Category "Simulation"

Previous few blog articles primarily addressed Abaqus 2020x enhancements. Let’s have a look at the extended products enhancements that include ISight, Tosca and FeSafe.

ISight Enhancements

  • Export of Approximations: Till 2019x release, the export of approximation models was limited to coefficient data or excel spreadsheet format. In 2020x release, the RBF and RSM approximation models can be exported to FMU as well.
  • New components: Functional Mock Up (FMU) and Computer Simulation Technology (CST) components are now available in ISight workflows.

Tosca Enhancements

  • Sensitivities support: Though not essentially an enhancement in 2020x, it is worth mentioning that all four modules of Tosca now accept Abaqus sensitivities for all types of non-linearities. However, supported analysis steps are Static and Frequency only. Inertia relief included.
  • New Response: Plastic strain PEMAG now supported for shape, size and bead optimization.
  • Algorithm stabilized: Higher volume fractions eventually lead to convergence and stability concerns. While convergence is an Abaqus issue, stability of optimization has been improved in topology module with large volume fractions.

Fe-Safe Enhancements in 3DX:

  • App enhancement: While the role is still a separate license called as durability engineer role, the mechanical and structural scenario have been enhanced to include the fatigue interface.

Simultaneous execution: Though it is well understood that any fe-safe analysis requires stress results from a stress analysis, user now has an option to simulate both structural and durability cases at the same time. The backend data management architecture takes care of sequencing and linking.

  • Material enhancement: The entire Fe-safe material database can now be imported in the 3DEXPERIENCE Platform. Surface finish factors supported as well.
  • Element nodal outputs: This is perhaps a KEY enhancement. The fatigue is a surface phenomenon so averaged stresses at the nodes on surface are most appropriate for fatigue analysis. In prior releases of 3DX, only integration point stresses were supported. Starting 2019x FD06, element nodal stresses are available for fatigue.
  • Loading enhancements: Loading blocks now include residual stresses as well as implicit dynamics step. All Fe-Safe algorithms with and without mean stress correction are now supported. Both SN curve as well as EN curve algorithms are now supported in 3DX.
  • Coming Soon!! Linux and COS execution on cloud.

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This is a relatively bigger blog compared to previous ones because of an obvious reason; it covers a broad spectrum of non-linear enhancements which is Abaqus core technology. The blog covers four sections: additive manufacturing, element technology, material enhancements and fracture mechanics along with few other minor enhancements

Additive manufacturing:

  • Pattern based thermo-mechanical analysis: While in many cases laser scan paths are available to simulation users it is not always true. For those situations in which machine users do not wish to share their machine IP’s, a pattern based approach has been introduced which uses a raster scan path instead of a trajectory scan path. Material orientation and Anisotropic behavior are supported but not suitable for detailed microstructure simulation. This application is different from eigen strain simulation.
  • Event series enhancement: 2GB data size limit of event series was removed in 2019xGA and now event series can include up-to 420 million events.
  • Free surface evolution enhancements: In case of tie constraints, algorithm has been enhanced to include ties that are not activated until the underlying element becomes active.
  • Output enhancements: MAXPSCRT has been introduced to include maximum principal stress crack initiation criterion. It is available for both field and history outputs. BLADEINTERFERER has been introduced to predict clash between recoater and printed part. This will be available in 2020xFD01.

Element Technology:

  • Shear panel element update: SHEAR4 was introduced in 209xFD01 to model thin reinforced plates. It supports buckling. Equivalent shear flow output called SQEQ is supported.
  • Pyramid heat transfer element: DC3D5 has been introduced to manage transition between tetrahedral and hexahedral elements in thermal analysis.
  • Fluid pipe element enhancements: These elements now support following Non Newtonian flows as well:

Material enhancements:

  • VUMAT enhancement: A parameter has been added to define alternate bulk and shear modulus that can be used by explicit to find suitable time increment. It is called EFFMOD and visible in viewer. Abaqus CAE support is available from 2020xFD01.
  • Kinematic hardening enhancement: The material model has been enhanced to model stress relaxation behavior for metals subjected to step strain input. Suitable for metals that show viscoelastic like behavior during step inputs.

