In the aerospace industry, open hole specimens of composite laminates have been used in standardized tests to generate design allowables. Using finite element method (FEM) based tool MicMac/FEA with AB AQUS code interface and statistical design of experiments, Shah, et al. in 2010 [11] studied average-property-based failure envelope with uncertainty estimates of open hole specimen with quasi-isotropic carbon fiber-epoxy laminate. However, their FEM model is deterministic, without uncertainty analysis. In this paper, based on Shah’s FEM model, we developed FEM model of uni-axial strength test of holed composite laminates using ABAQUS with a serious of quadrilateral S4R and trilateral S3R shell element designs. The mesh density ranges from the original 8 × 8 (very coarse) to 48 × 48 (very fine). For each of the meshes, we compute the failure strength from Hasin failure criteria. Then we use a 4-parameter logistic function nonlinear least squares fit algorithm to obtain an estimate of the failure strength at infinite degrees of freedom (d.o.f) as well as its uncertainty at 50,000-d.o.f. and relative error convergence rates. Our results are then compared with Shah’s with the additional advantage that our results have uncertainty quantification that can be compared with experimental data. The significance and limitation of our method on the uncertainty quantification of FEM model of uniaxial strength test of holed composite laminates are discussed.

Adhesive bonding technology is widely used for connecting composite pipes recent years, for the adhesive joints have many advantages such as weight reduction, ease of manufacture, and more importantly, uniform stress distribution and less stress concentration within the joint region. Nevertheless, one of the limitations of adhesive joints is the difficulty in predicting the joint strength due to the presence of defects in the adhesive due to improper curing process. This paper presents an experimental study of single-lap joints with disbond defects at the adherend-adhesive interface. Different sets of adhesively-bonded singlelap joints containing varied disbond conditions were prepared and tested. The joints used carbon fiber reinforced polymer (CFRP) laminates as substrates and epoxy resin as adhesive, with ultrathin aluminum foil (10um) as disbond defects in different sizes and locations. The full deformation fields were measured using the digital image correlation (DIC) method. The samples were subjected to tensile load till failure to determine the bond strength. Before the tensile test, the defective adhesive joints were detected by a phased-array ultrasonic instrument to identify the bond-line quality of joints. The results show that the disbond defects can be detect by ultrasonic phased-array technique, and the detriment of disbond defect to the failure process can be observed and recorded by DIC system. Based on the findings, the failure modes and failure mechanism of bonded CFRP joint were further discussed.

In the small scale LNG infrastructure, composite materials are scarcely employed. Potentially, cost effective solutions for LNG applications could be developed thanks to the advantages of composite materials over metals such as weight savings, design flexibility and recyclability. The research presented in this paper focuses on the mechanical performance of fully recyclable, thermoplastic Polypropylene (PP) composite tapes at cryogenic LNG temperatures. Quasi-static tensile tests performed on [±45] laminates made of plain woven plies of PURE ® show that at −196°C the behavior is bilinear with the failure strain of 6.5% and failure stress of 37 MPa. Such non-brittle failure behavior of PP is desirable for cryogenic applications. The other results presented in the paper contains [0/90] laminate results and the interlaminar shear strength characteristics at room and cryogenic temperatures.

