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Strain-life testing of a 4130 pressure vessel steel was conducted in air and in a high-pressure gaseous-hydrogen environment. Hydrogen causes an order of magnitude decrease in lifetime compared to in-air performance at the same strain-amplitudes. This decrease in lifetime in hydrogen is accompanied by various effects, such as a shift in the cyclic stress-strain curve, different influences on the elastic and plastic components of the strain-life data, and a distinct difference in the evolution of the microstructural texture prior to failure. For comparison, preliminary data from testing of a higher strength pressure vessel steel is presented, showing a difference in elastic/plastic partitioning may be accompanied by a difference in reduction in lifetime due to hydrogen.

The deformation fields near fatigue crack tips grown in hydrogen and in air were measured using high-energy x-ray diffraction. A larger magnitude of elastic strain was observed in the hydrogen case compared to the air case. The magnitude of elastic strain was quantified through an effective crack tip stress intensity factor. The dislocation profile ahead of the crack was probed via x-ray line broadening and electron back-scatter diffraction was used to assess the crack path (intergranular vs. transgranular). Ahead of the crack tip grown in hydrogen, an order of magnitude lower dislocation density, compared to a baseline density far from the crack, was observed. This decrease in dislocation density was not observed in the air case. These differences are discussed in terms of two leading hydrogen embrittlement mechanisms, Hydrogen Enhanced Localized Plasticity (HELP) and Hydrogen Enhanced Decohesion (HEDE). We have observed a decrease in transgranular cohesion (transgranular HEDE), as well as an increase in intergranular fracture. The measurements of dislocation activity support a model of a decrease in intergranular cohesion (intergranular HEDE) which is likely facilitated by the HELP mechanism. This suggests that the increase in fatigue crack growth rate is due to a sum of the two effects of hydrogen, in which the crack grows faster in the transgranular fracture mode and faster due to an increase in a new mode of intergranular fracture.

The deleterious effect of hydrogen on steel is a long-standing problem. Embrittlement in the presence of hydrogen is, in part, a consequence of the fast diffusion of hydrogen in ferritic steels. Because of the identical chemical properties but large differences in mass between hydrogen isotopes, interaction of hydrogen isotopes with steel structures are of interest as a tool to study the role of diffusion in hydrogen embrittlement under all-else-equal conditions. In this paper, we present tensile and fatigue data for steel samples measured in air, in hydrogen, and in deuterium. Tensile measurements show deuterium causes a loss of ductility comparable to the loss due to hydrogen. In fatigue, a large pressure effect on deuterium-assisted fatigue crack growth was observed, an effect which is not exhibited in uniaxial tensile measurements. With sufficient pressure to show an enhanced fatigue crack growth effect, the fatigue crack growth rate is well-predicted assuming a scaling of the diffusion coefficient by 1 / 2 . These results suggest surface adsorption kinetics play a large role in hydrogen-assisted fatigue crack growth at low pressure. At higher pressures, hydrogen-assisted fatigue crack growth is primarily affected by the kinetics of diffusion of hydrogen within the steel lattice.

Hydrogen will be a crucial pillar in the clean-energy foundation, and therefore, the development of safe and cost-effective storage and transportation methods is essential to its success. One of the key challenges in the development of such storage and transportation methods is related to the interaction of hydrogen with structural materials. Despite extensive work, there are significant questions related to the hydrogen embrittlement of ferritic steels due to challenges associated with these steels, coupled with the difficulties with gauging the hydrogen content in all materials. Recent advancements in experimental tools and multi-scale modeling are starting to provide insight into the embrittlement process. This review focuses on a subset of the recent developments, with an emphasis on how new methods have improved our understanding of the structure-property-performance relationships of ferritic steels subjected to mechanical loading in a hydrogen environment. The structure of ferritic steels in the presence of hydrogen is described in terms of the sorption and dissociation processes, the diffusion through the lattice and grain boundaries, and the hydrogen-steel interactions. The properties of ferritic steels subjected to mechanical loading in hydrogen are also investigated; the effects of test conditions and hydrogen pressure on the tensile, fracture, and fatigue properties of base metal and welds are highlighted. The performance of steels in hydrogen is then explored via a comprehensive analysis of the various embrittlement mechanisms. Finally, recent insights from in situ and high-resolution experiments are presented and future studies are proposed to address challenges related to embrittlement in ferritic steels.

