1. Abaqus Plugins

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Inertia welding simulation using Abaqus/Standard. To obtain more uniform contact pressure in the weld interface and to avoid. Through crack: elastic line sp.

This example examines the inertia friction welding process of the pipes shown in. The specific arrangement considered is the resulting as-welded configuration shown in. In this weld process kinetic energy is converted rapidly to thermal energy at a frictional interface. The resulting rapid rise in interface temperature is exploited to produce high-quality welds. In this example the weld process is simulated, and the initial temperature rise and material plastic flow are observed.

An important factor in the process design is control of the initial speed of the flywheel so that, when the flywheel stops, the temperature rises to just below the melting point, which in turn results in significant flow of material in the region of the weld joint. Understanding the friction, material properties, and heat transfer environment are important design aspects in an effective inertia welding process; therefore, simulation is a helpful tool in the process design. The principal interaction occurs at the weld interface between the pipes; however, a secondary concern is the possibility of contact of weld flash with the side of the pipes. The weld-interface friction behavior is assumed to follow that described by Moal and Massoni (1995), where the ratio of shear stress to the prescribed pressure is observed to be a complex function of interface slip rate.

The heat generation from the frictional sliding, combined with plastic deformation, contributes to the temperature rise in the pipes. At each remesh point the current model configuration represents a significant change in the pipes' shape and in the current analysis mesh. Abaqus/CAE is used to extract the outer surface of the pipes, reseed the surface, and remesh the pipe regions. This process employs the Abaqus Scripting Interface command, which is used to extract orphan mesh parts representing the deformed pipes.

These parts are then passed to the command. This command creates a geometric Part object from the orphan mesh imported earlier. Once the profile of the deformed part has been created, options in the Mesh module are used to remesh the part.

The new mesh results in a new Abaqus/Standard analysis, and the map solution procedure maps state variables from the previous analysis (see ). The pipes are modeled as axisymmetric. The element formulation used is the fully coupled temperature-displacement axisymmetric elements with twist degrees of freedom (element types CGAX4HT and CGAX3HT), where the twist degree of freedom enables modeling of rotation and shear deformation in the out-of-plane direction.

Abaqus Plugins

The hybrid formulation is required to handle the incompressible nature of the material during the plastic flow. The mesh is divided into two regions for each pipe. In the region near the weld interface, smaller elements are created (see ). During the remeshing process, the region near the weld surface is recalculated so that the new flash region is also meshed with smaller elements (see ).

The material model defined for this example approximates the high-temperature behavior of Astroloy, where it is reported by Soucail et al. (1992) using a Norton-Hoff constitutive law to describe the temperature and strain-rate viscoplastic behavior. Livro purga em angola pdf reader. A similar model is defined in Abaqus as a rate-dependent perfectly plastic material model. For the loading in this model, these material parameters result in the onset of local plastic flow only after the interface temperature has exceeded roughly 1200�C, near the material solidus temperature of 1250�C. Above this temperature the Mises flow stress is highly sensitive to variations in temperature and strain rate. A special adjustment in the flow stress at high strain rates is necessary to avoid divergence during the iteration procedure of the nonlinear solution. In the material model definition an extreme case of stress data is defined when the strain rate is 1.0 � 10 6 s �1.

Stress data when the strain rate equals zero are also defined to be the same as the stress data at strain rate 1.0 � 10 �5 s �1. As a result of large deformation, thermal expansion is not considered in the material model. The contact interactions include a pair of interactions that define the weld interface between the pipes, which is identified in. This pair of interactions is symmetrical: one interaction defines the top pipe as the master surface with the bottom pipe as the slave surface, and the second interaction reverses the master-slave pairing. This “balanced master-slave” arrangement is important for the analysis to obtain more uniform contact pressure in the weld interface and to avoid hourglass effects, and it is combined with a softened contact interaction property to promote a sharing of the local contact pressure among nodes on both sides of the interface. To simulate the Moal and Massoni (1995) friction definition, the weld interface friction model is defined in user subroutine (see ).

This model is nonlocal in the sense that the interface pressure for all contact nodes is the applied pressure of 360 MPa, and the sliding velocity is computed based on the rotational angular velocity of the flywheel. This treatment of the friction force helps stabilize the solution. Frictional heat generation is calculated based on the frictional traction and the sliding velocity.

Nondefault contact controls definitions are used to improve convergence. These definitions include delaying the friction computation upon contact and automatic tolerance control to avoid contact chattering. The two remaining contact interactions address the possibility of self-contact near the weld area in the pipes.

Self-contact in the flash area can cause problems during remeshing: the command that was used to generate the new, current configuration geometry performs curve-fit operations that can result in self intersections of the boundary, which lead to invalid part topology and a meshing failure. To avoid this problem, a softened contact model that introduces a normal pressure with a small separation distance (�0.01 mm) is used. It is important to keep this separation distance as small as practical to avoid causing any nonphysical contact behavior. The actuator-sensor interaction, which acts through user subroutine, enables the simulation of a flywheel attached to the top pipe. The user element also has a sensor role in the analysis, measuring the weld upset, or axial shortening, of the weld assembly. When a critical user-defined upset distance is exceeded, the user element subroutine calls XIT to terminate the analysis and signal a remesh point. This parameter, the allowed “upset distance,” correlates well with the extent of mesh deformation in the weld region.

The example simulation creates multiple output database (.odb) files, requiring 22 remeshings to reach the simulation time of 5.0 seconds. The results in the first analysis before the first remeshing show that the temperature rises very fast near the weld interface. At about 1.6 seconds the temperature reaches 1172�C and the material starts to flow, squeezing out to form flash (see ).

After 2.31 seconds and 5 remeshings the flash extends enough to fold back and contact the pipe (see ). At 3.51 seconds the flywheel velocity slows down to 3.51 rad/s, the temperature starts to drop, and the material flow slows down.

At this point a considerable amount of flash build-up can be observed (see ). After 5.0 seconds the flywheel stops, the temperature drops below 1000�C, and the pipes are welded (see ). If a lower initial flywheel velocity is selected, the temperature may not reach a level high enough for the material to flow.

For this case the initial velocity is reduced to 20 rad/s. Shows the configuration at 5.0 seconds, where not much deformation is observed and the temperature near the interface is about 250�C. The history plot of the maximum temperature for Case 2 in shows the pipe temperature reaches only 700�C about 1.1 seconds before it cools down. In this case the material is not hot enough to initiate the material flow, and welding will not be successful. If a higher initial velocity of the flywheel is selected, the material becomes so hot that it starts to melt.

For this case the initial velocity of the flywheel is set at 70 rad/s. Shows that the temperature rapidly reaches 1360�C (at about 0.9 seconds), which is well beyond the melting temperature at 1250�C, before convergence failures stop the analysis. Shows the history plot of the maximum temperature in the pipes for Case 3.

In this case the excessive energy results in melting and a failed weld.