Pipelines are a practicable means for delivering large quantities of gaseous hydrogen over long distances and for distributing it as a transportation fuel at fueling stations in urban and rural settings. Glass-fiber-reinforced polymer (GFRP) pipelines are a promising alternative to the present-day use of low-alloy steel in pipelines for hydrogen transmission. GFRP pipelines offer advantages of lower capital cost and improved lifecycle performance, compared to steel pipelines. The technical challenges for adapting GRFP pipeline technology from oil and natural gas transmission, where it is in extensive service worldwide, to hydrogen transmission consists of evaluating the hydrogen compatibility of the constituent materials and composite construction, identifying the advantages and challenges of the various manufacturing methods, testing polymeric liners and pipelines to determine hydrogen permeability and leak rates, selecting options for pipeline joining technologies, establishing the necessary modifications to existing codes and standards to validate the safe and reliable implementation of the pipeline. We performed examined the technical feasibility of using a commercially available spoolable glass-fiber-reinforced polymer (GFRP) pipeline for hydrogen transmission. We used an accelerated aging process based on the Arrhenius model to screen for hydrogen-induced damage in the pipeline and in the pipeline’s constituent materials. We also measured hydrogen leakage rates in short lengths of the pipeline. The accelerated aging process involved immersing GRFP pipeline specimens in pipeline-pressure hydrogen (6.9 MPa/1000 psi) at an elevated temperature (60°C) to promote an accelerated interaction of hydrogen with the pipeline structure. To assess specific effects on the constituent materials in the pipeline, specimens of fiberglass rovings, resin matrix and liner materials were immersed together with the pipeline specimens, and specimens of all types were subjected to either a one-month or an eight-month exposure to hydrogen at the elevated temperature. At the conclusion of each exposure interval the pipeline specimens were evaluated for degradation using hydrostatic burst pressure tests to assess the overall integrity of the structure, compression tests to assess the integrity of the polymer matrix, and bend testing to assess the integrity of the laminate. The results of these tests were compared to the results obtained from identical tests performed on un-conditioned specimens from the same manufacturing run. Tensile tests and dynamic mechanical analysis were performed on multiple specimens of constituent materials. We measured the hydrogen leak rate in GFRP pipeline lined with pipeline-grade high-density polyethylene (PE-3408). The thickness of the liner was 0.526 cm and its inside diameter was 10.1 cm. The hydrogen pressurization during the leak rate measurements was 10.3 MPa (1500 psia) — the maximum recommended pressure — and all measurements were done at ambient temperatures in an air-conditioned laboratory. The pipeline was closed on each end using a steel cap with elastomer (O-ring) seals. The leak rate was calculated from the temperature-compensated pressure decay curve. Changes in pipeline volume that occurred due to pressure-induced dimensional changes in the pipeline length and circumference were measured using strain gauge sensors. These volumetric changes occurred at the earliest measurement times and diminished to near zero at the long measurement times during which the steady-state leak rate was determined. Leak rate measurements in three different lengths of pipeline yielded a leak rate was significantly lower than the predicted rate from the standard analytical model for a cylindrical vessel.

The performance of filament-wound FRP composite is dependent on the properties of constituent materials (i.e. fiber, matrix and fiber-matrix interface) as well as on the manufacturing and design parameters (e.g. fiber lay-up, laminate stacking sequence, mandrel diameter, winding tension, winding time, fiber wet-out, etc.). In the first part of this work, we present a sensitivity analysis approach to ascertain the degree of influence of various mechanical and material design parameters on the structural failure of the composite laminated pipes. In the second part, sensitivity analysis results were used to design pipes with improved mechanical strength.

Hypervelocity impacts onto the outer structure of spacecraft induce shock waves, which in case of multimaterial structures interact with the material interfaces. This interaction is expected to produce different deformation patterns for laminates compared to the patterns appearing for materials with homogeneous density. In order to exhibit these different features and to show that the Smoothed Particle Hydrodynamics computational method is capable of describing them, a numerical hypervelocity impact experiment is performed for three plates. The first one is a laminate, with discontinuous density and material parameters, the second is a simple homogenized version of the laminate and the last is a monolithic metal plate.

The combination of fibre volume fraction, fibre orientation and lay-up sequence in composite materials makes it possible to design a multitude of composite pressure vessels and pipes. Analytical models, based on the classical laminate theory and numerical predictive techniques offer a means to optimize the lay-up sequence in order to maximize the strength to weight / cost ratio. This study looks at the validity of using analytical models prescribed in the design by analysis filament wound composite standards and compares the results with realistic test and numerical models. The results show that the classical laminate theory accurately establishes the design load in symmetric and balanced lay-up laminates when appropriate material properties are assigned. However in the case of asymmetric or unbalanced lay-up sequences, the bending and twisting stiffness geometrically strengthens the pipes such that the classical hoop and axial loading conditions based on isotropic material properties, no longer apply. In such instances the analytical solutions can underestimate the design load by more than 33%. An analytical solution that accurately establishes the loading configuration and magnitude is required. On the other hand numerical models gave good agreement with the experimental test results immaterial of the lay-up sequences, when appropriate end coupling, pressure loading and material properties are applied.

Filament wound composite pipes are being used in more and more applications. However, the impact behavior of these pipes is of particular importance in many applications. The sudden failure of these pipes under low velocity impact loads can be dangerous especially when the medium inside the pipe is hazardous or toxic in nature. The impact response of a composite laminate depends upon various factors such as thickness, stacking sequence and number of layers. The primary focus of this paper is parametric study of low velocity impact damage of CFRP and GFRP pipes under varying design parameters using finite element analysis. The simulation results are then used along with the ANN (Artificial Neural Networks) to fit a function to estimate the amount of absorbed energy.

