Ultimate Elastic Wall Stress Test Research Articles

ALTERNATIVE METHOD FOR QUALIFICATIONS OF GLASS FIBRE REINFORCED EPOXY PIPES (GRE)

This paper discusses the Ultimate Elastic Wall Stress (UEWS) test for GRE pipes under pure hydrostatic loading. UEWS appears to provide an attractive alternative to the currently used procedure laid down in ISO 14692, which involves an expensive series of long term constant pressure tests, as described in ASTM 2992, running for a period in excess of 10,000 hours.
 The pipes were subjected to biaxial loading, which was attained by combinations of hoop and axial stress. Loads were applied as groups of cycles which, were gradually increased until the UEWS had been determined. UEWS test has proved to be one of the most effective in terms of accuracy and speed. Moreover, it has been found to be sensitive to changes in key manufacturing and raw material parameters.
 Modelling results are also showed a harmonic approach and accepted to that obtained experimentally. This encourages to apply the proposed modelling for further biaxial load ratios.

Performance Simulation of Glass Fibre/Epoxy Composite Pipes under Multiaxial Stress Loading

Nowadays composite material especially Glass fibre reinforced epoxy (GRE) composites is one of the most widely used composite materials in such areas, especially in the marine, building and oil industry due to their lightweight, high strength and chemical/corrosion resistant properties. The aim of this paper is to provide an improved understanding of the performance of glass fibre reinforced epoxy (GRE) pipe under combined pressure and axial loads. The performances of GRE composite pipes is investigated through finite element modelling of ultimate elastic wall stress test under multi-axial loading ranging from pure axial to pure hoop loadings. ANSYS software will be used for finite element modelling of GRE pipes. A stress-strain response was obtained for each winding angle and the results for modelling then compared with those experimental computed through laminate theory. It is also concluded that the experimental results stress, which represent the onset of non-linearity were very much dependent on the transverse and shear stress response, and these values were found to be consistent with the predicted values from the commonly used Tsai-Wu failure criterion.

Strain response and damage modelling of glass/epoxy pipes under various stress ratios

This paper presents the stress–strain response and general lifetime damage modelling of glass fibre reinforced epoxy (GRE) composite pipes subjected to multi-ratios stress loadings at room temperature (RT). This particular modelling work was developed to predict the non-linear stress–strain response caused by the fatigue static and cyclic loading in the multiaxial ultimate elastic wall stress (UEWS) tests by considering the effects of matrix cracking within the laminates. Although the UEWS procedure is not a standard protocol used for qualification of GRE pipes, it appears to offer an option to existing procedures delineated in ASTM D2992. The ply properties initially expressed as a function of crack density was computed as a function of increasing stress and strain using shear lag approximation. In general lifetime damage model, the effects of stress developed in each ply from ultimate elastic wall stress (UEWS) test were expressed in a single quadratic term of axial and hoop stress. The term then solved to produce limits with respect to axial and hoop stress, which represented in a graphical form of failure envelope. The predictions from both models are found to be in good agreement with the data from the multiaxial UEWS tests of ±55° filament wound GRE pipes. These models thus enable for the long term performance prediction of the pipes under combined loadings.

Ultimate Elastic Wall Stress (UEWS) Test under Biaxial Loading for Glass-Fibre Reinforced Epoxy (GRE) Pipes

This paper presents the results of an experimental investigation into the Ultimate Elastic Wall Stress (UEWS) of ±55° filament wound composite pipes. The UEWS test appears to provide an attractive alternative to the current method, and has proved to be one of the most effective in term of accuracy and speed. Moreover, it has been found to be sensitive to changes in key manufacturing and raw material parameters. The pipes were subjected to biaxial loading, which was achieved by combinations of hoop and axial stress. Loads were applied as groups of cycles which, were gradually increased until the UEWS had been determined. Various ratios of hoop to axial stress were applied to the pipes, ranging from pure axial to pure hoop loading at room temperature and at 65°C. These ratios were investigated by applying different pressures in both the main and small chambers built inside the pipe, and therefore it was unnecessary to add any external loads to the pipe wall. Tests were also conducted to observe leakage through the pipe wall. The main failure mode observed was weepage through the pipe wall, which was due to intensive matrix microcracking. The results from the UEWS tests are presented in the form of failure envelopes showing the effects of testing at an elevated temperature. Finally, degradation in the elastic properties of the pipe wall is also discussed and plotted against wall stress.

Acoustic emission monitoring of multiaxial ultimate elastic wall stress tests of glass fibre-reinforced epoxy composite pipes

This paper describes the acoustic emission (AE) monitoring of multiaxial ultimate elastic wall stress (UEWS) tests of filament wound glass fibre-reinforced epoxy composite pipes under hydrostatic, pure axial and pure hoop loadings at room temperature. The purpose of AE monitoring is to quantitatively identify and characterise damage inception and evolution, which leading to different failure mechanisms via an analysis of AE parameters. AE parameters such as counts and energy released were plotted against time, and changes of these AE activities were monitored. A 3D correlation plot between AE amplitude and duration against time for each loading condition was produced and analysed. The AE measurement of both hydrostatic and pure axial loading suggested that matrix cracks were initiated early in the tests and possible had progressed into delamination failure just before UEWS point was reached at 200 MPa of hoop stress and 63 MPa of axial stress, respectively. No clear damage initiation and progression was observed for pure hoop loading condition. Significant AE events were only noted when buckling induced delamination and debonding failure, which followed by fibre fracture at the outer surface of the pipe.

