Stiffness Ratio Research Articles

Structural design of new mesh-type high-damping rail pad and comparative experimental study on the mechanical property with the traditional rail pads

Commonly used rail pads (RPs) in urban rail transit fastening systems comprise prismatic and grooved rail pads (PRP and GRP). This research introduced novel mesh-type and mesh-type high-damping rail pads (NMTRP and MTHDRP) to mitigate RP’s stress and enhance damping efficiency while optimizing elastic material utilization. A finite element model (FEM) of the fastening system was established and validated through stiffness and hammering tests of the RPs. The FEA results revealed that the mesh-type RP offered advantages in uniform stress distribution and efficient material usage. The MTHDRP has a significantly lower stress level than the PRP and GRP because of the damping block, it will prolong the MTHDRP’s service life. Both NMTRP and MTHDRP displayed reduced static and dynamic stiffness in comparison to PRP and GRP. Notably, MTHDRP demonstrated the lowest dynamic-to-static stiffness ratio at 1.45, indicating superior dynamic stiffness retention capacity relative to the other three RPs. The hammering test found that the MTHDRP exhibited the highest damping ratio among the four RPs and consistently lower vibration amplitudes in the time and frequency domains at the rail, clip, track bed, and ground when compared to the other RPs. Furthermore, analysis of the 1/3 octave frequency band of the acceleration signal underscored MTHDRP’s excellence, with vibration levels reduced by 4.31, 4.37, 4.21, and 1.43 dB at the rail, clip, track bed, and ground, respectively, in comparison to PRP. These findings affirm the superior vibration reduction performance of MTHDRP relative to the other three RPs and underscore its potential for enhanced foundation protection when incorporated into rail systems.

Design considerations for patient-specific bone fixation plates: a literature review.

In orthopedic surgery, patient-specific bone plates are used for fixation when conventional bone plates do not fit the specific anatomy of a patient. However, plate failure can occur due to a lack of properly established design parameters that support optimal biomechanical properties of the plate.This review provides an overview of design parameters and biomechanical properties of patient-specific bone plates, which can assist in the design of the optimal plate.A literature search was conducted through PubMed and Embase, resulting in the inclusion of 78 studies, comprising clinical studies using patient-specific bone plates for fracture fixation or experimental studies that evaluated biomechanical properties or design parameters of bone plates. Biomechanical properties of the plates, including elastic stiffness, yield strength, tensile strength, and Poisson's ratio are influenced by various factors, such as material properties, geometry, interface distance, fixation mechanism, screw pattern, working length and manufacturing techniques.Although variations within studies challenge direct translation of experimental results into clinical practice, this review serves as a useful reference guide to determine which parameters must be carefully considered during the design and manufacturing process to achieve the desired biomechanical properties of a plate for fixation of a specific type of fracture.

Numerical modeling strategies and parametric analyses of platform-type and balloon-type cross-laminated timber (CLT) shear walls under lateral loads

Despite great contributions having been made on the topic of numerical modeling methods for cross-laminated timber (CLT) shear walls under lateral loads, it is still challenging to simulate the nonlinear wall behavior with both computational efficiency and modeling accuracy. In this paper, a series of novel modeling strategies are developed, aiming to provide a potential solution to this challenge. The modeling strategies involve the revised version of a uniaxial hysteretic model for dowel-type timber joints, physical and phenomenological modeling methods for typical CLT connections (i.e., hold-down and angle bracket connections), and a fiber-section-based modeling method for CLT shear walls. The modeling strategies were validated by existing experimental data, and the modeling results showed that the proposed fiber-section-based model is capable of simulating the lateral performance of both platform-type and balloon-type CLT shear walls with sufficient accuracy while maintaining desirable computational efficiency. The fiber-section-based model was then used to conduct parametric studies, investigating the influence of construction methods, wall aspect ratios, connection stiffness, and vertical load magnitudes on the lateral performance of CLT shear walls. The studies showed that the initial stiffness and ductility ratio of balloon-type CLT shear walls were 39.1–47.1% and 13.7–19.4% larger than the platform-type ones, while the ultimate capacity was less affected by construction methods. Slenderer CLT shear walls had lower ultimate capacities and initial stiffnesses, as well as smaller ductility ratios. Stiffer hold-down connections contributed to larger initial stiffness but resulted in the CLT shear wall failing in a less ductile manner. The vertical load had positive impacts on the ultimate capacity, initial stiffness, and ductility ratio of CLT shear walls, although the effect on the ultimate capacity was quite limited.

