Friday, January 23, 2009

Pressure penetration analysis of an air duct kiss seal



Seals are common structural components that often require design analyses. In this example, a nonlinear finite element analysis of seals is performed. Pressure penetration effects between the seal and the contacting surfaces are to be considered in these analyses, to make routine analyses of seals more realistic and accurate. Analyses of clutch seals, threaded connectors, car door seals and air duct kiss seals are some applications where pressure penetration effects are important. The surface-based pressure penetration capability is used to simulate pressure penetration between contacting surfaces.

Submodeling of a stacked sheet metal assembly



Sheet metal stampings stacked and fitted on top of each other and secured together via mechanical fasteners such as bolts or rivets are commonly used in the automotive industry. Examples include seat belt anchors and seating track assemblies. The submodeling capability in ABAQUS facilitates economical, yet detailed, prediction of the ultimate strength and integrity of such jointed assemblies. A global model analysis of an assembly is first performed to capture the overall deformation of the system. Subsequently, the displacement results of this global analysis are used to drive the boundaries of a submodeled region of critical concern. The submodeling methodology provides accurate modeling that is more economical than using a globally refined mesh in a single analysis

Self-contact in rubber/foam components: rubber gasket



This example demonstrates the use of the single-surface contact capability available for two-dimensional large-sliding analysis. Components that deform and change their shape substantially can fold and have different parts of the surface come into contact with each other. In such cases it can be difficult to predict at the outset of the analysis where such contact may occur and, therefore, it can be difficult to define two independent surfaces to make up a contact pair.
This model is used to analyze an oil pan gasket, which enhances the sealing of the oil pan against the engine block. The primary objective is to reach or exceed a threshold value of contact pressure where oil will not leak at the gasket bead/cover/engine block interfaces.

Self-contact in rubber/foam components: jounce bumper



Components that deform and change their shape substantially can fold and have different parts of the surface come into contact with each other. In such cases it can be difficult to predict at the outset of the analysis where such contact may occur and, therefore, it can be difficult to define two independent surfaces to make up a contact pair.
A jounce bumper, sometimes referred to as a “helper spring,” is a highly compressible component that is used as part of the shock isolation system in a vehicle. It is typically located above the coil spring that connects the wheels to the frame. Microcellular material is used because of its high compressibility and low Poisson's ratio value at all but fully compressed configurations.
The bumper initially sits against a fixed flat rigid surface on one end; on the other end, another flat rigid surface is used to model the compression of the bumper. The geometry of the bumper is such that it folds in three different locations. Separate surfaces are defined at the locations where self-contact is expected. This modeling technique produces an economical analysis because the scope of contact searches is limited.

Analysis of an automotive boot seal



Seals are common structural components that often require design analyses. In this example, a nonlinear finite element analysis of seals is performed. Pressure penetration effects between the seal and the contacting surfaces are to be considered in these analyses, to make routine analyses of seals more realistic and accurate. Analyses of clutch seals, threaded connectors, car door seals and air duct kiss seals are some applications where pressure penetration effects are important. The surface-based pressure penetration capability is used to simulate pressure penetration between contacting surfaces.

Damage and failure of a laminated composite plate



This example demonstrates how to model nonlinear material behavior in a composite laminate. The material model in this example includes damage, resulting in nonlinear behavior. It also includes various modes of failure, resulting in abrupt loss of stress carrying capacity.

Indentation of a thick plate



This example illustrates the use of adaptive meshing and distortion control in deep indentation problems.

Transient loading of a viscoelastic bushing



This example demonstrates the automatic incrementation capability provided for integration of time-dependent material models and the use of the viscoelastic material model in conjunction with large-strain hyperelasticity in a typical design application. The structure is a bushing, modeled as a hollow, viscoelastic cylinder. The bushing is glued to a rigid, fixed body on the outside and to a rigid shaft on the inside, to which the loading is applied. A static preload is applied to the shaft, which moves the inner shaft off center. This load is held for sufficient time for steady-state response to be obtained. Then a torque is applied instantaneously and held for a long enough period of time to reach steady-state response. We compute the bushing's transient response to these events.

Stress-free element reactivation



This example demonstrates element reactivation for problems where new elements are to be added in a stress-free state. Typical examples include the construction of a gravity dam, in which unstressed layers of material are added to a mesh that has already deformed under geostatic load, or a tunnel in which a concrete or steel support liner is installed.

