2008 international ansys conference - cad-it · 2008 international ansys conference fatigue...
Post on 18-May-2018
233 Views
Preview:
TRANSCRIPT
© 2008 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary
2008 International ANSYS Conference
Fatigue analysis and design optimization of a trailer hitch system
Erke Wang, Rainer RauchCADFEM GmbHGermany
© 2008 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. Proprietary
Fatigue analysis and design optimization of a trailer hitch system
ContentDescription of customer needs
Some remarks on the fatigue assessment of welded parts
Workbench work flow to analyze welded structures
Fatigue analysis and comparison to test results
Return on Invest
DXplorer study based on parameterized DM-model
Summary
© 2008 ANSYS, Inc. All rights reserved. 3 ANSYS, Inc. Proprietary
Customer needs• Every part has to pass a fatigue test with 2.E6 cycles• Testing time approximately 4 days• Increased complexity of component – removable trailer hitch• Increased loading due to increasing performance of towing vehicle (SUV)
Tests facility
Fatigue analysis and design optimization of a trailer hitch system
Location of failure
© 2008 ANSYS, Inc. All rights reserved. 4 ANSYS, Inc. Proprietary
German SUVs
Fatigue analysis and design optimization of a trailer hitch system
VW Touareg 850 Nm BMW X6 300 kW (407 HP)
Audi Q7 368 kW (500 HP)Porsche Cayenne 368 kW (500 HP)
© 2008 ANSYS, Inc. All rights reserved. 5 ANSYS, Inc. Proprietary
Stress in welded structures
What stress component can we use as a reference?
Measure and calculate stresses at locations adjacent to the weld
define reference weld geometries
Geometry of weld cannot be modeled in detail
Fatigue analysis and design optimization of a trailer hitch system
Material properties vary over weld cross section
© 2008 ANSYS, Inc. All rights reserved. 6 ANSYS, Inc. Proprietary
Fatigue analysis and design optimization of a trailer hitch system
Approaches to assess welded structures welded structures
• Nominal stress approach
• Structural hot spot stress approach
• Notch stress approach
• Linear elastic fracture mechanics
Not valid for the approval of automotive components
During the product development cycle, the following approaches are widely used to assess the welded structures life cycle, depending on the nature of the problem, the appreciated approach will be used.
© 2008 ANSYS, Inc. All rights reserved. 7 ANSYS, Inc. Proprietary
Nominal stress approach:
Structural hot spot approach:
Measure and calculate stresses atlocations adjacent to the weld
Notch stress approach:
define reference weld geometries
Approaches to assess welded structures welded structures
Way too conservative – useful for structures like cranes
AFS /=
sSSREF DD= *
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 8 ANSYS, Inc. Proprietary
Structural hot spot approach: stresses can be calculated using shell or solid elements
Comparison of allowable stress component for welded detail
Approaches to assess welded structures welded structures
According to the design detail, there are N° of welded details in catalogue available(IIW-Recommendations), which describe where the stress could be measured.
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 9 ANSYS, Inc. Proprietary
MPaFAT 6363 ∂Δ≡
Approaches to assess welded structures:
According to the catalogue, one reference SN curve can be chosen to compare with calculated stress results.
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 10 ANSYS, Inc. Proprietary
Approaches to assess welded structures:
• There are several approaches to assess welded structures
• Nominal stress approach
• Structural hot spot stress approach
• Notch stress approach
• Linear elastic fracture mechanics Not valid for the approval of automotive components
Way too conservative – useful for structures like cranes
N° of welded details in catalogue (IIW-Recommendations) is limited
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 11 ANSYS, Inc. Proprietary
Approaches to assess welded structures:Notch stress approach – R1MS - Radius 1 Max Stress (acc. to IIW-Recommendations)
Geometric detail of the weld seam
Pros and Cons:
+ concept for suitable for the FE-process
+ no structural detail list necessary
+ straightforward in result interpretation
- high number of elements
IIW-Recommendations FE Model
Radius=1mm
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 12 ANSYS, Inc. Proprietary
Approaches to assess welded structures:
„Fatigue assessment of a welded component in a construction machinery based on different methods” J. Martinsson, J. Samuelsson IIW DOCUMENT No. XIII-1905-01
Notch stress approach
• With this approach, the FE model must be modeled in weld region with very fine mesh,
• this leaded to a very large FE model. • Because of the hardware performance
and software efficiency issues, this approach was not widely used in product development process
Accuracy
Fatigue analysis and design optimization of a trailer hitch system
Geometric detail of the weld seam
IIW-Recommendations FE Model
© 2008 ANSYS, Inc. All rights reserved. 13 ANSYS, Inc. Proprietary
Notch stress approach – an economic way based on ANSYS Workbench technology
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 14 ANSYS, Inc. Proprietary
A short revive on the submodel - technique
Global modelPhysical Model Submodel
1.
