Shear Conditions Research Articles

Fabrication of high-strength and tough PLA/PBAT composites via in-situ copolymer formation using an adaptable epoxy extender.

Developing biodegradable polymers with superior mechanical performance offers a sustainable solution to address the severe environmental challenges posed by conventional plastics. Poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT), two prominent biodegradable plastics, exhibit complementary mechanical properties. However, their inherent incompatibility and significant viscosity mismatch cause significant challenges for effective blending via the conventional methods. Herein, we propose an innovative strategy that integrates kinetic and thermodynamic principles to fabricate PLA/PBAT composites with high strength and high toughness. An adaptable ternary copolymer, presenting strong affinity with both PLA and PBAT segments, was employed as an epoxy chain extender (EE) to covalently couple PLA and PBAT under high shear conditions. The high-shear reactor reduced the size of the dispersed phase and significantly expanded interface area, providing abundant reaction sites for EE. This enabled the in-situ generation of abundant PLA-PBAT copolymers, as evidenced by increased melt viscosities and higher molecular weight of the resulting products. By optimizing the EE content to 2.5 wt%, PLA/PBAT composite achieved an exceptional balance between strength (47.6 MPa) and toughness (229.3 MJ/m3), representing improvements of 47 % and 34-fold, respectively, over conventional PLA/PBAT blend. This work provides a scalable and robust platform for developing high-performance biodegradable composites from immiscible polymers.

A Computational Fluid Dynamics Analysis of BiPAP Pressure Settings on Airway Biomechanics Using a CT-Based Respiratory Tract Model.

Central and Obstructive Sleep Apnea (CSA and OSA), Chronic Obstructive Pulmonary Disease (COPD), and Obesity Hypoventilation Syndrome (OHS) disrupt breathing patterns, posing significant health risks and reducing the quality of life. Bilevel Positive Airway Pressure (BiPAP) therapy offers adjustable inhalation and exhalation pressures, potentially enhancing treatment adaptability for the above diseases. This is the first-ever study that employs Computational Fluid Dynamics (CFD) to examine the biomechanical impacts of BiPAP under four settings: Inspiratory Positive Airway Pressure (IPAP)/Expiratory Positive Airway Pressure (EPAP) of 12/8, 16/6, and 18/8 cmH2O, compared to a without-BiPAP scenario of zero-gauge pressure. Utilizing a computed-tomography-based respiratory tract model from the nasal cavity extending to the 13th generation, we analyzed parameters such as static pressure, shear stress, and airway wall normal force across different airway regions. Our results indicate that BiPAP, particularly at higher IPAP settings, effectively increases static pressure, thereby improving airway patency and potentially reducing the risk of airway collapse in both CSA and OSA. Lower EPAP, on the other hand, helps reduce the work of breathing during exhalation, which is particularly useful for patients who have difficulty exhaling against higher pressures or need to exhale CO2 more effectively. This comparative analysis confirms that BiPAP not only maintains open airways but does so with an adjustable approach that can be used for the specific needs of patients with various respiratory dysfunctions, thereby offering a versatile and effective treatment option.

Study on the Adhesion Properties of Raw Coal and Adhesive Clogging Characteristics of Underground Coal Bunkers

The automation and continuous operation of coal production are fundamental to the construction of high-yielding and efficient mines. Underground coal bunkers, serving as the pivotal link between various production and transportation segments, are vital for the seamless operation of mines. Nonetheless, the adhesive properties of raw coal can lead to increasingly severe issues, such as the adhesive clogging of coal bunkers. To address this issue, this paper first employs a self-designed raw coal shear testing apparatus to conduct experiments under varying conditions of shear interfaces, moisture content in raw coal, and compaction forces. Obtaining the adhesion behavior characteristics and adhesion parameter variation patterns of raw coal at coal-coal and coal-wall interfaces under various influencing factors. Subsequently, leveraging the adhesion property parameters of raw coal and the engineering conditions of the 1011 roadway coal bunker in Taoyuan Coal Mine II, a numerical model for coal bunker discharge using irregular particles was developed with the PFC2D numerical simulation software. Based on these, we obtained the influence patterns of various factors, such as coal bunker convergence angle, coal storage height, and coal moisture content, on the coal particle flow pattern, bunker wall pressure, and adhesive clogging distribution characteristics of the coal bunker during the discharge process, thereby revealing the mechanisms underlying the adhesive clogging phenomenon. The findings offer significant insights for optimizing solutions to the adhesive clogging issues in underground coal bunkers and ensuring their safe and efficient operation.

