Search Results (86)

This work studies the water-exit problems of slender cylinders under various conditions through experimental investigation. An experimental platform was equipped with high-speed photography. A total of 13 experimental cases with varying head shapes (conical, spherical, and truncated cone designs), length-to-diameter ratios (5:1–7:1), ejection velocities (7.24–17.93 m/s), and elastic moduli (227.36–279.14 MPa) were conducted to capture water-exit characteristics. The investigation identified ejection velocity as the predominant parameter governing cavity morphology and stability, with higher velocities correlating to increased cavity dimensions and reduced drag coefficients by 54%. Conical head shape resulted in superior drag reduction characteristics, forming a typical cigar-shaped cavity with clear and regular boundaries. Additionally, an increased length-to-diameter ratio substantially improved drag reduction performance by 33%. Material elastic moduli proved crucial for water-exit stability, as cylinders with lower moduli experienced severe bending deformation and even trajectory changes, while higher moduli cylinders maintained their form with minimal deformation. This study illuminates the physical mechanisms of slender body water-exit under multi-factor coupling conditions, providing experimental evidence and theoretical guidance for cross-media vehicle design and underwater equipment optimization. Full article

The three-point bending test is a key method for determining parameters related to the mechanical fracture properties of rocks. In this study, shale outcrops from Changning County, Sichuan Province, China, were selected. Three-point bending experiments were performed on shale semi-circular disks with a central straight crack, tested both perpendicular and parallel to the bedding direction. The corresponding load–displacement curves and crack opening displacements were obtained. The opening displacements of the specimens were measured through digital image technology, and the tensile strength and stiffness of the specimens were further calculated. A finite element model of the three-point bending test was developed. By integrating the finite element model with the experimentally obtained load–displacement curves, the anisotropic elastic moduli of the shale were inversely determined. Fracture toughness was calculated using two approaches: a formula from the International Society for Rock Mechanics and numerical methods using the finite element model, which was appropriately configured with the previously obtained elastic modulus values. The stress intensity factors for each specimen were calculated and compared. The energy release rate of shale was computed based on the fracture toughness. Results showed that both the fracture toughness and energy release rate of shale were greater in the perpendicular bedding direction than in the parallel direction. As an example, one specimen’s elastic modulus, opening displacement, and energy release rate obtained from experiments were input into the numerical simulation of the three-point bending test. The simulated load–displacement curve matched the experimental results well. This study provides a comprehensive approach to evaluating the anisotropic mechanical fracture properties of shale formations, which is essential for improving the accuracy of hydraulic fracture prediction models and enhancing the efficiency of shale gas extraction. Full article

Biomechanical parameters of plant tissues and organs are increasingly recognized as key factors in plant development and application, increasing the demand for convenient devices for their study. The paper presents an original device for performing a three-point bending test using the inverse method, which is a modification of the classical (straight) three-point test. The designed device was tested in experiments to determine the modulus of elasticity of flax plant stems, and the results were compared with data obtained using the vibration method and the straight three-point bending test on a commercial instrument. Due to the high sensitivity associated with its design features, the device for the inverse three-point bending test is characterized by being able to adequately measure elastic moduli in plant stems over a wide range of values, from tens of MPa to tens of GPa. It also allows checking the effect of humidity, temperature, and water content on the mechanical properties of samples and is equipped with an automation system. The proposed device is quite affordable and can be effectively used both for young stem parts, whose mechanical properties are based on a hydroskeleton, and for mature, poorly hydrated parts with cell walls highly developed in sclerenchymatous tissues. Full article

