptista et al., 2007)S31803 R=0.1 (Baptista et al., 2007)
S31803 R=0.1 (Baptista et al., 2007)Grade 43A R=-1 (Booth, 1981)Grade 43A R=0.5 (Booth, 1981)
Grade 43A R=0 (Knight, 1976)
Grade 43A R=0 (Knight, 1976)Grade 43A R=0 (Knight, 1976)Supereiso70 R=0 (Knight, 1976)Supereiso70 R=0 (Knight, 1976)Supereiso70 R=0 (Knight, 1976)BS15 R=-1 (Gurney, 1968)S355 R=0 (Braun et al., 2020)F51 R=0 (Braun et al., 2020)S690 R=0 (Braun et al., 2020)S900 R=0 (Braun et al., 2018)SUS316L R=0.1 (Iwata et al., 2006)m=3Median of m=3.90
!" = 3.9
Ref.: 1 Al-Karawi et al., Fatigue crack repair in welded structures via tungsten inert gas remelting and high frequency mechanical impact. Journal of Constructional Steel Research, 172 (2020). https://doi.org/10.1016/j.jcsr.2020.1062002 Braun & Wang, A review of fatigue test data on weld toe grinding and weld profiling. International Journal of Fatigue, submitted for publication (2020) 3 Ahola et al., Fatigue strength assessment of ground fillet-welded joints using 4R method. International Journal of Fatigue, 142 (2021). https://doi.org/10.1016/j.ijfatigue.2020.105916
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Weld geometry assessment
11.12.20 9
0 20 40 60 80 100 120 140 160Weld Length [mm]
0.5
1
1.5
Radiu
s [m
m] Weld 1 Weld 2 Weld 3 Weld 4
0 20 40 60 80 100 120 140 160Weld Length [mm]
120140160
Angle
[°]
0 20 40 60 80 100 120 140 160Weld Length [mm]
6
8
10
Leg
Leng
th [m
m]
0 20 40 60 80 100 120 140 160Weld Length [mm]
1.5
2
2.5
K t,b [-
]
0 20 40 60 80 100 120 140 160Weld Length [mm]
22.5
33.5
K t,t [-
]
1 2 3 4 GlobalWeld Number
0
0.5
1
Radiu
s [m
m]
1 2 3 4 GlobalWeld Number
0
100
Angle
[°]
1 2 3 4 GlobalWeld Number
0
5
10
Leg
Leng
th [m
m]
1 2 3 4 GlobalWeld Number
0
2
4
K t,b [-
]
1 2 3 4 GlobalWeld Number
0
2
4
K t,t [-
]
(b)
Local ExtremeGlobal Extreme
Mode ValueCrit. Value
(a)
0 20 40 60 80 100 120 140 160Weld Length [mm]
0.5
1
1.5
Radiu
s [m
m] Weld 1 Weld 2 Weld 3 Weld 4
0 20 40 60 80 100 120 140 160Weld Length [mm]
120140160
Angle
[°]
0 20 40 60 80 100 120 140 160Weld Length [mm]
6
8
10
Leg
Leng
th [m
m]
0 20 40 60 80 100 120 140 160Weld Length [mm]
1.5
2
2.5
K t,b [-
]
0 20 40 60 80 100 120 140 160Weld Length [mm]
22.5
33.5
K t,t [-
]
1 2 3 4 GlobalWeld Number
0
0.5
1
Radiu
s [m
m]
1 2 3 4 GlobalWeld Number
0
100
Angle
[°]
1 2 3 4 GlobalWeld Number
0
5
10
Leg
Leng
th [m
m]
1 2 3 4 GlobalWeld Number
0
2
4
K t,b [-
]
1 2 3 4 GlobalWeld Number
0
2
4
K t,t [-
]
(b)
Local ExtremeGlobal Extreme
Mode ValueCrit. Value
(a)
Ref.: Renken et al. (2020). An algorithm for statistical evaluation of weld toe geometries using laser triangulation, under preparation.
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Weld geometry assessment
11.12.20 10
§ IIW Round Robin study on weld geometry measurement systems & algorithm
§ First results published 1§ Higher measurement effort leads to more locations that do not fulfil
ISO5817 requirements 2
Ref.: 1 Schubnell et al. (2020). Influence of the optical measurement technique and evaluation approach on the determination of local weld geometry parameters for different weld types. Welding in the World, 64(2), 301-316. https://doi.org/10.1007/s40194-019-00830-02 Renken et al. (2020). An algorithm for statistical evaluation of weld toe geometries using laser triangulation, under preparation.
