ISO 6238:2018

INTERNATIONAL ISO
STANDARD 6238
Third edition
2018-08
Adhesives — Wood-to-wood adhesive
bonds — Determination of shear
strength by compressive loading
Adhésifs — Joints collés de bois à bois — Détermination de la
résistance au cisaillement par effort de compression
Reference number
©
ISO 2018
© ISO 2018
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ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Apparatus . 1
5 Test specimens. 3
6 Preparation of test blocks . 4
7 Conditioning of test blocks . 5
8 Preparation of test joints . 5
9 Procedure. 6
10 Expression of results . 6
11 Test report . 7
Annex A (normative) Information required prior to testing . 8
Annex B (normative) Timber species, surfaces, quality and moisture content.9
Foreword
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URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 11,
Products.
This third edition cancels and replaces the second edition (ISO 6238:2001), of which it constitutes a
minor revision.
The changes compared to the previous edition are as follows:
— the references in Clause 2 have been updated;
— Clause 3 has been inserted and subsequent clauses have been renumbered;
— the document has been editorially revised.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2018 – All rights reserved

INTERNATIONAL STANDARD ISO 6238:2018(E)
Adhesives — Wood-to-wood adhesive bonds —
Determination of shear strength by compressive loading
1 Scope
This document specifies a method for determining the shear strength of wood-to-wood adhesive
bonds, with a standard specimen loaded in compression and under specified conditions of preparation,
conditioning and testing. This method is intended for testing only those adhesives used in bonding
wood to wood.
This method is not intended for use in testing manufactured products.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 7500, Metallic materials — Verification of static uniaxial testing machines — Part 1: Tension/
compression testing machines — Verification and calibration of the force-measuring system
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
4 Apparatus
4.1 Apparatus for preparation of adhesive
4.1.1 Balance and other suitable equipment, capable of measuring the proportions of the adhesive
mix to within a tolerance of ±1 %.
4.1.2 Mixing equipment, to ensure homogeneous mixing of the constituents with minimum aeration
of the adhesive (except foamed adhesive).
4.1.3 Spreading equipment, such as a wire-wound bar, roller spreader, curtain coater or suitable
hand applicators, capable of spreading the adhesive uniformly within ±5 % of the desired spread.
4.1.4 Equipment, designed to exert the required pressure evenly over the whole bonded area
within ±5 % of the desired value, for example a press or clamps. If necessary, heated platens capable of
maintaining the prescribed temperature within ±2 °C during compression.
4.2 Apparatus for the determination
4.2.1 Analytical balance, capable of weighing to 0,000 1 g.
4.2.2 Linear measuring device, reading to 0,05 mm, e.g. vernier calipers or micrometer.
4.2.3 Tensile-testing machine, operating in the compression mode, capable of maintaining a pre-
determined constant cross-head rate. The machine shall be capable of determining a maximum load.
The measured strength shall be between 15 % and 85 % of the capacity of the machine. The machine
shall permit the measurement and recording of the applied force with an accuracy of ±1 %. The testing
machine shall be fitted with a shearing tool containing a self-alignment seat to ensure uniform lateral
distribution of the force.
NOTE A shearing tool as shown in Figure 1 has been found satisfactory.
The equipment shall be calibrated regularly in accordance with ISO 7500-1.
It is recommended that the machine be autographic, giving a chart that can be read in terms of
millimetres of cross-head movement as one coordinate and applied force as the other coordinate. It is
also recommended that inertialess equipment be used.
2 © ISO 2018 – All rights reserved

Dimensions in millimetres
Key
1 test specimen
2 oil hole
Figure 1 — Example of shearing tool for compressive shear testing of specimen A
5 Test specimens
5.1 The timber species, timber quality and timber moisture content for the specimens shall be as
described in Annex B.
5.2 Individual test joints shall comply with the form and dimensions shown in Figure 2. The individual
test joints shall be cut from bonded blocks prepared as described in Clauses 6 and 7.
L and W represent the length and the width of the bonded area. The user shall select either the
geometry of specimen A (bonded area 40 mm × 50 mm) or the geometry of specimen B (bonded area
25 mm × 25 mm). T represents the thickness, which is 20 mm for specimen A and 10 mm for specimen B.
In cases of dispute, only specimen A shall be used.
5.3 For adhesive quality control purposes, test a minimum of three test joints from each of three
different bonded blocks, prepared as described in Clauses 6 and 7.
5.4 Where greater precision is required, test a minimum of five test joints from each of four different
bonded blocks.
Dimensions in millimetres
a
Direction of grain.
b
L and W = 40 mm × 50 mm for specimen A or 25 mm × 25 mm for specimen B.
c
T = 20 mm for specimen A or 10 mm for specimen B.
Figure 2 — Shape and dimensions of test specimen
6 Preparation of test blocks
6.1 Blocks shall be cut from the timber, preferably of a size such that five test joints may be cut from
one bonded block as shown in Figure 3. The grain direction shall be parallel to the longest dimension of
the block. The blocks shall have surfaces substantially free from saw marks. The blocks shall be weighed
and assembled in pairs so that blocks of approximately the same relative density are bonded together.
The test blocks shall be knife-planed to ensure the bonding faces are flat, smooth and parallel to the
surface where pressure will be applied; they shall be free from dirt, dust or other contamination. Unless
otherwise agreed between the interested parties, the thickness of each of the blocks shall not vary by
more than 0,1 mm to ensure even pressure during cure.
6.2 Prepare and apply the adhesive to the blocks in accordance with the procedure recommended by
the manufacturer of the adhesive. Assemble and compress the coated blocks, also in accordance with the
recommendations of the manufacturer of the adhesive. Number each bonded block. The net mass of the
adhesive applied may be verified by weighing the blocks before and after spreading the adhesive.
4 © ISO 2018 – All rights reserved

Dimensions in millimetres
a
Direction of grain.
b
Saw kerf.
Figure 3 — Method of cutting test specimens from bonded blocks
7 Conditioning of test blocks
Upon release of pressure, condition the bonded blocks at a relative humidity of (50 ± 5) % and a
temperature of (23 ± 2) °C, either for a period of 7 days or until they attain a constant mass, whichever
is the longer period. (Constant mass is considered to be reached when the results of two successive
weighing operations, carried out at an interval of 6 h, do not differ by more than 0,1 % of the mass of the
bonded block.)
Conditioning may be extended beyond this limit by agreement between the interested parties.
NOTE Other conditions of humidity and temperature can be used by agreement between the interested
parties.
The blocks shall be conditioned in accordance with ISO 291.
8 Preparation of test joints
8.1 Reduce the width of the test blocks to (L ± 0,5) mm by planing or sawing an approximately equal
amount from each side. Before cutting off the test joints, cut approximately 10 mm from each end, then
cut off the individual test joints as shown in Figure 3. When preparing the test specimens, make sure
that the loaded surfaces are smooth and parallel to each other and perpendicular to the height. While
reducing the lengths of the overlap to (W ± 0,5) mm, ensure that the saw cuts extend to, but not beyond,
the bondline. Also ensure that the saw cuts are perpendicular to the major axis.
Number each test joint consecutively from one end of the bonded block to the other.
8.2 Store the test joints in the conditioning atmosphere described in Clause 7, until tested. The bonded
blocks may be briefly removed for the cutting operations.
9 Proced
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