Performance of all-Polypropylene composites at LNG temperatures

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. © Copyright 2017 ASME. Pressure Vessels and Piping Divisio

Cryogenic crashworthiness of LNG fuel storage tanks

Shipping is gradually embracing natural gas as bunker fuel. The most viable way to store natural gas on board is in its liquid form. Gas needs to be cooled to cryogenic temperatures and in practice moderately pressurized. On board ships, solely double walled pressure tanks are used for this purpose. Loss of containment due to a collision, is one of the hazards to be addressed, because of both the flammable nature of natural gas and the low temperatures which will cause brittle fracture of the ship’s structure when spilled. This paper reports how the crash energy absorbing capacity of cryogenic tanks has been investigated, computationally and experimentally. Results show that the tanks can absorb a significant amount of energy without bursting. This information is considered in the frame of a larger picture and the required distances by the guidelines between the ship hull and tank on the deck is open to discussions. © 2015 Taylor & Francis Group, London

Wrinkling, fracture, and necking: The various failure modes in maritime crash

Depending on the state of stress, material can fait in a number of different modes during a collision. Three modes are identified here as material separation in the absence of necking, material separation after the onset of necking, and localized buckling/wrinkling. Through a series of case studies, the states of stress present in a collision are analyzed. Of particular interest is leakage in a scaled fuel tank that could not have been predicted by FEA due to resolution and may have been ignored even with sufficient resolution because it was in a region of generally compressive stresses. Following the review of case studies, the aforementioned failure mechanisms are reviewed, and the corresponding states of stress are summarized. It is shown that the current state of technology for failure after the onset of necking is insufficient but quickly improving. Concepts are taken from the sheet metal industry to understand the onset of buckling/wrinkling, but there is little readily available to simulate failure after the initial onset

Characterising microstructural organisation in unidirectional composites

Understanding the three-dimensional variability of unidirectional composites is relevant to the material performance and the development of advanced material modelling strategies. This work proposes a new methodology for the characterization of unidirectional composites, showcased on carbon fibre/poly(ether-ether-ketone) tapes. Three microstructural descriptors were here introduced, each representing an increasing level of complexity in the fibre architecture: from a tortuosity-based single fibre trajectory analysis to fibre groups’ behaviour, to fibre network interconnectivity. The methodology was developed and validated on real material datasets acquired via X-ray computed tomography. A facile method for image analysis was used to reconstruct the three-dimensional fibrous architecture at a single fibre path resolution. The approach bridges a gap in the traditional approach and nomenclature typical of the composite field to describe and quantify complex fibre organization in unidirectional composites, highlighting micro- and mesoscopic features, such as edge-core effects in the fibre arrangement, possibly occurring in tow spreading. The study of the parameter interdependence showed relationships, which will provide further insight for future research in the study of microstructure formation of unidirectional composites, its evolution during processing or loading, and input for advanced modelling techniques based on Representative Volume Elements.Aerospace Manufacturing TechnologiesAerospace Structures & Computational Mechanic

The role of matrix boundary in the microstructure of unidirectional composites

Finding new ways to evaluate the variability of microstructures, and its effect on macroscopic properties such as permeability and mechanical performance [1,2] is of increasing interest in the composite field. The variability of microstructural features at a three-dimensional level is not fully understood and its effect on macroscale properties is not well established, and mostly analyzed at a phenomenological level [3]. We introduced in recent work a method based on X-ray Computed Tomography for the threedimensional reconstruction of the fibrous microstructure of unidirectional tapes at a single fibre resolution [4]. A schematic of the workflow is represented in Figure 1. Three descriptors are introduced in the work to describe increasing level of complexity in the microstructural organization, from a single fiber path level with differential tortuosity, to group behavior with collective motion, to fibre network connectivity with length of contact. These descriptors and their interdependence highlight local effects like edge-core segregation in microstructural characteristics. However, in order to achieve a more complete definition of the unidirectional tape domain, understanding of matrix-based features and its interrelation with fiber architecture descriptors is needed. In this work, we expand the methodology of Gomarasca et al. [4], to account for matrix-based phenomena such as tape boundary variability, and void formation and morphology. This will be showcased on a unidirectional composite tape including both fiber-based and matrix-based analysis. These methods enable advanced characterization and modelling of microstructural formation and evolution during composite manufacturing

Methodology for the identification of hydrogen gas permeation path in damaged laminates

The main bottleneck of using composites for cryogenic storage of clean hydrogen fuel is the permeation of gas molecules. In this work, the permeation of hydrogen gas through thermally cycled thermoplastic composite laminates with two different stacking sequence is investigated. The experimental study is based on a methodology of cryogenically cycling the composite specimen and measuring the permeability in a dedicated hydrogen permeation setup. An optical microscope and X-ray computed tomography scanner are employed to investigate the existence of cracks. The results reveal that thermal cycling does not have a profound influence on permeability, while the stacking sequence has a considerable effect. Laminates with dispersed 0° layers resulted in lower permeation values compared to the laminate with grouped 0° layers at the laminate’s core. The imaging techniques did not reveal any observable crack which supports the hypothesis that permeation is mostly driven by bulk diffusion in the polymer.Aerospace Manufacturing Technologie