Shell-to-solid submodeling and shell-to-solid coupling of a pipe joint



Submodeling is the technique used in ABAQUS for analyzing a local part of a model with a refined mesh, based on interpolation of the solution from an initial global model (usually with a coarser mesh) onto the nodes on the appropriate parts of the boundary of the submodel. Shell-to-solid submodeling models a region with solid elements, when the global model is made up of shell elements. Shell-to-solid coupling is a feature in ABAQUS by which three-dimensional shell meshes can be coupled automatically to three-dimensional solid meshes. The analysis is tested as a static process in ABAQUS/Standard

Hydrostatic fluid elements: Modeling an airspring



Airsprings are rubber or fabric actuators that support and contain a column of compressed air. They are used as pneumatic actuators and vibration isolators. Airsprings are considerably more flexible than other types of isolators. The airspring's inflation pressure can be changed to compensate for different loads or heights without compromising isolation efficiency. Static analyses are performed in ABAQUS/Standard. A three-dimensional, half-symmetry model that uses finite-strain shell elements is used to model the rubber spring; three-dimensional, hydrostatic fluid elements is used to model the air-filled cavity; and rebar to model the multi-ply steel reinforcements in the rubber membrane. In addition, a three-dimensional, element-based rigid surface is used to define the contact between the airspring and the lateral metal bead. The cord-reinforced rubber membrane is modeled using a hyperelastic material model with steel rebar. In all analyses the air inside the airspring cavity has been modeled as a compressible or “pneumatic” fluid satisfying the ideal gas law.

Notched beam under cyclic loading



This example illustrates the use of the nonlinear isotropic/kinematic hardening material model to simulate the response of a notched beam under cyclic loading. The model has two features to simulate plastic hardening in cyclic loading conditions: the center of the yield surface moves in stress space (kinematic hardening behavior), and the size of the yield surface evolves with inelastic deformation (isotropic hardening behavior). The component investigated in this example is a notched beam subjected to a cyclic 4-point bending load.

Jointed rock slope stability



This example illustrates the use of the jointed material model in the context of geotechnical applications. The stability of the excavation of part of a jointed rock mass, leaving a sloped embankment was examined.

Collapse of a concrete slab



This problem examines the use of the smeared crack model for the analysis of reinforced concrete structures. A square slab is supported in the transverse direction at its four corners and loaded by a point load at its center. The slab is reinforced in two directions at 75% of its depth.

Indentation of an elastomeric foam specimen with a hemispherical punch



A cylindrical specimen of an elastomeric foam is indented by a rough, rigid, hemispherical punch. Examples of elastomeric foam materials are cellular polymers such as cushions, padding, and packaging materials. This problem illustrates a typical application of elastomeric foam materials when used in energy absorption devices. Design sensitivity analysis is carried out for a shape design parameter and a material design parameter to illustrate the usage of design sensitivity analysis for a problem involving contact.

Parametric study of a linear elastic pipeline under in-plane bending



Elbows are used in piping systems because they ovalize more readily than straight pipes and, thus, provide flexibility in response to thermal expansion and other loadings that impose significant displacements on the system. The elbow is, thus, behaving as a shell rather than as a beam. This example demonstrates the ability of elbow elements to model the nonlinear response of initially circular pipes and pipebends accurately when the distortion of the cross-section by ovalization is significant.

Elastic-plastic collapse of a thin-walled elbow under in-plane bending and internal pressure



Elbows are used in piping systems because they ovalize more readily than straight pipes and, thus, provide flexibility in response to thermal expansion and other loadings that impose significant displacements on the system. Thus, even under pure bending, complex interaction occurs between an elbow and the adjacent straight pipe segments; the elbow causes some ovalization in the straight pipe runs, which in turn tend to stiffen the elbow. This interaction can create significant axial gradients of bending strain in the elbow, especially in cases where the elbow is very flexible. The analyses predict the response up to quite large rotations across the elbow, so as to investigate possible collapse of the pipe and, particularly, the effect of internal pressure on that collapse.

Thursday, January 22, 2009

Axisymmetric analysis of bolted pipe flange connections

A bolted pipe flange connections are composed of hubs of pipes, pipe flanges with bolt holes, sets of bolts and nuts, and a gasket. These components interact with each other in the tightening process and when operation loads such as internal pressure and temperature are applied.

To establish an optimal design, a full stress analysis determines factors such as the contact stresses that govern the sealing performance, the relationship between bolt force and internal pressure, the effective gasket seating width, and the bending moment produced in the bolts. This example shows how to perform such a design analysis by using an economical axisymmetric model and how to assess the accuracy of the axisymmetric solution by comparing the results to those obtained from a simulation using a three-dimensional segment model. In addition, several three-dimensional models that use multiple levels of substructures are analyzed to demonstrate the use of substructures with a large number of retained degrees of freedom.