Critical Flaw Research Articles

Mechanical properties of MoW–HfN surrogate cermet fuel for nuclear thermal propulsion

AbstractThe mechanical performance of MoW‐HfN, a surrogate cermet for MoW‐UN Nuclear Thermal Propulsion (NTP) fuel, was characterized from room temperature to 1600°C. The modulus of elasticity and flexure strength were obtained from four‐point bend tests. Those tests revealed a loss of stiffness with increasing temperature and systematic increase in ultimate strength up to about 1400°C. This was followed by loss of ultimate strength and the onset of plastic deformation, attributed to the increased ductility of the MoW matrix above 1400°C. Chevron notch tests show that failure originates from features with a critical flaw size of ∼30 εm, which is comparable to the mean particle size of the ceramic phase. X‐ray diffraction (XRD) and Williamson–Hall (WH) analysis suggest that residual stress may contribute to the observed strength‐versus‐temperature behavior.

Expanded vermiculite acting as artificial flaws to enhance the tensile properties of high-strength engineered cementitious composites

In this study, an expanded vermiculite (EV) was proposed to substitute silica sand, and act as artificial flaws in high-strength engineered cementitious composites (ECC) to improve its ductility. Experimental and analytical investigations were conducted on the mechanical behavior, micromechanical analysis and microstructural analysis of ECC from macro-, meso-, and micro-scales. The results demonstrated that the inclusion of EV reduced the compressive strength of ECC composites from 77.6 MPa to 60.2 MPa, although this does not hinder its role as a constituent of high-strength concrete (60 MPa). However, compared with that of 2.56 % in reference ECC mixture, due to the EV addings, the strain capacity of ECC mixtures was increased up to 8.22 %. On the other hand, incorporating fine EV particles (0.15 mm, 0.42 mm, and 2 mm) was positive to the tensile strength of ECC mixtures with a 23 % improvement, while the addition of coarser EV (1–3 mm and 3–5 mm) led to an 8 % reduction. At microscale, the incorporation of EV reduced the critical flaw size and increased the flaw size, significantly increased the number of active flaws, as a result, more micro-cracks were initiated, and thus greatly improving ductility of ECC.

Fast fracture in toughened glass when impacted randomly by Ice

Modelling the triggering of fracture at a pre-existing flaw is an evolving method of predicting ultimate failure in glass. This fracture mechanics approach of modelling has been shown to give more reliable predictions than a calibrated probabilistic distribution model (as is commonly adopted) when dealing with hail impact which is highly transient in nature. The dynamic stress intensity factor controlling fast crack growth is sensitive to the complex stress state surrounding the critical flaw. Finite element simulations of localised stresses in 3D could incur high computation cost which is compounded by the need to repeat computations until convergence and to simulate multiple strikes in emulating a storm scenario. In this study, closed-form expressions were developed to waive away the need of any simulations. With hail impact, boundary conditions of the glass panel need not be factored into the modelling, as the highly transient stresses are wave controlled. Input parameters are the thickness and level of prestress in glass; offset of position of strike from the known crack and its depth; and the size, velocity, and temperature of the ice impactor. Results from 40 test scenarios involving 5 offset distances, 3 crack depths, 2 glass thicknesses, and 2 sizes of ice were used to validate the prediction, and to reveal the sensitivity of the outcome of the impact to changes in the impact position relative to the known crack.

The paradox of growing technical capacities with low global governance: a review of Voluntary National Reviews’ SDG health-related indicators

