Time-dependent response of thermoplastic matrix composite material under the cyclic loadings

Abstract

Under the service conditions, steel pipelines coated with the thermal protection system are subjected to cyclic loadings of axial tension and hydrostatic pressure. The finite element method generally used to simulate the behavior of composite structures under these loadings allows us to estimate the stresses generated in the system and to conclude on several origins of damage. However, for the framework of displacement or deformation analyses in such multilayer systems, these calculations do not allow a better prediction of their behavior. The methods used do not take sufficiently into account the characteristics of the different coating materials to predict their response in service conditions under cyclic loading. In this paper, we consider the viscosity of the thermoplastic materials used for the five layers coating system. Finite element calculations allow us to observe the areas of highest stress concentration at the interface with the steel pipe. Simulations allowed us to observe that the applied loads lead to increases in residual deformation in the thermoplastic matrix composite material. Cyclic tensile loading causes cracks in the matrix of the syntactic foam material. The study carried out here makes it possible to justify the origin of the failure mechanism in the composite material at the time of the installation of the pipelines which could limit the duration of their use in an offshore environment. The tensile failure of the syntactic foam considered as the polypropylene matrix composite material on which cyclic loads have been applied, is due to the stress level at a given temperature.

Analysis and numerical investigations on the temperature-dependent creep behavior of polypropylene matrix composite used for coating of offshore pipeline

“…13 This material exhibits an irreversible behavior which takes into account the viscoplasticity of the matrix. 22 In addition, the level of the stress applied on the material is assumed not to cause damage: ( ɛ p = 0). Therefore, the total strain of the material is given by:where εtrue¯e, εtrue¯ve, and εtrue¯vp are the strains of elastic, the viscoelastic, and the viscoplastic, respectively.

Figure 5.Thermal insulation materials.

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“…This residual part of the viscous strain is a viscoplastic strain. 22,23,32 The viscoplastic model that we consider is that of ref. 33 which is generally used for the constant load profile applied on the composite materials.…”

“…13 This material exhibits an irreversible behavior which takes into account the viscoplasticity of the matrix. 22 In addition, the level of the stress applied on the material is assumed not to cause damage: (ε p = 0). Therefore, the total strain of the material is given by:…”

“…In addition, a study by microscopic observation was allowed to highlight the effects of porosity defects generally present in syntactic foams with polymer matrix. 21 On the other hand, the polymeric nature of the matrix led to the establishment of a viscoelastic model without deterioration of syntactic foams with a thermoplastic matrix 22 and a thermoset matrix. 23 An experimental study was carried out by ref.…”