Chapter 72: Automated Bolt Modeling

72 Automated Bolt Modeling

Summary 1290

Introduction 1291

Modeling Details 1291

Results 1296

Input File(s) 1299

Video 1300

MD Demonstration Problems

CHAPTER 721290

SummaryTitle Chapter 72: Automated Bolt Modeling

Features Automated Bolt Modeling and Segment to Segment Contact

Geometry & Boundary Conditions

Material properties• Linear elastic material for flanges and bolts• Flanges: E = 1e+007 psi, = 0.3, Bolts: E = 3e+007 psi, = 0.3

Analysis characteristics Nonlinear static analysis

Contact PropertiesBoth bolts are glued and touching to the left flange and right flange respectively. Both plates are touching together.

Element type 3-D 4-noded tetrahedron (CTETRA) elements and RBE2 element

FE results

Fixed End

Bolt 2

Bolt 1

Control Grid Points

3,000 lbf Applied

Load step-4; stress-SZZ

1291CHAPTER 72

Automated Bolt Modeling

IntroductionBolt modeling is important in analyses of engine assemblies. Gasket joints, which are used in such assemblies to prevent steam or gas from escaping, are often fastened by a number of bolts. In a typical loading sequence of an engine assembly, the bolts are first fastened until a certain pre-tension force is present in the bolts. This can be achieved by shortening the bolts until the desired force is reached. Next, the bolts are “locked”, that is, the amount of shortening remains fixed, while the assembly is subject to other (thermo-) mechanical loads. Finally, the bolts are loosened again, either by decreasing the shortening or by releasing the bolt forces.

Modeling DetailsThe geometry of the model, shown in Figure 72-1, is a structure having two flanges connected through two bolts. The materials of bolts and the flanges are different. The left end of the left side flange is clamped and force of 3000 lbf is applied via RBE2 element. In order to apply pre-tensioning on the bolts, automatic bolt creation and assisted bolt creation option is used for Bolt-1 and Bolt-2 respectively, where the pre-tension force (2000 lbf) has been applied at each bolt location via control nodes.

Figure 72-1 Model of the Flange

Element ModelingFour-noded tetrahedron elements (CTETRA) have been used for flanges and bolts. Properties of the elements are defined trough PSOLID entry. Additional nonlinear properties for the solid elements corresponding are specified using the PSLDN1 entry.

PSOLID 1 1 PSOLID_bPSLDN1 1 1 + + C4 SOLID L PSOLID_b

Fixed End

Bolt 2

Bolt 1

Control Grid Points

3,000 lbf Applied

MD Demonstration Problems

CHAPTER 721292

Material ModelingLinear isotropic material properties are defined using MAT1 entry. Elastic modulus and Poisson’s ratio are the material constant input for this analysis.

MAT1 1 3.E+7 0.3 Iso_boltMAT1 2 1.E+7 0.3 Iso_flan

Bolt ModelingIn various engineering applications, it is necessary to define a pre-stress in, for example, bolt or rivets before applying any other structural loading. A convenient way do this is via the BOLT entry. The key idea is to split the element mesh of the bolt across the shank in two disjoint parts, such that duplicate grid points appear at the cut, and to create an overlap or gap between the two parts via multi-point constraints, which is done internally using the BOLT entry. If the motion of these parts is somehow constrained in the direction in which the gap or overlap is created, then an overlap (shortening) will introduce a tensile stress in each of the parts and a gap (elongation) will result in a compressive stress.

In this exercise, one coordinated systems (LCS4) is created automatically when automatic bolt creation option is used for Bolt-1 and other local coordinated systems is created manually (LCS6) using 3 points when assisted bolt creation option is used for Bolt-2.The local C/S is described through CORD2R entry.

