Adhesives — Determination of the mode 1 adhesive fracture energy of structural adhesive joints using double cantilever beam and tapered double cantilever beam specimens

ISO 25217:2009 specifies a method, based upon linear elastic fracture mechanics (LEFM), for the determination of the fracture resistance of structural adhesive joints under an applied mode I opening load, using double cantilever beam (DCB) and tapered double cantilever beam (TDCB) specimens.

Adhésifs — Détermination de l'énergie de fracture adhésive en mode 1 des adhésifs structurels utilisant des éprouvettes de rayon de cantilever double et des éprouvettes de rayon de cantilever double effilées

General Information

Status
Published
Publication Date
22-Apr-2009
Current Stage
9093 - International Standard confirmed
Start Date
01-Oct-2014
Completion Date
23-Nov-2020
Ref Project

Buy Standard

Standard
ISO 25217:2009 - Adhesives -- Determination of the mode 1 adhesive fracture energy of structural adhesive joints using double cantilever beam and tapered double cantilever beam specimens
English language
24 pages
sale 15% off
Preview
sale 15% off
Preview

Standards Content (sample)

INTERNATIONAL ISO
STANDARD 25217
First edition
2009-05-01
Adhesives — Determination of the
mode 1 adhesive fracture energy of
structural adhesive joints using double
cantilever beam and tapered double
cantilever beam specimens
Adhésifs — Détermination de l'énergie de fracture adhésive en mode 1
des adhésifs structurels utilisant des éprouvettes de rayon de cantilever
double et des éprouvettes de rayon de cantilever double effilées
Reference number
ISO 25217:2009(E)
ISO 2009
---------------------- Page: 1 ----------------------
ISO 25217:2009(E)
PDF disclaimer

This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but

shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In

downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat

accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.

Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation

parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In

the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

COPYRIGHT PROTECTED DOCUMENT
© ISO 2009

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,

electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or

ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2009 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 25217:2009(E)
Contents Page

Foreword............................................................................................................................................................ iv

1 Scope ..................................................................................................................................................... 1

2 Normative references ........................................................................................................................... 1

3 Symbols and abbreviated terms ......................................................................................................... 1

4 Principle................................................................................................................................................. 3

5 Apparatus .............................................................................................................................................. 3

6 Specimens ............................................................................................................................................. 3

6.1 Number of specimens .......................................................................................................................... 3

6.2 Conditioning.......................................................................................................................................... 4

6.3 Manufacture of adhesive joint specimens .........................................................................................4

6.4 Measurement of specimen dimensions..............................................................................................6

6.4.1 DCB substrates ..................................................................................................................................... 6

6.4.2 TDCB substrates................................................................................................................................... 6

6.4.3 DCB and TDCB substrates .................................................................................................................. 6

6.5 Preparation of specimens.................................................................................................................... 7

7 Procedure .............................................................................................................................................. 7

7.1 Test set-up and data recording ........................................................................................................... 7

7.2 Initial loading (the precracking stage)................................................................................................ 7

7.3 Re-loading: Testing from the mode I precrack .................................................................................. 8

7.4 Measurement of machine compliance................................................................................................ 9

8 Data analysis ......................................................................................................................................... 9

8.1 Determination of the raw data from the load-displacement trace ................................................... 9

8.1.1 General................................................................................................................................................... 9

8.1.2 Initiation values..................................................................................................................................... 9

8.1.3 Propagation values............................................................................................................................. 10

8.2 Determination of G ........................................................................................................................... 10

8.2.1 General................................................................................................................................................. 10

8.2.2 Double cantilever beam (DCB) .......................................................................................................... 10

8.2.3 Tapered double cantilever beam (TDCB) ......................................................................................... 12

9 Test report ........................................................................................................................................... 13

9.1 Test report for the DCB test............................................................................................................... 13

9.2 Test report for the TDCB test ............................................................................................................ 14

Annex A (informative) Measurement of test system compliance................................................................ 16

Annex B (normative) Procedure to follow when unstable or “stick-slip” crack growth is observed

during the fracture test....................................................................................................................... 18

Annex C (normative) Procedure to detect the occurrence of plastic deformation during a DCB or

TDCB adhesive joint test ................................................................................................................... 19

Annex D (informative) Summary of background theory............................................................................... 20

Bibliography ..................................................................................................................................................... 24

© ISO 2009 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 25217:2009(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 25217 was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 2, Mechanical

properties.
iv © ISO 2009 – All rights reserved
---------------------- Page: 4 ----------------------
INTERNATIONAL STANDARD ISO 25217:2009(E)
Adhesives — Determination of the mode 1 adhesive fracture
energy of structural adhesive joints using double cantilever
beam and tapered double cantilever beam specimens
1 Scope

This International Standard specifies a method, based upon linear elastic fracture mechanics (LEFM), for the

determination of the fracture resistance of structural adhesive joints under an applied mode I opening load,

using double cantilever beam (DCB) and tapered double cantilever beam (TDCB) specimens.

