1、BRITISH STANDARD BS 7991:2001 Determination of the mode I adhesive fracture energy G ICof structure adhesives using the double cantilever beam (DBC) and tapered double cantilever beam (TDCB) specimens ICS 83.180 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBS 7991:2001 This
2、British Standard, having been prepared under the direction of the Materials and Chemicals Sector Policy and Strategy Committee, was published under the authority of the Standards Policy and Strategy Committee on 23 October 2001 23 October 2001 The following BSI references relate to the work on this
3、standard: Committee reference PRI/52 Draft for comment 99/123593 DC ISBN 0 580 33283 7 Committees responsible for this British Standard The preparation of this British Standard was entrusted to the Technical Committee PRI/52, Adhesives, upon which the following bodies were represented: Contract Floo
4、ring Association European Resin Manufacturers Association SATRA Footwear Technology Centre UK Steel Association University of Bristol Nat. Physical Lab. DETR - represented by BRE Timber Research and Development Association (TRADA) British Adhesives and Sealants Association (BASA) TWI Centre for Adhe
5、sive Technology British Woodworking Federation The Tile Association Amendments issued since publication Amd. No. Date CommentsBS 7991:2001 BSI 23 October 2001 i Contents Page Committees responsible Inside front cover Foreword ii Introduction 1 1S c o p e 4 2 Normative references 4 3 Symbols and abbr
6、eviated terms 4 4 Principle 5 5A p p a r a t u s 5 6S p e c i m e n s 6 7 Procedure 7 8 Data analysis 8 9 Test report 11 Annex A (normative) Measurement of testing system compliance 16 Annex B (normative) Procedure to follow when unstable or “stick-slip” crack growth is observed during the fracture
7、test 17 Annex C (normative) Procedure to detect the occurence of plastic deformation during a DCB or TDCB adhesive joint test 18 Annex D (normative) Test report sheets 20 Bibliography 26 Figure 1 Geometry for the adhesive joint specimens 13 Figure 2 Schematic loaddisplacement curve for the DCB test
8、14 Figure 3 Linear fits 15 Figure 4 Schematic resistance curve (R-curve) with G ICvalues for initiation (i.e. the lowest value among NL, VIS, or MAX/5 %) and for propagation (PROP) versus observed crack length a 15 Figure A.1 Schematic loaddisplacement trace obtained during the system compliance mea
9、surement 17 Figure B.1 Schematic loaddisplacement trace for a tapered double cantilever beam specimen, exhibiting unstable “stick-slip” crack growth behaviour 18 Figure C.1 Typical loaddisplacement trace for a tapered double cantilever beam specimen, showing loading and unloading lines and the displ
10、acement offset 19BS 7991:2001 ii BSI 23 October 2001 Foreword This test method BS 7991 has been prepared under the direction of PRI/52, Adhesives standards policy committee with substantial input from the European Structural Integrity Society (ESIS) Technical committee 4 on Polymers, Adhesives and C
11、omposites. The standard provides 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 the Double Cantilever Beam (DCB) and Tapered Double Cantilever Beam (TDCB) specim
12、ens. The resistance to crack initiation is measured from both a release film inserted into the bondline during manufacture and from a mode I precrack. This dual initiation procedure ensures that a minimum value of fracture resistance G ICcan be identified. The test methods then specify that a resist
13、ance curve (R-curve) be drawn for the joint for which the steady-state values of G ICassociated with crack propagation have to be determined. This method is practised because the adherends are of relatively simple form and round-robin tests have demonstrated that the repeatability and reproducibilit
14、y of the results are of the same order as standardized fracture mechanics test methods for measuring G ICof bulk polymers. However, there is an increased complexity in the procedures required for adhesive joint testing, and thus it is necessary to standardize the procedure in order to obtain reprodu
15、cibility. The test does not necessarily reflect how the adhesive would perform in service. Such data would normally be obtained by performing tests that simulate and/or accelerate the expected loading and environmental conditions. Excel spreadsheets for the test reports are available free of charge
16、at http:/www.me.ic.ac.uk/materials/AACgroup/. A British Standard does not purport to include all the necessary provision 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 obligatio
17、ns. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 27, an inside back cover and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued.BS 7991:2001 BSI 23 October 2001 1 Introduction The
