Hugo Faria

Load sharing ability of the liner in type III composite pressure vessels under internal pressure

In this work, the load sharing ability of metallic liners in type III composite overwrapped pressure vessel was investigated by means of accurate numerical models based on finite element method in order to realistically represent the hybrid metal-composite structure. The varying thickness of the composite layers throughout the dome, as well as their angles, were accounted for in the model. The study focused on the influence of material properties and liner-to-composite thickness ratio on the stress and strain distribution between liner and composite at the cylindrical, dome, and polar boss regions. Two novel concepts for the evaluation of the structural response of a composite overwrapped pressure vessel were introduced, namely: (i) the liner stress and strain fractions, and (ii) the correlation with liner-to-composite thickness ratio. The results show complex overall behavior close to the onset of plasticity of the liner, which is critically investigated. A decrease in liner stress fraction was found for higher internal pressure loads since the stress field is increasingly dominated by the composite overwrap. Also, the von Mises equivalent stress along the longitudinal profile of the structure showed a peak at the dome of the liner, whereas for the composite, the peak was at the shoulder region. This was justified considering that, at low pressure, the liner operates elastically in compression-tension mode and the composite in tension-tension mode.

Long-Term Design of Composite Pipes and Tanks

In order to improve the reliability and confidence of composite solutions for piping and tanks in the several industrial applications they serve, deeper knowledge on the long-term behavior is needed. In this work a practical predictive approach for the long-term properties of these structures was established. It is based on experimental data previously obtained in comprehensive experimental programs for different types of GFRP pipes, thus covering a wide range of laminate constructions and manufacturing processes. In this paper, the principles, applicability and validation of the design criterion developed are presented and discussed.Copyright

Applicability of Optical Fiber Bragg Grating Sensors in the Structural Health Monitoring of Composite Overwrapped Pressure Vessels

Composite overwrapped pressure vessels (COPV) have been increasingly pointed to as the most effective solution for high pressure storage of liquid and gaseous fluids. Reasonably high stiffness-to-weight ratios make them suitable for both static and mobile applications. However, higher operating pressures are sought continuously, to get higher energy densities in such storage systems, and safety aspects become critical. Thus, reliable design and test procedures are required to reduce the risks of undesired and unpredicted failures. An in-service health monitoring system may contribute to a better product development, design and optimization, as well as to minimize the risks and improve the public acceptance.Within the scope of developing different COPV models for a wide range of operating pressures and applications, optical fiber Bragg grating (FBG) sensors were embedded in the liner-composite and composite-composite interfaces during their manufacture in order to allow the online strain monitoring during preliminary testing and service-life. The ability of these measuring systems to effectively assess the strain fields was to be investigated. Simultaneously, a finite element analysis (FEA) was made using the ABAQUS® platform. In this numerical analysis, accurate and realistic simulation of the different materials, geometry and loading conditions was approached. Particularly, the anisotropic nature of the wound laminate and the varying orientation of the fibers were attained. However, the cohesive zones were not attributed independent properties.Comparison between experimental and numerical data was addressed. In general, although the experimental-numerical data agreement was not as good as desired, a preliminary insight to both the structural health monitoring (SHM) system and the numerical modeling approaches was actually achieved. Full characterization and validation shall be further addressed in the continuation of the present work.The first set of results and difficulties on the development and implementation of this SHM system to COPV are presented and discussed in this paper.Copyright

Realistic Modeling of the Failure of Composite Pipes Under Ring Deflection and Internal Pressure Loading Conditions

Realistic numerical models of the behavior of glass-fiber reinforced plastic (GFRP) pipes under two loading conditions — ring deflection and internal pressure — representative of their typical applications were developed and experimentally validated. A 2D modeling approach was implemented, using cohesive elements to accurately represent at the layer/laminate level the damage mechanisms leading to failure of these composite structures and estimate their ultimate strength under those loading conditions. The innovative and advantageous feature of these models is their ability to identify the load level at which damage is initiated, its location and the way it propagates thus giving a realistic assessment to the composite pipes’ behavior. Inter-layer delamination and transverse fiber breakage were identified as main damage mechanisms occurring up to the catastrophic failure of the pipes. The numerical-experimental procedure conducted in this study allowed also to determine the proper values of material’s physical properties such as inter- and intra-layer energy release rates governing the failure mechanisms.© 2011 ASME

Long-term behaviour of GRP pipes

The main objective of the research programme [1] described is the study of creep and relaxation behaviour of glass-reinforced thermosetting (GRP) pipes, in order to find alternative methods to predict the long-term properties, rendering a considerable reduction of the time needed for testing and assuring, as far as possible, equivalent reliability when compared to the existing methods. Experimental procedures were performed and are presented here, together with discussion of results, as well as predictive methodologies studied.