Experimental and Theoretical Investigations of Creep on a Composite Pipe under Compressive Transverse Loading

Roham Rafiee,Amin Ghorbanhosseini 한국섬유공학회 2021 Fibers and polymers Vol.22 No.1

The use of Glass Fiber Reinforced Polyester (GFRP) pipes in the industry increased considerably in the pastdecades. These pipes are used in various applications such as conveying water, sewage, seawater, industrial wastewater,petroleum and also in power plants and chemical industries. These pipes are resistance to corrosion resistance and thus theyare exploited for long-term purposes. Unlike metals, creep occurs in polymeric materials at any temperature. GFRP pipes aregenerally designed to withstand against the internal pressure and also transverse compressive force as the two main loadcases. Design architecture of composite layers, i.e. number of layers and their fiber orientations, is done based on the initialresponse of the pipe structure to the aforementioned loadings known as short-term behavior. But evaluating the long-termperformance of the pipes is one of the important design requirements according to the working life of these pipes. In thisstudy, the long-term behavior of a GFRP pipe undergoing transverse loading is investigated experimentally and theoretically. The influence of structural parameters including the thickness of liner, lay-up orientation and number of layers are evaluated.

Aeroelastic investigation of a composite wind turbine blade

Rafiee, Roham,Fakoor, Mahdi Techno-Press 2013 Wind and Structures, An International Journal (WAS Vol.17 No.6

Static aeroelastic is investigated in a wind turbine blade. Imposed to different loadings, the very long and flexible structures of blades experience some changes in its preliminary geometry. This results in variations of aerodynamic loadings. An iterative approach is developed to study the interactions between structure and aerodynamics evaluating variations in induced stresses in presence of aeroelasticity phenomenon for a specific wind turbine blade. A 3D finite element model of the blade is constructed. Aerodynamic loading is applied to the model and deflected shape is extracted. Then, aerodynamic loadings are updated in accordance with the new geometry of the deflected blade. This process is repeated till the convergence is met. Different operational conditions consisting of stand-by, start-up, power production and normal shut-down events are investigated. It is revealed that stress components vary significantly in the event of power production at the rated wind speed; while it is less pronounced for the events of normal shut-down and stand-by.

Aeroelastic investigation of a composite wind turbine blade

Roham Rafiee,Mahdi Fakoor 한국풍공학회 2013 Wind and Structures, An International Journal (WAS Vol.17 No.6

Static aeroelastic is investigated in a wind turbine blade. Imposed to different loadings, the very long and flexible structures of blades experience some changes in its preliminary geometry. This results in variations of aerodynamic loadings. An iterative approach is developed to study the interactions between structure and aerodynamics evaluating variations in induced stresses in presence of aeroelasticity phenomenon for a specific wind turbine blade. A 3D finite element model of the blade is constructed. Aerodynamic loading is applied to the model and deflected shape is extracted. Then, aerodynamic loadings are updated in accordance with the new geometry of the deflected blade. This process is repeated till the convergence is met. Different operational conditions consisting of stand-by, start-up, power production and normal shut-down events are investigated. It is revealed that stress components vary significantly in the event of power production at the rated wind speed; while it is less pronounced for the events of normal shut-down and stand-by.

On The Stiffness Prediction of GFRP Pipes Subjected to Transverse Loading

Roham Rafiee,Mohammad Reza Habibagahi 대한토목학회 2018 KSCE Journal of Civil Engineering Vol.22 No.11

The main objective of this study is to predict the stiffness of GFRP pipes subjected to compressive transverse loading. An experimental study is performed to measure the stiffness of a composite pipe with a core layer of sand/resin composites. Then, a simple analytical modeling constructed on the basis of solid mechanics is used to estimate the stiffness of the investigated pipe as the back-of-envelope technique widely used by industrial sectors. The simulation of stiffness test is conducted using finite element modeling wherein both large deformation and inelastic behavior of material is taken into account as the sources of nonlinearity. The results reveal that a very good estimation with high level of accuracy can be reached by proper selection of the element and performing nonlinear analysis.

The influence of production inconsistencies on the functional failure of GRP pipes

Roham Rafiee,Mahdi Fakoor,Hadi Hesamsadat 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.19 No.6

In this study, a progressive damage modeling is developed to predict functional failure pressure of GRP pipes subjected to internal hydrostatic pressure. The modeling procedure predicts both first-ply failure pressure and functional failure pressure associated with the weepage phenomenon. The modeling procedure is validated using experimental observations. The random parameters attributed to the filament winding production process are identified. Consequently, stochastic simulation is conducted to investigate the influence of induced inconsistencies on the functional failure pressures of GRP pipes. The obtained results are compared to realize the degree to which random parameters affect the performance of the pipe in operation.

Linkage Learning Optimization of Aeroelastic and Structural Behavior of Composite Wings

Roham Rafiee,Touraj Farsadi,Majid Ahmadi Tehrani,Parsa Sharifi 한국항공우주학회 2023 International Journal of Aeronautical and Space Sc Vol.24 No.5

The paper aims to develop a systematic numerical design for composite wings optimization subject to aerodynamic loading and to assess the aeroelastic and structural performance of the optimized composite wing. Aeroelastic tailoring is a powerful method for utilizing the anisotropic features of composite materials used in lightweight aerospace structures. The present proposed methodology combines three different analysis tools: a commercial FE software commonly used in industry, an in-house reduced order aeroelastic framework for aeroelastic analyses with tailoring capabilities, LLGA, in-house linkage-learning genetic algorithms for optimization of stacking sequences. As a multidisciplinary problem where structural and aeroelastic behaviors are interacted, developed multi-level optimization scenario in this research converges to the optimal design in a very short time. The proposed methodology implemented as a computer code can effectively be applied to any arbitrary air vehicle’s composite wing by changing input data.

Equivalent reinforcement isotropic model for fracture investigation of orthotropic materials

Mahdi Fakoor,Roham Rafiee,Shahab Zare 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.30 No.1

In this research, an efficient mixed mode I/II fracture criterion is developed for fracture investigation of orthotropic materials wherein crack is placed along the fibers. This criterion is developed based on extension of well-known Maximum Tensile Stress (MTS) criterion in conjunction with a novel material model titled as Equivalent Reinforced Isotropic Model (ERIM). In this model, orthotropic material is replaced with an isotropic matrix reinforced with fibers. A comparison between available experimental observations and theoretical estimation implies on capability of developed criterion for predicting both crack propagation direction and fracture instance, wherein the achieved fracture limit curves are also compatible with fracture mechanism of orthotic materials. It is also shown that unlike isotropic materials, fracture toughness of orthotic materials in mode I cannot be introduced as the maximum load bearing capacity and thus new fracture mechanics property, named here as maximum orthotropic fracture toughness in mode I is defined. Optimum angle between crack and fiber direction for maximum load bearing in orthotropic materials is also defined.