2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.
ISO 291, Plastics — Standard atmospheres for conditioning and testing
ISO 10365, Adhesives — Designation of main failure patterns
3 Symbols and abbreviated terms

For the purposes of this International Standard, the following symbols and abbreviated terms apply:

A insert film length (mm), i.e. the distance between the end of the specimen and the tip of the

insert film (see Figure 1)

a crack length (mm), i.e. the distance between the load-line (intersection of plane through

pin-hole centres or centres of the hinge axes and plane of crack) and the tip of the precrack or

crack on the edge of the specimen (see Figure 1)

a precrack length (mm), measured from the load-line to the tip of the mode I precrack

a insert film length (mm) between the load-line and the tip of the insert film (see Figure 1)

B width of the specimen (mm)
C compliance δ/P of the specimen (mm/N)

C compliance of the calibration specimen used to measure the system compliance (mm/N)

C compliance of the specimen at maximum load (mm/N)
max
C compliance of the tensile-loading system (mm/N)

C compliance of the tensile-loading system and the calibration specimen used to measure this

total
(mm/N) (see Annex A)
© ISO 2009 – All rights reserved 1
---------------------- Page: 5 ----------------------
ISO 25217:2009(E)

C initial compliance of the specimen, neglecting start-up effects, e.g. due to play in the specimen

fixture (mm/N) (see Figure 2)

C initial compliance of the specimen, C , raised by a factor 1,05 (mm/N) (see Figure 2)

0+5 % 0

E flexural modulus of the arms of the substrate beam, calculated from the DCB mode I crack

propagation test (GPa)

E independently measured flexural or tensile modulus of the arms of the substrate beam (GPa);

if the substrate is a fibre composite, E is the longitudinal modulus of the material in the

direction of fibre alignment
F large-displacement correction

G critical strain energy release rate, or adhesive fracture energy, for the applied mode I opening

load (J/m )
H thickness of the load-block (mm)
h thickness of the substrate beam at a crack length a (mm)
h thickness of the adhesive layer (mm)
l total length of the specimen (mm)

l distance from the centre of the loading pin or of the piano hinge axis to the mid-plane of the

arm of the substrate beam to which the load-block or the piano hinge is attached (mm)

(see Figure 1)

l distance between the centre of the pin-hole in the load-block and the edge of the load-block,

measured towards the tip of the insert (starter film) or the tip of the mode I precrack (mm)

(see Figure 1)
l total length of the load-block (mm) (see Figure 1)

MAX/5 % either the maximum load on the load-displacement curve or the point of intersection of a

straight line with the load-displacement curve with the slope of the straight line corresponding

to C (see Figure 2)
0+5 %
m specimen geometry factor [see Equation (1)]
N load-block correction
NL onset of non-linearity on the load-displacement curve (see Figure 2)

n slope of a plot of log C versus log a, or log (C/N) versus log a if load-blocks are being

10 10 10 10
used
P load measured by the load-cell of the test machine (N)

PROP increments of the crack length during stable crack growth (propagation) that are marked on

the load-displacement curve (see Figure 2)
r correlation coefficient of linear fits
r.h. relative humidity during the test (%)

VIS onset of visually recognizable crack growth at the edge of the specimen that is marked on the

load-displacement curve (see Figure 2)
2 © ISO 2009 – All rights reserved
---------------------- Page: 6 ----------------------
ISO 25217:2009(E)
∆ crack-length correction for a beam that is not perfectly built-in (mm)
δ displacement of the cross-head of the test machine (mm)
δ displacement of the cross-head, corrected for system compliance effects (mm)
cor
4 Principle

A double cantilever beam (DCB) specimen or a tapered double cantilever beam (TDCB) specimen is used to

determine the adhesive fracture energy, G , of structural adhesive joints.

Resistance to both crack initiation and propagation is determined. The resistance to crack initiation is

determined from both a non-adhesive insert placed in the adhesive layer and from a mode I precrack. The

resistance to crack propagation is determined from the mode I precrack. The adhesive fracture energy, G ,

(also termed the critical strain energy release rate) for applied mode I loading is calculated and a

resistance-curve (R-curve), i.e. a plot of the value of G versus crack length, is determined.