The role of matrix boundary in the microstructure of unidirectional composites

Finding new ways to evaluate the variability of microstructures, and its effect on macroscopic properties such as permeability and mechanical performance [1,2] is of increasing interest in the composite field. The variability of microstructural features at a three-dimensional level is not fully understood and its effect on macroscale properties is not well established, and mostly analyzed at a phenomenological level [3]. We introduced in recent work a method based on X-ray Computed Tomography for the threedimensional reconstruction of the fibrous microstructure of unidirectional tapes at a single fibre resolution [4]. A schematic of the workflow is represented in Figure 1. Three descriptors are introduced in the work to describe increasing level of complexity in the microstructural organization, from a single fiber path level with differential tortuosity, to group behavior with collective motion, to fibre network connectivity with length of contact. These descriptors and their interdependence highlight local effects like edge-core segregation in microstructural characteristics. However, in order to achieve a more complete definition of the unidirectional tape domain, understanding of matrix-based features and its interrelation with fiber architecture descriptors is needed. In this work, we expand the methodology of Gomarasca et al. [4], to account for matrix-based phenomena such as tape boundary variability, and void formation and morphology. This will be showcased on a unidirectional composite tape including both fiber-based and matrix-based analysis. These methods enable advanced characterization and modelling of microstructural formation and evolution during composite manufacturing.Aerospace Manufacturing TechnologiesAerospace Structures & Computational Mechanic

Methodology for the identification of hydrogen gas permeation path in damaged laminates

The main bottleneck of using composites for cryogenic storage of clean hydrogen fuel is the permeation of gas molecules. In this work, the permeation of hydrogen gas through thermally cycled thermoplastic composite laminates with two different stacking sequence is investigated. The experimental study is based on a methodology of cryogenically cycling the composite specimen and measuring the permeability in a dedicated hydrogen permeation setup. An optical microscope and X-ray computed tomography scanner are employed to investigate the existence of cracks. The results reveal that thermal cycling does not have a profound influence on permeability, while the stacking sequence has a considerable effect. Laminates with dispersed 0° layers resulted in lower permeation values compared to the laminate with grouped 0° layers at the laminate’s core. The imaging techniques did not reveal any observable crack which supports the hypothesis that permeation is mostly driven by bulk diffusion in the polymer

Cryogenic fatigue and stress-strain behavior of a fibre metal laminate

Abstract\ud \ud This paper reports on the cryogenic fatigue life of Al 2024 / Stycast 2850 FT composite sandwiches loaded under cyclic strain, as well as on the strength of their constituent materials at 77 K. These Fibre Metal Laminate (FML) specimen serve as a model for an alternative class of cryogenic structural materials that might be used e.g. in downstream LNG applications. FMLs, such as the GLARE ™, are already used in the aeronautic industry, where they provide better damage tolerance, corrosion resistance and lower specific weight. Their cryogenic performance, however, is yet to be understood. Preliminary results show that the metal/filled- epoxy combination presented here withstands repeated cool-down to 77 K. Moreover, its cryogenic fatigue life is at least 20 times longer than at room temperature. These observations are consistent with the measured stress-strain behaviour of the metal and the epoxy, as well as with the shear strength of the bond between them. The Youngs modulus, yield strength and tensile strength of the Stycast 2850 FT roughly double when cooled down to 77 K. In addition to this, the bond strength with the GLARE-type coated Al increases significantly. These preliminary experiments indicate that cryogenic FML are technically feasible

Cryogenic fatigue and stress-strain behavior of a fibre metal laminate

\u3cp\u3eThis paper reports on the cryogenic fatigue life of Al 2024 / Stycast 2850 FT composite sandwiches loaded under cyclic strain, as well as on the strength of their constituent materials at 77 K. These Fibre Metal Laminate (FML) specimen serve as a model for an alternative class of cryogenic structural materials that might be used e.g. in downstream LNG applications. FMLs, such as the GLARE ™, are already used in the aeronautic industry, where they provide better damage tolerance, corrosion resistance and lower specific weight. Their cryogenic performance, however, is yet to be understood. Preliminary results show that the metal/filled- epoxy combination presented here withstands repeated cool-down to 77 K. Moreover, its cryogenic fatigue life is at least 20 times longer than at room temperature. These observations are consistent with the measured stress-strain behaviour of the metal and the epoxy, as well as with the shear strength of the bond between them. The Youngs modulus, yield strength and tensile strength of the Stycast 2850 FT roughly double when cooled down to 77 K. In addition to this, the bond strength with the GLARE-type coated Al increases significantly. These preliminary experiments indicate that cryogenic FML are technically feasible.\u3c/p\u3