1. Generate Submodel (Design Modeler!)
2.
2. Transfer Displacements as Boundary Conditions on Submodel
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 15 ANSYS, Inc. Proprietary
Submodel examplesGlobal model without welded detailShell element
Submodel with welded detailSolid element
Global model
Local model 1
Local model 3
Local model 2
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 16 ANSYS, Inc. Proprietary
Submodel examples
Fatigue analysis and design optimization of a trailer hitch system
Submodel
Global model
Submodel with different mesh
© 2008 ANSYS, Inc. All rights reserved. 17 ANSYS, Inc. Proprietary
Work flow1. Analyze global structure using a
uniform element size
2. Identify hot spots
3. Prepare Submodel -geometry feasible for the R1MS-assessment
4. Calculate local results with different Submodels
5. Use Workbench Fatigue for Life time estimation
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 18 ANSYS, Inc. Proprietary
(1) Analyze global model – (2) identify potentially critical location
/copy,file,rst,,..\voll,rst save,file,db /copy, file,db,,..\voll,db
critical location
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 19 ANSYS, Inc. Proprietary
(3) Prepare Submodel(s) acc. to IIW-Recommendations
/prep7 cmsel,s,CUTnwrite,cut,nodeallssave fini /clear /post1 resu,..\voll,db /post1 file,..\voll,rst set,last alls cbdo,cut,node,,cbdo,cbdo fini resu /prep7 /inp,cbdo,cbdo alls /solu
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 20 ANSYS, Inc. Proprietary
Check results for all defined submodelsN° of cycles estimated
N° of cycles in test
Test 1 600.000 790.000Test 2 600.000 880.000
N° of cycles estimated
N° of cycles in test
Test 1 870.000 1.3 Mill.Test 2 870.000 1.1 Mill.
N° of cycles estimated
N° of cycles in test
Test 1 > 2 Mill. @ 2 Mill. test stop
Test 2 > 2 Mill. 1.75 Mill.
Model 1
Model 2
Model 3
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 21 ANSYS, Inc. Proprietary
Estimated life at maximum load amplitude (realistic test scenario?)
Reviewing results with ANSYS Fatigue (Model 1)
log [N]
log Δδ[MPa]
2E6
225
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 22 ANSYS, Inc. Proprietary
Reviewing results with ANSYS Fatigue
log [N]
log Δδ[MPa]
2E6
225
Estimated life at a varying load amplitude (more realistic test scenario)
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 23 ANSYS, Inc. Proprietary
ROI for the analyzed structures
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 24 ANSYS, Inc. Proprietary
Do the simulations pay off?
Cost for prototype: 400 – 1.200.- Euro
Test rig 3 days: 2.500.- Euro
Preparation/Docu: 500.- Euro
Cost per test: 3.400 – 4.200.- Euro
TECS Professional: 4.100.- Euro
Engineer: 60.000.- EuroCost per year: 64.100.- Euro
Preventing 16 unsucessful tests each year pays off all cost for simulation!
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 25 ANSYS, Inc. Proprietary
Do the simulations pay off?
Time to analyze a complete trailer hitch system: 1 – 5 days
Uncounted numbers:
- Costs for re-design (CAD, PDM, Customer discussions)
- Delay in project
- Reputation and acknowledge technical know how
- Knowledge about the product
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 26 ANSYS, Inc. Proprietary
Knowledge about the product – or how to optimize products
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 27 ANSYS, Inc. Proprietary
Parameterize geometry – generate dependent parameters to guarantee feasible models during optimization run
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 28 ANSYS, Inc. Proprietary
Define Boundary Conditions and depedent parameters in welded detail
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 29 ANSYS, Inc. Proprietary
Check sensitivity of geometry parameters on loading of the critical welds
Select pipe diameter and wall thickness (integers)
Check all relevant stresses and displacements
Review sensitivities
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 30 ANSYS, Inc. Proprietary
DXplorer – Simulation Driven Design
Freeze design by direct use of simulation results
Extended product knowledge
Fatigue analysis and design optimization of a trailer hitch system
Simulation as applied Science to replace the try-and-errorprocess
© 2008 ANSYS, Inc. All rights reserved. 31 ANSYS, Inc. Proprietary
Accuracy
Summary• ANSYS Workbench delivers the possibility to assess
even complicated welded details with local models.
• The submodel approach is extremely efficient – all documentation is done via the structured tree.
• ANSYS Fatigue Module provides the opportunity to account for fatigue effects like mean stresses and load history.
• With the ANSYS DesignXplorer design decisions are based on knowledge not on presumptions.
Fatigue analysis and design optimization of a trailer hitch system
© 2008 ANSYS, Inc. All rights reserved. 32 ANSYS, Inc. Proprietary
Thanks!
Fatigue analysis and design optimization of a trailer hitch system
top related