Residual Stresses and Deformations in Steel Structures

228 Pages·2001·12.99 MB·English

by  Lars Fuglsang Andersen

Technical University of Denmark
Residual Stresses and
Deformations in Steel Structures
Lars Fuglsang Andersen
PhD thesis
December 2000
Department of
Naval Architecture
And offshore engineering

Residual Stresses and Deformations in Steel
Structures
Lars Fuglsang Andersen
DEPARTMENT OF NAVAL ARCHITECTURE AND OFFSHORE ENGINEERING
TECHNICAL UNIVERSITY OF DENMARK KGS. LYNGBY
(cid:1)
DECEMBER 2000
Department of Naval Architecture and O(cid:11)shore Engineering
Technical University of Denmark
Studentertorvet, Building 101E, DK-2800 Kgs. Lyngby, Denmark
Phone [phone], Telefax [phone]
e-mail [email protected], Internet http://www.ish.dtu.dk/
Published in Denmark by
Department of Naval Architecture and O(cid:11)shore Engineering
Technical University of Denmark
c L. F. Andersen 2000
(cid:13)
All rights reserved
Publication Reference Data
Andersen, L. F.
Residual Stresses and Deformations in Steel Structures.
PhD thesis.
Department of Naval Architecture and O(cid:11)shore Engineering,
Technical University of Denmark, December, 2000.
ISBN 87-89502-46-9
Keywords: Numerical welding simulation, dynamic meshing,
weldingresponse prediction,experimentalresidual
stress evaluation.
Preface
Thisthesisissubmittedasapartialful(cid:12)lmentoftherequirementsfortheDanishPhDdegree.
The work has been performed in collaboration with the Department of Naval Architecture
and O(cid:11)shore Engineering, the Technical University of Denmark, and Odense Steel Shipyard
Ltd.duringthe periodof June 1997toFebruary 2001, includingsix months’leave ofabsence.
The study has been supervised by Professor Dr. Techn. J(cid:28)rgen Juncher Jensen, whose help
and encouragement have been highly appreciated.
The study was (cid:12)nancially supported by the Danish Academy of Technical Science (ATV)
and Odense Steel Shipyard Ltd. The support is greatly acknowledged.
Special thanks to Lars-Erik Lindgren at Lule(cid:23)a University of Technology for inspiring discus-
sions and a pleasant stay. Also thanks to my co-supervisors Lars Malcolm Pedersen, Ann
Bettina Richelsen and Henning Kierkegaard for their interest.
Thanks to my colleagues at ISH, friends and family for invaluable help and support. Special
thanks to Linda for her support and understanding during the entire study.
i
ii Preface
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Executive Summary
The objective of the present thesis is to contribute to the understanding of process-related
distortions and stresses in steel structures. The following main aspects are covered:
1. Production strategy emphasising distortion minimisation
2. EÆcient numerical simulation of welding
3. Experimental method for residual stress evaluation
The work concerning production strategy primarily serves to put welding simulation and
residual stress evaluation into an overall perspective and to describe the factors motivating
the present work. However, instead of merely describing the problems caused by geomet-
rical distortions, a new production strategy is proposed with the emphasis on the e(cid:11)ect of
distortion minimisation. The intention is merely to establish a basis for discussion of the
technological paradigm of a shipyard and its relation to competitive power.
The objective of the second part of the thesis is to enable welding response prediction in
large-scale industrial welding applications. This objective is achieved by the development
of a dedicated ’welding simulation package’ using a commercial software as platform for the
software development. Initially, a basic model is established allowing the essential welding
mechanics to be captured. Dynamic activation of (cid:12)llet elements, dynamic coupling of parts,
contact modelling and tack weld modelling are identi(cid:12)ed as essential factors for accurate
prediction of the distortion (cid:12)eld. On this basis, the computational eÆciency is subsequently
increased by the implementation of a graded element and the development of an eÆcient
dynamic mesh re(cid:12)nement scheme. An investigation of the mesh density in dynamic meshing
shows that good predictions of the qualitative distortion pattern may be obtained with
few elements if the mesh density is appropriately distributed. The experienced increase in
eÆciency is considerable and allows not only models to be computed within shorter time but
also to simulate welding applications which were previously far beyond the computational
capability.
For further increase of the computationaleÆciency, a template combiningseveral techniques
such as dynamic meshing and substructuring is developed. The combination of local solid
iii
iv Executive Summary
models and a global shell model makes it possible to represent properly the boundary condi-
tions for the weld region and to calculate the distortions in a large-scale structures by taking
into account variations in structural sti(cid:11)ness, welding sequence, tack weld positioning, weld-