CORD2R 6 0 1.625 0.75 3.04E-8 1.625 0.750.189808+ + 1.542650.921013 3.04E-8 BOLT_2

The BOLT entry is described below:

• New bulk data entry creates MPCs internally to all six degrees of freedom

• (GTi,GBi) are pairs of (usually are coincident) grids on top and bottom

• Same number of grid points should be in TOP and BOTTOM

• GRIDC is the control grid point (usually not connected to any element)

• Bolt loads prescribed on GRIDC

• Global Coordinate System has to be defined at the Control Node if the bolt direction is not a Basic Coordinate direction

• Loads in directions other than the bolt direction are possible

• The BOLT force can be output by MPCFORCE request output at each Control Node (GC)

• The new bulk data option, BOLT, supports only small rotations in this release. Since it is targeted to analyses of engine gasket joints, this is not considered a severe limitation

1 2 3 4 5 6 7 8 9 10

BOLT ID GRIDC +

+ TOP GT1 GT2 GT3 GT4 GT5 GT6 GT7 +

+ GT8 GT9 etc. +

BOTTOM GB1 GB2 GB3 GB4 GB5 GB6 GB7 +

GB8 GB9 etc.

1293CHAPTER 72

Automated Bolt Modeling

• Sufficient boundary conditions must be applied on the control grid to suppress any rigid body modes if the two parts of the structure are not constrained

• In a contact analysis, the amount of shortening is limited to the sum of the sizes of the elements in the direction in which the shortening is prescribed. If the shortening exceeds this limit, the contact surface patches will start to overlap each other, leading to problems with sliding.

BOLT 24910 6129 TOP 6130 6131 6132 6133 6134 6135 6136++ 6137 6138 6139 6140 6141 BOTTOM 5705 5706 5708 5764 5765 5767 5790++ 5792 5793 5861 5798 5795

Loading and Boundary ConditionsFigure 72-1 shows the loading and boundary conditions applied on the finite element model of the solid structure. Analysis is done in 5 load steps explained below.

Load step-1: Pre-tension force of 2000 lbf applied to Bolt-1

Load step-2: Pre-tension force of 2000 lbf applied to Bolt-2 and locking of the Bolt-1 using the SPC1 entry.

Load step-3: Locking of the Bolt-1 and Bolt-2 using SPC1 entry.

Load step-4: Load step-3 + point load of 3000 lbf applied to right face of the right flange via RBE2.

Load step-5: Remove the point load from load step-4.

SPCADD and LOAD cards define the single point constraint set and load set respectively. Displacement constraints and concentrated nodal forces are specified using SPC1 and FORCE cards, respectively.

Step-1SPCADD 49 6 8 11 12LOAD 50 1. 1. 7

Step-4SPCADD 52 6 8 11 12 13 14LOAD 52 1. 1. 10

$Force (2000lbf) applied on ‘control grid point’ of the Bolt-1 in automatically created coordinatesystem.FORCE 7 6129 4 1999.999 0.0 0.0 1

$Force (2000lbf) applied on ‘control grid point’ of the Bolt-2 in manually created coordinatesystem.FORCE 9 6142 6 1999.999 0.0 0.0 1.

$Force (3000lbf) applied on master node of the RBE2 elementFORCE 10 6156 3000. 0.0 0.0 1.

MD Demonstration Problems

CHAPTER 721294

$ Fix left endSPC1 12 123456 265 266 323 324 325 427+

$ X and Y translation d.o.f for bolt-1 is fixed (would be generated automatically if automaticbolt creation is used in SimXpert)SPC1 6 12 6129

$ X and Y translation d.o.f for bolt-2 is fixed (would be generated automatically even if assistedbolt creation is used in SimXpert)SPC1 8 12 6142

$ X, Y translation and all rotation is fixed for master node of RBE2 elementSPC1 11 12456 6156

$ To lock the bolt-1 for the coming load step, Z translation of first bolt is fixed in the comingload step.SPC1 13 3 6129

$ To lock the bolt-2 for the coming load step, Z translation of first bolt is fixed in the comingload step.SPC1 14 3 6142

