LMS Durability Technologies

Transcription

1 Durability Technologies Virtual prototyping solutions for a more efficient and better quality durability engineering process Virtual Prototyping for Durability - BA copyright International 1998

2 Fatigue design process Component/vehicle design design CAE CAE models models (FEM, (FEM, MBS) MBS) Building Building prototypes prototypes Virtual Virtual test test track track Dynamic Dynamic simulation simulation Simulation of rig test not ok Field Field data data collection collection Data Data consolidation consolidation Statistical Statistical & rainflow rainflow analysis analysis of of data data Virtual Prototyping for Durability - BA copyright International 1998 Loads Loads data data base base Tired of of waiting for for physical testing? Need better design? Simulate (virtual )durability Test tests! Test scenario scenario More time time for for Accelerated analysis Accelerated & testing synthesis! testing Shorter development time! ok Rig test ok not ok Sign-off

3 Virtual prototyping for durability step 1: external loads to internal forces from given external loads (spindle forces) compute internal forces acting on components external loads Virtual Prototyping for Durability - BA copyright International 1998 internal forces problem dynamics nonlinear elements (spring, damper, etc) nonlinear geometry solution multi body simulation dynamic FEA

4 Virtual prototyping for durability step 2: internal forces to stress tensor history L 1 L 2 t t e s x from given forces acting on the component, determine time history of the local pseudo stress tensor based on theory of elasticity e s x e s y t loading frequency below lowest natural frequency: quasi static superposition e t xy e s y e t xy t t loading frequency above lowest natural frequency: modal superposition Virtual Prototyping for Durability - BA copyright International 1998

5 Virtual prototyping for durability step 3: stress tensor to damage model fatigue damage is initiation and growth of short cracks, but different levels of detail are required for different applications analysis approaches/models available for: long life (high cycle fatigue): stress-life shorter life (low cycle fatigue): strain-life seam welds spot welds Virtual Prototyping for Durability - BA copyright International 1998

6 Virtual prototyping for durability step 3b: strain-life approach g xh a initiation and growth of small cracks under elastic-plastic deformation estimate elastic-plastic `notch response from pseudo stresses based on theory of elasticity g xy e y Virtual Prototyping for Durability - BA copyright International 1998 analyse potentially critical (crack) planes simultaneously to find most severe damage maximum damage defines critical plane

7 Virtual prototyping for durability step 3b: strain-life critical plane approach g xy g xh a e y g xy time e ey g xh a = 0 o time damage accumulation 10 o o g xh 170 o time damage accumulation N Virtual Prototyping for Durability - BA copyright International D(a=0 o ) D(a=170 o ) D = max[ [ D(a) ) ]

8 Virtual prototyping for durability - data flow - multi body model road profile, driving directions FEM model multi body simulation internal forces spindle forces time domain FALANCS FEM solver stress from unit load cases Virtual Prototyping for Durability - BA copyright International 1998 your favorite FEM post processor pseudo stress result file

9 BMW 5 series knuckle inner side: predicted vs.. real crack initiation * * * * repeats fatigue life average life in test: 2400 repeats predicted life: : 3055 repeats Virtual Prototyping for Durability - BA copyright International 1998

10 FALANCS: node elimination technique Rainflow projector: detect representative elements Loop over shortened load histories: Produce shortened load histories eliminate eliminate non-damaging non-damaging sections sections from from load load history history if if simultaneously simultaneously non-damaging non-damaging at at all all representative representative elements elements determine determine amount amount of of damage damage eliminated eliminated Eliminate non-critical nodes analyze analyze remaining remaining nodes nodes with with shortened shortened load load history history eliminate eliminate nodes nodes with with damage damage < max(d) max(d) -- eliminated(d) eliminated(d) Virtual Prototyping for Durability - BA copyright International 1998

11 Load history: original (lab test) and shortest length (node elimination phase 1) force longitudinal lateral short history original history vertical verified by by tests Virtual Prototyping for Durability - BA copyright International 1998 time

12 virtual prototyping for durability: proven by real life application cases Virtual Prototyping for Durability - BA copyright International 1998

13 virtual prototyping for durability: benefits find critical locations automatically (without guess work) within reasonable time true multiaxial analysis (incl. critical planes) seam welds & spot welds quasi-static & modal superposition shell and 3D elements interfaces to most FEA environments no need to learn new FEA postprocessor same GUI and data bases for FEM and non-fem expert and non-expert mode internal force based analysis options for quicker design decisions Virtual Prototyping for Durability - BA copyright International 1998