Fatigue behaviour of an epoxy adhesive under mixed-mode conditions
Mário Rui Oliveira Cunha, Ricardo João Camilo Carbas, Eduardo André Sousa Marques, Alireza Akhavan-Safar, Lucas Filipe Martins da Silva
The aim of this study is to characterize the fatigue behaviour of a structural epoxy adhesive loaded in mixedmode conditions. To this effect, several fracture tests were carried out: Double Cantilever Beam (DCB) for pure mode I, End Notched Flexure (ENF) for pure mode II, and mixed-mode testing, using an apparatus that enables the application of mixed-mode loadings to an adhesive and with high strength steel adherends. The fracture envelope was calculated using experimental data and it was found to be compatible with a quadratic criterion. A novel quadratic law criterion was developed to fit the envelope. The fatigue behaviour was studied recurring to fatigue crack growth curves for the same types of loads studied in the quasi-static tests. A relationship between mixed-mode phase angle and the Paris law slope was found, where the existence of mode II loads was found to delay crack propagation. By performing fatigue tests at 60% and 80% of the maximum load, it was noticed that increasing the load leads to the increase of the threshold energy release rate values.
1 da Silva LF, Öchsner A, Adams RD. Handbook of adhesion technology. Heidelberg: Springer International Publishing; 2018.
2 Brussat T, Chiu S, Mostovoy S. Fracture mechanics for structural adhesive bonds. Burbank: Lockheed-California CO; 1977.
3 Voloshin A, Arcan M. Pure shear moduli of unidirectional fibre-reinforced materials (FRM). Fibre Science and Technology. 1980;13(2):125-134.
4 El-Hajjar R, Haj-Ali R. In-plane shear testing of thick-section pultruded FRP composites using a modified Arcan fixture. Composites. Part B, Engineering. 2004;35(5):421-428.
5 Yoon S and Hong C. Modified end notched flexure specimen for mixed mode interlaminar fracture in laminated composites. International Journal of Fracture. 1990;43(1):R3R9.
6 Xiao F, Hui C-Y, Kramer E. Analysis of a mixed mode fracture specimen: the asymmetric double cantilever beam. Journal of Materials Science. 1993;28(20):5620-5629.
7 Park S, Dillard DA. Development of a simple mixed-mode fracture test and the resulting fracture energy envelope for an adhesive bond. International Journal of Fracture. 2007;148(3):261-271.
8 ASTM International. Standard test method for mixed mode I-mode II interlaminar fracture toughness of unidirectional fiber reinforced polymer matrix composites. West Conshohocken: ASTM; 2013.
9 Chaves FJ, da Silva L, De Moura M, Dillard D, Esteves V. Fracture mechanics tests in adhesively bonded joints: a literature review. The Journal of Adhesion. 2014;90(12):955-992.
10 Costa M, Carbas R, Marques E, Viana G, da Silva L. An apparatus for mixed-mode fracture characterization of adhesive joints. Theoretical and Applied Fracture Mechanics. 2017;91:94-102.
11 Fernlund G, Spelt J. Mixed-mode fracture characterization of adhesive joints. Composites Science and Technology. 1994;50(4):441-449.
12 Chaves FJ, de Moura M, da Silva L, Dillard DA. Numerical validation of a crack equivalent method for mixedmode I+ II fracture characterization of bonded joints. Engineering Fracture Mechanics. 2013;107:38-47.
13 da Silva L, Esteves V, Chaves F. Fracture toughness of a structural adhesive under mixed mode loadings. Materialwissenschaft und Werkstofftechnik. 2011;42(5):460-470.
14 Stamoulis G, Carrère N, Cognard J-Y, Davies P, Badulescu C. On the experimental mixed-mode failure of adhesively bonded metallic joints. International Journal of Adhesion and Adhesives. 2014;51:148-158.
15 Chai H. Shear fracture. International Journal of Fracture. 1988;37(2):137-159.
16 Benzeggagh M, Kenane M. Measurement of mixed-mode delamination fracture toughness of unidirectional glass/epoxy composites with mixed-mode bending apparatus. Composites Science and Technology. 1996;56(4):439-449.
17 Fernández MVC. Fracture Characterization of Composite Bonded Joints Under Fatigue Loading. [doctor thesis] Porto: Universidade do Porto; 2013.
18 De Goeij W, Van Tooren M, Beukers A. Composite adhesive joints under cyclic loading. Materials & Design. 1999;20(5):213-221.
19 Jablonski D. Fatigue crack growth in structural adhesives. The Journal of Adhesion. 1980;11(2):125-143.
20 ASTM E647-15e1, Standard Test Method for Measurement of Fatigue Crack Growth Rates, ASTM International, West Conshohocken, PA, 2015.
21 Yoder G, Cooley L, Crooker T. Procedures for precision measurement of fatigue crack growth rate using crackopening displacement techniques. In: ASTM International. Fatigue crack growth measurement and data analysis. West Conshohocken: ASTM International; 1981.
22 ASTM International. Standard test method for fracture strength in cleavage of adhesives in bonded joints. West Conshohocken: ASTM; 2004 NF T 76-142. Méthode de préparation de plaques d’adhésifs structuraux pour la réalisation d’éprouvettes d’essai de caractérisation. 1988.
23 ASTM D638-14, Standard Test Method for Tensile Properties of Plastics, ASTM International, West Conshohocken, PA, 2014.
24 Costa M, Carbas R, Benedita M, Marques E, Viana G, da Silva LFM, et al. Static assessment of the mixed-mode behaviour of three epoxy adhesives. Engineering Fracture Mechanics. 2017;182:552-565.
25 Azari S, Jhin G, Papini M, Spelt J. Fatigue threshold and crack growth rate of adhesively bonded joints as a function of load/displacement ratio. Composites. Part A, Applied Science and Manufacturing. 2014;57:59-66.
26 Azari S, Papini M, Schroeder J, Spelt J. Fatigue threshold behavior of adhesive joints. International Journal of Adhesion and Adhesives. 2010;30(3):145-159.
27 Pirondi A, Nicoletto G. Mixed mode I/II fatigue crack growth in adhesive joints. Engineering Fracture Mechanics. 2006;73(16):2557-2568.
28 Hafiz T, Abdel-Wahab M, Crocombe A, Smith P. Mixed-mode fatigue crack growth in FM73 bonded joints. International Journal of Adhesion and Adhesives. 2013;40:188-196.
29 Azari S, Papini M, Schroeder J, Spelt J. The effect of mode ratio and bond interface on the fatigue behavior of a highly-toughened epoxy. Engineering Fracture Mechanics. 2010;77(3):395-414.