Two-phase cryogenic flow meters: Part II – How to realize the two-phase pressure drop method

The pressure drop method to find the mass flow rate of the two-phase helium and hydrogen flows is discussed in this paper. This method is based on a combination of the narrowing device and the RF void fraction sensor described earlier. Advantages of this approach with respect to the calorimetric one are demonstrated and its metrological characteristics for different flow patterns are estimated. The discussed cryogenic technologies and methods may be used for others applications, for example, to solve some tasks in oil-producing industry.     

Deep cryogenic treatment of AISI 302 stainless steel: Part I – Hardness and tensile properties

The effects of deep cryogenic treatment (DCT) on the static mechanical properties of the AISI 302 austenitic stainless steel were investigated through experimental testing. The results of the tensile and hardness tests are discussed and compared to data and microstructural observations from the DCT literature concerning the same class of steel. In addition, the influence of two important treatment parameters, such as the soaking-time and the minimum temperature, is analysed through a full factorial design of experiments (DOE) and by means of a first approximation model in order to obtain confirmation and suggestions about the possible use of the DCT as a standard practice to improve the mechanical properties of stainless steels. A particular focus is given to the registered changes of the elastic modulus and of the hardness as representative measures of two different deformation mechanisms.     

The shear ramp: A new test method for the investigation of coated fabric shear behaviour – Part I: Theory

A new test method for the investigation of architectural coated fabric shear properties is proposed. The method relies on the biaxial pre-tensioning of the orthotropic specimen, where fibres are aligned with the loading directions. The shear deformation is enabled by means of linear stress ramps. In the first part of the paper, the theory behind the new test method is given. The shear stress distribution in a square plate loaded with a shear ramp is analytically calculated by means of Airy stress functions and by applying the Rayleigh–Ritz method. The difference between isotropic and orthotropic materials is investigated and compared to FEM results. Finally, a simple estimation of the shear stress in the sample is proposed.     

Deep cryogenic treatment of AISI 302 stainless steel: Part II – Fatigue and corrosion

During the last decade, the interest about deep cryogenic treatment (DCT) is grown beyond its successful application on tool steels. The use of such cold treatment has shown positive effects on carburized steel fatigue life and some promising results were also noticed on stainless steels and on other materials. In this article, the DCT effects on fatigue and corrosion resistance of the AISI 302 austenitic stainless steel are analysed starting from the results of an extensive experimental campaign that was performed on both hardened and solubilized material conditions. The analysis includes an evaluation of the influence that the most important treatment parameters have on the final result. Considering their statistical significance at different reliability levels, the results show that the DCT can improve the fatigue behaviour of the solubilized AISI 302, while no important changes are noticed on the hardened material. Moreover, no difference was detected on the corrosion resistance of the cryotreated material, ensuring that such key-property for this class of steel is not compromised by the cryogenic treatment.     

Modeling the inelastic deformation and fracture of polymer composites – Part I: Plasticity model

A new transversely-isotropic elastic–plastic constitutive model for unidirectional fiber reinforced polymers (FRP) is presented. The model is able to represent the fully nonlinear mechanical behavior under multi-axial loading conditions and under triaxial stress states prior to the onset of cracking. Since associated flow rules often give a wrong prediction of plastic Poisson coefficients, a non-associated flow rule is introduced to provide realistic predictions of the volumetric plastic strains. This paper focusses on the simulation of triaxiality dependent plasticity based nonlinearities of FRP until failure occurs. The onset and propagation of failure is predicted by a new smeared crack model presented in an accompanying paper (Camanho et al., 2012). In order to demonstrate the capabilities of the new material model, a yield surface parameter identification for IM7-8552 carbon epoxy is presented and simulations of quasi-static transverse and off-axis compression tests and of uniaxial compression tests superimposed with various values of hydrostatic pressure are shown as a model verification.     

Physico-chemistry and cytotoxicity of ceramics: Part I – Characterization of ceramic powders

The morphology of Al2O3, ZrO2/Y2O3, AIN, B4C, BN, SiC, Si3N4, TiB2, TiC, TiN ceramic, graphite and diamond powders has been studied by scanning electron microscopy (SEM) and the specific area of each powder was determined with the BET method. X-ray diffraction (XRD) investigations have been carried out in order to evaluate the crystallinity and determine the constitutive phases. The chemical composition was assessed by classical chemical analyses and by X-ray microprobe; some powders were studied by the laser micro-Raman technique. Correlations have been established between all these results.     