Tensile process of carbon fiber composite laminate was monitored by acoustic emission technique. And the acoustic emission signals by tensile specimens of different winding angles were analyzed. The results show that carbon fiber released signals of different characteristics in different stages. So, the acoustic emission technique can effectively distinguish the different stages such as delaminating, detaching and fracture. Also, different angles in specimen’s layers of carbon fiber had different mechanical properties and failure mechanisms. Analysis on experimental data showed that acoustic emission testing technique can determine the process of different internal activities in carbon fiber composite laminate. Therefore, it can be used in the integrity evaluation for carbon fiber composite materials.

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.

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.

For automotive applications high pressure storage of compressed hydrogen (CH2) becomes more and more important especially regarding the future sustainable mobility based on renewable energy. The filament winding technology is highly industrialized today to meet the requirements for a high-quantity production of lightweight fiber reinforced pressure vessels used for hydrogen-powered cars using fuel cells or combustion engines. However, the main disadvantage of the conventional wet winding process is the low lay-down rate. A decrease of the cycle time to increase the production rate can be realized by the simultaneous feed of a large number of rovings circumferentially arranged around the mandrel. A team of engineers at the Institut fuer Verbundwerkstoffe (Institute for Composite Materials) now further developed the ring winding technology to manufacture pressure tanks with a diameter up to 500 mm (20 inch) with fully wrapped dome sections. This large ring winding head with 12 radial movable arms and multiple payout eyes allows an accordingly higher material output and reduces the cycle time significantly. The profitability analysis considering ring winding head configurations with different number of feed-eyes show the optimization potential regarding the reduction of the production costs of FRP pressure cylinders. A critical review regarding reachable process efficiency is also given in this paper. A modified “tube siphon impregnation unit” is the most important component of the ring winding head due to its compact and modular design. This clean impregnation of 48 carbon fiber rovings near the winder minimizes possible resin leakages. In comparison to a conventional resin bath the amount of hazardous waste, for example contaminated acetone, can be reduced. FRP laminates (fiber reinforced plastic) with a reduced number of crossing points and less ondulation of fiber bundles result higher load bearing capacity and increased mechanical properties. Regarding the degree of interweaving the multi feed-eye configuration of a ring winding head makes it more challenging to define an optimized winding pattern with the given winding angle. The split disk test method was used for comparative investigations regarding the influence of undulations on the material properties of filament wound laminates.

The world’s first filament-wound ASME Section X [1] Class II FRP(fiber reinforced plastic) vessels were built by Tankinetics Inc. in 2010. These vessels had semi-elliptical top and bottom, and were supported on skirts as shown in Fig.1. This paper is focused on the novelty of these vessels from design and fabrication standpoints. The design pressure is 50.76 psig. Ashland Derakane™ 470 resin is selected for the corrosion liner, and Derakane™ 510 N resin is used in the structural layer. The design is based on ASME Section X code [1] method A. For wind and seismic analysis, IBC 2006[3] and NBCC 2005[4] codes are followed. The domed top and bottom were made by hand lay-up method while the cylindrical shell section and skirt were made by filament winding technology. Filament winding is chosen for these pioneer vessels because it can produce stiffer, higher-strength laminates with much less fabrication time as compared to traditional hand lay-up process.

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.

Filament winding is a well-established process for the production of high-end fully wrapped composite pressure vessels. This type of tanks can be designed for service pressures that exceed 700 bar and are ideal for storage of gas fuels like compressed hydrogen in automotive and lightweight applications. As the demand for composite pressure vessels increases, lower costs and better product quality become very important. Impregnation is one of the most important steps in the wet winding process. During this step the dry continuous fibers are combined with the liquid matrix in order to create a fully impregnated semi-finished product. The properties of the impregnated roving have a major effect on the laminate quality and the efficient processing of the liquid matrix has a big influence on the manufacturing costs. The present work is related to the development of a new impregnation method for the processing of carbon fiber rovings. The developed impregnation unit (siphon impregnation system) consists of a sinusoidal cavity without any moving parts. This combined with an automated resin mixing-dosing system this allows complete wet-out of the fibers, precise calibration of the resin fraction, and stable processing conditions. The paper focuses on the modeling of the impregnation process inside the siphon unit. Mathematical expressions for the fiber compaction, the gradual increase of the roving tension, the static pressure, the capillarity of the roving, and the fiber permeation are presented, discussed, and experimentally verified. These expressions were implemented in an algorithm which can model the impregnation process by taking input parameters into account like winding speed, resin dosing, viscosity, and roving tex. The model was solved and the processing parameters of winding tension, fiber volume fraction, and impregnation degree have been simulated. An experimental set-up based on a filament winding machine was used for the validation of the model. Trials with different processing parameters and long run tests have been performed. The results proved that the model can accurately simulate the impregnation process. The good impregnation degree of the wound samples confirmed the efficiency of the siphon impregnation unit.

