Zone Face Research Articles

A slip-line field model for independently characterizing shearing and ploughing effects in metal cutting processes

This study proposes a new slip-line field model to separately characterize the shearing-included cutting process and the pure-plough cutting process. The shear plane and dead metal zone in relation to the shearing effect are modelled by straight slip-lines, while the deformation area in relation to the ploughing effect is treated to have straight boundaries. The boundaries of the dead metal zone and ploughing area are determined by considering tool-workpiece frictional behaviours. The stresses acting on the boundaries of the ploughing area, dead metal zone and shear plane are separately modelled considering the thermal–mechanical coupling effect. Based on the minimum energy principle, the shear angle is originally modelled by following the dynamic requirement of chip flow to balance the forces acting on dead metal zone, shear plane and rake face. By iteratively solving the coupling effect among the temperature, stress and shear angle, the total cutting forces are acquired by integration operation through straight slip-lines. Experiment results and finite element simulations validate the proposed slip-line field model in predicting the shear angle and cutting forces for both micro and regular milling processes.

Factors Influencing the Efficiency of Construction Projects in Jimma Zone, Jimma, Oromia, Ethiopia

The construction sector plays a crucial role in the Ethiopian economy, making a substantial contribution to economic growth. However, various challenges have been identified as impacting the performance and growth of the Ethiopian construction industry. Projects in the Jimma Zone face numerous issues related to cost, time, and quality. This study aimed to evaluate how factors like resource management, stakeholder management, procurement management, and quality management influence project performance in the Jimma Zone. Data was collected through a structured questionnaire distributed to employees of Jimma Zone Employers and Contractors. A total of 62 questionnaires were distributed, with an 80.65% response rate, providing sufficient data for statistical analysis. Findings were presented using charts and tables. Quality management challenges included the absence of a quality management system and insufficient management commitment. Regression analysis indicated that resource and stakeholder management factors significantly influenced project cost and time performance, while quality management factors had a positive but not significant impact. Resource, stakeholder, and quality-related factors significantly influenced project quality performance, whereas procurement management factors did not have a significant impact. The study suggests that focusing on resource and stakeholder management could enhance project performance in the Jimma Zone.

Flyrock in surface mining - Limitations of current predictive models and a better alterative through modelling the aerodynamics of flyrock trajectory

Historical approaches to the problem of flyrock based on correlation studies and regression analysis, including artificial neural networks and similar techniques, are inherently incapable of addressing two core issues - root causes of flyrock and projection velocity. A further shortcoming of correlation techniques is that they give no information on the influence of rock size and shape on the flight distance. The scaled depth of burial model for crater blasting in the collar zone and bench face does not specifically address the question of flyrock velocity. A third approach, based on flight trajectory calculations, often neglects the very significant effects of air resistance on the trajectory. Some trajectory models incorporate air resistance but use an implausible fragment velocity model that cannot propel sizeable rocks to distances much beyond 150 m. Nonetheless, trajectory calculation incorporating the effects of air drag affords the most promising approach to the prediction of flyrock range. A unique and insightful feature of the proposed realistic flight modelling is that it collapses all suspected causes of flyrock, many of which are not well understood, to just a single parameter - the launch velocity. This indicates that the root causes of flyrock lie in the mechanisms of momentum transfer to broken rock and suggests new avenues of study.

