Effects Of Thickness Ratio Research Articles

Study on the electromagnetic wave absorption performance of dual-loss type composite MWCNT/CIP/GF/EP

Abstract The electromagnetic properties of single-loss glass fiber (GF) absorbing composites with the addition of multi-walled carbon nanotube (MWCNT) particles and single-loss GF absorbing composites with the addition of carbonyl iron powder (CIP) particles in the X-band were studied. Using CST electromagnetic simulation combined with experiments, dual-loss MWCNT/CIP/GF/epoxy resin absorbing composites were designed and prepared. The effects of thickness ratio and periodic layering on the absorbing properties of dual-loss GF absorbing composites were investigated. The results show that by changing the thickness ratio and periodic layering, the impedance matching and attenuation characteristics of the dual-loss GF absorbing composites can be altered, thereby affecting the overall absorbing performance. The optimal group exhibited a maximum reflection loss of −55.3 dB at 8.5 GHz, with an effective absorption bandwidth of 3.0 GHz, covering 71.4% of the X-band.

Effect of thickness ratio on microstructure evolution and coordinated behavior of Mg/Al composite plates in one-pass asymmetric rolling with differential temperature rolls

To explore how varying matrix thicknesses influence interfacial morphology, microstructure, and mechanical properties of Mg/Al composite plates, this study prepared composite plates with distinct thickness ratios using an asymmetric rolling process featuring differential temperature rolls. The findings indicate that the Mg alloy largely exhibits significant recrystallization and sub-grained, while the Al alloy largely demonstrates a sub-grained characteristic. Notably, there exists a strong positive correlation between bonding strength at the interface and thickness ratio. As the thickness ratio increases, enhanced shear deformation at the interface triggers more slip system initiation, resulting in a gradual reduction of texture intensity in both the Mg and Al layers. Specifically, when the AZ31B/Al6061 thickness ratio reaches 5, the recrystallization level of the Mg layer is relatively elevated, accompanied by a fine and uniform grain size in the Al layer. This situation decreases the likelihood of stress concentration at the interface, which results in exhibiting relatively optimal elongation and bonding strength.

Effects of thickness ratio on phase structures, mechanical properties, and wear behaviors of CrN/ZrB2 bilayer films

CrN/ZrB2 bilayer films leveraging the wear resistance of CrN and the mechanical properties of ZrB2 were successfully produced and characterized. DC magnetron sputtering was used to deposit CrN/ZrB2 bilayer films with a thickness of approximately 1 μm and various ZrB2/CrN sublayer thickness ratios (TZrB2/TCrN = 10.85, 5.78, 4.50, 2.29, and 1.04). The thickness ratio was controlled by adjusting the deposition times of the individual sublayers. The effects of thickness ratio on the films' phase structures, mechanical properties, and wear resistance were investigated. The ZrB2 sublayer initially formed with a nanocrystalline structure; as its thickness increased, its texture became (001). As the thickness of the CrN sublayer increased, the CrN (111) reflection became more dominant, and the hardness of the CrN/ZrB2 bilayer films decreased from 19.8 to 11.6 GPa. In the CrN/ZrB2 bilayer films, the CrN sublayer was softer than the harder ZrB2 sublayer; specifically, the wear rate of the monolithic ZrB2 film was 6.45 × 10−5 mm3/N·m. This hardness enabled the bilayer films to exhibit excellent wear resistance with wear rates of 1.04–1.68 × 10−6 mm3/N·m. The wear behaviors of the CrN/ZrB2 bilayer films were classified into two tribological mechanisms in accordance with wear track observations. For the samples with high TZrB2/TCrN ratios, the shear mechanism dominated the wear behavior and resulted in the formation of a transfer layer on the worn surface. By contrast, the samples with low TZrB2/TCrN ratios had a ploughing mechanism in which a deformed track was generated on the surface.

On discontinuous stress and strain evolutions in machining of dissimilar laser cladded workpiece

During subsequent machining of laser cladded workpiece, the stress transferred in depth direction is different with conventional cast workpiece due to the geometrical discontinuity, resulting in the stress difference and strain discontinuity at the interface between the cladding layer and substrate. Elastic and plastic deformation will occur in the cladding layer and substrate, respectively, which ultimately reduces the service life of the cladded workpiece. In this study, the stress and strain evolution in subsequent machining of laser cladded workpiece was investigated using an orthogonal cutting model by finite element method. A dimensionless thickness ratio between uncut chip thickness and cladding layer thickness was set and the maximum thickness ratio without equivalent plastic strain (PEEQ) discontinuity at the interface was determined. In addition, the results indicated that the maximum thickness ratio first decreased and then increased with the increase of cutting speed, while increases with the increase of the yield strength of substrate. The synergetic effects of thickness ratio, cutting speed and yield strength of substrate on the strain discontinuity at the interface were also investigated based on Taguchi method. The optimal combination of parameters is determined based on the regression model and divided into areas with considering machining efficiency as well. The map of cutting configurations facilitates the selection of proper machining parameters in order to estimate the strain discontinuity in machining laser cladded workpiece, ensuring a better service life of the workpiece.

