Experimental determination of fracture toughness for adhesively bonded composite joints

Abstract The characterization of fracture toughness or critical energy release rate of adhesive joint in composite structures is a key parameter. In the present study, fracture toughness of adhesively bonded composite joints is experimentally investigated for the basic fracture modes. Experiments are conducted on the double cantilever beam, end notched flexure and edge crack torsion specimens to determine the fracture toughness of three modes, namely mode-I, mode-II and mode-III. Specimens are bonded with epoxy adherent and cured at room temperature. The fracture toughness values of mode-II and mode-III are 2.6 and 4.6 times respectively of mode-I. Acoustic emission (AE) technique is also employed to aid in determining the fracture toughness of bonded joints. The results indicate that AE signals have good correlation with load–displacement behavior to determine the fracture initiation stage especially in the mode-II loading.

[1]  W. S. Teo,et al.  The fracture behaviour of adhesively-bonded composite joints: Effects of rate of test and mode of loading , 2012 .

[2]  L. Carlsson,et al.  Modification of the edge crack torsion specimen for mode III delamination testing. Part II – experimental study , 2011 .

[3]  Barry D. Davidson,et al.  Evaluation of the accuracy of the four-point bend end-notched flexure test for mode II delamination toughness determination , 2000 .

[4]  S. Donaldson.  Mode III interlaminar fracture characterization of composite materials , 1988 .

[5]  L.F.M. da Silva,et al.  Fracture toughness determination of adhesive and co-cured joints in natural fibre composites , 2013 .

[6]  L. F. Silva,et al.  Fracture toughness of bulk adhesives in mode I and mode III and curing effect , 2011 .

[7]  M.F.S.F. de Moura,et al.  Pure mode II fracture characterization of composite bonded joints , 2009 .

[8]  M. D. de Moura,et al.  Mode II Fracture Toughness of a Brittle and a Ductile Adhesive as a Function of the Adhesive Thickness , 2010 .

[9]  Farhad Asgari Mehrabadi.  Analysis of pure mode III and mixed mode (III + II) interlaminar crack growth in polymeric woven fabrics , 2013 .

[10]  A. Brunner,et al.  8 – Acoustic emission in delamination investigation , 2008 .

[11]  J. Ratcliffe.  Characterization of the Edge Crack Torsion (Ect) Test for Mode III Fracture Toughness Measurement of Laminated Composites , 2013 .

[12]  P. Compston,et al.  The Influence of Loading Rate on the Mode III Fracture Properties of Adhesively Bonded Composites , 2009 .

[13]  John W. Gillespie,et al.  Finite element analysis of the end notched flexure specimen for measuring mode II fracture toughness , 1986 .

[14]  W. Johnston,et al.  Mode II Interlaminar Fracture Toughness and Fatigue Characterization of a Graphite Epoxy Composite Material , 2010 .

[15]  J. Mohan,et al.  Mode I fracture toughness of co-cured and secondary bonded composite joints , 2014 .

[16]  M.F.S.F. de Moura,et al.  Crack equivalent concept applied to the fracture characterization of bonded joints under pure mode I loading , 2008 .

[17]  D. A. Dillard,et al.  Fracture Mechanics Tests in Adhesively Bonded Joints: A Literature Review , 2014 .

[18]  Farhad Asgari Mehrabadi,et al.  Mode III Interlaminar Fracture in Woven Glass/Epoxy Composite Laminates , 2013 .

[19]  Richard A. Pethrick,et al.  Design and ageing of adhesives for structural adhesive bonding – A review , 2015 .

[20]  Shankar Kalyanasundaram,et al.  On crack-initiation conditions for mode I and mode II delamination testing of composite materials , 2000 .

[21]  W. Wagner,et al.  Adhesive Joints in Composite Laminates - A Combined Numerical/Experimental Estimate of Critical Energy Release Rates , 2011 .

[22]  L. F. Silva,et al.  Testing adhesive joints : best practices , 2012 .

[23]  B. Davidson,et al.  Observation of Intralaminar Cracking in the Edge Crack Torsion Specimen , 2014 .

[24]  Lauren A. Ferguson,et al.  Numerical simulation of mode-III fracture incorporating interfacial mechanics , 2015, International Journal of Fracture.