Workshop Description
 
MOTIVATION
 
NIST's work on the fundamental mechanisms of work hardening is driven by industrial needs.  Metal forming is an enormous industry in the United States, with value added amounts in the tens of billions of dollars annually.  It is one of the nation's largest consumers of mild and high strength steel, as well as aluminum alloys.  The automobile industry is the largest single user of sheet metal:  sheet metal products comprise approximately 33% of the weight of an automobile.  An improvement in the efficiency of metal forming operations would have a large impact on the U.S. economy.
 
The cost of forming complex metal parts such as automobile panels is dominated by two factors: the large initial cost of designing and producing the die, and the cost of the metal sheet.  NIST work in this area is aimed at reducing the time and expense of designing dies.  Most dies are still designed using rules-of-thumb that are based upon long experience with specific metal alloys.  Increasingly, however, dies are being designed using Finite Element Analysis (FEA) which predicts the behavior of the metal sheet during stamping.  In practice, the die never produces an acceptable part on the first attempt, and the die must be extensively redesigned and reworked.   The redesign process is done by hand using intuition by experienced craftsmen.  Reworking involves resurfacing the die contour, reprogramming the cutter path, and re-machining.  This expensive and time consuming process is repeated until a properly shaped panel is produced with an acceptable failure rate.  For mild steel parts, a total of 8-10 tryout steps are often required.
 
Improvements in this process are extremely important to the automotive industry, which is attempting to switch to high strength steels and aluminum alloys to save weight and improve fuel economy.  The behavior of these materials during stamping is vastly different from the currently used mild steel, and poorly understood.  The time and cost of die production for use with these materials is projected to be unacceptably high without improved FEA modeling tools.  Such improvements would eliminate much of the trial-and-error that currently exists, thereby decreasing the time and cost of new product development, and allowing production of lower-tolerance parts.  Since improved FEA would primarily reduce the high initial fixed costs for a stamping run, small-run manufacturing costs would be reduced by an even greater margin.
 
The fundamental reason why current FEA codes are inadequate is that the models used to predict the behavior of the metal sheet are strictly empirical and do not reflect the microstructural changes that are responsible for the observed changes in mechanical behavior during deformation.  Understanding this process is a necessary prerequisite to developing more accurate deformation models based on changes in the dislocation microstructure.
 
HISTORY
 
Research on the microstructural basis of work hardening (dislocations) was a tremendously active field in the 1940's through roughly the mid seventies.  Work in the field diminished significantly at this time for several reasons, in large part due to a perception that the problem was too complex to solve adequately with the tools (theoretical, computational, and experimental) then available.  Funding sources dried up and work in this field came mostly to a halt (although a few researchers continued to make slow but steady progress).
 
The first NIST workshop on work hardening and dislocations was held at NIST in the summer of 1995. This meeting was informal and exploratory in nature, and was held to determine whether the past twenty years of progress in science and technology provided the necessary tools for further advancements in the basic understanding of work hardening.  The unanimous conclusion was that the time was ripe for a renewed effort, and that a renaissance in the field was likely in the near future.  In large part, this conclusion was driven by new large-scale computer simulations of dislocations in 3D being conducted by Kubin and Canova in France.  However, it became clear that significant progress could only be achieved through collaborative efforts.  Owen Richmond from ALCOA challenged all of the participants to work on developing a quantitative model for the deformation of single-crystal Al.
 
Robb Thomson and Lyle Levine at NIST began working full time in this area, with most of the early research aimed at developing new experimental methods for studying the development of dislocation structures in situ and in bulk-thickness samples.  Work was aimed primarily at aluminum, due in large part to an active collaboration with researchers at ALCOA.

Over the next few years, NIST personnel organized American Physical Society focus sessions on the fundamental mechanisms of mechanical properties (primarily work hardening).  The organizers of these focus sessions were:

 
Lyle Levine (NIST) & Robb Thomson (NIST), Kansas City, MO, March 1997
Lyle Levine (NIST) & Hussein Zbib (WSU), Los Angeles, CA, March 1998
 
From the large response to these meetings, it was clear that activity in the field was growing rapidly.  A second (much larger) workshop was planned to be held in conjunction with a Short Course on the same topic being held by LLNL.  The workshop was held in Pleasanton, CA in June 1998, and it was organized by Lyle Levine & Robb Thomson (NIST) and Hussein Zbib & John Hirth (WSU).

DESCRIPTION OF WORKSHOP

The purpose of the workshop was to explore the current status of this multi-disciplinary field and to promote collaborative efforts.  The workshop was open only to invited participants.  The invitation list included all of the most prominent U.S. researchers in the field along with a few very prominent researchers from outside the U.S.
 
RESULTS
 
All of the participants agreed that the workshop was a great success.
During the presentations and the discussion sessions, several important points were made.  The most important point was that there exists a severe lack of communication between researchers working on different length and time scales.  For example, researchers conducting atomistic simulations want their work to be relevant to work going on at larger length scales, but they were mostly in the dark concerning what simulations would be relevant.  On the opposite end of the spectrum, researchers who are developing three dimensional dislocation dynamics codes require atomistic-level information on stacking fault energies, kink pair nucleation processes, cross-slip nucleation, and junction formation and breaking.  This workshop was therefore instrumental in allowing important connections to made between the diverse research groups.

The groundwork was also laid for several collaborative research endeavors that directly affect NIST's research efforts in this field.  Drs. Levine and Thomson from NIST are currently involved in two large multi-institution collaborations with people they met at this workshop.  In addition to participants from several national laboratories and Universities, these two collaborations include participants from more than 20 companies including steel and aluminum producers, FEA software companies, automobile manufactures, and aerospace companies.
 
Finally, it was decided at the workshop that international communication in the field was lacking, and that a full international conference on the fundamentals of work hardening should be held.   Work on this conference began immediately.  The conference, called Dislocations 2000, will be held at NIST on June 19-22, 2000.  Full details may be found on the NIST Dislocations 2000 web site.