Search

The natural environment in the high-altitude regions of Northwest China is extremely harsh, characterized by numerous salt lakes. The high concentrations of chloride salts, sulfates, and alkali metal ions in these areas can induce alkali–silica reactions (ASRs) in concrete. These reactions generate harmful gel within the concrete, causing expansion and cracking, which significantly impacts the durability of concrete structures. This study investigates the evolution of the mechanical properties in high-performance concrete (HPC) under long-term ASR by incorporating different admixtures and varying the equivalent alkali content. A three-dimensional random aggregate mesoscopic model was used to simulate static compression tests under various operational conditions. Non-destructive testing methods were utilized to determine the expansion rate, internal, and surface damage variables of the concrete. The experimental results indicate that the 10-year expansion rate differs from the 1-year rate by approximately 1%, and under long-term ASR mitigation measures, the internal damage in the HPC is minimal, though the surface damage is more severe. As the equivalent alkali content increases, the compressive strength of the concrete cubes decreases, initially rising before falling by 5–15% over time. The HPC with only air-entraining agent added exhibited better mechanical performance than the HPC with both air-entraining and corrosion inhibitors added, with the poorest performance observed in the HPC with only a corrosion inhibitor. A relationship was established between the surface and internal damage variables, with the surface damage initially increasing rapidly before stabilizing as the internal damage rose. Numerical simulations effectively describe the damage behavior of HPC under static uniaxial compression. Comparisons with actual failure morphologies revealed that, in the cube compression tests, crack propagation directly penetrated both coarse and fine aggregates rather than circumventing them. The simulations closely matched the experimental outcomes, demonstrating their accuracy in modeling experiments. This study discusses the compressive mechanical properties of concrete under prolonged ASR through a combination of experimental and simulation approaches. It also delves into the impact of surface damage on the overall mechanical performance and failure modes of concrete. The findings provide experimental and simulation support for the concrete structures in regions with high alkali contents. [ABSTRACT FROM AUTHOR]

This study systematically investigates the impact of the material properties of soft magnetic composites (SMCs) on the powder metallurgy forming process. It proposes a suitable material selection process for various motor types and shapes and determines the optimal forming conditions for each SMC material. This study employed the Taguchi design method to identify key control factors such as powder type, forming temperature, and forming speed, and analyzed their effects on relative density. Simulation results indicated that AncorLam HR exhibited superior properties compared with AncorLam and Fe-6.5wt.%Si. The optimal conditions determined through signal-to-noise ratio (SNR) calculations were AncorLam HR at 60 °C and five cycles per minute (CPMs). Validation through simulation and SEM analysis confirmed improved density uniformity and reduced defects in products formed under optimal conditions. Final prototype testing demonstrated that the selected conditions achieved the target density with minimal variance, enhancing the mechanical properties and performance of the motors. These results suggest that the appropriate application of SMC materials can significantly enhance motor efficiency and reliability. [ABSTRACT FROM AUTHOR]

The prediction of mechanical behavior and fatigue life is of major importance for design and for replacing costly and time-consuming tests. The proposed approach for polymers is a combination of a fatigue model and a governing constitutive model, which is formulated using the Haward–Thackray viscoplastic model (1968) and is capable of capturing large deformations. The fatigue model integrates high- and low-cycle fatigue and is based on the concept of damage evolution and a moving endurance surface in the stress space, therefore memorizing the load history without requesting vague cycle-counting approaches. The proposed approach is applicable for materials in which the fatigue development is ductile, i.e., damage during the formation of microcracks controls most of the fatigue life (up to 90%). Moreover, damage evolution shows a certain asymptote at the ultimate of the low-cycle fatigue, a second asymptote at the ultimate of the high-cycle fatigue (which is near zero), and a curvature of how rapidly the transition between the asymptotes is reached. An interesting matter is that similar to metals, many polymers satisfy these constraints. Therefore, all the model parameters for fatigue can be given in terms of the Basquin and Coffin–Manson model parameters, i.e., satisfying well-defined parameters. [ABSTRACT FROM AUTHOR]

We present a macroscale constitutive model that couples magnetism with thermal, elastic, plastic, and damage effects in an Internal State Variable (ISV) theory. Previous constitutive models did not include an interdependence between the internal magnetic (magnetostriction and magnetic flux) and mechanical fields. Although constitutive models explaining the mechanisms behind mechanical deformations caused by magnetization changes have been presented in the literature, they mainly focus on nanoscale structure–property relations. A fully coupled multiphysics macroscale ISV model presented herein admits lower length scale information from the nanoscale and microscale descriptions of the multiphysics behavior, thus capturing the effects of magnetic field forces with isotropic and anisotropic magnetization terms and moments under thermomechanical deformations. For the first time, this ISV modeling framework internally coheres to the kinematic, thermodynamic, and kinetic relationships of deformation using the evolving ISV histories. For the kinematics, a multiplicative decomposition of deformation gradient is employed including a magnetization term; hence, the Jacobian represents the conservation of mass and conservation of momentum including magnetism. The first and second laws of thermodynamics are used to constrain the appropriate constitutive relations through the Clausius–Duhem inequality. The kinetic framework employs a stress–strain relationship with a flow rule that couples the thermal, mechanical, and magnetic terms. Experimental data from the literature for three different materials (iron, nickel, and cobalt) are used to compare with the model's results showing good correlations. [ABSTRACT FROM AUTHOR]

In this study, hot compression experiments were conducted on cast TC21 titanium alloy using a Gleeble-1500D thermal simulation compression tester, and the hot-compressed specimens were heat-treated. The data obtained after analyzing the thermal compression of cast TC21 titanium alloy were analyzed to construct a thermal machining diagram with a strain of 0.8 and to optimize the machining window. This study investigated the microstructure of the alloy after hot pressing experiments and heat treatment, applying the study of the microstructure evolution law of cast TC21 titanium alloy. The analysis of the tissue evolution law established the dynamic and static recrystallization volume fraction as a function of heat deformation parameters. The results show that the optimal processing window for cast TC21 titanium alloy is a deformation temperature in the range of 1373 K–1423 K and a strain rate of 0.1 s−1. The increase in deformation volume and deformation temperature both favor recrystallization and make the recrystallization volume fraction increase, but the increase in strain rate will inhibit the increase in the recrystallization degree to some extent. The dynamic and static recrystallization equations for the cast TC21 titanium alloy at different temperatures were constructed. The experimental measurements of recrystallization volume fraction are in good agreement with the predicted values. [ABSTRACT FROM AUTHOR]