Structural steel mechanical properties of strength and ductility for a given microstructure are predominately driven by the average ferrite grain/packet size and by the through-thickness homogeneity of the ferrite grain/packet size in the final product. Fatigue performance, a ductility property, in air for applications of wind towers, bridges or high-rise buildings along within environments of high-pressure gaseous hydrogen for various pipeline systems is critical to the end-use design. Fracture and fatigue testing of a commercially produced low carbon 20 mm thick API X60 Sour Service steel had been completed which showed good and stable performance when compared to other commercially produced pipeline and structural steel microstructures. This commercially produced API steel was reported as “Alloy D” in prior published work. The microstructure was predominately polygonal ferrite with industrial quality of steel cleanliness, minimum of microstructural banding and a small but relatively homogenous through-thickness grain size required for a successful API X60 Sour Service specification/application. Based on the initial fatigue performance reported for the “Alloy D” through-thickness microstructure a more comprehensive study on the effect of the through-thickness grain size/homogeneity on fatigue was initiated. To isolate and study this effect of the, laboratory developed samples of a low carbon API X60 Sour Service steel with the same alloy design as “Alloy D”, which is characterized by a predominately single-phase polygonal ferrite microstructure with excellent cleanliness and no microstructural banding. Two sets of steels were made with the only difference being variations in average through-thickness and homogeneity of the final ferrite grain size.

Strain-life testing of a 4130 pressure vessel steel was conducted in hydrogen gas through the careful adaptation of an existing hydrogen-gas mechanical-testing apparatus. The strain-life mechanical results reveal that hydrogen has a significant effect on the strain-life, and impacts both the elastic and plastic responses of the material. Microscopy analysis shows a distinct difference in the microstructural development of the material after cyclic loading in air compared to after loading in hydrogen gas. These experimental results will inform coupled damage and deformation modeling.

Several welds and associated heat-affected zones (HAZs) on two API X70 and two API X52 pipes were tested to determine the fatigue crack growth rate (FCGR) in pressurized hydrogen gas and assess the area of the pipe that was most susceptible to fatigue when subjected to hydrogen gas. The relationship between FCGRs for welds and HAZs compared to base metal is discussed relative to local residual stresses, differences in the actual path of the crack, and hydrogen pressure effects.

This study presents an in-depth characterization of the microstructures, crystallographic orientations, and dislocation characteristics beneath hydrogen-induced quasi-cleavage fracture features of an as-quenched, lath martensitic (α') 22MnB5 steel. The fracture surfaces of gaseous hydrogen-embrittled martensitic specimens were analyzed by a combination of multiple analytical tools: scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and transmission Kikuchi diffraction (TKD). The dominant fracture mode in the hydrogen-affected zones was quasi-cleavage fracture, which involved significant plasticity, evidenced by plastic zones near tear ridges and a high density of dislocations beneath the quasi-cleavage facets. The martensite constituent sizes, variant orientations, and boundaries influenced the quasi-cleavage surface morphologies. Fractography revealed the occurrence of {100}α'-type cleavage across martensitic laths, developing relatively “flat” quasi-cleavage surfaces, in addition to {110}α'-type cracking likely along lath and block boundaries, and fracture along non-cleavage planes. The likelihood of the formation of the relatively “flat” quasi-cleavage surfaces increased with increasing martensitic constituent sizes. Substantial dislocation bands formed on intersecting {112}α' slip planes within a martensite block below the hydrogen-induced cleavage fractures on {100}α' planes. River markings on the quasi-cleavage surfaces were found to originate from the complex, hierarchical lath martensitic microstructure. Steps and ridges on the quasi-cleavage facets generally linked with the various martensitic boundaries, suggesting that they were produced as a result of crack deviations at those boundaries. The fracture paths and martensite quasi-cleavage mechanisms are discussed in the context of the role of hydrogen and Cottrell cleavage model.

This work aims to create finite element models to simulate the three ISO 11114-4 test methods applicable to hydrogen gas cylinders, coupled with calibrated constitutive models, to predict the deformation response of each. Experimental measurements are used to calibrate a monotonic constitutive model and a constitutive model of cyclic deformation. Six finite element solid models are discussed: monotonic tensile test of dog bone-shaped specimens, strain-controlled fatigue test of dog bone-shaped specimens, ISO test Method A, ISO test Method B, and ISO Method C (from ISO 11114-4), and a gas cylinder. Each finite element solid model is paired with the appropriate constitutive model based upon loading conditions. The modeling results are then combined with a new damage parameter in an attempt to compare each of the test methods to the others, as well as to in-service conditions. It is shown that the proposed damage parameter may be used to correlate all test methods considered (except for ISO Method A, a burst-disc test) as well as in-service conditions. The calibrated damage parameter may be coupled with any geometry, loading condition, and boundary condition modeled within a finite element package to predict the onset of critical damage in the material for which the coupled constitutive model is calibrated to. Parametric modelling study results provide estimated cycles to the onset of crack extension for DOT 3AA cylinders having varying sizes of internal thumbnail-shaped cracks. This work provides the baseline for measurements and models in air, with similar work in hydrogen to follow.

