Low Stress Welding Simulations
Welding is a fundamental manufacturing technique ud to join metal components. While a variety of welding process exist, most involve the application of heat to induce coalescence of the metal in the adjoining parts.
The gas welding technique us the heat from a gas flame to melt together the contacting edges of the parts being joined. A filler material may or may not be ud.
The introduction of very high temperatures in the region of the welded joint caus steep temperature gradients in the structure. As a weld cools, residual stress may be produced in the weld zone; such stress may cau the structure to distort. The ability to predict the residual stress state allows for the prediction of final part shapes and a more complete understanding of how residual stress can affect the load capacity of a structure.
The finite element models described in this article reprent structural beams. The stru
ctures are formed by welding plate ctions together rather than producing the ction directly in a mill. The cross-ctional size of the components can make direct manufacture impractical.
The techniques discusd here are bad on a generic model but are transferable to a range of applications.
Finite Element Analysis Approach
The simulation us a quentially coupled approach in which a thermal analysis is followed by a stress analysis. The temperature results from the thermal analysis are read into the stress analysis as loading to calculate the thermal stress effects. The thermal analysis makes u of ABAQUS ur subroutines DFLUX, GAPCON, and FILM. The objective of the simulation is to predict post-weld deformation and residual stress distribution.
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宫颈炎最佳治疗方法Figure 1: Mesh of the structure being welded.
停滞期The model is constructed using solid and shell elements. A solid reprentation is ud in the weld area to ensure more accurate capture of the high solution gradients. Regions ou
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tside the weld zone, where thermal gradients are not as vere, are modeled with shell elements to reduce the overall model size. The transition between the shell and solid regions is achieved using tied contact for the thermal analysis and shell-to-solid coupling for the stress analysis. The mesh is shown in Figure 1 (left). The weld bead is shown in red.
Thermal Analysis Procedure
The thermal analysis is performed to calculate the heat transfer resulting from the thermal load of the moving torch. Three ur subroutines are activated for the thermal analysis:
人参多少钱一克DFLUX: Ud to define the welding torch heat input as a concentrated flux. The heat source travels along the weld line to simulate the torch movement.
GAPCON: Ud to activate the conduction of heat between the deposited weld material and the parent materials once the torch has pasd a given location.
FILM: Similar to GAPCON in functionality, but ud to activate film coefficients to simulate convective ambient cooling once the torch pass a given location.
The simulation is run as a fully transient heat transfer analysis.
Structural Analysis Procedure
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The structural analysis us the thermal analysis (temperature) results as the loading. The objective of the structural analysis is to determine the stress and strains induced in the weld region during the cooling transient. Boundary conditions are applied to restrain the system against rigid body motion.
李白介绍Figure 2: Nodal temperatures in a typical region of the weld as the torch travers the weld line.
Results and Conclusion
Typical thermal results are shown in Figure 2 (left), which displays a contour of nodal temperature as the torch travels along the weld line.
The weld is initialized at 1800° C, but no heat is allowed to transfer from the weld until the torch pass. As the torch pass a given point on the weld line, the flux input is initiated, resulting in a localized increa in temperature to more than 2000° C.
Figure 3: Transient temperature profile at three points in the torch path.
In addition, as the torch pass the same weld line point, conductive and convective heat transfer is activated, causing a rapid drop in temperature as thermal energy is transferred to the surrounding structure and environment.
Figure 3 (right) shows the 35 s transient temperature profile at three points clo to the start of the torch path. The peak temperature is reached when the torch is activated. A sharp temperature drop is obrved after the torch pass.
Figure 4: Von Mis stress in the weld region at t=35 s.
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The stress respon of the structure is driven by the high thermal gradients. Figure 4 (left) and Figure 5 (below), respectively, show plots of the von Mis stress and the effective plastic strain approximately 35 s into the process.
