Simulations are powerful tools that replicate real-world scenarios, allowing engineers to analyze, predict, and optimize the performance of designs under various conditions. Understanding the fundamentals of simulation with ABAQUS CAE is essential for leveraging its powerful capabilities to analyze and optimize complex engineering problems accurately.

Abaqus has 3 distinct stages of simulation:

1. Pre-processing – The physical problem is created using Abaqus/CAE (graphically) or using any other preprocessor; thereafter an input file is generated.
2. Simulation/Solve – This process happens in the background for solving the numerical problem using implicit/explicit solvers and store the output variables in a binary file ready for post-processing.
3. Post-processing – The visualization module of Abaqus/CAE reads the neutral binary output database file and displays the output in various ways like contours and graphs. Other post-processing tools can also be used for this.

ABAQUS has no built-in system of units. The input data must be taken care of to have consistent unit system. Abaqus/CAE is divided into functional units called modules. Each module contains only those tools that are relevant to a specific portion of the modeling task. The following list of the modules available within Abaqus/CAE briefly describes the modeling tasks you can perform in each module.

Pre-processing modules

1. Part – Create individual parts by sketching or importing their geometry.
2. Property – Create section and material definitions and assign them to regions of parts.
3. Assembly – Create and assemble part instances.
4. Step – Create and define the analysis steps and associated output requests.
5. Interaction – Specify the interactions, such as contact, between regions of a model.
6. Load – Specify loads, boundary conditions, and fields.
7. Mesh – Create a finite element mesh.
8. Optimization – Create and configure an optimization task.
9. Job – Submit a job for analysis and monitor its progress.
10. Visualization – View analysis results and selected model data.
11. Sketch – Create two-dimensional sketches.

Once the setup is complete, Abaqus performs Finite Element Analysis (FEA) to convert the physical problem into a system of algebraic equations. The unknown variables, like displacements and temperatures, are approximated within each element, and the local element equations are assembled into a global system. Appropriate numerical techniques, such as direct solvers for linear problems or iterative methods for non-linear problems, are employed to solve these equations. After running the simulation, Abaqus generates detailed results on stress, strain, deformation, and other variables. These insights help manufacturers optimize design, reduce costs, enhance safety, and accelerate development, ultimately leading to better decision-making and a competitive edge.

Let us explore Abaqus through an example problem.

Problem Statement

A compression analysis of a rubber seal performed to determine the seal’s performance. The goal is to determine the seal’s Compression Load-Deflection (CLD) curve, deformation and stresses. The analysis will be performed using Abaqus/Standard.

The top outer surface of the seal is covered with a polymer layer, and the seal is compressed between two rigid surfaces (the upper one is displaced along the negative Y-direction; the lower one is fixed). During compression, the cover contacts the top rigid surface; the outer surface of the seal is in contact with the cover and the bottom rigid surface; in addition the inner surface of the seal may come into contact with itself.

Geometry and Materials

For any FEA model, accurate CAD geometry must be created. Abaqus supports both the construction of geometry using its CAD modules and the importation of CAD from other tools. Abaqus facilitates modelling axisymmetric, 2D planar and 3D parts. The seal is modelled as 2D deformable parts to simplify the analysis.

Accurate material definition in Abaqus is crucial for realistic simulation results, as it ensures the correct representation of material behaviors under various conditions. This precision is vital for predicting performance, reliability, and safety in engineered products. In this case, the seal is made of rubber, which exhibits highly non-linear stress-strain behavior, including hyper-elasticity, and large deformations. One of Abaqus’s strengths is its ability to calibrate materials, which we will discuss in upcoming blogs.

Geometries can be modeled as “Parts” in Abaqus, and instances of these parts combine to form the “Assembly.” This assembly is the geometric configuration to which loads and boundary conditions are applied to study the behavior.

Contact, Loads and Boundary Conditions

In Abaqus, defining accurate contact interaction properties is essential for simulating how surfaces engage, separate, and transfer forces. Achieving contact convergence is crucial, as it ensures the solution stability and accuracy during iterative nonlinear analysis.

Multiple surface sets are created to assign surface –to- surface and self-contact interactions to capture the contact properties between the layers of the seal. Finite sliding formulation is used as large deformations are expected to occur during the event of loading.

Translations and Rotations are arrested at multiple points on the top and bottom of the seal assembly, and a compressive load is applied in the form of displacement in Y direction on the top of the seal.

Discretization and Analysis

Meshing the parts/assembly by choosing the appropriate elements and sizes play a critical role in the convergence and accuracy of results. The Abaqus/Standard element library offers a comprehensive range of elements for accurately modeling complex geometries and behaviors in static and low-speed dynamic analyses.

Here, 4-node bilinear plane strain quadrilateral, hybrid, constant pressure element (CPE4H) is used for the seal as it a Hyper-elastic material prone to self-contact; 4-node bilinear plane strain quadrilateral element (CPE4) is used for the cover. Plane strain elements are typically used in 2D models representing a slice of a 3D structure. Abaqus Elements will be discussed in detail in the future articles.

Understanding the physics of the problem is crucial, including whether it is static or dynamic, linear or nonlinear, implicit or explicit. Dynamic problems differ from static ones due to the involvement of inertial effects and time. In this scenario, the seal undergoes a static load, causing it to deform.

The type of analysis and the required outputs are defined in the Step module. Compressive loads on seal is a highly non-linear problem. Material nonlinearity in rubber seal analysis involves accounting for the complex stress-strain behavior of rubber, including hyper-elasticity which is captured by the material properties. Geometric nonlinearity addresses the large deformations the seal undergoes; this can be defined in the Step module by turning on “Nlgeom”.

Results and Visualization

Abaqus has two categories of outputs viz. field and history. Field outputs provide data on variables such as stress, strain, and displacement across the model at specified increments, essential for understanding the overall behavior. History outputs capture time-dependent variables at specific points, aiding in detailed analysis of dynamic or transient events. The reaction force and spatial displacement at the location of load are requested in the history output, later combined to form the CLD diagram.

Abaqus has a post-processing visualization module where the requested outputs can be viewed as contour plots, graphs, animations etc.

Need for FEA analysis:

1. Accurate Stress-Strain Behavior: Captures nonlinear material properties like hyperelasticity and viscoelasticity.
2. Deformation Prediction: Models large deformations to predict seal behavior under compression.
3. Contact Simulation: Simulates contact interactions to assess sealing effectiveness and wear.
4. Load Distribution: Analyzes load distribution across the seal to optimize design and material usage.
5. Performance Validation: Provides reliable data on seal performance under varying conditions for product improvement.

The seal manufacturer benefits from FEA simulation in several ways:

1. Cost Reduction: Identifies design flaws early, reducing prototyping and testing costs.
2. Performance Optimization: Optimizes product performance and durability.
3. Risk Mitigation: Minimizes potential failures and improves reliability.
4. Time Savings: Shortens development cycles by accelerating design iterations.
5. Competitive Edge: Enhances product competitiveness through superior design and reliability.