Alcides Sá

On the prediction of long-term creep-failure of GRP pipes in aqueous environment

Polymer Composites, 2009

The aim of this work was to study the long-term failure of GRP (Glass fiber-reinforced Polymer) p... more The aim of this work was to study the long-term failure of GRP (Glass fiber-reinforced Polymer) pipes under the influence of moisture absorption. These pipes are used in water transportation, which has an important effect on the mechanical properties of the polymeric matrix. The GRP pipes are usually tested under ring deflection or internal pressure conditions. This study presents and analyzes experimental creep-rupture data obtained from standard test methods under ring deflection conditions. This loading configuration simulates in laboratory the conditions verified in a subsoil installation. The creep testing was carried out under constant dead weight on unconditioned and preconditioned samples in a submerged condition. The diametrical deflection of samples was measured periodically, and the time to failure of each sample was recorded. The main purpose of this work was to determine the short and long-term rupture energies of GRP pipes and assess the influence of moisture preconditioning on those values. The observed failure mode was always the same. It was concluded that the energy at failure decreases with time. The influence of the preconditioning on the creep-rupture of GRP pipes was considered negligible. Different time-dependent failure models were described and used for long-term extrapolation of the experimental data. The maximum strain at failure decreased about 12% from 0.1 to 1,000 hr of creep testing. Furthermore, data extrapolation to 50 years predicts a reduction of strength of about 60%, founded on the most conservative time-dependent failure criterion.

Download

Influence of moisture absorption on GIC and flexural properties of GRP pipes

Journal of Reinforced Plastics and Composites, 2010

In this work the moisture diffusion process and the influence of moisture on mechanical propertie... more In this work the moisture diffusion process and the influence of moisture on mechanical properties (critical strain energy release rate in mode I (GIC), flexural modulus and ultimate flexural strength) of GRP pipes was assessed. The research was performed on specimens conditioned in two different environments, water at room temperature and water at 50°C. In this case it was verified that the water diffusion can be well described by the Fick’s second law. The critical strain energy release rate in mode I, GIC, shows a decrease between 5% and 10% when conditioned in water. The temperature of the conditioning does not have so much influence on the GIC values. The conditioning either in water at room temperature or at 50°C has an influence on the flexural modulus and strength of the pipes in the hoop direction, between 10% and 20%, respectively. The longitudinal modulus was more significantly affected by the conditioning in water at 50°C with a 30% decrease.

Influence of moisture absorption on creep of GRP composite pipes

Polymer Testing, 2007

The aim of this work was to study the influence of moisture absorption on long-term creep behavio... more The aim of this work was to study the influence of moisture absorption on long-term creep behavior of composite pipes. These pipes are used in water transportation which has an effect on the mechanical properties and on the polymeric composite matrix. Glass-reinforced thermosetting plastics (GRP) pipes are typically tested under ring deflection and/or internal pressure conditions. In this study, experimental creep data obtained from standard test methods under ring deflection conditions were used. This loading configuration simulates in the laboratory the external loads induced in a subsoil installation. The creep tests were performed on unconditioned and preconditioned specimens. Long-term mechanical behavior prediction based on short-term test data is necessary for design. For this purpose dynamic mechanical thermal analysis (DMTA) tests were performed on specimens machined from GRP pipes. Ten specimens were tested as delivered. Another 10 specimens were conditioned in water at room temperature and another 10 were conditioned in water at 50 C, until saturation. The time-temperature superposition principle (TTSP) and extrapolation using a power law relation were applied to DMTA data for long-term creep prediction. Both methods were found to be conservative, i.e. predict higher stiffness reduction than the creep tests. Although creep tests were quite dissimilar from the DMTA tests, extrapolation using a power law relation appeared to be accurate enough to be used as a predictive tool for project design. Finally, comparisons of the DMTA data for different environment conditioning enabled the assessment of the hygrothermal effects on modulus.