This work presents modifications for two constitutive models for the prediction of the flow behavior of titanium-based alloys during hot deformation. The modified models are the phenomenological-based Fields-Backofen and the physical-based Zerilli-Armstrong. The modifications are derived and suggested by studying the hot deformation of titanium-based alloy Ti55531. The predictability of the modified models along with the original Fields-Backofen and another modified Zerilli-Armstong models is assessed and evaluated using the well-known statistical parameters correlation coefficient (R), Average Absolute Relative Error (AARE), and Root Mean Square Error (RMSE), for the Ti55531 alloy, and validated with other two different titanium-based alloys SP700 and TC4. The results show that the modified Fields-Backofen gives the best performance with R value of 0.996, AARE value of 3.34%, and RMSE value of 5.64 MPa, and the improved version of the modified Zerilli-Armstrong model comes in the second-best place with R value of 0.992, AARE value of 3.52%, and RMSE value of 9.15 MPa for the Ti55531 alloy. [ABSTRACT FROM AUTHOR]

Friction, wear, and the consequent energy dissipation pose significant challenges in systems with moving components, spanning various domains, including nanoelectromechanical systems (NEMS/MEMS) and bio-MEMS (microrobots), hip prostheses (biomaterials), offshore wind and hydro turbines, space vehicles, solar mirrors for photovoltaics, triboelectric generators, etc. Nature-inspired bionic surfaces offer valuable examples of effective texturing strategies, encompassing various geometric and topological approaches tailored to mitigate frictional effects and related functionalities in various scenarios. By employing biomimetic surface modifications, for example, roughness tailoring, multifunctionality of the system can be generated to efficiently reduce friction and wear, enhance load-bearing capacity, improve self-adaptiveness in different environments, improve chemical interactions, facilitate biological interactions, etc. However, the full potential of bioinspired texturing remains untapped due to the limited mechanistic understanding of functional aspects in tribological/biotribological settings. The current review extends to surface engineering and provides a comprehensive and critical assessment of bioinspired texturing that exhibits sustainable synergy between tribology and biology. The successful evolving examples from nature for surface/tribological solutions that can efficiently solve complex tribological problems in both dry and lubricated contact situations are comprehensively discussed. The review encompasses four major wear conditions: sliding, solid-particle erosion, machining or cutting, and impact (energy absorbing). Furthermore, it explores how topographies and their design parameters can provide tailored responses (multifunctionality) under specified tribological conditions. Additionally, an interdisciplinary perspective on the future potential of bioinspired materials and structures with enhanced wear resistance is presented. [ABSTRACT FROM AUTHOR]

Antimicrobial resistance (AMR) is a worldwide healthcare problem. Multidrug-resistant organisms (MDROs) can spread quickly owing to their resistance mechanisms. Although colonized individuals are crucial for MDRO dissemination, colonizing microbes can lead to symptomatic infections in carriers. Carbapenemase-producing Enterobacterales (CPE) are among the most important MDROs involved in colonizations and infections with severe outcomes. This review aimed to track down the first reports of CPE in Africa, describe their dissemination throughout African countries and summarize the current status of CRE and CPE data, highlighting current knowledge and limitations of reported data. Two database queries were undertaken using Medical Subject Headings (MeSH), employing relevant keywords to identify articles that had as their topics beta-lactamases, carbapenemases and carbapenem resistance pertaining to Africa or African regions and countries. The first information on CPE could be traced back to the mid-2000s, but data for many African countries were established after 2015–2018. Information is presented chronologically for each country. Although no clear conclusions could be drawn for some countries, it was observed that CPE infections and colonizations are present in most African countries and that carbapenem-resistance levels are rising. The most common CPE involved are Klebsiella pneumoniae and Escherichia coli, and the most prevalent carbapenemases are NDM-type and OXA-48-type enzymes. Prophylactic measures, such as screening, are required to combat this phenomenon. [ABSTRACT FROM AUTHOR]

This work focuses on understanding the mechanical behavior of CMT (cold metal transfer)-welded joints in AA6061-T651 aluminum alloy while establishing a correlation with the microstructural features observed in the weld zones. Furthermore, the mathematical framework of a coupled continuum damage mechanics and anisotropic plasticity model under finite strain formulation is presented. The aim is to accurately describe the mechanical behavior, fracture, and damage evolution of CMT-welded joints in AA 6XXX alloys. The calibration of the proposed model is performed using experimental data obtained from uniaxial tensile tests conducted on various weld zones, including the base material, heat-affected zone, and fusion zone. To capture the overall behavior of the welded joint, a composite framework is employed. This framework incorporates multiple in-series elasto-viscoplastic elements, each representing a specific welding zone. Demonstrating robust predictive capabilities, the model successfully predicts critical mechanical properties, including yield stress, ultimate tensile stress, and strain to fracture, for 6061-T651 aluminum alloy CMT welds and their respective weld zones. Notably, the model achieves a high degree of accuracy, with accuracy of approximately 0.8, 0.98, and 0.9, respectively, compared with experimental values. The experimental results and numerical simulations exhibit a close agreement, validating the accuracy and predictive capability of the proposed model. Additionally, the model demonstrates its ability to capture the evolution of damage throughout the loading process. The proposed modeling approach effectively captures the unique characteristics of each welding zone and provides valuable insights into the fracture and damage evolution of the welds. [ABSTRACT FROM AUTHOR]

