polymers performance overview bruce duncan...

Polymers Performance Overview

Bruce Duncan

Wednesday 18th April 2007

“Measurements for Materials Performance” 2004-2007

Scope and Aims: “The Performance of Materials programme will develop measurement methodologies and models for the assessment, prediction and ongoing evaluation of the properties of materials in a service environment critical to maintaining fitness for purpose.

Knowledge and best practice will be promoted to users through new facilities, standardised test methods and access to experts.”

E01: Non-destructive Adhesion Measurement of Coatings

• Project run by TWI and NPL• Focussing on engineering coatings, e.g.

– thermal spraying– plating– physical/chemical vapour deposition– polymer based

• Aim to develop NDE technique(s) to identify defective coatings– Supplied with coatings by industry


• Assess/prioritise available NDE techniques– Review report issued

• Report on most promising techniques– Thermography – static and flash (pulse)– Acoustic microscopy– Acoustic emission– Terahertz imaging– Surface acoustic waves

• Measurement protocols and case studies• GPG to assist method selection


static

• ThermographyFlash thermography

Heat conduction

Subsurface defect

IR radiationFlash lamp

Thermal camera

to PC

Yellow: Oxide interlayerBlue: Carbon interlayerPurple: Gold interlayerRed: Greasy substrateGreen: Clean substrate

Improving adhesion

Good adhesion appears hotPoor adhesion

appears cold

flash


• Ultrasonic technique that uses focused ultrasonic waves to image defects (15 or 75 MHz)

• Waves travel through specimen and portion reflected back by defects

Scanning acoustic microscope (SAM)


Terahertz imagingLimited to non-conducting materials

Flat Painted Panels - Aged

F1 F3

F5

Circled regions indicate defects


• Scanning acoustic microscopy able to detected delamination of coatings but not poor adhesion interface.

• Heat transmission thermography able to detect delamination but not poor adhesion.

• Flash thermography able to identify poorly adhered coatings thathave not delaminated.

• Laser surface acoustic wave also able to detect poorly adhered coatings

• Terahertz able to detect defects in organic coatings

F02: Sensing the Onset of Damage at Polymer Surfaces due to Environmental Exposure

• Weathering of Surfaces– Case study on durability or recycled plastics

• Autocatalytic degradation of previously weathered materials• Nano-indentation sensitive to surface embrittlement

– 'Weathering of Recycled Photo-Degraded Polyethylene', A. S. Maxwell, Feb 2007 (Submitted to Polymer Science and Engineering 2007)

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

1500 1600 1700 1800 1900 2000

Wavenumber (cm-1)

Abs

orba

nce

0 days UV exposure40 days UV exposure60 days UV exposure100 days UV exposure

IR

0

0.02

0.04

0.06

0.08

0.1

0.12

0 days UV ageing 40 days UVageing

60 days UVageing

100 days UVageing

Har

dnes

s (G

Pa)

HDPE-AHDPE-B

Nano-indentation

F02: Sensing the Onset of Damage at Polymer Surfaces due to Environmental Exposure

• Environmental Stress Cracking– Development of accelerated techniques– Strain hardening modulus correlates well with long-term ESC ranking– Suite of ISO standards published ISO FDIS 22088 parts 1-6– 'Prediction of Environmental Stress Cracking Resistance in

Polyethylenes', A. A. S. Maxwell and G. Pilkington, (Draft paper 2007)

9

10

11

12

13

14

15

16

17

1 10 100 1000 10000Time (hours)

Stre

ss (M

Pa)

LLDPE 1

LLDPE 2

LLDPE 3

0

5

10

15

20

25

30

ExxonMobil LLDPE Flexirene ExxonMobil 3518PALLDPE Polymer Grades

Stra

in h

arde

ning

mod

ulus

(MPa

)4 notch tests

1 2 3

Strain hardening

F04 Accelerated Ageing Protocol For Service in Hostile Conditions

• Four case studies completed– Weathering

• Good correlation of gloss and hardness with residual strength

– Full immersion, no load– Full immersion, continuous load

(flexure)• Residual strength falls with stress

and temperature– Intermittent exposure, no load

0 25 50 75 1000

100

200

300

400

500

Flex

ural

Str

engt

h (M

Pa)

Gloss Retention (%)

25 30 35 40 45 50 550

100

200

300

400

500

Flex

ural

Str

engt

h (M

Pa)

Barcol Hardness

F04 Accelerated Ageing Protocol For Service in Hostile Conditions

• Accelerated Weathering: Performance Testing of Polymer Matrix Composites, W R Broughton, G D Pilkington and D K Ratnakela, (NPL Measurement Note, DEPC-MN047, March 2007)

• Measurement Good Practice Guide No. 103: Accelerated Environmental Ageing of Polymeric Materials, W R Broughton and A S Maxwell

• Review of accelerated ageing methods and lifetime prediction techniques for polymeric materials, A S Maxwell, W R Broughton, G Dean and G D Sims, DEPC-MPR 016, March 2005

F07 Permeation, Absorption and Desorption of Liquids and Gases in Polymer and Multilayer Systems

