BS-5350-C5-1990.pdf

BRITISH STANDARD BS 5350-C5: 1990 Methods of test for Adhesives Part C5: Determination of bond strength in longitudinal shear Licensed Copy: sheffieldun sheffieldun, na, Mon Dec 04 16:03:15 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5350-C5:1990 This British Standard, having been prepared under the direction of the Adhesives Standards Policy Committee, was published under the authority of the Board of BSI and comes into effect on 28 September 1990 © BSI 07-1999 First published July 1976 Second edition September 1990 The following BSI references relate to the work on this standard: Committee reference ADC/9 Draft for comment 88/55672 DC ISBN 0 580 18408 0 Foreword This Part of BS 5350 has been prepared under the direction of the Adhesives Standards Policy Committee. It supersedes BS 5350-C5:1976 which is withdrawn. The standard provides a method of assessing the strength of adhesives by determining the shear strength of overlap joints between rectangular adherends. This method is widely practised because the adherends are of simple form and the results are reasonably reproducible. However, since the stress applied to the adhesive is not a simple shear but contains other components, the breaking load is not a simple function of the width or the length of the overlap but is also influenced by the elastic properties and dimensions of the adherends, the bond-line thickness and the rate of change of stress. Hence it is necessary to standardize the procedure in order to obtain reproducibility. The test does not necessarily reflect how the adhesive would perform in service. Such design data would normally be obtained using the construction materials and configuration used in the actual design. In this revision, the scope has been amended to exclude testing of wood-to-wood bonds for which other standards exist and several changes have been made to the procedure to align it with procedures in other recent Parts of BS 5350. At the same time, the references to other British Standards have been brought up-to-date. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: sheffieldun sheffieldun, na, Mon Dec 04 16:03:15 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5350-C5:1990 © BSI 07-1999i Contents Page ForewordInside front cover 1Scope1 2Principle1 3Apparatus1 4Procedure1 5Expression of results3 6Test report3 Appendix A Method for determination of moisture content of wooden slips4 Figure 1 Single overlap joint4 Figure 2 Double overlap joint4 Figure 3 Test adherend with locating hole4 Figure 4 Preparation of specimen from large sheet adherends5 Figure 5 Assembly jig: general arrangement6 Figure 6 Clamping device for holding five close-contact joints6 Publications referred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Mon Dec 04 16:03:15 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii blank Licensed Copy: sheffieldun sheffieldun, na, Mon Dec 04 16:03:15 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5350-C5:1990 © BSI 07-19991 1 Scope This Part of BS 5350 describes the method for testing adhesives using rigid adherends than can be produced to the required dimensional tolerances and that will withstand the forces applied to them. It is not applicable to the testing of bonds between identical pieces of wood, for which there are other, specific standards. The method described in this Part of BS 5350 is applicable to all types of adhesive. Although primarily intended for use in normal ambient conditions, the basic method is also applicable to testing under a wide range of temperature and other environmental conditions. No account is taken of other mechanical properties of the adhesives or adherends that may affect the validity or usefulness of the test. The use of a particular adherend material to test an adhesive does not necessarily imply that that adhesive is the one most suitable for the adherend material. This method of test is intended for ranking and quality control of adhesives and not for obtaining data for design purposes. NOTEThe titles of the publications referred to in this Part of BS 5350 are listed on the inside back cover. 2 Principle A single or double overlap joint (see Figure 1 and Figure 2) between rectangular adherends is strained to rupture by a longitudinal tensile force, i.e. a force that is parallel to the major dimensions of the adherends and in the same plane as the bond-plane (bond-line). The reported result is the observed force at rupture. 3 Apparatus 3.1 Testing machine. The testing machine shall comply with the requirements for machines of grade B of either BS 5214-1 or BS 5214-2 as appropriate. In addition, the response time of the machine shall be short enough not to affect the accuracy with which the breaking load can be measured. The range of the machine shall be such that the specimens break at loads between 15 % and 85 % of the full-scale reading. 