Elements: An Engineering Simulation Blog

With the combination of increased CPU speed and advances in simulation algorithms, nonlinear analyses have become more mainstream and are now reliably and more quickly solved. One example of the advancement of algorithms is the mesh Nonlinear Adaptivity (NLAD) capabilities in ANSYS® Mechanical™ Workbench™ and MAPDL (Classic ANSYS).

Nonlinear adaptivity refers to the capability of the FEA solution process to adapt to changing conditions during a nonlinear analysis. The solution process uses a feedback mechanism to discretely or continuously adjust some internal parameters automatically so that an accurate and convergent solution is obtained.

Adaptive meshing is an example of an adaptive process. For instance, in highly nonlinear problems, excessive calculated deformation can cause analyses to fail due to poorly shaped elements. In these cases, a remesh in the middle of the nonlinear solve can return the mesh back to well-shaped elements and allow the solve to continue. In many cases, this is the only way to get a high deformation solve to converge properly.

One question often facing engineers performing any type of simulation analysis is, “How can I simplify my model and still get accurate results?”

A case in point for FEA analyses: When engineers have a large assembly with multiple parts but are interested in the simulation results of only one of the parts, only the part of interest needs to be fully modeled and meshed. The remaining parts can be reduced to a point mass where their effects are accounted for, but they are not fully meshed. As a result, this approach significantly reduces the size of the overall model as well as the solution time. In other words, it is a much smaller model to solve.

Stress linearization is a technique used to decompose a through-thickness elastic stress field into equivalent membrane, bending, and peak stresses for comparison with appropriate allowable limits.

• Membrane stress is the average stress through the thickness (P/A)
• Bending stress is the linearly varying stress through the thickness (Mc/I)
• Peak stress is the total stress minus the membrane plus bending stress

Stress linearization was developed in the pressure vessel industry by Kroenke and Gordon in the 1970s. It was first implemented in Section III (nuclear vessels) and Section VIII, Division 2 (commercial vessels) of the ASME Boiler and Pressure Code. Although widely used in industry thereafter, specific guidance was not included in ASME Boiler & Pressure Vessel Code (BPVC) Section VIII Div. 2 until 2007.

While ANSYS Workbench can be used to validate designs, care must be taken in how the stresses and their locations are handled.

Ron Gagnon
Sr FEA Consulting Engineer
Fatigue & Fracture ExpertMechanical fatigue is a VERY popular topic with the ANSYS user community, with many engineers and designers attending our fatigue-related webinars over the past few years.

Luckily, all our fatigue-related webinars—as well as all recent webinars—are recorded and available anytime. Learn more about mechanical fatigue and how to use ANSYS and nCode DesignLife to solve fatigue models in these webinars:

Exploring Basic Fatigue Calculations In ANSYS® Workbench™
Thermo-Mechanical Fatigue (TMF) using ANSYS® nCode DesignLife™
Weld Fatigue Analysis

For the first time, engineers can gain instant, accurate access to the Granta materials database within ANSYS Workbench™, speeding up their materials selection and improving their workflows.

In late 2018, ANSYS, Inc. acquired Granta Design, the premier provider of materials information technology. Through the MI:Materials Gateway window within ANSYS Workbench, you can access validated materials information in several categories, including steel, plastics, and aerospace.

If you know which material you’re looking for, you can select it directly. Or you can search with keywords like “aluminum 6061,” and the material’s property datasheets will be shown to you. You can also ask Granta to show you materials with defined specs, like yield strength above or below a certain value. You can then compare and contrast different materials.