ing parameters etc. The basic capability needed for a welding response prediction tool is
thus established.
Figure 1: Predicted shape of a fully welded assembly (scale 15).
The objective of the third part of the thesis is to enable residual stress evaluation in steel
platesinordertoallowthe potentialin(cid:13)uenceofresidualstress onprocess-relateddistortions
tobeevaluated. Ashortreviewofexistingexperimentalstressmeasuringmethodsshowsthat
none of these are suitable for the purpose, and a modi(cid:12)edincremental hole-drillingtechnique
isthereforedeveloped. Ananalysisofthehole-drillingcon(cid:12)gurationrevealsthatconsiderable
improvementsmaybeobtainedbyoptimisingthehole-drillingcon(cid:12)gurationtoplatesof(cid:12)nite
thickness. This results in a set of guidelines improving the stress calculationaccuracy, which
is supported by an extensive error analysis. As the incremental hole-drilling technique does
not allowthe residualstresses tobe resolved through the entire plate thickness, itis modi(cid:12)ed
to include two coupled measurements which solve the problem.
Synopsis
Form(cid:23)alet med n(cid:26)rv(cid:26)rende studium er at bidrage til forst(cid:23)aelsen af procesrelaterede deforma-
tioner og sp(cid:26)ndinger i st(cid:23)alkonstruktioner. Arbejdet er inddelt i f(cid:28)lgende hovedomr(cid:23)ader:
1. Produktionsstrategi fokuseret p(cid:23)a deformationsminimering
2. Beregningse(cid:11)ektiv simulering af svejsedeformationer
3. Eksperimentel metodeudvikling for evaluering af residualsp(cid:26)ndinger
Arbejdet omhandlende produktionsstrategi, s(cid:26)tter svejsesimulering og residualsp(cid:26)ndings-
m(cid:23)aling ind i et overordnet perspektiv og beskriver de faktorer, der motiverer dette studium.
Derudover foresl(cid:23)as en ny produktionsstrategi med fokus p(cid:23)a minimering af deformationer.
Hensigten er at skabe et grundlag for diskussion af et skibsv(cid:26)rfts teknologiske paradigme og
dets relation til konkurrenceevne.
Form(cid:23)alet med anden del af studiet er at g(cid:28)re det muligt at forudsige svejsedeformationer
og sp(cid:26)ndinger i relativt store industrielle svejseapplikationer. Dette m(cid:23)al n(cid:23)as gennem etab-
lering af en dedikeret ’svejsesimuleringspakke’, der udarbejdes med et kommercielt software
som platform for programudviklingen. Indledningsvist etableres en grundmodel, der tillader
modellering af de v(cid:26)sentlige svejsee(cid:11)ekter. Dynamisk aktivering af tilsatsmateriale, dy-
namisk kobling af de enkelte dele under svejsning og kontaktmodellering identi(cid:12)ceres som
v(cid:26)sentlige faktorer for bestemmelse af deformationsm(cid:28)nsteret. Baseret p(cid:23)a denne grund-
model for(cid:28)ges beregningse(cid:11)ektiviteten herefter ved implementering af graduerede elementer
og udvikling af dynamiske netgenereringsalgoritmer. En analyse af net(cid:12)nheden viser, at
deformationsm(cid:28)nsteret med god n(cid:28)jagtighed kan forudsiges ved anvendelse af relativt f(cid:23)a ele-
menter, s(cid:23)afremt disse fordeles hensigtsm(cid:26)ssigt. En v(cid:26)sentlig e(cid:11)ektivisering opn(cid:23)as herved og
tilladerikke kun hurtigere beregningmenogs(cid:23)asimuleringafsvejseapplikationer, der tidligere
var uoverkommelige.
For yderligere at (cid:28)ge beregningse(cid:11)ektiviteten udvikles en metode, der kombinerer forskel-
lige teknikker som f.eks. dynamisk netgenerering og superelementer. Kombinationen af
en global skal-element model og lokale ’solid’-modeller tillader passende modellering af
randbetingelserne for svejseomr(cid:23)adet samt deformationsberegning i sammensatte konstruk-
tioner under hensyntagen til variationer i strukturel stivhed, svejser(cid:26)kkef(cid:28)lge, placering af
v
vi Synopsis
h(cid:26)ftes(cid:28)mme, svejseparametre m.v. Den grundl(cid:26)ggende funktionalitet som er n(cid:28)dvendig for
et generelt svejsesimuleringsv(cid:26)rkt(cid:28)j er hermed etableret.
Form(cid:23)aletmedtredje delafrapporteneratevaluereresidualsp(cid:26)ndningstilstandenist(cid:23)alplader
for herigennem at kunne estimere deres potentielle ind(cid:13)ydelse p(cid:23)a procesrelaterede deforma-
tioner. En hurtig gennemgang af eksisterende eksperimentelle metoder til residualsp(cid:26)nd-
ingsm(cid:23)aling viser, at disse ikke er umiddelbart egnede til form(cid:23)alet, og en modi(cid:12)ceret inkre-
mentel hulboringsmetode udvikles som f(cid:28)lge heraf. En analyse af hulboringskon(cid:12)gurationen
afsl(cid:28)rer, at v(cid:26)sentlige forbedringer kan opn(cid:23)as ved optimering af kon(cid:12)gurationen til plader
af endelig tykkelse. Dette resulterer i et s(cid:26)t retningslinier, der minimerer usikkerheden
i sp(cid:26)ndingsberegningen, hvilket kommer til udtryk i den efterf(cid:28)lgende og omfattende fe-
jlanalyse. Idet inkrementel hulboring ikke tillader residualsp(cid:26)ndingsm(cid:23)aling gennem hele
pladens tykkelse, modi(cid:12)ceres denne til at omfatte to koblede m(cid:23)alinger, hvorved problemet
l(cid:28)ses.