Safe Domain Research Articles

The Effect of α‐Al(MnCr)Si Dispersoids on Activation Energy and Workability of Al‐Mg‐Si‐Cu Alloys during Hot Deformation

The hot deformation behaviors of homogenized direct‐chill (DC) casting 6061 aluminum alloys and Mn/Cr‐containing aluminum alloys denoted as WQ1 were studied systematically by uniaxial compression tests at various deformation temperatures and strain rates. Hot deformation behavior of WQ1 alloy was remarkably changed compared to that of 6061 alloy with the presence of α‐Al(MnCr)Si dispersoids. The hyperbolic‐sine constitutive equation was employed to determine the materials constants and activation energies of both studied alloys. The evolution of the activation energies of two alloys was investigated on a revised Sellars’ constitutive equation. The processing maps and activation energy maps of both alloys were also constructed to reveal deformation stable domains and optimize deformation parameters, respectively. Under the influence of α dispersoids, WQ1 alloy presented a higher activation energy, around 40 kJ/mol greater than 6061 alloy’s at the same deformation conditions. Dynamic recrystallization (DRX) is main dynamic softening mechanism in safe processing domain of 6061 alloy, while dynamic recovery (DRV) was main dynamic softening mechanism in WQ1 alloy due to pinning effect of α‐Al(MnCr)Si dispersoids. α dispersoids can not only resist DRX but also increase power required for deformation of WQ1 alloy. The microstructure analysis revealed that the flow instability was attributed to the void formation and intermetallic cracking during hot deformation of both alloys.

Hunting Algorithm for Multi-AUV Based on Dynamic Prediction of Target Trajectory in 3D Underwater Environment

In the research of multi-robot systems, multi-AUV (multiple autonomous underwater vehicles) cooperative target hunting is a hot issue. In order to improve the target hunting efficiency of multi-AUV, a multi-AUV hunting algorithm based on dynamic prediction for the trajectory of the moving target is proposed in this article. Firstly, with moving of the target, sample points are updated dynamically to predict the possible position of a target in a short period time by using the fitting of a polynomial, and the safe domain of the moving target, which is a denied area for the hunting AUVs, is built to avoid the target’s escape when it detects AUVs. Secondly, the method of negotiation is adopted to allocate appropriate desired hunting points for each AUV. Finally, the AUVs arrive at desired hunting points rapidly through deep reinforcement learning (DRL) algorithm to achieve hunting the moving target. The simulations show that hunting AUVs can surround the moving target of which the trajectory is unknown rapidly and accurately by the algorithm in the 3D environment with complex obstacles and results obtained is satisfactory.

Elevated Temperature Compression Deformation Behavior of Commercial Pure Zr Combined with the Constitutive Equation and Processing Map

The compression deformation behavior of commercial pure zirconium at elevated temperature is systematically investigated at different conditions. The corresponding deformation mechanism of pure Zr is clarified for analyzed flow stress, work hardening rate, activation energy, and microstructure. A modified Arrhenius‐type equation is proposed for future numerical simulation, which shows a good relativity between the theoretical and experimental data. The apparent deformation activation energy is 209 kJ mol−1, indicating that a cross‐slip of dominant dislocation mechanism controls the deformation process. Established based on the dynamic material model (DDM), processing maps indicate that the optimum processing conditions are 700–900 °C at 0.1–0.14 s−1 and 905–950 °C at 3–20 s−1 with the high efficiency of power dissipation. Microstructure examination reveals that the main restoration mechanism in the safe domain is related to dynamic recrystallization and the unstable regional microstructure results in the flow localization and cracking behavior.

AK-ARBIS: An improved AK-MCS based on the adaptive radial-based importance sampling for small failure probability

