Hard Layer Thickness Research Articles

Analysis of the effect of rock layer structure on the toppling failure evolution of soft-hard interbedded anti-dip slopes

The soft-hard interbedded anti-dip rock slopes (SHIADRS) are unique among all layered rock slopes, as the mechanical properties of hard and soft rock layers are completely dissimilar. These slopes are abundant in south-western China. Therefore, this study examined the evolution of SHIADRS toppling failure using a centrifuge model test. The test results indicate that the entire SHIADRS failure process can be roughly divided into three stages: 1) the slight deformation stage involving tension and bending of rock layers, 2) the development stage involving tensile cracks at the slope top and the formative stage of toppling zones as well as 3) the total failure stage. Furthermore, the toppling deformation process of the SHIADRS can be divided into three stages concurrently, based on the magnitude of the displacement rate: 1) stable deformation stage, 2) unstable deformation stage, and 3) accelerated deformation stage. The universal distinct element code (UDEC) is utilised further to investigate the impact of rock layer structures on SHIADRS failure patterns. The simulation results indicate that variations in the thickness of soft and hard rock layers have no significant effect on the failure process and macroscopic failure patterns of SHIADRS. Additionally, the failure patterns of anti-dip hard rock slopes, anti-dip soft rock slopes and SHIADRSs were discussed, with SHIADRSs having the most complex failure pattern. Based on the fracture mechanics theory and the independent cantilever beam model, an improved method for calculating the stability of SHIADRS is proposed, which can determine the stability of rock layers by calculating the residual sliding force.

Modelling of Magnetic Stray Fields in Multilayer Magnetic Films with In-Plane or Perpendicular Anisotropy

The magnetic stray field is an unavoidable consequence of magnetic multilayers, which may have a significant influence on the performance of spintronic devices. Based on Maxwell’s magnetostatics theory, here we numerically calculated the distributions of magnetic stray fields and self-demagnetizing fields in a series of patterned multilayer thin-film structures with either an in-plane or a perpendicularly magnetized ferromagnetic layer. The stray field above the ferromagnetic layer is inhomogeneous, showing the dramatic changes near the sample edge, but the uniformity in the center region could be improved with the increasing sample size. The stray field strength tends to zero for large samples, increases with the increase in the hard-layer thickness, and decreases with the increase in the distance D away from the ferromagnetic layer. In the multilayer samples, the separately simulated stray field and self-demagnetizing field within the soft layer agree well with the classic magnetostatic relationship of B=μ0(Hd+M). For the in-plane magnetized trilayer sample, the magnetic-flux density within the soft ferromagnetic layer slightly decreases in the antiparallel magnetization alignment and increases in the parallel alignment state with the increase in the intermediate non-magnetic-layer thickness. In contrast, for the sample with the perpendicular magnetization, the magnetic-flux density decreases as the non-magnetic layer is thickened for both the antiparallel and parallel state. This study may provide a theoretical basis for the design of thin-film spintronic devices.

Experimental study on reinforcement of marine clay by artificial hard shell layer composite foundation

In situ curing artificial hard shell layer composite foundations have been used to reinforce marine clay. But during construction, it is still designed and used according to the reinforced cushion composite foundation, and not combined with the characteristics of artificial hard shell layer. This will inevitably cause some economical or practical problems for the design and construction of artificial hard shell layer composite foundation. In this article, the effect of different thickness of hard shell layer and pile spacing on the bearing capacity of artificial hard shell layer composite foundation is studied by laboratory model experiment. The effects of settlement, ultimate bearing capacity, pile-soil stress ratio and pile axial force on the performance of artificial hard shell layer composite foundation is analyzed through load plate experiments of single pile, soil between piles, single pile composite and multi-pile composite foundation. The results show that the composite foundation has better performance when the ratio of thickness of hard crust to pile spacing is between 1.4 and 1.8, and the pile-soil stress ratio is about 35. At the same time, it is found that by increasing the thickness of hard shell layer and pile spacing, the pile skin friction can be higher.