The economical and efficient transportation of hydrogen gas is necessary for it to become a widespread source of energy. One way to improve the economics is to lower the cost of building hydrogen gas pipelines. The recent modification to the ASME B31.12 Code for Hydrogen Piping and Pipelines begins to lower the cost of building pipelines for hydrogen service by allowing the use of high-strength steel that will provide the same margin of safety with thinner pipe walls. Less steel directly impacts the cost of materials and welding. A means of improving efficiency would be to increase the hydrogen gas pressure to augment the volume of products transmitted through the pipeline. The recent B31.12 code modification characterized dozens of fatigue crack growth test results conducted in hydrogen gas pressurized up to 21 MPa with an upper boundary of fatigue crack growth rate (FCGR), defined as a function where all measured FCGRs fall below this boundary. In this study, different pipe geometries, strengths, and pressures with established design protocols were evaluated to determine if the code would require further modifications should linepipes be designed for higher hydrogen gas pressures, up to 34 MPa. It was shown through a numerical exercise that the code could be minimally modified and safety margins would be adequate for those pressures for steels up to and including API-5 L Grade X70.

Surface-active trace compounds present in diesel fuels protect pumps and injectors against premature wear through boundary lubrication. Due to the vast number of hydrocarbon compounds found in petroleum distillate fuels, it is difficult to measure the concentration of trace lubricity-enhancing compounds in neat diesel fuel samples. We report herein the direct measurement of trace polycyclic aromatic hydrocarbons (PAH) in diesel fuels through 1H and 13C nuclear magnetic resonance spectroscopy and relate the presence of PAH with fuel lubricity measured with a high-frequency reciprocating rig. Carboxylic acids and nitrogen heterocyclic PAH were not detected in the diesel fuels tested. The data provide further evidence that surface-active PAH compounds improve the lubricity of diesel fuels.

A comprehensive testing program to determine the fatigue crack growth rate (FCGR) of pipeline steels in pressurized hydrogen gas was completed. Four steels were selected, two X52 and two X70 alloys. Other variables included hydrogen gas pressures of 5.5 MPa and 34 MPa, a load ratio, R, of 0.5, and cyclic loading frequencies of 1 Hz, 0.1 Hz, and 0.01 Hz. Of particular interest was whether the X70 materials would exhibit higher FCGRs than the X52 materials. The American Petroleum Institute steel designations are based on specified minimum yield strength (SMYS), and monotonic tensile tests have historically shown that loss of ductility correlates with an increase in yield strength when tested in a hydrogen environment. The X70 materials performed within the experimental spread of the X52 materials in FCGR, except for the vintage X52 material at low (5.5 MPa) pressure in hydrogen gas. This program was developed in order to provide a modification to the ASME B31.12 code that is based upon fatigue, the primary failure mechanism in pipelines. The code modification is a three-part Paris law fit of the upper bound of measurements of FCGR of pipeline steels in pressurized hydrogen gas. Fatigue crack growth data up to 21 MPa (3000 psi) are used for the upper bound. This paper describes, in detail, the testing that formed the basis for the code modification.

Hydrogen will likely play a key role in a future clean energy economy. However, fundamental understanding of the deleterious effects of hydrogen on the fatigue and fracture properties of pipeline steels is lacking. Furthermore, engineering tools for design and lifetime prediction of pipeline steels in gaseous hydrogen are yet to be developed and implemented into national codes. A constitutive model that couples deformation and hydrogen-diffusion, supporting a phenomenological predictive model for fatigue crack growth, is presented for pipeline steels in high-pressure gaseous hydrogen. The semi-empirical model is predicated upon the hypothesis that one of two mechanisms dominates the fatigue crack growth response, depending upon the applied load and the material’s hydrogen concentration. The model correlates test results well, and illustrates how the deformation mechanisms contribute to fatigue crack propagation in pipeline steels in environments similar to those found in-service.

This work proposes a phenomenological fatigue crack propagation (FCP) model for API-5L X100 pipeline steel exposed to high-pressure gaseous hydrogen. The semi-empirical model is predicated upon the hypothesis that one of two mechanisms dominate the fatigue crack growth (FCG) response depending upon the crack extension per cycle ( da / dN ) and the material hydrogen concentration. For da / dN between approximately 1 × 10 −5 mm/cycle and 3 × 10 −4 mm/cycle, fatigue crack growth in hydrogen is markedly increased over that in laboratory air, resulting in a Paris exponent over two and a half times that of air and producing a predominately intergranular crack propagation surface. Fatigue crack growth in hydrogen at da/dN above approximately 3 × 10 −4 mm/cycle result in FCP rates over an order of magnitude higher than that of lab air. The Paris exponent in this regime approaches that of lab air and the crack morphology is predominately transgranular. Increasing the hydrogen test pressure from 1.7 MPa to 20.7 MPa increases the FCG rate by as much as two, depending upon the stress intensity factor. It is proposed that the FCG response in hydrogen at da / dN −4 mm/cycle is primarily affected by the hydrogen concentration within the fatigue process zone, resulting in a hydrogen-dominated mechanism, and that the FCG response in hydrogen at da / dN >3 × 10 −4 mm/cycle results from fatigue-dominated mechanisms. The proposed model predicts fatigue crack propagation as a function of applied Δ K and hydrogen pressure. Results of fatigue crack growth tests in gaseous hydrogen as well as fracture morphology are presented in support of the proposed model. The model correlates well with test results and elucidates how the proposed mechanisms contribute to fatigue crack propagation in pipeline steel in environments similar to those found in service.