BackgroundThis study delves into the States’ accountability for health-related Sustainable Development Goal (SDG) indicators from 2016 to 2020. An analysis of Voluntary National Reviews (VNR) is employed as an instrument to scrutinize the alignment of States’ indicators with the global indicator framework, shedding light on global health governance within the context of the 2030 Agenda and States’ strategic prioritization. A curation of 60 health-related indicators from 195 VNRs, produced during the aforementioned period, is organized into thematic groups.ResultsOur results highlight a concerning discrepancy in the reporting frequency of various health-related themes. The findings reveal a paradoxical coexistence characterized by the concurrent strengthening and diminution of the global health governance articulated in the Agenda’s global health governance. This manifests in the increased utilization and consistency of health-related indicators over the study years, coupled with an emphasis on infectious diseases and child and maternal health indicators. Conversely, a discernible governance decline is evidenced by the inadequate representation of health-related indicators in VNRs, notably within the domains of universal health coverage and health system indicators. Furthermore, High-Income States exhibit diminished accountability.ConclusionsThe VNRs unveil a paradox wherein burgeoning technical capacity coexists with governance deficits, a phenomenon attributable to both statistical capabilities and political preferences. The prevalent use of proxy indicators in VNRs oversimplifies the presentation of official indicators, thereby compromising the aspirational goal of pioneering statistical innovations for measuring intricate issues in the SDGs. In light of our conceptualization of the 2030 Agenda’s global health as a regime complex governance, we advocate for comprehensive investigations into each health regime cluster. This approach aims to unravel disputes, discern patterns, and elucidate States’ preferences concerning specific thematic areas. Functioning as an accountability mechanism for the Agenda’s governance, VNRs underscore States’ adaptability and short-term learning capabilities, offering valuable insights for identifying harmful goal prioritization. The discretionary nature of indicator selection by States in the VNRs, enabled by the Agenda’s proposition of a contextual adaptation of the SDGs and a blind eye to the guideline’s request to review all SDG indicators, highlights a critical flaw in the VNR as an accountability mechanism.

Investigation of Variability of Flaw Strength Distributions on Brittle SiC Ceramic

The present paper investigates flaw strength distributions established using various flexural tests on batches of SiC bar test specimens, namely four-point bending as well as three-point bending tests with different span lengths. Flaw strength is provided by the elemental stress operating on the critical flaw at the fracture of a test specimen. Fracture-inducing flaws and their locations are identified using fractography. A single population of pores was found to dominate the fracture. The construction of diagrams of p-quantile vs. elemental strengths was aimed at assessing the Gaussian nature of flaw strengths. Then, empirical cumulative distributions of strengths were constructed using the normal distribution function. The Weibull distributions of strengths are then compared to the normal reference distributions. The parameters of the Weibull cumulative probability distributions are estimated using maximum likelihood and moment methods. The cumulative distributions of flexural strengths for the different bending tests are predicted from the flaw strength density function using the elemental strength model, and from the cumulative distribution of flexural strength using the Weibull function. Flaw strength distributions that include the weaker flaws that are potentially present in larger test pieces are extrapolated using the p-quantile diagrams. Implications are discussed regarding the pertinence of an intrinsically representative flaw strength distribution, considering failure predictions. Finally, the influence of the characteristics of fracture-inducing flaw populations expressed in terms of flaw strength interval, size, dispersion, heterogeneity, and reproducibility with volume change is examined.

Chinese Spelling Correction as Rephrasing Language Model

This paper studies Chinese Spelling Correction (CSC), which aims to detect and correct potential spelling errors in a given sentence. Current state-of-the-art methods regard CSC as a sequence tagging task and fine-tune BERT-based models on sentence pairs. However, we note a critical flaw in the process of tagging one character to another, that the correction is excessively conditioned on the error. This is opposite from human mindset, where individuals rephrase the complete sentence based on its semantics, rather than solely on the error patterns memorized before. Such a counter-intuitive learning process results in the bottleneck of generalizability and transferability of machine spelling correction. To address this, we propose Rephrasing Language Modeling (ReLM), where the model is trained to rephrase the entire sentence by infilling additional slots, instead of character-to-character tagging. This novel training paradigm achieves the new state-of-theart results across fine-tuned and zero-shot CSC benchmarks, outperforming previous counterparts by a large margin. Our method also learns transferable language representation when CSC is jointly trained with other tasks.

On Efficient Parallel Secure Outsourcing of Modular Exponentiation to Cloud for IoT Applications

Modular exponentiation is crucial for secure data exchange in cryptography, especially for resource-constrained Internet of Things (IoT) devices. These devices often rely on third-party servers to handle computationally intensive tasks like modular exponentiation. However, existing outsourcing solutions for the RSA algorithm may have security vulnerabilities. This work identifies a critical flaw in a recent outsourcing protocol for RSA proposed by Hu et al. We demonstrate how this flaw compromises the security of the entire RSA system. Subsequently, we propose a robust solution that strengthens the RSA algorithm and mitigates the identified vulnerability. Furthermore, our solution remains resilient against existing lattice-based attacks. The proposed fix offers a more secure and efficient way for IoT devices to leverage the power of third-party servers while maintaining data integrity and confidentiality. An extensive performance evaluation confirms that our solution offers comparable efficiency while significantly enhancing security compared to existing approaches.