Dynamic Stability of an Asymmetric Sandwich Beam Resting on a Paternak Foundation

The parametric dynamic stability of a pinned-pinned asymmetric sandwich beam resting on a Pasternak foundation with viscoelastic core, subjected to an axial pulsating load is investigated. The effects of thickness ratio of two elastic layers (h31), elastic modulus ratio(E3/E1), the ratio of modulus of the shear layer of Pasternak foundation to the Youngs modulus of elastic layer (Gs/E1), the ratio of length of the beam to the thickness of the elastic layer (lh1), the ratio of in phase shear modulus of the viscoelastic core to the Youngs modulus of the elastic layer (G2/E1), the ratio of thickness of Pasternak foundation to the length of beam (δ/l), coreloss factor (η) the ratio of thickness of viscoelastic layer to that of elastic layer (h21) on the non-dimensional static buckling load are considered. In addition to these the effects of the above parameters on the regions of parametric instability have been studied.

Effect of thickness ratio on interfacial structure and mechanical properties of Mg/Al composite plates in differential temperature asymmetrical rolling

Mg/Al composite plates with different thickness ratios were prepared by different temperature asymmetrical rolling + isothermal symmetrical rolling. The effects of different thickness ratios of component metals on microstructure, interface structure, and mechanical properties of composite plates were studied. It was found that the thickness of blocky intermediate compounds β(Mg2Al3) and γ(Mg17Al12) formed in the second pass rolling is inversely proportional to the component metal thickness ratio, and the maximum thickness of metallurgical bonding layer reaches 7.8 μm when the thickness ratio is 2. The main grains in matrix and clad plates are equiaxed grains and deformed grains, respectively. With the increase of thickness ratio, recrystallization of Mg layer increases first and then decreases, while Al side increases gradually because of the difference reduction of component metals. Due to the fine grain strengthening of matrix, the dislocation strengthening and low texture of clad plate, and the proper thickness of intermediate compounds, composite plate with a thickness ratio of 3 has the best mechanical properties. Its ultimate tensile strength and yield strength are 277.4 MPa and 253.9 MPa, respectively. Its elongation is the highest, up to 18.7%.

Effect of Thickness Ratio on the Magnetic Properties of the Magnetostrictive Thin Film Composite

Magno-elastic coupling characteristics in giant magnetostrictive thin films depend on a myriad of factors, comprising variability in Young’s modulus, thermally induced pre-stresses, the direction of the applied magnetic field and the substrate to film thickness ratio, demagnetization field etc. Due to the aforementioned reasons, the giant magnetostrictive thin films usually display characteristics that may contrast with the bulk giant magnetostrictive materials. This work studies magnetostrictive film on a compliant substrate using a generalized 3-D magneto-thermo-elastic nonlinear constitutive model with the elasticity theory to include such stimuli sensitive coupled magneto-thermo-elastic response. The numerical simulation of the magnetostrictive film on the compliant substrate in the form of a cantilever shows good agreement with the existing experimental data. The substrate and film thickness ratio effect on the thermal strain, Young’s modulus, magnetization and magnetostriction of films was meticulously analyzed. It has been revealed that the magneto-elastic responses rely strongly on the substrate-to-film thickness ratio. Thus, it is possible to obtain the tunable properties by controlling the composite film's thickness ratio in the design state of smart devices.

Dislocation equilibrium positions in bilayer structures

The stability of an edge dislocation embedded in a two-dimensional structure composed of one layer of ZnS and one layer of Ge has been theoretically investigated from a Peach–Koëhler force-based analysis in the absence of misfit stress and layer bowing effects. The effect of thickness ratio between the two layers of heterogeneous elastic coefficients has been characterized on the different equilibrium positions of the dislocation through the study of the climbing component of the Peach–Koëhler force. It is found that the number (from 3 to 5) and nature (stable or unstable) of these equilibrium positions distributed in both layers vary significantly as a function of the thickness ratio.

