A WCu composite coating with high W retention was fabricated by cold spraying using a novel W@Cu core-shell powder. The impact and deposition mechanism of W@Cu core-shell powder during cold spraying ...were investigated using finite element modeling in comparison to typical WCu satellite powder. The results revealed that the W@Cu core-shell powder shows non-local strain and dispersive residual stress in the final coating, resulting in a low rebound energy and interfacial bonding energy. As a result of employing the core-shell powder, a cold-sprayed WCu composite coating with a high W content can be prepared, and the coating has a non-pancake-like layer morphology. After optimizing the core-shell powder with a Ni transition layer, the final coating demonstrated super-high W retention (98.3 %) and decreased bulk porosity (1 %).
•WCu composite coating with high W content was prepared by cold spray using core-shell powder at low pressure.•Nonlocalized strain and dispersive residual stresses are the keys to preparing high W content coating.•The final coating showed super-high W retention and reduced bulk porosity.
Landslide dams consist of unconsolidated heterogeneous material and lack engineering measures to drain water and control pore water pressure. They may be porous and seepage through them could ...potentially lead to piping failure. In this research, the internal processes within a long-existing landslide dam are assessed under transient seepage force. The implemented approach includes a 3D finite element numerical simulation executing fully coupled flow-deformation and consolidation methods based on hydraulic data measurements and geotechnical laboratory tests. The nonlinear constitutive model ‘Hardening Soil’ is applied to accurately calculate the stress-induced pore water pressure, effective stress, deformation, and flow. Further, the possibility of slope failure due to seepage force is investigated through the strength reduction method. The results highlight the dependency of the seepage flow on the corresponding variation of the relative permeability and saturation in the soil mediums under different rates of seepage force. Small rates of seepage force, however, impose deformation at the dam's crown. High effective stress is obtained at negative small rates of seepage force where the long duration of fluctuation is modeled. In the drawdown simulation, there is a reverse relation between effective stress and the rate of the seepage force. Through the modeling process and based on the measured data, two seepage paths are detected within the landslide dam, while their activation depends on the lake level. The modeling approach and the required data analysis are suggested for utilization in further studies regarding the seepage process understanding at the long-existing landslide dams and their hazard assessments in addition to the common geomorphological approaches.
•Transient seepage is simulated in a long-existing landslide dam.•The ‘Hardening soil’ constitutive model is applied in the simulations.•Modeling is based on the hydraulic measurements and geotechnical laboratory tests.•Two seepage paths are detected based on the field measurements and modeling.
Crumb rubber modified bitumen (CRMB) can be considered as a binary composite system where rubber particles are embedded in the bitumen matrix. The bitumen-rubber interaction process (mainly swelling) ...significantly changes the mechanical properties of both bitumen and rubber phases. This study aims to predict the complex moduli of CRMB binders with more representative constituent parameters using micromechanical models. To achieve this goal, frequency sweep tests using a dynamic shear rheometer were performed on the liquid phase of CRMB and swollen rubber samples to represent the essential properties of bitumen matrix and rubber inclusion. In addition, the numerical swelling model was developed to estimate the effective volume concentration of rubber after swelling. Results show that the liquid phases of CRMB are stiffer and more elastic than the neat bitumen while the swollen rubber is softer and more viscous than the dry rubber. The effective volume concentration of rubber can increase to 2.126 times as the blend percentage based on the finite element analysis. Using the liquid phase of CRMB binder and swollen rubber properties as the micromechanical model inputs yield more accurate predictions. The used four micromechanical models predict well at higher frequencies while underestimating the complex modulus at lower frequencies.
Display omitted
•The bitumen matrix is stiffer than neat bitumen and rubber inclusion is softer than dry rubber.•The volume concentration of rubber increased to approximately two times after swelling from simulation.•The predicted complex shear modulus of CRMB using micromechanical models correlated well with experimental results.