Creep Laws enhancement: Current creep models have A with dimensionality that creates ambiguity. The strain and time laws have been enhanced as follows to make A dimensionless. These enhancements are applicable to all the creep models.

Viscoelastic material enhancement: The prony series has now been enhanced to include frequency domain as well. Earlier prony series was valid in time domain only.

Yield surface enhancement: The non quadratic yield surface has been introduced in 2019xFD04. It is referred to as Barlat Plasticity. The stress component requires 18 coefficients and 1 exponent.

  • Metallurgical phase enhancement: In prior releases, the effect of additive manufacturing and other heat treatment processes on material properties at microstructural level required USDFLD subroutine. Effective 2020xFD01, this routine has been included on the material definition itself. Inservice performance of printed parts can now be more accurately simulated.

Injection Molding:

  • 3DX injection molding compatibility: The fiber orientation and residual stresses from third party simulation such as Moldflow can now be converted to a SIM file format. That means the 3DX structural simulation apps can now read moldflow results to predict in-service loads and warpage from third party plastic injection results.

Pre-tension enhancements

  • Non linear enhancement: In earlier releases, the direction of pre-tension section normal was not updated even in general step. Effective 2020xGA, the cut section normal direction can be updated in large displacement or large rotation analysis. It is activated as follows in the input file

*PRE-TENSION SECTION, FOLLOWER = (YES/NO)

Fracture Mechanics enhancements

  • Linear elastic fatigue enhancements: Linear elastic fatigue crack model was introduced recently in collaboration with NASA ACC team to model crack propagation for cyclic fatigue cycles. It allows for change in contact conditions as well as non-linear geometry effects. Several enhancements have been made in this model in recent FD’s. In 2019x FD03, an alternative method to smoothening of crack front was introduced. In 2019x FD04, mode dependent stiffness degradation was introduced.
  • Cohesive elements for Multiphysics: Couples temperature-displacement cohesive elements have been introduced to simulate debonding due to thermal expansion as well as hydraulic fracture. These elements are COH2D4T, COHAX4T, COH3D6T, COH3D8T. Coupled temperature-displacement-pore pressure elements available as well to include gap conductance effect. There is no change in the structural response of these elements.

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While few of the Abaqus explicit enhancements in 2020x have been discussed in previous blogs on contact, this particular blog article specifically focuses on many more enhancements in explicit, with or without contact.

  • DT based element deletion: While explicit jobs never exit with fatal errors due to lack of convergence, they can still give fatal errors because of severe element distortion. An element deletion criterion has been introduced that allows user to set a trigger for element deletions based on element area, element volume, stable time increment and characteristic length. These triggers can be defined either as absolute or as ratios.
  • Linear Kinematic conversion: This is yet another approach to avoid fatal errors because of severe element distortion. In this approach, the elements are transformed to linear elements based on certain trigger threshold on distortion. It is applicable to most of continuum tetrahedral and hexahedral elements.

Enhanced CEL approach: Conventional CEL approach is good for solids only. When applied to liquids and gases, it may cause leakage especially when fluids create high pressure gradient, when fluids have large tangential velocity or at the location of sharp corners. The enhanced CEL contact formulation fixes this problem and is applicable to both solid and shell meshes. However, this enhanced formulation is more expensive in memory and computation.

Hybrid message parsing (HMP): This is an enhancement in parallel processing that can combine MPI (DMP) based parallelization and Threads (SMP) based parallelization. The solution can utilize thread based parallelism within a node as well as MPI to communicate between the nodes. It results in fine grained dynamic load balancing because when a thread completes its own elements computation work, it helps other threads within the same MPI rank.

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Subsequent to the blog article on few functionalities in Abaqus CAE 20202x, this particular blog article mentions enhancements in Abaqus solver 2020x contacts and constraints. The enhancements would be mentioned in reverse chronological order and few of these have been introduced in FP’s of 2019x as well.

