An Integrated Computational Welding Mechanics With Direct-Search Optimization for Mitigation of Distortion in an Aluminum Bar Using Side Heating

Using a computational weld mechanics (CWM) frame-work for exploring a design space, a recent direct-search algorithm from Kolda, Lewis and Torczon is modified to use a least-square approximation to improve the method of following a path to the minimum in the algorithm. To compare the original and modified algorithms, a CWM optimization problem on a 152 × 1220 × 12.5 mm bar of Aluminum 5052-H32 to minimize the weld distortion mitigated by a side heating technique is solved. The CWM optimization problem is to find the best point in the space of side heater design parameters: power, heated area, longitudinal and transverse distance from the weld such that the final distortion is as low as possible (minimized). This CWM optimization problem is constrained to keep the stress level generated by the side heaters, in the elastic region to avoid adding an additional permanent plastic strain to the bar. The number of iterations, size of design of experiments (DOE) matrix required and CPU time to find the minimum for the two algorithms are compared.

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A Direct-Search Computational Weld Mechanics Optimization Using Least-Square Approximation

ASME 2011 Pressure Vessels and Piping Conference: Volume 6, Parts A and B ◽

10.1115/pvp2011-57960 ◽

2011 ◽

Author(s):

Mahyar Asadi ◽

John A. Goldak

Keyword(s):

Optimization Problem ◽

Search Algorithm ◽

Direct Search ◽

Least Square ◽

Design Parameters ◽

Transverse Distance ◽

Heated Area ◽

Direct Search Algorithm ◽

Weld Distortion ◽

Heater Design

Using a frame-work for exploring a design space in Computational Weld Mechanics (CWM), a recent direct-search algorithm from Kolda, Lewis and Torczon is modified to use a least-square approximation to improve the method of following a path to the minimum in the algorithm. To compare the original and modified algorithms, a CWM optimization problem on a 152 × 1220 × 12.5 mm bar of Aluminum 5052-H32 is solved to minimize the weld distortion mitigated by a side heating technique. The CWM optimization problem is to find the best point in the space of side heater design parameters: power, heated area, longitudinal and transverse distance from the weld such that the final distortion is as low as possible (minimized). This CWM optimization problem is constrained to keep the stress level generated by the side heaters, in the elastic region to avoid adding an additional permanent plastic strain to the bar. The number of iterations, size of DOE matrix required and CPU time to find the minimum for the two algorithms are compared.

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Can a Weld in Welded Structure Be Made With Zero Residual Stress?

Volume 6B: Materials and Fabrication ◽

10.1115/pvp2015-45991 ◽

2015 ◽

Author(s):

Stanislav Tchernov ◽

John A. Goldak

Keyword(s):

Residual Stress ◽

Optimization Problem ◽

Design Space ◽

Design Parameters ◽

Cpu Time ◽

Welded Structure ◽

Transverse Distance ◽

Heated Area ◽

Open Question ◽

Heater Design

While solving a sequence of seventeen optimization projects to predict the values of the side heater parameters that would be expected to minimize camber distortion in an edge welded bar, the design parameters that reduced distortion to effectively zero were not unique. This raised the question if any of the designs that minimized the distortion effectively to zero also minimized the residual stress. To answer this question three different measures of residual stress were evaluated for all 1451 designs. The Computational Weld Mechanics (CWM) optimization problem is to find the best point in the 4D space of side heater design parameters: flux, heated area, longitudinal and transverse distance from the weld such that the final residual stress is as low as possible (minimized). To evaluate the objective function for each point in the 4D design space, the associated 3D transient non-linear thermal visco-elastic-plastic stress analyzes was solved. A FEM mesh with 6600 8-node brick elements and 9438 nodes was solved for 166 time steps in 10 minutes of single-core CPU time. In the seventeen optimization projects, 1451 weld analyses were solved in 75 quad-core CPU hours by one person in two calendar weeks. The residual stress was effectively reduced to zero in some designs. These designs also reduced distortion to effectively zero. Whether a design that effectively reduces the residual stress to zero is unique remains an open question.

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