• Influence of Temperature and Stress on moisture diffusion coefficient (D)– Significant temperature dependence: can be

the largest component of the uncertainty budget for D

– D increases with tensile stress: dramatically above yield stress

– Observations of the Influence of Temperature and Stress on Diffusion of Moisture in a Rubber-Toughened Epoxy Adhesive, Bruce Duncan and Gordon Pilkington, Draft paper 2007

– Measurement Good Practice Guide No. 102: Absorption and Diffusion of Moisture In Polymeric Materials, B C Duncan and W R Broughton, March 2007

D depends on temperature

F07 Permeation, Absorption and Desorption of Liquids and Gases in Polymer and Multilayer Systems

• Investigation into the role of interfaces in diffusion– 3-D finite difference model – Dielectric sensors for assessing local moisture levels– Uptake in different joint configurations – faster than predicted in the

initial stages– Diffusion of Moisture in Adhesive Bonds, B C Duncan, G Pilkington,

J S Nottay, C R G Allen, K Lawrence, J Urquhart and S J Roberts,DEPC-MPR 062, March 2007

0

0.5

1

1.5

2

2.5

0 5 10 15 20 25 30 35 40 45

Square Root Time (h1/2)

Moi

stur

e A

bsor

ptio

n (%

)

Grit and Etched

Milled & Etched

1-D Analytical Model PredictionsPredicted using 3-D FV model

F09 Prediction of the Lifetime of Adhesive Joints under Sustained Loading

Develop methods for characterising non-linear creep behaviour in structural adhesive joints

NPL Report DEPC-MPR 011 “A Review of Creep Modelling for Toughened Adhesives and Thermoplastics”

Model developed for characterising non-linear creep behaviour in structural adhesives

“Modelling Non-Linear Creep Behaviour of an Epoxy Adhesive”accepted for publication in International Journal of Adhesives and Adhesion

Characterise creep behaviour in thermoplastics and welded thermoplastics – polypropylene

Model developed for characterising non-linear creep behaviour in amorphous polymers

Paper “A Model for Non-Linear Creep in Polypropylene” to be submitted to Journal of Plastics, Rubber and Composites

Creep Modelling

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0 100000 200000 300000 400000 500000 600000 700000

time (s)

stra

in

superposition

experimental

differential equation

4.5 MPa

6.7 MPa

polypropylene

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0.02

0 100000 200000 300000 400000 500000 600000

time (sec)

stra

in

superpositiondifferential equationexperiment

9 MPa 6.8 MPa

polypropylene

−σ−σ+

−+σ=ε

01

1010

n

01

1

0

100 t

ttexp)(D

ttt

tt

expD)t(

Superposition for non-linear behaviour (2-step loading)

F09 Prediction of the Lifetime of Adhesive Joints under Sustained Loading

Develop measurement techniques and predictive model for characterising cyclic fatigue behaviour of structural adhesives

Measurement Good Practice Guide No. 104: Fatigue and Creep Testing of Adhesives and Thermoplastics

Produce design protocols for above areas in electronic form accessible via the internet

Module added to Adhesives Design Toolkit

F10 Adhesive Design Toolkit

www.adhesivestoolkit.com

F10 Adhesive Design Toolkit

• Adhesive selection - Want to find an adhesive for a particular application but don'tknow where to start? Try this module.

• Adhesive suppliers - Looking for who supplies what to where? Try this module. • Case Histories - A searchable selection of case histories but we are always looking

for more. • Stress analysis - A powerful tool to enable stress analyses to be carried out on a

variety of co-axial joints. Change joint geometries, features, adherends, cureconditions (hot or cold) and see what effect it has on the stress profile.

• Design guidance - It is easy to produce a poor adhesive joint and blame the adhesive. This module is designed to assist with the process and enable the user to avoid 'obvious' mistakes.

• Standards (NEW) - This module covers most, if not all, of the available standards(e.g. BSI, ISO, ASTM etc) that are relevant to adhesives and adhesive bonding. The information provided lists the standard reference number, the title and a short summary of each standard.

• Design, Preparation and Testing (NEW) - This module provides detailed information relating to the design, preparation and testing of adhesives and adhesively bonded structures.

• Forensic assessment (NEW) - Forensic analysis forms an important part both in the optimisation of bonding processes, understanding the factors that affect bond quality, and in the evaluation of bond failures.

F12 Development of test methods for determining the criticality of defects in composite materials systems under long-term loading

• Development of defect tolerance test methods for long-term loading – Development of open hole tension and compression fatigue tests– New method for assessing damage tolerance of carbon fibre panels

(based on compression after impact test)– Methods for monitoring defect growth, such as flash thermography– Applying Impact Excitation Methods to assess damage from vibration

modes

F12 Development of test methods for determining the criticality of defects in composite materials systems under long-term loading

• International standardisation of candidate test methods – Round Robin on

compression after impact test

Polymers Performance Website

www.npl.co.uk/performance/polymer_performance_iag_homeUsername: PolPerf Password: FPERF

Polymers Performance Website

polymers performance overview bruce duncan...

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