Nathusius’ bats, Pipistrellus nathusii, bypass mating opportunities of their own species, but respond to foraging heterospecifics on migratory transit flights

In late summer, migratory bats of the temperate zone face the challenge of accomplishing two energy-demanding tasks almost at the same time: migration and mating. Both require information and involve search efforts, such as localizing prey or finding potential mates. In non-migrating bat species, playback studies showed that listening to vocalizations of other bats, both con-and heterospecifics, may help a recipient bat to find foraging patches and mating sites. However, we are still unaware of the degree to which migrating bats depend on con-or heterospecific vocalizations for identifying potential feeding or mating opportunities during nightly transit flights. Here, we investigated the vocal responses of Nathusius’ pipistrelle bats, Pipistrellus nathusii, to simulated feeding and courtship aggregations at a coastal migration corridor. We presented migrating bats either feeding buzzes or courtship calls of their own or a heterospecific migratory species, the common noctule, Nyctalus noctula. We expected that during migratory transit flights, simulated feeding opportunities would be particularly attractive to bats, as well as simulated mating opportunities which may indicate suitable roosts for a stopover. However, we found that when compared to the natural silence of both pre-and post-playback phases, bats called indifferently during the playback of conspecific feeding sounds, whereas P. nathusii echolocation call activity increased during simulated feeding of N. noctula. In contrast, the call activity of P. nathusii decreased during the playback of conspecific courtship calls, while no response could be detected when heterospecific call types were broadcasted. Our results suggest that while on migratory transits, P. nathusii circumnavigate conspecific mating aggregations, possibly to save time or to reduce the risks associated with social interactions where aggression due to territoriality might be expected. This avoidance behavior could be a result of optimization strategies by P. nathusii when performing long-distance migratory flights, and it could also explain the lack of a response to simulated conspecific feeding. However, the observed increase of activity in response to simulated feeding of N. noctula, suggests that P. nathusii individuals may be eavesdropping on other aerial hawking insectivorous species during migration, especially if these occupy a slightly different foraging niche.

Analysis of the Influence of Fault Fracture Zone on Mining Response Based on FDM-DEM Coupling

Fault slip will cause a change in mining stress at the longwall face, which will cause adverse effects. In this study, on the basis of Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) and Particle Flow Code in 3 Dimensions (PFC3D), the sliding of the fault fracture zone and its impact on the longwall working face were analyzed. The rock mass of the fault fracture zone with a certain thickness was constructed using rigid random model particles. The coupling between the wall element of PFC3D and the zone element of the continuous medium in the software was used to realize the transmission of force and displacement, and the interaction between the fault fracture zone and the working face was studied. The influence of the slip of different fault zone positions on the fault and working face was also explored using the method of externally disturbing the fracture zone of the fault. The numerical results showed that as the distance between the fault and the working face continued to decrease, the peak stress concentration in front of the longwall face first increased, then decreased, and gradually shifted to the vicinity of the fault zone. The stress mutation and fault slip occurred within a certain distance of the longwall face from the fault. When fault slip activation begins, the stress near the fault zone showed a sudden change of varying degrees with the advancement of the longwall face. This sudden change was caused by the influence of mining activities from the activation distance of the rock in the fault fracture zone and the rolling extrusion of the rock mass in the fracture zone. When the fault zone closer to the working face was disturbed, the influence on the fault zone and longwall face was greater. When the fault zone near the coal seam was disturbed, the rock mass and working face near the fault zone brought different degrees of dynamic responses, which were mostly instantaneous and had high frequency and amplitude. The results of this research could help in the mining of longwall mining affected by fault zones and have a certain guiding role in coal mining before crossing faults.

Critical Comparison of Phase-Field, Peridynamics, and Crack Band Model M7 in Light of Gap Test and Classical Fracture Tests

