as the best potential compliance with existing stan 
of measuring the stress is necessary.  Once the de 
dards.  It was decided to use the draft ISO STEP
gree of stress can be identified and measured inex 
AP 226 as the basis for the development of a ge 
pensively, corrective actions can be taken to reduce
neric list of objects.
the stress and thereby reduce distortion before other
A  draft  ship  breakdown  structure  was  devel 
manufacturing processes are impacted.
oped  for  mechanical  products.    The  proposed
Traditional methods of measuring stress are Strain
breakdown uses an object oriented approach simi 
Gage Hole Drilling (SGHD) and X Ray Diffraction
lar to the approach recommended by ISO 10303.
(XRD).    Other  methods,  such  as  Synchrotron  and
Four levels of indenture from the ship to the main 
Neutron Diffraction, are available but are considered
tenance  part  are  proposed.  A  definition  is  pro 
to not have a high degree of reliability.  The Univer 
vided for each object along with a list of proper 
sity of New Orleans, College of Engineering (UNO
ties  for  identification  and  RAM  data  exchange.
COE)  has  recently  undertaken  a  project  to  assess
The  draft  breakdown  structure  is  currently  be 
the capabilities of a new technology for measuring
ing reviewed by the project advisory board.
residual stress in materials.  This technology is called
The immediate objective is to turn the proposed
Laser Holographic Hole Drilling (LHHD).  In the mid 
draft into an official draft with the American Society
1980s, research found that holographic hole drilling
for Testing and Materials.  A further objective would
caused an interference fringe pattern related to the
be to expand the scope of the standard.  In particu 
displacements that occurred as a result of the hole
lar, advisory board members expressed the need to
drilling to the sub surface residual stress.  In 2000,
include software applications, which are becoming a
in plane sensitive electronic speckle pattern inter 
critical element in modern ship design with respect
ferometry with automated fringe analysis was de 
to RAM assessment. This project is sponsored by the
veloped for rapid stress analysis.  The attainment of
Office of Naval Research s Navy Manufacturing Tech 
real time or near real time results of the tests are
nology Program through the Gulf Coast Region Mari 
now available.  Typically one RS measurement takes
time Technology Center (GCRMTC) at UNO COE.
only five minutes.
The research team at UNO COE will measure RS
Test
in test specimens by using several techniques in 
cluding SGHD, XRD, and LHHD.  SGHD and XRD
were selected as they are the industry standards.
Measurement of Residual Stress in Steel
Each of the three methods for measuring RS has
Plates
its advantages and disadvantages.  However, if the
results of this project are as anticipated, LHHD may
become the preferred method of measuring RS in
Laser  Holographic  Hole  Drilling  research  con 
the shipbuilding industry.  The advantages of LHHD
ducted at the University of New Orleans, College of
over other methods include portability and quick 
Engineering has the potential of making residual
ness, no surface preparation, no costly strain gages,
stress analysis measurements an inexpensive, quick,
automated drilling and data analysis, requires only
and highly accurate process for industry.
two  material  properties  (Young s  Modulus  and
Poisson s Ratio), and it is semi destructive (it does
The shipbuilding industry is beginning to imple 
require hole drilling).  By comparing the results of
ment new technologies such as automated welding,
the three technologies, using identical base mate 
cutting,  and  material  movement  in  shipbuilding
rial conditions, the most effective test method will
processes.  In order for these technologies to work
be decided upon.
as envisioned, the shipyards will have tighter di 
mensional  control  of  parts  and  must  develop  in 
creased control of distortion of parts.  The distor 
Evaluation of Hex Chrome Exposure Levels
tion  of  steel  plates  is  almost  always  due  to  the
in the Shipbuilding Industry
Residual Stress (RS) that is caused by manufactur 
ing processes.  Some of those processes are milling,
The University of New Orleans, College of Engi 
drilling, cutting, grinding, and welding   all neces 
neering measured Hex Chrome exposure levels un 
sary steps in the manufacturing of ships.  Since the
der  actual  field  conditions  for  arc  welding  in  the
elimination of RS is not possible using today s manu 
shipbuilding industry.
facturing process, an inexpensive and quick method
17
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