Fatigue crack growth tests were conducted on two pipeline steel alloys, API 5L X52 and X100. Baseline tests were conducted in air, and those results were compared with tests conducted in pressurized hydrogen gas. All tests were run at (load ratio) R = 0.5 and a frequency of 1 Hz, except for one test on X100, run at 0.1 Hz. Tests were conducted at hydrogen pressures of 1.7 MPa, 7 MPa, 21 MPa, and 48 MPa. Fatigue crack growth rates for both X100 and X52 were significantly higher in a pressurized hydrogen environment than in air. This enhanced growth rate appears to correlate to pressure for X100 but may not for X52.

Hydrogen is known to have a deleterious effect on most engineering alloys. It has been shown repeatedly that the strength of steels is inversely related to the ductility of the material in hydrogen gas. However, the fatigue properties with respect to strength are not as well documented or understood. Here, we present the results of tests of the fatigue crack growth rate (FCGR) on API X70 from two sources. The two materials were tested in air, 5.5 and 34 MPa pressurized hydrogen gas, and at both 1 and 0.1 Hz. At these hydrogen pressures, the FCGR increases above that of air for all values of the stress intensity factor range (ΔK) greater than ~7 MPa · m1/2. The effect of hydrogen is particularly sensitive at values of ΔK below ~15 MPa · m1/2. That is, for values of ΔK between 7 and 15 MPa · m1/2, the FCGR rapidly increases from approximately that found in air to as much as two orders of magnitude above that in air. Above 15 MPa · m1/2, the FCGR remains approximately one to two orders of magnitude higher than that of air.

The tensile properties of X52, X65, and X100 pipeline steels have been measured in a high-pressure (13.8 MPa) hydrogen gas environment. Significant decreases in elongation at failure and reduction of area were observed when testing in hydrogen as compared with air, and those changes were accompanied by noticeable changes in fracture morphology. In addition to baseline characterization of the effects of strength and microstructure on the X52, X65, and X100 alloys, the influence of strain rate and hydrogen gas pressure was studied for only the X100 alloy.

Scanning electrochemical microscopy has been used to examine the molecular transport properties of photopolymerized poly(ethylene glycol) (PEG) hydrogels having different mesh sizes. Both the molecular weight (508 Da or 3000 Da) of the PEG diacrylate macromer and its weight percent (20 wt%, 40 wt%, or 60 wt%) in solution prior to photopolymerization were varied. Mesh size was estimated from equilibrium swelling measurements and a thermodynamic model. Estimated mesh sizes ranged from ca. 10 A for 60 wt% PEG 508 gels to ca. 100 A for 20 wt% PEG 3000 gels. The electrochemically active diffusing species, ferrocenemethanol, was detected via oxidation at a platinum microelectrode. For a given hydrogel, multiple approach curves showed a consistent relationship between current and distance. Electrochemically estimated diffusivities followed the same trend as predictions based on mesh size and ranged from 25% to 80% of the diffusivity in aqueous solution. As a proof of concept, scanning electrochemical microscopy was successfully used to map the topography of hydrogels with complex architecture, which are being designed as cell scaffolds.

A high pressure, electron-beam directed-vapor deposition process has been used to deposit partially stabilized zirconia containing 7% mass yttria at deposition pressures of 7.5–23 Pa. Anisotropic, ultra-small-angle X-ray scattering (USAXS) was then used to determine the surface area, shape and orientation of pores within the coatings. The total surface area of the ellipsoidal shaped pores was found to increase with deposition pressure. However, the through-thickness thermal conductivity measurements reveal the existence of a minimum thermal conductivity in coatings deposited at an intermediate pressure. Observations of the anisotropic X-ray scattering intensity at this intermediate pressure indicated greater proportions of both feather-like (oblate) pores with their major dimension at about 60° to the plane of the coating and fine columnar (prolate) pores oriented perpendicular to the coating plane. Since these oblate pore orientations are most efficient at impeding conductive thermal transport through the coating, it is believed that the change in preferred pore orientations with pressure is responsible for the higher thermal resistance of coatings grown in the intermediate pressure regime.

We demonstrate a hydrogen gas chamber suitable for lattice strain measurements and capturing radiographs of a steel specimen under a mechanical load using high energy synchrotron x-rays. The chamber is suitable for static and cyclic mechanical loading. Experiments were conducted at the 1-ID-E end station of the Advanced Photon Source, Argonne National Laboratory. Diffraction patterns show a high signal-to-noise ratio suitable for lattice strain measurements for the specimen and with minimal scattering and overlap from the gas chamber manufactured from aluminum. In situ radiographs of a specimen in the hydrogen chamber show the ability to track a growing crack and to map the lattice strain around the crack with high spatial and strain resolution.

