2Linear Gaps What is a “linear gap”? Why do I want linear gaps? What is theory/implementation?Patran interfaceExamplesLimitationsConclusions
3What is a “linear gap”?The linear gap is a contact element in its simplest form:DOF-to-DOF gaps with initial openingsLinear, therefore does not include:frictionlarge displacementsmaterial non-linearityXYNode 2P = 30 lbs.UgapNode 1UinitUses iterative solver todetermine open/closed status.Node 3
4Why do I want linear gaps? Successful analysis will use proper boundary conditions and load paths.Linear gaps can solve a large class of problemsHeel-toe interactionHole bearingSimple contactsBridge SupportsFitting contactsEfficient when compared to nonlinear methods
5Theory / Implementation The linear gaps provide for simple contact, (compressive) forces only.MPC’s are used to define the gapsThe displacements and mpcforces are used to determine if each gap is “welded” or “free”Displacement criteria: no penetration (MPC displacement >=0)MPCFORCE criteria: compressive force only (MPCforce <=0)An iterative procedure is used to solve the model based on displacements/mpcforces
6X Y Node 2 P = 30 lbs. Ugap Node 1 Uinit Node 3 Uy (opening) Y Uy (closing)Uy (initial)Opening Grid Uyopening - positive disp will open the gapClosing Grid Uyclosing - positive disp will close the gapInitial Opening Uyinitial - initial separation between gridsThe equation for the gap displacement can be written as:Uygap = Uyopening - Uyclosing + UyinitialRearranging in MPC format and setting Uyclosing as thedependant (first) term:Uyclosing - Uyopening + Uygap - Uyinitial = 0Node 3
7Theory / Implementation SPOINTs are defined for Ugap and UinitSPOINTSUPORT puts SPOINT 55 (Ugap) in the R-set for iteration.SUPORT 55 0SPC defines initial gap opening =.05 (Uinit)SPCMPC Entry: (Eq. of motion: Uy3 - Uy2 + Ugap - Uinit = 0)$ SID G1 C1 A1 G2 C2 A2MPC$ G3 C3 A3 G4 C4 A4
8MSC.Patran InterfacePCL Utility developed to easily create linear gaps and write appropriate MSC.Nastran input entries.Easy Creation/Deletion of linear gapsUseful graphics for visualizationSpecial VerificationCreates complete, run-ready, MSC.Nastran jobStores gaps on MSC.Patran dbSession file support
9CREATING GAPS Initial Assumption: Opened or Closed Special Cases Initial opening defined by nodal distance (automatically calculated) or by user specified valueCreate gaps within tolerance; if coincident nodes identify the opening node based on Node IDSelect Nodes (and direction) on both sides of gap, interface will automatically determine “Opening” and “Closing” Nodes and check for SPC/MPC conflicts
10CREATING GAPS Initial Assumption: Opened or Closed Initial opening defined by nodal distance (automatically calculated) or by user specified valueUser defines “Opening” Node(s), “Closing” Node(s), and directions.
11Gap Display: No Options Gap Display: All Options VISUALIZING GAPSGap Display: No Options(0.15)(0.15-S)(-S)Gap Display: All Options
14VERIFYING GAPSIf any LBC (SPC’s) have been added during the session, “Reload” the form and select appropriate boundary conditions“Rechecks” any model changes related to MPC and/or SPC changes (MPC’s include RBAR, RBE2, RBE3, etc.)
15L-Bracket Heel-Toe Analysis 100 Pounds0.25” ThickAluminum3.0”Shear Bolt = .248 DiameterShear Hole= .250 DiameterLinear gaps defined in radial direction to distribute bearing load1.0”2.0”Tension Bolt: 0.5 inches long, .250 Diameter,attached to plate with RBE3 and fixed at bottom“Gap to Ground” along bottom surface
16Force Transfer at Shear Bolt Force Transfer at Tension Bolt Local Stress DistributionForce Transfer at Shear BoltLocal Stress DistributionForce Transfer at Tension Bolt
17Interference Fit Interference Gaps: Opening node is plate Closing node is pinInitial Gap determined by nodal distancePlate 5 X 4 X .1.500 hole .40 from edgePin .506 dia X .1 thick(All Aluminum)
18Non-uniform force distribution caused by edge effect
19Limitations Remember “simple gaps” only NO LARGE DISPLACEMENTSNO FRICTIONNO MATERIAL NONLINEARITYOtherwise use SOL 106 with CGAP/PGAPwith or without PARAM,LGDISPwith or without MATS1etc.
20Additional Information MSC.Nastran V70.5 Release Guide; Section 3.5, download from:McCullough, John and Proctor, Lance, “LOCAL ANALYSIS OF FASTENER HOLES USING THE LINEAR GAP TECHNOLOGY OF MSC/NASTRAN,” 1999 MSC Aerospace Users’ Conference. Download from:
21ConclusionSimple gap contact is available in SOL 101 of MSC.NASTRAN V70.5 or later.Constrained Displacement ITERative technique (CDITER).Simple gaps -- no frictionWorks with large modelsReduces the complexities inherent with SOL 106 (gap stiffness, convergence, etc.)Allows use of GPFORCE (now available in SOL 106 in V2001)Used in instances where non linearity's do not exist, but contact is required.