The pullout performance of square and dsr screw threads

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Issue: 06 | Jun-2014, Available @ http://www.ijret.org 310
THE PULLOUT PERFORMANCE OF SQUARE AND DSR SCREW
THREADS
Darshith S1
, Ramesh Babu K2
1
PG student, GT&TC, Mysore, Karnataka, India
2
Assistant professor, GT&TC, Mysore, Karnataka, India
Abstract
The screw threads used for fastening purpose are subjected to various type of loading. The majority of screw thread failure occurs
during tensile loading. The pullout is test is the measure of tensile loading. In this study the square and newly innovated DSR
screw threads are designed. The finite element analysis is carried out for the designed models by adopting the experimental
condition. The square and DSR screw threads are tested for the directional deformation, total deformation and von-mises stress.
Keywords: Finite element analysis, Pullout test, Square screw threads. Tensile loading
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1. INTRODUCTION
In many components the bolts may be subjected to a variety
of loading conditions, such as tension, compression, shear,
bending and torsion, which they must withstand without
suffering any permanent deformation or damage.
The strength of bolts is specified in terms of a tensile test of
the threaded fastener. The load versus elongation
characteristics of a bolt is more significant than the stress
versus strain diagram of the parent metal because
performance is affected by the presence of the threads. Also,
the stress varies along the bolt as a result of the gradual
introduction of force from the nut and the change in section
from the threaded to the unthreaded portion. The weakest
section of any bolt in tension is the threaded portion. [1].
Threaded components are generally used in assemblies
when a load-bearing connection that can be disassembled
without destructive methods is required in a design. The
mechanical performance of such components, and of the
assemblies in which they are used, is determined through
evaluation of properties such as axial or tensile strength,
torsional strength, shear strength, resistance to vibration
loosening, fatigue resistance, resistance to thermal cycling,
and hydraulic pressure integrity [2].
In view of a finite element analysis, two primary
characteristics of a bolted joint are a pretension and a mating
part contact. The pretension can generally be modeled with
a thermal deformation, a constraint equation, or an initial
strain. For a thermal deformation method, the pretension is
generated by assigning virtual different temperatures and
thermal expansion coefficients to the bolt and the flange. In
the case of the constraint equation method, the pretension is
a special form of coupling, with which equations can be
applied to govern the behavior of the associated nodes.
Initial strain method is more direct approach, in which the
initial displacement is considered as a portion of the
pretension on the structure with a bolted joint. A contact
modeling can be addressed using point-to-point, point-to-
surface, or surface-to-surface elements [5].
Numerous studies have reported the deformation and
damage to bolts under high tensile forces which were
exerted under low strain rates, but little is known about the
behaviour of bolts under high strain rates. Therefore, this
paper aims to measure the tensile strength and examine the
ways bolts are damaged when loaded in tension.
2. SCREW THREAD DESIGNING
The screw threads are designed according to ASTM
(American Society for Testing Materials) standards. The
every parameters, such as pitch (P), flank angle (θ), depth of
truncation of triangular height at crest (S1), depth of
truncation of triangular height at root (S2), effective
diameter (E), major diameter (D), minor diameter (d) and
depth of thread (h) of screw threads is considered during the
designing.
Fig: 1 Elements of basic form of symmetric thread
The relations existing between the elements for a screw
having equal flank angle are given by the following
equations
D= E+ ((1/2) p cot θ)-2 S1
d = E- ((1/2) p cot θ) +2 S2

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h =(1/2) p cot θ) – (S1+ S2)
The distance H is known as the height of fundamental
triangle, is given by
H= (1/2) p cot θ [3]
Fig: 2 Square threads.
The figure.2 describes the two dimensional square threads.
The screw threads are designed by using Ansys, the product
of SAS.IP.
The DSR thread is newly innovated thread. The DSR screw
thread is course thread, but having the advantages of the
square threads. The DSR thread is designing by keeping the
advantages of square threads. The sub tooth is provided in
the dedendumof square threads. The contact area between
the bolt and nut is directly proportional to strength of the
fastener.
Fig: 3.DSR threads
The figure.3 illustrates the DSR screw threads. The sub teeth
length is equal to pitch diameter of the screw thread and
width is equal to the half of the major teeth.
Table: 1. Design parameters of square and DSR threads.
Parameters Square threads DSR threads
OD 10mm 10mm
MD 9mm 9mm
H - 1mm
D - 0.5mm
3. TENSILE STRENGTH OF SCREW THREDS
The minimum tensile strength of a screw is the tensile stress
from which there could be rapture in the shank of thread
(not in head or shank joint) [4].
Tensile strength at rapture of thread
Rm= max tensile force F (N)/ stress area As (mm2
)
4. FINITE ELEMENT MODEL DESIGN,
CALIBRATION AND VALIDATION
The pullout phenomenon is simulated using the
ANSYS14.5. The thread bolt is assembled with the mating
nut, there should not be any interference between the
assembled bolt and nut.
4.1 Defining Contact
The Contact Tool allows examining contact conditions on
an assembly both before loading, and as part of the final
solution to verify the transfer of loads (forces and moments)
across the various contact regions. In square screw threads
17 edges selected to define the contact. In square screw
threads also the frictional contact is established between the
bolt and nut. . In DSR screw threads 41 edges selected to
define the contact. The frictional contact is given between
the bolt and nut.
Fig: 4. Defined contact in square threads.
Fig: 5. Defined contact in DSR threads
4.2 Meshing
The area which surrounds the screw andincludes the areas
where high stresses are expected to be developedwas
meshed with a fine and uniform mesh. The goal of meshing
in ANSYS Workbench is to provide robust, easy to use