Comparative Study on Hyperelastic Constitutive Models for the Static and Dynamic Behavior of Resilient Mounts.

Resilient mounts play a vital role in anti-vibration and shock-absorption systems, making precise estimation of their static and dynamic stiffness essential for ensuring optimal mechanical performance and effective design. This study investigates the behavior of resilient mounts by analyzing their static and dynamic stiffness characteristics through the application of various hyperelastic constitutive models. Seven hyperelastic models were reviewed and systematically compared using numerical simulations, experimental data, and analytical solutions. The model parameters were calibrated and optimized based on experimental results obtained from quasi-static loading tests, including tension, compression, and shear conditions. Additionally, frequency response simulations were employed to evaluate the dynamic behavior of the resilient mounts under varying preload scenarios. The results provide practical insights into the performance of hyperelastic models and offer a comprehensive guideline for selecting suitable models for resilient mount applications, contributing to improved accuracy in both static and dynamic performance predictions.

Determination of Mechanical Properties of Blind Rivet Joints Using Numerical Simulations and Experimental Testing.

This study explores the tensile performance of blind rivet joints in galvanized steel sheets, focusing on their behavior under shear and normal load conditions. Blind rivets are frequently used in structural applications due to their ease of installation and ability to be applied from one side, making them highly effective in industries like aerospace and automotive. Two types of DIN 7337-4.8 × 8 blind rivets-galvanized steel St/St and stainless steel A2/A2-paired with galvanized steel sheets DX51D + Z275, were experimentally tested to assess how their material properties affect their joint strength, deformation patterns, and failure modes. Single-lap shear, double-lap shear, and pure normal load tests were conducted in multiple configurations to evaluate joint performance under varying loading conditions, simulating real-world stresses. Using custom-built equipment, controlled forces were applied perpendicular to the rivet joints to replicate practical loading conditions. The results revealed distinct differences in the load-bearing capacities of the two materials, offering valuable insights for applications where corrosion resistance and structural integrity are critical. Finite element analysis (FEA) was then used to simulate the behavior of the joints, with the results validated against experimental data. To enhance the reliability of numerical simulations in optimizing the design of rivet joints, a methodology was proposed to calibrate non-linear FEA models to experimental results, and a substantial agreement of 92.53% was achieved via optimization in ANSYS OptiSLang. This research contributes to our broader understanding of riveted connections, providing practical recommendations for assessing the performance of such joints in various engineering fields.

Estimating punching performance in fiber-reinforced polymer concrete slabs utilizing machine learning and gradient-boosted regression techniques

ABSTRACT The study explores the perforating shear performance of Fiber-Reinforced Polymer (FRP) concrete blocks using machine learning techniques like Gradient-Boosted Regression Trees (GBRT), k-nearest Neighbours (KNN), and Lasso Regression. It aims to predict the structural integrity of FRP blocks under shear conditions based on experimental data. The models were assessed using Coefficient of Determination (R2), Root Mean Square Error (RMSE), and Mean Absolute Error (MAE). GBRT demonstrated superior performance during training with an R2 of 0.9786, RMSE of 52.75, and MAE of 34.12, indicating strong predictive accuracy and minimal error. It outperformed KNN (R2 = 0.92, RMSE = 83.91, MAE = 45.71) and Lasso Regression (R2 = 0.71, RMSE = 162.45, MAE = 115.83). In validation, GBRT again excelled with an R2 of 0.93, RMSE of 76.23, and MAE of 58.46, confirming its robustness in generalizing unseen data. KNN showed lower performance in validation (R2 = 0.86), with increased error values, while Lasso lagged further behind (R2 = 0.681, RMSE = 185.23, MAE = 138.34). GBRT consistently outperformed traditional regression methods, highlighting its potential for more accurate and reliable structural analysis in FRP concrete slabs.