Hydrogen production techniques based on solar-water splitting have emerged as carbon-free energy systems. Many researchers have developed highly efficient thin-film photoelectrochemical (PEC) devices made of low-cost and earth-abundant materials. However, solar water splitting systems suffer from short lifetimes due to catalyst instability that is attributed to both chemical dissolution and mechanical stress produced by hydrogen bubbles. A recent study found that the nanoporous hydrogel could prevent the structural degradation of the PEC devices. In this study, we investigate the protection mechanism of the hydrogel-based overlayer by engineering its porous structure using the cryogelation technique. Tests for cryogel overlayers with varied pore structures, such as disconnected micropores, interconnected micropores, and surface macropores, reveal that the hydrogen gas trapped in the cryogel protector reduce shear stress at the catalyst surface by providing bubble nucleation sites. The cryogelated overlayer effectively preserves the uniformly distributed platinum catalyst particles on the device surface for over 200 h. Our finding can help establish semi-permanent photoelectrochemical devices to realize a carbon-free society. Photoelectrodes made of earth-abundant materials can contribute to low-cost and carbon-free hydrogen production, but suffer from a short lifetime. Here the authors report cryogel overlayer to increase the operation time of the device by regulating evolving hydrogen bubble dynamics. [ABSTRACT FROM AUTHOR]

Resistance spot welding is a process with high variability regarding the quality of the produced joints. This means that key performance indicators (KPIs) such as geometrical and mechanical features as well as failure modes can deviate from the initial design even if the same process parameters are used. The industry has developed quality assurance programs and quality control methods for tracking these KPIs; however, most of them are based on offline or/and destructive practices. On the other hand, state-of-the-art approaches have made online quality assessment feasible and proved its necessity if a 100% quality rate is required. However, limited attention has been given to "closing the loop" and providing feedback for preventing and correcting process anomalies that cause quality variations in real time. In this study, the main gaps between the state of practice and the state of the art are discussed in the context of quality assurance for resistance spot welding. Finally, the role and importance of digital twins by taking into consideration the entire welding ecosystem in quality assurance are discussed in order to form the prospects for the road ahead. [ABSTRACT FROM AUTHOR]

Titanium alloys have emerged as the most successful metallic material to ever be applied in the field of biomedical engineering. This comprehensive review covers the history of titanium in medicine, the properties of titanium and its alloys, the production technologies used to produce biomedical implants, and the most common uses for titanium and its alloys, ranging from orthopedic implants to dental prosthetics and cardiovascular devices. At the core of this success lies the combination of machinability, mechanical strength, biocompatibility, and corrosion resistance. This unique combination of useful traits has positioned titanium alloys as an indispensable material for biomedical engineering applications, enabling safer, more durable, and more efficient treatments for patients affected by various kinds of pathologies. This review takes an in-depth journey into the inherent properties that define titanium alloys and which of them are advantageous for biomedical use. It explores their production techniques and the fabrication methodologies that are utilized to machine them into their final shape. The biomedical applications of titanium alloys are then categorized and described in detail, focusing on which specific advantages titanium alloys are present when compared to other materials. This review not only captures the current state of the art, but also explores the future possibilities and limitations of titanium alloys applied in the biomedical field. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Polytechnic is the property of Journal of Polytechnic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Directed energy deposition (DED) is a crucial branch of additive manufacturing (AM), performing repairs, cladding, and processing of multi-material components. 316L austenitic stainless steel is widely used in applications such as the food, aerospace, automotive, marine, energy, biomedical, and nuclear reactor industries. Nevertheless, there is need for process parameter optimization and a comprehensive understanding of the individual and complex synergistic effects of process parameters on the geometry, microstructure, and properties of the deposited material or component. This is essential for ensuring repeatable manufacturing of parts across a single or series of platforms over time, or for minimizing defects such as porosity. In this study, the response surface methodology (RSM) and central composite design (CCD) were employed to investigate the effects of laser power, laser scan speed, and powder mass flow rate on layer thickness, density, microstructure, and microhardness of 316L steel processed by Laser Engineered Net Shaping (LENS®) DED. Polynomial empirical prediction models correlating the applied processing parameters and the studied responses were developed. [ABSTRACT FROM AUTHOR]

In order to accurately and efficiently analyze the distribution law and motion status of lubricating oil in the spiral bevel gearbox of the electric multiple unit (EMU), a high-fidelity 3D CFD model of the spiral bevel gearbox of the EMU was established for the first time. The moving particle semi-implicit method was used to visualize the lubricating-oil flow field distribution characteristics of the gearbox. The distribution characteristics of lubricating oil in the gearbox with varying gear rotation speeds, initial lubricating-oil volume levels and oil temperatures were analyzed. It was found that the initial lubricating-oil volume is the factor with the largest influence, while the influences of gear rotation speed and oil temperature are relatively small. By analyzing the churning loss under various simulation conditions, it was found that the churning loss is positively correlated with the gear rotation speed and initial oil volume, and is more affected by the initial oil volume. The churning loss is negatively correlated with the oil temperature, and both are nonlinear relationships. The proportion of churning loss related to the driven gear is higher compared to that of the driving gear. These results can provide a theoretical basis for the subsequent optimization of the gearbox. [ABSTRACT FROM AUTHOR]

In manufacturing, thermomechanical processes such as static annealing and hot working are commonly used to tailor the microstructure of metals to achieve favourable macroscopic material properties that meet specific application requirements. To improve sequential manufacturing processes and to accurately predict the microstructural changes of the material along the process chain, physically motivated constitutive models are required that simultaneously account for the effects of recovery and recrystallisation, as well as grain size dependencies. To this end, Cho et al. [Int. J. Plasticity 112, 123–157 (2019)] proposed a macroscopic hypo‐elasticity based large strain thermoplasticity model that aims at the unification of the effects of static and dynamic recovery and recrystallisation, as well as grain growth and refinement. In the present contribution, the hypo‐elasticity based large strain recrystallisation formulation proposed by Cho et al. is transferred to a hyper‐elasticity based large strain thermoplasticity framework to overcome the limitations typically accompanied with hypo‐elasticity based formulations. For this purpose, an isotropic temperature dependent hyper‐elastic Hencky type formulation defined in logarithmic strains is combined with a temperature dependent von Mises yield criterion. The recrystallisation modelling approach by Cho et al. is adopted, assuming a non‐associated temperature dependent proportional hardening rate in the form of an Armstrong‐Frederick type hardening minus recovery format, wherein the proportional hardening related internal variable is interpreted as a measure of dislocation density. It is shown that the hyper‐elasticity based format results in a thermodynamical consistency condition that effectively constrains the physically motivated evolutions of recrystallised volume fraction and average grain size. To investigate the capability of the model to predict the material response of unified recrystallisation thermodynamically consistently, representative thermomechanical sequential loading conditions including static annealing and hot working are studied. [ABSTRACT FROM AUTHOR]