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Fatigue strength assessment considering residual stresses
11.12.20 11
§ Gesamtlebensdauer-Wöhlerlinien§ deutlicher Eigenspannungseinfluss
Lastwechsel Ngesamt
Nen
nspa
nnun
gssc
hwin
gbre
ite [M
Pa]
Lastwechsel NgesamtN
enns
pann
ungs
schw
ingb
reite
[MPa
]Schweißzustand spannungsarm geglüht
R = 0 (Schweißzustand)R = -1 (Schweißzustand)R = -3 (Schweißzustand)R = -∞ (Schweißzustand)
R = 0 (spannungsarm)R = -1 (spannungsarm)R = -3 (spannungsarm)R = -∞ (spannungsarm)
Ref.: N. Friedrich, Experimental investigation on the influence of welding residual stresses on fatigue for two different weld geometries. Fatigue Fract Eng M, 43 (2020) 2715-2730. https://doi.org/10.1111/ffe.13339
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(1) transiente thermische AnalyseLast: einheitliche Temperatur auf
Nahtquerschnitt
Ergebnis: Temperaturverteilung über der Zeit
(2) elastisch-plastische StrukturrechnungLast: Temperauren aus (1)
Ergebnis: Eigenspannung und Verzug
1300°C
Vereinfachter FE-Simulationsansatz
Schweißsimulation
Temperatur [°C]
keine
Kalibrierung
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1
2
3
4
5
6
l = 375 mm
b =
150 m
m<t = 10 mm>
Schweißsimulation• angewendet auf fiktive Kleinprobe mit
Kreuzstoß• angenommener Werkstoff: S355
Querrichtung(zur Naht)
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Schweißsimulation
330 mm
55 mm
Quereigenspannung [MPa]
Querrichtung
(zur Naht)
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Eigenspannungsmessung
Eigenspannungsmessungen:• Röntgendiffraktometrie
(ifs TU-Braunschweig)• Messtiefe bis ~ 5 μm• auf 3 Proben
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Eigenspannungsmessungen:• Bohrlochverfahren• Auswertung unter Annahme
konstanter Eigenspannungen bis 1 mm Tiefe
Eigenspannungsmessung
(gleiche Farbe ≙ gleiche Probe)
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Überlagerung mit äußerer Last
" = $!"#$!$%
= %
σt
Span
nung
am
N
ahtü
berg
ang
[MPa
]
" =-1 " =-∞
F
Nennspannungsschwingbreite [MPa]
F
$!"#
$!$%
mit Eigenspannungenohne Eigenspannungen
mit Eigenspannungenohne Eigenspannungen
mit Eigenspannungenohne Eigenspannungen
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Schwingversuche – Risserkennung
Fzyklisch
Fzyklisch
Riss
0.09
-0.15
-0.12
-0.09
-0.03
0.03
0.12
0.15
-0.06
0.00
0.06
[%]
Deh
nung
Schweißnaht
Risserkennung mittels digitaler Bildkorrelation
0.90
0.50
0.55
0.60
0.70
0.80
0.95
1.00
0.65
0.75
0.85
Schweißnaht
Deh
nung
Schweißnaht
Versuchsbeginn
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7. Schwingversuche – Risserkennung
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Schwingversuche – Risserkennung
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Ice-structure interaction andtemperature effects
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Collision scenario
2211.12.20
Service
TankSide
TankDoublebottom
Container ship comparable to ship„FORESIGHT”
that transited the Northern Sea Route in 2009
Ice class: FSICR IA
Length: 134.4 m
Beam: 22.5 m
Draught: 8.08 m
Engine: 8400.0 kW
Ship speed (acc. POLARIS):
1.543 m/s (3 kn)
Wind and Current speeds:
0 m/s
Source: Victor (distributed via shipspotting.com)
Ice Floe:
• Diameter d = 8.5 m• Thickness t = 0.8 m (acc. FSICR)
• Total mass for a circular plate:à "!"!#$ = "%$"& +"'()*" = 82.6 +
Ship:
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Heat transferHow cold could a ship structure can actually become in winter?