  • Interference fit in Abaqus explicit: This feature has been in waiting list since long by users and its finally available now. Earlier releases of explicit had an option of strain free adjustment only for overclosures. From 2020x, if initial overclosure is “x” and interference is defined as “y”, then strain free adjustment is performed till “x-y” and rest is treated as interference being resolved through a smooth amplitude curve. That means a “two in one advantage” for explicit. Moreover, it is supported in Abaqus CAE.

Change in contact status legend: To make output more meaningful for the users, the contact status has been changed to bonded and “not in contact” as shown below. This is applicable to both standard and explicit.

Rate dependent cohesive damage: The damage initiation and damage evolution laws now have parameters to include rate dependency in cohesive contact for explicit. Earlier this feature was available in cohesive elements approach only. Effective since 2019xFD04.

  • Material based general contact property assignment: The conventional process of property assignment in general contact is a three-step process. First, define sets of elements. Second, use sets to define surfaces. Third, use surfaces in property definition. From 2020x, material can be directly called for surface assignment if that approach helps. This is true for both standard and explicit.

Thermal expansion of rigid bodies: The analytical and discrete rigid bodies have been existing in Abaqus since long. However, when it comes to combined structural and thermal steps, a body very rigid from structural perspective may expand well when heated. To incorporate this effect, thermal expansion of rigid bodies feature is now included in Abaqus standard. This is applicable to kinematic couplings as well as for bodies are not explicitly defined through a CAD geometry.

  • Small sliding in general contact: This is again a BIG enhancement based in users request. Small sliding substantially reduces the contact search time because it is based on flat surface approximation. When used correctly, it results in convergence improvement and less overall solution time. However, its absence in general contact was a bit bothersome. From 2020x, small sliding exists in general contact for standard.

General contact enhancement for Multiphysics: Beam elements have been introduced in general contact for thermal and thermal electrical procedures. This may be helpful in approximating some large size applications such as heat exchangers by modeling pipes as beam elements.

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Computer aided engineering has always been a role of a specialist. This statement is very much evident from the fact that more than 50 percent of analysts today have a graduate degree; either an MS or a PhD. This is because these physics-based simulations are a lot more than collection of icons, toolbars and pull-down menus. Unless the user is well familiar with the core engineering aspect of the problem being solved as well as with the underlying governing equations that solve the problem, he is very likely to make an error in modeling that would lead to erroneous results. In such situations “a stress solver becomes a stress creator.”

If one dissects the subject of computer aided engineering, he would see several branches of it. The main ones are: finite element analysis, computational fluid dynamics, multi-physical simulation as well as multi body dynamics. Each of these branches have several sub-branches of it. For example, finite element analysis can be divided into structural analysis, thermal analysis, coupled analysis. The structural analysis can be further sub-divided into linear static structural, non linear static structural, linear dynamic, non linear dynamic etc. As one moves keeps digging inside, simulation becomes more niche and more specialized. This justifies the need of a specialist with many years of experience with advanced technical and academic credentials.

While we, at TATA Technologies do not provide work experience or academic credentials, we do transfer expertise in computer aided engineering and many other fields of engineering through dedicated technical trainings as well as on the job trainings. We offer software products specific trainings such as Dassault Systemes portfolio, Siemens PLM portfolio, Autodesk portfolio as well as several industry vertical trainings such as modeling of welds and connectors in automotive chassis, design for light weight etc. We do provide small sessions on best practices as well such as effective element selection in Abaqus, overcome convergence problems in non linear simulation etc.

We train people with various levels of experience and knowledge. The student may be a fresh designer out of college who has recently joined his first organization or may be a subject matter expert with years of design or simulation experience and trying to learn something new. As mentioned, we teach both software as well as methodologies and workflows.

If you have a high end engineering software in your organization that seems to be underutilized because of lack of human resource, please get in touch with us.

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Its end of the year 2019 and just like any other prior year DS is ready with new release, both for standalone products as well as 3DX roles. Accordingly, we are ready with our blog series “what’s new in 2020”. So lets start with Abaqus CAE first. The later blog articles will include solver functionality enhancements as well.