The pivotal problem in reliability analysis is how to use a smaller number of model evaluations to get more accurate failure probabilities. To achieve this aim, an iterative method based on the Monte Carlo simulation and the adaptive Kriging (AK) model (abbreviated as AK-MCS) has been proposed in 2011 by Echard et al. But for small failure probability, the number of the candidate points is extremely large for convergent solution. These points need to be evaluated by the current Kriging model to select the best next sample for updating the Kriging model in AK-MCS method, and the large candidate points will make the adaptive updating process of Kriging model much more time-consuming. Therefore, to improve the applicability of the AK-MCS method for small failure probability, the adaptive radial-based importance sampling (ARBIS) is employed to reduce the number of candidate points in the AK-MCS method, and an ARBIS combined with AK model method (abbreviated as AK-ARBIS) is proposed. The idea of the ARBIS is adaptively to find the optimal β-sphere, i.e., the largest sphere of the safe domain, and then samples inside the optimal β-sphere is directly recognized as safety and do not need to call the true limit state function to judge their states (safe or failed). During the adaptive process of finding the optimal β-sphere, the Kriging model is ceaselessly updated layer after layer based on the U learning scheme in each sampling pool which only contains the samples between the current spherical rings. The updating process of Kriging model stops until the optimal β-sphere is adaptively found and the convergent condition is satisfied. By finding the optimal β-sphere, the total number of candidate samples is reduced which only includes the samples outside the optimal β-sphere. Besides, the whole candidate sampling pool is partitioned into several sub-candidate sampling pool sequentially. The proposed method not only inherits the advantage of the AK-MCS but also reduces the reliability analysis time of the AK-MCS from two aspects. One is the size reduction of the candidate sampling pool, the other is the reduction of the actual limit state function evaluations because the sampling points locating inside the adaptively searched optimal β-sphere do not need to participate in the training process. By analyzing a highly nonlinear numerical case, a non-linear oscillator system, a simplified wing box structural model, an aero-engine turbine disk and a planar ten-bar structure, the effectiveness and the accuracy of the proposed AK-ARBIS method for estimating the small failure probability are verified.

Design of Streamline Dies for Drawing Driven by Fracture

This paper presents an efficient analytical method for design of streamline dies driven by fracture. The method is based on Bernoulli’s theorem relating pressure and velocity along any streamline extended to ideal flows in plasticity. The Cockroft-Latham criterion is adopted to predict the initiation of ductile fracture. In order to apply the method developed, it is not necessary to know the solution to the boundary value problem of plasticity. The final result is a simple relation between geometric parameters of the process and the constitutive parameter involved in the fracture criterion. Since the latter is supposed to be known for a given material, the relation determines a safe domain for drawing without fracture.

Damage tolerance reliability analysis combining Kriging regression and support vector machine classification

Damage tolerance analysis associates a Fracture Mechanical model with the Failure Assessment Diagram to define the state of a space engine component. The reliability analysis treats the variability of numerical models assessing the probability of failure within Linear Elastic Fracture Mechanics (LEFM) hypotheses. However, these models, while providing quantitative information in the safe domain, give only qualitative information for failed components. This work proposes an original methodology to combine Kriging regression and the Support Vector Machine classification along with transition criteria between both approaches. To accurately describe the limit state, we define a specific enrichment strategy. The efficiency of the proposed methodology is illustrated on reference test cases.

Time-dependent reliability analysis of RC beams shear and flexural strengthened with CFRP subjected to harsh environmental deteriorations

Time-dependent reliability analysis of existing reinforced concrete (RC) beams strengthened with externally bonded carbon fiber reinforced polymer (CFRP) wraps is conducted. Corrosion effect in terms of remaining cross sectional area of steel reinforcement is modelled as a non-stationary Gaussian process and the probability of failure is estimated as a solution to the first passage probability from the safe domain. Moreover, flexural and shear limit states are modeled in a series system formulation. It was found that the steel stirrup ratio strongly influenced the reliability of beams subject to harsh environments and in some cases beam may experience brittle fracture during its service life. Furthermore, it is found that the upper bound of the system probability of failure is significantly higher than its corresponding individual limit states due to correlation between flexural and shear failure modes.

Deformation response and microstructural evolution of as-cast Mg alloys AM30 and AM50 during hot compression

AbstractThe present study deals with the hot deformation behaviour of as-cast Mg alloys AM30 and AM50. The alloys have been investigated for mechanical and microstructural evolution in the temperature range 423–623 K and strain rate range of 10−3–10 s−1. A safe processing domain is identified for as-cast AM30 and AM50 alloys from the strain rate sensitivity map. The deformed microstructure of both AM30 and AM50 alloy reveals the occurrence of dynamic recovery and recrystallization for temperature above 523 K. Although the two alloys show similar behaviour in the hot deformation regime, they deviate at 623 K and low strain rate, where AM30 is fully recrystallized while AM50 attains necklace structure after deformation. This is likely due to the difference in the rate of dynamic recovery in the two alloys owing to the difference in Al concentration. Continuous dynamic recrystallization was the recrystallization mechanism active in the processing regime as deduced from the EBSD investigation.