Objective: It is hypothesized that the way nano- and micro-hybrid polymer-based composites are structured and cured impacts the way they respond to aging. Material and methods: A polymer–ceramic interpenetrating network composite (Vita Enamic/VE), an industrially polymerized (Brillinat CriosST/BC), and an in situ light-cured composite with discrete inorganic fillers (Admira Fusion5/AF5) were selected. Specimens (308) were either cut from CAD/CAM blocks (VE/BC) or condensed and cured in white polyoxymethylene molds (AF5) and subjected to four different aging conditions (n = 22): (a) 24 h storage in distilled water at 37 °C; (b) 24 h storage in distilled water at 37 °C followed by thermal cycling for 10,000 cycles 5/55 °C (TC); (c) TC followed by storage in a 75% ethanol–water solution; and (d) TC followed by a 3-week demineralization/remineralization cycling. CAD/CAM samples were also measured dry before the aging process. Three-point bending test, quantitative and qualitative fractography, instrumented indentation test (IIT), SEM, and reliability analyses were used. Uni- and multifactorial ANOVA, Tukey’s post hoc test, and Weibull analysis were performed for statistical analysis. Results: A significant (p < 0.001) and very strong effect of the parameter material was observed (η_P² > 0.9). VE exhibited two to three times higher elastic moduli and hardness parameters compared to BC and AF5, which were comparable. Strength was highest in BC but was accompanied by high beam deformation. The effect of aging was comparatively smaller and was more evident in the IIT parameters than in the flexural strength or modulus. Reliability was high (m > 15) in VE and BC, regardless of aging protocol, while it was significantly reduced in AF5 following aging protocols b-d. Conclusions: TC was the method of artificial aging with a significant impact on the measured parameters, while demineralization/remineralization cycling had little or no impact. Clinical relevance: The degradation of composites occurred irrespective of the structuring and curing method and manifested in a low deterioration in the measured properties. Full article

This article is devoted to a mathematical model of a new piezoelectric sensor used for measuring bending strains. The first simple model of a piezoelectric sensor of bending deformations (we will call it a classical sensor) was presented in our previous paper. The classical sensor is a one-dimensional three-layer structure, in which the two outer layers are made of piezoelectric ceramic with preliminary polarization across the thickness of the sensor, and one elastic middle layer is located between these piezoelectric layers. In the present modified model of the new sensor, piezoelectric stacks are used instead of simple piezoelectric elements. As shown in the paper, this kind of piezoelectric composite sensor with stacks allows us to significantly increase the value and stability of the measured electrical signal and increase the accuracy of strains measurement. Piezoelectric ceramic is a brittle material. The use of stacks significantly reduces brittleness by enclosing thin layers of piezoelectric ceramic in a metal matrix. Piezoelectric laminated stacks have a periodic structure, and we will use the mathematical homogenization method to correctly determine their effective moduli (physical constants). Increasing the reliability of the proposed sensors, as well as the accuracy and stability of their deformation measurements, is aimed at enhancement of the mechanical safety of building structures, increasing the efficiency of their monitoring. The most important characteristic of any sensor is its efficiency. Our first classical bending strain sensor has a simple structure and an efficiency approaching the value of the coupling coefficient k₃₁ (k₃₁ is a constant describing a known physical property of a piezoelectric material). Our classic piezoelectric flexural strain sensor has an efficiency of the order of the coupling coefficient k₃₁. For piezoelectric materials with a strong piezoelectric effect, the k₃₁ value is approximately 0.30–0.35. The efficiency of our classical sensor is hundreds of times greater than the efficiency of the most popular tangential (longitudinal) strain sensor, developed by Lord Kelvin. The efficiency of the flexural strain sensor using stacks is of the order of the coupling coefficient k₃₃. For the sensor with piezoelectric stacks, the value of efficiency is approximately 0.60–0.70. Note that the efficiency of the improved sensor is twice as high as the efficiency of our classic flexural strain sensor. Full article

