A nonlinear transient analysis is performed in three load steps using structural-thermal options of SOLID226 and CONTA174.
FSW simulation includes factors such as nonlinearity, contact, friction, large plastic deformation, structural-thermal coupling, and different loadings at each load step. The solution settings applied consider all of these factors.
The first load step in the solution process converges within a few substeps, but the second and third load steps converge only after applying the proper solution settings shown in the following table:
Table 28.4: Solution Settings
| Solution Setting | Description of Setting and Comments |
|---|---|
| ANTYPE,4 | Transient analysis. |
| NLGEOM,ON | Includes large-deflection effects or large strain effects, according to the element type. |
| TIMINT,OFF,STRUC | To speed up convergence in a coupled-field transient analysis, the structural dynamic effects are turned off. These structural effects are not important in the modeling of heat generation due to friction; however, the thermal dynamic effects are considered here. |
| KBC,0 | The loads applied to intermediate substeps within the load step are ramped because the structural dynamic effects are set to off. |
| AUTOTS,OFF for the first load step | Do not use automatic time stepping. |
Automatic time stepping is turned off (AUTOTS,OFF) for the first load step where the tool is plunging, and its temperature remains constant. After the first load step, the automatic time stepping is activated (AUTOTS,ON). The time step size (DELTIM) is set to 0.1 when the tool is plunging (1st load step), and to 0.01 when the tool rotates and generates frictional heating (2nd and 3rd load steps).
The time step values are determined based on mesh or element size. For stability, no time-step limitation exists for the implicit integration algorithm. Because this problem is inherently nonlinear and an accurate solution is necessary, a disturbance must not propagate to more than one element in a time step; therefore, an upper limit on the time step size is required. It is important to choose a time step size that does not violate the subsequent criterion (minimum element size, maximum thermal conductivity over the whole model, minimum density, and minimum specific heat).
Example 28.5: Defining the Solution Settings
/solu
antype,4 !Transient analysis
kbc,0 !Ramped loading within a load step
nlgeom,on !Turn on large deformation effects
timint,off,struc !Structural dynamic effects are turned
!off.
!Load Step1
autots,off !Do not use automatic time stepping
.
.
.
!Load Step2
autots,on !Use automatic time stepping