Effects of the layer thickness ratio on the enhanced ductility of laminated aluminum

• The layer thickness ratio ( r c / f ) is vital for tuning the strength and ductility of laminated Al. • The decrease of r c / f leads to better deformation accommodation because of the approaching interfacial strain gradient. • The interfacial cracks propagation path is altered with increasing the r c / f . • The effects of r c / f on the fracture behavior is discussed by a criterion of microcracks connectivity. The layered structural parameters have been reported to be critical for tuning the tensile properties of laminated metals. Here, we investigated the effects of the thickness ratio ( r c / f ) of coarse-grained layers (CLs) to fine-grained layers (FLs) on the enhanced ductility of the laminated Al. The local strain evolution demonstrates that the strain delocalization ability of laminated Al is improved with the decrease of r c / f . The interfacial strain gradients, which can produce extra work hardening, gradually approach and cover the CLs with the r c / f decreasing, explaining the trend of uniform elongation in laminated Al with various r c / f . The integrated fracture morphology characterization reveals that the increase of the r c / f leads to an improvement in the tolerance of the interfacial microcracks, which is corresponding to the variation of fracture elongation in the laminated Al. Moreover, there is an evident transition of transverse propagation path of interfacial microcracks from the CLs to FLs with increasing the r c / f . Based on a geometrical criterion of microcracks connectivity, the preferential transverse propagation path of interfacial microcracks in these laminated Al was rationalized. The calculation based on this criterion also predicted the critical r c / f corresponding to the optimal combination of strength and fracture elongation. This work deepens the understanding of the role of structural parameters of laminated metals in achieving the strength and ductility synergy.

Effect of Taper and Perforation on Heat Transfer Coefficient of a Passive Horizontal Heat Sink

The present study focuses on the numerical investigation of a passive horizontal base heat sink with perforated fins. Fins of the rectangular and trapezoidal cross-section are considered for the study. A detailed parametric numerical study is carried out considering the thickness ratio range (0.33–1); 4–6 mm size of square perforation; 6, 12, and 18 number of perforation and Rayleigh number 592–3044. Significant effect of thickness ratio, size of square perforation, and the number of perforations is observed on the heat transfer coefficient. The heat transfer coefficient increases with the decrease in the thickness ratio and increases with the number of perforation and size of square perforation in trapezoidal cross-section fins. 11.7% of increment in heat transfer coefficient was observed in perforated heat sink when it is compared to the non-perforated heat sink. Mass of the passive heat sink decreases with an increase in the size of perforation, number of perforations, and decrease in the thickness ratio. Mass reduction of up to 58% is observed in perforated heat sinks. A significant improvement in the performance factor is observed for the present study parameters range of Rayleigh number, the thickness ratio, size of perforation, and the number of perforations.

Bandgaps for flexural waves in infinite beams and plates with a periodic array of resonators

ABSTRACT The subject of seismic metamaterials, inspired from novel ideas in optics and acoustics, has attracted great attention in the last decade for potential applications in earthquake engineering. Simple structure systems, like beams and plates, with periodically attached mechanical resonators provide a simple physical model to interpret the existence of certain frequency bandgap in dispersion relations and to simulate the mechanism of flexural energy attenuation. In this work, we consider simple structure systems of beams and plates with periodically attached resonators. The resonator is composed of a spring, a damper and a mass attached along the beam direction. We utilize the Timoshenko beam model and the Mindlin plate theory to incorporate the shear effect. The plane wave expansion method together with the Bloch theorem is used to expand the governing field into an eigenvalue problem of an infinite complex system, allowing us to characterize the band structures of the dispersion relations. Local resonance and Bragg bandgaps are identified and examined. The effect of thickness ratios, the damping ratio and the shear modulus are exemplified to demonstrate how these factors will affect the formation of bandgaps. This formulation demonstrates a feasibility that a periodic array of mechanical resonators together with suitable material and geometric parameters of beams and plates can be designed to tune with the dispersion behavior in the control of flexure waves. This study may open up new potential in the control of wave propagation in complex continuum systems through the interaction of adequately designed resonators.