Model tests on progressive collapse mechanism of a shallow subway tunnel in soft upper and hard lower composite strata

Numerous subway tunnels have been built in soft upper and hard lower composite strata. However, the stability and bearing capacity of composite strata are difficult to predict compared to homogeneous strata, so collapse always occurs in composite strata. The evolution of progressive failure leading to the collapse of shallow subway tunnels in soft upper and hard lower composite strata is complicated and merits further research. Based on the Qingdao subway tunnel, scaled model tests have been conducted to explore the progressive collapse mechanism of shallow subway tunnels in soft upper and hard lower composite strata. The results demonstrate that the stress distribution and collapse process of composite strata are significantly impacted by hard lower layer thickness above the tunnel roof. A stable collapse arch cannot be formed when only the soft layer is above the tunnel roof, and collapse quickly extends to the ground surface once failure occurs in the soft upper layer. As the thickness of the hard lower layer increases, a temporary stable collapse arch cannot only be formed in the hard lower layer but also in the soft upper layer during collapse; thus, a slow and progressive collapse process of the composite strata is observed under an increasingly imposed load. The greater the thickness of the hard lower layer above the tunnel roof, the higher the stability and bearing capacity of the composite strata. Additionally, the collapse mechanism of composite strata is further investigated using the discrete element method, and the minimum rock-span ratio is suggested for various buried depth tunnels based on whether a closed load-bearing arch can be formed in the hard lower layer. Finally, the proposed rock-span ratio is successfully applied in Qingdao subway tunnels, allowing for a suitable reference for constructing similar engineering.

Numerical analysis on the bearing mechanism of branch tunnel in upper softer and lower hard ground

It is of great interest to investigate the excavation disturbance mechanism of branch tunnel in the upper soft and lower hard ground. In this paper, a fine 3D numerical simulation, considering the longitudinal gradient of tunnel, was performed to investigate the bearing mechanism of branch tunnel. By comparison of the characterises of stress redistribution, two different bearing mechanisms were obtained: the beam bearing mechanism dominates the capacity of super-large section, and the beam bearing zone and stress concentration zone are identified in the arch zone; In the small interval section, the arch bearing mechanism works, and the stress loosening zone and arch bearing zone appears above the arch. The attributed reasons are related to the thickness of hard layer above the arch and the span of tunnel. Correspondingly, the arch settlement in the super-large section is much larger than that of the small interval section, while the deformation at arch foot of both sections moves outside. Furthermore, through the analysis of the maximum principal stress direction, the determination method of the outer boundary of the pressure arch was discussed.

Application of microbial induced carbonate precipitation for loess surface erosion control

China is one of the countries with the most serious soil erosion disaster, especially in Loess Plateau region. A new strategy for loess surface erosion control using MICP technology in terms of spraying was proposed. The feasibility, mitigation mechanism and the effects of MICP treatment cycle and cementation solution (CS) concentration were investigated through the rainfall erosion test and penetration test. It is found that the proposed MICP technique shows the ability to mitigate the rainfall erosion of loess. Final accumulative soil erosion weight could reach a maximum reduction of 200 times after only 3 cycles of MICP spaying treatment and almost no soil loss was observed since 5 cycles of treatment. The mitigation mechanism can be attributed to the MICP induced double layer structure, namely the upper hard crust layer on soil surface and the lower weak cemented layer, which is attributed to the bonding effect of the precipitated calcium carbonate (CaCO3) between soil particles and the filling effect in pores. The high structure strength of the hard crust can resist the impact of raindrops as well as can resist runoff erosion. The low permeability of the hard crust effectively prevents the rainwater infiltration to soft the subsurface weak cemented layer and deep uncemented soil. With increasing MICP treatment cycles, the amount CaCO3 and the thickness of the hard crust layer increases accordingly, leading to higher soil structure strength and erosion resistance. The CaCO3 content generally decreases with increasing depth. It is also found that the loess treated by 1.0 M CS presents the highest CaCO3 content, hard crust layer thickness and soil structure strength as compare with the samples treated by 1.5 M and 0.5 M CS. Taking into account the overall effectiveness, efficiency and cost, 5 cycles of MICP treatment with 1.0 M CS is optimal for the mitigation of the rainfall erosion of the tested loess.

Hard/soft magnetic bilayer. Monte Carlo study

The influence of the soft and hard magnetic layers thickness on reversal magnetization process of the hard/soft magnetic bilayer in an external magnetic field has been studied using Monte Carlo method. It is shown the critical value of the magnetization reversal field Hirr doesn’t change with a decrease in the hard magnetic layer thickness up to 20 atomic monolayers. Phase diagrams of the magnetic bilayer have been plotted. The results have been shown to compare with experimental and theoretical data.