Formulation and implementation of a hypoplastic constitutive model for interface behavior of mechanical joints

The effects of the contact interface must be considered during the design process of the assembly structures connected by mechanical joints. An advanced three-dimensional (3D) constitutive model is needed to describe the complex behavior of the contact interface in a detailed finite element (FE) model. However, the simplified Coulomb friction law, which is a bilinear model without considering the microslip behavior and stiffness degradation, is often applied to the surface-surface contact element for modeling the interface in commercial FE programs. In this paper, a new 3D hypoplastic constitutive model for the nonlinear interface behavior is presented. This model is built on the framework of hypoplasticity developed by Kolymbas and the hypothesis of continuous media. First, the general hypoplastic model is derived based on the kernel formula and several restrictions and simplified according to the characteristics of the contact interface. Then, the coefficients of the model are associated with the widely used physical parameters by combining the model with the initial stiffness ratio, normal contact law and Coulomb law. Benefiting from the hypoplastic theorem, the deduced constitutive model has a simple mathematical formulation in which only five parameters are contained. Simulations of several monotonic and cyclic shear tests show that the model can represent the salient characteristics of the joint interface (e.g. stick/microslip/macroslip behaviors, motion coupling and pressure-dependency). Thus, it can be used to predict the response of the joint interface from arbitrary multi-axial load histories more precisely. The constitutive model is then implemented in a commercial FE program via analysis of a double-beam structure subjected to harmonic excitation. And vibration experiments on several preload levels are performed to validate the effectiveness and the applicability of the proposed model to the real joints. The results calculated from the FE model with the improved reduction techniques are in good agreement with the experimental data.

Utility of shear wave elastography for diagnosing carpal tunnel syndrome with psoriatic arthritis.

Carpal tunnel syndrome (CTS) is a type of peripheral entrapment neuropathy and common for the patients with psoriatic arthritis (PsA). Shear wave elastography (SWE) is a new ultrasonography technique that can be used for diagnosing CTS, but not studied in PsA patients. The aim of this study to measure the stiffness of median nerve and hand muscles by quantitative SWE to identify whether SWE can be used for diagnosing CTS in patients with PsA or not. To diagnose CTS, all patients had electrodiagnostic study. The stiffness values of the median nerve, abductor pollicis brevis, and abductor digiti minimi were determined using SWE. Muscle stiffness ratio was also calculated. Consideration is given to 48 patients with PsA (93 wrists) and 29 healthy volunteers (57 wrists). Median nerve stiffness was found to be significantly higher, and abductor pollicis brevis' stiffness and muscle stiffness ratio were significantly lower in PsA patients' wrists compared to control group (p = 0.002, p < 0.001, p = 0.001, respectively) and in CTS wrists compared to others (p < 0.001, p < 0.001, p = 0.001, respectively). Receiver operating characteristic analysis identified 28.2 kPA as the median nerve stiffness cut-off point for differentiating CTS in PsA patients (p = 0.001). We found that SWE has a good diagnostic value for CTS with PsA patients; hence, we can conclude that SWE could diagnose CTS in PsA patients.

An improved pull-out model for the composites with curved reinforcement

Due to the low bending stiffness and large aspect ratio, nanofillers with curved morphology are ubiquitous in composites, providing a potential avenue to achieve superior mechanical properties and functionalities. However, the theoretical understanding of the morphology-properties relationship in such composites remains constrained due to the difficulties in precisely defining the boundary conditions required for establishing a fully analytical model. In this study, we propose an improved shear-lag model that overcomes these challenges to investigate the influence of reinforcement's curved morphology on the pull-out mechanical behaviors of composites, which enables accurate prediction of stress distributions and interfacial debonding. Our investigation reveals that among the two morphology-related parameters, namely waviness and curvature, the pull-out behaviors and properties of the composites are more sensitive to the former parameter. A higher degree of waviness actually contributes to enhanced load transfer efficiency and larger pull-out loads. Meanwhile, we demonstrate that the load transfer from the curved reinforcement to the matrix, as well as the maximum pull-out load, can be improved by increasing the length and volume fraction of graphene, as well as the frictional stress. Additionally, we identify a critical Young's modulus ratio of approximately 16 between the reinforcement and matrix, serving as a predictive criterion for determining debonding locations. Overall, this study provides deep insights into the pull-out behavior of composites with curved reinforcement and presents theoretical inspirations for designing and optimizing advanced composites to achieve high strength and toughness simultaneously.

