Have you ever found yourself wondering which Abaqus element formulation is most suitable for your analysis? With the vast options provided within Abaqus Standard and Abaqus Explicit, novice and experienced users alike often find themselves asking this very question, and for good reason: selecting the appropriate element type with respect to your simulation objectives is vitally important for obtaining accurate results. In this blog series, we aim to highlight some of the key aspects one should consider when determining the optimal Abaqus element formulation for a given analysis.
Article 3: Understanding Element Functionality in Abaqus
Because Abaqus can be used to simulate such a diverse array of problems, understanding the full range of its capabilities can sometimes be overwhelming. A good place to start when trying to grasp the breadth of features is to review the various element types available. Since we have already discussed some of the fundamental principles governing Abaqus elements, including nomenclature and dimensionality, we can now start to explore the extensive collection of special purpose elements at our disposal:
Stress/Displacement Elements
Diffusive Elements (Heat Transfer)
Forced Convection Heat Transfer Elements
Coupled Temperature-Displacement Elements
Pore Pressure Elements
Fluid Pipe and Fluid Pipe Connector Elements
Coupled Temperature-Pore Pressure Elements
Piezoelectric Elements
Electromagnetic Elements
Coupled Thermal-Electric Elements
Coupled Thermal-Electrical-Structural Elements
Acoustic Elements
Poroeleastic Acoustic Elements
Stress/Displacement Elements
Stress/Displacement elements, by far the most commonly used type of finite element, can be used to model a wide range of mechanical behavior. Although some codes can only simulate linear conditions, Abaqus can be used to understand complex non-linear behavior, including hyperelasticity, plasticity, large deformations, and contact (among others). Possessing only displacement degrees of freedom, stress/displacement elements can be used to perform static, quasi-static, implicit transient dynamic, explicit transient dynamic, modal dynamic, steady-state dynamic, acoustic, shock, coupled acoustic-structural, and fracture analyses.
Diffusive Elements (Heat Transfer)
Diffusive elements, otherwise known as heat transfer elements, are used to represent scenarios in which heat storage (specific heat and latent heat effects) or heat conduction must be considered. Available in Abaqus Standard and containing only temperature degrees of freedom, diffusive elements can be used in both steady-state and transient analyses to predict thermal behavior. Capable of accounting for convective and radiative contributions to heat transfer, these versatile elements can be used to simulate a litany of problems ranging from simple, single-component analyses to highly complex assemblies with gap conductance and cavity radiation.
Forced Convection Heat Transfer Elements
Much like diffusive elements, forced convection heat transfer elements allow for heat storage (specific heat) and heat conduction; however, as the name suggests, they also account for the convection of heat by a fluid flowing through the mesh at a prescribed flow rate (forced convection). A potential scenario which could warrant the use of these elements is when simulating a fluid-filled pipe with an initial temperature pulse: the initial temperature pulse will diffuse due to conduction in the fluid and pipe, but it will also be transported down the pipeline.
Coupled Temperature-Displacement Elements
Coupled temperature-displacement elements should be employed when simulating conditions in which the stress state is dependent on the temperature and the temperature is dependent on the displacement (or strain). A classic example is a metal stamping or forging operation in which the heat generated from the plastic deformation or friction influences the temperature-dependent material properties (and vice versa).
Pore Pressure Elements
Pore pressure elements, which are only available in Abaqus Standard, are a special subset of elements which can be used to represent fully or partially saturated fluid flow through a deforming porous medium. Utilizing a combination of displacement and pore pressure degrees of freedom, pore pressure elements can be used for performing soils and geostatic analyses.
Fluid Pipe & Fluid Pipe Connector Elements
Fluid pipe and fluid pipe connector elements are special-purpose elements that are commonly used when performing soils or geostatic analyses. Fluid pipe elements are suitable for modeling incompressible pipe flow and fluid pipe connector elements are used when modeling the junction between two pipes. Containing only pore pressure degrees of freedom and available in Abaqus Standard, fluid pipe elements are commonly used to simulate the viscous and gravity pressure losses occurring in a fluid pipe network while fluid pipe connector elements allow for the definition of discrete viscous pressure loss terms within a fluid network.
Coupled Temperature-Pore Pressure Elements
Coupled temperature-pore pressure elements (which are also only available in Abaqus Standard) are appropriate when modeling environments in which the stress, fluid pore pressure, and temperature strongly influence one another. A relevant example is that of a subterranean pipeline which heats the surrounding permafrost, thereby changing the soil load bearing capacity and, in turn, influencing the stress in the pipe.
Piezoelectric Elements
Piezoelectric elements are required when modeling problems in which an electric potential gradient induces strain, while stress causes an electric potential gradient in the material. Available in Abaqus Standard and containing both displacement and electric potential degrees of freedom, piezoelectric elements can be used in static stress, implicit dynamic, steady-state dynamic, natural frequency, and transient modal analyses.
Electromagnetic Elements
Electromagnetic elements should be used for problems involving magnetic fields as well as those in which there is coupled behavior between electrical and magnetic fields. Specifically, electromagnetic elements are required when performing magnetostatic and eddy current analyses within Abaqus. Magnetostatic analyses ignore electromagnetic coupling and simply use Maxwell’s equations to compute the magnetic fields due to direct currents. Eddy current analyses, on the other hand, assume fully coupled behavior between electric and magnetic fields, which are solved for simultaneously.
Coupled Thermal-Electrical Elements
Coupled thermal-electrical elements are appropriate for modeling heating that occurs as a result of electrical current passing through a conductive material, otherwise known as Joule heating. This type of problem requires full coupling since the temperature-dependent electrical conductivity influences the heat generated, which in turn impacts the electrical conductivity. Coupled thermal-electrical simulations are regularly performed on PC boards and other products in the high-tech industry: electrical current is used to power the processors (and other components), which in turn generates heat, thereby changing the conductivity, and altering the generation of additional heat.
Coupled Thermal-Electrical-Structural Elements
Coupled thermal-electrical-structural elements can be used in situations that require displacement, temperature, and electrical behavior to be solved simultaneously (because the state of each influences the behavior of the others). Such a scenario might be encountered during the spotwelding process: the pressure between the weld tips influences the electrical current, which influences the temperature.
Acoustic Elements
Acoustic elements are used to model small pressure changes in acoustic media and are suitable when performing acoustic and coupled acoustic-structural analyses. Although acoustic elements can be used alone, whereby the acoustic pressure is controlled by a single pressure degree of freedom, they are more commonly used in conjunction with a structural model in a coupled analysis.
Poroelastic Elements
Poroelastic elements are special purpose, volumetrically coupled acoustic elements used to model porous media undergoing small displacements and small changes in pressure. Containing both displacement and pressure variables, poroelastic elements are used in acoustic and, more commonly, coupled acoustic-structural analyses.
As we’ve seen today, the full breadth of Abaqus’ capabilities are quite astounding. Whether you’re interested in simulating the mechanical, thermal, electrical, magnetic, acoustic or coupled physics of (almost) anything, Abaqus has a solution (and an elegant one, at that)! Stay tuned for future installments of our Element Selection blog series for more tips and tricks that can be used when determining the elemental makeup of your Finite Element Analysis (FEA) model!
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