In this study, 3D-printed reinforced concrete beams were tested for flexural performance and compared with the analytical model based on the material test results. Two cementitious mixes (PSU and GCT) were designed for concrete printing and were mechanically tested and compared. Anisotropies in the compressive strength and modulus of elasticity of printed concrete were observed, applied to the analytical prediction of flexural bending behavior, and validated by actual test results. Significant differences between analytical predictions and experimental tests of the bending behaviors of the printed concrete beams were observed. Furthermore, higher compressive strengths and moduli of elasticity were observed when the loading direction was perpendicular to the printed layers or with the PSU mix. The effect of anisotropic mechanical properties on a reinforced beam was compared to the flexural bending tests for both mixes. The analytical model based on the material test results was compared to the flexural bending test results. The significant errors in the prediction of printed concrete’s structural performance, from 10% to 50%, suggest that factors other than reduced compressive strengths may influence the structural behaviors of printed concrete beams. Full article

Given the dominant failure mode of steel bridge deck pavement layers, which is flexural–tensile damage, the dynamic modulus parameters conventionally determined through uniaxial compression testing are found to be inadequate for the design or performance analysis of these layers. In order to simulate the actual stress of a pavement structure under wheel load, the four-point bending fatigue test method and uniaxial compression test method are used to measure the dynamic modulus of an epoxy asphalt mixture, and the differences between the two test methods are analyzed. Furthermore, the four-point bending fatigue test is employed to investigate the dynamic modulus and phase angle properties across varying temperatures and frequencies, facilitating the creation of master curves for these properties and utilizing Sigmoidal models to correlate dynamic modulus data at diverse temperature conditions. This study delves into the influence of epoxy resin content, mixture composition, and aging on the dynamic modulus. The experimental results show that the dynamic modulus measured by uniaxial compression exceeds that obtained from bending fatigue tests, with the difference initially increasing and then decreasing as temperature rises. This discrepancy significantly impacts the mechanical calculations of pavement layers, underscoring the importance of selecting the appropriate testing method. Temperature, frequency, and epoxy resin content have pronounced effects on the viscoelastic properties of the mixtures. Specifically, as temperature increases, the dynamic modulus undergoes a decrease, whereas the phase angle exhibits an increase. Additionally, the dynamic modulus augments with an increase in loading frequency, while the phase angle exhibits varied trends with frequency shifts across different temperatures. Both the WLF and Sigmoidal models are effective in constructing master curve representations for the dynamic flexural modulus and phase angle. The incorporation of epoxy resin transforms asphalt from a primarily viscous to a more elastic material, significantly enhancing the viscoelastic properties of the mixture. Notably, mixtures with 50% and 60% epoxy resin content exhibit comparable dynamic moduli and phase angles, while displaying notably superior performance compared to those with 40% epoxy resin content. For large-scale steel bridge deck pavement, 50% epoxy resin content is recommended. Moreover, epoxy asphalt mixtures demonstrate robust aging resistance, with minimal variations in the dynamic modulus and phase angle before and after aging. The research results can enable the acquisition of dynamic modulus and phase angle data in the whole temperature domain and the whole frequency domain, and provide reliable mixed performance parameters for the study of different application environmental performance of steel bridge deck pavement. Full article

This paper investigates wrinkling dynamics of two-dimensional multicomponent vesicles subjected to time-dependent extensional flow. By employing a non-stiff, pseudo-spectral boundary integral approach, we inspect the wrinkling patterns that arise due to negative surface tension and differential bending within a two-phase system. We focus on the formation and evolution of the wrinkling behaviors under diverse phase concentrations, extensional rates, and vesicle sphericity. Our findings demonstrate that for slightly perturbed circular vesicles, the numerical simulations align well with perturbation theory. For elongated vesicles, the wrinkling patterns vary significantly between phases, primarily influenced by their respective bending moduli. In weak flows, buckling behaviors are observed for elongated vesicles, where the membrane bends inward in regions with lower bending modulus. Full article

