Cohesive zone model based analytical solutions for adhesively bonded pipe joints under torsional loading

Adhesively bonded pipe joints are extensively used in pipelines. In the present work, cohesive zone model (CZM) based analytical solutions are derived for the bonded pipe joints under torsion. The concept of the minimum relative interface rotation ϕmϕm is introduced and used as the fundamental variable to express all other parameters, such as external torsion load, distribution of interfacial shear stress, length of elastic zone and softening zone, etc. It is found that when the bond length of the pipe joint is longer than a certain value, further increase in bond length cannot bring any significant increase in torsion load capacity. Given that the bond length of the pipe joint is long enough, the torsion load capacity is indeed independent of the shape of cohesive laws and the bond length. Consequently, simplified expressions of the torsion load capacity are derived as a function of the interface fracture energy, torsion stiffness of the pipe, and the geometric properties of the pipe joints. Depending on the torsion stiffness ratio of the pipe and the coupler, the macroscopic-debonding can initiate at the right end, left end or both ends simultaneously. It is interesting to note that the maximum torsion load capacity is achieved when the torsion stiffness of the pipe and the coupler are identical. Good agreement with finite element analysis (FEA) result validates the accuracy of the current model. 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.