Round Robin Exercise Research Articles

Benchmarking predictive methods for small-angle X-ray scattering from atomic coordinates of proteins using maximum likelihood consensus data.

Stimulated by informal conversations at the XVII International Small Angle Scattering (SAS) conference (Traverse City, 2017), an international team of experts undertook a round-robin exercise to produce a large dataset from proteins under standard solution conditions. These data were used to generate consensus SAS profiles for xylose isomerase, urate oxidase, xylanase, lysozyme and ribonuclease A. Here, we apply a new protocol using maximum likelihood with a larger number of the contributed datasets to generate improved consensus profiles. We investigate the fits of these profiles to predicted profiles from atomic coordinates that incorporate different models to account for the contribution to the scattering of water molecules of hydration surrounding proteins in solution. Programs using an implicit, shell-type hydration layer generally optimize fits to experimental data with the aid of two parameters that adjust the volume of the bulk solvent excluded by the protein and the contrast of the hydration layer. For these models, we found the error-weighted residual differences between the model and the experiment generally reflected the subsidiary maxima and minima in the consensus profiles that are determined by the size of the protein plus the hydration layer. By comparison, all-atom solute and solvent molecular dynamics (MD) simulations are without the benefit of adjustable parameters and, nonetheless, they yielded at least equally good fits with residual differences that are less reflective of the structure in the consensus profile. Further, where MD simulations accounted for the precise solvent composition of the experiment, specifically the inclusion of ions, the modelled radius of gyration values were significantly closer to the experiment. The power of adjustable parameters to mask real differences between a model and the structure present in solution is demonstrated by the results for the conformationally dynamic ribonuclease A and calculations with pseudo-experimental data. This study shows that, while methods invoking an implicit hydration layer have the unequivocal advantage of speed, care is needed to understand the influence of the adjustable parameters. All-atom solute and solvent MD simulations are slower but are less susceptible to false positives, and can account for thermal fluctuations in atomic positions, and more accurately represent the water molecules of hydration that contribute to the scattering profile.

Probabilistic Graphical Model for Sizing Assessment in Ultrasonic Testing in Dissimilar Metal Weld

This work investigates an approach for evaluating the uncertainty associated with flaw sizing in Ultrasonic Testing in nuclear inspections using Bayesian Belief Networks (BBN). BBN graphically represents the probabilistic relationship between the sizing accuracy and some of the variables that cause its deviation. The data for BBN training was collected from sizing information of Round-Robin trials reported in the literature and supplemented with sizing results obtained using the Ultrasonic Testing module of CIVA Non-Destructive Evaluation software. The test specimen used in the Round-Robin exercise and simulations was a dissimilar metal welded pipe. Given the available data, the variables considered causing sizing inaccuracy are the flaw’s actual depth, tilt angle, and position in relation to inner and outer surfaces.

8-MW wind turbine tower computational shell buckling benchmark. Part 2: Detailed reference solution

An assessment of the elastic–plastic buckling limit state for multi-strake wind turbine support towers poses a particular challenge for the modern finite element analyst, who must competently navigate numerous modelling choices related to the tug-of-war between meshing and computational cost, the use of solvers that are robust to highly nonlinear behaviour, the potential for multiple near-simultaneously critical failure locations, the complex issue of imperfection sensitivity and finally the interpretation of the data into a safe and economic design.This paper presents a detailed reference solution to the computational buckling analysis of a standardised benchmark problem of an 8-MW multi-strake wind turbine support tower. Both linear and nonlinear analyses are performed, including advanced GMNIA with several different models of geometric imperfections. The crucial issue of interpreting the imperfection amplitude in a way that is compliant with the new prEN 1993-1-6 is discussed in detail. The solution presented herein is intended for use by analysts in both industry and academia for training, verification and calibration of finite element models and is intended to initiate a public repository of such computational solutions for metal civil engineering shell structures.This paper is the second of a pair. The first paper [37] presents a synthesis of 29 submissions to an international round-robin exercise performed on the same benchmark problem.

How Reproducible are Surface Areas Calculated from the BET Equation?

Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer-Emmett-Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method wasdeveloped in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro- and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already-measured raw adsorption isotherms wereprovided to sixty-one labs, who wereasked to calculate the corresponding BET areas. This round-robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called "BET surface identification" (BETSI), expands on the well-known Rouquerol criteria and makes an unambiguous BET area assignment possible.

Surface Water Dynamics from Space: A Round Robin Intercomparison of Using Optical and SAR High-Resolution Satellite Observations for Regional Surface Water Detection

Climate change, increasing population and changes in land use are all rapidly driving the need to be able to better understand surface water dynamics. The targets set by the United Nations under Sustainable Development Goal 6 in relation to freshwater ecosystems also make accurate surface water monitoring increasingly vital. However, the last decades have seen a steady decline in in situ hydrological monitoring and the availability of the growing volume of environmental data from free and open satellite systems is increasingly being recognized as an essential tool for largescale monitoring of water resources. The scientific literature holds many promising studies on satellite-based surface-water mapping, but a systematic evaluation has been lacking. Therefore, a round robin exercise was organized to conduct an intercomparison of 14 different satellite-based approaches for monitoring inland surface dynamics with Sentinel-1, Sentinel-2, and Landsat 8 imagery. The objective was to achieve a better understanding of the pros and cons of different sensors and models for surface water detection and monitoring. Results indicate that, while using a single sensor approach (applying either optical or radar satellite data) can provide comprehensive results for very specific localities, a dual sensor approach (combining data from both optical and radar satellites) is the most effective way to undertake largescale national and regional surface water mapping across bioclimatic gradients.

Virtual round robin – A new opportunity to study NDT reliability

Round robin exercises have traditionally been difficult to arrange in the field of non-destructive testing (NDT). To create a representative round robin exercise, representative mock-ups with representative flaws are needed. The mock-ups are costly and transporting them around the world to facilitate testing by numerous laboratories is difficult. The few round robins that have been completed have often contributed significantly to our understanding on the capability of the used NDT methods and procedures.Recently, the increased use of automated inspections together with the development of virtual flaws (independently by Trueflaw and EPRI) has enabled a new type of round robin, where instead of moving samples around the world, the round robin is focused on the data analysis and only pre-acquired data files are distributed. This makes conducting a round robin much more cost-effective both in terms of arrangement and in terms of inspection effort from the participating companies. In addition, the virtual flaw technology allows unprecedented number and variety of flaws to be included. With high number of flaws included, the results present statistically meaningful sample and can be further analyzed to estimate the probability of detection (POD) with standard statistical tools. In connection with the international project “PIONIC”, such a virtual round robin was arranged for the first time.The exercise showed, that virtual flaws and virtual round robins can be used to extract important information about NDT reliability and performance. Also, some points of development were identified for further studies: the sizing and detection files should be better optimized for their respective uses and the data could be further obfuscated to avoid any possibility of inspectors learning to recognize repeating signal patterns.12 inspectors submitted results to the virtual round robin. The results showed a90/95 ranging from 1.2 to 7.0 mm – a significant variation in performance. The difference was mainly attributed to different inspection strategies. In addition, an unexplained tendency to miss big cracks was noted on some result sets. One of the data files did not contain any flaws. None of the inspectors correctly identified the file as flawless.

Results of an international round-robin exercise on electrochemical impedance spectroscopy

ABSTRACT To check the reproducibility of electrochemical impedance spectroscopy (EIS) measurements, 19 laboratories have performed round-robin (RR) testing on EIS using various instruments and three different systems: a dummy cell and two electrochemical systems of practical interest in the nuclear corrosion domain. The general conclusion drawn from the tests performed with the dummy cell is that the actual commercially available instruments for EIS measurements are suitable to produce good quality data. Differences in the EIS diagrams for the tested electrochemical systems were observed and discussed. This RR exercise, involving for the first time a large number of laboratories, shows that intrinsic scatter (large or small) is present in the impedance data and that reproducibility should be readily checked. While EIS is an excellent technique for investigating the kinetics of electrochemical systems, great care has to be taken on planning and conducting the experiments. Recommendations are given to help obtaining reliable EIS results.

