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This work presents a numerical-experimental methodology to study the fatigue behavior of dented pipes under internal pressure. A full-scale experimental program on dented pipes containing gouges were achieved. Two types of defects were... more
This work presents a numerical-experimental methodology to study the fatigue behavior of dented pipes under internal pressure. A full-scale experimental program on dented pipes containing gouges were achieved. Two types of defects were studied: metal loss (plain dent) and sharp notch. Both defects acting independently reduce the fatigue life performance but their combination is highly detrimental and must be avoided. We did not find a severity threshold (e.g. dent depth or crack depth) where these defects could coexist. In addition, based on numerical analyses we proposed a new expression for stress concentration factor (SCF) in line with transversal indentation. This information was successfully integrated into a simple fatigue model where the fatigue life predictions were practically inside the window of experimental results.
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Accidents by trawling impact have the potential of environmental consequences, in terms of safety, monetary values and reputation. Aware of this situation a technology development plan on “Pipeline subject to high interference loads” has... more
Accidents by trawling impact have the potential of environmental consequences, in terms of safety, monetary values and reputation. Aware of this situation a technology development plan on “Pipeline subject to high interference loads” has been established at STATOIL in close collaboration with GASSCO. The overall achievement is to adapt and introduce more reliable assessment methods in the load and response of pipelines under a trawling impact scenario. Polymeric coating systems have been manly designed and used as thermal isolating material for flow assurance; and little attention has been addressed to mechanical benefits to dissipate energy by large deformation. This property is of special interest to handle impact events typically found during the trawl board impact scenario. The experimental results show the beneficial effect of polymeric coating to protect the steel pipe against indentation when compared to an uncoated system. The results presented in this work focus on new deve...
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A constitutive model for thermoplastics is outlined in this paper. The model consists of two parts: A hyperelastic-viscoplastic response due to in ermolecular resistance denoted Part A, and an entropic hyperelastic response due to re-ori... more
A constitutive model for thermoplastics is outlined in this paper. The model consists of two parts: A hyperelastic-viscoplastic response due to in ermolecular resistance denoted Part A, and an entropic hyperelastic response due to re-ori ntation of molecular chains called Part B. Both parts are developed within a framework for finite strains. The main constituents are the Neo-Hookean model describing large elastic deformations, the pressure-sensitive Raghava yield function, a non-associated visco-plas tic flow potential and Anand’s stressstretch relation representing the intramolecular st iffness. The 11 non-zero coefficients of the model are identified from uniaxial tension and comp ression tests on two materials, HDPE and PVC, which are respectively semi-crystalline an d amorphous thermoplastics. Subsequently, it is employed in numerical simulatio ns f three-point bending tests on the same materials. The model gives satisfactory predictions when compared to experimental behaviour.
This paper presents a hyperelastic-viscoplastic constitutive model for thermoplastics [1]. It is partly based on a model proposed by Boyce et al. [2]. The model involves a hyperelasticviscoplastic response due to intermolecular... more
This paper presents a hyperelastic-viscoplastic constitutive model for thermoplastics [1]. It is partly based on a model proposed by Boyce et al. [2]. The model involves a hyperelasticviscoplastic response due to intermolecular resistance, and an entropic hyperelastic response due to re-orientation of molecular chains. A Neo-Hookean material model is selected for describing large elastic deformations. Moreover, the Raghava plastic yield surface [3] is introduced to capture the pressure sensitivity behaviour, and a non-associative visco-plastic flow potential is assumed for volumetric plastic strain control. The strain-rate effects are formulated in a format well-suited for structural applications. Finally, the intramolecular stiffness is represented with Anand’s stress-stretch relation [4]. The model is developed within a framework developed for finite elastic and plastic strains, using a multiplicative decomposition of the deformation gradient. It is implemented as a user-defined m...