Research Activities

FRP Pipe Connections Subject to Combined Bending & Internal Pressure

This research project was initiated to investigate the bending limits of fiberglass (FRP) piping during hydrotest. The bending limits of above ground FRP piping systems are not well characterized and are seldom considered in the design of piping systems. It is theorized that leaks occurring during the hydrotest of these systems is often caused by bending stress in the system. Hydrotest leaks necessitate costly repairs and create a negative impact on the reliability of FRP products.

Combined bending and internal pressure tests will be conducted to establish bending limits and leakage failure envelopes for commercial pipe products. The tests will be conducted at hydrotest pressure on pipe samples with bell-spigot, taper/taper, butt-wrap and flange-flange connections. The test matrix includes 4”, 8” and 12” pipe samples.

In addition to the experimental work, 3D analytical models will be developed for the pipe connections. The models will utilize ply-level, nonlinear 3D elements. Local failure criteria will include all the applicable modes of ply material failure, and adhesive fracture at the bond lines. The connection failures will be analyzed using progressive ply failure techniques to predict leakage. Once the analytical models are shown to provide an accurate prediction of failure, the models will be used to evaluate alternative connection geometry and material parameters that may be of interest.

This project will result in improved characterization of FRP pipe products, improved design of FRP pipe systems and improved performance of FRP pipe systems, both in hydrotest and in subsequent service.

Micromechanical Modeling of Deformation, Damage and Failure of Steel-Strip Laminate (SSL) Pipe

The current demand for lightweight composite pipe systems with large diameters for high pressure applications has led to the recent development of a spirally wound steel-strip laminate (SSL) pipe by Ameron International. The SSL pipe combines the superior corrosion resistance of glass fiber reinforced epoxy (GRE) with the high structural strength of martensitic steel. A special helical finite element algorithm has been developed for 3-D micromechanical modeling of deformation, damage and failure of the SSL pipe with the incorporation of elastoplastic constitutive equation for steel strips, nonlinear elastic constitutive equation for epoxy gap fillers and adhesives, and anisotropic elastic constitutive equation with shear nonlinearity for glass fiber reinforced epoxy (GRE) inner and outer jackets. The model and method developed are expected to aid future microstructure design and optimization, improvement of the manufacturing process, performance evaluation and prediction of the SSL pipe.

High –Temperature Oxidation and Damage of Polymer-Matrix Composites

The development of high-temperature polymers and their composites has been driven primarily by the need for heat-resistant materials in high-speed aerospace structural and propulsion systems. The mechanical behavior of polymer-matrix composites depends on the chemical ad environmental history such as temperature, oxidation and humidity besides the loading/deformation history. Especially at high temperature (up to 371°C/700°F), thermal oxidation leads to weight loss and material degradation and moreover creep, physical and chemical aging may happen. The research project aims to establish constitutive equations for fiber-reinforced polymer-matrix composites subjected to high-temperature oxidation, aging and creep based on irreversible thermodynamics and micromechanics. An advanced computational mechanics methodology will be developed for life prediction of high-temperature polymer-matrix composites involving damage.

Long-Term Multiaxial Durability and Life Prediction of Polymer-Matrix Composites with Aging and Damage

This research project combines an advanced experimental study and modern multiaxial damage mechanics, time-dependent aging and failure theories to study the effects of offshore E & P environments on thermomechanical property degradation of glass/epoxy and carbon/epoxy composites under multiaxial creep loading. This study will provide thorough understanding of long-term failure behavior and effective life prediction methodology for polymeric composite structures.

Multiaxial Yielding Behavior and Elastoplastic Collapse Modeling of Thermoplastic Liners

A combined experimental, theoretical and computational study has been conducted to investigate elastoplastic buckling and postbuckling collapse of thermoplastic liners in composite pipes. Multiaxial plastic yielding experiments have been performed on a thermoplastic liner to determine its yield criteria and flow constitutive equations at different stress biaxiality ratios and temperatures. A combined theoretical and computational modeling effort has also been conducted to determine plastic buckling modes, critical annular pressure loading and postbuckling collapse behavior of thermoplastic liners with various geometric, loading and defect parameters. Based on the experimental and computational results obtained and the analytical methods and models developed, many important conclusions have been drawn in the study for future design, analysis, testing and safe applications of thermoplastic liners used in a composite pipe.

Vortex-Induced Vibration (VIV) of Composite Production Risers

To understand the effect of inherent matrix viscoelastic properties and material damping of the polymer composites on riser dynamics and to effectively utilize these material features for advancing composite riser design for deepwater offshore environments, efforts are made to develop advanced analytical methods for investigating dynamic responses of rigid composite risers in offshore floating production systems. Polymer viscoelasticity and composite micromechanics theories are used to establish viscoelastic laminate structural stiffness properties of a composite riser. Composite structural dynamic analysis methods are then developed to investigate the basic nature of composite riser dynamics subjected to combined current, wave and VIV loading.  Several case studies are carried out, using the methods developed, on rigid composite production risers (CPR) in a 3,000-ft TLP. Numerical results are given to illustrate the fundamental characteristics of dynamic deformations and stresses in the CPR’s. Contributions of fluid damping, polymer composite material dissipation and their relative criticalities on riser dynamics are determined.

Basic Research on Adhesive Joints of RTM Connectors

During years 2000 and 2001, a basic research project has been developed in CEAC regarding analysis and optimization of adhesive joints. The object of the study is the joint between pultruded profiles and resin transfer molding connectors. Though a number of joints can be applied, such as threaded and mechanically bolted or pin joints, the project has focused on bonded joints. Both finite element and experimental analyses have been carried out in order to study this type of joints.

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