Cellulosic fibers obtained from Barley straw were utilized to reinforce PHB. Four different processed fibers were employed as reinforcing material: sawdust (SW), defibered (DFBF), delignified (DBF), and bleached (BBF) fibers. The composite was processed from two different perspectives: a discontinuous (bach) and an intensification process (extrusion). Once processed and transformed into final shape specimens, the materials were characterized by mechanical testing (tensile mode), scanning electron microscopy, and theoretical simulations by finite elements analysis (FEA). In terms of mechanical properties, only the elastic moduli (Et) exhibited results ranging from 37% to 170%, depending on the reinforcement composition. Conversely, strengths at break, under both tensile and bending tests, tended to decrease, indicating poor affinity between the components. Due to the mechanical treatment applied on the fiber, DFBF emerged as the most promising filler, with mechanical properties closest to those of neat PHB. DFBF-based composites were subsequently produced through process intensification using a twin-screw extruder, and molded into flowerpots. Mechanical results showed almost identical properties between the discontinuous and intensification processes. The suitability of the material for agriculture flowerpots was demonstrated through finite analysis simulation (FEA), which revealed that the maximum von Mises stresses (5.38 × 10⁵ N/m²) and deformations (0.048 mm) were well below the limits of the composite materials. Full article

The need, or even the obligation, to take care of the natural environment compels a search for new technological solutions, or for known solutions to be adapted to new applications. The maxim is ‘don’t harm, but improve the world for future generations’. In the wood industry in particular, given that it is based on a natural raw material, we must look for ecological solutions. Trees grow, but the demand for wood exceeds the volume of tree growth. In industrial manufacturing, one of the ways to make full use of wood is through chipless processing, which occurs during rotary cutting (peeling). In addition, wood is a natural material, each fragment of which has a range of properties. In addition, wood defects in quality manipulation generate a lot of waste. The aim of this study was to analyse the quality effect of the tested layered composites for flooring materials on production application. The practical purpose was to exchange actual sawing-based production for chipless production. The composite base layers were made of pine wood (Pinus L.) veneers with differing quality classes. The samples were subjected to three-point bending tests to calculate the moduli of elasticity and stiffness, which are the most important parameters. Because both analysed parameters describe product quality, the analyses were based on the creation of Shewhart control charts for each parameter. In theory, these control charts are tools for analysing whether the production process is stable and yields predictable results. To have full control over the process, five elements have to be applied: central line (target), two types of control lines (upper and lower) and two types of specification lines (upper and lower). New types of layered composites for flooring may be applied to production once verified using Shewhart control charts. It turns out that it is possible to produce the base layer of the flooring materials using the rotary cutting (peeling) method without having to analyse the quality of the raw material. This is a way to significantly increase the efficiency of production in every element of manufacturing. Full article

The rise of straintronics—the possibility of fine-tuning the electronic properties of nanosystems by applying strain to them—has enhanced the interest in characterizing the mechanical properties of these systems when they are subjected to tensile (or compressive), shear and torsion strains. Four parameters are customarily used to describe the mechanical behavior of a macroscopic solid within the elastic regime: Young’s and shear moduli, the torsion constant and Poisson’s ratio. There are some relations among these quantities valid for elastic continuous isotropic systems that are being used for 2D nanocrystals without taking into account the non-continuous anisotropic nature of these systems. We present in this work computational results on the mechanical properties of six small quasi-square (aspect ratio between 0.9 and 1.1) graphene nanocrystals using the PM7 semiempirical method. We use the results obtained to test the validity of two relations derived for macroscopic homogeneous isotropic systems and sometimes applied to 2D systems. We show they are not suitable for these nanostructures and pinpoint the origin of some discrepancies in the elastic properties and effective thicknesses reported in the literature. In an attempt to recover one of these formulas, we introduce an effective torsional thickness for graphene analogous to the effective bending thickness found in the literature. Our results could be useful for fitting interatomic potentials in molecular mechanics or molecular dynamics models for finite carbon nanostructures, especially near their edges and for twisted systems. Full article