Abstract The recently conceived gap test and its simulation revealed that the fracture energy Gf (or Kc, Jcr) of concrete, plastic-hardening metals, composites, and probably most materials can change by ±100%, depending on the crack-parallel stresses σxx, σzz, and their history. Therefore, one must consider not only a finite length but also a finite width of the fracture process zone, along with its tensorial damage behavior. The data from this test, along with ten other classical tests important for fracture problems (nine on concrete, one on sandstone), are optimally fitted to evaluate the performance of the state-of-art phase-field, peridynamic, and crack band models. Thanks to its realistic boundary and crack-face conditions as well as its tensorial nature, the crack band model, combined with the microplane damage constitutive law in its latest version M7, is found to fit all data well. On the contrary, the phase-field models perform poorly. Peridynamic models (both bond based and state based) perform even worse. The recent correction in the bond-associated deformation gradient helps to improve the predictions in some experiments, but not all. This confirms the previous strictly theoretical critique (JAM 2016), which showed that peridynamics of all kinds suffers from several conceptual faults: (1) It implies a lattice microstructure; (2) its particle–skipping interactions are a fiction; (4) it ignores shear-resisted particle rotations (which are what lends the lattice discrete particle model (LDPM) its superior performance); (3) its representation of the boundaries, especially the crack and fracture process zone faces, is physically unrealistic; and (5) it cannot reproduce the transitional size effect—a quintessential characteristic of quasibrittleness. The misleading practice of “verifying” a model with only one or two simple tests matchable by many different models, or showcasing an ad hoc improvement for one type of test while ignoring misfits of others, is pointed out. In closing, the ubiquity of crack-parallel stresses in practical problems of concrete, shale, fiber composites, plastic-hardening metals, and materials on submicrometer scale is emphasized.

Charge density wave order in the kagome metal AV3Sb5 (A=Cs,Rb,K)

We employ polarization-resolved electronic Raman spectroscopy and density functional theory to study the primary and secondary order parameters, as well as their interplay, in the charge density wave (CDW) state of the kagome metal AV3Sb5. Previous x-ray diffraction data at 15K established that the CDW order in CsV3Sb5 comprises of a 2x2x4 structure: one layer of inverse-star-of-David and three consecutive layers of star-of-David pattern. We analyze the lattice distortions based the 2x2x4 structure at 15K, and find that U lattice distortion is the primary order parameter while M and L distortions are secondary order parameters for Vanadium displacements. This conclusion is confirmed by the calculation of bare susceptibility that shows a broad peak at around qz=0.25 along the hexagonal Brillouin zone face central line (U-line). We also identify several phonon modes emerging in the CDW state, which are lattice vibration modes related to V and Sb atoms as well as alkali atoms. The detailed temperature evolution of these modes' frequencies, HWHM, and integrated intensities support a phase diagram with two successive structural phase transitions in CsV3Sb5: the first one with a primary order parameter appearing at TS=94K and the second isostructural one appearing at around 70K.

Nonsymmorphic band sticking in a topological superconductor

Single-crystal x-ray diffraction recently identified the space group of the weakly correlated yet exotic time reversal symmetry (TRS) breaking superconductor $\mathrm{La}\mathrm{Ni}{\mathrm{Ga}}_{2}$ to be nonsymmorphic $Cmcm$. This symmetry causes band sticking on a zone face pierced by four Fermi surfaces, leading to two nodal Fermi lines and a nodal Fermi loop on that zone face ${k}_{z}=\frac{\ensuremath{\pi}}{c}$. These line singularities are examples of perfectly flat (in energy and in geometry) nodal structures that lie precisely at a single energy, with that energy being the Fermi level ${E}_{F}$, even under variation of the carrier density. Projections onto surfaces perpendicular to that zone face produce collapsed drumhead state regions of zero area on the edges of the surface Brillouin zone. Although small by most measures, spin-orbit coupling splits the line and loop degeneracies on the Fermi surfaces (FSs) in the normal state except at two symmetry-related Dirac points, which topologically are locally dispersionless in one direction (zero velocity and infinite mass) while linear in the other two directions. The band sticking and distinctive Fermi surface placed Dirac points are most impactful in establishing $\mathrm{La}\mathrm{Ni}{\mathrm{Ga}}_{2}$ as a topological superconductor in the bulk, with the degenerate FSs providing a natural platform for the superconducting order-parameter symmetry necessary for describing this TRS breaking superconductor. Unlike most other crystal symmetries, spin-orbit coupling leaves intact a nodal line piercing the FS, resulting in Dirac points situated at ${E}_{F}$ lying along nodal lines. Additionally, the degeneracy exactly at the Fermi energy is central in placing $\mathrm{La}\mathrm{Ni}{\mathrm{Ga}}_{2}$ precisely at a Lifshitz FS instability, independent of band filling and protected by $Cmcm$ symmetry. The eight-band low-energy Bogoliubov--de Gennes quasiparticle spectrum is presented along one dispersive direction for varying strengths of TRS breaking. We include a discussion of energetics of gauge symmetry and magnetic order resulting from TRS breaking, incorporating information from experimental data. These results suggest a scenario where TRS breaking rather than gauge-symmetry breaking (superconductivity) might be the driving order parameter.