5 Apparatus

5.1 Tensile-testing machine, capable of producing a constant cross-head displacement rate between

0,1 mm/min and 5 mm/min in displacement control. The test machine shall be equipped with

a) either a fixture to introduce the load to the pins inserted into the load-blocks or directly into the substrate

beams;

b) or grips to hold the piano hinges that allow rotation of the specimen end (see Figure 1).

The test machine shall incorporate a load-cell that shall be calibrated and be accurate to within ± 1 % in the

chosen load-range.
NOTE Loads are typically expected to be in the range of 100 N to 5 000 N.

The opening displacement of the test specimen shall be deduced from the position of the cross-head. The test

machine shall be equipped with means for recording the complete load versus displacement curves (loading

and unloading) during the test.

5.2 Travelling microscope or video camera, with suitable magnification, capable of measuring the crack

length along the edge of the specimen to an accuracy of at least ± 0,5 mm.

5.3 Micrometer or vernier calipers, capable of measuring the thickness of the substrate arms and bonded

joints with an accuracy of at least ± 0,02 mm.

5.4 Micrometer or vernier calipers, capable of measuring the width of the joints with an accuracy of at

least ± 0,05 mm.
5.5 Typewriter correction fluid (“white ink”) or white spray-paint.
6 Specimens
6.1 Number of specimens
A minimum of four joints shall be tested.
© ISO 2009 – All rights reserved 3
---------------------- Page: 7 ----------------------
ISO 25217:2009(E)
6.2 Conditioning

Most adhesives will absorb small quantities of water from the atmosphere which may have a significant

influence on the measured properties. Following specimen preparation, the adhesive will generally be dry. If

testing is carried out within a few days of specimen manufacture, then it is not necessary to condition the

specimen under controlled humidity since negligible absorption of water will take place in the thin adhesive

layer. However, if the specimen is tested after longer times or if the influence of absorbed water on the

properties is of interest, then the humidity shall be controlled by conditioning and the properties will depend on

the conditioning time.

In addition, if composite substrates are used, then it may be important to dry these prior to manufacture of the

joint. The properties of some adhesives are very sensitive to the presence of small amounts of moisture in a

substrate prior to curing. The drying out of the substrates prior to cure will ensure that the integrity of the

adhesive joint is not influenced by pre-bond moisture effects.
6.3 Manufacture of adhesive joint specimens

The DCB specimen shall be as shown in Figures 1 a), 1 b) or 1 c). The TDCB specimen shall be as shown in

Figure 1 d).

The thickness of the film to be inserted in the adhesive layer during manufacture shall be less than 13 µm.

The film shall be non-stick. A PTFE film is recommended. If aluminium foil is used, the foil shall be coated with

a release agent prior to use. Appropriate surface treatments for metallic substrates can be found in

[1]
ISO 17212 .

The thickness of the adhesive layer shall be carefully controlled and shall be less than 1 mm (see Notes 1

and 2). The thickness of the layer shall not vary by more than 20 % within a joint, nor shall the average

thickness of the layer in one joint differ by more than 20 % from that in another joint in the sample. When fully

cured, remove any excess adhesive by mechanical means that do not weaken the bond, so as to leave the

joint with smooth sides.

It should be recognized that the value of G measured from these tests will depend upon the thickness of the

adhesive layer in the joint. The value of the layer thickness shall be determined by the user, based upon the

adhesive manufacturer's recommendations or upon consideration of the intended application.

It is not within the scope of this International Standard to specify full manufacturing details of the joints to be

tested. Such information should be sought from the adhesive manufacturer and/or the substrate manufacturer.

NOTE 1 The analysis used here assumes that the adhesive layer makes a negligible contribution to the overall

compliance of the joint. In round-robin studies and supporting tests, values of h from 0,1 mm to 1,0 mm have been used

with acceptable results. Values of h > 1,0 mm may be used, but the validity of the analysis has not been demonstrated for

these thicker layers.

