T.E. Tay

Homogenization and Stress Analysis of Multilayered Composite Offshore Production Risers

An approach for stress analysis of multilayered composite cylinders is proposed for the analysis of new composite risers used in deep-water oil production of offshore petroleum industries. Risers essentially comprise long cylindrical sections connected end-to-end. In the formulation, only stresses and strains that are continuous through the thickness of the multilayered composite risers are taken to be equal to reported solutions for homogenous orthotropic hollow cylinders using homogenized material properties. These stress and strain solutions are then used to calculate the remaining discontinuous stresses and strains from the material properties of individual layers of materials. The homogenized elastic constants of cylindrically orthotropic composite risers are derived from forcedeformation equivalence, taking into account the stress and strain distributions in each layer. Four typical loading conditions are considered in the stress analysis, namely, internal and external pressures, axial loading, bending, and torsion. Examples of homogenized elastic constants and stress analyses of composite cylindrical structures with different layups and materials are presented to demonstrate the application of the proposed method. The results compared very favorably with those from other solutions. This method provides practical benefits for the design and analysis of composite risers. Because there is no requirement to explicitly enforce interfacial continuity in this method, stress analyses of composite cylinders with many layers of different fiber angles or materials can be carried out efficiently. The homogenized elastic constants can greatly expedite the analysis of entire composite riser systems by replacing complex models of riser sections with homogenized riser sections. [DOI: 10.1115/1.4024695]

Stress intensity factors of cracks in finite plates subjected to thermal loads

Abstract In the framework of cracked plate thermoelastic problems, the perturbation effects caused by the presence of a crack on thermal stresses, displacements and stress intensity factors in an isotropic linear elastic medium with varying crack surface heat conductivity under uniform heat flow are studied. The disturbance due to the crack results in a non-smooth temperature modification of the original field and induces singular character of the thermal stresses near the crack tip. This disturbing temperature distribution is solved numerically by using the distributed dipole method. Finite element solutions under the above temperature distribution are presented. Numerical results of mixed mode stress intensity factors are given for various geometric cases of a plate. It is shown that, for the case of a crack situated in the finite plate center subjected to a uniform heat flow, the geometry does not affect the mode I thermal stress intensity factor K I significantly, and K I is negligible compared with the mode II thermal stress intensity factor K II . Only the mode II thermal stress intensity factor K II is significant and shows a very localized phenomenon in the near-field region of a crack. For all cases studied here, the values of the mode II thermal stress intensity factor in a smaller plate are dependent on the geometric size of the plate. As the geometric size of the plate increases, the value of K II is close to the solution of an infinite plate.

Holographic determination of the residual strength of arbitrarily clamped, centrally thinned circular plates

In holographic inspection, the perturbed fringe patterns which reveal internal defects in components are generally distinct. However, in the case of a uniformly loaded circular flat plate containing a central circular defect, distinct fringe perturbation is not visually obvious except through quantitative analysis of the fringe pattern. During the analysis, ambiguities frequently arise in correctly assigning the fringe order, which is often fractional, at the centre of the plate. With the use of carrier fringes, accurate fringe orders at the central region of the plate can be determined. These, together with an iterative procedure, enable accurate estimation of both the size and depth of the defect. As the present method also determines the actual clamping condition along the plate boundary, the use of the von Mises yield criterion enables estimation of the residual strength, expressed in terms of the proportional reduction in the allowable pressure which can be applied to the defective plate.

Plastic strain measurement in polypropylene using laser speckle technique

Abstract This paper presents a laser speckle technique and a computer based image processing system for strain measurement in plastics. A new correlation parameter, the Integrated Peak Spectral Intensity Coefficient H 1 is proposed. Test results on polypropylene specimens subjected to uni-axial stretching show a correlation between the Integrated Peak Spectral Intensity Coefficient H 1 and strain. The advantages of this method are its non-contacting nature, absence of gauge marks, no limitation on specimen design and it enables measurement of plastic strains of up to 40%.

Prototyping and testing of composite riser joints for deepwater application

The high strength to weight ratio, good corrosion resistance, and excellent fatigue property make carbon fiber-reinforced plastics a competitive material solution to replace steel in deepwater riser application. In this work, scaled-down composite riser joints were fabricated using a filament-winding machine. The prototypes comprise several carbon fiber-reinforced plastic layers wound over an aluminum liner. They consist of a middle tubular section and two metal-composite interface end fittings for the transfer of load between joints. A series of mechanical tests, including tension and combined tension-bending loading tests were performed to characterize their structural capacity and evaluate the improvement in performance over a purely metallic mandrel. In addition, finite element analyses incorporating elastic–plastic properties of the metallic liner, interfacial failure, and complex carbon fiber-reinforced plastics failure modes were carried out. The numerical predictions are in good agreement with the experimental measurements. The experimentally verified FE framework was then extended to design and analyze a full-scale composite riser model for performance prediction to accelerate the application of composite risers by shortening product development cycle and reducing prototyping costs.