Behaviour and modelling of TPU

Abstract

In towed marine seismic, a spread of sources and receivers behind a purpose made acquisition vessel are used to conduct seismic surveys. The receivers are grouped in streamers, each of length up to 12-14 km. The active sections consist of a core, which houses the sensors and the distributed acquisition electronics. The core is protected by a streamer skin. The streamer skin is extruded and made up of two layers. The outer layer is manufactured from thermoplastic polyurethane (TPU).

Skin puncture is a frequent failure mode of active sections, and the main suspected cause is impact with other equipment. The purpose of this thesis is to investigate the behaviour of the TPU currently used, and seek to find measures that can reduce the occurrences of material failure. To gain knowledge on this particular TPU behaviour, a number of material tests have been performed. Finite element analysis (FEA) has been used to investigate the impact scenario. Selected model parameters have been varied one by one to identify how they influence the severity of the impact. Rather than using nominal material properties, a material model was calibrated based on the test results. This allows for more accurate simulation results. At the Structural Impact Laboratory (SIMLab) at NTNU, various constitutive models for finite element purposes have been developed. The SIMLab Polymer Model (SPM) is specifically intended for mechanical analysis of thermoplastic components and was used for the analysis.

The material tests revealed a very ductile material, with a notable rate dependence. Tests of the material from different stages of the streamers service life were conducted. Observations included modest softening from a heat treatment and no detectable effect from operation. Results from FEA suggest that reducing friction and selecting blunt geometries for the equipment in contact with the streamers have the most positive effect on the impact severity.