On the resistance to penetration of stiffened plates,Part I – Experiments

The paper deals with hull damage in ships which are subjected to grounding actions. A ship is assumed to settle vertically on a rock. It is further assumed that contact actions are local and restricted to one plate section. The scenario is analyzed by conducting a series of panel indentation experiments. Various configurations of stiffened panels are loaded laterally by a cone shaped indenter until fracture occurs. The specimen dimensions represent a 1:3 scale of the dimensions found in medium sized tankers. Naturally, because damaged hull and cargo tanks may have severe environmental consequences, e.g. as exemplified by high profiled grounding accidents such as the Exxon Valdez grounding which lead to the discharge of nearly 240,000 barrels of oil, focus is on the plastic deformation and fracture resistance of the panel.     

Characterization of high-velocity impact damage in CFRP laminates: Part I – Experiment

This study investigated mechanisms of the extension of high-velocity impact damage in CFRP laminates. To this end, damage states due to near-perforation impact were studied in detail. This study consists of two parts. Part I presents the experiment results of high-velocity impact tests for CFRPs with specified stacking sequences. A crater and splits were observed on the impacted surface, while multiple splits with fiber breaks extended on the back surface. The cross-section beneath the impact point included catastrophic ply failure with extensive fiber breaks. Impacted specimens also exhibited a particular delamination pattern consisting of pairs of symmetric fan-shaped delaminations emanating from to the impact point and elongated delamination along the cracks in the bottom ply. These damage patterns were common to all of the stacking sequences. Part II of this study presents a numerical analysis of high-velocity impact based on smoothed-particle hydrodynamics and discusses damage extension mechanisms.     

Cyclic deformation behavior of austenitic Cr–Ni-steels in the VHCF regime: Part I – Experimental study

A stable (AISI 316L) and a metastable (AISI 304L) austenitic stainless steel were investigated with respect to their VHCF behavior. The focus of the paper lies on the investigation of the cyclic deformation behavior of the two materials at very low stress amplitudes. The 304L steel is characterized by a pronounced cyclic softening during its initial stage of cyclic deformation. In the course of the following loading cycles, a phase transformation (γ-austenite → α′-martensite), accompanied by volume expansion is associated with the reduction of the global plastic strain amplitude and induces compressive stresses in the near surface layer. As a consequence, the material shows no failure up to 10⁹ cycles at 240 MPa. In contrast, the type 316L steel has a higher stacking fault energy and the microstructure remains fully austenitic during cyclic deformation when analyzed by means of magneto-inductive methods. In this case, very localized plastic shear occurs and the slip band topography reveals the formation of pronounced intrusions. Microcracks initiate from these intrusions in the VHCF regime and samples failed also beyond 10⁷ cycles. This study presents a comparative investigation of the damage evolution – including dislocation morphology and phase transformations – during cyclic loading for both materials. The combined effect of the individual deformation mechanisms is investigated for both materials in the context of a microstructure-sensitive simulation discussed in Part II of this study.     

Postbuckling behaviour of a pressurized stiffened composite panel – Part I: Experimental study

Results of an experimental study of the buckling and postbuckling behaviour until the collapse of a cylindrical stiffened composite panel are presented. The specimen is subjected to a uniform pressure on one of its faces using a combination of gas and liquid inside a hermetic box. The present analysis shows the postbuckling load carrying capacity of elements of this kind without developing failure mechanism. Due to the high sensitivity to geometric imperfections of these structures, a simple procedure to obtain their measurements once the specimen is placed in the experimental device is set out. The data registered in these tests will be used for the subsequent validation of the numerical model in order to develop more accurate solutions. This will produce a significant increment in the fidelity of those predictions, making possible a reduction in the number of tests to be performed in real applications.     

The shear ramp: A new test method for the investigation of coated fabric shear behaviour – Part II: Experimental validation

The shear ramp is a new test method for the investigation of coated fabric shear behaviour. The implementation of the method with a biaxial test rig is given and compared to the off-axis biaxial extension of a specimen with 45° oriented fibres. Based on experimental observations and finite element analyses, it is shown that both test methods give similar results for a wide range of coated fabrics if the proper stress correction factors are used. An estimation of these factors is given for both test methods for PVC–polyester as well as PTFE–glass fabrics.     

Analysis of intermetallic swelling on the behavior of a hybrid solution for compressed hydrogen storage – Part I: Analytical modeling

This study focuses on the mechanical response of a hybrid solution dedicated to gaseous hydrogen storage. This solution is made of a carbon/epoxy composite overwrapped on a metal liner first coated with intermetallic material. The composite helps to reinforce the structure, while the liner prevents it from any leakage. In case of deficiency, the intermetallic material behaves as a sponge and interrupts the leakage by absorption and micro-cracks reduction. This hybrid solution or this specific use of intermetallic material has never been presented before. The laminate composite is anisotropic, whereas the liner is an elastic–plastic material. The intermetallic is purely thermo elastic and its study is limited to its mechanical contribution. Using these hypotheses, the suggested analytical model provides an exact solution for stresses and strains on the cylindrical section of the hybrid solution submitted to thermomechanical static loading and hydrogen leakage. The swelling effect of the intermetallic on the behavior of the structure is then investigated.     