The mechanical properties of fibre-managed Eucalyptus nitens (E. nitens) cross-laminated timber (CLT) have previously been extensively studied, proving the material to be structurally safe and reliable. However, the vibration performance of CLT manufactured from this relative new construction species is not yet fully understood, especially under different support conditions. In this study, three types of support conditions, including roller–roller, bearer–bearer and clamp–bearer support conditions, were examined under vibration impulse-response testing performed using a simple but effective and repeatable excitation method consisting of a basketball dropped from a known height and an accelerometer. Six three-ply E. nitens CLT panels considered to have different moduli of elasticity in different layers and one strength-class C24 spruce CLT as a controlled reference were included in this study. The results suggest that the fundamental frequency values can effectively reflect the inherent characteristics of CLT panels (bending stiffness and density); however, no obvious relationship was observed between damping ratios and these inherent properties. The values of frequency constant λ₁ were determined to analyse the effect of different support conditions on the values of fundamental frequency. The average values of λ₁ for the roller–roller (9.6) and bearer–bearer (10.1) supports align with the theoretical values (9.87) for simply support (S-S) conditions. However, when clamping loads were applied at one edge of the bearer support, the average values of λ₁ increased up to 10.8 but remained far below the theoretical values for clamped–pinned (C-S) support (15.4). Full article

In this study, moso bamboo was used as a raw material. To increase the plasticity of bamboo to achieve a greater softening effect, the softening method of hydrothermal treatment was used. Hardness and the flexural elastic modulus were used as the evaluation indices, and the crystallinity and main functional groups of the softened bamboo were analysed using X-ray diffraction and Fourier-transform infrared spectroscopy. Combined with the examination of timber colour, micromorphology, bending strength, and nanomechanical tests, our analysis showed the effects of the hydrothermal treatment on bamboo. The results showed that the hardness and flexural moduli of bamboo decreased with the increase in hydrothermal treatment temperature. However, cracking occurred after 3.5 and 4 h of treatment at 180 °C and 190 °C. This indicated that the softening effect was most pronounced when the treatment temperature and time were 180 ℃ and 3 h, respectively. The cellulose crystallinity of bamboo increased and then decreased with the increase in treatment temperature. Cracks were produced in the cell structure, starch locally disappeared, and the hardness and the elasticity modulus of the thin-walled bamboo cells first increased and then decreased with the increase in treatment temperature. Full article

A database of non-linear elastic parameters in axial tension and compression is provided for continuous carbon fibre polymer composites and carbon fibres of different stiffnesses. Composite laminates manufactured by conventional or automated processes are tested in bending, and parameters are extracted for strains of less than 0.5%. While fibre composites with fibres of standard and intermediate moduli exhibit a stiffening of ∼15 GPa/% (of strain) and a softening of ∼20 GPa/%, those with high-modulus carbon fibres exhibit much higher values of ∼50 GPa/% for both. This database is useful for designing composite structures in a stiffness-based design and for correlating the processing of carbon fibres with their nanostructure and induced properties. The latter is discussed in terms of reorientation of crystallites of graphene sheets vis-à-vis the carbon fibre axis during loading. Full article

In order to investigate the mechanism of the effect of asymmetric reinforcement on the static-bending properties of wood, this paper tests and analyzes the static-bending properties of SPF wood and seven different types of asymmetric fiber surface-reinforced wood (AFRWC) formed by SPF wood as the substrate and bamboo and carbon fibers as the reinforcement materials. The results of the study found that (1) the moduli of rupture of the seven types of AFRWC were increased to varying degrees, but the static-bending moduli of elasticity increased or decreased; (2) the asymmetric reinforcement changed the cross-section strain distribution and damage type of the wood in static bending; (3) the results of the cross-section strain-field tests and the ABAQUS finite element simulation showed that the asymmetric reinforcement method of bonding the bamboo material and the two layers of CFRP in the compression and tensile zones, respectively, can greatly enhance the static-bending performance of the wood. The error between the simulated and measured values of specimens MOR and MOE is only −0.7% and −7.3%, respectively. This type of asymmetric reinforcement makes it possible to obtain a more reasonable cross-section stress distribution. Full article