Exploring the geomorphological adequacy of the landslide susceptibility maps: A test for different types of landslides in the Bidente river basin (northern Italy)

Landslide susceptibility modelling is a crucial tool for implementing effective strategies in landslide risk mitigation. A plethora of statistical methods is available for generating accurate prediction images; however, the reliability of these models in terms of geomorphological adequacy is often overlooked by scholars. This critical flaw may result in concealed prediction errors, undermining the trustworthiness of the obtained maps. A key aspect of evaluating the geomorphological soundness of these models lies in factor analysis, specifically considering the correlation of explanatory variables with the final susceptibility score rather than solely focusing on their impact on model accuracy.This study delves into research conducted in the Bidente river basin (Italy) that analyes results obtained from slide, flow, and complex susceptibility models using Weight of Evidence (WoE) and Multivariate Adaptive Regression Splines (MARS) statistical methods. The research critically examines each factor class's role in defining susceptibility scores for different landslide typologies. The comparison between susceptibility maps generated by WoE and MARS for each typology (slide = 0.78; flow = 0.85; complex: 0.79) (slide = 0.78; flow = 0.85; complex: 0.79)reveals good to excellent prediction skill, with MARS demonstrating a 5 % higher performance index.The study emphasises the importance of spatial relationships between variables and landslide occurrences, highlighting that individual classes of variables influence the final susceptibility score based on their combined role with other predictor classes. In particular, in this study, results highlight that lithotecnical and landform classification classes delimit the landslide domain, while topographic attributes (steepness, curvatures, SPI and TWI) modulate the score inside. The proposed approach offers insights into investigating the geomorphological adequacy of landslide prediction images, emphasising the significance of factor analysis in evaluating model reliability and uncovering potential errors in susceptibility maps.

The development of the analytical philosophy of language from the problem of meaning to the theory of speech acts

The subject of the study is the development of the analytical philosophy of language in the twentieth century from the problem of meaning, which was central to the logic of G. Frege, in logical positivism and in the philosophy of B. Russell, to the theory of speech acts, that is, the development from semantics to pragmatics. The main attention is focused on such problems as the problem of the essence of language, the problem of meaning and reference, the nature of communication, and the theory of speech acts. The purpose of the study is to identify the features of the concepts of meaning in different representatives of analytical philosophy. A special place is given in this context to the ideas of L. Wittgenstein and H. Putnam's. It is also important to find out the reasons for the transition of analytical philosophy to communication problems. The specific features of the concepts of speech acts by such thinkers as D. Austin and D. Searle are also considered. The article uses such research methods as historical and philosophical analysis, socio-critical, as well as comparative methods. The novelty of the research lies in identifying how philosophers followed the path of updating and deepening the problem of meaning and reference, as well as what the specifics of each solution are. The changes that took place in the philosophy of language in the twentieth century, introduced, first of all, by L. Wittgenstein during the "linguistic turn", are considered. Significant innovations introduced into the descriptive-analytical linguistic theory of speech acts related to the names of D. Austin and D. Searle are also shown. Austin's characterized and classified speech acts, D. Searle's combined the problem of speech communication with the problem of intentionality, as a fundamental ability of human consciousness. A critical flaw in the theory of speech acts is pointed out: in fact, it does not explain the nature of dialogue, since it presents a variety of monologues.