  • Partitioning enhancement: The partition method using sweet and extrude has been improved to include multiple disconnected edges at the same time. That means multiple partitions can be done in a single partition operation. Less clicks, less time.
  • Global renumbering: It is now possible to define renumbering in assembly context. And that is true for both dependent and independent part instances. For large assemblies, the user now does not need to switch multiple times between part and assembly modules to perform renumbering. In case of dependent part instances, any renumbering performed on an instance is automatically propagated to associated part at part level mesh.
  • Enhancement in query tool: The queries for points/nodes/distances can now be made with respect to a local coordinate system as well that can be a cartesian, cylindrical or spherical CS. Earlier only global cartesian CS was available for queries.
  • Shrink fit possible in explicit: This is a BIG enhancement for our explicit users. Perhaps those users who have struggled with the convergence of shrink fit in standard would appreciate this feature. Earlier initial overclosures in explicit could only be adjusted strain-free thereby making explicit step ineffective for shrink fit. Now explicit step has option of treating initial overclosures as interference fit. This is applicable for both contact part as well as general contact inexplicit. Big relief.
  • Hyperfoam test data evaluation: Computation of material coefficients using uniaxial and multiaxial test data has been a very useful feature of Abaqus CAE. However this functionality was limited to hyperelasticity and viscoelasticity. Now hyperfoam material evaluation can also be done using curve fitting techniques.

Enhancements in copying models: The copy model feature has been enhanced to include constraints as well. However, if constraints refer to named sets and surfaces, those sets and surfaces should exist in the target model.

BC/Load manager with color coded cells: Lastly, the looks and feel of BC, Load and interaction manager has been enriched by making it color coded as shown below. It matters if this manager has to be used in a simulation report.

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FEMAP! That can be defined as a dedicated standalone, windows based pre and post processor for different types of finite element analysis simulations. It has a long history since its inception in 1985. The product was earlier with Unigraphics Systems which was acquired by Siemens PLM Solutions few years back. Every branded FEA software product gets upgraded every year with new valuable features that look good as well as feel good. FEMAP is no exception. Here we are looking at new functionalities in FEMAP release 12.0.

PAD and WASHER enhancement: Pads and Washers are used to effectively partition the geometry to get high quality isoparametric meshes around stress raisers such as holes. Till now this functionality was available only for circular geometries. Now the feature includes arbitrary geometries that may include tangential discontinuity

COPY/ROTATE/REFLECT: This functionality allows users to copy/rotate/reflect geometries along with associated meshes, loads and boundary conditions. The command can be executed successively to create different types of patterns with respect to translation and rotation.

Mesh Point Editor: Hard points are points defined by fixed coordinates on a curve or a surface that constrain the mesher by creating nodes at these specified locations. Hard points are desired at assembly level meshing to ease connection between different parts through node to node connectivity instead of using contacts. Hard points are further useful in connecting solid or surface mesh with a beam mesh which is a common application in civil structures such as concrete reinforcements. FEMAP 12 has a hard point editor through which hard points data can be imported into Femap via an external file or a clipboard. View/options can be used to control the display of hard points.

COHESIVE elements: These elements are used in modeling phenomenon such as delamination and material damage. Common real-life examples are peeling of a tape or evolution of a crack. NASTRAN solution sequences 401 and 402 have cohesive elements capability so it’s worth to include cohesive meshing capability in FEMAP.

Mesh->editing->cohesive meshing command has been added that work similar to mesh->editing->edge split command with a difference that cohesive command adds layers of cohesive element at the split with user defined element thickness and adjusts the size of original elements to achieve mesh compatibility.

BEAM Centerline Finder: This feature was earlier available as an API but now it has been included in the GUI of FEMAP 12.0. For arbitrary shapes, sometimes it is not possible to define all the section properties of beams. This feature extracts the beam properties using cross section of underlying solid geometry. User has two options. First option is to interactively pick curves and cross section of underlying solid. Second option is to pick only solid and FEMAP uses longest edge of the solid as curves for associated beams.


