Dynamic mechanical properties of AM- manufactured stainless steel material A.B. Spierings, G. Levy, K. Wegener Inspire – institute for rapid product development irpd St. Gallen, Switzerland CIRP STC-E Paris, 27.01.2012 1
Dynamic mechanical properties of AM-manufactured stainless steel material
A.B. Spierings, G. Levy, K. Wegener
Inspire – institute for rapid product development irpd St. Gallen, Switzerland
CIRP STC-E
Paris, 27.01.2012
1
Agenda
� Background & Motivation
� Mechanical properties of stainless steel
� Dynamic material qualification
� Case study
Spierings, Adriaan © 01/2012 inspire AG2
Background & Motivation
� AM technologies, especially Beam Melting Technologies such as SLM, offer an interesting way to highly improved functional & structural parts for
– Aerospace applications
– Automotive
– Machine industry
– Medical applications (implants, instruments)
– 2
Spierings, Adriaan © 01/2012 inspire AG3
www.botzeit.de Inspire-irpd Inspire-irpd
Background & Motivation
� However, the success of AM-technologies in industry requires a furtherdevelopment in different areas:
Exemplaryapplications
Material knowhow
Processknowhow &development
Affordablemachines
AM-productionenvironment
√√√√
≈≈≈≈ √√√√
≈≈≈≈ √√√√
----
Production environment
«Lab environment» / first applications – R&D driven
Spierings, Adriaan © 01/2012 inspire AG4
Inspire-irpd is involved in all fields
Background & Motivation
� Focus on material properties and integrity
– Static mechanical properties � Widely investigated / known
– Dynamic mechanical properties � Only partially investigated
– Fracture behaviour (da/dN, KI,II,C,-) � Almost no results available
– General material integrity � Many investigations and analysis
– Internal stresses available / R&D topic of high interest– Microstructure
– 2
– Korrosion behaviour
– 2
Industrial applications
Mechanical properties:
static, dynamic, fracture behaviour, 2
MicrostructureInternal stresses
Porosity
Spierings, Adriaan © 01/2012 inspire AG5
Mechanical properties
� We know that mechanical properties are different to «conventionally» processed materials, due to2
– Fine grained, columnar microstructure � anisotropy
– Internal stresses– BRINKSMEIER, E., LEVY, G., MEYER, D. & SPIERINGS, A. B. 2010. Surface Integrity of Selective-Laser-Melted Components.
CIRP Annals - Manufacturing Technology, 59, 601-606.
– Some porosity
Viewing direction
Main grain
orientation
90° F
F
Main grain
orientation /
dendrits
Builddirection
Viewing direction
0°
F Fz
Spierings, Adriaan © 01/2012 inspire AG6
SPIERINGS, A. B. & LEVY, G., 2009. Comparison of density of stainless steel 316L parts produced with selective laser melting
using different powder grades. In: BOURELL, D. L., ed. Proceedings of the Annual International Solid Freeform Fabrication Symposium,August 3-5 2009 Austin, Texas. 342-353.
Mechanical properties
� Static mechanical properties
– For many materials known
– Typically good static properties(Hall-Petch !)
���� Many materials meet the
requirements for static applications.
� Dynamic mechanical properties– Partially analysed
– Typically lower strength compared to conventionally processed materials
� Is this dramatic and hindering a use of AM-materials in more dynamic
(industrial) applications?
Rm
0
100
200
300
400
500
600
700
800
900
Type 1 Type 2 Type 3
Powder Types
(MPa)
0
100
200
300
400
500
600
700
800
900
30um - 0° 45um - 0°
30um - 90° 45um - 90°
Literature
Spierings, A.B. et.al; Influence of the particle size distribution on surface quality and mechanical properties in additive manufactured stainless
steel parts; Rapid Prototyping Journal, 2011. 17(3): p. 195 - 202.
Spierings, Adriaan © 01/2012 inspire AG7
Dynamic material qualification
� Analyse of dynamic properties of AM-processed stainless steel
– Machines & Materials
Material: SS-316L
ConceptLaser - M1
• ≈ 100 W• v = 425 mm/s• Layer thickness 30 µm• Hatch 0.13 mm
• Build direction: vertical
• Powder- D50 ≈ 15 µm
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SLM machine @ Inspire-irpd
Dynamic material qualification
� Analyse of dynamic properties of AM-processed stainless steel
– Test setup
S-N specimens
• Surface finishing- as-built- machined
- polished
• Testting (ASTM-E739) at- R = 0.1 («severe»)- 50 Hz
• 50 samples for SS 316L
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� Results
– As-built
– & Machined
– & polished
Dynamic material qualification
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� Conclusions
– Values are comparable toconventional materials, dependingon the specific conditions(annealed or not, 2)
polished
as-built
machined
– As-built samples: Lower endurancestrength compared to machined, polished
– Only small differences in fatigue rangebetween as-built – machined – polished
samples!
Dynamic material qualification
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Dynamic material qualification
� Open questions
– Surface quality
– Interestingly, the surface quality did not play a highly significant role.↔ conventional machining (grooves) !!� other factors play a more important role.
This behaviour was also shown on other materials!
– Differences in S-N curves: z- versus xy-direction
– The grain size plays an important role in fatigue,especially during crack initiation (∆Kth ↑ for d↓).
– Crack growth in the current (z-direction) specimens:� load acting ⊥ to the long axis of the grains� for cracks: «coarse grained structure»
– Expectation for xy-built specimens: Lower values compared to z-built specimens� «fine grained structure»
Spierings, Adriaan © 01/2012 inspire AG12
Z-specimens (left), xy-specimens (right)
Dynamic mechanical properties
� Challenges: Are the dynamic mechanical properties sufficient forindustrial applications?
– We need to qualify the materials� Material database
– We can optimise the part-design� Topological optimisation
� Optimization of stress flow
– We need to optimise the processes� Reduction of porosity
� Reduction of internal stresses Answer
Optimised
processes
Design
Optimization
Qualification
of materials
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Design
• Geometry• Joints• Material selection• Surface condition• 2
Stress distribution
Material
• Static• Dynamic• da/dN• Fracture
toughness
Application
• Leightweight• Functionally
optimised
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Case study
� Formula student car 2011
Production of heavily loaded brackets for the Formula Student Cars 2010 & 2011, ETH Zurich
� Bracket development (leightweight)
���� Dynamically loaded
AMZ Formula Student Car 2010 & 2011, 1st place winner in Silversone 2010.
�Exemplare case study:Motivation for an industrial use of SLM for functional, load-bearing parts.
Spierings, Adriaan © 01/2012 inspire AG
15
Formula student car of ETHZ
� Version 2011:
Different brackets (Version 2011)
Spierings, Adriaan © 01/2012 inspire AG
Brackets, produced by inspire-irpd
SPIERINGS, A. B., et.al, 2011. Production of functional parts using SLM – Opportunities and limitations. In: BÀRTOLO, P. J., ed. Virtual and Rapid Manufacturing: Advanced Research in Virtual and Rapid Prototyping, September 28-October 1 2011, Leira, Portugal. CRC Press, Taylor & Francis, London, 785-790.
Dynamic material qualification
� Outlook («Materials»)
– Analyse more materialsS-N measurements done
– 316L
– 1.4313
– Some measurements on 1.4542
– Analyse not only S-N curves, but also– Crack propagation curves (da/dN)
– KI,C
– Planned: Measurements on Aluminium (S-N, da/dN)
Spierings, Adriaan © 01/2012 inspire AG16
Materials
SLM machine
equipment
Applications
Processdevelop-ment &
Simulation
SLM fields of activity @ inspire-irpd