An Inexpensive Reflected Darkfield Epi-Illuminator for a Standard Polarized Light Microscope

The analysis of environmental particles often requires reflected or epi-darkfield illumination. For example, an opaque spherical particle might be a cenosphere from a diesel engine, a fungal spore, a toner sphere, insect frass, a paint sphere (of any color), flyash, or a magnetite sphere, just to name a few possibilities. Reflected darkfield illumination and the ability to quickly change the type of illumination without moving the slide removes the uncertainty. The assessment of combustion residues in environments exposed to smoke from a fire has been plagued by the assumption that discovery of opaque particles equates to discovery of combustion residue. For the microscopist, the absence of immediately available reflected darkfield illumination and the inability to change the type of illumination quickly without moving the slide is a critical flaw in the analysis. There is a relatively inexpensive solution to the first problem, i.e., a darkfield epi-illuminator, using LED technology, designed to fit on a standard polarized light microscope (PLM) objective.

Evaluating the mechanical integrity and reliability of multi-channelled flat-sheet ceramic membranes for filtration applications

Ceramic membranes represent an emergent filtration technology that is receiving increasing research attention, particularly concerning their filtration behaviour (i.e., permeability, selectivity, and fouling) and industrial scalability. Given the inherent brittleness of ceramic materials, mechanical properties of ceramic membranes, especially those related to fracture, are also important pieces of information although nonetheless rarely evaluated. Therefore, a methodological approach for assessing the mechanical integrity and reliability of multi-channelled flat-sheet ceramic membranes is presented here. Specifically, a flat-sheet SiC ceramic membrane designed for submerged outside-inside vacuum-driven filtration was subjected to four-point bending, tensile, and compressive tests, and the experimentally measured failure loads were converted to failure stresses and analysed by Weibull diagrams. It was found that the ceramic membrane is ∼1.4 times stronger and ∼2.9 times less reliable in compression than in bending, and ∼3.3 times stronger and ∼5.4 times more reliable in bending than in tension. These differences in mechanical integrity and reliability are rationalized by considering the fracture modes (i.e., modes I or II) and critical flaw populations (i.e., flaws of the membrane layer or support) responsible for failure. Finally, relevant implications for ceramic “membranologists” interested in mechanical characterisation are discussed.

Buen Vivir, subjective poverty, and school conditions in 2017 Ecuador

AbstractIn May 2017 in Ecuador, the government of Rafael Correa handed over the presidency after 10 years and several mandates. His administration established the redefinition of the constitutional bases: the buen vivir cultural development and policy approach with a new transformative educational policy that sought to contribute to inclusion, overcoming inequalities, and poverty. His government benefited from high oil and commodity prices and broad popular support. This research has set out to review the results of the official national survey ENEMDU completed in December 2017. With a descriptive, bivariate, and multidimensional quantitative data analysis, we sought to shed light on the correlations between subjective poverty associated with buen vivir, school conditions, and ICT access and use of the school population in 2017. Results indicate a critical flaw in the buen vivir policies that failed to achieve their most valued and declared objective with indigenous and rural populations.

Synergistic effect of ozone and non-oxidizing bacteriostatic agent on biofouling control of reverse osmosis membranes

Biofouling was the critical flaw of the reverse osmosis (RO) process. Both strong oxidizing and non-oxidizing bacteriostatic agents had obvious defects facing this problem. This study firstly compared the single and synergistic effect of a strong oxidizing agent (ozone) and a commercial non-oxidizing bacteriostatic agent (FR110) on RO membrane fouling control of reclaimed water, to find a more high-efficiency and practical approach. Consequently, the synergistic application of ozone and FR110 at low dosages effectively reduced the fouling of the RO membranes (18% normalized flux alleviation than the control group). Further analysis suggested that FR110 could induce a thinner fouling layer, while ozone pretreatment could lead to a loose fouling layer. The bacterial community analyses suggested that the relative abundance of biofouling-related genera was the key reason causing fouling differences. Phenotypic prediction confirmed the advantages of the synergetic application of FR110 and O3 in reducing the biofilm-forming capacity. Pure-strain experiments showed the synergetic application of FR110 and O3 could inhibit the overgrowth and secretion of certain biofilm-forming strains, such as Pseudomonas aeruginosa PAO1. In summary, synergistic disinfection was a promising way to regulate the bacterial community structure and biofilm-forming potentials, hoping for high-efficiency biofouling control in the RO system.