The unequal distribution of water risks and adaptation benefits in coastal Bangladesh

Increasing flood risk, salinization and waterlogging threaten the lives and livelihoods of more than 35 million people in Bangladesh’s coastal zone. While planning models have long been used to inform investments in water infrastructure, they frequently overlook interacting risks, impacts on the poor and local context. We address this gap by developing and applying a stochastic-optimization model to simulate the impact of flood embankment investments on the distribution of agricultural incomes across income groups for six diverse polders (embanked areas) in coastal Bangladesh. Results show that increasing salinity and waterlogging negate the benefits of embankment rehabilitation in improving agricultural production while improved drainage can alleviate these impacts. Outcomes vary across income groups, with risks of crop loss being greatest for the poor. We discuss the need for planning models to consider the interacting benefits and risks of infrastructure investments within a local political economy to better inform coastal adaptation decisions. People living in Bangladesh’s coastal zone face multiple water-related risks. This modelling study finds that rising salinity and waterlogging negate the benefits of rehabilitating embankments for reducing crop loss, with impacts being greatest for the poor. Drainage was found to reduce negative impacts.

Electronic instabilities of kagome metals: Saddle points and Landau theory

We study electronic instabilities of a kagome metal with a Fermi energy close to saddle points at the hexagonal Brillouin zone face centers. Using parquet renormalization group, we determine the leading and subleading instabilities, finding superconducting, charge, orbital moment, and spin density waves. We then derive and use Landau theory to discuss how different primary density wave orders give rise to charge density wave modulations, as seen in the AV$_3$Sb$_5$ family, with A=K,Rb,Cs. The results provide strong constraints on the mechanism of charge ordering and how it can be further refined from existing and future experiments.

The J-integral for mixed-mode loaded cracks with cohesive zones

The J-integral quantifies the loading of a crack tip, just as the crack tip opening displacement (CTOD) emanating from the cohesive zone model. Both quantities, being based on fundamentally different interpretations of cracks in fracture mechanics of brittle or ductile materials, have been proven to be equivalent in the late 60s of the previous century, however, just for the simple mode-I loading case. The relation of J and CTOD turned out to be uniquely determined by the constitutive law of the cohesive zone in front of the physical crack tip. In this paper, a J-integral vector is derived for a mixed-mode loaded crack based on the cohesive zone approach, accounting for the most general case of a mode-coupled cohesive law. While the J_1-coordinate, as energy release rate of a straight crack extension, is uniquely related to the cohesive potential at the physical crack tip and thus to the CTOD, the J_2-coordinate depends on the solution of the specific boundary value problem in terms of stresses and displacement gradients at the cohesive zone faces. The generalized relation is verified for the Griffith crack, employing solutions of the Dugdale crack based on improved holomorphic functions.

Elastic–plastic problem for a circular hole plate with regard to crack initiation in elastic zone

A plane elastic–plastic problem of stress distribution in a circular hole thin plate involving initiation and propagation of cracks in an elastic zone, is considered. It is assumed that the stress level is such that the circular hole is entirely enclosed by the plastic deformations zone. The plate material satisfies the Tresca–Saint Venant plasticity condition. It is supposed that cracks initiation and fracture of the plate material occur in the loading process in the elastic zone. Location and size of prefracture zone in the plate material are unknown in advance and are to be determined. The methods of theory of perturbations and theory of singular integral equations are used. As a crack appearance condition, we use the criterion of critical opening of prefracture zone faces. The interface of elastic and plastic deformations and also the location and sizes of crack initiation zones are found.