A Hybrid Predictive Approach for Chromium Layer Thickness in the Hard Chromium Plating Process Based on the Differential Evolution/Gradient Boosted Regression Tree Methodology

The purpose of the industrial process of chromium plating is the creation of a hard and wear-resistant layer of chromium over a metallic surface. One of the main properties of chromium plating is its resistance to both wear and corrosion. This research presents an innovative nonparametric machine learning approach that makes use of a hybrid gradient boosted regression tree (GBRT) methodology for hard chromium layer thickness prediction. GBRT is a non-parametric statistical learning technique that produces a prediction model in the form of an ensemble of weak prediction models. The motivation for boosting is a procedure that combines the output of many weak classifiers to produce a powerful committee. In this study, the GBRT hyperparameters were optimized with the help of differential evolution (DE). DE is an optimization technique within evolutionary computing. The results found that this model was able to predict the thickness of the chromium layer formed in this industrial process with a determination coefficient equal to 0.9842 and a root-mean-square error value of 0.01590. The two most important variables of the model were the time of the hard-chromium process and the thickness of the layer removed by electropolishing. Thus, these results provide a foundation for an accurate predictive model of hard chromium layer thickness. The derived model also allowed the ranking of the importance of the independent input variables that were examined. Finally, the high performance and simplicity of the model make the DE/GBRT method attractive compared to conventional forecasting techniques.

Microstructure evolution and damage mechanism of layered titanium matrix composites under tensile loading

In order to better guide the design of layered metal matrix composites, the failure mechanism of a kind of Ti based layered composite was investigated. The results showed that this layered composites possessed better uniform deformation ability compared with the materials of each layer. Increasing the hard composite layer thickness led to the enhancement of tensile strength but descend of deformation ability. The micro-cracks in the Ti layer provided plasticity, while the unique network microstructure in the composite layer restrained the slip bands from the network central region. These slip bands propagated through network skeleton and caused TiB whiskers fracture and interface debonding between the metallic matrix and TiB whiskers. Numerical simulation indicated that interface cracks in the composite layer were prone to propagate first. Larger composite layer thickness led to crack convergence more likely to occur and thus resulted in the drop of ductility with increasing the hard composite layer thickness.

Magnetic Recording Using a Spin Torque Oscillator

Magnetic Recording Using a Spin Torque Oscillator

Microstructural control and layer continuity in deformation bonding of metallic laminated composites

An experimental and simulation study is carried out to investigate the microstructure and tensile behavior of the roll-bonded metallic laminated composites incorporating a single hard layer. To control the microstructure, the effect of the hard layer thickness, hard layer material and layer sequence on the layer continuity is investigated in term of the strain partitioning, degree of necking and strain amplification factor. It is found that at low strain regimes, the thickness reduction of different layers is almost identical and the strain is partitioned equally between the layers. At high strain regimes, depending on the thickness and hardness ratio, unstable necks and rupture occur in the hard layer that lead to the strain partitioning between the constituent layers and cause the deformation to be inhomogeneous. Generally, the strain partitioning, degree of necking and strain amplification factor increase with decreasing the thickness ratio and increasing the hardness ratio. Results show that these parameters are affected by changing the layer sequence. Tensile test results reveal that the tensile strength of the fragmented structure is higher than that of the layered or continuous structure. In all cases, the experimental and simulation results are in a good agreement.

Combined Bearing Capacity of Spudcans on a Double Layer Deposit of Strong-Over-Weak Clays

An extreme sea storm process can lead to a jack-up rig under the combined loading condition of vertical load (V), horizontal load (H), and moment (M) to have stability problems. This paper presents the analysis of combined bearing capacities of a circular spudcan on layered clays with a strong layer overlying a comparatively weaker layer. Numerical models combined with displacement- based load tests, swipe tests, and constant ratio displacement probe tests are adopted to calculate the uniaxial bearing capacities, failure envelopes in combined V-H, V-M planes, and failure envelopes in a combined V-H-M load space, respectively. A parametric study on the effects of vertical load level V, the layer strength ratio su,t/su,b, and the hard layer thickness t1 on the bearing capacities is then performed. Results show that the vertical load level is a key factor that influences the values of H and M and the size of the H-M failure envelope. The existence of the underlying weak clay decreases the bearing capacities in all directions, and the vertical capacity Vult is affected more than the horizontal (Hult) and moment (Mult) capacities based on a single uniform deposit. The influence of the underlying weak clay on H-M failure envelope is mainly shown where H and M are coupled in the same direction. In contrast, little difference is observed when H and M are coupled in opposite directions.

Scratch behavior of multilayer polymeric coating systems

A three-dimensional finite element method modeling along with experimental study on multilayer acrylic coating systems on a hard and brittle substrate has been performed to understand their scratch-induced deformation and damage mechanisms. The experimental results show that, while all else kept the same, an increase in soft (i.e., low Young's modulus and low strength) base layer thickness or hard (i.e., high Young's modulus and high strength) top layer thickness improve the scratch resistance of brittle coating systems by delaying the onset of cracking. The onset of plowing is delayed with the increase in hard top layer thickness, whereas increase in soft base layer thickness results in an earlier onset of plowing. The numerical analysis of the stress and strain field explains the mechanics behind the observed scratch behavior in the multilayer coating systems. The study provides insights toward designing scratch-resistant multilayer coating systems.