Autonomous bonobo optimization algorithm for power allocation in wireless networks

Bonobo optimizer (BO) is a recent metaheuristic algorithm inspired by the social behavior of bonobos. BO maintains a robust search strategy based on two distinct phases that involve interesting mechanisms, such as the fission–fusion method for selection and an efficient process for producing new candidate solutions. Despite its remarkable capacity, BO presents a critical flaw that corresponds to an inappropriate balance between exploration and exploitation. Under such conditions, suboptimal or even poor solutions can be obtained. This paper proposes a modified BO algorithm in which the trajectory of each search agent is modified dynamically through the adaptation of the main parameters of the algorithm. With this new mechanism, the algorithm allows for the exploration and exploitation of different regions of the solution space and determines the global optimum in a faster manner. The performance of the proposed algorithm is evaluated by considering two scenarios. One is the optimization of 23 benchmark functions and the second is the problem of power allocation in wireless networks. The results show that the proposed scheme enhances the performance of the basic BO method by increasing the robustness and providing a better solution quality.

Interfacial fracture behavior and adhesive strength in tensile and shear loading of SiC-PyC-SiC composites by micro-scale specimens

Micromechanical tests were performed to understand the local fracture behavior and adhesive strength of a fiber-reinforced ceramic matrix composite (silicon carbide fiber reinforced silicon carbide matrix with the pyrolytic interphase in between, SiCfiber/PyC/SiCmatrix) and to determine the mode-dependent interfacial fracture toughness. A combined approach of pico-second laser ablation and focused ion beam milling was used to fabricate notched and unnotched micro-cantilever and in-plane micro-shear specimens for mode I and II testing. Due to the complexity of the sandwich system, finite element simulations were implemented, which took into account the elastic heterogeneity, the influence of PyC thickness, Young's modulus and beam thickness. This allowed us to obtain mode-specific geometry functions and to increase the accuracy of the obtained stress intensity factor. In all cases, a failure at the SiCfiber/PyC interface was observed. While straight through notched specimens exhibit a systematic overestimation of fracture toughness due to the less accurate alignment of notch root and PyC layer, curved notched specimens show a very low interfacial fracture toughness of 0.24 ± 0.02 MPa√m and 0.17 ± 0.06 MPa√m in mode I and mode II, respectively. Combined with tests on unnotched specimens, a critical flaw size for the present microstructure of the PyC phase of ca. 21 nm was identified. The data underlines the important role of the PyC interlayer in damage resistant ceramic composites and the developed methodology, which can be used for systematic studies of their properties as a function of process, geometry, and boundary conditions.

Blending hydrogen in existing natural gas pipelines: Integrity consequences from a fitness for service perspective

Blending hydrogen in existing natural gas pipelines compromises steel integrity because it increases fatigue crack growth, promotes subcritical cracking and decreases fracture toughness. In this regard, several laboratories reported that the fracture toughness measured in a hydrogen containing gaseous atmosphere, KIH, can be 50% or less than KIC, the fracture toughness measured in air. From a pipeline integrity perspective, fracture mechanics predicts that injecting hydrogen in a natural gas pipeline decreases the failure pressure and the size of the critical flaw at a given pressure level. For a pipeline with a given flaw size, as shown in this work, the effect of Hydrogen Embrittlement (HE) in the predicted failure pressure is largest when a failure occurs by a brittle fracture. The HE effect on failure pressure diminishes with a decreasing crack size or increasing fracture toughness. The safety margin after a successful hydrostatic test is reduced and therefore the time between hydrotests should be decreased. In this work, all those effects were quantified using a crack assessment methodology (level 2, API 579-ASME FFS) considering literature values for KIH and KIC reported for an API 5L X52 pipeline steel. To characterize different scenarios, various crack sizes were assumed, including a small crack with a size close to the detection limit of current in-line inspection techniques and a larger crack that represents the largest crack size that could survive a hydrotest to 100% of the steel Specified Minimum Yield Strength (SMYS). The implications of a smaller failure pressure and smaller critical crack size on pipeline integrity are discussed in this paper.