Simplified approach for ductile fracture mechanics SSTT and its application to Eurofer97

Abstract The determination of fracture-mechanical properties is often very challenging, because the available standards like ASTM E1820 need specific size-requirements for the specimen dimensions to obtain valid fracture toughness. Especially in the ductile regime, where the presence of plasticity around the crack tip is affected by the multiaxial stress state and its triaxiality, the size-requirements are frequently not met. The fulfilment of the size-requirements needs the testing of big specimens, which is often not possible. If we now think of specimens, which are irradiated in test modules for future fusion reactors, their size cannot be as big as required, because the available volume for irradiation is restricted. This fact highlights the need of Small Specimens Test Techniques (SSTT) for the determination of fracture-mechanical properties in the ductile regime. The presented work focuses on an approach for the determination of fracture-mechanical properties in the ductile regime including stable crack growth and crack-resistance behavior. The authors have developed the initial approach some years ago and within this work the approach was simplified as much as possible. The basic idea of the approach is, that the crack growth can be simulated using Finite Element Method combined with a cohesive zone model. The cohesive zone model is a two parametric model, namely the cohesive stress σ c and the cohesive energy Γ c , which are identified on small specimens only. The new simplified approach was now validated on ferritic-martensitic steel Eurofer97 at room temperature. In the past, the approach used complicated features like a CCD camera system and has now been simplified in a way that no CCD camera system is required. The main part of the approach is the identification of cohesive zone parameters (cohesive stress σ c and energy Γ c ) on small specimens. The cohesive stress σ c can be determined on notched round tensile specimens with different notch root radius to account for different stress states or stress triaxialities in the specimen. With dedicated Finite Element modelling a local fracture stress dependent on stress triaxiality can be identified. The cohesive energy Γ c can be carried out by simulating the small fracture-mechanical specimen using the Finite Element Method combined with the cohesive zone model and parameter fitting to experimental results. The cohesive energy Γ c is treated to be identified, if the simulated crack-resistance curve describes the experimental behavior. After identification of these parameters, a big fracture-mechanical specimen can be simulated using the cohesive zone parameters already determined on small specimens. Finally, the crack-resistance curve of a big specimen can be predicted and a valid fracture toughness can be identified if the size-requirements of the big specimens are met. In case the requirements are not fulfilled, a bigger specimen geometry can be simulated until all size criteria are met. With this method, the testing of big specimens can be avoided. For the future there is a Round Robin exercise planned including defined test matrices to demonstrate the general applicability of the approach.

Dynamic Compression Strength of Ceramics: What was Learned from an Interlaboratory Round Robin Exercise?

The dynamic compressive strength of a commercial alumina was determined by five participants using the Split-Hopkinson pressure bar (SHPB) method with a dumbbell-shaped specimen. Each participant used their own SHPB test apparatus and imaging set-up to conduct the tests and capture the fracture process. The dumbbell-shaped specimen was designed to increase the likelihood of fracture commencing in the specimen gage section rather than at the interface of the specimen and the SHPB bars. The participants had a good success rate (between 40 and 80%) of tests being deemed valid, even though this was the first time several of the participants had used this specimen geometry. The average dynamic compression strength from the five participants were in excellent agreement with each other and ranged from 4.40 to 4.92 GPa with a grand average of 4.61 GPa ± 0.25 GPa (the average of the laboratory averages). The high success rate and remarkable consistency of the results show that the dumbbell-shaped specimen is the most optimum specimen geometry investigated to-date to determine the dynamic compression strength of advanced ceramics using the SHPB test methodology.