3D hygro-elastic shell model for the analysis of composite and sandwich structures

The present work proposes the study of the hygrometric loading effects in the static analysis of multilayered composite and sandwich plates and shells. The employed model is based on a general exact 3D shell theory valid for one-layered and multilayered sandwich and composite plates, cylinders and cylindrical/spherical shell panels. The employed 3D equilibrium equations are developed in an orthogonal mixed curvilinear coordinate system for spherical shells in order to obtain the other simpler geometries as particular cases. A layer-wise approach is employed and equilibrium equations are solved in the thickness direction via the exponential matrix method. The partial derivatives in the in-plane directions are exactly calculated by assuming simply-supported edges and harmonic forms for the variables. The presented 3D shell model is extended to hygro-elastic cases by considering moisture content amplitudes imposed at the external surfaces of the structures in steady-state conditions. The moisture content profile through the thickness of the structures can be included in the 3D shell model using three different methodologies: it can be calculated by solving the steady-state 3D or 1D version of the Fick diffusion law, or it can be “a priori” assumed as linear through the thickness. Therefore, the developed system includes three non-homogeneous second order differential equilibrium equations that are solved after the introduction of opportune mathematical layers to consider the curvature effects through the thickness. The reduction to a first order differential equation system is obtained by redoubling the number of variables. The exponential matrix method is employed to accurately define both general and particular solutions. The implemented 3D hygro-elastic shell model is firstly validated and then it is employed with confidence for new benchmarks where the effects of thickness ratio, geometry, lamination scheme, material, thickness layer and imposed moisture content values at the external surfaces are investigated for composite and sandwich plates and shells. Showed results demonstrate the importance of an accurate developing of the elastic part of the 3D shell model combined with an appropriate evaluation of the moisture content profile through the thickness. Assumed linear moisture content profiles are correct only for thin one-layered isotropic structures, the use of the 1D Fick diffusion law allows only the correct definition of the material layer effect, the use of its 3D version allows the correct definition of both material and thickness layer effects.

Effect of Thickness Ratio on Interfacial Morphology and Mechanical Properties of Mg/Al Composite Plates in Differential Temperature Asymmetrical Rolling

Effect of Thickness Ratio on Interfacial Morphology and Mechanical Properties of Mg/Al Composite Plates in Differential Temperature Asymmetrical Rolling

Effect of Thickness Ratio on Ferroelectric Polarization and Hysteresis Behaviors of BaTiO3/SrTiO3 Superlattices

We study the effect of thickness ratio on the ferroelectric polarization and hysteresis behaviors of BaTiO3/SrTiO3 superlattices using Landau-Ginzburg-Devonshire theory by considering the electrostatic coupling and interface intermixing. Interface intermixing gives rise to inhomogeneous internal electric field and polarization in superlattices. The hysteresis loops of polarization and internal electric field as a function of the applied electric field are investigated by varying the thickness ratio of the superlattices. The hysteresis loops for each individual layer are calculated. The effects of thickness ratio on remnant polarization, remnant internal electric field and coercive field are examined.

Dynamics of ferroelectric polarization and internal electric field in PbTiO3/SrTiO3 superlattices

We study the dynamics of polarization and internal electric field in the PbTiO3/SrTiO3 (PT/ST) superlattices using the Landau–Khalatnikov equation. Apart from the polarization hysteresis loop, the hysteresis loop of the internal electric field is also observed. The effects of thickness ratio and temperature on the switching dynamics of superlattices are investigated. We found that the dynamics of polarization switching is directly correlated with the internal electric field. The change of sign in the internal electric field implies the occurrence of polarization switching in the ferroelectric superlattices.

Plasticity solutions for ground deformation prediction of shallow tunnels in undrained clay

Elastic-plastic contraction solutions of a cavity within an infinite soil mass are widely used to estimate ground response curves of deep tunnels. The pressure-convergence response of soil around shallow tunnels, however, tends to vary with tunnel embedment ratio. To account for the embedment ratio effect, this paper presents a general solution procedure for undrained contraction analysis of a thick-wall cylinder or spherical shell of isotropically hardening soils, by which a set of analytical and semi-analytical large strain solutions for several Cam-Clay soil models is derived. Results obtained with the new solutions show that the cavity contraction response highly depends on the soil stress history (overconsolidation ratio) and the radial thickness of the surrounding soil. A limit ratio of the outer to the inner radii exists, beyond which the thickness ratio effect becomes negligible. The limit ratio for a spherical shell is smaller than that for a hollow cylinder, and it decreases with the overconsolidation ratio of soil. Based on the analogy between cavity contraction and tunnel convergence, theoretical methods for predicting ground response curves of shallow plane-strain tunnels in clays are proposed and validated by comparing with relevant experimental and numerical simulation results. The solutions can also provide valuable benchmark methods for verifying various numerical programmes.

