Realistic simulation using FEA tools to design and optimize plastics

REALISTIC SIMULATION USING FEA TOOLS
TO DESIGN AND OPTIMIZE PLASTICS
Arindam Chakraborty, PhD, PE
Partner, Virtual Integrated Analytics Solutions (VIAS)
Houston, TX
www.viascorp.com
May 10, 2017

Agenda
© 2017 Virtual Integrated Analytics Solutions Inc.
• VIAS Overview
• Realistic Simulation
• FEA of Plastics
• Durability of Plastics
• Design Optimization
• Simulation for Additive Manufacturing
• Case Studies
• Concluding Remarks
2

VIAS Overview
Engineering
Consultancy
Training
Hardware
Software
• Multiple Industry Experience
• Presence in Houston (Main Office), Chicago, Cincinnati, Detroit,
San Francisco,
• Team consists of Ph.D. and Masters in Solid Mechanics, Fluid
Mechanics, Materials and Corrosion, Numerical Analysis,
Statistics; Optimization and Reliability
• Solution partner of Dassault Systèmes SIMULIA products –
Abaqus, Isight, fe-safe, Tosca
• Provide Virtual Design Experience through Collaboration and Data
Analytics – Provides Automation and Customization
• Provide 3D Printing and AM Simulation Services
4

Our Technical Capabilities
Design by Analysis and
Validation using
Simulation
FEA based Fracture /
Damage Mechanics
Optimization and
Reliability
Multi-physics
Simulations (CFD,
Thermal Analysis)
Composites and
Elastomer Modelling
Delamination, De-
bonding and Crack
Propagation
S-N and e-N based
Fatigue Analysis
Simulation Automation /
Plugin
In Environment Testing
and Test Program
Support
Additive Manufacturing
Simulation
5

What is Realistic Simulation?
© 2017 Virtual Integrated Analytics Solutions Inc. 7
• “Realistic Simulation” is a simulation that is physically realistic and “life
like” in every way
• Enables engineers to create life like models that will behave similarly to the real part / product.
• Typically, start with simple models and increase the complexity, model size and the physics as
confidence in simulation results increase their
• Enables building up expertise and most importantly find value in the simulation

Why Realistic Simulation?
• Designers often create innovative concepts,
but retreat to conventional shapes due to
limited time and resources for physical
prototyping and testing
• Simulation enables designers to virtually
test new innovative concepts
▪ Reduces design time and the expensive cost
of physical testing
▪ Lowers material cost and improves
sustainability by light-weighting
▪ Reduces damage cost during production
and transport by eliminating bad designs
quickly
Courtesy Mechanical Design and Analysis Corporation, 2010 SCC

Challenges in Modelling Plastics and Polymers
• Polymeric materials are complex in their mechanical
behavior
• Exhibit large strain, anisotropic and irreversible
response which is often accompanied by stable
localized necking behavior
• Modelling failure and fracture a challenge
• Simulation software/ models must deal with severe
non-linearities
Blow Molding (Plastic Bottle)
Necking (ASTM D638 Hyperelastic)
Viscoelastic Rubber
Seal Insertion
Fracture/
Delamination
Viscous Paste

FEA for Thermo-Mechanical Response of Plastics
• Initial FEA simulation codes were largely
developed for heavy duty components and were
concerned predominantly with metals
• Plastics/ Polymers have much higher strains and
large displacements in comparison to metallic
materials
• Modern FE codes accommodate large strain
formulations, including hyperelasticity,
viscoelasticity
• Non-linear codes (Abaqus) perform better since
they are designed to accommodate large
deformations
• Physically Motivated Models - material response from a viewpoint of the microstructure
• Phenomenological Models - material response from the viewpoint of continuum
mechanics

Necking in Polymer – Strain Rate Effect
Necking: Testing vs Simulation
(ASTM D638 Specimen)
Necking: Strain Rate
Dependence

FEA of Plastic Fabrication
• Plastic part fabrication generally entails the process
of injection molding
• The main aim for the injection molding process is
to maintain uniform wall thickness of the
component
• A non-uniform thickness during the process causes
▪ Sink marks within the component
▪ Residual stresses due to uneven shrinkage
▪ Warping of component
▪ Voids within components
• FEA gives us an opportunity to preemptively
predict, visualize and minimize these effects