Maintenance Operations and its Management in Oil Industry in Kuwait

The maintenance in oil area need to undertake entire shutdowns together with generic refinery turn-around, unit shutdowns on a full accountability foundation and Scaffolding services. The in-house equipment and equipment: the in-house Maintenance workshop facility ought to be completely outfitted with lathe machines, shaping machine, hole spindle lathe machine, horizontal boring machine, radial drilling machine, pipe threading machine, valve lapping machine, mechanical seal lapping machine, welding computing device and all sorts of specialized warmness exchanger re-tubing gear and tools. Maintenance operations in this zone face many troubles in management, price and technical problems. This study aims to study the and count the failures occurred in equipments of Kuwait Oil Company (KOC) in 2019, and study the maintenance strategies used in petroleum industry in the Kuwait state, a maintenance programs or steps will be suggested and investigated in order to improve the maintenance operations. Availability of devices are calculated depending on downtime of the devices at KOC. The data were collected about failures frequency occurred for the KOC company equipments. Most of oil equipments have good availability but in the case of KOC four devices have availability less than 90% which means more failure and downtime, the company adopted a Zero S/D PM Strategy or Philosophy which decreasing failures by 75% and improve the availability of KOC devices. Planning and management of maintenance and monitoring operations in any company decreasing failure frequency of equipments and so downtime of equipments which improves the equipments availability.

La « compétence de la survie » du traducteur en zone de conflit : l’anxiété et la prise de décision

Abstract Translators and interpreters operating in the war zone face numerous factors that alter their cognitive and emotional capabilities, among which: fear, anxiety troubles and post-traumatic stress disorder. This article explains the cerebral processes that generate anxiety, emotion and cognitive complexity, advances the new notion of “laboratory stress” and establishes the link between these processes and anxiety and decision‑making. Finally, the article suggests emergency exists such as positive appraisal and the innovative notion of sociocognitive counter‑conditioning.

Giant Van Hove Density of States Singularities and Anomalies of Electron and Magnetic Properties in Cubic Lattices

Densities of states for simple (sc) and base-centered (bcc) cubic lattices with account of nearest and next-nearest neighbour hopping integrals $t$ and $t'$ are investigated in detail. It is shown that at values of $\tau \equiv t'/t = \tau_\ast$, corresponding to the change of isoenergetic surface topology, the formation of van Hove $\bf k$ lines takes place. At small deviation from these special values, the weakly dispersive spectrum in the vicinity of van Hove lines is replaced by a weak $\bf k$-dependence in the vicinity of few van Hove points which possess huge masses proportional to $|\tau - \tau_\ast|^{-1}$. The singular contributions to the density of states originating from van Hove points and lines are considered, as well as the change in the topology of isoenergetic surfaces in the $\bf k$-space with the variation of $\tau$. Closed analytical expressions for density of states as a function of energy and $\tau$ in terms of elliptic integrals, and power-law asymptotics at $\tau = \tau_\ast$ are obtained. Besides the case of sc lattice with small $\tau$ (maximum of density of states corresponds to energy level of X $\bf k$-point), maximal value of the density of states is always achieved at energies corresponding to \textit{inner} $\bf k$-points of the Brillouin zone positioned in high-symmetry directions, and not at zone faces.