Mechanical properties of consolidated water-saturated natural gas hydrate-bearing silty-clayey sediments under undrained shearing conditions

Mechanical properties of consolidated water-saturated natural gas hydrate-bearing silty-clayey sediments under undrained shearing conditions

The Mechanical Performance of Resistance Welded Thermoplastic Composite Double Overlap Joint Tested Under Static and Fatigue Loading

ABSTRACTThe results of testing resistance welded joints using double lap shear (DLS) specimens are presented. The welded joints of polyetheretherketone reinforced with carbon 5‐harness satin weave (CF/PEEK) were made using two steel meshes with wire diameters of 0.04 mm and 0.1 mm. Additionally, the impact of welding with thin glass fabric (48 gsm) as an electrical insulator on joint strength was investigated. The specimens with selected process parameters were then fatigue‐tested at various percentages of their static shear strengths at a load ratio R = 0.1 and frequency f = 10 Hz. The performances of resistance welded DLS‐B specimens were compared with the current state of art, especially in the context of the use of SLS specimens. The failure modes of the specimens were presented, and a linear stress‐life (S–N) curve was drawn and analyzed.

Foreshocks, aftershocks, and static stress triggering of the 2020 Mw 4.8 Mentone Earthquake in west Texas

Foreshocks are the most obvious signature of the earthquake nucleation stage and could, in principle, forewarn of an impending earthquake. However, foreshocks are only sometimes observed, and we have a limited understanding of the physics that controls their occurrence. In this work, we use high-resolution earthquake catalogs and estimates of source properties to understand the spatiotemporal evolution of a sequence of 11 foreshocks that occurred ~ 6.5 hours before the 2020 Mw 4.8 Mentone earthquake in west Texas. Elevated pore-pressure and poroelastic stressing from subsurface fluid injection from oil-gas operations is often invoked to explain seismicity in west Texas and the surrounding region. However, here we show that static stresses induced from the initial ML 4.0 foreshock significantly perturbed the local shear stress along the fault and could have triggered the Mentone mainshock. The majority (9/11) of the earthquakes leading up to the Mentone mainshock nucleated in areas where the static shear stresses were increased from the initial ML 4.0 foreshock. The spatiotemporal properties of the 11 earthquakes that preceded the mainshock cannot easily be explained in the context of a preslip or cascade nucleation model. We show that at least 6/11 events are better classified as aftershocks of the initial ML 4.0. Together, our results suggest that a combination of physical mechanisms contributed to the occurrence of the 11 earthquakes that preceded the mainshock, including static-stressing from earthquake-earthquake interactions, aseismic creep, and stress perturbations induced from fluid injection. Our work highlights the role of earthquake-earthquake triggering in induced earthquake sequences, and suggests that such triggering could help sustain seismic activity following initial stressing perturbations from fluid injection.

Investigating the Influence of Hydrogel and Oleogel Ratios on Physico Chemical Characteristics, Microstructure, Rheology, and Texture of a Food Grade Bigel.

Bigels are promising technological advancements for application in the food industry, e.g., texture modification, controlled release, bioactive encapsulation, etc. Here, we focus on the fabrication and characterization of food-grade bigels from flaxseed-beeswax oleogel (OG) and pectin hydrogel (HG) under high shear conditions. Bigels were characterized by using FTIR, XRD, DSC, fluorescence microscopy, rheology, and texture analysis. Bigels retained the characteristics of both OG and HG, as evident from the OG's physical colloidal interactions and the HG's H-bonding in the bigel. Microscopic images revealed intricate network structures from both the HG and OG, with an increased OG fraction contributing to better homogeneity. The rheological properties of the bigels were in agreement with the textural attributes, revealing insights into the enhancement of tactile qualities. The synergistic effect of the OG and HG in bigels resulted in improved viscoelasticity and gel strength. Overall, the study helps in a holistic understanding of the interplay between composition and various attributes of bigels.