Solution Paradigm 11
22
12
033 
11
22
12
033 
Fatigue Life Prediction
Given the material properties and
strain history of a rubber
component, compute the number of
cycle repeats that will be endured
before the fatigue process produces
cracks of a given size
Crack Driving
Force
Crackgrowth
rate
StrainHistory
NominalStrain
Time
11
22
12
Material
Properties
Nonrelaxing Option
Quantify Strain Crystallization, Min
and Mean Strain Effects
Thermal Option
Quantify dissipative properties,
thermal properties, temperature
dependence
Hyperelastic Option
Simple, Planar, and Equibiaxial
tension, Mullins Effect

Design Optimization
• Process Integration and Design Optimization
• Integrate Disparate Simulation Tools without programming
• Automate Simulation Process Flows

Simulation for Evolving Technologies: Polymer AM
Part level simulation with support structures
Tool Path information from slicer (GrabCad)
Warping Effects –
Mobius Arm
Material Orientations during layup
Abaqus Thermal Model vs
Thermal Imaging Data

Multi-scale Infill Homogenization: Polymer
Extrusion Methods
Geometric Infill's
Multi-scale material homogenization
using RVE Method
Representative Volume Elements
(RVEs)

Case Study: Impact Analysis (Handgun Slider)
Preliminary Prototype Test
Prototype Simulation
0
5000
10000
0 10 20 30
Stress(psi)
Strain (%)
Material Stress-Strain Data (Test)
Polycarbonate
(Higher Strain Rate)
Polycarbonate
(Lower Strain Rate)
Softer Polymer (Low
Strain Rate)
Polymer
Metal Cage (For
Stiffness)

Case Study: Plastic Bottle Drop

Case Study: Residual Stress
• Residual stresses may be introduced into plastic parts produced by the injection
molding process
▪ As a result, the part may warp or experience a reduction in strength
▪ The design of an injection molded product can be improved if the effect of
residual stresses on the final shape and performance of the product are predicted
accurately
• Abaqus and Moldflow can be used for this purpose

Case Study: Fatigue Life of Polyurethane
Fixed
Step 1: Fit piston and rubber seal inside liner
Step 2: Apply Pressure
Translation of piston and
urethane seal inside liner using
reference point of rigid body
Rigid body with center point at
the axis as reference
Pressure = 5000 psi
Number of cycles for
Pressure Load = 120
cycles /min
Temperature: 170 F

Determine the stress field from FEA model in the rubber seal within the mud pump
piston under application of cyclic operating pressure

• The lowest fatigue cycles in the seal is 2.7E+06 cycles.
• Region with lowest fatigue cycles matches with the failure
location of the actual sample

Case Study: Collapse under Pressure
Optimize device wall thickness for specified collapsing pressures
0
200
400
600
800
1000
1200
1400
1600
1800
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5
Stress(psi)
Strain(in/in)
Stress-Strain Curve for Floelle Device and Silicone PenroseTube
MED-4810 MED-4815 MED-4050 (Silicone Penrose Tube)
Hyperelastic material
using Marlow strain
energy potential
model

Case Study: Blow Moulding - Plastic Bottle
• Challenge
▪ Check if a new bottle design can be
manufactured
▪ Expensive prototype cost to validate a
new bottle design
• Simulation
▪ Incorporate the geometry of new bottle
design and physical phenomena
involved in the Blow Molding process
• Value
▪ Quickly eliminate bad designs and
drastically reduce cost of prototyping
and testing
▪ Capture realistic thickness distribution
of package after blow molding
▪ Optimize preform shape to produce a
desired final thickness distribution

Case Study: Thickness Optimization
• Top Load (TL) thickness optimization
• Vary thickness smoothly along bottle height
▪ Use 5 thickness values as optimization
parameters
• Constraints – minimum TL force > 100 N
• Optimization target – minimize mass
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 50 100 150 200 250
Target Thickness
STH
• Mass: 43% reduction
• Meets target Top Loading Force

Highlights for Simulating Plastics
• Simulation can
– Capture complex material response (hyperelastic, elastic-viscoplastic, …)
– Include large deformation, dynamic response
– Provide tools to optimize design, perform reliability study
– Automate the analysis workflow
– Perform fatigue and fracture assessment for rubbers

Plugins, Plugins, Plugins

Summary
• In summary, simulation that mimics realistic scenarios helps by
– Increasing design robustness and confidence in product quality
– Decrease in development costs and improvement in product performances
– Providing a best possible starting point for futuristic and more advanced designs
– Functional design and optimization

Thank you
40

Realistic simulation using FEA tools to design and optimize plastics

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