2311.12.20
T∞,water
T∞,cargohold
T∞,air
T∞,tank,db
T∞,service
T∞,tank2
T∞,tank1
T∞,tank3
T∞,tank4
Service = -59°CTank1 = -54°CTank2 = -31°CTank3 = -18°CTank4 = -12°C
Averaged temperatureover the height of thecollision area ≈ -20°C
• In the rules and guidelines of the classificationsocieties -60 °C can be found as the lowesttemperature for material tests on steels used inshipbuilding. This value corresponds well withdifferent temperature measurements whereextreme values below -50 °C were measured in thearea of the Northern Sea Route.
• In contrast, liquid seawater cannot become colderthan -2 °C
Ref.: Kubiczek et al. (2019). Simulation of temperature distribution in ship structures for the determination of temperature- dependent material properties, 12th European LS-DYNA Conference Koblenz.
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Temperature dependent material properties and the effect on the structural response in case of collision
2411/12/2020
à neglecting the structural temperature leads to a conservative overestimation of thepermanent deflection.
à consideration of extreme values leads to an underestimation of the permanent deflectionbecause the structure is assumed to be too stiff.
0.700.750.800.850.900.951.001.05
20°C -20°C -60°Cmaterial temperature
max Force [-] perm. deflection [-]
-10%
-22%
+1% +3%
0100200300400500600700
0.00 0.10 0.20 0.30 0.40
eng.
str
ess
[N/m
m²]
eng. strain [-]
20°C -20°C -60°C
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Measurement locations on board Polarstern
§ Strain gauges and temperature sensors in void space 100
§ Strain gauges on F-Deck (10800 aB)§ Strain gauges and temperature
sensors in void space 92
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Temperature measurements
§ Temperature measurementon steel structure withPT1000 sensors every 5 minutes
Data provided by the ship's weather station:
§ Measurement of watertemperature 5m belowwaterline
§ Measurement of airtemperature 29m abovewaterline
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Temperature measurements
15
20
25
30
35
40
31.7 1.8 2.8 3.8 4.8 5.8 6.8 7.8
tem
pera
ture
[°C]
date [-]
V92_p1 V92_p2 V92_p3 V92_p4 ambient_air ambient_water
Ship in drydock Ship in water
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Ship: R.V. PolarsternCruise-No.: PS 122/1Date: 20.09.2019 –15.12.2019Port: Tromsö – Arctic Ocean
Source: http://www.awi.de date [-] in 2019
tem
pera
ture
[°C]
Source: https://dship.awi.de/
Temperature measurements
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Research approach
§ Two steels
§ Three weld details
§ Two methods
11.12.20 29
Development of fatigue assessment methods that take
temperature effects into account based on micro-structural support effect
hypothesis
Extension of SED and stress averaging
approach
S–N curve independent of temperature
∆"
#
FE modelling
Material tests to relate DBTT and FTT
Charpy tests
$
Charpy transition curve
%&
Fatigue tests
S–N curve (RT)
∆"
#
S–N curve (-20 °C)
Statistical assessment of fatigue test results
∆"
$Regression curve
Comparison with state-of-the-art methods
Conclusions and recommendations for
further work
Low temperature S–N curve
∆"
#Design curve
Temperature modification factor
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Results for SED method and comparison with state-of-the-art methods
11.12.20 30
104 105 106 107
Cycles to failure Nf
0.01
0.1
1
5
Aver
aged
stra
in en
ergy
den
sity
W [N
mm
/mm
3 ]
0.0580.1050.192
S235 S500WT RTWT -20 °CWT -50 °CWR RTWR -20 °CWR -50 °C
Rc(T)run out
104 105 106 107
Experimental cycles to failure Nf
104
105
106
107
Pred
icted
cycle
s to
failu
re N
f,pre
dfo
r Ps =
97.