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There have been quite a few market whispers about MSC Software and its products since the company’s acquisition by Symphony Technologies few years back. It’s flagship pre-processing tool called MSC Patran has been under spotlight since the introduction of new equivalent tool by MSC Software (now Symphony) called MSC Apex.  MSC Software adopted a similar strategy during 2008-09 by introducing a bunch of multi-disciplinary pre-processing tools such as MD Patran and later SimExpert. All these products had a very long gestation period with little luck in making a long term market presence.

Many veteran FEA analysts, particularly in aerospace domain are well familiar with the pains of using MSC Patran in geometry cleaning, meshing and composite modeling environments. The objective of this blog is to take a deep dive into these issues and demonstrate how an alternative product called Femap from Siemens can alleviate many of these unaddressed issues.

Femap has been a part of FEA community since more than 30 years and it was developed with the mission of having a dedicated PC based pre and post processor for engineering FEA. It is solver neutral as well as CAD independent solution that offers high performance modeling and analysis capabilities to solve toughest engineering problems.

  • Mid surface extraction

Almost all FEA pre-processors have this embedded tool but as the geometry becomes more and more complex, many of them fail to extract mid surfaces correctly. The automatic feature of Femap makes this job not only easy with minimum number of clicks but offers higher fidelity as well. User does not need to select opposite faces multiple times in case thickness changes in space. Just enter the maximum thickness value a part has and Femap does the rest for you. Its further possible to combine the mid surfaces so they appear as a single entity in the history tree.

 

  • Tools in the meshing toolbox

Before creating a mesh, the meshing toolbox offers multiple value added features to clean and modify the underlying geometry for a better mesh.

  • Project curve:

This features splits the extracted surface at the boundary of thickness transition so that the underlying elements are able to update the shell thickness property as the thickness changes on either side of the split.

  • Feature removal options

There are many features in CAD that may not be needed in FEA analysis and holes are the prominent ones. It is possible to close holes and similar geometries with just a click, if needed. By default, a point entity is created at the geometric center of the closed holes to make sure a kinematic constraint can be applied at those points, if needed.

  • Pad and washers

These features allow for mesh refinement in the vicinity of holes and depending on the geometry of holes, either a washer (circular) or a pad (square) option may be chosen. The feature creates iso-parametric meshes around the holes based on the distance of influence defined by the user. This is an “on the fly” feature that updates an existing mesh every time this feature is executed instead of creating a new mesh.

  • Dynamic node repositioning

This is a very handy feature to improve mesh quality on the fly. With the mesh quality contour option active, user can dynamically move any node of the mesh either on surface or on a curve until its quality improves which is instantly perceived by the user as element color changes from red to green. The effect of this tool is very local and only a few elements in the vicinity of selected node are considered at a time.

  • API’s for automating repetitive tasks

Most of Nastran based BDF’s include multiple RBE’s. Femap understands the pain of creating these RBE’s manually and applying boundary conditions to them. The custom tools provide an option to create RBE’s by selecting peripheral curves or nodes. The independent nodes are created automatically. Using API’s it is further possible to completely automate the RBE generation process.

The grouping options in custom tools provide an option to automatically define a group for independent nodes of all the RBE2’s in the model. This group can later be used to create constraints on RBE’s without picking each independent node individually.

 

In this series of ‘what’s new in 2019” release we will highlight new features in standalone fe-safe as well as in durability apps of 3D Experience platform. General enhancements as well as specific enhancements in fe-safe/rubber are included.

