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Strain ageing phenomena in metallic alloys: Experiments and modelling
No full textStatic and dynamic strain ageing phenomena induced by the interaction between dislocations and solute atoms, are ubiquitous in engineering metallic alloys. In Nickel-based superalloys used for turbine disks in jet engines, negative strain rate sensitivity is observed at service tempature and results in the devlopment of Portevin-Le Chatelier bands. A viscoplastic constitutive model will be presented which captures the serrations in tensile notch samples and biaxial tension specimens. Finite element simulations then show the impact of DSA on the burst of turbine disks [1]. Static strain ageing is associated to the formation of L¨uders bands in steel sheets. We illustrate the impact of their propagation on the viscoplastic behaviour of zinc coatings on galvanized steel sheets, by means of crystal plasticity applied to zinc grain
Advances and structural applications of Isogeometric Analysis
Get PDFIsogeometric Analysis (IGA) is a successful simulation framework originally proposed by T.J.R. Hughes et al., in 2005, with the aim of bridging Computational Mechanics and Computer Aided Design. In addition to this, thanks to the high-regularity properties of its basis functions, IGA has shown a better accuracy per degree-of-freedom and an enhanced robustness with respect to standard finite elements in many contexts - ranging from solids and structures to fluids, as well as to different kinds of coupled problems – opening also the door for the approximation in primal form of higher-order partial differential equations. After a concise introduction of the basic isogeometric concepts, this lecture aims at presenting some IGA recent advances with a special focus on interesting structural applications in several fields where the characteristics of IGA seem to be of great advantage. In particular, applications that will be discussed include the simulation of fluid-structure interaction in different situations, studies on the effect of mechanicallyinduced stresses on prostate cancer growth, thermo-mechanical simulations of additive manufacturing processes, electro-mechanical simulations for biological tissues, and the use of phase-field modeling of fracture and other problems
Power Distribution of various Rotor Configurations in a Vertical Stirred Mill determined with DEM
Get PDFVertical stirred milling is a well-recognized technology for fine grinding applications in the mineral processing industry. It is increasingly used due to the higher energy efficiency compared to horizontal mills. Vertical arrangement leads to high grinding intensity and power draw in the bottom grinding chambers, thus bottom rotors may wear out more than upper rotors. Modelling power draw is of great interest proven by the effort in previous work. An analytical power model for this type of mills based on measurement data was developed by Heath et al. [1] and a particle-based approach was presented by Larsson et al. [2].
In this contribution a DEM model to determine the torque distribution along the shaft for every grinding compartment in a vertical stirred mill with castellated rotors [3] is presented. Different rotor configurations are evaluated, whereby the rotors vary in diameter, alignment and spacing. An optimized configuration with a combination of different rotors could be developed, which leads to a more even power distribution and a significant reduction of load on the bottom rotors. Simulations also reveal particle dynamics, which explain field experience in terms of wear. Furthermore, the influence of grinding media filling level on power draw is investigated. Higher filling levels increase power draw following an exponential trend. This model allows to optimize the rotor configuration along the shaft, which has a strong impact on rotor and liner wear, critically influencing operational cost
Methods 3D DEM investigation into the liquefaction characteristics of highly crushable pumice sand
Get PDFPumice sand particles present engineering challenges due to their tendency to crush and compress. Although laboratory and field tests can assess their behaviour, these methods are often time-consuming and costly. This study investigates the liquefaction behaviour of crushable pumice sand using the Discrete Element Method (DEM). In the model, each pumice particle is represented as a sphere that fractures into 14 smaller spheres when a critical contact force is exceeded. Initially, single particle crushing tests are conducted to determine breakage characteristics based on particle size. Subsequently, using the open-source code YADE, three-dimensional loose specimens are prepared and isotopically consolidated under specified confining pressures. These numerical specimens undergo cyclic loading under undrained conditions. The findings indicate that the DEM model successfully replicates experimental results, providing insights into how particle crushing influences cyclic deviator strain. Microscale observations also shed light on the development of force chains within the specimens, enhancing the understanding of pumice sand behaviour during cyclic loading
Impact of outlet boundary condition schemes for the lattice Boltzmann method regarding the Stefan phase-change problem
Get PDFIn several industrial applications, there are systems that depend on multiphase flows.