7%
Conservative
Unconservative
Line of equality±2 life factor
(a) (b) (a) Weld toe failure
+ SD
- SD
Nomina
l stres
s meth
od
Structu
ral st
ress e
xtrap
olatio
n
Structu
ral st
ress li
neari
zatio
n
Xiao & Yam
ada 1
mm co
ncep
t
Efective
notch
stres
s con
cept
SED conc
ept R c
(T = RT)
SED conc
ept R c
(T)-1
0
1
2
3
Fatig
ue s
treng
th d
evia
tion
dev
= N
f,exp
- N
f,pre
d,97
.5%
RT-20°C-50°C
(b) Weld root failure
Nomina
l stres
s meth
od
Structu
ral st
ress e
xtrap
olatio
n
Structu
ral st
ress li
neari
zatio
n
Xiao & Yam
ada 1
mm co
ncep
t
Efective
notch
stres
s con
cept
SED conc
ept R c
(T = RT)
SED conc
ept R c
(T)-1
0
1
2
3RT-20°C-50°C
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Ice load measurementsShip: R.V. PolarsternCruise-No.: PS 122/1Date: 20.09.2019 –15.12.2019Port: Tromsö – Arctic Ocean
Source: http://www.awi.de
Frame 1
Frame 3
Frame 4
Frame 5
Frame 6
Frame 2
date [-] in 2019
stra
in[µ
m/m
]
measured shear strains during a winter storm
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I. Test Program large scale tests
Rigid structure Deformable structure
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Test setup for the deformable structures
11.12.20 33
Spacing: 350 mmFB 240 x 12
Plate thickness 10 mm
Panel 1
Panel 2 & 3
Panel 1
Panel 2
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Force curve of the brittle test runagainst Panel 1
Stroke 1 Stroke 2Reconstruction
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Deformation of the panel
Initial Post
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Deformation of the stiffeners
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Stroke 1 Stroke 2
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Ice-Extrusion Test simulations
11.12.20 39
D=100Cone 100
D=200Cone 200
D=800Cone 800
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Results Ice-Extrusion Tests
4011.12.20
0
20
40
60
80
100
120
140
160
180
0 20 40 60 80 100 120 140
Forc
e [k
N]
Displacement [mm]
Konus200_G25_A20_V10_1 Dyna_Simulation
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Ice Pessures - Cone 200
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The loaded area of the LS-Dyna simulation is currently larger than measured. Accordingly, the contact pressures (F/loaded area) are underestimated. The maximum pressures of the simulation are in the magnitude of 30 to 50 MPa. This in accordance with the TekScan results.
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Application to the large scale extrusiontests
Panel 1Panel 2
Panel 1
Panel 2
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Untersuchung der Schwingfestigkeit hybrid additivund subtraktiv gefertigterProben aus AISI 316L
M. Braun, S. Hellberg, I. Kryukov, S. Böhm, R. E. Wu, S. Ehlers, S. Sheikhi
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Motivation
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Ref.: Scudino et al. (2015)
Ref.: Köhler et al. (2011)
Crankshaft of medium-speed four-stroke diesel engineSLM Cu-10Sn bronze propeller
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Hybrid additive and subtractive manufacturing
Base plateBase plate
Base plate
Lifting TableLifting TableLifting Table
Spindle
1. Powder distribution
'n' repetitions Every 'n' repetitions
Powder distribution
2. Laser processing
Metalpowder Laser
3. Milling
Back to step 1
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Specimen preparation§ Material: 316L
§ Renishaw AM250-System
§ 200W Ytterbium fibre laser
§ Argon atmosphere
§ Layer thickness: 40 µm
§ Specimens shape acc. to ASTM E466-15
§ Built in vertical direction
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© Renishaw
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Test program
Condition As-built Heat-treated Machined + Heat-treated
Heat treatment
– 2h @ 650 °C(furnace cooled)
2h @ 650 °C(furnace cooled)
Machining – – 1 mm thickness reduction by turning
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Material characterisation
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§ High strength and ductility
§ Grains partially extend over several layers
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Computer tomography scan
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Computer tomography scan
11.12.20 50
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Post-treatment of selective laser melted parts
11.12.20 51
Unbehandelt Bearbeitet
Rautiefe Rt 41,929 ± 0,065 5,062 ± 0,063
Mittenrauwert Ra 6,295 ± 0,041 1,024 ± 0,005
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Fatigue test results
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Effect of surface roughness
§ Surface roughness as-built:!, ≈ 6.3 µm → !- = 20 – 55 µm
§ Surface roughness machined:!, ≈ 1.0 µm → !- = 4 –16 µm
§ Estimated difference: ≈10%
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0 100 200Surface roughness Rz
0.75
0.8
0.85
0.9
0.95
1
Surfa
ce fa
ctor
f SR
for R
m =
600
N/m
m2
fSR = 0.147e-0.1035Rz
+ 0.8528e0.0005721Rz
R2 > 0.99
Data by Rennert (2012)
Ref.: Rennert, R. (Ed.) (2012): FKM Richtlinie
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Thank you for your attention!
12/11/20