Polymer composites are an excellent alternative to replace more traditional materials in the fabrication of pressure cylinders for common applications. They minimize the weight and improve the mechanical, impact and corrosion behavior, which are relevant characteristics for almost all current and future large scale pressure cylinder applications, such as liquid filters and accumulators, hydrogen cell storage vessels, oxygen bottles, etc. A new generation of composite pressure vessels has been studied in this work. The vessels consist on a thermoplastic liner wrapped with a filament winding glass fiber reinforced polymer matrix structure. A conventional 6-axis CNC controlled filament winding equipment was used to manufacture the thermosetting matrix composite vessels and adapted for production of thermoplastic matrix based composite vessels. The Abaqus 6.4.2 FEM package was used to predict the mechanical behavior of pressure vessels with capacity of approximately of 0.068 m3 (68 liters) for a 0.6 MPa (6 bar) pressure service condition according to the requirements of the EN 13923 standard, namely, the minimum internal burst pressure. The Tsai-Wu and von-Mises criteria were used to predict composite laminate and thermoplastic liner failures, respectively, considering the elasto-plastic behavior of the HDPE liner and the lamina properties deducted from the micromechanical models for composite laminates. Finally, the results obtained from the simulations were compared with those obtained from the experimental pressure tests made on the thermoplastic liners and final composite vessels.

A multi-scale fatigue life prediction methodology of composite pressure vessels subjected to multi-axial loading has been proposed in this paper. The multi-scale approach starts from the constituents, fiber, matrix and interface, leading to predict behavior of ply, laminates and eventually the composite structures. The life prediction methodology is composed of two steps: macro stress analysis and micro mechanics of failure based on fatigue analysis. In the macro stress analysis, multiaxial fatigue loading acting at laminate is determined from finite element analysis (FEM) of composite pressure vessel, and ply stresses are computed using a classical laminate theory (CLT). The micro-scale stresses are calculated in each constituent (i.e. matrix, interface, and fiber) from ply stresses using a micromechanical model. Micromechanics of failure (MMF) was originally developed to predict the strength of composites and now extended to prediction of fatigue life. Two methods are employed in predicting fatigue life of each constituent, i.e. an equivalent stress method for multi-axially loaded matrix, and a critical plane method for the interface. A modified Goodman diagram is used to take into account the generic mean stresses. Damages from each loading cycle are accumulated using Miner’s rule. Each fiber is assumed to follow a probabilistic failure depending on the length. Using the overall micro and macro models established in this study, Monte Carlo simulation has been performed to predict the overall fatigue life of a composite pressure vessel considering statistical distribution of material properties of each constituent and manufacturing winding helical angle.

In composite structural design, a fundamental requirement is to furnish the designer with a set of elastic constants. For example, to design for a given temperature a laminate consisting of transversely isotropic fiber-reinforced laminae, we need five independent elastic constants of each lamina of interest, namely, E 1 , E 2 , ν 12 , G 12 , and ν 23 . At present, there exist seven tests, two of mechanical-lamina, two of thermal-expansion-lamina, and three of thermal-expansion-laminate types, to accomplish this task. It is known in the literature that the mechanical tests are capable of measuring E 1 , E 2 , and ν 12 , whereas the two thermal-expansion-lamina tests will measure α 1 and α 2 , and the three thermal-expansion-laminate tests yield an over-determined system of three simultaneous equations of the remaining two unknown elastic constants, G 12 and ν 23 . In this paper, we propose a new approach to determining those five elastic constants with uncertainty bounds using the extra information obtainable from an over-determined system. The approach takes advantage of the classical theory of error propagation for which variance formulas were derived to estimate standard deviations of some of our five elastic constants. To illustrate this approach, we apply it to a set of experimental data on PEEK/IM7 unidirectional lamina. The experiment consists of the following tests: Two tensile tests with four samples of unidirectional specimens to measure E 1 , E 2 and ν 12 ; two thermal-expansion-lamina tests for coefficients (α 1 and α 2 ) each using four [(0) 32 ]T unidirectional specimens; and three thermal-expansion-laminate tests on four samples of [(+30/−30) 8 ] s laminates. The results of our new approach are compared with those of a similar but more ad hoc approach that has appeared in the literature. The potential of applying this new methodology to the creation of a composite material elastic property database with uncertainty estimation and to the reliability analysis of composite structure is discussed.

