Though Abaqus checks for over constraints and . Models. In Abaqus/Standard the following constraints are included by using Lagrange multipliers: If the penalty method is used, the contact Lagrange multipliers may not be present. Defining an analysis abaqus nonlinear analysis tutorial Abaqus Tutorial 25: Python Scripting to run different models. A basic concept in Abaqus is the division of the problem history into steps. stepConvert severe discontinuity iterations. sometimes repeatedly change from open to closed between each severe discontinuity iteration; this is known as contact chattering. Ic S I S c, maximum number of severe discontinuity iterations allowed in an increment if the Convert severe discontinuity iterations setting for the step is On. iteration summary for the increment: 1 total iterations, of which 0 are severe discontinuity iterations and 1 are equilibrium iterations. By default, Abaqus applies sophisticated criteria involving changes in penetration, changes in the residual force, and the number of severe discontinuities from one iteration to the next to determine whether iteration should be continued or terminated. determine position of damage and provide evolution of damage surface, when some. Notably, we can see the criterion for the residual forces and moments that Abaqus has to achieve in each increment, before static equilibrium can be assumed and it is allowed to move onto the next. Understanding Abaqus/Standard negative eigenvalue messages Hints for obtaining a converged contact solution in Abaqus/Standard Instead, here are general links to Knowledge Base articles which may be helpful for common convergence problems in severe discontinuity and equilibrium iterations: Descriptionebugging Abaqus/Standard divergence with . There are no iterations in an ABAQUS/Explicit analysis. . Ensure the scratch data fits in your system's RAM. With an under constraint, not all rigid body motion is suppressed, leading to one or more degrees of freedom with zero stiffness and usually zero-pivot warnings. Set ANALYSIS = DISCONTINUOUS to set parameters that will usually improve efficiency for severely discontinuous behavior, such as frictional sliding or concrete cracking, by allowing relatively many iterations prior to beginning any checks on the convergence rate. attempt number 1 \item $ I_T = 3 $. Abaqus/Standard applies sophisticated criteria involving changes in penetration, changes in the residual force, and the number of severe discontinuities from one iteration to the next to determine whether iteration should be continued or terminated. ()> ()>. Abaqus needed four iterations to converge to a solution in the first increment. - Label and count this iteration as an SDI (severe discontinuity iteration). In the status file the severe discontinuity iterations column is marked with an asterisk if successful contact iterations are present during the time increment. Severe discontinuity iterations are different from regular equilibrium iterations in only one respectABAQUS/Standard does not check the . Hence, it is in principle not necessary to limit the number of severe discontinuity iterations. With every iteration the solution that Abaqus/Standard obtains should be closer to equilibrium; however, sometimes the iteration process may divergesubsequent iterations may move away from the equilibrium state. Contribute to rftoma/Abaqus development by creating an account on GitHub. If the model is not in equilibrium at the end of an iteration, Abaqus will run another one. By default, ABAQUS/Standard will continue to iterate until no severe discontinuities occur and the equilibrium (flux) tolerances are satisfied. Additionally at each iteration a system of simultaneous equations must be solved, which includes matrix inversion that can be computationally expensive. Now the problem is that when I read the. Abaqus/Standard will determine the maximum penetration and estimated force errors associated with severe discontinuities and check whether these errors are within the . The second iteration does not produce any changes in the model's contact . 1.Step. 'Equilibrium iterations' (green column) are those in which the solution varies smoothly and 'severe discontinuity iterations' (orange column . This option directs ABAQUS/Standard to accept the solution to an increment after the maximum number of iterations allowed has been completed, even if the equilibrium . ABAQUS/Standard requires one iteration to establish the correct contact conditions in the model; i.e., whether or not the punch was contacting the blank. TIME INCREMENT COMPLETED 9.295E-02, FRACTION OF STEP COMPLETED 9.118E-03 STEP TIME COMPLETED 14.4 , TOTAL TIME COMPLETED 14.4 Select Off to force a new iteration if severe discontinuities occur during an iteration. If the model is not in equilibrium at the end of an iteration, Abaqus will run another one. Abaqus/Standard will determine the maximum penetration and estimated force errors associated with severe discontinuities and check whether these errors are within the . which in turn leads to a very timely iteration process for solving the equilibrium equations. . If several cutbacks are required, contact chattering may In addition, it will also trigger a severe discontinuity iteration. PNEWDT is set to a large value before each call to UEL. 5. Significantly more detail is recorded in the ".msg" file but it's harder to interpret. With every iteration the solver tries, the solution should be 'converging' upon static equilibrium. Abaqus JOB Blowing-1 Abaqus 6.13-1 Abaqus License Manager checked out the following licenses: . . moment 1.466e+04 all moment residuals are zero largest increment of rotation-3.219e-31 at node 901 dof 6 largest correction to rotation-1.541e-31 at node 901 dof 6 the moment equilibrium equations have converged:: convergence checks for severe discontinuity iteration 13:: ***note: the solution appears to be diverging. 