Recently, metal matrix composites (MMCs) reinforced with nano-particles receive increasing attention from academia and industries. The cutting mechanism of nano MMCs is believed to be different when ...compared to composites reinforced with micro particles. This paper presents cutting mechanism comparison between SiC/Al metal matrix composites (MMCs) reinforced with micro and nano-particles using finite element method. The cutting mechanisms are investigated in terms of the von Mises stress distribution, tool-particles interaction, chip formation mechanism and surface morphology. It is found that the particles in nano size remained intact without fracture during the cutting process and are more likely to produce continuous chips, while the particles in micro size are easy to break and tend to form discontinues chips. Better machined surface quality with less defects can be obtained from nano size reinforced MMCs compared with their micro size counterparts. The model validation was carried out by conducting machining experiments on two types of MMCs and good agreements are found with the simulation results.
Display omitted
•Protective performance of ACH and full-covered helmet under blast wave were quantitatively analysis by the degree of cranial injury.•ACH does not provide blast protection and may ...even slightly aggravate cranial injury.•Fully-covered helmet can reduce the brain acceleration, strain, displacement, pressure, von-Mises stress and energy absorption.•The lighter fully-covered helmet can effectively reduce head injury by 35%, especially by reducing acceleration, strain and pressure.
Blast traumatic brain injury (BTBI) is the major type of injury, existing helmets are mainly designed to resist bullets and fragments, so it is necessary to study the explosion- proof performance of helmets. In this study, the validated finite element models including head, Advanced Combat Helmet (ACH), fully-covered helmet based on the prototype of Iron Man helmet were used to establish the blast wave-helmet-head fluid–solid coupling model, dynamic responses such as blast wave flow field pressure, skull stress, brain tissue pressure, displacement and energy absorption were obtained through simulations.
Quantitatively analyzed the protective performance of helmets show that wearing ACH can’t reduce the severity of brain injury, but rather increased about 5% compared to without wearing helmet. Wearing fully-covered helmet with same thickness as ACH can reduces the degree of brain injury by about 5%. Fully-covered helmet with same weight as ACH provides better protection, which can reduce the degree of brain injury to 65% than without wearing helmet. Research show that optimizing the shape and thickness of helmet can greatly reduce the brain injury, lighter fully-covered helmet can provide better protection for the brain under blast wave environment. The results can provide reference for new design of helmets.
A three dimensional finite element model of the human eye is developed to evaluate the force which will be applied over the surface of cornea during tonometry and gonioscopy tests. The standard ...tonometers and gonioscopy experiences deformation from 0.5mm to 3mm of the cornea is adopted during both point contact and boundary contact on the surface of the cornea. The results demonstrate the maximum force experienced by the tonometer with point contact at the center of the cornea for the maximum possible deformation of the cornea during tonometry. The study also analyzes for the force experienced by the tonometer or goniolens with boundary layer contact for the defined deformation of the cornea along the direction from cornea towards the retina.
•Numerical model to predict the shielding response of a lossy dielectric polymer nanocomposite sample in a waveguide.•Model implementation and predictions via finite element approach.•Flexibility in ...shape of the sample and spatial distribution of the complex permittivity within the sample.•Verification via benchmark analytical predictions.•Model is used to design optimal geometries of a sawtooth-shaped layer for absorption-dominated shielding.
A three-dimensional numerical model is constructed to predict the EMI shielding performance of a polymer nanocomposite shield in a rectangular waveguide. The Helmholtz wave equation for the electric field is implemented in component form and the set of coupled equations is solved via the finite element approach. Mesh convergence and model verification is performed by comparing free space model predictions for a flat, uniform layer to benchmark solutions calculated via transfer matrix theory. The capability of the model is showcased by exploring the role of geometry on the shielding performance of a sawtooth-shaped composite layer in a rectangular waveguide. Increasing the inclusion angle of the sawtooth, which is proportional to the ratio of the sawtooth amplitude and repeat unit width, reduces the transmitted power through the shield and increases the ratio of absorption to reflection of wave power by the shield. Thus, a rational design of this sawtooth geometry allows to overcome the typical trade-off between total shielding effectiveness and wave absorption contribution, thereby resulting in highly performant absorption-dominated shields.
Display omitted
•Realistic fracture simulated by XCT image-based mesoscale concrete models.•Micro/macro fracture presented in detail to elucidate fundamental mechanism.•Tensile strength found inversely proportionate ...to void fraction statistically.•Relative ratio of cohesive strength in cement and interface is a key factor.