Sensitivity of Altimeter Wave Height Assessment to Data Selection

This paper addresses the issue of how the selection of buoys and the calculation of altimeter averages affect the metrics characterising the errors of altimetric wave height estimates. The use of a 51-point median reduces the sensitivity to occasional outliers, but the quality of this measure can be improved by demanding that there is a minimum number of valid measurements. This had a marked impact in both the open ocean and the coastal zone. It also affected the relative ordering of algorithms’ performances, as some fared poorly when a representative value was gleaned from a single waveform inversion, but had a much better ranking when a minimum of 20 values were used. Validation procedures could also be improved by choosing altimeter-buoy pairings that showed a good consistency. This paper demonstrated an innovative procedure using the median of the different retrackers analysed, which can be easily extended to other data validation exercises. This led to improved comparison statistics for all algorithms in the open ocean, with many showing errors less than 0.2 m, but there was only one strong change in the relative performance of the 11 Jason-3 retrackers. For Sentinel-3A, removing the inconsistent coastal buoys showed that all of the new algorithms had similar errors of just over 0.2 m. Thus, although improvements were found in the procedure used for the Sea State Round Robin exercise, the relative rankings for the buoy calibrations are mostly unaffected.

International Round-Robin on Stress Corrosion Crack Initiation of Alloy 600 Material in Pressurized Water Reactor Primary Water

The International Cooperative Group on Environmentally Assisted Cracking of Water Reactor Materials coordinated an international “Round-Robin” collaboration of 10 laboratories on stress corrosion crack (SCC) initiation in three heats of cold-worked Alloy 600 in high-temperature water. The various laboratories were able to produce good quality experimental crack initiation data, and the Round-Robin exercise highlighted the benefits in generating a significant body of data when assessing the susceptibility of a material to SCC. The compilation of data from multiple laboratories using common test techniques greatly assists the understanding of the material variability and gives confidence in the reliability of the results.

Cloud Detection: An Assessment Study from the ESA Round Robin Exercise for PROBA-V.

A Round Robin exercise was implemented by ESA to compare different classification methods in detecting clouds from images taken by the PROBA-V sensor. A high-quality dataset of 1350 reflectances and Clear/Cloudy corresponding labels had been prepared by ESA in the framework of the exercise. Motivated by both the experience acquired by one of the authors in this exercise and the availability of such a reliable annotated dataset, we present a full assessment of the methodology proposed therein. Our objective is also to investigate specific issues related to cloud detection when remotely sensed images comprise only a few spectral bands in the visible and near-infrared. For this purpose, we consider a bunch of well-known classification methods. First, we demonstrate the feasibility of using a training dataset semi-automatically obtained from other accurate algorithms. In addition, we investigate the effect of ancillary information, e.g., surface type or climate, on accuracy. Then we compare the different classification methods using the same training dataset under different configurations. We also perform a consensus analysis aimed at estimating the degree of mutual agreement among classification methods in detecting Clear or Cloudy sky conditions.

Round Robin into Best Practices for the Determination of Indentation Size Effects.

The paper presents a statistical study of nanoindentation results obtained in seven European laboratories that have joined a round robin exercise to assess methods for the evaluation of indentation size effects. The study focuses on the characterization of ferritic/martensitic steels T91 and Eurofer97, envisaged as structural materials for nuclear fission and fusion applications, respectively. Depth-controlled single cycle measurements at various final indentation depths, force-controlled single cycle and force-controlled progressive multi-cycle measurements using Berkovich indenters at room temperature have been combined to calculate the indentation hardness and the elastic modulus as a function of depth applying the Oliver and Pharr method. Intra- and inter-laboratory variabilities have been evaluated. Elastic modulus corrections have been applied to the hardness data to compensate for materials related systematic errors, like pile-up behaviour, which is not accounted for by the Oliver and Pharr theory, and other sources of instrumental or methodological bias. The correction modifies the statistical hardness profiles and allows determining more reliable indentation size effects.

Round robin using the depth of penetration test method on an armour grade alumina

