Stiffness Of Layer Research Articles

Material properties of nonpregnant and pregnant human uterine layers

The uterus has critical biomechanical functions in pregnancy and undergoes dramatic material growth and remodeling from implantation to parturition. The intrinsic material properties of the human uterus and how they evolve in pregnancy are poorly understood. To address this knowledge gap and assess the heterogeneity of these tissues, the time-dependent material properties of all human uterine layers were measured with nanoindentation. The endometrium-decidua layer was found to be the least stiff, most viscous, and least permeable layer of the human uterus in nonpregnant and third-trimester pregnant tissues. In pregnancy, the endometrium-decidua becomes stiffer and less viscous with no material property changes observed in the myometrium or perimetrium. Additionally, uterine material properties did not significantly differ between third-trimester pregnant tissues with and without placenta accreta. The foundational data generated by this study will facilitate the development of physiologically accurate models of the human uterus to investigate gynecologic and obstetric disorders.

On the characteristics of natural hydraulic dampers: An image-based approach to study the fluid flow behaviour inside the human meniscal tissue

The meniscal tissue is a layered material with varying properties influenced by collagen content and arrangement. Understanding the relationship between structure and properties is crucial for disease management, treatment development, and biomaterial design. The internal layer of the meniscus is softer and more deformable than the outer layers, thanks to interconnected collagen channels that guide fluid flow. To investigate these relationships, we propose an integrated approach that combines Computational Fluid Dynamics (CFD) with Image Analysis (CFD-IA). We analyze fluid flow in the internal architecture of the human meniscus across a range of inlet velocities (0.1 mm/s to 1.6 m/s) using high-resolution 3D micro-computed tomography scans. Statistical correlations are observed between architectural parameters (tortuosity, connectivity, porosity, pore size) and fluid flow parameters (Re number distribution, permeability). Some channels exhibit Re values of 1400 at an inlet velocity of 1.6 m/s, and a transition from Darcy’s regime to a non-Darcian regime occurs around an inlet velocity of 0.02 m/s. Location-dependent permeability ranges from 20-32 Darcy. Regression modelling reveals a strong correlation between fluid velocity and tortuosity at high inlet velocities, as well as with channel diameter at low inlet velocities. At higher inlet velocities, flow paths deviate more from the preferential direction, resulting in a decrease in the concentration parameter by an average of 0.4. This research provides valuable insights into the fluid flow behaviour within the meniscus and its structural influences. 3D models and image stack are available to download at https://doi.org/10.5281/zenodo.10401592. Statement of significanceThe meniscus is a highly porous soft tissue with remarkable properties of load transfer and energy absorption. We give insight on the mechanism of energy absorption from high resolution uCT scans, never presented before, and a new method which combine CFD and image. The structure is similar to a sandwich structure with a stiff outside layer and a soft internal layer made of collagen channels oriented in a preferential direction guiding the fluid flow, enabling it to accommodate deformation and dissipate energy, making it a potentially optimized damping system. We investigate architectural/ fluid flow parameters- fluid regimes relationship, which is of interest of the readers working on designing suitable biomimetic systems that can be adopted for replacement.

Bitumen emulsion effect on properties of asphalt-concrete mix for non-rigid road pavements (Tambov) .

During major repairs of non-rigid road surfaces and reconstruction of automobile roads, it is necessary to remove old coating with road cutters. During cold milling of the old coating, the material acquires the form of granules with the surface covered with a bitumen film. Over time, the bitumen film loses its properties, and to reuse the material, it is necessary to restore the binder properties. The introduction of the bitumen emulsion in the composition of asphalt-concrete mix, allows to restore the binder properties affecting not only strength properties of the asphalt-concrete mix, but also deformability and stiffness of the mixture layer under the compressive load.Purpose: Evaluation of the influence of the binder content on deformability and stiffness of the asphalt-concrete mix.Methodology: Asphalt granulate fractions are used in proportions 8 to 16 and 18 to 36 mm with a residual bitumen content of 2%. The bitumen emulsion EBK-2 is used as a binder. The ultimate strength of the asphalt layer is measured according to GOST 12801. Deformation of the mixture layer is measured on a TP-1-1500 hydraulic press.Research findings: The bitumen emulsion effect is shown for deformation and stiffness of the asphalt-concrete mix for the pavement construction.Value: It is shown that the bitumen emulsion in regeneration of asphalt granulate affects deformability and stiffness of the layer subjected to compaction load. The development of deformation and stiffness of the mixture layer under the load with different binder content, particles size, and layer thickness are established. Analytical dependences are suggested for deformation and stiffness of the loaded layer, its thickness during paving, and percentage of bitumen emulsion in the mixture.