3.2 Grips. The grips shall be free to swivel about axes in the mean plane of the bond plane. They shall grip the adherends sufficiently firmly to avoid slipping but not so firmly as to cause excessive crushing. Grips that operate by bolting through the adherend shall not be used because such grips give rise to undesirable stress concentrations. 4 Procedure 4.1 Adherends 4.1.1 Selection. The two adherends in a single overlap joint shall be identical unless the test is being carried out to verify compliance with a specification which requires that the adherends are of different materials. In a double overlap joint involving two adherend materials, the two outer adherends shall be of identical material and dimensions. The adherend or adherends shall be fully described in the test report. If practicable, select the materials for the adherends from the list given in Part A2 of this standard. The most commonly used materials are as follows. a) Wood 1) Beechwood (European beech). One face of the wood shall be planed and the other planed or smoothly sawn. The wood shall be flat and free from splits, knots, whorls and dote. The angle of inclination of the grain across the face of each test specimen shall not be greater than 1 in 9, and the grain shall not be obviously inclined to the face. The moisture content of the wood at the time of test shall be 12 ± 2.5 % as determined by the method given in Appendix A. NOTEThe angle of the growth rings relative to the face is not critical and may be between 0° and 90°. 2) Plywood. Birch plywood, 3 ply, all layers birch, weather-proof and boil-proof (WBP) grade. The test piece shall be cut with the grain (outer layers) in the long direction, shall be flat and shall have no defects. NOTE 1Defects in plywood are defined in BS 6566-6. NOTE 2Specific test methods for wood adhesives are detailed in BS 1204 (relating to structural adhesives) and BS 3544 and BS 4071 (relating to non-structural adhesives). b) Metals 1) Mild steel (cold rolled) type CR1E as defined in BS 1449-1. 2) Aluminium-coated aluminium alloy as specified in BS L 165. c) Plastics 1) Phenolic laminated sheet of a type specified in BS 3794-1. 2) Rigid pressed PVC sheeting of type A1 as specified in BS 3757. 4.1.2 Dimensions. The adherends shall be rectangular and of the following dimensions (see also Figure 3): Length:100 ± 1.5 mm; Width:25 ± 0.25 mm; Licensed Copy: sheffieldun sheffieldun, na, Mon Dec 04 16:03:15 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5350-C5:1990 2 © BSI 07-1999 The thickness of the adherends shall be such that they are able to withstand the forces that are required for the test, and shall be stated in the test report. NOTEThe choice of thickness of the adherends depends on the adherend materials, the adhesive and on the particular application and should be agreed between the purchaser and the supplier of the adhesive. For general use the following thicknesses are recommended: Metals: 1.5 ± 0.15 mm; Non-metals (other than wood): 3 ± 0.15 mm; Wood: 5 ± 0.15 mm. If the central adherend in a double overlap joint is of the same material as the two outer adherends it shall have a thickness of twice that of one of the outer adherends. 4.1.3 Preparation. Before bonding, prepare the surfaces of the adherends in accordance with the recommendations in the instructions supplied by the manufacturer of the adhesive. In the absence of such recommendations, select the appropriate procedure from those given in BS 5350-A1. It is recognized that in some circumstances it may be necessary to test contaminated surfaces. Prepare the specimens individually, or cut them from a large sheet (see 4.4 and Figure 4). NOTEIt is recommended that adherends cut from large sheets should, because of the flatness requirement (see 4.1.2), be sawn rather than sheared. 4.2 Length of overlap The length of the overlap shall be reported in the test report. NOTE 1It is recommended that an overlap of 25 ± 0.5 mm be used unless there are overriding practical or technical considerations for using a different size. NOTE 2With very strong adhesives the adherends may yield or even break before the bond ruptures. In this case the overlap may be reduced or the adherend thickness increased; the latter is preferable. 