This study presents information on the behavior of paint baking (PB) after resistance spot welding of the 5- and 6xxx series aluminum alloys. The weld parameters are optimized, and the weld specimens are baked three times for 20 min at 180 °C to simulate the heat treatments required for paint baking. The mechanical properties of the samples were characterized by using the lap shear test, micro/nanoindentation hardness, and fatigue test. As the mechanical properties of the weld are affected by the characteristics of the heat-affected zone and those of the fusion zone, the microstructure of the cross-sections was also analyzed through optical and electron microscopy. The investigation of the 6xxx series welds showed that the post-processing heat treatment decreased both the strength and the toughness of the weld, which resulted from the reduced hardness of the microstructure. Additionally, the lap shear test indicated that the failure mode for the 6xxx series changed from nugget failure to partial nugget failure after the paint baking process. However, the mechanical properties of the 5xxx welds were not affected as much as the 6xxx series during baking heat treatment. The fatigue test for the 6xxx series showed a different tendency from the lap shear test. Its fatigue properties improved due to an increased elastic modulus after the heat treatment. [ABSTRACT FROM AUTHOR]

Sodium zinc phosphate glasses modified by Tl2O addition of composition Na2−xTlxZnP2O7 (x = 0, 0.005, 0.01, and 0.015) are synthesized following the melt quenching technique. The structure of the glass samples is analyzed by the Fourier transform infrared absorption spectroscopy. The results suggest that the phosphate network is polymerized by the addition of Tl+ ions. The electrical conductivity, electric modulus, and dielectric constant characteristics of the glasses are measured over a wide continuous frequency range of 10−2 Hz–1 MHz and in the temperature range 293–473 K by the impedance spectroscopic method. The ac conductivity data are analyzed following the power law exponent (S) and the proposed correlated barrier hopping mechanism (CBH) is the most suitable conduction mechanism in the studied compositions. The electrical modulus formalism is applied to analyze the electric data to study their dielectric relaxation. Non‐Debye type relaxation is obtained. From the obtained results, the present glass can be used as a high‐energy capacitor. [ABSTRACT FROM AUTHOR]

Background: Anti-GBM disease is a rare vasculitis mediated by pathogenic antibodies against collagen IV. Anti-GBM disease presents with rapid progressive glomerulonephritis and leads to kidney failure if untreated. KDIGO recommends plasma exchanges (PEX) for antibody elimination and steroids plus cyclophosphamide (CTX) to suppress antibody production. CTX is associated with severe side effects including gonadal toxicity. Rituximab (RTX) and mycophenolate mofetil (MMF) might be a less toxic but equally efficient alternative to CTX. Studies in pediatric anti-GBM disease patients receiving RTX and MMF instead of CTX are lacking., Methods: A retrospective survey in 8 tertiary German centers was performed. The clinical data of patients diagnosed between 2014 and 2022 were collected and analyzed., Results: Five adolescent patients treated with PEX and RTX and/or MMF due to anti-GBM disease were analyzed. All patients had anti-GBM antibodies, hematuria, glomerular proteinuria, and pulmonary hemorrhage. eGFR was 124 ml/min/1.73 m 2 (range 47-162), and all patients were non-dialysis-dependent but with relevant histological kidney affection (mean crescents on kidney biopsy 77%). Antibody clearance was achieved after 13 PEX cycles (range 6-31). Four out of 5 patients received methylprednisolone pulses. All patients received oral prednisolone and MMF, and four patients received a median of 4 RTX doses (range 2-4). After a mean follow-up of 27 months, 4/5 patients had conserved or improved kidney function, while one patient (20%) developed kidney failure., Conclusions: In this small series of pediatric non-dialysis-dependent anti-GBM disease patients, first-line treatment with RTX and MMF showed a favorable kidney outcome in 4/5 cases and had an acceptable side effect profile., (© 2024. The Author(s), under exclusive licence to International Pediatric Nephrology Association.)

The biomechanics of woodpeckers have captivated researchers for decades. These birds' unique ability to withstand repeated impacts, seemingly without apparent harm, has piqued the interests of scientists and clinicians across multiple disciplines. Historical and recent studies have dissected the anatomical and physiological underpinnings of woodpeckers' protective mechanisms and sparked interest in the development of woodpecker-inspired safety equipment. Despite the intuitive appeal of translating woodpecker adaptations into strategies for human traumatic brain injury (TBI) prevention, significant challenges hinder such innovation. Critical examinations reveal a lack of direct applicability of these findings to human TBI prevention, attributed to fundamental biological and mechanical dissimilarities between humans and woodpeckers. Additionally, some commercial endeavors attempting to capitalize on our fascination with woodpeckers are rooted in unsubstantiated claims about these birds. This paper explores the narrative surrounding woodpecker biomimicry, including its origins and history, and highlights the challenges of translating findings from unconventional animal models of TBI into effective human medical interventions., (© 2024 American Association for Anatomy.)