The Analysis of Anchoring Mechanism of Rock Slope in Two Layers Based on the Nonlinear Twin-Shear Strength Criterion

The nonlinear strength criterion is introduced into the paper firstly, and then the geometric anchoring characteristic model of rock slope separated from two layers according to rock type with the fracture surface of log-spiral curve considering nonlinear twin-shear criterion subjected to seismic loads is established. Finally, some correlated influential parameters are analyzed, and the conclusions are drawn, showing that the intermediate principal stress has great influence on the total anchoring force of bolt P, so when different criteria are selected, the influence of intermediate principal stress should not be omitted. The effects of thickness ratio h1/h2 on total anchoring force increase gradually with the increase of inclination angle ϕ . The total anchoring force P decreases gradually with the increase of inclination angle ϕ and surcharge load q. The total anchoring force increases gradually with the increase of horizontal seismic acceleration coefficients kh and geometric coefficients mi and GSI.

Effect of interfacial imperfections on SH-wave propagation in a porous piezoelectric composite

ABSTRACT The role of porous piezoelectric materials is very crucial in modern days, especially in designing underwater object detection devices. Therefore, the present article deals with SH-wave propagation in a porous piezoelectric layer sandwiched between an upper mechanically bonded porous layer and lower mechanically and electrically bonded piezoelectric layer. Bonding parameters have been considered to describe the effect of electrical and mechanical imperfections on the interface. The effect of thickness ratio, electro-mechanical bonding parameters on phase velocity are studied extensively. The imperfections at interfaces reduces phase velocity of SH-wave. The influence is found significant when large imperfections persist at the interface.

Influence of short-fiber composite base on fracture behavior of direct and indirect restorations

ObjectivesThe aim was to examine the influence of short-fiber composite (SFC) core on the fracture-behavior of different types of indirect posterior restorations. In addition, the effect of thickness ratio of SFC-core to the thickness of the veneering conventional composite (PFC) on fracture-behavior of bi-structured composite restorations was evaluated.Materials and methodsMOD cavities with removed palatal cusps were prepared on 90 intact molars. Five groups of direct overlay restorations (n = 10/group) were fabricated having a SFC-core (everX Flow) with various thicknesses (0, 1, 2, 3, 4 mm) and layer of surface PFC (G-aenial Anterior), remaining the thickness of the bi-structure restoration to be 5 mm. Four groups of CAD/CAM-made restorations (Cerasmart 270 and e-max CAD) were fabricated either with 2-mm layer of SFC-core or without fiber reinforcement. Intact teeth (n = 10) were used as control group. Restorations were statically loaded until fracture. Fracture patterns were evaluated visually. Data were analyzed using ANOVA (p = 0.05).ResultsWith indirect overlay restorations, no statistically significant differences (p > 0.05) were observed in the load-bearing capacities between restorations reinforced by 2-mm SFC-core (bi-structured) and those fabricated from plain restorative materials. ANOVA displayed that direct overlay restorations made from 4-mm layer thickness of SFC-core had significantly higher load-bearing capacities (3050 ± 574 N) (p < 0.05) among all the groups tested.ConclusionsRestorations (direct/indirect) combining SFC-core and a surface layer of conventional material demonstrated encouraging achievement in reference to fracture behavior.Clinical relevanceThe use of flowable short-fiber composite as reinforcing base with large direct and indirect restorations may result in more repairable failure.

Effect of thickness ratio of overlaying layer to hydrate bearing stratum upon the settlement of seabed sediments during Natural Gas Hydrate Dissociation

The dissociation of natural gas hydrate in the process of exploitation will weaken the mechanical properties of the surrounding soil, which will lead to the deformation and destruction of the seabed sediment, thus posing a potential threat to the safety of the undersea engineering infrastructures. In this paper, the finite difference method is used to simulate the vertical deformation of seabed sediments, and examine the effect of thickness ratio of the overlying layer to the HBS upon soil settlement via an established three-dimensional model of submarine hydrate mining. The main research results are as follows: The maximum settlement occurred at the top surface of HBS dissociation centre and the settlement decreased significantly from the mining well to the surrounding and from HBS to the overlying layer. The range of settlement trough on the top of HBS is far less than the overlaying layers. The thickness ratio of the overlying layer to the HBS will have a great influence on the distribution of sedimentation and deformation of seafloor sediments caused by hydrate dissociation. The deformation and the range of the settlement trough both decrease with the increasing thickness ratio of overlying layer to HBS. The research results will provide a strong theoretical reference for the stability of seabed and mining platform during hydrate mining.