Tracing hierarchical star formation out to kiloparsec scales in nearby spiral galaxies with UVIT

abstract Molecular clouds fragment under the action of supersonic turbulence and gravity, which results in a scale-free hierarchical distribution of star formation within galaxies. Recent studies suggest that the hierarchical distribution of star formation in nearby galaxies shows a dependence on host galaxy properties. In this context, we study the hierarchical distribution of star formation from a few tens of parsecs up to several kiloparsecs in four nearby spiral galaxies: NGC 1566, NGC 5194, NGC 5457, and NGC 7793, by leveraging large-field-of-view and high-resolution far-ultraviolet (FUV) and near-ultraviolet (NUV) observations from the UltraViolet Imaging Telescope (UVIT). Using the two-point correlation function, we infer that the young star-forming clumps (SFCs) in the galaxies are arranged in a fractal-like hierarchical distribution, but only up to a maximum scale. This largest scale of hierarchy ($l_ corr $) is ubiquitous in all four galaxies and ranges from 0.5 kpc to 3.1 kpc. The flocculent spiral NGC 7793 has roughly five times smaller $l_ corr $ than the other three grand design spirals, possibly due to its lower mass, lower pressure environment, and a lack of strong spiral arms. $l_ corr $ being much smaller than the galaxy size suggests that the star formation hierarchy does not extend to the full galaxy size and it is likely an effect set by multiple physical mechanisms in the galaxy. The hierarchical distribution of SFCs dissipates almost completely within 10$-$50 Myr in our galaxy sample, signifying the migration of SFCs away from their birthplaces with increasing age. The fractal dimension of the hierarchy for our galaxies is found to be between 1.05 and 1.50. We also find that depending upon the star formation environment, significant variations can exist in the local and global hierarchy parameters of a galaxy. Overall, our results suggest that the global hierarchical properties of star formation in galaxies are not universal. This study also demonstrates the capabilities of UVIT in characterising the star formation hierarchy in nearby galaxies. In the future, a bigger sample can be employed to better understand the role of large-scale galaxy properties such as morphology and environment as well as physical processes like feedback, turbulence, shear, and interstellar medium conditions in determining the non-universal hierarchical properties of star formation in galaxies. abstract

Influence of Laser Micro-Texturing and Plasma Treatment on Adhesive Bonding Properties of WC-Co Carbides with Steel.

This article presents research on advanced surface preparation methods for sintered carbides (WC-Co, grade B2) commonly used in the tool industry, particularly in the context of bonding these materials with C45 steel using adhesives. Sintered carbides are widely used due to their high hardness, wear resistance, and good ductility, making them ideal for manufacturing tools operating in harsh conditions. Traditional bonding methods, such as brazing and welding, often result in stresses and cracks. Adhesive bonding has therefore emerged as an effective alternative to mitigate these challenges. The research focuses on comparing the results obtained through modern surface treatment techniques, such as laser micro-texturing and plasma treatment, with traditional methods like grinding, abrasive blasting, and electrolytic etching. The influence of these methods on adhesion properties and the strength of adhesive bonds was evaluated through mechanical tests, including static shear and pull-off tests. An approximately 50% increase in the mechanical strength of adhesive joints was observed for surfaces treated with low-temperature plasma (operating voltage: 18 kV, flow of gasses: 20 l/min., treatment time: 60 s) and laser micro-texturing (infrared fiber laser, wavelength: 1064 nm (±5 nm), power: 20 W), as compared to mechanical grinding. The shear strength of the adhesive joints was equal to 32 MPa and 30 MPa on average in the case of treatment with low-temperature plasma made of helium and argon, respectively. The highest strength of an adhesive joint was equal to 34.5 MPa on average in the case of laser micro-texturing.

Impact of several seismic scenarios on the dynamic responses of self-steady structures of different heights

Seismic load resistance is a crucial aspect of safety for self-stabilizing reinforced concrete (RC) structures, which are particularly vulnerable to damage caused by destructive earthquakes. These structures, often used in high seismic risk areas, require special attention to ensure their stability and durability under significant dynamic demands. This study focuses on the dynamic responses of low- and medium-rise RC buildings subjected to various seismic response spectra, including those from historic earthquakes such as El-Centro, Kobe, and Boumerdès (recorded at the Dar El-Beida station in Algeria), as well as the spectrum provided by the Algerian seismic code RPA 99/version 2003. The analysis examines three structures with 1, 3, and 6 stories to evaluate the influence of these spectra on key parameters: shear forces, maximum displacements, the ratio between dynamic and static base shear, and overturning moments. These investigations contribute to a deeper understanding of structural behavior under diverse seismic scenarios. The findings emphasize the need to complement the RPA99/v2003 code with studies based on real earthquakes to better address various structural periods and ensure optimal seismic design practices.