General Lifetime Damage Model for Glass Fibre Reinforced Epoxy (GRE) Composite Pipes under Multiaxial Loading

This paper presents the modelling of a general lifetime performance for glass fibre reinforced epoxy (GRE) composite pipes similar to the well-known Tsai-Hill interactive failure criterion. Tsai Hill criterion is based on the Von Misses distortional energy criterion which was modified to satisfy the orthotropic nature of GRE composite pipes. The effects of stress developed in each ply from ultimate elastic wall stress (UEWS) test were expressed in a single quadratic term of axial and hoop stress through laminate theory. The term then solved to produce limits with respect to axial and hoop stress, which represented in a graphical form of failure envelope. The modelled envelop shows a good agreement with experimental data from the multiaxial UEWS test of ±55° GRE composite pipes. This indicates that such model can be used to predict the long-term performance of GRE pipes under combine loadings.

Effects of Winding Angles in Biaxial Ultimate Elastic Wall Stress (UEWS) Tests of Glass Gibre Reinforced Epoxy (GRE) Composite Pipes

This paper presents an experimental investigation into the influence of winding angles in multiaxial ultimate elastic wall stress (UEWS) tests of glass-fibre reinforced epoxy (GRE) composite pipes. Currently, UEWS test is one of the alternative methods used to the 1000-hour test procedure detailed in ASTM D2992 for the detection of manufacturing changes and reconfirmation of the design basis of composite pipes. A stress-strain response was obtained for each winding angle and the results then compared with those computed through conventional laminate theory. Experimental data showed that the UEWS point varies for each winding angle, and the difference becomes even more pronounced, especially when the angles deviated from the ideal ±55°. It is also concluded that the UEWS stresses, which represent the onset of non-linearity were very much dependent on the transverse and shear stress responses, and these values were found to be consistent with the predicted values from the commonly used Tsai Wu failure criterion.

Modelling of Multi-Axial Ultimate Elastic Wall Stress (UEWS) Test for Glass Fibre Reinforced Epoxy (GRE) Composite Pipes

This paper describes the modeling of multiaxial ultimate elastic wall stress (UEWS) at room temperature for glass fibre reinforced epoxy (GRE) composite pipes. The model developed, predicts the stress-strain response caused by the combined, static and cyclic of UEWS loading taking into effects of transverse matrix cracking within the laminates. The procedure, although not a standard method, seems to provide a good alternative to the current raw materials' re-qualification procedure delineated in ISO 14692 through ASTM D2992. The effective transverse and shear modulus of the lamina due to increasing presence of transverse matrix cracking were estimated. Classical laminate analysis was then applied to compute the corresponding ply properties as a function of increasing stress and strain. The model shows a good agreement with the experimental results of multiaxial UEWS tests on ±55° filament wound glass-reinforced epoxy pipes.

Qualification and lifetime modelling of fibreglass pipe

Procedures for qualifying fibreglass pipes are discussed here in relation to industry needs. The ultimate elastic wall stress (UEWS) test appears to provide an efficient means of rating pressure pipe, and indeed vessels, for the case where weepage failure occurs resulting from the accumulation of matrix cracks. The principle behind the UEWS test is to identify, from the pressure–strain response, a pressure level below which damage growth is either negligible or at least sufficiently low to avoid failure within the design life. The version of the UEWS test most often used involves the application of groups of 10 one‐minute pressure cycles at increasing pressure values, recording the hoop or axial strain. The onset of non‐linearity in the pressure–strain relationship can be accurately determined and enables a safe long term pressure level to be identified. The UEWS test appears to provide a desirable alternative to the currently used procedure laid down in ISO 14692, which involves an expensive series of long term constant pressure tests, as described in ASTM 2992, running for a period in excess of 10 000 h. It is shown here that the UEWS test reflects the cyclic fatigue behaviour of fibreglass pipe, but further work on the relationship between cyclic and static behaviour would be desirable. It has been shown that a Miner's law approach is effective in modelling damage due to combined static and cyclic effects, and that damage can be directly related to matrix crack growth. This approach could form the basis of a future procedure for describing lifetime behaviour of glass reinforced epoxy pipes under any required combination of static, fatigue, hydrostatic and non‐hydrostatic (multiaxial) loading.

The Use of the ultimate elastic wall stress (UEWS) in evaluating PVC polymer blends

AbstractThe UEWS test is described as a sensitive means to measure the stress in a material at which the first inelastic behavior becomes apparent. Particularly interesting observations have been made with PVC, where the aging of the material can be shown in a master curve diagram giving the relation between the UEWS and the age of the material at different molecular weights. Using this test as a tool, the performance of blends can also be measured. Blends of PVCs with different molecular weights and blends with various polystyrenes, polyvinyl acetate, and CPE are discussed.