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