Nanocomposites Based on Disentangled Ultra-High Molecular Weight Polyethylene: Aspects and Specifics of Solid-State Processing.

The stages of solid-state processing of nanocomposites, based on nascent disentangled ultra-high-molecular-weight polyethylene (d-UHMWPE) reactor powders (RPs) and carbon nanoparticles (NPs) of various types, were meticulously investigated. The potential for optimizing the filler distribution through variation of the processing parameters, and the impact of the d-UHMWPE RP and nanofiller type on the electrical conductivity of the resulting composites were discussed. The specifics of the dependences of conductivity and tensile strength on the deformation ratio for the composites, oriented under homogeneous shear conditions, were investigated. The obtained results and the results on piezoresistivity and temperature dependency of conductivity in the oriented and compacted composites demonstrated the independence of the UHMWPE matrix orientational strengthening on the filling. The interchangeability of high-temperature uniaxial deformation and deformation under homogeneous conditions for orientational strengthening and electrical conductivity changes in the preliminary oriented composite samples was confirmed. The potential for simultaneously achieving high strength and conductivity in composite tapes and the possibility of directly processing d-UHMWPE RP and NPs mixtures into oriented composite tapes were demonstrated. The overall results suggest that the studied composites may serve as a viable model system for investigating the deformational behavior of conductive networks comprising NPs of varying types and contents.

Tribological Performance of Glycerol-Based Hydraulic Fluid Under Low-Temperature Conditions

This study evaluated the tribological performance of a glycerol-based hydraulic fluid as a green alternative to conventional mineral-based hydraulic lubricants under low-temperature conditions, down to −20 °C. The performance of the glycerol hydraulic fluid (GHF) was compared against that of a mineral hydraulic fluid (MHF) using an SRV tribometer for steel-to-steel sliding contact under boundary lubrication conditions. Comparisons were also made at a moderate temperature to assess the fluids’ performance across different thermal conditions. The results show that the GHF demonstrated up to 55% lower friction coefficients under various test conditions than the MHF. With wear volumes up to 90% lower, the GHF produced thinner and less intense wear scars on the test discs compared to the deeper and more pronounced scars observed with the MHF. We conducted rheological tests which also revealed the green fluid’s stable viscosity transition with temperature changes and its Newtonian behaviour under the measured shear conditions, which may indicate its ability to maintain consistent lubrication.

In situ static elastic properties assessment and validation with pressuremeter testing using a formation tester tool

Pressuremeter testing (PMT) is a formation test that consists of inflating a cylindrical packer inside a borehole while measuring the radial deformation or injected fluid volume as a function of packer pressure. Provided that the stiffness of the packer measuring system is known and large enough compared to that of the formation, changes in packer pressure associated with changes in injected fluid volume provide a direct measurement of formation stiffness. In turn, the in situ static shear modulus is obtained from the formation stiffness at a length scale similar to that of the packer. Here, we report on the first field-scale campaign of PMTs in deep boreholes performed using a wireline formation tester (WFT) tool. We carried out PMT measurements as part of the characterization and appraisal of potential sites for a deep geological repository for radioactive waste in Switzerland. We performed multiple PMT inflation cycles to infer in situ static shear moduli at six stations spread across four boreholes. PMT-derived static shear moduli results were consistent with static shear moduli derived from sonic logs using independent dynamic-to-static elastic moduli transformations. PMT-derived static shear moduli and laboratory-derived static elastic moduli using samples from coring performed at the depths of the PMT stations were consistent, with slightly lower laboratory values. Furthermore, we report dynamic-to-static shear moduli transformations by using laboratory-scale data obtained on cores and field-scale derived from sonic logs and PMT. We observed differences between static and dynamic shear moduli derived from laboratory scale using cores and field scale using sonic logs and PMT. We report linear trend slopes of about 0.5 for the laboratory data and 0.7 for the field data. These first results show the viability of in situ PMT in deep boreholes with a WFT tool, as it can be performed at multiple depths in a single run, in a time-efficient manner, and in combination with micro-hydraulic and sleeve fracturing stress tests for an integral approach to in situ geomechanical assessment.

