Measurement of mechanical properties of pvc foam using a modified arcan fixture
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MEASUREMENT OF MECHANICAL PROPERTIES OF PVC FOAM USING A MODIFIED ARCAN FIXTURE PowerPoint PPT Presentation


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MEASUREMENT OF MECHANICAL PROPERTIES OF PVC FOAM USING A MODIFIED ARCAN FIXTURE. S T Taher 1 , O T Thomsen 1 , J M Dulieu-Barton 2 , S Zhang 2 1 Department of Mechanical and Manufacturing Engineering, Aalborg University, Denmark

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MEASUREMENT OF MECHANICAL PROPERTIES OF PVC FOAM USING A MODIFIED ARCAN FIXTURE

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Measurement of mechanical properties of pvc foam using a modified arcan fixture

MEASUREMENT OF MECHANICAL PROPERTIES OF PVC FOAM USING A MODIFIED ARCAN FIXTURE

S T Taher1, O T Thomsen1, J M Dulieu-Barton2, S Zhang2

1 Department of Mechanical and Manufacturing Engineering, Aalborg University, Denmark

2 School of Engineering Sciences, University of Southampton, UK

5th International Conference on Composites Testing and Model Identification

EcolePolytechniqueFédérale de Lausanne (EPFL), Switzerland

February 14-16, 2011


Outline

Outline

  • Background and key-methods

  • Modified Arcan fixture (MAF)

  • Digital image correlation (DIC) setup

  • Tensile and shear testing

  • Nonlinear finite element analysis (FEA)

  • Conclusions

  • Ongoing and future work

  • Acknowledgement


Background

Background

  • Polymer foam cored sandwich structures are often subjected to aggressive service conditions which may include elevated temperatures.

  • Previously, the Arcan test rig has been used to measure bidirectional properties of polymer foams used for sandwich core materials, especially in the bidirectional tensile-shear stress region.

  • A modified Arcan fixture (MAF) has been developed to characterize polymer foam materials with respect to their tensile, compressive, shear and bidirectional mechanical properties. In presented work tensile and shear properties obtained using short Dogbone (SD) and Butterfly Shape (BS) specimens.


Key methods

Key methods

  • Measurement of mechanical properties of selected polymer foam core materials (with focus on closed cell PVC) subjected to tension, compression and shear loading using a modified Arcan fixture (MAF).

  • A full field technique is used for non-contact measurement of the specimen deformations - Digital Image Correlation (DIC)


A new bidirectional fixture

A new bidirectional fixture

Classical Arcan fixture with circular distribution of griping holes

New fixture with spiral distribution of griping holes


Bidirectional material test fixture patent no pa 201100050

Bidirectional Material Test Fixture (Patent No: PA 201100050)

Quasi-spiral passed griping holes

Fixture arm

Butterfly shape specimen

Metallic base bounded to foam specimen


Specimens for maf fixture

Specimens for MAF fixture

BS Shear & SD tensile BL compressive

bidirectional

Note: Thickness of all specimens is 15 mm


Dic system and setup

DIC system and setup

Load cell

Light

CCD

camera

CCD

camera

  • System:

    • ARAMIS 4 M (GOM GmbH)

    • Lenses: 50 mm (Family C)

    • Resolution: 2048x2048 pixels

    • Strain accuracy: up to 0.01 % (ARAMIS hardware manual)

  • Setup:

    • 2D measurement

    • Measurement on both sides of specimen

    • Synchronized with two CCD cameras and load cell data


Dic setup for modified arcan fixture maf

DIC setup for modified Arcan fixture (MAF)


Tensile sd test results using dic raw data

Tensile SD test results using DIC (raw data)

Smoothing technique: Robust local regression using polynomial model (MATLAB)


Dic aramis problem with large shear strain measurement

DIC (Aramis) problem with large shear strain measurement

Facet size: 60 pixels

Steps: 30 pixels

“Solution” techniques:

Using a new pattern

Dividing the images to two groups for analysis


New technique for pattern generation

New technique for pattern generation

Classical technique New technique

  • Making white background surface (here using zinc oxide powder)

  • Spraying black speckles on white background

Facets and overlap

12

Smearing black ink onto the surface

Spreading white powder (zinc oxide) onto the surface

Cleaning top of the surface to visualize cell walls


New pattern dic results up to 70 of failure strain stage i

Dividing the images in two analyses

New pattern DIC results up to 70% of failure strain (Stage I)

Image 1 Image 60 Image 80 Image 100

  • Last 30% of analysis (Stage II)

Image 120 Image 140

  • Facet:60 pixels

  • Step: 30 pixels

  • No smoothing applied to results


Bs shear stress strain response

BS shear stress-strain response

  • DIC correlation lost around 40% of failure strain when using the first image as a reference for the analysis of all images (ARAMIS software)

  • DIC correlation improved up to 70% of failure strain using new pattern (stage I)

  • Rest of curve (stage II) computed in a new analysis using 70% strain image as the new reference image for the image correlation

Stage I (new pattern) Stage II

Old Pattern

Smoothing technique: Robust local regression using polynomial model (MATLAB)


Different shear specimens butterfly shaped bs

Different shear specimens(Butterfly shaped - BS)

Fracture initiates at gauge section

  • Radius 6.67 mm

  • Radius 4.5 mm

  • Radius 2.5 mm


Correction factors for measured surface strains

Correction factors for measured surface strains

DIC

camera

a

a

Gauge section

Gauge section

Y

Z X

a

a


Bilinear material approximation for nonlinear fea

Bilinear material approximation for nonlinear FEA

Gauge line

Gauge line

(Strain%)

(True strain)


Nonlinear fe modelling for shear test

Nonlinear FE modelling for shear test

Gauge section shear strain

Gauge line shear strain

  • ANSYS 12.1

  • Nonlinear material model – bilinear at present (sequentially linear in the future)

  • Large deformations

  • Element type: solid186 (higher order solid element)

  • Number of nodes: 35k

(True strain)


Measurement of mechanical properties of pvc foam using a modified arcan fixture

Possible convergence

problem?

Nonlinear correction factors after FEA iterations


Fea corrected stress strain curves

Shear and tensile stress-strain behaviour of H100 PVC foam after “corrections”

FEA “corrected” stress-strain curves

Experimental shear stress-strain data and “corrected” curve for H100 foam based on nonlinear FE analysis


Maf measurement of orthotropic properties divinycell h100 cross linked pvc foam

MAF measurement of orthotropic properties – Divinycell H100 (cross-linked PVC foam)

  • * Indices 1 and 2 represent the through-thickness and in-plane directions, respectively.

  • ** linear elastic properties measured using DIC at the University of Southampton

  • *** Standard test data by DIAB


Conclusions

Conclusions

  • H100 Divinycell cross linked PVC foam show significant orthotropic material behaviour.

  • BS specimen with smallest radius (2.5 mm) in shear test failed at gauge section and was selected as a reference shape for shear test by MAF.

  • Nonlinear FEA was used to correct measured surface strains to obtain “corrected” stress-strain data. As expected, the strain correction factor obtained displayed it highest values in the linear region of the foam material.

  • There is a good agreement between the material properties by standard tests data and the MAF data


Ongoing and future work

Ongoing and future work

  • Compressive testing

  • Thermal degradation measurements in thermal chamber using DIC

  • Nonlinar material modeling using ABACUS

  • Bidirectional shear-axial testing


Acknowledgement

Acknowledgement

The work presented has been co-sponsored by the Danish Council for Independent Research Technology and Production Sciences (FTP), Grant Agreement 274-08-0488, “Thermal Degradation of Polymer Foam Cored Sandwich Structures”, and the US Navy, Office of Naval Research (ONR), Grant Award N000140710227, The ONR program manager was Dr. Yapa D. S. Rajapakse. The financial support received is gratefully acknowledged.


Thank you q a

Thank youQ & A


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