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Fast Generation of Allowable for CFRPAnthony CHERUET / e-Xstream Engineering

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Overview

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Virtual Allowable with Digimat VA

1 Digimat Technology

Challenges with Composites

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From Coupon to Components

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e-Xstream engineering

• The company• Founded in 2003

• Acquired by MSC Software in Sep 2012

• The Business: • 100% focused on material modeling

• A team of 50 people • 65% PhDs

• 25% MS & BS Engineering

• 10% Marketing, Finance & Admin

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Louvain-la-Neuve

Bascharage

Munich

Belgium

Luxembourg

Germany

U.S.

E-Xstream Engineering

• More than 300 hundreds customers in the world: aerospace, automotive, materials suppliers and academics.

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Digimat to simulate Multiple Types of Multi-Phase material with one Single Tool

• Digimat, Unique Solution for Multi-Materials

Short Fiber Reinforced Plastics Long Fiber ThermoplasticsWoven & Braided Composites

Hybrid Composites

Carbon Nanotubes

Mucell

Unidirectional fiber

sandwich panel

DFC

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Multi-Scale Modeling Technology

• Prediction of Non-Linear Anisotropic Macroscopic behavior from constituents properties and microstructure

Semi-Analytical method

Mean-Field homogenization

• Mori-Tanaka

• Fast model preparation/solution

• Easy coupling with FE solver

RVE Direct Analysis method

Full-Field homogenization

• Build the accurate RVE geometry

• Compute it by FEM directly

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Digimat, the multi-scale material modeling platform

Tools= knowledge transfer

Solutions• Workflow oriented• Integrated environments

eXpertise• Knowledge transfer

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Overview

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Virtual Allowable with Digimat VA

1 Digimat Technology

Challenges with Composites

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3

From Coupon to Components

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• The introduction Composites Materials required to re-scale completely the procedure of material testing

Insertion of Composites material relies on a Building Block Approach for Certification (by testing)

• First step of material characterization is done at the coupon level

• Required a very large experimental test matrix

• 1 to 2 years of testing

• cost in M$

• In 1980: Choices were limited

between few materials, mainly

Aluminum

• In 2000 : Introduction of

Composites materials has

enlarged the choice between

materials, combination of ply

stacking.

• The concern has also changed:

focus more on the damage

tolerance, effect of environment…

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• TODAY: Generation of Allowable done by physical tests during long and costly campaign

• Need to cover different configurations

• Coupon type (UN, OH, FH, Bearing)

• Layup

• Environment conditions: RTD, ETW

• Need a lot of replicate to extract a statistical evaluation of the material properties (e.g. B-basis) accounting several sources of variability:

• Material Properties

• Process

• Experimental

Insertion of Composites material relies on a Building Block Approach for Certification (by testing)

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• Substantial Time Savings

• High Quality Data Early in the Design Cycle

• Substantial Cost Savings

• Expansion of the Design Space

Why Not Use Virtual Testing?

Digimat VA is a Virtual Testing Solution for Laminate Allowable Computation

Productive Tools to Define, Solve and Post Process a complete test matrix for specific Standard Tests

Benefits

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• At the opposite of metallic material which exhibit non-linear yielding, the only reliable and observable event in a CFRP test is the final failure

• Failure stress or strain are seen as the allowable of the composite, determined for a standard condition

Need 1: Progressive Failure Modeling to compute Allowable of CFRP

• Different failure modes appear depending on the angle between reinforcement and loading direction

• Fiber Breaking in longitudinal plies• Matrix Cracking in transverse plies

s

e

erupture

srupture

•Need for a Progressive Failure Modeling to simulate properly up to the final rupture of laminated structure

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• Variability of the properties is also more important for composites than for metallic materials

Variability of Composite Materials

• Allowable:• A material property value that is statistically derived from test data coming from a stable process• Value that will be used for the design but that must be of confidence b-basis value

Materials (Constituents) Variability

Process Variability

Post-Process Variability

•Need for the definition of a test matrix allowing to capture the variability expected during manufacturing coming from several sources

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Overview

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Virtual Allowable with Digimat VA

1 Digimat Technology

Challenges with Composites

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3

From Coupon to Components

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Digimat VA is a vertical solution to efficiently set up and compute virtual allowables

1. Material

Calibration

2. Lay-up definition

3. Tests Geometry 5. Mesh Settings

6. Allowable

Computation

4. Variability

7. Statistical

Results

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• Mean-field homogenization in a RVE to calibrate anisotropic stiffness of the ply

• Specific capabilities for UD and 2D woven (Basic and Advanced description of the weave pattern)

Progressive Failure Modeling in Digimat

Constituent materials Microstructure Anistropic properties of

the plyFiber

(transversly isotropic)

Resin (TD or TP)

Fibers

Volume fraction

Phases Properties were calibrated Volume Fraction is assumed to match the stiffness (for UD and woven)

Yarn

Weaving Pattern

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• Definition of anisotropic damage evolution law at the ply level

Progressive Failure Modeling in Digimat

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Fiber Failure Matrix Failure

Hashin 2D criteria is used for UD

Multi-Components 2D is used for woven

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• Digimat-VA creates multiscale material models based on composite datasheet