Abstract The depth of penetration (DOP) method is a well-known ballistic test method for characterisation and ranking of ceramic armour materials. The ceramic tile is bonded to a backing material of semi-infinite thickness, and the penetration depth of the projectile gives a measure of the performance of the ceramic. There is, however, an inherent variability in the results from this test method. In this work, the accuracy and the variability of the DOP method has been investigated in a round robin exercise. Six ballistic test centres took part in the exercise. A test protocol was developed, in which the threat type (projectile and impact conditions) and a procedure on how to prepare the targets were specified. The targets consisted of alumina tiles of two different thicknesses that were bonded to polycarbonate backing cubes. Two different 7.62 mm armour piercing projectiles were employed; one with a hard steel core and one with a tungsten carbide core. The projectiles and the other materials all came from single material batches in order to avoid batch-to-batch variations in material properties. These materials were distributed between the ballistic test centres. The test results of the different ballistic test facilities were collected and compared. There was not a lot of variation between the average DOP values obtained at each laboratory, but the variation in penetration depth between shots was high. The consequence of this variation may be less confidence in the test results, and a statistical method was used to evaluate the required number of tests that are sufficient to obtain an average result with high confidence. In most cases, the required number of tests is much higher than what is practically feasible. This work was conducted as part of the European Defence Agency-project CERAMBALL.

Characterization of crystallographic texture of Zirconium alloy components by neutron diffraction

The reproducibility of the determination of crystallographic texture of Zr-based components by neutron diffraction has been studied through a small round-robin exercise, with the participation of texture and residual stress diffractometers from five international laboratories. Both constant-wavelength and polychromatic neutron beams have been used to define the texture of specimens from a warm-rolled and annealed Zircaloy-4 plate, and from a Zr-2.5%Nb pressure tube. Measurements were also compared to synchrotron high energy X-ray diffraction experiments, as a complementary volumetric technique with much shorter data collection times compared to neutrons. Results are qualitatively consistent and reproducible in terms of pole figures and orientation distribution function, underlining the suitability of neutrons for bulk texture measurements. Expected uncertainty of measurements has been quantified by global parameters such as texture indexes and Kearns factors, and local parameters associated to the main texture components (volume fraction, centroids, and widths of fiber components). The typical uncertainties found for these parameters are compared to spatial differences found in a small batch of cold-rolled Zr-2.5%Nb pressure tubes.

Round robin exercise on ball indentation technique in India: Indian nuclear reactor materials

This paper presents outcome of round robin exercise on usage of ball indentation technique to predict strength properties of three different materials which are used in Indian nuclear reactors. The main objectives were to evolve a standardized procedure of determining the mechanical properties by the Ball Indentation technique and quantification of the variation in strength and fracture properties due to ageing through such tests. Standard uniaxial tensile tests were also carried out to quantify the differences between strength properties predicted by ball indentation and those determined using conventional tests. Three different materials studied were, carbon-manganese steel (Grade: SA 333Gr.6), stainless steel (SA312 Type 304LN) and zirconium alloy (Zr-2.5Nb). The carbon-manganese steel and stainless steel materials were drawn from extruded pipes while Zr-2.5Nb was drawn from pressure tubes, used in Indian Pressurized Heavy Water Reactors. Ball indentation tests were carried out on materials in as received and in aged conditions. The ageing was simulated artificially. The carbon-manganese steel and stainless steels were subjected to cold work while Zr-2.5Nb alloy was subjected to heat treatment at different temperatures with varying hold times and in some cases with charged hydrogen. The round robin exercise was conducted within different research centers of Department of Atomic Energy (DAE), India. This was a blind exercise in which all the conventional tests were carried out by a group (who was not involved in Ball Indentation tests) after the completion of ball indentation tests by participants.The paper presents the prediction of strength properties, using ball indentation, by different participants. The reasons of scatter in the results among the various participants and differences with respect to conventional test results are discussed in the paper.

Comparing results of X-ray diffraction, \xb5-Raman spectroscopy and neutron diffraction when identifying chemical phases in seized nuclear material, during a comparative nuclear forensics exercise

This work presents the results for identification of chemical phases obtained by several laboratories as a part of an international nuclear forensic round-robin exercise. In this work powder X-ray diffraction (p-XRD) is regarded as the reference technique. Neutron diffraction produced a superior high-angle diffraction pattern relative to p-XRD. Requiring only small amounts of sample, µ-Raman spectroscopy was used for the first time in this context as a potentially complementary technique to p-XRD. The chemical phases were identified as pure UO2 in two materials, and as a mixture of UO2, U3O8 and an intermediate species U3O7 in the third material.

