Investigators:

Dr. Pan Michaleris             (Principal Investigator)
Shashank Rajadhyaksha    (Graduate Student, MS99)
Janak Shanghvi                  (Graduate Student)
Matt Shandler                    (Undergraduate Student, BS 99)

Sponsor(s): Navy Joining Center

Abstract

Welding distortion in thin section large structures is usually caused by buckling under welding residual stresss.  A design approach is developed to predict welding induced distortion and evaluate the structural integrity. Process enhancements involving thermal pre-tensioning of the components are investigated to minimize residual stress and distortion. A thermo-elasto-plastic model of the process is optimized combining conventional analysis, design sensitivity analysis, and numerical optimization. Sensitivities of the modelís response (residual stress) with respect to the design variables (pre-heat conditions) are computed via the direct differentiation approach.  Experimental and industrial implementation results demonstrate the effectiveness of the design approach.

Background
 
 

Michaleris and Sun (1997) demonstrated that the residual stress is reduced when the weld region is cooled and the base metal adjacent to it is heated before welding (steady state thermal tensioning process).  To eliminate the need of cooling, Michaleris (1997) investigated a localized variation of the thermal tensioning process, where no cooling was used and small local regions of the base metal were heated simultaneously with the welding (transient thermal tensioning).  The investigation of Michaleris (1997) revealed that:

• Transient thermal tensioning using no cooling and localized heating can produce panels with zero residual stress on the plate.  Such panels will have no buckling distortion.  They will also have improved structural integrity.  Furthermore, they will have negligible longitudinal shrinking, and thus they will facilitate the implementation of a neat cut manufacturing approach.
• Only systematic and automated analysis methods using design optimization techniques can be used to investigate the transient thermal tensioning process in a cost efficient manner.

The objective of this project is to develop Finite Element formulations suitable for modeling transient thermal tensioning on wide panels with multiple stiffeners.

Methodology

Both Lagrangian models (fixed to the plate) and Eulerian (control volume moving along with the torches) will be investigated in this project.  The Lagrangian formulations are expected to lead to short-term but computationally expensive solutions.  The Eulerian formulations will offer accurate and computationally efficient solutions; however, they will require extensive development.  The methodology that will be developed in this project will facilitate the generation of guidelines for the implementation of thermal tensioning in a shipyard environment.

Publications

P. Michaleris, and X. Sun.  Finite Element Analysis of Thermal Tensioning Techniques Mitigating Weld Buckling Distortion, Welding Journal, 76(11): 451-457s, 1997.

P. Michaleris. Prediction and Minimization of Welding Induced Distortion, in International Institute of Welding (IIW-X/XV-RSDP-10-97), 1997.

P. Michaleris, and A. DeBiccari.  Prediction of Welding Distortion, Welding Journal, 76(4): 172-180s, 1997.

P. Michaleris, D.A. Tortorelli, and C.A. Vidal.  Design and Analysis of Weakly Coupled Thermoplasticity with Applications to Weldment Design Optimization.  International Journal of Numerical Methods in Engineering, 38:1259-1285, 1995.

Michaleris, P., Dantzig, J. A., and Tortorelli, D.A. 1999. Minimization of welding residual stress and distortion in large structures,Welding Journal, to appear.

Rajadhyaksha, S. and Michaleris, P. 1999. Optimization of thermal processes using an Eulerian formulation and application in laser hardening, International Journal for Numerical Methods in Engineering, to appear.

Rajadhyaksha, S. and Michaleris, P. 1999. Optimization of thermal processes using an Eulerian formulation and application in laser surface hardening, Optimization in Industry, Engineering Fundation, Banff, Canada.

Rajadhyaksha, S. and Michaleris, P. 1999. Analysis of thermo-mechanical processes and design sensitivities evaluation using an Eulerian formulation and application in welding, 5th US National Congress on Computational Mechanics, Bourlder, CO.