This paper presents an improved testing system for isothermal and thermal-cycling experiments of polymers in compression. Due to the low thermal conductivity of polymers and the high thermal mass of commercially available compression platens, significant problems arise; large differences between the prescribed and polymer temperature, temperature variation through the sample and a slow temperature response are observed. Here, in experiments performed on an acrylic network polymer, the largest temperature difference between the core of the cylindrical compression samples (10 mm diameter/height) and the prescribed air temperature reaches 20.7 °C and 64.8 °C when respective cooling/heating rates of 1 °C/min and 10 °C/min are used. Based on the analysis of the existing system, an improved compression platen design for thermal management that provides a faster temperature response and a more uniform sample temperature distribution is proposed. The peak temperature difference was reduced to 4.5 °C at a cooling/heating rate of 10 °C/min using the improved testing system.

A microfabricated device has been developed for imaging of a single, adherent cell while quantifying force under an applied displacement. The device works in a fashion similar to that of a displacement-controlled uniaxial tensile machine. The device was calibrated using a tipless atomic force microscope (AFM) cantilever and shows excellent agreement with the calculated spring constant. A step input was applied to a single, adherent fibroblast cell and the viscoelastic response was characterized with a mechanical model. The adherent fibroblast was imaged by use of epifluorescence and phase contrast techniques.

We demonstrate the rapid growth of grains in nonpassivated, sputtered Al-1 at. pct Si interconnects during 200 Hz thermal cycling induced by alternating current. Mean grain diameters were observed by use of automated electron backscatter diffraction (EBSD) to increase by more than 70 pct after an accumulated cycling time of less than 6 minutes over a temperature range of 200 °C, which corresponded to a total strain range of 4 × 10−3. Plasticity in growing grains primarily took the form of topography formation at the free surface and grain rotation, while consumed grains tended to retain relatively high dislocation content. Grain growth was characterized by means of pairwise comparisons in EBSD pattern quality across moving boundaries. Out of 92 cases where a grain was observed to grow into its neighbor, 61 cases indicated that the growing grain had a higher average pattern quality factor than that of the consumed grain, at the 95 pct confidence level. The results are consistent with a strain-induced boundary migration mechanism, wherein stored plastic strain energy differences from grain to grain drive growth, some of which was observed after only 10 seconds of cycling.

Pipelines are widely accepted to be the most economical method for transporting large volumes of hydrogen, needed to fuel hydrogen-powered vehicles. Some work has been previously conducted on the fatigue crack growth rates of base metals of pipeline materials currently in use for hydrogen transport and on pipeline materials that may be used in the future. However, welds and their heat-affected zones are oftentimes the source and pathway for crack initiation and growth. The heat-affected zones of welds can exhibit low resistance to crack propagation relative to the base metal or the weld itself. Microstructural irregularities such as chemical segregation or grain-size coarsening can lead to this low resistance. Therefore, in order to have adequate information for pipeline design, the microstructures of the heat-affected zones must be characterized, and their mechanical properties must be measured in a hydrogen environment. With that in mind, data on the fatigue crack growth rate is a critical need. We present data on the fatigue crack growth rate of the heat-affected zones for two girth welds and one seam weld from two API 5L X52 pipes. The materials were tested in hydrogen gas pressurized to 5.5 MPa and 34 MPa at a cyclic loading rate of 1 Hz, and an R ratio of 0.5.Copyright © 2015 by ASME

There is a need for experimental techniques that allow the simultaneous imaging of cellular cystoskeletal components with quantitative force measurements on single cells. A bioMEMS device has been developed for the application of strain to a single cell while simultaneously quantifying its force response. The prototype device presented here allows the mechanical study of a single, adherent cell in vitro. The device works in a fashion similar to a displacement-controlled uniaxial tensile machine. The device is calibrated using an AFM cantilever and shows excellent agreement with the calculated spring constant. The device is demonstrated on a single fibroblast. The force response of the cell is seen to be linear until the onset of de-adhesion with the de-adhesion from the cell platform occurring at a force of approximately 1500 nN.

Experiments studying cardiovascular geometries require a working fluid that matches the high index of refraction of glass and silicone, has a low viscosity, and is safe and inexpensive. A good candidate working fluid is diethyl phthalate (DEP), diluted with ethanol. Measurements were made of index of refraction and viscosity of varied dilutions at a range of temperatures, and empirical models are proposed. Material compatibility tests showed that only specific formulations of ABS, acrylic, vinyl and PVC are compatible. A silicone elastomer additionally tested negative for change in compliance with DEP exposure.

A measurement system has been designed and constructed at NIST for the study of the mechanical properties of synthetic and bovine vascular materials. The measurement technique was validated on latex, where good agreement was found with the Neo-Hookean model. Measurements were also made on expanded polytetrafluoroethylene, which is commonly used for vascular grafts. The measurements of this material were carried out over a pressure range greater than would be seen in vivo. However, the strains were still small enough to effectively apply the Neo-Hookean model to these data.