Initial Degradation Issues in AEMWE and the Importance of Catalyst/Ionomer Binding

With the recent development of highly alkaline stable anion exchange membranes (AEMs) and ionomers (AEIs), anion exchange membrane water electrolyzer (AEMWE) has garnered attention due to its ability to achieve high hydrogen production rate at a low cost. The performance of AEMWE is determined by the anode catalyst layer, which can be made up of either a mixture of metal nanoparticles and polymer binders or a single metal. Although the integral metal has high mechanical properties, its performance is limited due to low electrochemical surface area and difficulties in mixing with binders, which makes it unsuitable for use in pure water. Catalyst layers made up of a combination of metal nanoparticles and polymeric binders can achieve high performance with a large surface area, but they often have low durability due to detachment of the anode catalyst layer from the porous transport layer substrate during water electrolysis. To prevent this, the anode catalyst layer must have high physical stiffness and it can be achieved by the strong bonding between the metal nanoparticles and the ionomer binder. This presentation investigates the phenomenon of initial performance degradation in AEMWE with an anode catalyst layer composed of metal nanoparticles, highlights the significance of the physical stiffness of the anode catalyst layer, and proposes that the issue can be resolved by introducing a polymer binder with high adhesion between the metal nanoparticles and the ionomer binder.

Dynamic analysis of a pedestrian timber truss bridge at three construction stages

This article investigates the dynamic behaviour of a single span pedestrian timber truss bridge by in situ testing and numerical modelling. The in situ dynamic tests were performed at three different construction stages: (1) on only the truss structure, (2) on the finished bridge without the asphalt layer and (3) on the finished bridge with the asphalt layer. The objective is to better understand how the different parts of the bridge contribute to the overall dynamic properties. The experimental results show that the damping ratios increased significantly for the first lateral mode (from 1.0 to 3.8%) and the first torsional mode (from 1.2 to 3.5%) between stage 2 and stage 3 due to the asphalt layer. The damping ratio is around 1.6% for the first bending mode for the finished bridge. The experimental and numerical results indicate that the stiffness of the asphalt layer is important to consider at stage 3 (10 °C) for the first lateral and torsional mode, but not for the first bending mode. Finally, it was concluded that longitudinal springs must be applied at the pot bearings in order to get agreement with the experimental results at all the three stages.

Kinematic response of floating piles in two-layered soils subjected to vertically incident S-waves

A rigorous solution is proposed for the kinematic transverse response of a single floating pile in the two-layered soil by vertically propagating S-waves. The soil displacements of the two layers are solved by Helmholtz decomposition and the method of separation of variables. The soil mode functions with a series of eigenvalues are calculated and satisfy the weighted orthogonality. The unknown coefficients in the solution functions are obtained in light of the boundary conditions. An infinite series of algebraic equations with unknown coefficients can be solved by truncating the series number. The cutoff frequency, soil reaction factor, and pile curvature along the shaft are investigated for different properties of the adjacent soil. For the pile in the soil with soft upper and stiff lower layers, the dimensionless cutoff frequency is smaller than that of homogeneous soil, but it follows opposite rules when the upper layer is rigid.