NOTE 2 For some toughened adhesives, the value of G determined by this method has been shown to be a strong

function of the thickness of the adhesive layer, h . As a result, careful consideration is required when selecting the value of

h . For the selection of h , it is instructive to determine the size of the plastic zone ahead of the crack tip. The radius of this

a a

zone, r , may be approximated for the conditions of plane stress (as exists at the edges of the joint) and plane strain (as

exists in the central part of the joint) as follows:
⎛⎞ ⎛⎞
1 EG 1 EG
aIC aIC
⎜⎟ ⎜⎟
r = (plane stress); r = (plane strain)
p p
2 2
2π⎜⎟ 6π⎜⎟
σ σ
y y
⎝⎠ ⎝⎠
[4]

where E and σ are Young's modulus and the yield strength of the adhesive, respectively. Kinloch and Shaw argued

a y

that, as the value of r was greater at the edges of the joint, where plane stress conditions exist, then the plane stress

value was more applicable to the direct comparison with the adhesive layer thickness, h . If h << 2r , then the plastic

a a p

zone may be largely suppressed and a low value of G would be anticipated. If h ≈ 2r , then the value of G may reach

IC a p IC

a maximum, as shown in Reference [4], as the plastic zone fully develops and potentially distorts due to the presence of

the nearby adhesive-substrate interface. If h > 2r , then the value of G would be expected to become independent of h ,

a p IC a

which is the most desirable condition, subject to the constraint imposed by Note 1 above.

4 © ISO 2009 – All rights reserved
---------------------- Page: 8 ----------------------
ISO 25217:2009(E)
a) DCB specimen with load-blocks
b) DCB specimen with piano hinges (alternative loading arrangement)
c) DCB specimen with metallic substrates where loading holes may be
drilled through the arms of the substrate (alternative loading arrangement)
Figure 1 (continued on next page)
© ISO 2009 – All rights reserved 5
---------------------- Page: 9 ----------------------
ISO 25217:2009(E)
d) TDCB specimen
Key
1 substrates
2 adhesive

NOTE The crack length, a, is the distance between the load-line (intersection of the plane through the pin-hole

centres or the hinge axes and the plane of crack) and the tip of the precrack or crack on the edge of the specimen. The

value of h is the thickness of a substrate arm. For the TDCB specimen, the value of h is a function of the crack length, a.

Figure 1 — Geometry of adhesive joint specimens
6.4 Measurement of specimen dimensions
6.4.1 DCB substrates

Measure the thickness of each DCB substrate using a micrometer (5.3) before bonding. Make the

measurements at three points along the length of the beam, at 30 mm from either end, and at the mid-length.

Calculate the mean value of the thickness of each substrate, h. Determine the thickness of the adhesive layer,

h , by subtracting the substrate thicknesses, 2h, from the total thickness of the joint.

6.4.2 TDCB substrates

Measure the thickness of each TDCB substrate using vernier calipers or a micrometer (5.3) before bonding.

Make the measurements at three points along the contoured section of the beam, at 30 mm from either end

and at the mid-length of the contoured section. Measure the crack length at each of these positions. Calculate

m from Equation (1) (see Annex D).
31a
+= m (1)

Repeat the measurements of the total beam thickness after bonding. Determine the adhesive layer thickness,

h , by subtracting the substrate thicknesses, 2h (measured at the locations described), from the total thickness

of the joint at each of the three locations.
6.4.3 DCB and TDCB substrates

Remove any excess adhesive from the sides of the beam. After bonding, measure the width of the DCB or

TDCB joint with vernier calipers or a micrometer at three points along the length of the beam, at 30 mm from

either end and at the mid-length. Calculate the mean value, B.
6 © ISO 2009 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 25217:2009(E)
6.5 Preparation of specimens

Apply a thin layer of typewriter correction fluid (“white ink”), or white spray-paint, on the edges of the specimen

after conditioning to facilitate the detection of crack growth.

NOTE Some typewriter correction fluids and paints contain solvents which can harm the adhesive or the laminate

matrix material of a composite substrate. An aqueous solvent is usually preferred.

Apply marks every 1 mm from the tip of the insert or the mode I crack for at least the first 10 mm, then apply

marks every 5 mm. Apply marks for every 1 mm for the final 5 mm.

For the DCB test specimen, the extent of crack propagation should be approximately 65 mm, and for the

TDCB test specimen the extent of crack propagation should be approximately 100 mm.

7 Procedure
7.1 Test set-up and data recording

Perform the test at one of the temperatures specified in ISO 291 or at another temperature agreed between

the interested parties. After mounting the specimen in the fixture of the test machine, support the end of the

specimen, if necessary, to keep the beam orthogonal to the direction of the applied load. Record the load and

the displacement signals of the test machine, electronically or on a paper chart, throughout the test, including

the unloading cycle.