A gas-pressure chamber has been designed, constructed, and tested at a moderate pressure (3.4 MPa, 500 psi) and has the capability of mechanical loading of steel specimens for neutron scattering measurements. The chamber will allow a variety of in situ neutron scattering measurements: in particular, diffraction, quasielastic scattering, inelastic scattering, and imaging. The chamber is compatible with load frames available at the user facilities at the NIST Center for Neutron Research and Oak Ridge National Laboratory Spallation Neutron Source. A demonstration of neutron Bragg edge imaging using the chamber is presented.

A primary barrier to the widespread use of gaseous hydrogen as an energy carrier is the creation of a hydrogen-specific transportation network. Research performed at the National Institute of Standards and Technology, in conjunction with the U.S. Department of transportation and ASME committee B31.12 (Hydrogen Piping and Pipelines), has resulted in a phenomenological model to predict fatigue crack growth of API pipeline steels cyclically loaded in high-pressure gaseous hydrogen. The full model predicts hydrogen-assisted (HA) fatigue crack growth (FCG) as a function of applied load and hydrogen pressure. Implementation of the model into an engineering format is crucial for the realization of safe, cost-effective pipelines for the nation’s hydrogen infrastructure. Working closely with ASME B31.12, two simplified iterations of the model have been created for an engineering-based code implementation. The engineering-based iterations are detailed here and the benefits of both are discussed. A case study is then presented detailing the use of both versions. The work is concluded with a discussion of the potential impact that model implementation would have upon future hydrogen pipeline installations.

The National Institute of Standards and Technology has been testing pipeline steels for about 3 years to determine the fatigue crack growth rate in pressurized hydrogen gas; the project was sponsored by the Department of Transportation, and was conducted in close collaboration with ASME B31.12 Committee on Hydrogen Piping and Pipelines. Four steels were selected, two X52 and two X70 alloys. Other variables included hydrogen gas pressures of 5.5 MPa and 34 MPa, a load ratio, R, of 0.5, and cyclic loading frequencies of 1 Hz, 0.1 Hz, and a few tests at 0.01 Hz. Of particular interest to ASME and DOT was whether the X70 materials would exhibit higher fatigue crack growth rates than the X52 materials. API steels are designated based on yield strength and monotonic tensile tests have historically shown that loss of ductility correlates with increase in yield strength. The X70 materials performed on par with the X52 materials in fatigue. The test matrix, the overall set of data, implications for the future, and lessons learned during the 3-year extensive test program will be discussed.Copyright © 2014 by ASME

A model to predict fatigue crack growth of API pipeline steels in high pressure gaseous hydrogen has been developed and is presented elsewhere. The model currently has several parameters that must be calibrated for each pipeline steel of interest. This work provides a sensitivity analysis of the model parameters in order to provide (a) insight to the underlying mathematical and mechanistic aspects of the model, and (b) guidance for model calibration of other API steels.

Low thermal conductivity yttria stabilized zirconia (YSZ) coatings have been grown using a low-vacuum (0.20 Torr) electron beam directed vapor deposition process. In this approach, a transsonic helium jet was used to entrain and transport an evaporated YSZ flux to a substrate. The interaction of the helium jet with the coating surface resulted in many of the evaporated species making oblique angles of contact with the substrate. This resulted in the formation of a highly porous, columnar microstructure without substrate rotation. When the substrate was positioned perpendicular to the axis of the jet, coatings with intercolumnar pores normal to the substrate surface were formed. The ambient temperature thermal conductivity of a coating grown in this arrangement was 1.9 Wm/K, comparable to that of conventional, high-vacuum electron beam coatings. When the column and pore orientation was inclined (by tilting the substrate) the thermal conductivity was observed to fall. By alternating the inclination angle as growth progressed, coatings containing zig-zag columns and pores could be synthesized. Using this technique, YSZ coatings with thermal conductivities as low as 0.8 W/m K were obtained. The observed thermal conductivity reduction arises from the longer thermal diffusion path of the zig-zag pore micro-structures.

The conductivity of a thermal-barrier coating composed of atmospheric plasma sprayed 8 mass percent yttria partially stabilized zirconia has been measured. This coating was sprayed on a substrate of 410 stainless steel. An absolute, steady-state measurement method was used to measure thermal conductivity from 400 to 800 K. The thermal conductivity of the coating is 0.62 W/(m·K). This measurement has shown to be temperature independent.