Consequently, modelling these processes are very attractive for the scientific community. Having
a mesoscopic nature, the lattice Boltzmann method (LBM) presents advantages to deal with
complex geometries and complex processes, such as bubble merging, fluid-structure interaction,
etc. Several LBM models for multiphase flows were developed by the research community.
Usually, in the applications of multiphase flows, there are open boundaries where the fluid
with more than one phase leaves the domain. However, there are few works in the literature
regarding the impact of the BC schemes with the Allen-Cahn-based phase-field LBM, especially
considering liquid-gas phase change. Then, in this work, we explore the impact of three
schemes of open BC: the equilibrium scheme, the extrapolation scheme, and the convective BC
scheme. First, the impact of the BC schemes on a channel flow with a bubble inside is studied.
Next, the Stefan problem considering real properties (saturated HFE7100) is simulated. The
results showed that both the extrapolation and equilibrium schemes can introduce instabilities
and incoherences in the results, while the convective BC is the one that better conserves the
coherence of the results
Market Signal from Syntactic Authority: Syntactic Authority Index and Market Signal
Get PDFThis study presents the Syntactic Authority Index (SAI) as a quantitative measure of linguistic authority within financial discourse and evaluates its predictive capacity for market behavior. By detecting recurrent authority-bearing constructions such as deontic modalities, nominalizations, enumerations, and passive imperatives, the index demonstrates how linguistic form itself carries institutional weight. The regla compilada, understood as a Type-0 production that binds constraints to model decisions, functions as the generative substrate connecting syntax to observable financial reactions. Using multilingual corpora of earnings calls, investor letters, and regulatory filings, the research examines whether variations in the SAI precede abnormal returns, volume shifts, and regulatory enforcement events. Out-of-sample evaluations show that increases in syntactic authority correlate with short-term market anomalies while remaining independent of sentiment or tone. The signal intensifies under macroeconomic uncertainty or within firms under regulatory observation. These findings indicate that linguistic form operates as an actionable signal, showing that authority encoded in syntax can coordinate expectations and influence market conduct without relying on authorial intent. Acknowledgment / Editorial Note This article is published with editorial permission from LeFortune Academic Imprint, under whose license the text will also appear as part of the upcoming book AI Syntactic Power and Legitimacy. The present version is an autonomous preprint, structurally complete and formally self-contained. No substantive modifications are expected between this edition and the print edition. LeFortune holds non-exclusive editorial rights for collective publication within the Grammars of Power series. Open access deposit on SSRN is authorized under that framework, if citation integrity and canonical links to related works (SSRN: 10.2139/ssrn.4841065, 10.2139/ssrn.4862741, 10.2139/ssrn.4877266) are maintained
Comparison of stiffness and strength of flax, hemp and kenaf composites with other natural and synthetic fibers composites using fibre-specific parameters
No full textThe increasing adoption of natural fibres as composite reinforcement is a promising development in materials science. These fibres have a low carbon footprint and are biodegradable, and they also have remarkable properties such as low density and high specific stiffness and strength. However, the mechanical properties of these composites are influenced by various parameters, which can complicate comparisons due to their diverse internal structures. This study focuses on two key normalised parameters: the Tsai modulus, which represents the trace of the stiffness matrix tensor; and the area of the Omni failure envelope in stress space. Our analysis of published data on unidirectional flax, hemp, jute, and kenaf composites shows that trace-normalised longitudinal Young's modulus can effectively facilitate stiffness comparisons between natural and synthetic fibre composites. A new and innovative way of measuring strength is suggested. This is based on the radius of a circle that matches the area of the Omni stress envelopes. This method is both robust and reliable for quantifying and comparing material strength. Although, extensive mechanical data on natural composites is available, it is difficult to establish design criteria for comparing them. Addressing this gap presents a significant opportunity to unlock the full potential of natural fibres in composite applications, paving the way for a more sustainable future in engineering materials