Subcritical crack growth and arrest in the presence of a material interface

Reservoir systems often consist of layered rock formations that are naturally fractured. These can include both fractures that are confined within the main reservoir layer, and ones that penetrate adjacent confining layers or cut through into nearby reservoir strata. Layer-bound fractures have the effect of improving the overall permeability of a reservoir layer, however through-cutting fractures act as pathways for both fluid leakage and pressure communication between otherwise isolated formations. In this study, we investigate the subcritical propagation of a single crack from a stiff inner layer into more compliant and ductile outer layers. We model the crack growth numerically, by making use of recently formulated correction factors that account for the effect of mechanical boundaries on the crack tip energy release rate. Furthermore, we utilize a modified arc-length method to handle the stiff behaviour of the differential equations governing crack tip motion in a layered medium. Under different conditions, a fracture may be arrested permanently or temporarily at the layer boundary, propagate a short distance into the outer layer before arrest, or propagate critically in the outer layer forming a through-cutting fracture. We find that fractures are most likely to remain layer-bound in layers less than 5 m thick, a subcritical index below 10, and a low critical energy release rate relative to the confining layers. If the outer layer modulus is less than half that of the inner layer, the fracture is more likely to propagate a short distance into the confining layer before arrest. In the case of tectonic deformation characterized by steadily increasing far-field extensional strain, crack arrest at the layer boundary is likely to be only temporary, and the occurrence of layer-bound versus through-cutting fractures will be determined by the duration of said deformation together with the thickness and mechanical properties of the different layers.

Closed‐form solution for axially loaded end‐bearing piles in two‐layered soil

AbstractThis paper presents a mathematical model for the analysis of axially‐loaded end‐bearing piles embedded in a two‐layer elastic soil deposit. The governing equations of the soil layers surrounding the pile are cast by means of a Tajimi‐type continuum formulation, and this allows deriving a closed‐form expression that provides the frictional stresses that develop at the soil‐pile interface. The pile is treated as two virtual one‐dimensional elastic rods, and pile displacements are obtained by solving a system of linear equations that results from considering the boundary and continuity conditions. This results in improved efficiency compared to existing Tajimi‐based solutions for piles in layered soil, at no expense of accuracy. The model is used to study the effect of the relative stiffness of the soil layers on the serviceability behavior of axially‐loaded piles, and drawn conclusions of practical importance.

Kinematic response of the single floating piles in the two-layered soil subjected to vertically incident P-waves

An analytical model for the kinematic response of a single floating pile in a two-layered soil under vertically propagating P-waves is proposed by elastodynamics. A Heaviside step function is introduced to simulate the variability of the layered soil. The continuity of the pile and the fictitious soil column are considered based on Tajimi’s theory. The main contribution of the present solution is that the model of the fictitious soil column for the floating pile in the homogeneous soil under vertically propagating P-waves is extended to the two-layered soil with the simulation of the depth-dependent soil mode function. The effect of the properties of the soil layer and the shaft on the vibration of the soil–pile system is investigated. For the soil with the upper softer layer, the dimensionless cutoff frequency of the two-layered soil is smaller than that of homogeneous soil and the opposite trend is for the soil with an upper stiffer layer. For the soil with upper stiff and lower soft layers, the axial pile strain decreases with the decrease of the soil modulus ratio and the effect of soil modulus ratio on the soil resistance at the lower part of the shaft is negligible.

Vascular structure and stiffness in pediatric Mulibrey nanism using ultra-high frequency ultrasound

Mulibrey nanism (MUL) is a disorder with growth delay and congestive heart failure determining prognosis. We aimed to delineate arterial and venous morphology, and arterial stiffness in a representative pediatric MUL cohort. Twenty-three MUL and 23 individually sex and age-matched healthy controls were prospectively assessed in a cross-sectional study with ultra-high frequency ultrasound (48-70 MHz). Heart failure was present in 7 MUL patients, with severe congestive heart failure in 2. Pericardiectomy had been performed in 6 MUL. Arterial lumen diameters and arterial wall layer thickness (intima-media thickness and adventitia thickness) were smaller in MUL patients, but appropriate for body size when compared with controls. Systolic and diastolic blood pressure, aortic and carotid compliance, stiffness as well as central aortic pulsed wave velocity were all similar in MUL compared with controls. Plasma pro-BNP levels were variably elevated (>300 ng/L) in 9/23 MUL patients and in 4/18 MUL patients older than 5 years of age. Internal jugular vein (mean difference 0.054 mm, CI95% 0.024-0.084) and cubital vein (0.046 mm, CI95% 0.013 - 0.078) total wall thickness was elevated in MUL compared with controls. There were no statistically significant relations between vascular parameters and clinical or laboratory signs of heart failure or pericardiectomy. Arterial lumen, wall layer thickness and stiffness are appropriate for body size in MUL, and like healthy controls. Mild venous wall thickening in the upper body region may be due to increased venous pressures related to remodelling caused by diastolic heart failure.

