10.23.2.1 Overview of Modeling bolted connections Video This video demonstrates how to model a bolt that is held in place with a nut.
Video This video demonstrates how to model a bolt in a tapped (threaded) hole. Use the Bolt Connection command Connection command to model the following types of bolted connections with finite elements: •
A bolt that is held in place with a nut.
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A bolt in a tapped (threaded) hole.
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A bolt-type connection that is represented by only a spider element at the unction plane between two mating bodies.
Bolted connections are solver specific !ith Bolt Connection" Connection" how the software models the bolt depends on your specified solver environment. Typically" Typically" #$ elements are used to model the bolt%s shan&. To connect those #$ elements to t he nodes in the surrounding mesh" the software creates a spider-type connection. •
'n astran models" the software uses rigid or constraint elements to create the connection. ach connection has a single central node with multiple leg nodes that branch out from the central node in a spider-li&e pattern. *or more information" see Understanding spider elements in bolted connections.. connections 'n Aba+us and A,, models" the software uses specific types of constraint boundary conditions to create the connection.
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Solver
Bolt shank
Spider-tpe connection
astran
#$ elements" such as /A0 or /A1 elements2
0/3 or 0/4 elements
Aba+us
#$ elements" such as /4# or /3# elements2
25'1AT' 6U78'9 constraint
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A,,
#$ elements" such as /A1 or /A1#;; elements2
0'9"7 constraint e+uations
2ou can also choose to model the bolt with a #$ spring e lement" rather than with a #$ beam element. ,ee 1odeling the bolt%s shan& with a spring element for more information. The following graphic shows an assembly in the astran environment that is connected together by bolts in several tapped bolt holes. (A) shows the model with meshes created on the individual components.
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(/) shows the model with the bolt connections generated in the bolt holes.
!efining the characteristics of a bolt ou use the Bolt Connection dialog bo= to specify all the in formation necessary to create a bolted connection. This i nformation includes the type of bolt" &ey bolt dimensions" and attributes for the beam and connection elements that the software creates to model the bolt. The following graphic shows the &ey dimensions for the two main types of bolts. •
(A) is the diameter of the bolt%s head. 'n the Bolt Connection dialog bo=" you can select either the edge of a hole or the center point of the hole to define the location of the bolt%s head.
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(/) is the overall length of the bolt" including the head. 'f you create a bolt in a tapped hole" you must specify the bolt%s length in theBolt Connection dialog bo=. () is the diameter of the bolt%s nut. 'n the Bolt Connection dialog bo=" you can select either the edge of a hole or the center point of the hole to define the location of the bolt%s head. ($) is the diameter of the bolt%s shan&. ou control the diameter of t he bolt through the beam cross section you associate with the #$ e lement that represents the beam%s shan&. *or more information on beam cross sections" see /eam cross section overview. () is the effective thread length for a bolt. *or a bolt in a tapped hole" you must specify the effective thread length in theBolt Connection dialog bo=. ote
The specified "ffective #hread $ength must be less than the specified Bolt $ength.
/olt with a nut
Threaded bolt for a tapped hole
%dditional tools to facilitate bolt &odeling and definition The following commands can ma&e it easier for you to define bolted connections: •
The Circ'lar "dges smart selection method lets you select circular edges in your model based on a specified radius. This selection method is helpful when you select the hole edges that define the bolt%s head and nut.
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*or more information" see ,elect circular edges. •
The Clindrical (aces smart selection method lets you select cylindrical surfaces in a body based on specified minimum and ma=imum angle or radius values. This selection method is helpful when you create a Bolt in #ap type connection and need to select the tapped surface.
*or more information" see ,elect cylinder faces. •
The Circ'lar )&print command subdivides a face and creates a circular polygon edge around either a selected point or an e=isting circular or elliptical edge. !hen you model bolted connections" you can use Circ'lar )&print to create circular edges around the bolt holes. The result is a more structured" layered mesh around the bolt hole. *or more information" see 'mprinting circular edges on a face.
!efining a pre-load on a bolted connection After you use the Bolt Connection command to model bolts" you can use the Bolt *re-$oad command to define a pre-load on t he bolt. *or more information" see /olt pre-load.
+here do ) find it, 6n the %dvanced Si&'lation toolbar" clic& Bolt Connection
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10.23.2.2 nderstanding spider ele&ents in bolted connections The locations at which the software creates the spider-type connections depend on the bolt%s type. •
*or the Bolt +ith 't type" the software creates spider-type connections to the nodes on the contact surfaces for the head and the nut. 'n the following graphic (A) shows the bolt" while (/) shows a display of only the finite elements that comprise the bolt. otice th e spider connections at the bolt%s head and nut.
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*or the Bolt in #apped /ole type" the software creates spider-type connections to all nodes that lie along the length of the engaged threads in the tapped hole. ou use the "ffective #hread $ength option in the Bolt Connection dialog bo= to define the length of the engaged threads. 'n the following graphic (A) shows the bolt in a tapped hole" while (/) shows a display of only the finite elements that comprise the bolt. otice how the legs of the spider elements connect along that entire effective thread length.
