Week 5 Sphere pressing on a plate

Contact is said to occur when the surfaces of two separate objects touch each other such that the surfaces are mutually tangent to each other. The surfaces in contact do not interpenetrate and can transmit forces from one body to the other. In order to prevent the interpenetration between the surfaces, the ANSYS program or any FEA software has to establish relations between the surfaces and this is done using CONTACT FORMULATIONS. When penetration is prevented by the program, it is said to have enforced Contact Compatibility. When the program fails to enforce contact compatibility between two surfaces in contact, interpenetration occurs to a large extent and the solver will face convergence issues and be forced to stop.

In an interface, we define the contact and target. While deciding between these two, we should keep in mind that ANSYS considers the contact body as the one which is not allowed to penetrate into the target body. But the target is allowed to penetrate into the contact body. If you are unsure of the behaviour of your system, then you can choose Symmetric type of contact. Otherwise, an Asymmetric type of contact can be used.

Frictional: We can specify any non-negative value as the frictional coefficient. So, the contact will handle shear stresses up to what is specified by the frictional coefficient. After this value, sliding will start to take place.

STEP CONTROLS

Time is an essential parameter in tracking all the analysis even though the model is time-dependent or not. In a static analysis where it is time-independent, the analysis takes place as steps in which the steps are incremented linearly. The beginning time will be 0, and the time for the final load application is 1. If some more load is added, then the time is going to be 2. Here, the time is not considered as minutes or seconds but as a counter or tracker. The sub steps respective

to the load steps will vary linearly.

Large deflection

This option helps the solver whether the large deflection, large stain, large rotation happening in the simulation should be taken into account. It is available for static structural and transient structural analysis. Enabling this by ON will help the solver to consider the large strain happening, such as metal forming in a simulation and deflection.

SOLVER CONTROLS

Solver controls provide some properties based on the analysis type. For both the static structural analysis and transient structural analysis the common properties are

● Solver type

● Weak springs

● Large deflection

Solver type

Helps in choosing the required solver type for carrying out a simulation. It offers three options,

Program controlled: default option. The program automatically chooses the solver based on the model application.

Direct: This is one of the solver types where the solver uses a Sparse solver (solver handles a system of equations where the coefficient matrix entries contain mostly zero) to solve the model.

Iterative: This type, when chosen, solves the model in PCG (Preconditioned Conjugate Gradient) or ICCG (Incomplete Cholesky Conjugate Gradient) solver. This is mainly used for electric and electromagnetic simulations.

Result

Findings

Directional Deformation about Y- axis

4 mm displacement of Sphere is visible from the simulation

Equivalent Stress on Plate

Maximum stress developed in the plate is 3296.5 MPa, and it is higher than the young’s modulus (250 MPa) of structural steel NL. As the stress developed is higher than the young’s modulus, the plate got plastically deformed.

Equivalent Elastic Strain

Since the center portion of the plate is deforms more, here the strain developed is more.

Equivalent Elastic Strain on Sphere

The maximum stain developed in the sphere is near to the periphery.