Tests on the fatigue crack growth rate were conducted on four pipeline steels, two of grade API 5L-X52 and two API 5L-X70. One X52 material was manufactured in the mid-1960s and the other was manufactured in 2011. The two X70 materials had a similar vintage and chemistry, but the microstructure differs. The fatigue tests were performed in 5.5 and 34 MPa pressurized hydrogen gas, at 1 Hz and (load ratio) R = 0.5. At high pressures of hydrogen and high values of the stress intensity factor range (ΔK) there is no difference in the fatigue crack growth rates (da/dN), regardless of strength or microstructure. At low values of ΔK, however, significant differences in the da/dN are observed. The older X52 material has a ferrite-pearlite microstructure; whereas, the modern X52 has a mixture of polygonal and acicular ferrites. The X70 materials are both predominantly polygonal ferrite, but one has small amounts (∼5%) of upper bainite, and the other has small amounts of pearlite (

A tribometer at the National Institute of Standards and Technology in Boulder, Colorado is used to measure the coefficient of friction and the wear rate for various specimens in a controlled atmosphere of oxygen or non-corrosive gas. The wide range of demonstrated operating temperature of 80 to 1030 K is presently unavailable in any commercial apparatus. The machine uses ball-on-flat or ring-on-flat specimen geometries for comparison of conforming and non-conforming contacts. The tribometer can be loaded to produce a hertzian contact stress in excess of 12 GPa (1.7×10 6 Ibf in −2 ) and surface velocities from 0.06 m s −1 to 4.0 m s −1 . A range of environmental conditions this wide is unusual, especially the temperature range. The apparatus is described and some test results are compared with known values.

AISI 440C martensitic stainless steel is the material of choice for the high pressure oxygen turbopump (HPOTP) of the space shuttle main engine (SSME). Tests have been done over a range of sliding speeds from 0.5 to 2.0 m s−1, initial hertzian stresses from 0.915 to 3.66 GPa, and bulk temperatures from −184 °C (liquid oxygen temperature) to 760 °C, which cover the variations thought to exist in the HPOTP. Data are presented in the form of contour wear maps to allow a more direct view of the interdependencies of the major tribological variables than can be obtained with wear data presented vs. a single variable. Wear maps are used as a tool to aid in the determination of regions dominated by a given wear mode. Parametric combinations that result in transitions between wear modes are more easily detected with the use of wear maps. Wear maps can simplify design by identifying combinations of speed, load, and bulk temperature that need to be avoided, because of undesirable wear modes.

Unlubricated sliding friction and wear of 440C steels in an oxygen environment have been studied under a variety of load, speed, and temperature ranging from approximately -185 to 675 deg C. A specially designed test apparatus with a ball-on-flat geometry has been used for this purpose. The observed dependencies of the initial coefficient of friction, the average dynamic coefficient of friction, and the wear rate on load, speed, and test temperatures have been examined from the standpoint of existing theories of friction and wear. High contact temperatures are generated during the sliding friction, causing rapid oxidation and localized surface melting. A combination of fatigue, delamination, and loss of hardness due to tempering of the martensitic structure is responsible for the high wear rate observed and the coefficient of friction.

Determination of material parameters for soft tissue frequently involves regression of material parameters for nonlinear, anisotropic constitutive models against experimental data from heterogeneous tests. Here, parameter estimation based on membrane inflation is considered. A four parameter nonlinear, anisotropic hyperelastic strain energy function was used to model the material, in which the parameters are cast in terms of key response features. The experiment was simulated using finite element (FE) analysis in order to predict the experimental measurements of pressure versus profile strain. Material parameter regression was automated using inverse FE analysis; parameter values were updated by use of both local and global techniques, and the ability of these techniques to efficiently converge to a best case was examined. This approach provides a framework in which additional experimental data, including surface strain measurements or local structural information, may be incorporated in order to quantify heterogeneous nonlinear material properties.

A scanning thermal microscope with a Wollaston probe was used to investigate the spatial distribution and temporal variation of temperature in interconnect structures subjected to thermal cycling. The probe, utilized in passive temperature sensing mode, was calibrated from 20°C to 200°C using a single-layer aluminum microdevice. Spatial measurements were performed on nonpassivated aluminum interconnects sinusoidally heated by a 6 MA/cm2 current at 200 Hz. The interconnects were determined to have temperatures that decreased with position from a maximum located at the center of both the interconnect length and width. Time-resolved temperature measurements were performed on the same structures sinusoidally heated by a 6 MA/cm2 current at 2 Hz. Both the peak-cycle temperature and average-cycle temperature were found to decrease with increasing distance from the center of the width of the interconnects. Microsc. Res. Tech., 2008. Published 2008 Wiley-Liss, Inc.

Environmental conditions can have major influence on the lifetimes and reliability of active implantable medical devices (e.g., neurostimulators, cochlear implants, internal cardioverter defibrillators). These environmental conditions can range from those encountered by the device in processing and production to transportation and storage to actual operation. Although one might argue that the environmental conditions found in the first two situations are harsher than those of the third, failures that result from those situations are screened before implantation. If we assume that the active medical device is in perfect operational form at the time it is implanted, it will still experience a host of environmental conditions that can affect reliability. In fact, the ultimate goal of these medical devices is to restore the patient, wherever they may reside, to normal activities. A list of some environmental conditions that may be experienced by a device implanted in a representative patient is found in Table 1.

