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1、Airbag Analysis in LSDYNA Copyright Livermore Software Technology Corporation 2 Outline ?Introduction ?Airbag Types ?Generating FE mesh ?Fabric Modeling ?Definition of Control Volume ?Airbag Leakage ?Airbag Contact ?Airbag to Structure Contact ?Post-processing 3 Introduction ?Prediction of Occupant
2、response necessitates accurate airbag modeling ?Difficulties associated with numerical modeling of airbags can be broadly classified as ?Soft airbag properties ?Small fabric thickness ?Folding airbags still a difficult task ?atleast for a passenger side ?Determination of leakage ?Test measurement ?P
3、arametric Optimization seems promising ?Contact can be a nightmare 4 Types of Airbag (1) ?Driver Side ?Passenger Side ?Side Curtain Airbag ?. 5 Generating Airbag Mesh - Driver (1) ?Generally its a initially flat circular bag - folded to package ?Meshing must consider fold lines ?To achieve this, mes
4、h the surfaces that is already split accounting for fold lines ?Generate the mesh from the split-surfaces with any pre- processor ?Mesh could be 4-noded shells or 3-noded trias ?If 3-noded, set ESORT=1 ?invokes C0 shell 6 Generating Airbag Mesh - Driver (1) ?Ensure the mesh encloses a volume ?no cra
5、cks or free edges ?Represent tether using nonlinear discrete springs 7 Generating Airbag Mesh - Passenger ?Folding a passenger side airbag is still not accomplished by any pre-processor ?The alternative is to use a reference to the fully deployed bag geometry ?Generate the mesh for the fully deploye
6、d surface ?Scale or Resize to fit into container ?Use fully deployed nodal coordinates as the reference configuration ?No self contact is needed ! 8 Airbag Material ?Best modeled using *MAT_FABRIC ?Can be Isotropic or Anisotropic ?depends on test data ?Also Invokes efficient membrane formulation 9 C
7、ontrol Volume ?LSDYNA offers several types 10 ?Segment list ?Gas properties ?Heat Capacity at constant volume ?Heat Capacity at constant pressure ?Mass flow rate ?Temperature rate 11 Airbag Leakage ?Venting ?constant vent orifice area, A23 ?pressure dependent, LCA23 ?Fabric Porosity ?constant coeffi
8、cent ?time dependent 12 Airbag Self Contact ?Additional logic is needed to treat airbag self contact ?The newly implemented, segment based contact (SOFT=2), is most recommened ?It ignores initial penetration which is sometimes unavoidable in folded airbags ?The contact stiffness is automatically bas
9、ed on soft- constraint ?There is some cost penalty but works well if there are no other instabilities 13 Airbag to Structure Contact ?Since the airbag thickness is small (0.4mm), set the SST variable to 2-4 mm ?Invoke soft constraint option ?Always use a two-way contact 14 Post Processing ?ABSTAT - airbag statistics ?pressure ?volume ?mass inflow ?mass outflow ?leakage ?surface area ?RCFORC ?SLEOUT ?MATSUM