For brevity, the class of “composite materials” in this paper is intended to refer to one of its subclasses, namely, the fiber-reinforced composite materials. In developing composite material property databases, three categories of data are needed. Category 1 consists of all raw test data with detailed information on specimen preparation, test machine description, specimen size and number per test, test loading history including temperature and humidity, etc., test configuration such as strain gage type and location, grip description, etc. Category 2 is the design allowable derived from information contained in Category 1 without making further experimental tests. Category 3 is the same design allowable for applications such that new experiments prescribed by user to obtain more reliable properties for the purpose on hand. At present, most handbook-based composite material property databases contain incomplete information in Category 1 (raw data), where a user is given only the test average values of properties such as longitudinal, transverse, and shear moduli, major and out-of-plane Poisson’s ratios, longitudinal tensile and compressive, transverse tensile and compressive, and shear strengths, inter-laminar shear strength, ply thickness, hygrothermal expansion coefficients, specific gravity, fiber volume fraction, etc. The presentation in Category 1 ignores the inclusion of the entire test environment description necessary for a user to assess the uncertainty of the raw data. Furthermore, the design allowable listed in Category 2 is deterministically obtained from Category 1 and the user is given average design allowable without uncertainty estimation. In this paper, it is presented a case study where average design allowable failure envelopes of open hole specimens were obtained numerically for two different quasi-isotropic carbon fiber-epoxy laminates using the appropriate Category 1 data. Using the method of statistical design of experiments, it is then showed how the average design allowable can be supplemented with uncertainty estimates if the Category 1 database is complete. Application of this methodology to predicting reliability of composite structures is discussed.

Mandrels used in conventional filament winding processes for the production of (GFRP) fiberglass pipe are generally not actively heated. Mandrels, after being overwrapped by continuous bands of filaments impregnated with uncured resin, are then passively and indirectly heated as the resin/fiber matrix covering them is cured. Curing occurs by placing the mandrel and uncured laminate assembly in a convection oven or by radiating the mandrel/uncured laminate assembly with infrared heat energy for a period of time at elevated temperature to affect a cure of the composite laminate. Typically mandrels are rotated during cure to assure homogenous resin consistency within the matrix. When processed in this fashion, mandrels are typically the least heated part of the assembly; the heat energy being applied only to the outside surface of the uncured resin/fiberglass matrix. The energy thus applied must then be conducted first through the wall of the composite laminate. The laminate tends to be thermally insulative as it cures. Therefore the cure of the resin matrix occurs without any significant thermal input from the mandrel. Significant time and energy are required to bring the temperature of the mandrel and the inner surface of the laminate to a temperature which assures an optimum cure. A new application of a mature aerospace derived heat transfer technology now provides uniform, controllable and discrete energy to the mandrel. Mandrels incorporating this technology exhibit near isothermal temperatures, random point to point, on the mandrel surface. These temperatures can be set and controlled from below ambient to 220°C. Heatpipe technology provides these mandrels with essentially super thermal conductive characteristics due to the latent heat phase change heat transfer methodology used within them. Mandrels incorporating heatpipe technology absorb energy based on any localized energy input and transfer that absorbed energy throughout the mandrel in an isothermal manner. This super thermally conductive property provides additional uniform heat to the mandrel surface covered by the uncured resin matrix. When the necessary thermal energy input is provided, the mandrel now transfers that energy as heat uniformly throughout the mandrel surface. The mandrel, now being actively heated, lends that thermal energy to the cure sequence by heating the uncured resin/fiberglass matrix in contact with the mandrel’s surface. This extra energy provided to I.D. surface of the laminate results in a shorter duration cure due to an increase in the surface area actively being heated. Heatpipe thermally enhanced (HPTE); mandrels not only have characteristics described above but also permit the use of increased thermal energy throughputs which provide thermal energy transfer rates, unachievable with existing processes. This increased heat transfer rate can result in a further reduction of the cure cycle. When coupled with an induction power supply and induction coil, these HPTE mandrels can be heated directly while rotating. The induction power absorbed by these HPTE mandrels is of a magnitude that permits resin matrices to be cured entirely from the mandrel side or “inside out” without the need for a convection or infrared oven.