Disrupted stiffness ratio alters nuclear mechanosensing

The ability of endothelial cells to sense and respond to dynamic changes in blood flow is critical for vascular homeostasis and cardiovascular health. The mechanical and geometric properties of the nuclear and cytoplasmic compartments affect mechanotransduction. We hypothesized that alterations to these parameters have resulting mechanosensory consequences. Using atomic force microscopy and mathematical modeling, we assessed how the nuclear and cytoplasmic compartment stiffnesses modulate shear stress transfer to the nucleus within aging endothelial cells. Our computational studies revealed that the critical parameter controlling shear transfer is not the individual mechanics of these compartments, but the stiffness ratio between them. Replicatively aged cells had a reduced stiffness ratio, attenuating shear transfer, while the ratio was not altered in a genetic model of accelerated aging. We provide a theoretical framework suggesting that dysregulation of the shear stress response can be uniquely imparted by relative mechanical changes in subcellular compartments.

Plate and stiffener buckling in transversely loaded steel panels

AbstractStiffened plates may be loaded by axial forces in two directions, i.e., along and transverse to the stiffeners, by in‐plane shear force, and by out‐of‐plane loads as from traffic or water pressure. Special care must be taken for buckling effects caused by the compressive in‐plane forces.The buckling behaviour of plates stiffened with four trapezoidal stiffeners was investigated for the case of compressive axial force directed transverse to the stiffener direction. The width and length of the stiffened plate and the ratio between the plate‐ and stiffener stiffnesses were varied. The investigation aimed to determine criteria to ensure that the dominating buckling mode was either buckling of the plate between the stiffeners, or a predictable buckling pattern of the stiffeners. For this, two formulas are presented, giving the necessary plate‐to‐stiffener stiffness ratio or the maximum length of the panel. Furthermore, capacity approaches for the axial resistance for transverse axial loading are studied, applying the Effective Width Method (EWM) and the Reduced Stress Method (RSM). Comparisons with nonlinear FE‐simulations show that the predictions range from 45% to 99% of the FE‐results.

Structural design and experimental evaluation of a coarse-fine parallel dual-actuation XY flexure micropositioner with low interference behavior.

This paper proposes a novel two degree of freedom large range coarse-fine parallel dual-actuation flexure micropositioner (CFPDFM) with low interference behavior. First, the structure and working principle of the CFPDFM are introduced. Then, based on the stiffness matrix method, the analytical models of the motion range, input stiffness, and amplification ratio of the mechanism are established. Subsequently, the accuracy of the analytical model is verified by finite element analysis and experiments. Moreover, the dual-servo cooperative drive control strategy is designed to improve the closed-loop positioning ability of the CFPDFM. Finally, the CFPDFM experimental system is built to verify the plane trajectory tracking performance. The results reveal that the micropositioner can achieve a total range of 3.02 × 3.11mm2, a resolution of ≤40nm, low interference performance of coarse and fine actuators, good cross-axis decoupling, and planar complex trajectory tracking performance, while possessing a compact structure. It can be used in many plane positioning situations requiring large range and high precision.

