SAMPE 2016_PREDICTING STRESS RELAXATION BEHAVIOR

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Transcript of SAMPE 2016_PREDICTING STRESS RELAXATION BEHAVIOR

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Predicting Stress Relaxation Behavior of Fabric Composites Using Finite Element Based Micromechanics ModelAnand Vijay KaruppiahGraduate Research AssistantMentor: Dr. Suresh Keshavanarayana Raju Wichita State University

ContentsIntroductionLiterature ReviewFinite Element Based Micromechanics ApproachResults & DiscussionConclusion

Introduction

What is Viscoelasticity ? E.g. Polymers, Fiber Reinforced CompositeWhat is stress Relaxation?

Woven Fabric Composite: E.g. Plain Weave, Satin Weaveetc.Aerospace Structural Applications:

1. http://www.aerooptimal.com/industries/composite-structures

Stress Relaxation

Problems Faced in ExperimentsStress distribution is Inhomogeneous and unknownSlippageOut-of-plane Bending Deformation (Buckling)

Before Loading After LoadingMicro viewMacro viewUniaxial loading

3-Point Bending (Flexural Loading)

Finite Element based Micromechanics Model Approach

Literature ReviewPlain Weave Architecture2001(Shrotriya ,P et al.)

2012 (Kawai Kwok)

1. Three-dimensional viscoelastic simulation of woven composite substrates for multilayer circuit boards by Shrotriya .P et al.2. Micromechanical modeling of deployment and shape recovery of thin-walled viscoelastic composite space structures by Kawai Kwok

AssumptionThe Unit cell model is idealized to contain a linearly viscoelastic matrix and orthogonally interlaced unidirectional (UD) composite tows (fiber bundles) with waviness and straight regions. Both fill and warp tows are assumed to contain equal fiber volume fraction.Cross section of tows are assumed to be a flattened lenticular shape.

Woven Fabric Type: 8-Harness satin Weave

Procedure followedStep 1:Calculating the Design Parameters

Waviness (Crimp) angleAspect ratio of tow cross sectionFiber Volume fraction of TowLength of the Unit cell

Microscopic Image of 5320-8HS cross sectionFilaments with ResinLaminateTow cross section

Method: Subcell Modeling ApproachThe model is assumed to contain repeating pattern of binary subcells within the unit cell itself.

Software's Used: CATIA V5, Hypermesh v10 and FORTRAN 90.

Step 2: Modeling the Unit cell of 8-Harness Satin Weave

1. Rao .M.P,Pantiuk .M, Modeling the Geometry of Satin Weave Fabric Composites. Journal of Composite Material, Vol. 43, No. 1/2009.

8-Harness Satin Weave

Step 1:ContinueDesign Parameters

hfhW

gwaiasaiashm

hwL

hwL

LT

Assembly of Binary Subcells for 8-Harness Satin Weave Architecture

Step 2: (Contact Bodies) Continued

Fill TowsWarp TowsNeat Resin

FEA Software Used: MSC Marc v2014Commercial software

Contact Method followed:Segment-Segment

1.MSC Marc 2011 r1 Reference Manual Vol. B: Element Library, MSC. Software Corporation, Santa Ana, CA, 2011, pp 611.2.MSC Marc 2011 r1 Reference Manual Vol. A: Theory and User Information, MSC. Software Corporation, Santa Ana, CA, 2011, pp 611.

Fiber Bundle/Tows Weave Architecture of 8-Harness Satin Unit Cell (RVE) of 5320-8HS Woven fabric (Vf=0.56)

Constituents Properties

Material and Sample FabricationMaterial Used: Cytec Cycom 5320-8 HS (Harness Satin) weave fabric prepreg and 5320-1 Pure Epoxy ResinOut-of-autoclave materialDimension: 36mm x 5mm x 0.51mmNominal cure temperature: 250F for 1hrRecommended post-cure temperature: 350F for 2hrs

Stacking Sequence for 5320-8HS[0/90/90/0][+45/-45/-45/+45]

Method used: Stress Relaxation

5320-8HS Prepreg Material

5320-1 ResinSilicon Mold

Molded 5320-1 Resin Specimen

Material and Sample Fabrication Cont.

Debulking SchemeDebulk time: 20 minutesManufacture Recommended Cure Profile

Stress Relaxation Recorded Displacement, Temperature0 t0 t1 t Time (min)Thermomechanical loading stress 0 t0 t1 t Time (min)Displacement TemperatureTest Procedure:

Step 3: Experimental determination of Viscoelastic properties of 5320-1 Epoxy ResinDynamic Mechanical Analyzer (DMA)

Test setup for 5320-1 Pure Epoxy Resin

5320-1 Resin

3-Point BendingTension

Master curve Formulation

Prony SeriesWilliam Landel Ferry (WLF) EquationStep:1Step:2Step:3

1.Cytec. CYCOM 5320-1 Epoxy Resin System. Accessed on [12/18/2015]; Available from http;//www.cemselectorguid.com/pdf/CYCOM_5320-1_031912.pdf.2.Cytec. CYCOM T650-35K Carbon Fiber. Accessed on [12/21/2015]; Available from: http://cytec.com/sites/default/files/datasheets/THORNEL_T650-35_052112.pdfTable 1. Elastic and thermal properties of the fiber and neat resin

iEi (MPa) (s)12.56E+022.75E+0222.33E+025.41E+0332.35E+029.41E+0442.59E+021.47E+0653.73E+021.38E+0765.86E+029.67E+0774.79E+028.05E+0883.70E+025.58E+0994.72E+023.34E+10