Crack nucleation in rod-type nuclear fuel pellet

A plane problem of fracture mechanics on crack nucleation in a rod-type nuclear fuel pellet is considered. Nuclear reactor fuel pellets in operation may be damaged in various ways; in particular, crack nucleation. We consider a problem for the case of a heat-releasing fuel pellet with cladding: as the heat release intensity increases, zones of heightened stress are formed in the nuclear fuel pellet. The heightened stress will promote the appearance of prefracture bands that are simulated as zones of weakened interparticle bonds of the material. Interaction of prefracture zone faces is simulated by placing bonds between faces that have a specified deformation pattern. The problem of equilibrium of a fuel pellet with prefracture zones is reduced to the solution of a system of singular integral equations. An analysis of the ultimate state of the zone of weakened interparticle bonds of the material is realized on the basis of the criterion of critical opening of prefracture zone faces.

Band structure diagram paths based on crystallography

Systematic and automatic calculations of the electronic band structure are a crucial component of computationally-driven high-throughput materials screening. An algorithm, for any crystal, to derive a unique description of the crystal structure together with a recommended band path is indispensable for this task. The electronic band structure is typically sampled along a path within the first Brillouin zone including the surface in reciprocal space. Some points in reciprocal space have higher site symmetries and/or have higher constraints than other points regarding the electronic band structure and therefore are likely to be more important than other points. This work categorizes points in reciprocal space according to their symmetry and provides recommended band paths that cover all special wavevector (k-vector) points and lines necessarily and sufficiently. Points in reciprocal space are labeled such that there is no conflict with the crystallographic convention. The k-vector coefficients of labeled points, which are located at Brillouin zone face and edge centers as well as vertices, are derived based on a primitive cell compatible with the crystallographic convention, including those with axial ratio-dependent coordinates. Furthermore, we provide an open-source implementation of the algorithms within our SeeK-path python code, to allow researchers to obtain k-vector coefficients and recommended band paths in an automated fashion. Finally, we created a free online service to compute and visualize the first Brillouin zone, labeled k-points and suggested band paths for any crystal structure, that we made available at http://www.materialscloud.org/tools/seekpath/.

Nonsymmorphic Weyl superconductivity inUPt3based onE2urepresentation

We show that a heavy fermion superconductor UPt_3 is a topological Weyl superconductor with tunable Weyl nodes. Adopting a generic order parameter in the E_2u representation allowed by nonsymmorphic crystal symmetry, we clarify unusual gap structure and associated topological properties. The pair creation, pair annihilation, and coalescence of Weyl nodes are demonstrated in the time-reversal symmetry broken B-phase. At most 98 point nodes compatible with Blount's theorem give rise to line node-like behaviors in low-energy excitations, consistent with experimental results. We also show an arc node protected by the nonsymmorphic crystal symmetry on the Brillouin zone face.

Topologically stable gapless phases in nonsymmorphic superconductors

We study topological stability of nodes in nonsymmorphic superconductors (SCs). In particular, we demonstrate that line nodes in nonsymmirphic odd-parity SCs are protected by the interplay between topology and nonsymmorphic symmetry. As an example, it is shown that the $E_{2u}$-superconducting state of UPt$_3$ hosts the topologically stable line node at the Brillouin zone face. Our theory indicates that the existence of spin-orbit coupling is essential for protecting such a line node, complementing the Norman's group theory argument. Developing the topological arguments, we also argue generalization to point nodes and to other symmetry cases beyond the group theory arguments.

Cracking in heat-releasing perforated material

A model of cracking in fuel isotropic material weakened by a doubly periodic system of cooling cylindrical channels of round cross section is mathematically described. It is assumed that with increasing intensity of the heat in the material its elastic properties become temperature dependent, and nucleation of cracks and failure of the material occur. It is assumed that the zone of cracks nucleation is a finite length layer containing a material with partially broken connections between separate structural elements in plastic flow state at constant stress. The determination of unknown parameters characterizing the initiating crack is reduced to the solution of a singular integral equation. An analysis of the ultimate state of the zone of the weakened interparticle bonds of the material is realized on the basis of the criterion of critical opening of prefracture zone faces.