Super Elastic Alloy Eyeglass Frame Design Using the ANSYS

CFD Services | ANSYS Consulting | FEA Services | CivilFEM | CFD Consultant | Engineering Consulting Firm

Super Elastic Alloy Eyeglass Frame

Design Using the ANSYS Workbench

Environment

Peter R. Barrett, P.E.Patrick Cunningham, M.S.M.E

© 2011 CAE Associates – 1579 Straits Turnpike, Suite 2B, Middlebury, CT 06762 – (203) 758-2914

g ,

http://www.caeai.com/computational-fluid-dynamics.php

http://www.caeai.com/engineering-analysis-simulation.php

http://www.caeai.com/structural-thermal-analysis.php

http://www.caeai.com/engineering-software-consulting-civilfem.php

http://www.caeai.com/computational-fluid-dynamics.php

http://www.caeai.com/

ANSYS, Inc. Proprietary© 2004 ANSYS, Inc.

Super Elastic Alloy Eyeglass Frame Design Using the ANSYS Workbench EnvironmentSuper Elastic Alloy Eyeglass Frame Design Using the ANSYS Workbench Environment

Peter R. Barrett, P.E.Patrick Cunningham

60 Middle Quarter MallWoodbury, CT. 06798(203)263-4606 Fax (203)266-9049


Analysis Goal

• The goal of the analysis is to determine the configurations of the eyeglass frame that can tolerate being stepped on and still be capable of recovery meeting stiffness design requirements.


Analysis Tools

• Demonstrate the use of sensitivity analysis at the concept stages of an eyeglass frame design.

• Tools used include:– The ANSYS Workbench Environment

• Parametric geometry is created using DesignModeler• Boundary conditions, material constants, and meshing

controls are defined using the Simulation tool.• Sensitivity studies are run using DesignXplorer

– ANSYS’s super-elastic material model


Integration of the Analysis Tools

DesignModeler• Develop fully parametric geometry

models.• Remove geometric details that have

little bearing on the analysis result.• Slice up geometry and reform parts

to enable sweep meshing in the Simulation tool.

Simulation• Define material models.• Auto or manually define contact

element pairs.• Apply boundary conditions.• Apply Solution Controls.• Debug the initial analysis run.• Define input and output variables for

the sensitivity study. DesignXplorer• Define tolerances on the input • Determine the critical parameters of

the system. • Optimize within the input/response

characterization. • Create a deterministic result of the

optimum configuration.


Design Modeler Parametric Model Development

• The geometric model is built using the parametric feature capabilities of the Workbench/DesignModelertool.

• Each dimension used in the development of the geometry is converted to a named parameter that is accessible as an input variable for the sensitivity study.

• Parameter relationships and dependences are defined to prevent conflicts during model regeneration


Setting up the Analysis Environment

• Once the geometry is complete in DesignModeler it is attached in the Simulation Tool

• Meshing, material properties, boundary conditions, and solution controls are defined in the solution tool

• Toggling between the design and analysis tools is possible at any time using the Workbench tabs


Meshing in Workbench

• DesignModeler is also used to slice the geometry in the desired regions to enable automatic sweep meshing in the DesignSimulationtool.

• Mesh sizing controls are added in the DesignSimulation tool.

• A coarse finite element mesh is used for this example.


Super Elastic Material Model

• Nitinol is an acronym for Nickel Titanium Naval Ordinance Laboratory since the alloy was originally developed at the U.S. Naval Laboratory.

• It is used to describe a family of materials, which contain a nearly equal mixture of nickel and titanium.

• Nitinol alloys are attractive because they are biocompatible and are at their optimum super-elastic behavior (9% strain fully recoverable) at room temperature when processed properly.


Stress vs. Strain for a Nitinol Material Model using ANSYS

• Constant Definition • SIG-SAS (C1) Starting stress value for the forward phase transformation • SIG-FAS (C2) Final stress value for the forward phase transformation • SIG-SSA (C3) Starting stress value for the reverse phase transformation • SIG-FSA (C4) Final stress value for the reverse phase transformation • EPSILON (C5) Maximum residual strain • ALPHA (C6) α material responses ratio between tension and compression• YMRT (C7) Modulus for Martensite (This is Beta in 8.0/8.1)


Material properties

• The material properties are defined in the Simulation tool using the Preprocessing Command Builder.

• The Preprocessing Command Builder enables access to the ANSYS material model GUI.


Creating Rigid Target Surfaces

• In the Workbench Simulation module contact pairs are automatically defined between adjacent parts when the geometry is attached.

• For this case we have opted to define the crushing surfaces as rigid target elements which do not require underlying solid elements.