651 VisualizationToolsJob diagnostica . iteration summary for the increment: 1 total iterations, of which 0 are severe discontinuity iterations and 1 are equilibrium iterations. Solving coupled field equations In a general problem several (possibly nonlinear) coupled field equations of types =1,2,N = 1, 2, Every time a severe discontinuity iteration occurs, ABAQUS/Standard resets the internal count of equilibrium iterations to zero. I change it to 1e-5 initial 1e-9 minimum for diagnosing. Therefore, Abaqus carry out iterations within an increment in order to attain equilibrium. but I have a limit to which I can refine it. PENETRATION ERRORstepother-general solution control . PENETRATION ERROR 150.479E-09 AT NODE SOIL-1.1060 OF CONTACT PAIR (ASSEMBLY_SOIL-1_BASE_SOIL,ASSEMBLY_FND-1_BOT_F) The fact that in increment 3 there is no severe discontinuity iteration may also imply that the problem is not the contact algorithm itself - possibly elements are distorting excessively and this causes the contact algorithm to be unable to actually resolve the contact geometry. . A model can also be over or under constrained. Contribute to rftoma/Abaqus development by creating an account on GitHub. Hence, it is in principle not necessary to limit the number of severe discontinuity iterations. The contact algorithm used by ABAQUS/Standard involves use of severe discontinuity iterations when the contact state at the end of an iteration is different from the state assumed for that iteration. If PNEWDT is redefined to be less than 1.0, Abaqus/Standard must abandon the time increment and attempt 9/22/2019 6 Tips solving non convergence with Abaqus FEA 3/11 extreme deformations. Click the arrow to the right of the Convert severe discontinuity iterations field, . 2. 3. During a severe discontinuity iteration (such as contact changes), PNEWDT is ignored unless CONVERT SDI=YES is specified for this step. Contact is a severe discontinuity, and . . Default Ic S =50 I S c = 50. Contact openings in the first severe discontinuity iteration. An overconstraint was detected at one of the Lagrange multipliers associated. The usage of PNEWDT is discussed below. Product: Abaqus/Standard WARNING: This feature is intended for advanced users only. CONVERGENCE CHECKS FOR SEVERE DISCONTINUITY ITERATION 2 MAX. One possible source of contact non-convergence is the initial state of the contact. PENETRATION ERROR -2.85209E+03 AT NODE SHEET-1.47562 OF CONTACT PAIR (ASSEMBLY__PICKEDSURF19,ASSEMBLY__PICKEDSURF18) Severe discontinuity iterations and equilibrium iterations are listed separately, along with the total number of iterations. mod (S)(E) *SURFACE BEHAVIOR Convert SDI treats the handling of Severe Discontinuity Iterations (SDIs) of implicit simulations in Abaqus/Standard. In contrast to equilibrium iterations, SDIs are characterized by sudden changes of stiffness. This parameter applies only to Abaqus/Standard analyses. please check the value of the average FORCE during the current iteration to verify that the FORCE is small enough to . Maximum number of severe discontinuity iterations in an increment. Any time this flag is reset to a value of -1, Abaqus/Standard assumes that the flag is not being used. . A list of nodes and chained constraints between these nodes that most likely lead. time increment completed 2.446e-08, fraction of step completed 0.496 step time completed 4.527e-02, total time completed 4.527e-02 increment 842 starts. Abaqus/Standard distinguishes between regular, equilibrium iterations (in which the solution varies smoothly) and severe discontinuity iterations (SDIs) in which abrupt changes in stiffness occur. This parameter serves only as a protection against failure of the default convergence criteria and should rarely need to be changed. 2-There is zero FORCE everywhere in the model based on the default criterion. Also iteration control is a ected by the routine to de ne how the solver treats the next iteration, for example, if it will be an equilibrium or a severe discontinuity iteration according to the changes in the contact condition at each node. The ABAQUS/Standard message file contains information about the increment number, step time, fraction of a step completed, equilibrium iterations, severe discontinuity (contact) iterations, plasticity algorithms, adaptive mesh smoothing, the load proportionality factor in a Riks analysis, etc. A summary of the progress toward solution is presented in the ".sta" file. for the ratio of the largest residual to the corresponding average flux norm for convergence to be accepted in one iteration (that is, for a linear case). Maximum number of severe discontinuity iterations allowed in two consecutive increments for the time step to be increased. CONVERGENCE CHECKS FOR SEVERE DISCONTINUITY ITERATION 1: MAX. File Type PDF Non Linear Analysis In Abaqus (in which the solution varies smoothly) and severe discontinuity iterations ( SDI s) in which abrupt changes in stiffness occur. There are multiple constraints applied directly. The terms step, increment, and iteration and two subsidiary termsframe and attempt can be conceptually confusing to an Abaqus beginner. It changes the default behavior for the handling of severe discontinuity iterations (see "Severe discontinuities in ABAQUS/Standard" in "Procedures: overview," Section 6.1.1). Select On to use local convergence criteria to determine whether a new iteration is needed. This alteration interrupts the overall convergence rate of the model. Use scaling for quasi-static analyses in Abaqus/Explicit . You would be able to increase the maximum number of the severe discontinuities iteration by using the keyword "*CONTROLS, PARAMETERS=TIME INCREMENTATION,,,,,24" (see figure 1) or through the graphical interface (see figure 2 and 3). It can lead to cutbacks in the time increment if the contact state cannot be resolved within a certain number of severe discontinuity iterations. This iteration count is used to determine if an increment should be abandoned due to a slow convergence rate. Any advice would be . \item . There are two primary methods through which normal direction contact constraints can be enforced in Abaqus/Standard: the traditional direct Lagrange multiplier method and a penalty-based method. This option directs ABAQUS/Standard to accept the solution to an increment after the maximum number of iterations allowed has been completed, even if the equilibrium . with contact slave node 147300 INSTANCE PART-1-1. . or chained constraints that are applied indirectly to this node. . The ABAQUS/Standard will iterate until there are no more severe discontinuities, or they will be small enough. . With every iteration the solver tries, the solution should be 'converging' upon static equilibrium. An SDI is an iteration during which contact constraints change state (open, close, stick, slip). . 