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meshing tools that will simplify the mesh generation
process. These tools have the benefit of being highly
automated along with having a moderate to high degree of
user control. The quad dominant meshing is adapted for the
meshing of the bolt and nut assembles. This is one type of
surface meshing. The Quadrilateral Dominant method
(default), the body is free quad meshed. The minimum edge
length in DSR screw thread is 0.25mm. At the contact
region the edge size is reduced to 0.15mm. The minimum
edge length in square screw thread is 1.0mm. At the contact
region the edge size is reduced to 0.15mm. There are 4295
nodes and 1255 element in the two dimensional square
threads. There are 5179 nodes and 1491 elements in the two
dimensional DSR screw thread. The figure.7 illustrates the
meshing of two dimensional DRS and square threads.
Fig: 6. Meshing of square threads.
Fig: 7. Meshing of DSR screw threads
4.3 Defining Loads
The load is applied in the form of force. The force is applied
on the bottom face of the bolt. The load is acting in the
negative Y-axis. For experimental purpose 1000N is applied
for the analysis.
Fig: 8. Force applied for square screw threads
Fig: 9. Force applied for DSR screw threads
4.4 Defining Support
The Frictionless Supports are given in this case. The
Frictionless Supports applied to neighboring faces that meet
at an angle, the nodes on the edge are subject to two separate
combinations of degrees of freedom constraints, one from
each Frictionless Support. The Mechanical application
attempts to identify a suitable orientation to the nodal
coordinate system that accommodates both frictionless
supports and, if successful, constrain its axes accordingly.
Fig: 10. Support applied for square screw threads

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Fig: 11. Support applied for DSR screw threads
5. RESULTS
The tensile load is applied in the Y-axis, so the directional
deformation is applied in Y-axis. The total deformation is
also determined. The von-mises is determined for both
square and DSR threads.
Table: 2 Square thread analysis results
Minimum directional
deformation
-2.2349e-003 mm
Maximum directional
deformation
3.5194e-006 mm
Minimum total deformation 9.9161e-006 mm
Maximum total deformation 2.2381e-003 mm
Minimum von-mises stress 1.7934e-003 MPa
Maximum von-mises stress 68.328 MPa
Table: 3 DSR thread analysis results
Minimum directional
deformation
-1.7282e-003 mm
Maximum directional
deformation
3.4508e-006 mm
Minimum total deformation 3.2465e-006 mm
Maximum total deformation 1.7324e-003 mm
Minimum von-mises stress 9.2818e-006 MPa
Maximum von-mises stress 79.493 MPa
5.1 Directional Deformation
The figure 12 and 13 shows the directional deformation in
Y-axis. The both DSR and square threads are loaded to
1000N in vertical direction. The DSR threads are less
directionally deformed.
Fig: 12. Directional deformation of square screw threads
Fig: 13. Directional deformation of DSR screw threads
5.2 Total Deformation
The DSR and square threads are tested for total deformation.
The DSR threads are having good values than the square
threads in total deformation. The DSR thread are having less
directional and total deformations, hence it can withstand
more tensile strength
Fig: 14. Total deformation of square screw threads
Fig: 15. Total deformation of DSR screw threads

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5.3 Von-Mises Stress
The figure 16 and 17 shows the von-mises stress in DSR and
square threads. The DSR threads are having more von-mises
stress than square threads.
Fig: 16. Von-mises stress in square screw threads
Fig: 17. Von-mises stress in DSR screw threads
The both DSR and square threads are subjected to tensile
and square deformations, but the DSR threads subjected to
less deformation. The total deformation is also determined
for the screw threads, the DSR threads shows less total
deformation against the square threads, but DSR threads are
having more von-mises stress compared to square threads.
6. CONCLUSIONS
From the above experimentation we may conclude that. The
DSR screw threads are having
(i) More pullout strength than square screw threads.
(ii) More contact area than the square screw threads.
(iii) More adjustmental accuracy.
(iv) Less mis-alignment
REFERENCES
[1]. Geoffrey L. Kulak, John W. Fisher, John H. A. Struik,
“Guide to Design Criteria for Bolted and Riveted Joints
Second Edition” American institute of steel construction,
inc.
[2]. F.M. Leon, N.G. Pai, D.P. Hess, “The effect of thread
dimensional conformance on yield and tensile strength”,
Engineering Failure Analysis 8 (2001) 49-56.
[3]. P.A. Sidders, “Guide to world screw threads” First
American edition.
[4]. Howard. E. Adt, Screw thread production to close
limits, first edition, The Stirling press, New York.
[5]. Jeong Kim, Joo-Cheol Yoon, Beom-Soo Kang, “Finite
element analysis and modeling of structure with bolted
joints”, Applied Mathematical Modelling 31 (2007) 895–
911.

The pullout performance of square and dsr screw threads

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The pullout performance of square and dsr screw threads