Two-dimensional meso-scale finite element models with realistic aggregates, cement paste and voids of concrete are developed using microscale X-ray Computed Tomography images. Cohesive elements with traction–separation laws are pre-embedded within cement paste and aggregate–cement interfaces to simulate complex nonlinear fracture. Tension tests using a large number of images were simulated with statistical analysis. The very different load-carrying capacities and crack patterns demonstrate the effects of random distribution of phases. It is found that the tensile strength decreases as the void fraction increases, and the relative strength of cement paste and interfaces dominates the microcracking behaviour, which in turn affects macrocracking and load-carrying capacity.
In the study, three different higher order finite element models (HOFEMs) are developed to perform the transient analysis of functionally graded (FG) microplates subjected to different dynamic loads, ...namely, sinusoidally distributed step and exponential blast loads. A normal and shear deformable plate theory with five unknowns is used to present displacement field and modified strain gradient theory is employed for small-scale effect. A rectangular four-noded element and Newmark's method is used to solve transient analysis of FG microplates. The effects of boundary condition, type of dynamic loading, thickness to material length parameter, aspect ratio, gradient index and CPU time are investigated. It is found that two of the HOFEMs developed based on the C1 and C2 continuity requirements produced almost same numerical results. However, the one with 36 unknows per element yields slightly different results than the others. The HOFEM satisfying the C1 continuity requirement consumes the minimum computational time.
•Three different higher order finite element models (HOFEMs) are developed.•Transient analysis of FGM microplates is performed by using the MSGT.•Sinusoidally distributed step and sinusoidally distributed exponential blast loads are applied.•A normal and shear deformable plate theory with five unknowns is used.
Large-scale seismic structural tests are crucial to validating both structural design methodologies and the effectiveness of seismic isolation devices. However, considering the significant costs of ...such tests, it is essential to leverage data from completed tests by taking advantage of numerical models of the tested structures, updated using data collected from the experiments, to complete additional studies that may be difficult, unsafe or impossible to test physically. However, updating complex numerical models poses its own challenges. The first contribution of this paper is to develop a multi-stage model updating method suitable for high-order models of base-isolated structures, which is motivated and evaluated through modeling and model updating of a full-scale four-story base-isolated reinforced-concrete frame building that was tested in 2013 at the NIED E-Defense laboratory in Japan. In most studies involving model updating, all to-be-updated parameters are typically updated simultaneously; however, given the observation that the superstructure in this study predominantly moves as a rigid body in low-frequency modes and the isolation layer plays a minor role in all other modes, this study proposes updating parameters in stages: first, the linear superstructure parameters are updated so that its natural frequencies and mode shapes match those identified via a subspace system identification of the experimental building responses to low-level random excitations; then, the isolation-layer device linear parameters are updated so that the natural frequencies, damping ratios and mode shapes of the three isolation modes match. These two stages break a large-scale linear model updating problem into two smaller problems, thereby reducing the search space for the to-be-updated parameters, which generally reduces computational costs regardless of what optimization algorithm is adopted. Due to the limited instrumentation, the identified modes constitute only a subset of all modes; to match each identified mode with a FEM mode, the second contribution is a procedure proposed to compare each identified mode with a candidate set of FEM modes and to select the best match. Further, nonlinear isolation-layer device models are proposed, updated and validated with experimental data. Finally, combining the isolation-layer devices’ nonlinear models with the updated superstructure linear FEM, the final result is a data-calibrated nonlinear numerical model that will be used for further studies of controllable damping and validation of new design methodologies, and is being made available for use by the research community, alleviating the dearth of experimentally-calibrated numerical models of full-scale base-isolated buildings with lateral–torsional coupling effects.
•Developed two-stage modal linear model updating method for base-isolated buildings.•Evaluated with full-scale E-Defense shake-table experimental measured responses.•Proposed a new algorithm to match model modes to those from system identification.•Nonlinear isolation-layer device models are calibrated from experimental data.•Combined partially linear model predicts well the structure time–history responses.
PDF
