Table Of ContentSCHOOL
S"Sk'''-?oS'E
BOLTED JOINT STUDIES IN GRP
by
David M. Fox
B.S., Chemical Engineering
Rose-Hulman Institute of Technology, 1984
Submitted to the Department of Ocean Engineering and the
Department of Matenals Science and Engineering
in Partial Fulfillment of the Requirements for the Degrees of
Naval Engineer
and
Master of Science in Matenals Science and Engineering
at the
Massachusetts Institute of Technology
May 1994
1994 David M. Fox. All rights reserved. The author hereby grants to MIT and the
U.S. Government permission to reproduce and to distribute publicly paper and
electronic copies of this thesis document m whole or in part.
DUDLEYKNOXLIBRARY
NAVALPOSTGRADUATE SCHOOl,
BOLTED JOINT STUDIES IN GRP
by
DAVID M. FOX
Submitted to the Department of Ocean Engineering and the Department of Materials
Science and Engineering on 6 May 1994 in partial fulfillment of the requirements for
the Degrees of Naval Engineer and
Master of Science in Materials Science and Engineering.
ABSTRACT
An experimental study was carried out to determine the bolt clampup force relaxation
behavior in countersunk, single-lap bolted joints between glass/vinylester resin
laminates and steel panels. Additionally, the effect of bolt clampup force relaxation on
the bearing strength of such joints was studied.
Specially-instrumented bolts were used to measure clampup force relaxation in ten
countersunk joint specimens. A 100,000 pound capacity MTS testing machine was
used to evaluate the bearing strength in tension of sixteen countersunk bolted joint
specimens torqued to four different levels of initial torque, as well as four similar
protruding-head bolted joint specimens (at the same levels of torque).
The results of the relaxation experiments indicate that clampup force varies widely in
nominally identical joints at identical torque levels, by as much as a factor of two. In
countersunk bolt joints with sufficiently high initial clampup force, the clampup force
relaxed in accordance with the inverse power equation proposed by Shivakumar and
Crews for protruding-head bolt joints in graphite/epoxy laminates. Relaxation in the
present experiments proceeded faster than in the protruding-head joints studied by
Shivakumar and Crews; this is believed to have been due to the relative lack of
GRP
constraint provided at the surface by the countersunk bolt.
The results from the bearing strength experiments suggest that clampup force has only
a small beneficial effect on bearing strength in both countersunk and protruding head
single-lap joints, when compared to double-lap joints. The reduced effectiveness of
clampup force in increasing the bearing strength is believed to be a result of the
increased joint rotation and bolt bending inherent in single-lap joints. These
phenomena lead to delamination and brooming failure in the GRP, which can be
avoided in double lap joints with sufficient bolt clampup force. The countersunk
joints failed at a load approximately 20% lower than the protruding head joints.
Thesis Advisor: Frederick J. McGarry
Title: Professor of Civil Engineering and Polymer Engineering
Table of Contents
Abstract 2
List of Illustrations and Figures 5
List of Tables 6
Acknowledgements 7
Chapter 1. Introduction 8
1.1 Overview 8
1.2 Background 9
Theoretical Models of Bolted Joint Mechanical Behavior .... 11
Finite-Element Modelling of Bolted Joint Mechanical Behavior 17
Empirically-Derived Relaxation Predictive Equation 18
Related Work 18
Chapter 2. Experimental Procedure 20
2.1 Experimental Materials 20
Overview 20
Description of Materials 20
2.2 Experimental Set-Ups 25
Relaxation Experimental Set-Up 25
Bearing Strength Experimental Set-Up 28
Chapter 3. Experimental Results and Discussion 33
3.1 Results of the Relaxation Experiments 33
3.2 Results of the Bearing Strength Experiments 36
3.3 Discussion of Relaxation Experimental Results 39
Correlation of Initial Torque with Initial Clampup Force 39
Clampup Force Relaxation Behavior 45
3.4 Discussion of Bearing Strength Experimental Results 51
Bearing Strength Definition 51
Sequence of Events in Bearing Strength Tests 53
Effect of Clampup Force on the Failure Modes
in Each of the Two Joint Types 58
Effect of Clampup Force on Bearing Strength 59
Chapter 4. Conclusions and Recommendations 63
4.1 Conclusions Concerning Relaxation Behavior 63
4.2 Conclusions Concerning Bearing Strength Behavior 64
4.3 Recommendations 67