A new method for DEM simulation of dust-bearing granular flow – Modeling the effect of dust on the change in granule friction coefficient

The simulation of dust-bearing granular accumulation flow in the theoretical and practical aspects of the engineering field poses a significant challenge due to the massive computational requirements associated with cross-scale simulations. In this study, a novel approach is proposed to address this issue by developing a model that accounts for the impact of dust on granular flow through changes in the granule friction coefficient. Initially, the theoretical analysis was conducted to examine the effects of dust on granular flow. Subsequently, a method was developed to measure the equivalent friction coefficient of granules by combining theoretical analysis and experimental work. The proposed method was then employed to simulate the stability of a spherical granule pile in a drum influenced by dust content and compared against experimental results. The simulation results demonstrate agreement with the experimental results, indicating the feasibility of modeling the effect of dust on dust-bearing granular flow through the granule equivalent friction coefficient. The dust effect can be considered equivalent to a change in the granule friction coefficient, which facilitates the reduction of the computational load generated by the Discrete Element Method (DEM) method and enables cross-scale simulations.     

Thermal flow permeametry – A rapid method for finding local changes in flow channels

Solid bodies with flow channels can have very heterogeneous structure, whose local variations are difficult to analyze. Yet, this can play an important role affecting characteristics, such as, fluid flow property, strength and heat conductivity. This article presents a method named thermal flow permeametry (TFP) that is applicable for a quick analysis of variations in flow channels, even in meter-sized structures. For illustrating the method, we analyzed the local permeability levels of a large and extremely complex fiber structure. In TFP, hot air is ejected through a structure, while thermal camera measures local surface temperature variations during heating. Gray values of the thermal image are then plotted versus the structures local thickness, density and permeability. We showed that gray values link with local permeability, affected by thickness, density and flow channel tortuousness. We also found out that TFP is very sensitive to local changes in flow channels.     

On the mechanism of squat formation on train rails – Part II: Growth

Longitudinal cross-sectioning of squats reveals characteristic features of internal crack front propagation. Leading crack planes propagate over longer lengths and greater depths as compared to more superficial trailing crack planes. A favourite depth of crack propagation occurs in the subsurface (2–3 mm), is related to the residual longitudinal stress profile, and may lead to an internal crack ‘terrace’. Especially during deeper crack propagation and branching oxidation processes are found to be metallurgical drivers of crack growth. Contact surface modification during squat growth can be distinguished between phases of transient local stress redistribution and of dynamic wheel–rail contact. If the hypothesized shearing wedge in the failure mechanism loses its load bearing capacity, this gives rise to a redistribution of normal stresses within the actual contact ellipse and the formation of a hardness envelope along the crack pattern. This may partially explain why maturing squats show decoloured and hardened surface areas bordering the surface-breaking cracks. A second effect occurs for contact patches not matching the failure ‘envelope’: due to the Poisson effect the surface overlying the crack planes settles slightly, experiences reduced contact, and corrosive products, ‘pumped’ from inside the cracks, may accumulate on the surface (as confirmed by SEM-EDX analysis). During progressive growth of the defect the harder and decoloured envelope as well as the original wedge is pressed into the deeper elastic material, accompanied by a gradual expansion of the contact band and a bilateral bridging of the defect. This may cause high-frequency impact, resulting into progressive internal crack growth affecting the global stress response and rail fracture.     

Morphologies and growth mechanisms of aluminum nitride whiskers by SHS method—Part I

AlN whiskers grown by combustion of Al powder under high nitrogen pressure were investigated. Several types of whiskers' structures, such as wavy structure, crossed structure, stack structure, bead-necklace structure, branch structure, dendritic crystal, were found due to the variation of growth conditions. The causes of some structures were explained.     

Investigations of pulsed heat loads on a forced flow supercritical helium loop – Part A: Experimental set up

Cryogenic systems for future large superconducting tokamaks are expected to handle high pulsed heat loads due to cycling plasma operation. The superconducting magnets are cooled down with forced flow supercritical helium at 4.4 K and 5 bar. Cryogenic helium distributions can participate to the smoothing of pulsed loads and hence providing a stable interface with the refrigerator. An experimental set up named HELIOS has been designed and realized in CEA Grenoble to study pulsed load effects on a forced flow supercritical helium loop. The characteristics of the main components and the instrumentation with its calibration during reception tests are described in Part A. A first series of experiments was performed with pulsed loads in an isochoric configuration: large pressure and temperature changes in the circulating loop are observed, analyzed and compared as well to a thermohydraulic modeling described in Part B.