Background: Peritonitis is the leading cause of peritoneal dialysis (PD) discontinuation. However, few data concern risk factors of peritonitis development and catheter removal caused by treatment failure in pediatric patients., Methods: This single-center, retrospective study analyzed data from pediatric patients who underwent chronic PD between March 2002 and June 2022. The incidence rates of peritonitis by the person-year method were calculated, and they were stratified by patient age groups. Risk factors for peritonitis development and catheter removal were also analyzed by multivariate analysis using logistic regression model., Results: Ninety patients were enrolled, and 62 peritonitis episodes were observed in 41 (46%) patients. The incidence rate of peritonitis was 0.21 episodes per patient-year, which was the highest in children aged under 2 years old (0.26 episodes per patient-year). Moreover, 44 (71%) cases were successfully cured by antibiotics alone, although 17 (27%) cases required catheter removal, and 4 (6%) cases transitioned to chronic hemodialysis because of peritoneal dysfunction. One patient died. The risk factor for peritonitis development and catheter removal caused by treatment failure was PD insertion at under 2 years old (odds ratio = 2.5; P = 0.04) and Pseudomonas aeruginosa (odds ratio = 11.0; P = 0.04) in the multivariate analysis. P. aeruginosa was also a risk factor for difficulty in re-initiating PD (P = 0.004)., Conclusions: The incidence rate of peritonitis was the highest in children under 2 years old. P. aeruginosa peritonitis is a risk factor for catheter removal and peritoneal dysfunction., (© 2024. The Author(s), under exclusive licence to Japanese Society of Nephrology.)

An internal state variable (ISV)-based constitutive model has been used within a Lagrangian finite element analysis (FEA) framework to simulate ballistic impact of monolithic rolled homogenous armor (RHA) steel plates by RHA steel spheres and cylinders. The ISV model predictions demonstrate good agreement with experimental impact data for spherical projectiles. A simulation-based parametric sensitivity study was performed to determine the influence of a variety of microstructural and mechanical properties on ballistic performance. The sensitivity analysis shows that the lattice hydrogen concentration, material hardness, and initial void volume fraction are dominant factors influencing ballistic performance. Finite element simulations show that variation of microstructure properties could explain the reduced ballistic performance of high hardness materials previously documented in the literature. The FEA framework presented in this work can be used to determine material properties conducive to ballistic-impact resistance. [ABSTRACT FROM AUTHOR]

The step hollow shaft components are composed of two layers of different materials, they are formed using tube hydroforming process due to its high strength and rigidity, low weight and flexible profiles, compared to traditional casting, welding, and forming methods. These products are effectively used in industries such as the automotive, shipbuilding, aerospace and defense, and oil and gas sectors. The success of various double layer pipe hydroforming process depends on several factors, with the most important being the internal pressure path and axial loading path. This paper presents research on the effect of input loading paths on the hydroforming ability of a different two-layer metal structure - an outer layer of SUS304 stainless steel and an inner layer of CDA110 copper - using 3D numerical simulations on Abaqus/CAE software. Output criteria were used to evaluate the forming ability of the formed components, including Von Mises stress, Plastic strain component (PEmax), wall thinning, and pipe profile, based on which the input loading paths were combined during the forming process. These output criteria allow for more accurate predictions of material behavior during the hydroforming process, as well as deformation and stress distribution. This can support the design process, improve product quality, reduce errors, and increase production efficiency. The research results can be applied as a basis for optimizing load paths for the next experimental step in the near future, for undergraduate and graduate training, as well as allowing designers and engineers to optimize the process of hydroforming of different 2-layer tubes, reducing costs, improving accuracy, flexible design, minimizing risks, and increasing efficiency. [ABSTRACT FROM AUTHOR]

The woodpecker family (Picidae) includes numerous species that vary in size and plumage colouration, but which share many easily recognisable external features. These birds possess pronounced anatomical adaptions that enable them to exploit arboreal habitats and live in niches that are inaccessible to most other birds. The aim of this study was to increase our knowledge on the relationships between skull shape, habitat preference, pecking abilities and foraging habits of 10 European woodpecker species. A geometric morphometric approach was used to analyse two-dimensional cranial landmarks. We used principal component (PC) analyses on those measurements that may be related to habitat preference and foraging habits. The PCs resulted in descriptions of the relative length and width of the bill, variation in its relative size, orientation of the nostrils variation in the elongation of the neurocranium, the relative size and position of the palatine bone, length of the rostrum, and the thickness of the mandible bone. The analysis showed and confirmed the presence of some cranial elements that are strongly associated with habitat preference, pecking behaviour and excavation abilities. [ABSTRACT FROM AUTHOR]

The tensile residual stress (TRS) generated due to large thermal gradient during the laser directed energy deposition (DED) and laser based powder bed fusion (PBF) is one of the major concerns. TRS leads to lower tensile, fatigue strength, distortion, reduced corrosion resistance, pores, etc. This concerns can be mitigated using laser shock peening (LSP). The basic principles and characteristics of each process i.e., PBF, DED, and LSP process, followed by popular metallic materials used by PBF and LDED processes are discussed. The applications and drawbacks of each process are presented. This review paper discusses the recent progress on the LSP of laser based PBF/DED manufactured samples. Different approaches and challenges to hybrid AM + LSP are also presented in this paper i.e. LSP after every certain layer and LSP after the whole part is manufactured. Even though the LSP after every certain layer offers deep CRS inside a part, it is a very time-consuming and difficult process as constant removing, polishing, and resetting of the samples compromising the parts' accuracy. Frequent change of workstation between LSP and AM is also a major problem while benefits of LSP after the whole part is manufactured are limited to the surface. The introduction of finer grains after LSP led to an increased microhardness and reduced pores thus increasing the tensile and fatigue life of the parts. The challenges and future scope are delineated. [ABSTRACT FROM AUTHOR]

In this paper, the microstructure characteristics and mechanical properties (including nano‐indentation, tensile, and penetration behaviors) of the scales from pinecone fish (Monocentris japonica) were investigated. The M. japonica scales display a unique hierarchical structure and consist of three layers: an outer bone layer with high mineralization, an intermediate bone layer with obvious pore structures, and an inner collagen layer composed of multiple plies of collagen fibers. The hardness and indentation modulus of the three structural layers exhibit gradient changes, and decrease gradually from the outer layer to the inner layer. Tensile tests show that the tensile response and failure modes of the scales are different under dry and hydrated conditions. The dry scales have higher tensile strength (46.35 MPa) and Young's modulus (0.74 GPa), while the hydrated scales exhibit higher ultimate strain (20.18%) and toughness (4.57 MPa). Penetration tests indicate that the scales have a significantly high resistance to penetration, and increase the penetration force by more than six times compared with the descaled skin. Furthermore, the structure–property relationship of the M. japonica scales was discussed. It is found that the hard outer layer and the porous intermediate layer help to disperse the stress, and the soft inner layer containing collagen fiber plies helps to deflect the crack propagation, which are responsible for the excellent mechanical properties of the scales. The outcome of this study can provide a valuable biomimetic design inspiration for lightweight and high‐strength composite materials in engineering fields. Research Highlights: Microstructure characteristics and mechanical properties of the Monocentris japonica scales were investigated.The M. japonica scales can be divided into three layers rather than two layers.The M. japonica scales exhibited high tensile strength and penetration resistance. [ABSTRACT FROM AUTHOR]