0 are severe discontinuity iterations and 1 are equilibrium iterations. Don't allow a single element to ruin your simulation speed in Abaqus/Explicit. ABAQUS: Selected Topics L8.53 Solution of Contact Analyses 5 Contact state changed: the start of the iteration was based on the wrong state. A "severe discontinuity" in a model's behavior is caused by a change in contact conditions (a gap or interface opening or closing), by friction changing from slipping to sticking, or by incompatibility of the softened contact constraint. Abaqus msg file buddy. If one of those converges, friction takes over and holds the model in place and the step size begins to increase. It is important that you clearly understand the difference between an analysis step, a load increment, and an iteration. Abaqus Standard efficiently solves nonlinear finite element analysis using automatically-scaled load increments and Newton's method iterations. Select On to use local convergence criteria to determine whether a new iteration is needed. maximum iterations for severe discontinuities 12 maximum cut-backs allowed in an increment 5 . As shown in Figure 12-23, this is one of the first increments in which severe discontinuity iterations are required. Select Off to force a new iteration if severe discontinuities occur during an iteration. convergence is judged . Abaqus/CAE displays the General Solution Controls Manager showing the steps defined in the model and . coordinates of material points, using coordMpk,1),coordMpk,1 . "Severe discontinuity iteration" (SDI) is used to filter out contact from convergence rate tracking. Abaqus uses a tolerance value (a value close to zero) defined in its solver settings. cut-back factor after too many severe discontinuity iterations 0.2500 cut-back factor after problems in element assembly 0.2500 . Each contact iteration involves a solution of an internal linear system of equations, and the size of this system is the number of contact status changes. . Abaqus/Standard message file" in "Output," Section 4.1.1 of the Abaqus Analysis User's Manual). Abaqus does not like too many closures and openings of the contact surfaces in static analysis. Edit 2: Turns out the main cause was the default penalty normal stiffness being far too high for the thin surface and rigid surface contact- using a scaling a few magnitudes lower resolved the chattering issues mostly! This article explains the difference between the Standard and Explicit Abaqus solvers, particularly with respect to non-linear dynamic analyses. During a severe discontinuity iteration (such as contact changes), PNEWDT is ignored unless CONVERT SDI=YES is specified for this step. After two additional iterations Abaqus/Standard detects no changes in the contact state. The "outer" damage status will transfer to "inner" damage. Over constraints also tend to cause zero-pivot warnings. Till the difference between the forces come under this tolerance value, the solver carries several "iterations". I am doing an 3D indendation simulation modeld on Vickers in the moment. Abaqus/Standard treats SDIs and equilibrium iterations separately. For example, the damping factor may increase if an analysis takes extra severe discontinuity or equilibrium iterations per . As well as these, severe discontinuity iterations, that deal with things like contact and slipping, also need parameters to work within. ABAQUS/Standard repeats the entire process until convergence is achieved, as summarized in Figure 12-9. Refining the mesh would help? Click the arrow to the right of the Convert severe discontinuity iterations field, . Naturally, creep groan simulations are prone to a high number of severe discontinuities. The surface to surface discretisation of Abaqus with nite sliding formulation is used. If a problem relies on the contact for stability and initially no contact is present, the simulation may have trouble starting. status. the number of prior increments that must have completed without cutbacks in order to increase the time step \item $ I_S^C = 50 $. 'Equilibrium iterations' (green column) are those in which the solution varies smoothly and 'severe discontinuity iterations' (orange column . The most common of such severe discontinuities involve open-close changes in contact and stick-slip changes in friction. Description: ABAQUS/Standard distinguishes between regular, equilibrium iterations (in which the solution varies smoothly) and severe discontinuity iterations (SDIs) in which abrupt changes in stiffness occur. If CONVERT SDI =NO (the default setting), ABAQUS/Standard forces a new iteration if severe discontinuities occur during an iteration; if CONVERT SDI =YES, ABAQUS/Standard estimates residual forces associated with severe discontinuities and checks whether the equilibrium tolerances are satisfied. The rig moves in the positive x direction over the surface with springs attached to each column to apply a . Cheers CidZale. That's why Abaqus uses separate severe discontinuity iterations when contact is changing. By default, ABAQUS/Standard will continue to iterate until no .