Study on the O-/ U-type collapse of reinforced thermoplastic pipes (RTPs) subjected to hydrostatic external pressure: Experimental tests and numerical analysis

Abstract

Due to the anisotropy and progressive failure of composites, the collapse problem of RTPs is more complex compared with that of traditional steel pipes. To address this problem, the collapse behavior of RTPs subjected to external pressure was studied by conducting collapse tests and numerical simulations. Two different collapse modes including the O-type and U-type mode were observed during the collapse tests. It was the first time to observe the U-type collapse mode of RTPs in open literature. For O-type collapse mode, the cross-section turned into an ellipse. And for U-type collapse mode, it turned heart-shaped. Meanwhile, numerical simulations were conducted by combing eigenvalue analysis and arc-length method, in which the progressive failure of composites was considered by employing a fracture energy degradation model based on the Hashin criterion. To simulate the U-type collapse mode, eccentricity was also introduced. Research results indicated that the critical pressure obtained by tests and numerical simulations agreed well for both O-/U-type collapse modes. The collapse process could be described as “contraction-collapse point-large deformation”. It was found that the progressive failure of composites would reduce the pressure-resisting capacity greatly. For the composites, the shear failure, the matrix and fiber compressive failure were dominant failure modes.