Continuum damage mechanics (CDM) has sparked a lot of scientific attention during the last few decades. The CDM approach defines a damage variable as an effective surface density of microcracks or voids with a plane of representative volume element to circumvent the scale mismatches in the involved physics. The smallest volume element at which a solid is regarded as continuous and all of the material's properties are represented as homogenized variables is referred as the representative volume element. A vital and challenging issue in CDM is to quantify the damage variable D. The various direct and indirect techniques of damage appraisal methodologies are extensively discussed in this review. The direct method is qualitative, whereas the indirect method is quantitative. Damage assessment using an indirect approach is simple and can be obtained through experiments. The evaluation of damage by degradation of elasticity modulus, an indirect method, has proven to be more popular and accurate than the other methods for ductile materials. The present work reviews and summarizes the various ductile damage development models, their evolution through time, and the importance of CDM in contemporary engineering research. [ABSTRACT FROM AUTHOR]

Biopolymer functionalization is perceived as an innovative approach to revolutionizing bio-catalyzed chemical transformations. Lignin, the chief natural source of polyphenols, has an aromatic structure with plenty of beneficial chemical groups. Accordingly, lignin can be functionalized, copolymerized, or recombined with different types of chemicals to produce highly efficient catalysts. Moreover, the stability and biodegradability of lignin make it an efficient bio-immobilizer for diverse metals (Pt, Pd, Ag, Cu, Co, Fe, etc.), which are known for their excellent catalytic performances. In addition, the solid nature of the lignin-derived catalysts has excellent advantages in terms of simple catalyst recovery and reuse over consecutive cycles with high stability. The present work compiles the newly adopted approaches to valorize lignin in the field of catalysis. Lignin-derived acid and base catalysts, lignin metal-free catalysts, and lignin-supported metal catalysts have demonstrated the full potential of lignin in hydrolysis, esterification, oxidation, condensation, hydration, and multicomponent reactions. The synthesis methods, properties, and catalytic capacity of lignin-based catalysts were assessed and contrasted with conventional catalysts. Attractively, the inclusion of lignin in catalysis appeared as a novel upgrading strategy that offers eco-friendly and profitable materials, leading to simple and green chemical synthesis, as well as a revolutionary shift in the industrialization of biomass-derived materials generally, and functionalized lignin-based catalysts specifically. [ABSTRACT FROM AUTHOR]

Historically, titanium alloys have been developed disregarding the addition of eutectoid β-stabilisers as they generally lead to the formation of brittle intermetallic phases upon solidification of the alloy. However, such phenomenon can be prevented using powder metallurgy. Thus, this study considered the concurrent addition of cheap strong eutectoid β-stabilisers, namely Mn and Fe, for the development of new ternary Ti–Mn–Fe alloys, reducing the intrinsic cost of Ti alloys. It is found that the progressive addition of Mn and Fe in equal concentration enhances the densification of Ti during sintering, leading to lower amount of residual porosity, the transformation of the microstructure from purely lamellar to metastable, and the associated refinement of the microstructural features (grains and lamellae), as well as the stabilisation of a greater amount of β phase, and the formation of the metastable α″ phase. Such microstructural changes result in the strengthening (higher yield and ultimate tensile strength and hardness) and embrittlement of the alloy by changing the fundamental strain hardening mechanism of the ternary Ti–Mn–Fe alloys. [ABSTRACT FROM AUTHOR]

The residual stress of crystalline materials induced by deformation at grain level strongly correlates with crystal orientation. In the present work, the dependence of residual stress on crystallographic orientation in diamond cutting of polycrystalline aluminum is investigated by crystal plasticity finite element modeling and simulations. Furthermore, corresponding ultra-precision diamond cutting experiments, which have the same parameter setup with the finite element model, are also carried out. The crystallographic orientations of the specimens are depicted by electron backscattered diffraction characterization, and the surface residual stress is measured by X-ray diffraction. Both experiment and finite element simulation results demonstrate the anisotropic characteristics of the residual stress within machined polycrystalline aluminum, which exhibits the significant correlation with crystallographic orientation. Furthermore, finite element simulations of bi-crystal cutting are also performed, which indicate that the grain boundary also has a strong influence on the generation of residual stress. [ABSTRACT FROM AUTHOR]

In this study, the nonlinear vibration of a meshing gear pair with the teeth elasticity is investigated. The elastic elements between the teeth and the body of each gear wheel are introduced to partially incorporate the teeth elasticity in the model. This model was originally considered by the second author as a rigid-elastic modeling approach of meshing gear wheels, which is well-suited for multibody systems. The contact analysis of the meshing teeth is performed using the Kelvin-Voigt method. By deriving the equations of motion for the mentioned model, the results of the numerical solution are presented. The method of multiple scales is utilized here for the first time to analytically analyze the nonlinear vibration of a gear system in which the teeth elasticity is partially incorporated by considering identical elastic elements between the teeth and the gear body. In this study, the effect of system parameters on the frequency response including the primary, sub-harmonic, and super-harmonic resonances is investigated. The results of the analytical solution show that the effect of external excitation amplitude and intensity on the system response amplitude is the same in the primary and sub-harmonic resonances. The results obtained numerically and analytically for the model have an acceptable agreement. [ABSTRACT FROM AUTHOR]

