2018 ncode user group meeting material... · composite failure criteria in ncode designlife

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2018 nCode User Group Meeting 

February 28 ‐ March 1, 2018 – Novi, MI USA

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Analysis of Composite Materials for Improved Vehicle Performance and Reduced Weight

Jeff MentleyApplications Engineer

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• What is a fibre‐reinforced plastic composite material?

Ideal material when high stiffness‐to‐weight and strength‐to‐weight ratios are required –For example:

Introduction

“A structural composite is a material system consisting of two or more phases on a macroscopic scale, whose mechanical performance and properties are designed to

be superior to those of the constituent materials acting independently.”(Daniel and Ishai, 2006)

BMW i3(fireballbase.com)

Boeing 787 Dreamliner(1001crash.com)

(Bloomberg, 2013)

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• Use of composite materials is still expanding• Aerospace and Wind turbines largest users carbon fiber

• 43,500 tons used in 2012

• Aerospace 18%

• Wind turbines 23%

• Automotive use of carbon fiber to be >$6 billion by 2020, overtaking aerospace

Demand for Composites is Increasing

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• Categories of composite materials

Composite Materials

Injection Molded MoldingCompound

Continuousfibers

Discontinuous fibers

Particulate filler Other(e.g. sandwiches)

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• Categories of composite materials

Composite Materials

Unidirectional Woven fabrics Laminates

ContinuousFibers

Discontinuous Fibers

Particulate filler Other(e.g. sandwiches)

Unidirectional composite lamina(Jones, 1999)

Longitudinal direction

Transverse direction Fill

direction

Warp direction

Woven composite lamina(Jones, 1999)

Unbounded view of a laminate(Jones, 1999)

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Short Fiber Injection Molded Composites

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8Importance of Manufacturing on Material Properties

Courtesy of

Resulting material is:• Inhomogeneous• Anisotropic• Temperature sensitive• Environment sensitive (polyamides)• Viscous component to behaviour

2-D random

fibers alignedwith flow

fibers aligned transverse to flow

FLOW

Skin-core effect

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• Stress Life Analysis;  Material properties from nCode database• Linear anisotropic results from standard FE solution

• Nonlinear results from FE solution and multi‐scale modeler

• Stress Life Analysis;  Co‐processing with multi‐scale modeler• Every location requests an SN curve

• Curve created based on location using micro‐mechanics

• Strain Energy Density as damage parameter• FE uses anisotropic material model

• Fatigue calculation is isotropic

Short Fiber Approaches in nCode DesignLife

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Structural FE

Short fiber SN Fatigue Solution using Standard FE Stress Results

CAD GeometryManufacturing

simulation

Material data  (SN curves)

Service loads

• Orientation tensor file• Layered shell element results

Fatigue durability

Material parameters

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13Short Fiber SN Composite Engine – SN interpolation model

• Fibre share  = orientation tensor resolved in stress direction (0≤≤1)• Family of SN curves reverse engineered from coupon tests each associated with a 

value of • Abs Max Principal or Critical Plane stress calculated• l is critical plane or dominant stress direction • Local SN curve determined by interpolation or extrapolation based on l

…for example

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Structural FE

Short fiber SN Fatigue Solution Co‐computing with Multi‐scale Modelling

CAD Geometry

Manufacturing simulation

Material data (SN curves)

Service loads

Material parameters

Fatigue durability

Multi-Scale Modelling

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Damage equation

W =  (Nf)

Strain energy history

W(t) = ij(t) ij(t)/2

stiff                                                      not stiff

=

Strain Energy Damage Parameter – The Concept

flow

direction

Strain Energy Density Curve

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17Strain Energy Curve Based on Local Stresses and Strains

Stra

in E

nerg

y D

ensi

ty P

aram

eter

W

Net section stress-life curve converted to local strain energy-life curve based on the FE simulation results for each orientation

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Continuous Fiber Composite Failure Criteria

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• Limit or non‐interactive failure criteria• Maximum stress 

• Maximum strain 

• Partially interactive failure criteria• Christensen 

• Hashin‐Rotem

• Hashin

• Hashin‐Sun

• NU 

• Fully interactive failure criteria• Franklin‐Marin

• Hoffman 

• Norris 

• Norris‐McKinnon 

• Tsai‐Hill 

• Tsai‐Wu 

• Custom (Python‐based)

Composite Failure Criteria in nCode DesignLife

111

, 1, 1, , 1

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• Metals• For multiaxial load cases, a yield criteria is used to characterise the end of linear elastic 

behaviour

• Examples of yield criteria (Jones, 1999):• Maximum stress

• Tresca

• Von‐Mises

Failure Criteria for Composites

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• Material: Satin‐weave glass/epoxy

Example #2 ( ‐ plane)

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Refs:• Tang P. Naval Ocean Systems Center Technical Report Ref. AD-A208 188, March 1989 (p.95).

Tsai-Wu

HoffmanTsai-Hill

Max. stressTsai-Wu

Hoffman

Tsai-Hill

Max. stress

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22Tsai‐Hill Static Failure Criteria

, 1

Where S1, S2, S12 are strength parameters

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• Participant in U.S. Department of Energy project “Integrated Computational Materials Engineering (ICME) Development of Carbon Fiber Composites for Lightweight Vehicles”.

Fatigue of Composites R&D

https://energy.gov/sites/prod/files/2017/11/f46/FY_2016_Lighweight_APR.pdf

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• Formulation:

1

where  ,  and  are S‐N curves

• Solve the above fatigue failure equation for

• Damage parameter (Miner’s rule): For each block  of  cycles:

• Damage accumulation:

∑

Tsai‐Hill Fatigue Failure Criteria

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• Demand for the use of composites is increasing, especially in automotive.• Fatigue of short fiber composites can be analyzed now with DesignLife. • Continuous fiber composites are required for large structural components and 

DesignLife 2018 has new beta capabilities available for evaluation.

Summary

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Jeff Mentley

Applications Engineer

Jeff.Mentley@hbmprenscia.com