Download

On the prediction of long-term creep-failure of GRP pipes in aqueous environment

Polymer Composites, 2009

The aim of this work was to study the long-term failure of GRP (Glass fiber-reinforced Polymer) p... more The aim of this work was to study the long-term failure of GRP (Glass fiber-reinforced Polymer) pipes under the influence of moisture absorption. These pipes are used in water transportation, which has an important effect on the mechanical properties of the polymeric matrix. The GRP pipes are usually tested under ring deflection or internal pressure conditions. This study presents and analyzes experimental creep-rupture data obtained from standard test methods under ring deflection conditions. This loading configuration simulates in laboratory the conditions verified in a subsoil installation. The creep testing was carried out under constant dead weight on unconditioned and preconditioned samples in a submerged condition. The diametrical deflection of samples was measured periodically, and the time to failure of each sample was recorded. The main purpose of this work was to determine the short and long-term rupture energies of GRP pipes and assess the influence of moisture preconditioning on those values. The observed failure mode was always the same. It was concluded that the energy at failure decreases with time. The influence of the preconditioning on the creep-rupture of GRP pipes was considered negligible. Different time-dependent failure models were described and used for long-term extrapolation of the experimental data. The maximum strain at failure decreased about 12% from 0.1 to 1,000 hr of creep testing. Furthermore, data extrapolation to 50 years predicts a reduction of strength of about 60%, founded on the most conservative time-dependent failure criterion.

Download

Influence of moisture absorption on GIC and flexural properties of GRP pipes

Journal of Reinforced Plastics and Composites, 2010

In this work the moisture diffusion process and the influence of moisture on mechanical propertie... more In this work the moisture diffusion process and the influence of moisture on mechanical properties (critical strain energy release rate in mode I (GIC), flexural modulus and ultimate flexural strength) of GRP pipes was assessed. The research was performed on specimens conditioned in two different environments, water at room temperature and water at 50°C. In this case it was verified that the water diffusion can be well described by the Fick’s second law. The critical strain energy release rate in mode I, GIC, shows a decrease between 5% and 10% when conditioned in water. The temperature of the conditioning does not have so much influence on the GIC values. The conditioning either in water at room temperature or at 50°C has an influence on the flexural modulus and strength of the pipes in the hoop direction, between 10% and 20%, respectively. The longitudinal modulus was more significantly affected by the conditioning in water at 50°C with a 30% decrease.

Numerical analysis of singly curved shallow composite panels under three-point bend load

Composite Structures, 2008

The experimental methodology to test curved panels under three-point bend (3PB) load is assessed.... more The experimental methodology to test curved panels under three-point bend (3PB) load is assessed. The problem arises when mechanical and strength characterization of pipe material systems is required. Test specimens cut out from pipe samples oriented in the tangential direction were used to measure hoop modulus and strength. In this procedure singly curved beams with the same radius as the pipe are obtained. The present assessment was made using three different approaches: Finite Element Method (FEM) with nonlinear geometrical analysis, curved beam theory and an approximate 2D elasticity solution. It was verified that for some cases the nonlinear effect becomes important. Furthermore the maximum span achievable, which is limited by the specimen's geometry, can prevent the use of appropriate span/thickness ratios to avoid significant shear effects. However it was concluded that for typical GRP shell panels, with internal radius between 150 and 250 mm and a wall thickness of 12 mm, the 3PB tests display an almost linear relationship between applied load and maximum deflection. Moreover, reasonable accurate results, with an error lower than 5%, can be expected using the curved beam theory formulas. Finally some preliminarily experimental results are presented for the 250 mm radius beams with a thickness of 12 mm.

Download

Influence of moisture absorption on quasi-static and long-term failure of a GRP pipe under lateral compression

Tese de Mestrado. Mestrado em Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto... more

Download

An experimental and numerical assessment of DCB tests on glass/polyester curved beams cut out from pipes

Polymer Testing, 2008

The aim of this work is to define a suitable procedure in order to measure the interlaminar fract... more The aim of this work is to define a suitable procedure in order to measure the interlaminar fracture toughness of circumferential specimens cut out from ready-to-use glass reinforced polymer (GRP) pipes made by centrifugal casting. Double Cantilever Beam (DCB) tests were performed to assess the critical strain energy release rate in mode I (G Ic ), which was considered equal to initiation values. In fact, the intrinsic heterogeneous composition of these GRP pipes promoted the occurrence of uncontrollable fibre bridging, which disturbed crack propagation and avoided the attainment of a smooth R-curve. The specimen's geometry leads the mode I loading into a complex stress state at the tip of the crack opening. This mixed-mode situation was numerically quantified using the virtual crack closure technique. For that purpose, a 2D FEM analysis with interface finite elements was used. A progressive failure analysis including a cohesive mixed-mode damage model was also performed. This numerical model reproduced the DCB tests and allowed the estimation of mode II influence on the measured G Ic values. Two different data reduction schemes, modified compliance calibration (MCC) and compliance-based beam method (CBBM), were used to calculate the G Ic values. Both methods are based on the classical beam theory since it was proved by comparison with curved beam theory that this gives accurate results for the present case. These methods were assessed using a numerical model.

Download

Related Authors

Uploads

Papers by Alcides Sá

Log In