Temperature-induced coupled–decoupled transition in perpendicular pseudo spin valves

The effect of spacer and ferromagnetic layer thickness on temperature-dependent magnetostatic coupling in perpendicular magnetic anisotropy pseudo spin valves (PMA-PSVs) with the structure of [Ni/Co]5/Cu(dCu)/[Ni/Co]n is explored theoretically. We introduce an effective field that controls the domain replication mechanism and coupling in PSVs. The decoupling temperature (Tdecoupling) can be determined by considering the temperature dependence of the effective field and the coercivity of the hard layer of the PSVs. This study reveals that by increasing the spacer layer thickness, the effective field decreases and Tdecoupling has an increasing trend. Furthermore, by increasing the hard ferromagnetic layer thickness, which is accompanied by an increase in the anisotropy of the layer, Tdecoupling again has an increasing trend. The results are comparable to recently reported experimental ones for PMA-PSVs with various spacer thicknesses, dCu, and the number of bilayer repeats, n. As a practical result, this work gives a deep understanding of the magnetostatically driven domain replication mechanism and temperature-induced coupled–decoupled transitions in PMA-PSVs.

Magnetic properties of <italic>L</italic>1<sub>0</sub>-FePt(001)/<italic>A</italic>1-FePt bilayer exchange springs

Soft A 1-FePt (30 nm) films were magnetron-sputtered on MgO(001) single-crystal substrates at an elevated temperature of 400°C, and subsequently annealed at diffrent temperatures in range of T a=[400°C, 700°C] for 6 h in order to turn them into hard magnets with different degrees of A 1→ L 10 transformation. Then second layers of A 1-FePt with different thicknesses were covered at 100°C to obtain L 10-FePt/ A 1-FePt bilayer magnetic exchange springs with (001) textures. At T a≤600°C, the coverage of hard layer was ~100%, though the grain size increased with T a. The surface roughness reduced from 2.45 to 1.02 nm if the film was annealed at T a=500°C. The surface of hard layer flattened by annealing should benefit to improve the strength of interlayer exchange interaction. At T a=500°C and 600°C, A 1-FePt and L 10-FePt coexisted in the hard layer with an ordering degree of 0.61 and 0.84, respectively. The direction of magnetic easy axis began to switch from in plane to out of plane at T a=500°C, indicating a vertical magnetocrystalline anisotropy was generated. The out-of-plane magnetization curves showed rectangle-like shapes at 500°C≤ T a≤600°C, in spite of the soft phase left in hard layer, and a moderate coercive force of ~5 kOe was obtained at T a=500°C. This indicates the exchange interaction between coexistent two phases in hard layer was strong enough to pin the soft magnetic moments with the hard ones. At T a=700°C, the coercive force exceeded 20 kOe, which is too huge to be affected by exchange springs. By using the film of T a=500°C as hard layer, L 10/ A 1-FePt bilayer film with 20 nm thick soft layer kept rigid behaviors with almost the same coercive force of single hard layer, and respective reversal steps for soft layer and hard layer appeared in the magnetization curve if the thickness of soft layer was 30 nm, with a reduced coercive force of ~4 kOe. As double shoulders should appear in the hysteresis loop if the thickness of soft layer exceeds twice of domain wall thickness of hard layer, i.e., the so-called interlayer exchange length, this indicates that the hard/soft interlayer exchange length was in the range of 20 nm l ex L 10/ A 1-FePt exchange spring. The reason is due to that the coexistence of A 1-FePt and L 10-FePt in hard layers lowered the efficient uniaxial magnetocrystalline anisotropy. This lengthened distance of interlayer exchange could be maintained at T a=600°C. This is benefit to design the properties of magnetic springs for different applications.

Mechanics of an Asymmetric Hard-Soft Lamellar Nanomaterial.