Study the Wear Resistance and Corrosion of Ni-P/ PTFE Composite Coatings Prepared by Electrodeposition Method
Get PDFCoating is one of the effective ways to increase the corrosion resistance and wear of metallic substrates. Additionally, the composite coatings using nanoparticles can also further protect the substrate. In this study, using electrodeposition process and polytetrafluoroethylene (PTFE) particles (with concentrations of 10, 20 or 30 g /L), NiPTFE coatings were prepared and their corrosion and wear properties were investigated and compared with Ni-P coating. Using scanning electron microscopy (SEM) and X-ray diffraction (EDS) method, the surface morphology and elemental composition of the coatings were analyzed and finally, by using open circuit potential (OCP) techniques, electrochemical impedance spectroscopy (EIS) and TAFEL polarization techniques, the corrosion resistance of the resulting coatings in 3/5 wt.% NaCl solution were evaluated. Microhardness and pin on disk tests were also utilized to investigate the effect of PTFE concentration on the tribological properties of the coatings. The results of SEM and EDS studies confirmed the formation of nanocomposites. Electrochemical studies also showed that Ni-PTFE coatings, at a concentration of 20 g/L PTFE, had the highest electrochemical corrosion resistance. Microhardness also decreased with increasing PTFE particles in the coating and reached its lowest value. By using the wear test, the lowest coefficient of friction obtained in composite coatings with concentration of 20 g/L, which shows the applicability of PTFE particles as a solid lubricant in Ni-P coatings
RCS Simulation of Double S-Shaped Inlet with Radar Absorbing Materials Shedding Using Iterative Physical Optics with Impedance Boundary Condition
Get PDFThe inlet of an aircraft engine is a primary contributor to the aircraft’s forward electromagnetic scattering. S-shaped inlet and radar absorbing materials (RAM) coatings have been widely adopted as effective measures to reduce forward radar cross section (RCS). To investigate the influence of RAM shedding on the RCS reduction efficiency, the electromagnetic scattering characteristics of the inlet under five different shedding probabilities were calculated using the iterative physical optics (IPO) combined with impedance boundary condition (IBC). Numerical simulation results demonstrate that the forward RCS of the S-shaped inlets increases monotonically with shedding probability. In the yaw plane, intact non-magnetic RAM exhibits better RCS reduction efficiency (RRE) than that in the pitch plane across all scenarios. Specifically, at a shedding probability of 0.7, the remaining non-magnetic RAM maintains an RRE exceeding 40% in the pitch plane. Collectively, these results suggest that recoating the nonmagnetic RAM is recommended when the shedding probability exceeds 0.7 in either detection plane to sustain critical stealth performance.OPEN ACCESS Received: 20/05/2025 Accepted: 13/08/2025 Published: 27/10/202
Modeling and Thermal Analysis of a Ground Cooling System for Drilling Fluids in Ultra-Deep Wells
No full textElevated downhole temperatures in ultra-deep wells (>8000 m) accelerate thermal degradation of drilling fluids and tools, reducing operational safety and efficiency. The reduction of wellbore temperature is an important issue. In this paper, a cooling system model for a drilling fluid was designed. Additionally, a comprehensive analysis of the heat transfer behavior within ultra-deep wells was conducted. A miniaturized heat exchange cooling device was used to simulate various conditions, including fluid media, flow rate, drilling fluid/coolant temperature, and heat exchanger structure. This analysis elucidates the impact of various factors on cooling efficiency. The experimental results show that the cooling effect is best at a medium flow rate, with a refrigerant temperature of−10°C reducing the temperature of pure water from 60°C to 32°C. The experiment also found that the higher the temperature of the pure water and the lower the temperature of the coolant, the better the heat transfer efficiency. For water-based drilling fluid, the optimum cooling flow rate is around 0.52 m/s, with an average Reynolds number of 4966, and the maximum cooling range can exceed 30°C. Furthermore, the coil heat exchanger significantly improves the cooling rate compared to the straight-tube heat exchanger, although the pressure difference also increases. The cooling rate of oil-based drilling fluid at high flow rates is greater than that of water-based drilling fluid, and the pressure difference in the coil heat exchanger for oil-based drilling fluid, which has higher viscosity, increases significantly. This research provides an experimental basis for the design and optimization of drilling fluid surface cooling systems, which is crucial for improving the safety and efficiency of deep and ultra-deep wells drilling.OPEN ACCESS Received: 10/06/2025 Accepted: 15/08/2025 Published: 27/11/202