Brain Stiffness Follows Cuprizone-Induced Variations in Local Myelin Content

Brain maturation and neurological diseases are intricately linked to microstructural changes that inherently affect the brain’s mechanical behavior. Animal models are frequently used to explore relative brain stiffness changes as a function of underlying microstructure. Here, we are using the cuprizone mouse model to study indentation-derived stiffness changes resulting from acute and chronic demyelination during a 15-week observation period. We focus on the corpus callosum, cingulum, and cortex which undergo different degrees of de- and remyelination and, therefore, result in region-specific stiffness changes. Mean stiffness of the corpus callosum starts at 1.1 ± 0.3 kPa in untreated mice, then cuprizone treatment causes stiffness to drop to 0.6 ± 0.1 kPa by week 3, temporarily increase to 0.9 ± 0.3 kPa by week 6, and ultimately stabilize around 0.7 ± 0.1 kPa by week 9 for the rest of the observation period. The cingulum starts at 3.2 ± 0.9 kPa, then drops to 1.6 ± 0.4 kPa by week 3, and then gradually stabilizes around 1.4 ± 0.3 kPa by week 9. Cortical stiffness exhibits less stiffness variations overall; it starts at 4.2 ± 1.3 kPa, drops to 2.4 ± 0.6 kPa by week 3, and stabilizes around 2.7 ± 0.9 kPa by week 6. We also assess the impact of tissue fixation on indentation-based mechanical tissue characterization. On the one hand, fixation drastically increases untreated mean tissue stiffness by a factor of 3.3 for the corpus callosum, 2.9 for the cingulum, and 3.6 for the cortex; on the other hand, fixation influences interregional stiffness ratios during demyelination, thus suggesting that fixation affects individual brain tissues differently. Lastly, we determine the spatial correlation between stiffness measurements and myelin density and observe a region-specific proportionality between myelin content and tissue stiffness. Statement of significanceDespite extensive work, the relationship between microstructure and mechanical behavior in the brain remains mostly unknown. Additionally, the existing variation of measurement results reported in literature requires in depth investigation of the impact of individual cell and protein populations on tissue stiffness and interregional stiffness ratios. Here, we used microindentation measurements to show that brain stiffness changes with myelin density in the cuprizone-based demyelination mouse model. Moreover, we explored the impact of tissue fixation prior to mechanical characterization because of conflicting results reported in literature. We observe that fixation has a distinctly different impact on our three regions of interest, thus causing region-specific tissue stiffening and, more importantly, changing interregional stiffness ratios.

Topology optimization for piezoresistive nanomechanical surface stress sensors in anisotropic 〈111〉 orientations

Microelectromechanical systems (MEMS)-based piezoresistive nanomechanical sensors are compact sensing platforms widely employed in vapor sensing, environmental monitoring, and biosensing. Despite their extensive utility, their lower sensitivity relative to their optical readout counterparts has been a limiting factor, constraining the wider application of this technology. Prior research has suggested that alternative silicon orientations, such as 〈111〉 orientations in (110) wafers, can significantly improve the sensitivity of piezoresistive sensors. However, the complexity of optimizing two-dimensional stress distribution and handling anisotropic elasticity has made device design a formidable task, leaving this promising avenue largely unexplored. To address this challenge, we employ density-based topology optimization to generate a series of optimized designs for piezoresistive nanomechanical sensors manufactured along 〈111〉 orientations. The properties of the immobilization layer—the functional coating on the sensor—are parametrically varied to explore optimal designs. Our study reveals a transition in optimized designs from a double-cantilever configuration to a suspended platform configuration, dictated by the stiffness ratio between the immobilization layer and the silicon layer. This transition is attributed to the shift in the neutral plane and the prevailing stress relaxation mechanism. In addition, we scrutinize the effects of piezoresistor geometry and find that the optimized designs depend asymmetrically on the piezoresistor position, a characteristic stemming from the anisotropic elasticity in 〈111〉 orientations. These optimized designs, verified by finite element analysis (FEA), demonstrate a notable improvement in sensitivity of more than 20% when benchmarked against traditional rectangular designs and equivalent optimized designs in conventional orientations, thereby validating the effectiveness of the present model. This study provides crucial knowledge for the design of piezoresistive biosensors, facilitating more efficient geometric design in future sensor development.