Understanding the mechanical integrity of Zircaloy cladding with various radial and circumferential hydride morphologies via image analysis

The mechanical integrity of hydride reoriented reacor-grade Zr-Nb alloy cladding was investigated for various amounts of charged hydrogen and hydride morphologies. The specimens were charged with hydrogen from 0 to 1200 wppm. Hydride reorientation treatment was conducted by applying constant internal pressure (7.5 - 18.5 MPa) to hydrogen-charged cladding tubes subjected to cooling from 400 °C to result in various radial and circumferential hydride fractions. The hydride morphology was examined using optical microscopy. The Radial Hydride Fraction (RHF), Radial Hydride Continuous Path (RHCP), and maximum radial hydride length were obtained using the image analysis software PROPHET. Strain Energy Density (SED) of Zircaloy cladding with various hydride morphologies and concentrations were measured by Ring Compression Tests (RCTs) and analyzed with the results of image analysis. It was found that the RHF gives a strong correlation with the strength of Zircaloy cladding for RHF over 5%. Below 5% of RHF, SED is inversely correlated with the amount of hydrogen. SED exponentially decreased with the maximum hydride length. The fracture mechanics analysis revealed that this behavior supports that radial hydride serves as a critical flaw of hydrided Zircaloy under RCT. And the experimental result demonstrated that circumferential hydrides slightly increase the SED of Zircaloy affected by extensive radial hydride embrittlement by decreasing radial hydride connectivity.

Unveiling deformation twin nucleation and growth mechanisms in BCC transition metals and alloys

Twinning provides critical stress-relieving and flaw tolerance in body-centred cubic (BCC) transition metals (TMs) when dislocation plasticity is suppressed. Twin nucleation and growth mechanisms have been studied for over half a century without a consensus. Here, we use a reduced-constraint slip method to unveil the path to twin nucleation, growth and associated energy barriers in the entire BCC TM family. Twinning is surprisingly but essentially controlled by a normalized energy difference η between the hexagonal close-packed (HCP) and BCC structures in elemental TMs, and can be effectively tuned and quantitatively predicted by first-principles calculations in TM alloys. Fracture mechanics theory with η-based barriers enables predictions of critical solute concentrations to activate twinning and reverse ductile-to-brittle transitions in BCC TMs, as demonstrated in WRe alloys. The computational approach provides a unified and quantitative method to predict twinning and a practical tool for rapid screening of alloy compositions ensuring ductile behaviour.

Transparency and Information Asymmetry in Financial Markets

Abstract The paper deals with the application of aspects of behavioral finance in the context of investor protection reflected in EU financial regulation which puts an emphasis on disclosure requirements. Traditionally, financial regulatory frameworks maintain a status que assumption of “rational investors” contained within neoclassical economic theory, however reoccurring financial incidents have exposed a critical flaw in this understanding, consequently requiring a further examination of behavioral aspects within the context of financial regulation. It remains ambiguous how regulators may best use findings from behavioral finance to address flaws in their investor protection tools. Furthermore, neither expanding disclosure obligations nor enforcing a tougher paternalistic approach may suffice in their intent.

Prediction of Fatigue Crack Initiation under Variable Amplitude Loading: Literature Review

Metallic materials are widely employed in engineering constructions, and one of the most common failure mechanisms in metals is fatigue failure. Even though metal fatigue has been studied for almost 160 years, many problems remain unsolved. Fatigue in metal occurs when the metallic material is subjected to varying loads, resulting in failure due to damage accumulation. The fatigue process consists of a buildup of damage that leads to crack initiation, followed by a period of crack growth until the critical flaw size is reached. The sum of a start phase and a propagation phase represents the total life. To better understand the fatigue phenomenon at its different stages and predict the fatigue life, various types of prediction models have been developed and reported in the literature. This paper reviewed the different models that include microstructure scale parameters that can be used to predict how fatigue cracks start under variable amplitude loading, including the Modified Tanaka-Mura Model, Acoustic Second Harmonic Generation, and the Probability of Crack Initiation on Defects. For perfect life prediction under variable amplitude loading, a stress-based approach, a strain-based approach, and a continuum damage mechanics approach are reviewed. The purpose of this paper is to get overview of the current state of approaches to the life prediction of fatigue crack initiation with variable amplitude. Finally, gaps in knowledge about the prediction of fatigue crack initiation under variable loading at high temperatures are pointed out.