Shakedown of porous material with Drucker-Prager dilatant matrix under general cyclic loadings

This paper is concerned with the shakedown limit states of porous ductile materials with Drucker-Prager matrix under cyclically repeated loads. Using the hollow sphere model and Melan’s shakedown theorem based on time-independent residual stress fields, a macroscopic fatigue criterion is derived for the general conditions of cyclic loads. First, the case of the hollow sphere subjected to pure hydrostatic loading is studied and the limit states of collapse by fatigue or by development of mechanism are derived. Then, the general case involving shear effects with any arbitrary cyclic load fluctuations ranging from the pulsating load to the alternating one is considered. The key idea is in two steps: (i) the choice of appropriate trial stress and trial residual stress fields and (ii) then maximizing the size of the load domain in the spirit of the standard lower shakedown theorem. The new macroscopic shakedown criterion depends on the porosity, the friction angle, Poisson’s ratio, the two stress invariants of the effective stress tensor and the sign of the third one. Together with the limit analysis-based yield criterion corresponding to the sudden collapse by development of a mechanism at the first cycle, it defines the safety domain of porous materials subjected to cyclic load processes. Interestingly, it is found that the safe domain is little sensitive to variations of the friction angle, however, it is considerably reduced compared to the one under monotonic loads obtained by limit analysis. Finally, a comparative study between the analytical results and numerical predictions performed by micromechanics-based finite element simulations is conducted for different porosities and friction angles.

Procedures for sensor nodes operation in the secured domain

SummaryCurrently, the networks of mobile sensor nodes, which are IoT components, are increasingly a source of data for building situational awareness. Such networks can be a source of data for critical infrastructure systems if, in addition to the timeliness (freshness) of the data, it will also be possible to ensure the reliability of these data. Such requirements are met by a secure domain of sensor nodes, in which all sensor nodes are authenticated, sensitive data is stored in protected resources of sensor nodes, and data exchange in the domain and outside the domain is cryptographically protected. This paper presents the concept of a safe domain of sensor nodes for IoT and describes the data structures necessary to ensure security in the domain and the way of protecting the resources of each node. Particular attention was paid to the procedure of preparing a sensor node for work in a secured domain of sensor nodes.

Looking at the collapse modes of circular and pointed masonry arches through the lens of Durand-Claye’s stability area method

This paper addresses the problem of characterizing the mechanical behaviour and collapse of symmetric circular and pointed masonry arches subject to their own weight. The influence on the arch’s collapse features of its shape and thickness, as well as the friction between the arch’s voussoirs, is analysed. The safety level of arches is then investigated by suitably reworking in semi-analytical form the graphical method of the stability area proposed by the renowned nineteenth century French scholar, Durand-Claye. According to Durand-Claye’s method, the arch is safe if along any given joint both the bending moment and shear force do not exceed the values determined by some given limit condition. The equilibrium conditions corresponding to all possible symmetric collapse modes are individuated. As was expected, pointed and circular arches exhibit different collapse behaviours, in terms of both collapse modes and safe domain. The limit values of arch thickness and friction coefficient are determined and the results obtained consistently compared with those published by Michon in 1857.

Feature extraction for phenotyping from semantic and knowledge resources.

Phenotyping algorithms can efficiently and accurately identify patients with a specific disease phenotype and construct electronic health records (EHR)-based cohorts for subsequent clinical or genomic studies. Previous studies have introduced unsupervised EHR-based feature selection methods that yielded algorithms with high accuracy. However, those selection methods still require expert intervention to tweak the parameter settings according to the EHR data distribution for each phenotype. To further accelerate the development of phenotyping algorithms, we propose a fully automated and robust unsupervised feature selection method that leverages only publicly available medical knowledge sources, instead of EHR data. SEmantics-Driven Feature Extraction (SEDFE) collects medical concepts from online knowledge sources as candidate features and gives them vector-form distributional semantic representations derived with neural word embedding and the Unified Medical Language System Metathesaurus. A number of features that are semantically closest and that sufficiently characterize the target phenotype are determined by a linear decomposition criterion and are selected for the final classification algorithm. SEDFE was compared with the EHR-based SAFE algorithm and domain experts on feature selection for the classification of five phenotypes including coronary artery disease, rheumatoid arthritis, Crohn's disease, ulcerative colitis, and pediatric pulmonary arterial hypertension using both supervised and unsupervised approaches. Algorithms yielded by SEDFE achieved comparable accuracy to those yielded by SAFE and expert-curated features. SEDFE is also robust to the input semantic vectors. SEDFE attains satisfying performance in unsupervised feature selection for EHR phenotyping. Both fully automated and EHR-independent, this method promises efficiency and accuracy in developing algorithms for high-throughput phenotyping.