RaMM (Raman maturity method) study of samples used in an interlaboratory exercise on a standard test method for determination of vitrinite reflectance on dispersed organic matter in rocks

RaMM (Raman maturity method) is a thermal maturity tool for humic macerals in coals or as dispersed organic matter (DOM), expressed in equivalent vitrinite reflectance (EqVR). The EqVR values are based on a recently established calibration according to multi-linear regressions of selected parameters from Raman spectra of vitrinite and inertinite in a suite of Australian coals with vitrinite reflectance (VR) in the range 0.4–2.5%. The study contributes to the application of Raman spectroscopy for thermal maturity determinations as applicable to the petroleum exploration industry and researched by many groups worldwide.A suite of samples to apply the technique was made available from an interlaboratory round robin exercise on application of ASTM D7708, a method for determination of VR of DOM in sedimentary rocks. This exercise involved the distribution of two sets of six unknown rock samples to all participating laboratories. Collated VR results from some samples of the first set, having high maturities and low organic matter (OM) contents, showed a disturbingly high degree of scatter. Although general agreement exists between RaMM determinations and the average of ‘mean random’ VR values determined at the various laboratories, some important differences emerged for some samples in the range EqVR = 1.2–1.8%.On RaMM diagrams, which involve plots of EqVRs derived from the two regression equations defining the method, the pattern of distribution of vitrinite and inertinite changes with thermal maturity for ‘normal’ coals and with OM composition in subhydrous versus perhydrous coals.Most of the round robin samples contained solid bitumens having reflectances close to those of the associated vitrinite. Measurements taken from solid bitumen were avoided as much as possible, but because the RaMM study was done in air medium, some contamination of the humic maceral data was inevitable. Many of the solid bitumens and other potentially complicating components such as Tasmanites-related alginite can be identified on the RaMM diagram and eliminated from RaMM results for lower maturity samples (EqVR < 1.4%) whereas solid bitumen and humic macerals appear to provide similar EqVR for higher maturity samples (EqVR > 1.8%).The humic DOM of marine samples having EqVR >1.0% has spectral properties that differ from those of humic macerals of the same maturity in terrestrially deposited rocks; this could possibly explain any discrepancies between RaMM EqVR and VR data for the marine rocks.The presence of contaminating solid bitumen with reflectance similar to that of vitrinite, is the main complicating factor for thermal maturity evaluation using either VR or RaMM analyses of gas shales and tight oil reservoir rocks. To enable the best results from RaMM studies of these types of rocks, a preliminary study of the solid bitumen component should be carried out to determine its field on the RaMM diagram with the object of eliminating contaminating solid bitumen data from EqVR calculations.

Assessment of Ultimate Load Capacity of concrete containment structures against structural collapse

Nuclear safety regulations in India require assessment of containment structure for Ultimate Load Capacity (ULC) for internal pressure. ULC and associated behavior of containment is evaluated with respect to various performance indicators based on defined criteria. Non-linear FE analysis of the containment structures was carried out considering non-linear material properties of concrete and steel using ABAQUS and ANSYS software. Evaluation of ULC was undertaken to understand containment performance under severe accident conditions, as a round robin analysis based on 1:4 containment model test results conducted at SANDIA national Lab, USA. AERB also participated in the international round-robin exercise organized by BARC to assess the ULC of BARC’s containment test model (BARCOM). The test model is a 1:4 scale replica of 540MWe PHWR pre-stressed concrete inner containment structure of Tarapur Atomic Power Station Units 3&4. Based on the knowledge gained from these studies VVER 1000 reactor building constructed at Kudankulam (KKNPP) was assessed for ULC of its primary containment as a regulatory requirement. VVER containment study was first of its kind as it is a lined containment with cellular basement structure. Non-linear FE analysis in ABAQUS using layered shell model was performed to assess the ULC of the containment structure. Three times of design pressure is estimated to be ULC of the structure.

Effective SEM Analytical Techniques for the Cathodoluminescence Visualization of Intergranular Cements in Saint Peter Sandstone: A Round Robin Exercise

Effective SEM Analytical Techniques for the Cathodoluminescence Visualization of Intergranular Cements in Saint Peter Sandstone: A Round Robin Exercise