18、 test methods specified in this standard enable the fracture resistance of structural adhesive joints to be determined under mode I tensile loading conditions. The use of either the double cantilever beam (DCB) specimen or the tapered double cantilever beam (TDCB) specimen is accommodated. The metho
19、ds describe the measurement of the resistance to both crack initiation and crack propagation through the adhesive layer. Points of crack initiation are determined directly from an insert film, moulded into the centre of the bondline during joint manufacture, and from a mode I precrack created during
20、 the test. The property measured by these methods is the mode I adhesive fracture energy, G IC . G ICmay also be described as the critical strain energy release rate, the energy release rate or the fracture toughness of the joint. The double cantilever beam (DCB) specimen is well suited for testing
21、joints consisting of an adhesive bonding relatively thin sheets of fibre-composite materials, but may also be used when metallic substrates, which possess a relatively high yield stress, are employed e.g. Figure 1c). The tapered double cantilever beam (TDCB) is designed so that, over a large range o
22、f values of crack length, the rate of change of compliance with crack length is constant and so is independent of the value of crack length. This is useful since: a) relatively tough adhesives can be tested without plastic deformation of the arms occurring; b) the substrates can possess a relatively
23、 low yield stress, but again no plastic deformation of the arms is incurred during the test; and c) the measurement of the adhesive fracture energy G ICis independent of the crack length a; There are three analysis methods for both the DCB test and the TDCB tests. The corrected beam theory (CBT) met
24、hod and the experimental compliance method (ECM) are considered to be the more accurate methods for determining the values of G IC . NOTE DCB specimens are cheaper to manufacture so are the test specimen of first choice provided plastic deformation of the substrates is avoided. For tougher adhesives
25、 and substrates with lower yield stresses, i.e. in joints more likely to violate LEFM test conditions, the TDCB is favoured. To develop a linear change of compliance with crack length, the height of the specimen is varied by contouring the substrate beam so that the specimen geometry factor m is a c
26、onstant equation (1). The equations used to calculate adhesive fracture energy G ICin the double cantilever beam (DCB) test method (analysis methods 1 to 3) and in the tapered double cantilever beam (TDCB) test method (analysis methods 4 to 6) are described here. Analysis method 1: Simple beam theor
27、y (SBT) Double cantilever beam (DCB) The value of the adhesive fracture energy G ICis calculated using equation (2): (1) a is the crack length; and h is the thickness of the substrate beam at a; (2) where C is the compliance and is given by /P; and B is the width of the specimen; P is the load measu
28、red by the load-cell of the testing machine. 3a 2 h 3 - - 1 h - + m = G IC P 2 2B - = dC da - BS 7991:2001 2 BSI 23 October 2001 For thin adhesive layers, it has been shown by Mostovoy et al. 1 and Kinloch 2 that from simple beam theory, dC/da may be expressed as equation (3): Hence, by combining eq
29、uations (1), (2) and (3), equation (4) is obtained and G ICcan be calculated: Analysis method 2: Corrected beam theory (CBT) Double cantilever beam (DCB) The simple beam theory expression for the compliance of a perfectly built-in DCB specimen will underestimate the compliance as the beam is not per
30、fectly built-in (Hashemi et al. 3, Blackman et al. 4). The adhesive fracture energy G ICis calculated using equation (5a), or (5b) if load-blocks are used: The large displacement correction F and the load-block correction N are calculated as shown in equations (6) and (7) respectively (Hashemi et al
31、. 3): The flexural modulus E fis calculated as a function of the crack length a by using equation (8a) or (8b) if end blocks are used: This calculation is a useful check on the procedure as a value of the flexural modulus E findependent of crack length should be obtained. (3) where E s is the indepe
32、ndently-measured flexural or tensile modulus of the substrate. (4) (5a) (5b) (5) where N is a load-block correction; F is a large displacement correction; is the displacement; and is a crack-length correction for a beam that is not perfectly built-in. (6) (7) where l 1is the distance from the centre