If using a tensile-testing machine with a paper chart recorder, the following ratios of cross-head speed to chart

speed are recommended:
a) when testing joints with metallic substrates, a ratio of about 1:100;
b) when testing joints with fibre-composite substrates, a ratio of about 1:10.

Measure the crack length along the edge of the specimen to an accuracy of at least ± 0,5 mm using either a

travelling microscope or a video camera with suitable magnification (5.2). If unstable crack growth followed by

arrest (“stick-slip”) is observed during any stage of the test, follow the procedure in Annex B.

7.2 Initial loading (the precracking stage)

For testing from the insert (starter film), load the specimen at a constant cross-head rate of

a) either 0,1 mm/min to 0,5 mm/min for joints prepared using metallic substrates;

b) or 1,0 mm/min to 5,0 mm/min for joints prepared using fibre-composite (with polymeric matrix) substrates.

NOTE Lower values are more accurate for crack-length measurement. Fibre-composite refers to a material with

unidirectional, continuous fibres of carbon or glass in a polymer matrix with the fibre axis along the length of the specimen.

Record the point on the load-displacement curve at which the onset of crack movement from the insert is

observed on the edge of the specimen on the load-displacement curve or in the sequence of

load-displacement signals [VIS in Figure 2 a)].

Stop the loading as soon as the crack is seen to move on the edge of the specimen. Completely unload the

specimen at a constant cross-head rate of up to five times the loading rate. Mark the position of the tip of the

precrack on both edges of the specimen. If the crack lengths, a, on the edges of the specimen, i.e. the

distance between the load-line and the tip of the precrack, differ by more than 2 mm, consider the results to be

suspect and abandon the test.
© ISO 2009 – All rights reserved 7
---------------------- Page: 11 ----------------------
ISO 25217:2009(E)
7.3 Re-loading: Testing from the mode I precrack

For testing from the mode I precrack which has been formed as a result of the test procedure in 7.2, load the

specimen at a constant cross-head rate of

a) either 0,1 mm/min to 0,5 mm/min for joints prepared using metallic substrates;

b) or 1,0 mm/min to 5,0 mm/min for joints prepared using fibre-composite (with polymeric matrix) substrates.

NOTE Lower values are more accurate for crack-length measurement.

Record, on the load-displacement curve or in the sequence of load-displacement signals, the point at which

the onset of crack movement from the insert is observed to occur [VIS in Figure 2b)].

a) Testing from the insert with initiation b) Testing from the mode I precrack with initiation points

points NL, VIS and MAX/5 % NL, VIS and MAX/5 % and propagation points (PROP)
Key
X displacement, δ
Y load, P
1 initiation values
2 propagation values

NOTE This figure shows an example where the MAX and the 5 % offset points coincide such that they lie on the

same point on the curve. This is not generally the case. Usually, these points will be separated. The MAX/5 % point is

assigned to the point C or MAX, whichever occurs first.
0+5 %
Figure 2 — Schematic load-displacement curve for the DCB test (see Note)

After this, note as many crack-length increments as possible in the first 5 mm on the corresponding

load-displacement curves, ideally every 1 mm. Subsequently, note crack lengths at every 5 mm, until the

crack has propagated about 60 mm from the tip of the mode I precrack for the DCB test and about 95 mm for

the TDCB test. Note every 1 mm for the last 5 mm of crack propagation. Record a minimum number of fifteen

propagation points.

Next, unload the specimen at a constant cross-head rate of up to five times the loading rate. Record whether

the load-displacement curve returns to its initial point and, if not, follow the procedure in Annex C.

NOTE This might indicate that permanent plastic deformation of the arms of the specimen has occurred.

8 © ISO 2009 – All rights reserved
---------------------- Page: 12 ----------------------
ISO 25217:2009(E)

Mark the position of the tip of the crack, i.e. mark the distance between the load-line and the tip of the crack

on both edges of the specimen. If the crack lengths, a, on each of the two edges of the specimen, i.e. the

distance between the load-line and the tip of the crack, differ by more than 2 mm, abandon the test.

NOTE This might indicate asymmetric loading or other problems with the test.

Break the joints open to enable the locus of joint failure to be visually assessed. Visually assess the locus of

joint failure in accordance with ISO 10365.
7.4 Measurement of machine compliance

If the stiffness of the tensile-testing machine together with its associated grips and pins is not known,

determine the compliance associated with the machine set-up as specified in Annex A. Take the compliance

into account in the calculations presented in Clause 8, unless extensometry is used to measure the opening

displacement of the specimen during the
...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.