Durability roles in 3D EXPERIENCE Platform

  • Fatigue specialist role in 3D EXPERIENCE Platform is now available in 2019 GA though it was introduced in 2017x FD05. Perhaps one of the most interesting feature of any role on the platform is its “look and feel” apart from robust functionality behind the scene. Here is how latest fatigue specialist role looks like. The durability app is integrated into structural and mechanical scenario apps. Moreover, unlike standalone Fe-Safe, it is possible to visualize 3D model while creating scenario for durability in 3DX. Structural analysis case job and durability case job can be launched simultaneously from user interface.
  • Fatigue Loading: Number of complex loading scenarios are supported on the platform since 2018x release. These include superposition, sequence of stress or stress-strain frames, mean stress correction etc.
  • Dynamic case supported: There was enough requirement to support durability simulation for dynamic events.  Durability cases of FEA can now be used to define loading on the platform.
  • Surface finish: The Kt factor can be defined directly as a surface finish.
  • Cloud: The role is now available both on premise as well as on cloud.
  • Material properties/algorithms: Now include cast iron, SN curve definition, eN curve definition as well as constant amplitude endurance limit. The algorithms now include finite life, infinite life as well as stress based and strain-based algorithms.

      Enhancements in standalone Fe-Safe

  • Weld fatigue enhancement: No need to have perfectly structured meshes in region below the weld line nodes through the thickness for the calculation of nodal forces and structural stress. However, element faces should be present on the crack surface.
  • Integration of Tosca, Abaqus and Fe-Safe verity for the optimization of chassis sheet thickness with multiple seam welds.
  • Groups and sets created within Fe-Safe are now written out in the Fe-Safe ODB file.
  • A new algorithm called Prismatic Hull infinite life method was introduced in 2018xFD01 that is now available in 2019xGA.
  • Interpolation engine in Fe-safe Rubber: Abaqus Rubber models are computationally extensive and take long time to solve. In many situations full duty cycle takes long time to solve in abaqus. Now user can break up duty cycle in standard series of load combination levels. When imported in Fe-Safe rubber, solver can make interpolations to approximate full duty cycle stresses from standard series of stresses.

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2019 solver has number of enhancements that spans from fracture mechanics to element formulation to material formulation. Let’s start with what’s there on the fracture mechanics side:

Fracture mechanics enhancements

  • Introduction of new linear elastic fatigue crack growth procedure: Allows for change in contact conditions while loading, allows non-linear geometry behavior, mixed mode fatigue loading and viewer improvement. It is currently available for constant amplitude loading only. The input deck for mixed mode behavior looks as follows:
  • Improvements in contour integrals pre-processing and solving time. This applies to both J-integrals as well as K-integrals.
  • XFEM improvement to increase smoothness of 3D non-planar crack front. This is achieved by introducing non-local stress averaging algorithms to predict crack direction. Also limit new crack propagation direction to a certain angle from previous direction.
  • Symmetric cohesive elements have been introduced. Plane of symmetry must be perpendicular to one of the global axis though.
  • Introduction of UDMGINI subroutine to incorporate varied crack initiation criteria for different enrichment zones.

Element technology enhancements

  • Poro-elastic acoustic elements have been introduced to study wave propagation in coupled isotropic poro-elastic medium. It is only available in steady state dynamics analysis.
  • Displacement acoustics pressure elements have been introduced: C3D8A, C3D6A, C3D4A. Primary unknows are structural displacement and pore pressure. Same shape function used for displacement and pressure.
  • Shear panel element SHEAR4 in Abaqus has been introduced to model thin reinforced panels such as in fuselage. Intended to model response of buckled plate. Use is limited to linear elastic only.
  • Variable beam radius element formulation now available in Abaqus that can be well visualized in viewer as well.

Material enhancements

  • Low density foam has been introduced in Abaqus standard in 2019x FD01. This material has already been present in explicit. This material is useful in modeling highly compressible elastomeric foams.
  • Output variable SROCK for rock mechanics effective stress.
  • Enhancements to super-elastic materials to improve convergence and performance of material model. This application would be of interest in healthcare industry. An environment variable should be introduced to activate the model. Available from 2018x FD04.
  • Transverse shear stiffness modulus has been introduced for shell and beam sections. This now obviates the user material model to deal with plates of spatially varying thickness or plates made of composites.
  • Damage in concrete due to plasticity can now be modeled by defining failure criteria and element deletion criteria.
  • Two new outputs introduced in explicit for cohesive elements: equivalent nominal strain NEEQ and equivalent nominal strain rare NEEQR

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