4.3 Bonding Apply the adhesive and make the bond by the methods recommended by the manufacturer of the adhesive. In the absence of such recommendations, the procedure shall be such as to minimize variations, (e.g. thickness of adhesive, open and closed assembly time, pressing time). The adhesive layer shall cover completely the areas to be bonded and shall be of a uniform thickness. The thickness shall be stated in the test report. Methods of achieving a uniform thickness in the finished joints include the application of a predetermined quantity of adhesive (mass or volume), by use of an applicator, or the use of thin wire shims which remain in the joint. NOTE 1Since different adhesives and different applications may require different thicknesses of adhesive, the thickness of the adhesive layer should be agreed between the purchaser and supplier of the adhesive. Apply sufficient adhesive to avoid starvation (incomplete coverage of the bonded area) and to provide a slight surplus including fillets at the overlap. NOTE 2It is preferable to remove the surplus adhesive from the edges before it is set and whilst the specimen is still in the clamp, but if this is not possible it is permissible to remove the surplus after the adhesive has set. Assemble the test pieces either in a press or in a jig (see Figure 5) or by clamping (see Figure 6). NOTE 3If clamps are used, a jig to ensure correct overlap and accurate alignment of the adherends is recommended. If the jig is similar to the one shown in Figure 5, it will be necessary to drill a hole in each adherend as shown in Figure 3. General purpose jigs that allow the application of a pressure of 350 kPa are shown in Figure 5 and Figure 6. NOTE 4An assembly pressure of 350 kPa is commonly used. The jig shown in Figure 5 is used by placing a suitable weight on top of the joint or joints in between the four central locating pins. The jig shown in Figure 6 is used by screwing down until finger tight. This will give a force of approximately 0.2 kN, which on a 25 mm wide test piece with a 25 mm overlap will give a suitable pressure. NOTE 5A rubber pad with a hardness of IRHD 45 as determined by the method in BS 903-A26 has been found suitable for this type of clamp. Allow the assembly to set in the jig and then to condition without applied pressure for the times recommended by the manufacturer of the adhesive. NOTE 6Contact time is not critical for contact adhesives since the bond is formed as soon as the surfaces touch. For test purposes an assembly time of 30 s under pressure is sufficient. 4.4 Preparation of specimens from large sheets of adherend materials NOTEUnder some circumstances, for example when assessing the effect of storage time or other parameters on bond strength, a relatively large number of nominally identical test specimens may be required. It may then be more economical and effective to prepare the specimens by cutting them from larger sheets previously bonded together. In this case, carry out the following procedure. Use material complying with 4.1.1, with a thickness and flatness complying with 4.1.2 and having a width of 100 ± 1.5 mm and a length an integral multiple of 25 mm plus an allowance for slotting. Slot the sheets before bonding as shown in Figure 4 in which the necessity for slotting allowances is also indicated. Ensure that the surfaces of the adherends comply with the requirements of 4.1.2. Bond the adherends with an overlap joint as described in 4.3 using a press capable of applying a pressure of 350 kPa. Flatness:Within 0.5 mm over the length and width of the area of the specimen to be bonded and within 1.0 mm over the length of the specimen. Licensed Copy: sheffieldun sheffieldun, na, Mon Dec 04 16:03:15 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5350-C5:1990 © BSI 07-19993 Separate the bonded assembly into test specimens by extending the slots so that they join up along their length. 4.5 Standard conditions of storage and test In the absence of other requirements the adherends shall be prepared, stored and bonded and the assemblies conditioned and tested at 23 ± 2 °C and 50 ± 5 % r.h. The conditions shall be reported in the test report. NOTEConditions other than those quoted above may be required for particular service applications. 4.6 Testing Locate the assembly symmetrically in the testing machine with each grip 50 ± 1 mm from the nearest edge of the overlap. Ensure that the longitudinal force applied by the machine acts in the plane of the bond-plane by using packing pieces or other methods. When testing a double overlap joint, in order to avoid distorting the adherends place a packing piece within the grips between the adherends. Then set the machine in motion. Operate the machine so that the test joint is subjected to either: a) a force that increases at a constant rate; or b) a constant rate of separation; such that in either case the joint is broken in a period 65 ± 20 s. NOTE 1The machine should be operated under substantially constant conditions throughout the test although a stress-strain diagram may indicate non-linearity at the commencement and end of the test. NOTE 2If no previous experience is available for the type of joint under test, preliminary tests should