Anisotropy of non-Darcian flow in rock fractures subjected to cyclic shearing

Non-Darcian flow in rock fractures exhibits significant anisotropic characteristics, which can be affected by mechanical processes, such as cyclic shearing. Understanding the evolution of anisotropic non-Darcian flow is crucial for characterizing groundwater flow and mass/heat transport in fractured rock masses. In this study, we conducted experiments on non-Darcian flow in single rough fractures under cyclic shearing conditions, aiming to analyze the anisotropic evolution of inertial permeability and viscous permeability. We established quantitative characterization models for the two types of permeability. First, we conducted cyclic shearing experiments on four sets of 24 rough rock fractures, investigating their shear characteristics. Then, we performed 480 non-Darcian flow experiments to analyze the anisotropic evolution of viscous permeability and inertial permeability of these rock fractures. The results showed that viscous permeability exhibited significant differences only in the orthogonal direction, while inertial permeability exhibited differences in both orthogonal and opposite directions. With increase in the shear cycles, the differences in the orthogonal direction gradually increased, while those in opposite direction gradually decreased. Finally, we established characterization equations for the two permeabilities based on the proposed directional geometric parameters and validated the performance of these equations with experimental data. These findings are useful for the quantitative characterization of the evolution of non-Darcian flow in fractures under dynamic loading conditions.

Steel‑aluminum clinched joints mechanical properties and strength prediction under different geometric parameters

With the evolution of modularization and prefabrication in construction, there is a growing adoption of prefabricated thin-wall steel and aluminum structures for lightweight buildings and interior decoration. Clinching emerges as a proficient method for achieving heterogeneous metal connections, offering benefits such as streamlined processes, reduced material usage, environmental friendliness, and potential for automation. This study focuses on high-strength steel DP590 and aluminum alloy AW5754-H22, exploring various process parameters (including punch diameter, punch fillet radius, extensible die diameter, and extensible die depth) tailored for clinching experiments on thin steel and aluminum plates. The research analyzes how these process parameters affect the geometric characteristics of the joints and investigates their mechanical properties through static shear tests. Findings indicate that interlocks exceeding 0.29 mm lead to neck cracks during the clinching process. Additionally, the energy absorption of the specimens in button separation exceeds that in neck fracture by 44 % under comparable maximum failure loads in static shear. Optimal process parameters identified are SR5605-SR60310, achieving a maximum failure load of 4.14kN and an energy absorption value of 12.37 J in static shear tests. Finally, a method is proposed to calculate the shear strength of steel‑aluminum clinched joints based on the transmission dynamics of infectious diseases model (SIR model), accounting for the influence of geometric parameters on the static performance of the joints. This approach accurately describes the load-displacement curve trend and predicts the static shear strength of steel‑aluminum clinched joints effectively.

The Temperature-Dependent Monotonic Mechanical Characteristics of Marine Sand–Geomembrane Interfaces

The utilization of geomembrane reinforcement technology is pervasive in marine sand foundation reinforcement projects. However, the elevated temperatures and intricate stress conditions prevalent in marine environments exert a notable influence on the mechanical characteristics of geomembrane interfaces comprising marine sand, which impedes the efficacy of geomembrane reinforcement in marine sand foundations. Nevertheless, there is a lack of research investigating the temperature-dependent interfacial mechanical performance of geomembranes and marine sand under diverse stress states. In this study, a series of monotonic shear tests were carried out on the interface between geomembranes and marine sand within a temperature range of 5 °C to 80 °C. These experiments were carried out using a self-developed large-scale temperature-controlled interfacial dynamic and static shear device. The experimental results demonstrate that temperature has a pronounced effect on the monotonic mechanical characteristics of the geomembrane–marine sand interface, which displays clear temperature dependence. The findings of this study may help in the design and optimization of offshore projects where a marine sand–polymer layer interface exists.

A bone remodeling model involving two mechanical stimuli originated from shear and normal load conditions within the 3D continuum mechanics framework

A bone remodeling model involving two mechanical stimuli originated from shear and normal load conditions within the 3D continuum mechanics framework