ContactIn total, six deformable contact bodies are used. The first and second deformable body consists of all elements of left and right flange respectively. Third and fourth contact bodies consist of elements of Bolt-1 head and nut respectively. Fifth and sixth contact bodies consist of elements of Bolt-2 head and nut respectively

$ Contact Body: Deform_left_flangeBCBODY 1 3D DEFORM 28 0 $ Contact Body: Deform_right_flangeBCBODY 2 3D DEFORM 29 0

The BCTABLE entries shown below identify the admissible contact combinations, select the slave and master body for each combination, and set associated parameters. It is important to note that:

• The shaft part of the BOLT-1 and BOLT-2 have not been defined as a contact body to avoid the touching condition between shaft part of the BOLT-1 and BOLT-2 with holes of the left and right flange. If this touching condition will arises then correct magnitude of bolt pretension force will not be applied on the flanges and we will not get proper response of the bolt tightening/loosening.

• The ISEARCH entry is set to 0 (Double orders search, Default) the search order is from lower BCBODOY ID’s to higher ones first. If no contact is detected, then it searches the opposite order to force search order from the slave body to the master.

• Both bolts can touch the right flange and the both flanges can touch each other.

• The IGLUE entry is set to 1 for contact between both bolts and left flange to activate glued contact conditions (that is, no sliding and no separation) between these two contact bodies.

1295CHAPTER 72

Automated Bolt Modeling

BCTABLE 1 5 + $ Pair: Deform_bolt1_head / Deform_left_flange+ SLAVE 3 1 + + MASTERS 1 + $ Pair: Deform_bolt1_nut / Deform_right_flange+ SLAVE 4 + + MASTERS 2 +

• Segment-to-segment contact algorithm is used for this analysis, as compared to node-to-segment algorithm, the segment-to-segment algorithm will provide more accurate results in the contact area (specifically focusing on continuous contact stresses) and to make the results effectively independent of the numbering of the contact bodies and the contact detection order.

BCPARA 0METHOD SEGSMALL

Figure 72-2 Contact Table

Solution Procedure

The problem is analyzed in MD-Nastran using the SOL 400 routine which is an implicit nonlinear solutionprocedure. Control parameters for the nonlinear solution scheme are described through the NLSTEP entry. Total fiveNLSTEP have been used corresponding to each load-step.

NLSTEP 2 + + FIXED

3

2 615

4

Contact Body 1 2 3 4 5 61-Def-Deform_bolt1_head G2-Def-Deform_bolt1_nut T3-Def-Deform_bolt2_head G4-Def-Deform_bolt2_nut T5-Def-Deform_left_flange G G T6-Def-Deform_right_flange T T

MD Demonstration Problems

CHAPTER 721296

Results

Radius of the shaft (r) = 0.125 in; Pretension= 2000 lbf: Stress=2000/ (pi*r*r) = 40743.66 lbf/in2

Figure 72-3 Stress Component ZZ Load Steps 2 and 4

45,84146,99745,21444,14044,80145,130

Load step-1; stress-ZZ

Load step-2; displacement Z

Stress ZZ at nodes marked

1297CHAPTER 72

Automated Bolt Modeling

Figure 72-4 Stress Component ZZ Load Steps 2 and 4

Load step-2; displacement Z

Load step-4; displacement Z

MD Demonstration Problems

CHAPTER 721298

Figure 72-5 Stress Component ZZ Load Steps 2 and 4

Load step-2; stress-SZZ

Load step-4; stress-SZZ

1299CHAPTER 72

Automated Bolt Modeling

Figure 72-6 Stress Component ZZ Load Steps 2 and 4

Input File(s)Files Description

nug72.bdf MD input file

nug72.simxpert SimXpert Model file

Load step-2; stress-SZZ

Load step-4; stress-SZZ

MD Demonstration Problems

CHAPTER 721300

VideoClick on the image or caption below to view a streaming video of this problem; it lasts approximately 39 minutes and explains how the steps are performed.

Figure 72-7 Video of the Above Steps

Fixed End

Bolt 2

Bolt 1

Control Grid Points

3,000 lbf Applied