Table 2. Relaxation times and coefficients of the Prony series for 5320-1 Epoxy Resin

Step 4: Estimating the Material Properties of Viscoelastic Tows/Fiber Bundles

Hexagonal Array of 5320-UD

Stiffness matrix:

(Vf 0.77)

11 Stress contour under 140 C at 2000s b) 23 Stress contour under 140 C at 2000s

12 Stress contour under 140 C at 2000s

22 Stress contour under 140 C at 2000s

Step 5: Verification of Model Prediction

Homogenized solid model under flexural loading(FEA Model)Experimentation of 5320-8HS

5320-8HS

Overall View of Finite Element Analysis

[+-90] & [+-45] Homogenized laminate model5320-8HS unit cell (RVE) model Hexagonal array (Vf 0.77)

Fill TowsWarp Tows 8 Harness interlaced satin weave architecture

Stress Relaxation Behavior of Woven Fabric

2. Defining the Contact Body for 5320-8HS Unit cell model (Segment-Segment Contact Algorithm)Estimating the Viscoelastic Properties of Fiber Bundle with Known fiber and Resin Properties under different Load cases 3. Verification of Unit cell Model Prediction3. Applying Kinematic conditions of Periodic Symmetryand analyzing under different load cases

Accuracy of Micromechanical Model(Elastic Behavior)

5320-8HS SystemEXPERIMENTFEA (Unit Cell)% ERRORE11 (Msi)10.100010.69385.8789E22 (Msi)10.200010.70154.9163E33 (Msi)--1.8019--0.04800.04486.6693--0.4855----0.4851--G12(Msi)0.75500.73043.2532G23(Msi)--0.5723--G31(Msi)--0.5727--

Results and Discussion

Experimental Results

Experimental comparison of Effective Stress relaxation of 5320-8HS and 5320-1 at 140 C

Numerical Results

Stress Relaxation Behavior of 5320-8HS Unit cell under different load cases at 140 C

Comparison of Experimental and Numerical Results

(a) (b)

Flexural viscoelastic Behavior of 5320-8HS at 140 C a) [+-45] plies b) [+-90] plies

Stress contours for normal load along the warp direction at time of 2000 s a) Fill Tows b) Warp Tows c) 5320-8HS Unit Cella)b)c)Observation

Stress contours for normal load along the Fill direction at time of 60s, 500s, 1000s,1500s, 2000s a) Fill Tow#2 b) Warp Tow#2 a)b)

Stress contours of Neat Resin region around Fill tow#2 at time of 60s, 500s, 1000s,1500s, 2000s

Observation: (Contin.) (a) (b)

Distribution of 31 in 5320-8HS Laminate model at 2000 s Variation of 31 in 5320-8HS Laminate model along the width of the Specimen at 2000 s, 1500 s, 1000 s, 500s, 100 s, 6 s

32

ConclusionDeveloped Micromechanical model predictions are in good agreement with experimental results.Although the fiber reinforcement improves the mechanical properties of resin, it does not always improve its viscoelastic properties.Also, developed micromechanical model can be used to predict the viscoelastic behavior for different various fiber volume fraction.Therefore, this in turn reduces a lot of material testing cost and labor.Similar procedure can be followed for all woven fabric system

Future StudyIn our current research, we are focusing to validate the master curve generated from the elevated temperatures with micromechanical prediction.Also, we are focusing to enhance our computation using Parallel Processing Technique.

ReferencesKarami, G., Finite Element Micromechanics for Stiffness and Strength of Wavy Fiber Composites. Journal of Composite Material, Vol. 38, No. 4/2004.Shrotriya, P., Sottos, N., Viscoelastic response of woven composite substrates. Composite Science and Technology, Vol. 65, 2005, pp. 621634.Zhu, Q., Shrotriya, P., Geubelle, P., Sottos, N., Viscoelastic response of a woven composite substrate for multilayer circuit board applications. Composite Science and Technology, Vol. 46, 2003, pp. 394402.Kawai, K., Mechanical modeling of deployment and shape recovery of thin-walled viscoelastic composite space structures. 53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2012.Abadi, M.T., Micromechanical analysis of stress relaxation response of fiber-reinforced polymers. Composites Science and Technology 69 (2009): p.12861292.MSC Marc 2011 r1 Reference Manual Vol. B: Element Library, MSC. Software Corporation, Santa Ana, CA, 2011, pp 611.MSC Marc 2011 r1 Reference Manual Vol. A: Theory and User Information, MSC. Software Corporation, Santa Ana, CA, 2011, pp 611.Cytec. CYCOM 5320-1 Epoxy Resin System