Vibration characteristics of h-FGS plates resting on an elastic foundation under double blast loading

The main goal of this paper is to use the higher-order isogeometric analysis (IGA) to study the vibration behaviour of sandwich plates with an auxetic honeycomb core and two different functionally graded materials (FGM) skin layers (namely h-FGS plates) resting on an elastic foundation (EF) under double blast loading. Reddy's HSDT is used due to its simplicity and efficiency. The foundation model incorporates two parameters as springer stiffness (k1) and the shear layer stiffness (k2). The governing equation is derived from Hamilton's principle. After verifying the present approach, the effect of input parameters on the vibration characteristics of h-FGS plates is carried out in detail. The obtained results are expected to be useful for calculating and designing h-FGS plates in practice.

Two natural toughening strategies may inspire sustainable structures

Contemporary designs of engineering structures strive to minimize the use of material in order to reduce cost and weight. However, the approach taken by focusing on materials selection and on the design of the exterior shape of structures has reached its limits. By contrast, nature implements bottom-up designs based on a multiple-level hierarchy, spanning from nanoscale to macroscale, which evolved over millions of years in an environmentally sustainable manner given limited resources. Natural structures often appear as laminates in wood, bone, plants, exoskeletons, etc., and employ elaborate micro-structural mechanisms to generate simultaneous strength and toughness. One such mechanism, observed in the scorpion cuticle and in the sponge spicule, is the grading (gradual change) of properties like layers thickness, stiffness, strength and toughness. We show that grading is a biological design tradeoff, which optimizes the use of material to enhance survival traits such as endurance against impending detrimental cracks. We found that such design, when applied in a more vulnerable direction of the laminate, has the potential to restrain propagation of hazardous cracks by deflecting or bifurcating them. This is achieved by shifting material from non-critical regions to more critical regions, making the design sustainable in the sense of efficient use of building resources. We investigate how such a mechanism functions in nature and how it can be implemented in synthetic structures, by means of a generic analytical model for crack deflection in a general laminate. Such a mechanical model may help optimize the design of bioinspired structures for specific applications and, eventually, reduce material waste.

Analysis of Interlayer Crack Propagation and Strength Prediction of Steel Bridge Deck Asphalt Pavement Based on Extended Finite Element Method and Cohesive Zone Model (XFEM–CZM) Coupling

The extended finite element method (XFEM) was employed for the computational modeling of internal defects within a bond layer. Furthermore, a cohesive zone model (CZM) was implemented to characterize the behavior of the bond layer in response to interactions at both the bond layer/steel plate and bond layer/asphalt paving layer interfaces. The coupling of XFEM and CZM was used for a comprehensive analysis of crack propagation within the bond layer as well as the assessment of phenomena associated with interfacial debonding and delamination. The feasibility and accuracy of the XFEM–CZM coupling method were verified by comparing it with the virtual crack closure technique (VCCT), CZM, XFEM–VCCT, and experiments. A double cantilever beam experimental model was established to simulate the process of interlayer-type cracks expanding from the inside of the bond layer to the interface between the bond layer and the upper and lower layers, causing debonding. This was undertaken to analyze the damage failure mechanism of interlayer-type cracks in asphalt paving layers of steel bridge decks; to discuss the impacts of the initial crack length, the interface stiffness, the interface strength, and the thickness of the bond layer on the performance of the overall interlayer bond strength; and to carry out the significance analysis. The results showed that the initial crack length, interface stiffness, and bond layer thickness had different effects on the expansion path of interlayer cracks. The interlayer strength decreased with an increase in the initial crack length and interface stiffness, increased with an increase in the interface strength, and decreased with an increase in the thickness of the bond layer. The interface stiffness had the most significant effect on the strength.