Seismic Performance Analysis of Corrugated Steel Plate Shear Wall Connected with Beams Only

This paper studied the seismic performance of corrugated steel plate shear walls with vertical corrugated steel plates connected with beams only (CboSPSWs). A numerical model of a CboSPSW was developed. Then, a series of parametric analyses were conducted to determine the effects of the related parameters on the hysteretic performance of CboSPSWs, including the height–thickness ratio, aspect ratio, corrugation angle, stiffness of the free-edge stiffener, and surrounding frame stiffness. In addition, the limit of the stiffness of the free-edge stiffener of the CboSPSW was investigated. Finally, the serviceability of the existing design method, the Plate-Frame Interaction model (PFI), for CboSPSWs was examined. The results show that CboSPSWs have high values of strength and initial stiffness as well as good and stable energy dissipation capacities. The ultimate strength of the corrugated steel plate (CSP) can be improved significantly by free-edge stiffeners. When the flexural stiffness ratio exceeds 1.0, the increase of the average stress of the CSPs close to the beams is less than 20%, and the tension field develops fully in the CSPs in CboSPSWs. The PFI model can predict the shear strength and initial stiffness values of the hysteretic curves of CboSPSWs with good accuracy, which can be used in the design and plastic analyses of CboSPSWs.

Vibration response analysis of a two-stage vibration isolation system for large airborne equipment

PurposeThis paper aims to propose a two-stage vibration isolation system for large airborne equipment to isolate aircraft vibration load.Design/methodology/approachFirst, the vibration isolation law of the discrete model of large airborne equipment under different damping ratios, stiffness ratios and mass ratios is analyzed, which guides the establishment of a three-dimensional solid model of large airborne equipment. Subsequently, the vibration isolation transfer efficiency is analyzed based on the three-dimensional model of the airborne equipment, and the angular and linear vibration responses of the two-stage vibration isolation system under different frequencies are studied.FindingsFinally, studies have shown that the steady-state angular vibration at the non-resonant frequency changes little. In contrast, the maximum angular vibration at the resonance peak reaches 0.0033 rad, at least 20 times the response at the non-resonant frequency. The linear vibration at the resonant frequency is at least 2.14 times the response at the non-resonant frequency. Obviously, the amplification factor of linear vibration is less than that of angular vibration, and angular vibration has the most significant effect on the internal vibration of airborne equipment.Originality/valueThe two-stage vibration isolation equipment designed in this paper has a positive guiding significance for the vibration isolation design of large airborne equipment.

Comparative study between inerter and negative stiffness damped outrigger structures

Recently, damped outrigger structures have shown great potentials in suppressing vibrations of tall buildings subjected to seismic and wind excitations. To gain insight into the seismic performance of damped outrigger structures, this paper proposes a stochastic optimization-based sensitivity analysis procedure (SOSAP) for comparative study of damped outrigger structures implemented with inerter dampers (ID) and negative stiffness dampers (NSD) subjected to stochastic seismic excitation. The novelty of this procedure is it integrates stochastic optimization with seismic excitation modeled using the Clough-Penzien spectrum, Pareto optimal fronts dealing with conflict objectives, and sensitivity analysis of objectives values with respect to both discriminative and common design variables. First, the state-space representations of stochastic seismic excitation and structures implemented either with inerter damped outriggers (IDO) or negative stiffness damped outriggers (NSDO) are combined to yield the representations of the augmented structure-damper-earthquake systems. Pareto optimal fronts are then used to examine the tradeoffs between competing optimization objectives, which are defined as harmful interstory drift and floor absolute acceleration via the solutions of the Lyapunov equations. Subsequently, the stochastic seismic responses of the IDO and NSDO systems are compared by investigating the sensitivity of objective values with respect to inertance, negative stiffness ratio and viscous coefficient. The obtained optimal parameters of comparative IDO and NSDO systems are further examined under real earthquake records from the perspectives of dynamic response and energy balance. These investigations demonstrate the efficacy of the proposed SOSAP, reveal the comparative seismic performance between the IDO and NSDO systems dependent on the optimization objectives and the available amount of ID and NSD, which provides insight into the optimal design of tall buildings with different design strategies and conflicting objectives subjected to stochastic seismic excitation.