Objective: To describe clinical spectrum, as well as biochemical and histological factors that could predict severe presentations and renal outcomes among children with rapidly progressive glomerulonephritis (RPGN) due to postinfectious glomerulonephritis (PIGN). Material and Methods: A retrospective cohort study was conducted at Chiang Mai University Hospital, Thailand between February 2008 and January 2018. Ninety-six pediatric patients with PIGN were recruited. Clinical presentations, disease courses, laboratory data, renal histopathology, treatment, and outcomes were analyzed. Compare clinical manifestation and outcome between the two groups. Results: The median age (interquartile range, IQR) was 11 (8 to 13) years with a male-to-female ratio of 1.8:1. RPGN was identified in 51.04% (49/96 patients). PIGN children with RPGN exhibited a higher prevalence of nephrotic range proteinuria (69.4% versus 53.2%, p=0.04), nephrotic syndrome (46.9% versus 17%, p=0.002), and hypoalbuminemia (81.3% versus 53.8%, p<0.0001) compared with those without RPGN. Multivariate analysis revealed that anuria, and hypoalbuminemia were predicting factors of RPGN [odd ratios 0.07 (95% CI 0.01 to 0.77), p=0.03 and 0.23 (95% CI 0.08 to 0.69), p=0.006, respectively]. Follow-up data were available among 78 patients (81.3%) with a median follow-up time of 762 (256.3 to 1,293) days. Complete remission was identified in all of PIGN without RPGN but only 71.4% in the RPGN group. Kaplan-Meier analysis revealed that patients with RPGN had a longer recovery time of generalized edema at 14 days (95% CI 12 to 15.9) versus 9 days (95% CI 7 to 12), p=0.023; proteinuria at 16 weeks (95% CI 11 to 20.8) versus 8 weeks (95% CI 4.25 to 15.75), p<0.0001; and impaired glomerular filtration rate (GFR) of nine weeks (95% CI 4.8 to 13.2) versus two weeks (95% CI 1 to 8), p=0.003. Subgroup analysis of prognostic factors of PIGN with RPGN revealed that high BMI z-score and kidney replacement therapy (KRT) requirement were associated with poor renal outcomes. Conclusion: Hypoalbuminemia and anuria were predictive factors of RPGN in PIGN. High BMI z-score and low GFR required acute KRT were predictive factors of poor renal outcomes. [ABSTRACT FROM AUTHOR]

The clinical impact of infections due to extended-spectrum β-lactamase (ESBL)- and/or carbapenemase-producing Enterobacterales (Ent) has reached dramatic levels worldwide. Infections due to these multidrug-resistant (MDR) pathogens—especially Escherichia coli and Klebsiella pneumoniae—may originate from a prior asymptomatic intestinal colonization that could also favor transmission to other subjects. It is therefore desirable that gut carriers are rapidly identified to try preventing both the occurrence of serious endogenous infections and potential transmission. Together with the infection prevention and control countermeasures, any strategy capable of effectively eradicating the MDR-Ent from the intestinal tract would be desirable. In this narrative review, we present a summary of the different aspects linked to the intestinal colonization due to MDR-Ent. In particular, culture- and molecular-based screening techniques to identify carriers, data on prevalence and risk factors in different populations, clinical impact, length of colonization, and contribution to transmission in various settings will be overviewed. We will also discuss the standard strategies (selective digestive decontamination, fecal microbiota transplant) and those still in development (bacteriophages, probiotics, microcins, and CRISPR-Cas-based) that might be used to decolonize MDR-Ent carriers. [ABSTRACT FROM AUTHOR]

Under fatigue loading, the stiffness decrease in short-fiber reinforced polymers reflects the gradual degradation of the material. Thus, both measuring and modeling this stiffness is critical to investigate and understand the entire fatigue process. Besides evolving damage, viscoelastic effects within the polymer influence the measured dynamic stiffness. In this paper, we study the influence of a linear viscoelastic material model for the matrix on the obtained dynamic stiffness and extend an elastic multiscale fatigue-damage model to viscoelasticity. Our contribution is two-fold. First, we revisit the complex-valued elastic models known in the literature to predict the asymptotic periodic orbit of a viscoelastic material. For small phase shifts in an isotropic linear viscoelastic material, we show through numerical experiments that a real-valued computation of an "elastic" material is sufficient to approximate the dynamic stiffness of a microstructure with a generalized Maxwell material and equal Poisson's ratios in every element as matrix, reinforced by elastic inclusions. This makes standard solvers applicable to fiber-reinforced thermoplastics. Secondly, we propose a viscoelastic fatigue-damage model for the thermoplastic matrix based on decoupling of the time scales where viscoelastic and fatigue-damage effects manifest. We demonstrate the capability of the multiscale model to predict the dynamic stiffness evolution under fatigue loading of short-fiber reinforced polybutylene terephthalate (PBT) by a validation with experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a red-eared slider turtle is used as the prototype for the bionic design of the foamed silicone rubber sandwich structure. The effect of impact angle on the performance of the foamed silicone rubber sandwich structure against low-velocity impact is studied by the finite element method. The numerical model uses the intrinsic structure model of foamed silicone rubber with porosity and the three-dimensional Hashin fiberboard damage model. The validity of the model was verified after experimental comparison. Based on the finite element simulation of different impact angles and velocities, the relationship between impact velocity and residual velocity, as well as the penetration threshold at various impact angles are obtained, and the change law of impact resistance of foamed silicone rubber sandwich structure with impact angle and velocity, as well as the damage pattern of sandwich structure at different impact angles and velocities are given. The results can provide a basis for the impact resistance design of the bionic foamed silicone rubber sandwich structure. The results show that, at a certain impact speed, the smaller the impact angle, the longer the path of the falling hammer along the plane of the sandwich structure, the lighter the damage to the sandwich structure and the greater the absorbed energy, so that avoiding the impact from the frontal side of the sandwich structure can effectively reduce the damage of the sandwich structure. When the impact angle is greater than 75°, the difference in impact resistance performance is only 2.9% compared with 90°, and the impact angle has less influence on the impact resistance performance at this time. [ABSTRACT FROM AUTHOR]