Micromechanics of kink-band formation in bimetallic layered composites

Bimetallic layered composites with ultrathin layers possess high strength and hardness, and excellent shock resistance and radiation damage tolerance. However, they are prone to deformation localization and readily form kink-bands when subjected to layer parallel compression. Following this, we carried out extensive plane strain finite element finite deformation analyses to understand and rationalize the experimentally observed kink-band formation in these composites. In the calculations, both constituent materials were assumed to follow a rate-independent isotropic elastic-plastic constitutive relation with an ad-hoc thickness dependent yield strength. Our results demonstrate that in these composites, layer refinement, together with the strength differential between the layers of the constituent materials, is sufficient to trigger kink-banding. Importantly, this phenomenon occurs even in the absence of elastically stiff layers, geometrical imperfections (such as waviness of the layers), and extreme plastic anisotropy within the layers. Additionally, we performed parametric studies to investigate the individual effects of layer thickness, strength differential between the two constituent materials, and strain-hardenability of the materials on kink-band formation. The outcomes of our parametric studies reveal that the strain-hardenability of the constituent materials stabilizes the formation of kink-bands. Furthermore, it leads to a transition from the abrupt formation of through-width kink-bands to the onset and propagation of stable inclined wedge-shaped kink-bands, similar to the experimental observations.

Regulation of interfacial mechanics of soy protein via co-extraction with flaxseed protein for efficient fabrication of foams and emulsions

Enrichment of plant proteins with functionality is of great importance for expanding their application in food formulations. This study proposed an innovation to co-enrich soy protein and flaxseed protein to act as efficient interfacial stabilizers for generating foams and emulsions. The structure, interfacial properties, and functionalities of the soy protein-flaxseed protein natural nanoparticles (SFNPs) obtained by alkali extraction-isoelectric precipitation (AE) and salt extraction-dialysis (SE) methods were investigated. Overall, the foamability of AE-SFNPs (194.67 %) was 1.45-fold that of SE-SFNPs, due to their more flexible structure, smaller particle size, and suitable surface wettability, promoting diffusion and adsorption at the air–water interface. AE-SFNPs showed higher emulsion stability (140.89 min), probably because the adsorbed AE-SFNPs with smaller size displayed soft particle-like properties and stronger interfacial flexibility, and therefore could densely and evenly arrange at the interface, facilitating the formation of a stiff and solid-like interfacial layer, beneficial for more stable emulsion formation. The findings may innovatively expand the applications of SFNPs as food ingredients.

First-Principles Study on the Electronic and Mechanical Properties of the Cr(001)/Al(001) Structure.

We utilized spin-polarized density functional theory to analyze the properties of the Cr(001)/Al(001) structure. The interface was classified into three forms-bcc, bridge, and top-based on the bonding coordinates between Cr and Al atoms. The total density of states (DOS) of the structures is mainly influenced by the Cr (d) orbitals. The local DOS of the Cr atoms at the interface exhibits slight variations based on their coordination with neighboring Al atoms. The mechanical properties of a specific layer were analyzed by using the rigid grain shift (RGS) method, and the properties of all layers were analyzed by using the homogeneous lattice extension method. Our results confirmed that the bonding strength, as determined by the RGS method, follows a decreasing order from the strongest to the weakest: bcc, bridge, and top. We applied uniform deformation to the entire system in the thickness direction and allowed it to relax: we observed that deformation occurs mainly in the Al region and ultimately leads to failure regardless of the type of interface. Consequently, similar strain-stress curves were observed in all Cr(001)/Al(001) structures. The failure in the Al region is attributed to the lower stiffness of the Al-Al layers compared to the top interface despite the lower work of separation for the top interface.