This work represents the first application of a statistical mechanics based microstructural orthotropic hyperelastic model to pulmonary artery mechanics under normotensive and hypertensive conditions. The model provides an analogy between the entangled network of long molecular chains and the structural protein framework seen in the medial layer, and relates the mechanical response at macro-level to the deformation (entropy change) of individual molecular chains at the micro-level. A finite element approach was adopted to implement the model. Material parameters were determined via comparing model output to measured pressure–stretch results from normotensive and hypertensive trunks and branches obtained from a rat model of pulmonary arterial hypertension. Results from this initial study show that this model appears reasonable for the study of hyperelastic and anisotropic pulmonary artery mechanics. Typical tangent modulus values ranged from 200 to 800 kPa for normotensive arteries—this increased to beyond 1 MPa for hypertensive vessels. Our study also provokes the hypothesis that increase of cross-linking density may be one mechanism by which the pulmonary artery stiffens in hypertension.

Results of comparative tests on pulmonary arteries from untreated Long-Evans rats are presented from three sections of the artery: the trunk, and the right and left main extrapulmonary arteries. Analyses were conducted looking for mechanical differences between the flow (longitudinal) and circumferential directions, between the right and left main arteries, and between each of the mains and the trunk. The mechanical properties of rat pulmonary arteries were obtained with a bubble inflation technique. A flat disk of rat pulmonary artery was constrained at the periphery and inflated, and the geometry of the resulting bubble of material recorded from six different angles. To analyze the data, the area under the stress-strain curve was calculated for each test and orientation. This area, related to the strain-energy density, was calculated at stress equal to 200kPa, for the purpose of statistical comparison. The mean values for the area show that the trunk is less compliant than the main arteries; this difference is supported by histological evidence. When comparing the circumferential and longitudinal properties of the arteries, differences are found for the trunk and left main arteries, but with opposite orientations being more compliant. The mean values for the two orientations for the right main artery are statistically identical. There was indication of significant difference in mechanical properties between the trunk and the main arteries. The left main artery in the circumferential orientation is highly compliant and appears to strongly influence the likelihood that significant differences will exist when included in a statistical population. These data show that each section of the extrapulmonary arterial system should not be expected to behave identically, and they provide the baseline mechanical behavior of the pulmonary artery from normotensive rats.

A biaxial bubble test has been designed to ascertain the mechanical properties of rat pulmonary arteries. The analytical procedure used to estimate stress and strain from the resulting test data is presented along with some analytical results. The bubble test was performed by loading a flat piece of rat pulmonary artery into a test fixture beneath a circular opening; the material was subsequently pressurized from below, producing a "bubble" of deformed material. Due to the anisotropy of the rat pulmonary artery, the resulting bubble was ellipsoidal in shape. Test results were recorded in the form of side-view images taken from various angles at incremental values of pressure. Average strains were estimated with the use of image analysis to measure changes in the bubble perimeter during inflation. Formulations for isotropic materials were applied to estimate stresses based on the anisotropic geometry of the bubbles produced during testing; some results of this preliminary analysis are presented here. Results from this analysis show differences in mechanical properties of the rat pulmonary artery from those of healthy versus hypertensive rats.

A simple measurement system is described for evaluating damage to graphite-epoxy panels, such as those used in high-performance aircraft. The system uses a heating laser and infrared imaging system to measure thermal performance. Thermal conductivity or diffusivity is a sensitive indicator of damage in materials, allowing this thermal measurement to show various degrees of damage in graphite-epoxy composites. Our measurements track well with heat-flux damage to graphite epoxy panels. This measurement system, including analysis software, could easily be used in the field, such as on the deck of an aircraft carrier or at remote air strips.

An apparatus has been developed to measure the thermal conductivity of ceramic coatings. Since the method uses an infrared microscope for temperature measurement, coatings as thin as 20 μm can, in principle, be measured using this technique. This steady-state, comparative measurement method uses the known thermal conductivity of the substrate material as the reference material for heat-flow measurement. The experimental method is validated by measuring a plasma-sprayed coating that has been previously measured using an absolute, steady-state measurement method. The new measurement method has a relative standard uncertainty of about 10 %. The measurement of the plasma-sprayed coating gives 0.58 W·m(-1)·K(-l) which compares well with the 0.62 W·m(-1)·K(-l) measured using the absolute method.

We have measured the thermal conductivity of a Ni20Cr / 8% yttria-partially-stabilized-zirconia functionally graded 1.1 mm thick coating on a substrate of 403 stainless steel. We measured thermal conductivity of the as-received coated specimen, then thermally shocked the specimen and measured thermal conductivity again. The measurements were done using an absolute, steady-state technique over a temperature range from 400 K to 1200 K. The specimen was thermally shocked by heating in a furnace to 475 K, then quenching in water at 295 K. We discuss the effect of moderate thermal shock on the thermal conductivity of the coating.