Reliability Assessment and Optimization of Double Random Vibration Systems based on PDEM

The dynamic responses analysis method of structure with random parameters under stochastic seismic loads is proposed. The generalized probability density evolution equation for compound stochastic process is solved by the finite difference method. Then, for the first passage criterion, the dynamic reliability is analysed by establishing the one-dimensional integral in safe domain and the absorbing boundary condition. A new optimization method is coming up combining improved genetic algorithm and PDEM. Taking the parameters optimization of a three-story floor-shear frame structure with TMD under random seismic loads as an example, the correctness of the proposed method is verified by comparing interlayer displacement response and dynamic reliability.

Detailed mechanisms of hydrogen charging and hydrogen stress cracking of steel in liquid ammonia storage

The available polarisation curves of the literature are analysed in view of the theoretical analysis of the corrosive medium in Part I (J.-L. Crolet, Matériaux & Techniques107, 401, 2019) and the new views on passivation and hydrogen charging. The accurate electrochemical conditions of the respective cathodic and “anodic” hydrogen charging are thus defined, or more exactly the paradox of a protonic cathodic reaction only running at high potential. Similarly in the available exposure test results, the locus of the ternary redox equilibrium between ammonia and its two decisive contaminants, oxygen and water, separates contaminated ammonia into two domains, on the one hand, a safe domain where the undersaturated oxygen cannot act as an oxidiser, hence no anodic HSC at the free corrosion potential, and on the other hand, a dangerous domain where oxygen is supersaturated, hence oxidising conditions, steel passivation, high potentials, anodic charging and anodic HSC. Likewise, all the known features of this environmental cracking are also explained, with no exception nor contradiction, including the differences between the liquid and vapour phases. An experimental method is also proposed to directly check the occurrence of anodic charging, and proposals are also made for at the same time improving safety and reducing operational or capital expenditures.

EBSD Study on Processing Domain Parameters of Oxide Dispersion Strengthened 18Cr Ferritic Steel

This paper presents the results of an experimental study aimed to identify hot working domains in oxide dispersion strengthened (ODS) 18Cr ferritic steel over a wide range of temperatures (1323-1473 K) and strain rates (0.01-10 s−1). The experimental data were obtained by uniaxial compression test using the Gleeble-1500D simulator in this range of temperature and strain rate. An inverse relationship with temperature and positive strain rate sensitivity associated with dynamic recovery and recrystallization, which is influenced by temperature and strain rate, was derived from the flow stress. Based on the processing map generated at 0.5 true strain, using rate dynamic material model (DMM) approach and the calculated instability parameter $$\left( {\xi \left( \acute{\epsilon} \right)} \right) > 0$$ , the optimum processing domain has been determined for this steel. The most favorable processing parameters are found in the temperature ranges of 1350-1450 K with a strain rate of 0.01 s−1 and 1473 K with a strain rate 0.1 s−1 with peak efficiency of 30 and 35%, respectively. The material flow behavior was studied using scanning electron microscopy (SEM)-based EBSD microstructural characterization. The steel subjected to 1323 K at high strain rate 10 s−1 in the low-efficiency workability region showed low aspect ratio as compared to the elongated bamboo-like initial microstructure; however, minimum strain rate (0.01 s−1) showing that localized slip/shearing is the key mechanism and fiber texture studied from the intensity distribution of inverse pole figure showed the presence of significant amount of θ-fibers. In contrast, dynamic recrystallization dominated at higher efficiency region in the safe domain of processing map and γ-fiber texture was evident in the specimen deformed at 1373 and 1473 K with strain rate of 0.01 and 0.1 s−1, respectively, which is responsible for the change in the initial 〈1 1 0〉//ED α-fiber texture.

Effect of annealing-temperature-assisted phase evolution on conductivity of solution combustion processed calcium vanadium oxide films

In this work, the effect of annealing temperature on the conductivity of solution-combustion-synthesized calcium vanadium oxide (CVO) films was studied. Conductivity was tailored by the appearance of the phases like \(\hbox {CaVO}_{3}\), \(\hbox {CaV}_{2}\hbox {O}_{5}\) and \(\hbox {Ca}_{2}\hbox {V}_{2}\hbox {O}_{7}\) as a function of annealing temperature; \(\hbox {CaVO}_{3}\) and \(\hbox {CaV}_{2}\hbox {O}_{5}\) are responsible for high conductivity, whereas \(\hbox {V}^{5+}\) presence in \(\hbox {Ca}_{2}\hbox {V}_{2}\hbox {O}_{7}\) contributes towards dielectric nature. Evolution of phases of CVO was identified through X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. A detailed conductivity measurement as a function of annealing temperature helps us to identify the decreasing trend of conductivity with increasing temperature up to \(400{^{\circ }}\hbox {C}\); beyond this it behaves like an insulator. There was a stable conductivity while aging the films in ambient for a few days. This study revealed safe application temperature domain of CVO, and a clear correlation of electrical conductivity with the in-depth structural–compositional–morphological study.