Stability Analysis of Prefabricated Underground Granary Composite Silo Walls

The prefabricated steel plate-concrete composite silos have been recently used for underground granaries. As the buried depth and diameter-thickness ratio of underground silos increase, the calculation of elastic stability, which takes into account the effects of prefabricated joints, becomes a primary consideration in the design of the silo walls. In the present study, the equation to estimate the elastic critical pressure of double-layer heterogeneous cast-in-situ silos under uniform external pressure was proposed first. The theoretical solutions were then compared with the numerical results and the accuracy of the equation was verified. To derive the critical pressure of prefabricated steel plate-concrete silo walls, an equivalent joint design method was proposed and verified by a series of numerical analyses for different models. The results indicate that if the bending stiffness ratio of the joint is larger than the bending stiffness of the composite silo wall section, the prefabricated double-layer composite silo walls are equivalent to cast-in-situ double-layer composite silo walls, and the equation to evaluate the elastic critical pressure of double-layer heterogeneous cast-in-situ silo walls under uniform external pressure could be used to derive the critical pressure of prefabricated steel plate-concrete silo walls. The bending tests of the full-scale steel plate-concrete composite silo wall models with and without joints were conducted and the experimental results indicate that the assumption of a rigid connection between the steel plate and concrete was reasonable, and the equivalence of prefabricated composite silos to cast-in-situ composite silos to obtain the elastic critical pressure is feasible and the result is reliable.

Novel metamaterial structures with negative thermal expansion and tunable mechanical properties

The thermal expansion and stiffness characteristics are significant in determining the responses of lightweight mechanical metamaterials in a thermal environment. This paper proposed a novel trapezoid unit with negative thermal expansion (NTE) by three conventional materials with positive thermal expansion, and constructed a series of lightweight metamaterials by sharing edges and sharing vertexes. The effective linear coefficients of thermal expansion (CTE) of these metamaterial structures are theoretically explored by considering axial and bending deformations. Based on Euler beam theory, the effective linear elastic stiffnesses of these metamaterials are given accurately by the stiffness matrix method. The accuracy of the theoretical effective CTE and stiffness is well verified by numerical modeling. The effective linear CTE, elastic stiffness, and Poisson's ratio of these metamaterials can be programmable by controlling geometrical parameters and material properties. The NTE effect can be achieved in ET, EQ, EH, and VT metamaterials due to the presence of re-entrant structures, in which the ET metamaterial can fulfill the maximum magnitude NTE. The NTE and negative Poisson's ratio can simultaneously be realized in EQ metamaterial. Significantly, a broader range of CTE from negative to positive values can be fulfilled in these metamaterials compared with the conventional triangle unit. Furthermore, the high specific stiffness with extremely low thermal stress can be obtained in EQ, VT, and VH metamaterials, which benefits the stability controlling and enhancing natural frequencies of structures in a thermal environment.

Greek Key Inspired Fractal Metamaterials with Superior Stretchability for Tunable Wave Propagation

Stretchable materials that can sustain a large deformation are in high demand, because they find broad applications ranging from stretchable energy storage devices to tunable noise and vibration devices. One main challenge is creating strain‐releasing mechanisms from inherently brittle materials. This work explores a new approach to designing stretchable metamaterials, using a "kerfing" pattern inspired by the ancient Greek Key configuration. The kerfing architecture allows for substantial in‐plane elongation. In‐plane tensile experiments show an ≈8‐times increase in stretchability when the kerfing width is enlarged four times. With higher‐order fractal patterns, the fractal lattice exhibits a stretchability of up to ≈520%, far beyond the inherent deformability of the brittle constituent. Moreover, this design also enables the tunability of various mechanical properties, including stiffness, strength, toughness, and Poisson's ratio. Ashby‐type plots are presented, revealing the relationships between stretchability and other mechanical properties to aid in the design and fabrication of advanced engineering materials. To demonstrate a vital application of the achieved stretchability, elastic wave propagation in the proposed kerfing metamaterials is studied. Simulations indicate that multiple broad phononic bandgaps arise in these structures as the fractal order increases. These bandgaps prove to be adjustable not only through the fractal lattice geometry but also by means of applied mechanical loading. This investigation highlights the potential of fractal‐based layouts as a promising avenue for designing cutting‐edge stretchable metamaterials with customizable mechanical properties and functionalities.