Full-waveform simulation of DAS records, response and cable-ground coupling

SUMMARY Over the past several years, the use of optical fibre cables as ground motion sensors has become a central topic for seismologists, with successful applications of distributed acoustic sensing (DAS) in various key fields such as seismic monitoring, structural imaging and source characterization. DAS response is a combination of both instrument response and cable-ground coupling, with the latter having a strong, spatially variable, but yet largely unquantified effect. This limits the application of a large number of staple seismological techniques (e.g. earthquake magnitude estimation, waveform tomography) that can require accurate knowledge of a signal's amplitude and frequency content. Here we present a method for accurately simulating a DAS cable and its ground coupling. The scheme is based on molecular dynamic-like particle-based numerical modelling, allowing the investigation of the effect of varying DAS-ground coupling scenarios. We start by computing the full strain field directly, for each pair of neighbouring particles in the model. We then define a virtual DAS cable, embedded within the model and formed by a single string of interconnected particles. This allows us to control all aspects of the cable-ground coupling and their properties at an effective granular level through changing the bond stiffness and bond types (e.g. non-linearity) for both the cable and the surrounding medium. Arbitrary cable geometries and heterogeneous materials can be accommodated at the desired scale of investigation. We observe that at the meter scale, the cable-ground coupling and local site effects can substantially alter the recorded signal. We find that the stiffness of the thin layer of material to which the cable is coupled has the strongest effects, selectively amplifying portions of the wave train and contributing to substantial phase delays. These differences show that cable coupling and local site effects should be considered both when designing a DAS deployment and analysing its data when either true or along-cable relative amplitudes and/or frequencies are considered. The codes developed herein for calculating full waveform DAS responses and coupling are made publicly available.

J integral strain-curvature approach for multilayer fracture specimens with unknown thickness and stiffness of layers

In the coming years, many wind turbines will reach their planned design life, and it is of great interest to investigate if their service life can be extended so that the turbines can produce a larger amount of electricity before decommissioning. Such an assessment can include the measurement of the fracture mechanics properties of materials interfaces, e.g., for trailing edge bondlines, web foot bondlines and interfaces between layers in the load-carrying main spars. It would then be preferable to conduct the fracture mechanics testing and data analysis by approaches that give accurate results with the smallest amount of testing. In the present work we propose an approach for measurement of mixed mode fracture resistance (and mixed cohesive laws) that does not require knowledge of the stiffness properties and the elastic centre of the laminates of the test specimens. This is advantageous since the layer stiffness, layer thickness and the lay-up of a laminate cut from an old blade may not be known. Furthermore, the elastic properties of polymer resins of bondlines and matrix materials in fibre composites can have changed (aging) due to the blades long-time environmental exposure.

A shear-lag model for laminated beams with extreme modulus mismatch between layers

Multilayer laminated beams, comprised of alternating stiff and soft layers, are widely used in flexible electronics and photonics. These structures exhibit complex mechanical behaviors that deviate from the Euler–Bernoulli beam theory under conditions of extreme inter-layer modulus mismatch. Extending beyond prior studies on trilayer beams, we present an analytical framework for laminated beams with arbitrary number of layers subjected to various bending conditions, and validate our theory with finite element analysis. We define an equivalent flexural rigidity, exploring its dependence on position and deformation, and systematically examine the impact of the number of layers, applied deformation, layer properties, and the layer aspect ratio.

Large deformation Kirchhoff–Love shell hierarchically enriched with warping: Isogeometric formulation and modeling of alternating stiff/soft layups

This paper presents a large deformation Kirchhoff–Love shell model hierarchically enhanced with through-the-thickness warping functions, arbitrarily chosen by the user. Two unknowns are introduced for each of them, representing its amplitudes in two directions tangent to the shell surface. NURBS are used to approximate reference surface displacement and warping amplitudes in the weak form. The transverse shear strains are linear functions of the warping parameters only and naturally free from locking. A patch-wise reduced integration avoids membrane locking and improves efficiency. Particular attention is paid to the modeling of composites made up of multiple stiff layers coupled with soft interlayers. The alternating layup with high stiffness ratios induces a significant sectional warping with transverse shear strains concentrated in the soft layers. Two warping models are investigated: (WI) all stiff layers maintain the same director orthogonal to the deformed surface with independent transverse shear deformations of the soft layers; (WZ) a single zigzag function linking these deformations. The numerical tests confirm the great accuracy of the hierarchic shell model in reproducing the solid solution with a small number of discrete parameters, provided that the correct warping model is chosen. WI is reliable for all alternating layups. WZ reduces the unknowns to five per surface point, regardless of the number of layers, and is accurate for uniform soft layers.