Numerical and Experimental Analysis of Double-Sided Stepped Lap-Repaired CFRP Laminates Under Tensile Loading

  • Matta Seshadri
  • M. RamjiEmail author
Conference paper


Adhesive layer plays a critical role in the strength restoration of the scarf repaired carbon fibre-reinforced plastic (CFRP) laminates. In this work, Araldite 2015 is used. Hence, it is crucial to model the behaviour of adhesive layer accurately in case of numerical model. Modelling of adhesive layer by cohesive zone law characterises the fracture behaviour of the bonded joint accurately. In this paper, cohesive zone law parameters for mode I and mode II are determined by comparing numerical predictions to experimental observations of a double cantilever beam (DCB) for mode I and end notched flexure (ENF) for mode II fracture test. In this work, Araldite 2015 (supplied by Huntsman) is used for repair work. Strain energy release rate for both mode I and mode II is determined by performing DCB and ENF test, respectively. Traction–separation law for mode I is generated by direct method which involves differentiation of the relation between the strain energy release rate and crack tip opening displacement which is measured using digital image correlation (DIC) technique. Traction–separation law for mode II is generated by inverse method which involves fitting the numerical and experimental load–displacement curves. The obtained cohesive law is used to model the adhesive layer in numerical analysis of double-sided stepped lap joint repair of CFRP laminate subjected to tensile loading. The numerical predictions are validated by comparing the load–displacement curve obtained from the experimental study. A good agreement exists between numerical and experimental results confirming that the proposed cohesive law for mode I and mode II can be applied to model adhesive layer with CFRP as adherend.


Cohesive zone law Strain energy release rate Digital image correlation Double-sided stepped lap joint 

List of symbols


Crack length


Equivalent crack length


Initial crack length


Width of the specimen


Compliance of the specimen


Initial compliance


Flexural modulus


Mode I strain energy release rate


Mode I fracture toughness


Mode II strain energy release rate


Mode II fracture toughness


Height of single adherend


Total specimen length


Applied load on the specimen


Crack tip opening displacement (CTOD)


Displacement of the specimen


Damage initiation relative displacement


Ultimate relative displacement


Correction factor for root rotation effect


Adhesive thickness


Normal traction



The first author thank Dr. Viswanath R Chintapenta, Assistant Professor, Indian Institute of Technology Hyderabad for his guidance, lab mates in engineering optics lab and central workshop staff at Indian Institute of Technology Hyderabad.


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Copyright information

© Springer Nature Singapore Pte Ltd. 2018

Authors and Affiliations

  1. 1.Engineering Optics Lab, Department of Mechanical and Aerospace EngineeringIIT HyderabadHyderabadIndia

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