Digimat Material Definition

Based on NCAMP datasheet template, Digimat VA performs automatically a material calibration, builda micro-mechanical model and adds the Progressiv

e Failure Behavior of the Ply

Input Data per NCAMP format

Import Exp. Data

Constituent Properties Calibration

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Definition of the test matrix

Definition of the Layup• Can be Hybrid Layup

Definition of Parameterized tests (ASTM)(UNT, UNC, OHT, OHC, FHT, FHC (protusion and countersunk)

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Definition of the test matrix

Definition of the Mesh Settings and pre-vizualisation

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Digimat-VA turns a test matrix into FEA runsto obtain virtual allowables

Raw stress-strain

B-basis com

putation

Coupon simulation

• Embedded FEA solver

• Digimat Progressive Failure

• Micro-level variability

Test matrix definition

• Parameterized

Standard Tests

Virtual allowables

• Mean, B-basis, A-basis

• Root-cause analysis

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Progressive failure predicts a realistic strengthin a straightforward way

Matrix Failure located in 90 plies (D22)

[45/0/-45/90]2s

[45/0/-45/90]2s

Fiber Failure located in 0 plies (D11)

Reference Value = 47.6 ksi

Composites strength will be the maximum of the curve

Visualization of the Failure Pattern

• Example on OHT with quasi-isotropic layup of AS4/8552 (NIAR Report)

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A Digimat Progressive Failure model is valid acrossdifferent layups and coupon types

Material: Hexcel 8552 / IM7

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Validation case using Plain Weave AS4/8552

• NIAR provided experimental results to validate the implementation of the wovenreinforcement within Digimat

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• New filled hole test

• Bolt/countersunk fastener

• Tension & compression tests

• Smart analysis stop beyond load drop

• AS4/8552 UD validation based on NCAMP data

Digimat-VA opens up to filled hole test

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Overview

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Virtual Allowable with Digimat VA

1 Digimat Technology

Challenges with Composites

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B-basis generation

4 From Coupon to Components

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• Thanks to microscopic description of the composite, variability can be introduced at several levels

Introduction of Variability for Statistical Analyses

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• Insertion of Material (Constituent) variability

Computation of the Stiffness and Strength Ply properties with variability

Method 1: Coefficient of variability can be introduced directly based on the in

-house experience or provided by Materials Suppliers

Method 2: Build a methodology to reverse engineer the variability of the Fiber

and Resin knowing the variability observed experimentally at the lamina level

1. Determine constituents variabilities to converge towards the

experimental lamina b-basis

2. Re-use this variability when the lamina is used in a laminate

A complete case study has been realized based on the UD AS4/8552 Statistical

Analysis Report provided by the NIAR (NCAMP databasis) – Methodology

presented at NAFEMS, CAM-X, SAE, webinar.

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• Using this methodology, we identify the variability of the fiber and the resin that allow to reproduce correctly the variability at the lamina level

• With Digimat VA, we simulate 4 standard tests on a single ply, respecting the test matrix (nb batches * nb panels * nb coupons)

Prediction of b-basis at the lamina level

The prediction of the b-basis are correct too

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• Tests are then run with the calibrated material model including the variability and the default settings of Digimat VA

• Mean values are predicted within 10%, except for OHT3, OHC2 and UNC2

Running the test matrix accounting variability

Layup: 0/45/90• Layup 1: 25/50/25

• Layup 2: 10/80/10

• Layup 3: 50/40/10

Experimental Ply Variability

Identify Fiber/Resin Variability

Verify Ply Variability

Apply Fiber/Resin variability for Laminate

Allowable

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Effect of Defects due to Manufacturing in Digimat VA

• Need for new methodologies enabling to take into account micro or macro-scopic effect of defect coming from the manufacturing

• Methodologies that mix Material Engineering and Allowable Computation

• Effect of %, size distribution of Porosity on

mechanical stiffness and strength of Lamina

― Combination of Digimat VA micro-mechanics

material model and FE modeling of RVE

using Digimat FE

• Effect of Presence of Gaps on the

Laminate Strength

– Introduction of resin rich area

– Mapping of defect

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Overview

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Virtual Allowable with Digimat VA

1 Digimat Technology

Challenges with Composites

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3

From Coupon to Components

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Digimat Technology is available at each step of the Design Process

Material Engineering using Digimat FE & MF

Calibrations using Digimat-MF

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Allowable Generation Design and Stress AnalysesMaterial Engineering

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Prediction of Failure Mode/Loads of a Hybrid Laminate in Pin-loaded joint configuration

Material: Graphite/Epoxy (UNS12) UDGraphite/Epoxy (DMS2288) Wovens

Stacking:[( 45)3/90/( 45)2/04/90/04/( 45)2/90/[( 45)3]

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Prediction of Failure Mode/Loads of a Hybrid Laminate in Pin-loaded joint configuration

Net Tension

Shear Out

Bearing

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Conclusion

• Digimat-VA sets a first milestone for a Virtual Testing Solution

dedicated to the productive generation of virtual allowables

including variability

– Validated cases exist for UD and 2D woven

– Bearing will be the next test integrated

• Material Model can be used at the component level through coupled

analysis with any FEM solver

• Virtual Testing and Material Engineering must be used to speed-up

material development and to complement the test process

– Test Smarter: Save time and reduce test matrix

– Investigate design space: non-standard laminate, effect of defects