33、 of the loading pin to the mid-plane of the arm of the substrate beam to which the load-block is attached; and l 2 is the distance from the loading pin centre to the edge of the block (Figure 1). (8a) (8b) (8) dC da - 8 E s B - 3a 2 h 3 - 1 h - + = G IC 4P 2 E s B 2 - 3a 2 h 3 - 1 h- + 4P 2 E s B 2
34、- m = = G IC 3P 2Ba + - F = G IC 3P 2Ba + - F N - = F 1 3 10 - a - 2 3 2 - l 1 a 2 - - = N 1 = l 2 a - 3 9 8 - 1 l 2 a - 2 l 1 a 2 - 9 35 - a - 2 E f 8 a + 3 CBh 3 - = E f 8 a + C N - Bh 3 - 3 =BS 7991:2001 BSI 23 October 2001 3 Analysis method 3: Experimental compliance method (ECM) or Berrys metho
35、d Double cantilever beam (DCB) The logarithm of the compliance, or of the normalized compliance C/N, if load-blocks are being used, versus the logarithm of the crack length a are plotted. The slope of this plot n gives G ICas follows: The same large-displacement correction F and load-block correctio
36、n N, if applicable, are used as for the corrected beam theory method. Analysis method 4: Simple beam theory (SBT) Tapered double cantilever beam (TDCB) This is the same as in analysis method 1 except the value of m is a constant for this particular geometry. Analysis method 5: Corrected beam theory
37、(CBT) Tapered double cantilever beam (TDCB) The simple beam theory expression for G ICdescribed in analysis method 4 will incorrectly estimate the compliance of the specimen since: a) the positions of the loading pins, with their surrounding material, are not taken into account in deriving equation
38、(4); and b) as for the DCB specimen, the specimen does not behave as a perfectly built-in cantilever beam. Corrections (Blackman et al. 5) lead to equation (10). Hence, combining equations (2) and (10), equation (11) is obtained. In deriving equation (10), the value of m is approximated to 3a 2 /h 3
39、 , i.e. the term 1/h in equation (1) is neglected. The error in the value of G ICthat is introduced by this approximation is insignificant and round-robin testing has demonstrated good agreement between the values of G ICdeduced via equations (11) and (2) for tapered beams manufactured with aluminiu
40、m alloy substrates (Blackman and Kinloch 6). Analysis method 6: Experimental compliance method (ECM) Tapered double cantilever beam (TDCB) The adhesive fracture energy G ICis calculated using equation (2), where the values of C plotted against the crack length a produces a linear graph. (9a) (9b) (9
41、) (10) (11) (2) G IC nP 2Ba - F = G IC nP 2Ba - F N - = dC da - 8m E s B -10 . 4 3 3 ma - 1 3 - + = G IC 4P 2 m E s B 2 -10 . 4 3 3 ma - 1 3 - + = G IC P 2 2B - dC da - =BS 7991:2001 4 BSI 23 October 2001 1 Scope This standard specifies a method, based upon linear-elastic fracture-mechanics (LEFM),
42、for the determination of the fracture resistance of structural adhesive joints under an applied mode I opening load using the double cantilever beam (DCB) and tapered double cantilever beam (TDCB) specimens. 2 Normative references The following normative documents contain provisions which, through r
43、eference in this text, constitute provisions of this British Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. BS EN ISO 291:1997, Plastics Standard atmospheres for conditioning and testing. BS 5214-1:1995, Rubber and plastics test equ
44、ipment; tensile, flexural and compression types (constant rate of traverse) Description. ISO 5893:1993 BS EN ISO 10365:1992, Adhesives Designation of the main failure patterns. 3 Symbols and abbreviated terms For the purpose of this standard, the following symbols and abbreviated terms apply. A inse
45、rt film length, distance between the end of the specimen and the tip of the insert film NOTE 1 See Figure 1. a crack length, 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 edg
46、e of the specimen NOTE 2 See Figure 1. a p precrack length, measured from the load-line to the tip of the mode I precrack a 0 insert film length, distance between the load-line to the tip of the insert film NOTE 3 See Figure 1. B width of the specimen C compliance /P of the specimen C cs compliance
47、of the calibration specimen used to measure the system compliance C max compliance of the specimen at maximum load C sy compliance of the tensile loading system C total compliance of the tensile loading system and the calibration specimen used to measure this NOTE 4 See Annex A. C 0 initial complian
48、ce of the specimen neglecting start-up effects, e.g. due to play in the specimen fixture NOTE 5 See Figure 2. C 0+5% initial compliance C 0of the specimen increased by 5 % NOTE 6 See Figure 2. E f flexural modulus of the arms of the substrate beam, calculated from the DCB mode I crack propagation test E s independently measured flexural, or tens