Mapping potential risks of long-term wastewater irrigation in alluvial soils, Egypt

In Egypt, wastewater has been used for irrigation in areas with fresh water scarcity; however, continuous applications may cause potential risks. Thus, the current study aims to map the spatial distribution of soil contamination and human risks of long-term wastewater irrigation due to the exposure of heavy metals. Soils from nine sites in Al-Qalyubia Governorate, Egypt, were sampled and analyzed. Wastewater irrigation resulted in a buildup of heavy metals in soils compared to Nile fresh water-irrigated soil. The pollution index (PI) showed the decreasing order of Cd > Zn > Ni > Cu > Co > Pb > Cr. The soils were out of the safe domain, as the integrated pollution index of Nemero’s (IPIN) exceeded the safe limit of 0.7. The enrichment factor (EF) exceeded 1.0, proving anthropogenic effects. The geo-accumulation index (Igeo) indicated high threats associated with Cd. The calculated hazard index (HI) indicated that humans exposed to such contaminated soils would have a potential health risk, particularly children. It is recommended to perform a treatment to the wastewater used in irrigation to avoid such threats.

Projectile motion without calculus

Projectile motion is a constant theme in introductory-physics courses. It is often used to illustrate the application of differential and integral calculus. While most of the problems used for this purpose, such as maximizing the range, are kept at a fairly elementary level, some, such as determining the safe domain, involve not so elementary techniques, which can hardly be assumed of the targeted audience. In the literature, several attempts have been undertaken to avoid calculus altogether and keep the exposition entirely within the realm of algebra and/or geometry. In this paper, we propose yet another non-calculus approach which uses the projectile’s travel times to shed new light on these problems and provide instructors with an alternate method to address them with their students.

Environmental contours based on inverse SORM

It is well known that the full long-term response analysis is recognized as the most accurate and reliable method for evaluation of the extreme response in the design of ships and marine structures. However, such a method is time consuming for large and complex systems. To improve efficiency, the environmental contour method (ECM) is frequently used to approximate the long-term extreme response. The ECM is based on an environmental contour, which is traditionally obtained by the inverse first order reliability method (IFORM) with the assumption that the failure surface in the U space is approximated as a tangent plane at the design point. However, such an approximation underestimates the true failure probability if the failure surface in the U space is a concave set, and then the corresponding environmental contour would not be conservative for possible designs. In this work, a more conservative ISORM (inverse second order reliability method) contour is proposed. In this method, a specific second-order surface is applied to approximate the failure surface at the design point, and then the failure domain in the U space would always be overestimated since the corresponding safe domain is approximated and underestimated as a sphere, regardless of the shapes of the failure surfaces. Therefore, the generated environmental contour can be always conservative for design purposes. The differences of the environmental contours generated by different methods, i.e., the traditional IFORM and the proposed ISORM, are illustrated by relevant examples, such as the wave statistics, wind wave statistics, and first-year ice ridge statistics.

The roles of long period stacking ordered structure and Zn solute in the hot deformation behavior of Mg-Gd-Zn alloys

In order to investigate the roles of long period stacking ordered (LPSO) structure and Zn solute in the hot deformation behavior of Mg-Gd-Zn alloys, the Mg-12Gd-1Zn-1Mn-0.5Zr alloy containing LPSO phase or Zn solute was hot compressed under various deformation conditions in comparison with the Zn-free Mg-12Gd-1Mn-0.5Zr alloy. The results showed that the Zn-containing alloys had stronger softening effects, larger peak stress and higher average activation energy than the Zn-free one within the safe deformation domain. Both LPSO phase and Zn solute in α-Mg matrix increased the efficiency of power dissipation, narrowed down the flow stability regions of processing map and impeded the dynamic recrystallization (DRX), especially when Zn solute was mainly in α-Mg matrix. Furthermore, the LPSO phase or Zn solute in α-Mg matrix promoted the dynamic precipitation. A few Mg5Gd particles can be observed in the Zn-free alloy, while a large number of stacking faults (SFs) and LPSO phase were precipitated in the Zn-containing alloys, and they were eventually transformed into Mg5Gd particles at low strain rate.