Interfacial debonding of pipe joints under torsion loads: a model for arbitrary nonlinear cohesive laws

Adhesively bonded pipe joints are extensively used in pipelines. In the present work, Cohesive Zone Model (CZM) based analytical solutions are obtained for the bonded pipe joints under torsion. An integral form based general expression is derived which is suitable for arbitrary type of nonlinear cohesive laws. The concept of the minimum interfacial cohesive shear slip δ m is introduced and used in the fundamental expression of the external torsion load. It is found that, when the bond length of the pipe joint is large enough, the torsion load capacity is indeed independent of the shape of cohesive laws and the bond length. It is interesting to note that the maximum torsion load capacity is achieved when the torsion stiffness of the pipe and coupler are identical. A good agreement with finite element analysis (FEA) result indicates that the current model works well. The formulation to develop a simple test method for determining the τ–δ constitutive relationship in pipe joints under torsional loads is suggested. Parametric studies of various cohesive laws are conducted. This model deepens the understanding of the interfacial debonding problem of bonded joints. The fracture energy based formulas of the torsion load capacity derived in the present work can be directly used in the design of adhesively bonded pipe joints.