*or the Spider at 'nction type" the software creates spider-type connections to the nodes on the specified unction planes. 'n the following graphic (A) shows the two spider elements a t the unction plane. (/) shows a display of only the finite elements that comprise the spider-type connection.
ou can control whether the software creates the spider connection to the corner nodes or the corner nodes and the midnodes of the elements in the surrounding mesh. 'f you select the Connect Spider to Midnodes option in the Bolt Connection dialog bo=" the software creates the spider connection to the midnodes in addition to the corner nodes. 'n the following graphic" (A) shows a spider connection to only the corner nodes of the surrounding mesh. (/) shows a spider connection to both the midnodes and the corner node s.
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!efining spider-tpe connections at an inter&ediate 'nction plane *or the Bolt +ith 't and Bolt in #apped /ole types" you can use the Create Spider at 'nction *lane option in the Bolt Connection dialog bo= to have the software create an additional spider-type connection at an intermediate unction plane between the mating bodies. The following graphic shows an e=ample of a Bolt with 't type of bolt that was created with the Create Spider at 'nction *lane option selected.
(A) shows the location of the spider connection at the bolt%s head.
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(/) shows the location of the unction plane.
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() shows the location of the spider connection at the bolt%s nut" which is located on the underside of the unction plane.
This graphic shows only the finite element model of the bolt itself. otice the spider connections at th e bolt%s head (A)" unction plane (/)" and nut ().
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Controlling the sie of the spider-tpe connection The Spider !ia&eter option in the Bolt Connection dialog bo= controls the overall diameter of the spider connection. •
*or the Bolt +ith 't type" you can control the diameter of the connection at both the bolt%s head and nut.
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*or the Bolt in #apped /ole type" you can control the diameter of the connection at the bolt%s head.
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*or the Spider at 'nction type" you can control the diameter of the connection at the specified unction planes.
ou can define the diameter of the spider as eit her a percentage of the hole that you used to defi ne the location of the bolt%s head>nut or unction plane. ou can also define the spider%s diameter as a scale factor. 'n general" the diameter of the spider should be at least as large as t he bolt%s head and>or nut. *or a bolt connection to be sufficiently rigid" the spider elements must connect to a sufficient number of nodes on the bolt%s contact surfaces (the head" nut" and any unction planes). ou can use the Circ'lar )&print command to create circular edges around the bolt holes in the contact surfaces at the bolt%s head" nut" or unction plane. /y imprinting an additional circle around the ends of the bolt hole" you ensure that the legs of the spider elements created at the bolt%s head and nut have sufficient nodes in the surrounding mesh to which to connect. *or more information" see 'mprinting circular edges on a face. Tip 'f you use the %bsol'te !ia&eter option in the Circ'lar )&print dialog bo= to define a new circular edge around a bolt hole" use that diameter as the Spider !ia&eter value in the Bolt Connection dialog bo=. The following graphic shows a bolt hole surrounded by a larger imprinted edge that was created with the Circ'lar "dge command. •
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(A) shows the spider element when its diameter is e+ual to #??@ of the diameter of the hole. otice how the legs of the spider element only connect to the nodes on the edge of the bolt hole. (/) shows the spider element when its diameter is e+ual to the diameter of the imprinted edge (?mm). otice how the legs of the spider element now connect to the nodes along the edge of the imprinted circle.
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10.23.2.3 Modeling the bolts shank with a spring ele&ent ou can also model the bolt%s shan& as a ero-length spring element instead of a beam element. ou may want to model the bolt with a spring element if you want to directly define the stiffness at the bolted oint and ma&e force recovery simpler. !hen you solve your model" you can e=tract the forces or moments at the location of the spring.
'f you use a spring element to model the bolt%s shan&" the software creates two coincident nodes in the middle of the bodies on which the head and nut or the head and tap are defined. The software connects the two nodes with a ero-length spring element. The two nodes are the core nodes for two spidertype connection elements. •
*or the spider connection for the head of a bolt" the legs connect to all the nodes inside the head diameter on the specified head contact surface.
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*or the spider connection for the nut of a bolt" the legs connect to all the nodes inside the nut diameter on the specified nut contact surface.
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*or the spider connection for a tapped surface" the legs connect to all the nodes along the length of the tapped hole that lie within the specified "ffective #hread $ength.
The following graphic shows an e=ample of bolt between a head and a nut that is modeled with a spring element. •
(A) shows the location of the two coincident nodes that are connected by a ero-length spring element. The distance between the nodes shown here has been e=aggerated here for illustration purposes only. (/) shows the connections between the leg nodes of the bolt-side spider element and the nodes inside the head diameter.
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() shows the connections between the leg nodes of the nut-side spider element and the nodes inside the nut diameter.