• As a result, the rigid target surfaces and the contact pairs are defined using APDL commands.


Creating contact pairs using APDL

• The first step in the APDL generation of the contact pairs is to identify the surfaces on the model where the contact elements will be generated.

• This is easily done by defining Named Selections for the top and bottom surfaces in the Simulation tool.


Named Components in Workbench

• The named surface selections on the solid geometry will be transferred to ANSYS as nodal components.

• Named Solids will be transferred as Element Groups

• Loads are transferred as surface effect elements that can be further modified in ANSYS


Defining Contact Pairs using APDL

• The Preprocessing Commands worksheet is used to define the target elements in the following fashion: – Use *get commands to

determine the maximum element type number and real table defined.

– Define new contact and target element type numbers.

– Define new real tables for the contact pairs

– Use APDL commands to directly generate the nodes and elements of the rigid target surfaces.



• The Preprocessing Commands worksheet is also used to define the contact elements: – Select the nodal

components of the top and bottom surfaces.

– Select solid elements attached to the nodes.

– Specify element attributes.

– Use ESURF to generate the contact elements.



Notes: – A self contact pair is defined around the perimeter of

the lens frame. This pair could also have been defined using the manual contact capability in the Workbench Simulation tool.

– The target surfaces could also be defined using surface geometry and the resulting shell elements converted to rigid target elements using the EMODIF command in the Preprocessing Commands worksheet.


Boundary Conditions

• The following boundary conditions are applied to the model:

1. A frictionless support is applied on the bridge of the glasses to establish reflective symmetry. This is applied as a support inside the Simulation environment.

2. The lower rigid target is fixed in all degrees of freedom. This constraint is defined using the Processing Command worksheet.

3. The upper rigid target is displaced –1” in the vertical direction. This constraint is defined using the Processing Command worksheet.


Solution Controls

• The nonlinear solution controls are defined using the Preprocessing Command Builder.

• Multiple load steps (loading and unloading) are defined using the solution controls menu.

• Does require adding SOLVE commands to the Preprocessor Command Builder


Initial Solution in the Simulation Tool

• Prior to the sensitivity study, an initial solution is generated by solving in the Simulation environment.

• This is not a required step, but it is always recommended, particularly for debugging the nonlinear solution.


Postprocessing the initial Simulation

• Postprocessing of the initial simulation run can be done with a combination of the standard Simulation solution tools and the Postprocessing Command Builder.

• The Simulation environment only has access to the last converged solution and the results are limited to linear quantities with the exception on contact results.


Postprocessing the initial simulation

• The Postprocessing Command builder can be used to look at the full contents of the ANSYS result file.

• All results steps written to the ANSYS result file are accessible.

• All nonlinear results are accessible

• Time history plots and result combinations are also possible using the result viewer.


Time History plots using the PostprocessingCommand Builder

• The Postprocessing Command builder can be used to plot the hysteresis response of the shape memory alloy.


Time History plots using the PostprocessingCommand Builder

• Result plots and listings from the PostprocessingCommand Builder can be returned to the Simulation Environment. These figures are then included in the design report.


Setting up the Sensitivity study environment

• Once the initial solution is resolved, input and output variables for the sensitivity study are defined in the simulation environment.

• Input and output variables are defined by checking the box to the left of the parameter.

• In this case we specify the defining geometric parameters as the input variables


Setting up the Sensitivity study environment

• The output variables for this study are the Von Mises stress and the deformation in the load direction.

• The stress can be used to simulate the elastic response, while the displacement is used to measure stiffness


DOE Method of Design Explorer

• When the data is attached to a DesignXplorer session, the upper and lower bounds (or discrete values) of the input variables must be defined.


Design Explorer DOE – Solution

• For the DOE method used by DesignXplorer the number of deterministic solutions required is automatically determined based on the number of input variables.



• Sensitivity of Max. Von Mises stress vs. Frame thickness and Frame bottom radius are illustrated in the Figure.

• As expected the larger the larger radius / thinner frame produces the lowest stress values

• Specific data is extracted from the Response Tabs



• “Soft” Design Sets are created in Design Explorer directly from the DOE

• A chosen design can then be run explicitly to get the hard design results

• Data can also be exported to a spreadsheet for integration into design rules, etc.


Conclusions

• The combination of design modeler, design simulation and design explorer provide a valuable tool for upfront engineering

• Complex material models and Highly nonlinear analyses were easily adapted into the workbench environment

• Sensitivity results (example on right) provide valuable data for the design engineer to quickly determine the most relevant design parameters

Documents

Super Elastic Alloy Eyeglass Frame Design Using the ANSYS