Multiple kinds of peeling processes and instabilities in heterogeneous film peeling

Although it has been demonstrated that heterogeneous film can enhance adhesion properties without modifying the interface, there is still a dearth of comprehensive studies in the literature regarding the peeling process of such film and the potential instability that may occur during the peeling process. To address these issues, a peeling model based on the cohesion zone model and Euler-Bernoulli beam equation is proposed in this study. Our analysis revealed four previously unknown peeling behaviors: Firstly, there are nine kinds of peeling processes for heterogeneous film. Only one is stable, static peeling process, while the other eight exhibit instability when the peeling front reaches a certain position. Secondly, instability may occur at the interface from the stiff section to the compliant section of the homogeneous film, as well as at stiff section or compliant section. Moreover, two of these peeling processes experience two instabilities within one peeling period – one at the interface from the stiff section to the compliant section and another at stiff section. Thirdly, an optimal length fraction of the stiff section for enhancing adhesive performance exists and its value is largely determined by the strength of the interface material. Specifically, higher interfacial strength results in smaller values of the optimal length fraction. Finally, the maximum peeling force is positively correlated with the bending stiffness ratio, interfacial strength, interfacial toughness, and period length of heterogeneous film. But it is inversely related to the bending stiffness. These findings are crucial for understanding the peeling behavior of heterogeneous film and strongly adhesive interfaces found in nature, and can be applied to optimize adhesive design and performance in practical engineering applications.

Semi-analytical solution for the 3D response of a tunnel embedded in an elastic half-space subject to seismic waves

This paper presents a semi-analytical solution for the 3D problem of a cylindrical tunnel embedded in an elastic half-space subject to plane harmonic compressional and shear waves. Both the tunnel and soil are modelled as an elastic continuum. Conformal mapping is employed to transform the original physical domain with boundary surfaces of two different types onto an image domain with surfaces of the same type, which makes the problem easier to solve. The total wave field in the half-space consists of incident and reflected (from the half-space surface) plane waves, as well as directly and secondary scattered cylindrical waves, while the total wave field in the tunnel consists of refracted cylindrical waves. The secondary scattered waves, generated when the cylindrical waves directly scattered from the tunnel meet the half-space surface, are represented by cylindrical waves that originate from an image source, which is in line with the spirit of the method of images. The unknown amplitude coefficients of the cylindrical waves are determined from the boundary and continuity conditions of the tunnel–soil system by projecting those onto the set of circumferential modes, which results in a set of algebraic equations. Results show that the present method converges for a small number of circumferential modes. We observe very good agreement between the obtained results and those in literature. In a systematic evaluation, we demonstrate that the method works well for the frequency band of seismic waves, as well as for the complete considered ranges of the tunnel/soil stiffness ratio, the embedded depth of the tunnel, the vertical incident angle and the tunnel thickness. However, the results obtained for a moderate tunnel–soil stiffness contrast under the incident compressional wave are inaccurate when Hankel functions are used to represent the cylindrical waves in the tunnel, which is due to the refracted shear waves in the tunnel transitioning from propagating to evanescent (in the 3D case). These inaccuracies can be perfectly overcome by representing the waves in the tunnel by Bessel functions. We also find that the present method generally works better for the incident compressional wave than for the incident shear wave, as the condition number of the matrix (related to the mentioned algebraic equations) is often larger in the latter case. In view of engineering practice, we conclude that the tunnel is safer when the surrounding soil is stiffer, the tunnel is thicker and the vertical incident angle is larger. Finally, the present method, which is in general fast, elegant and accurate, can be used in preliminary design so as to avoid pronounced resonances, and to assess stress distributions and ground vibrations.

NUMERICAL AND THEORETICAL INVESTIGATION ON COMPOSITE COLD-FORMED STEEL JOINTS WITH LIGHTWEIGHT CONCRETE

This research intends to investigate behaviour of composite cold-formed steel joint numerically through finite element analysis by using ABAQUS and theoretically by referring to BS 5950-1:2000 and Green book P213 “Joint in Steel Construction-Composite Connection”. A composite joint is modelled by combination of composite beam and steel column with connection of HRS gusset plate and M12 bolts. The significant failure mode is local buckling in CFS column web which similar in experimental study, FEM numerical simulation and theoretical component calculation. The behaviour of the cold-formed steel composite joint will be expressed in moment-rotational and load-deflection relationship to determine the initial rotational stiffness and ultimate moment resistance. The findings from numerical and theoretical investigations are compared with the full-scale experimental study in three different thicknesses of gusset plate. A correlation in stiffness ratio and strength ratio are obtained in the range of 1.76 to 2.25, and 1.00 to 1.60 respectively indicating that the numerical modelling tends to underpredict the behaviour of the composite structures.