Shot peening is a surface modification technology with the metal surface nano machine (SNC), which can modify the surface microstructure and extend the fatigue life of Cu-19Ni alloy. The hardness, damage evolution and mechanical properties were investigated and characterized by scanning electron microscope (SEM), laser confocal microscope (LSM) and material surface performance tester (CFT). The results showed that the surface roughness and friction coefficient of Cu-19Ni alloy decreased with the increase of shot peening duration and diameter, while the microhardness and strength increased. Moreover, with the increase in shot peening duration and diameter, SEM observation showed that the fracture dimples became smaller, meanwhile, with the increase of small cleavage planes, shear tearing ridges and the thickness of the surface nano layer, the fracture mode gradually evolved from plastic to brittle fracture. The uniaxial tensile test of shot peened Cu-19Ni alloy was carried out by MTS testing machine combined with digital image correlation technology (DIC). The evolution of Cu-19Ni surface damage was analyzed, and the evolution equations describing the damage of large deformation zone and small deformation zone were established. The effect of shot peening on the damage evolution behavior of Cu-19Ni alloy was revealed. [ABSTRACT FROM AUTHOR]

Zero-backlash high-precision roller enveloping reducers (ZHPRER) possess a wide array of potential applications in the field of industrial robot because of their high precision and efficiency. This paper presents a pilot study to verify the applicability of this type of reducers in industrial robots. An industrial robot was designed such that its joint reducers were the roller enveloping reducers. A dynamic model for this robot which accounts for the dynamic responses of the reducers was also established using multibody dynamics. This dynamic model was then used for analyzing the dynamic behavior of the joint reducers and the body of the robot under different operating conditions. Simulation results yielded from the developed model were verified by comparing them with the data obtained from experiments. The present study for the first time confirms the evident advantages of ZHPRER for industrial robotic applications. Meanwhile, the proposed dynamic model for the industrial robot provides theoretical support for the subsequent design of error compensation control. [ABSTRACT FROM AUTHOR]

Various solid base catalysts have been used for biodiesel production from different edible and non-edible vegetable oils. Hitherto, reports pertaining to dual-basic metal oxides onto an acidic support is very limited. Herein, we have conducted a novel study using Na2O-K2O and MgO-CaO impregnated into Active Natural Mordenite (ANM) as Na2O-K2O/ANM and MgO-CaO/ANM for kapok seed oil transesterification. The physicochemical properties of the as-synthesized catalysts were analyzed using XRD, XRF-He, SEM, AAS, acidity, and surface area. The results showed that the activation of natural mordenite could reduce impurities, increase acidic strength, and the surface area. A series of ratio on Na2O:K2O and MgO:CaO was fine-tuned to give the highest biodiesel production. The catalyst, Na2O-K2O/ANM, with a concentration of 50% and ratio of 1:1 showed the lowest acidity, 0.352 mmol/g, and gave the highest yield of 72.29%. The highest yield, 84.54%, was obtained from MgO-CaO/ANM (40%; 2:1), with the lowest acidity of 0.331 mmol/g. Biodiesel properties, from the transesterification of the kapok seed oil, were characterized by SNI 7182:2015 standards. The characteristics of synthesized biodiesel met the used standard, and in terms of reaction activity, it is found that the alkalinity level of the catalyst is more influential than its surface area. [ABSTRACT FROM AUTHOR]

This study aims to focus on fatigue life assessment on GMAW of DMR249A steel (UNS K12249). The fatigue test was carried out using five levels of yield strength and completely reversed stress cycle. The fatigue behavior of HSLA steel correlated with tensile, impact, hardness, and microstructural characteristics. The maximum recorded fatigue life of the GMAW and parent metal is about 355 and 394 MPa, respectively. The fatigue properties of GMAW joints are relatively lower due to internal residual stress, grain deformation, and microstructural changes. Although, the produced S–N curves of the DMR249A steel were compared to the conventional IIW FAT curve. [ABSTRACT FROM AUTHOR]

Three RC beam-column subassemblages, in which the concrete columns were reinforced by multiple composite central reinforcements and multiple-steel stirrups, were tested under reversed cyclic loading. The test results show that the increase in axial compression ratio (increased from 0.2 to 0.35) had little effect on the energy dissipation, but increased the peak load by 60.5% and decreased the ultimate deformation by 34.4%. The increase in shear span ratio of the column (increased from 2.6 to 3.7) improved the energy dissipation and deformation capacity, but decreased the peak load by 17.6%. In addition, the stress–strain relationships of the concrete confined by multiple stirrups were represented by functions with different levels of confinement, and an equivalent coefficient was proposed to simplify the computation. Finally, the analytical methods to predict the yielding response and deformation constitution of the specimen were developed. [ABSTRACT FROM AUTHOR]

Copyright of Acta Médica Peruana is the property of Colegio Medico del Peru and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This research presents a comprehensive review regarding polymeric composite with and without damages under the influences of high-strain loading. Additionally, the kind of strain loading on the polymeric structure or structural component is studied from the year 2011 to 2022. However, most of the studies have been consolidated from 2017 to 2022. Also, this review reveals the necessity of a damaged structure under high-strain loading. The various numerical models, i.e., the rate-dependent cohesive zone model, thermomechanical numerical models, enhanced equation of motion and viscosity type of constitutive model, are helpful for easy understanding of different influencing parameters including the strain rate effects provided in details. [ABSTRACT FROM AUTHOR]

The Barcelona model is one of the most widespread models used in the nonlinear finite element method for simulating the real behavior of concrete. The strong robustness of this model can be attributed to two main reasons, the first one being its ability to account for the elastic stiffness degradation induced by plastic straining and the second one the aptness of considering the stiffness recovery effects under cyclic loading. This model was examined in the paper by comparing the generated stress-strain diagrams with several analytical solutions from the literature. The comparing process in the compression and tension cases with the closed-form solutions of Desayi, Krätzig, Lubliner and Thorenfeldt proved that the Barcelona model provided identical outcomes with Lubliner's formula, which was used as the hardening function in the finite element implementation of this model. What is more, this model provided the same curves in case of the others in the ascending branches, and for the descending branch, this study proved that the outcomes of the Barcelona model are completely different from the ones of Desayi in the compression case and slightly similar to Thorenfeldt's curves in the tension case. [ABSTRACT FROM AUTHOR]