Nanolayered lamellae are common structures in nanoscience and nanotechnology, but most are nearly symmetric in layer thickness. Here, we report on the structure and mechanics of highly asymmetric and thermodynamically stable soft-hard lamellar structures self-assembled from optimally designed PS1-(PI-b-PS2)3 miktoarm star block copolymers. The remarkable mechanical properties of these strong and ductile PS (polystyrene)-based nanomaterials can be tuned over a broad range by varying the hard layer thickness while maintaining the soft layer thickness constant at 13 nm. Upon deformation, thin PS lamellae (<100 nm) exhibited kinks and predamaged/damaged grains, as well as cavitation in the soft layers. In contrast, deformation of thick lamellae (>100 nm) manifests cavitation in both soft and hard nanolayers. In situ tensile-SAXS experiments revealed the evolution of cavities during deformation and confirmed that the damage in such systems reflects both plastic deformation by shear and residual cavities. The aspects of the mechanics should point to universal deformation behavior in broader classes of asymmetric hard-soft lamellar materials, whose properties are just being revealed for versatile applications.

Tribological behavior of VC/Ni multilayer coatings prepared by non-reactive magnetron sputtering

Ceramic–metal multilayer coatings generally exhibit considerably enhanced wear resistance, due to an attractive combination of metal and ceramic phases. In this work, VC/Ni multilayer coatings were prepared with non-reactive magnetron sputtering. Tribological behavior of the coatings was investigated by ball-on-plate dry sliding tests, followed by in-depth microscopic examination of the worn surfaces. The VC/Ni multilayer coatings exhibited the wear rates of 10−15m3/N m that was lowered by one order of magnitude in comparison with M2 tool steel. The results revealed that the wear process of coatings was influenced by the modulation period, and might further indicate that a sufficient thickness of hard layers was required to enhance the deformation resistance for optimizing the wear resistance of ceramic–metal multilayer coatings.

Hysteresis of misaligned hard–soft grains

The demagnetization process in hard/soft multilayer systems has been investigated systematically within a self-contained micromagnetic model when a deviation angle β between the easy axis and the applied field exists. Hysteresis loops, spin distributions and energy products have been calculated with a finite hard layer thickness th. Both remanence and coercivity of the multilayer system decrease as β increases, leading to a significant decrease of the maximum energy product. A 30° deviation of the easy axis could result in a drop of the maximum energy product by more than 60%, which offers a possible explanation on the large discrepancy between the experimental and theoretical energy products. The effect of the finite hard layer thickness on the demagnetization process is important, which can only be ignored when th is large enough.

Modeling interface exchange coupling: Effect on switching of granular FePt films

To raise the areal density of magnetic recording to ∼1 Tbit/in2, there has been much recent work on the use of FePt granular films, because their high perpendicular anisotropy allows small grains to be stable. However, their coercivity may be higher than available write-head fields. One approach to reduce the coercivity is to heat the grain (heat assisted magnetic recording). Another strategy is to add a soft capping layer to help nucleate switching via exchange coupling with the hard FePt grains. We have simulated a model of such a capped medium and have studied the effect of the strength of the interface exchange and thickness of hard layer and soft layer on the overall coercivity. Although the magnetization variation within such boundary layers may be complex, the net effect of the boundary can often be modeled as an infinitely thin interface characterized by an interface exchange energy density—we show how to do this consistently in a micromagnetic simulation. Although the switching behavior in the presence of exchange, magnetostatic, and external fields is quite complex, we show that by adding these fields one at a time, the main features of the M-H loop can be understood. In particular, we find that even without hard-soft interface exchange, magnetostatic coupling eliminates the zero-field kink in the loop, so that the absence of the kink does not (as has sometimes been assumed) imply exchange coupling. The computations have been done with a public-domain micromagnetics simulator that has been adapted to easily simulate arrays of grains.

Inclusion of surface anisotropy in the micromagnetic analysis of exchange-coupled hard/soft bilayers

The effects of surface anisotropy and interface anisotropy in soft and hard layers have been considered in the frame of a previously developed micromagnetic continuum model for the study of demagnetization processes in exchange-coupled bi- and multi-layers of soft/hard-type with planar and perpendicular anisotropy, in order to extend and generalize it. In particular, fields applied along the easy direction and strong interface ferromagnetic coupling have been considered. The theoretical results have been applied to a bilayer with perpendicular anisotropy in the hard layer and positive perpendicular surface anisotropy in the soft layer, in order to compare them with those obtained by considering the equivalent volume anisotropy in the soft layer. Moreover, the separate effects of positive perpendicular surface and interface anisotropies in the bilayer have been compared. We have deduced the nucleation field equation and obtained plots of the nucleation field as a function of the soft layer thickness and of the surface and interface anisotropies. Demagnetization curves have been also calculated. The nucleation process can be reversible (exchange-spring (ES) regime) or irreversible (rigid magnet (RM) regime) depending on magnetic and geometrical parameters. The critical equation, which allows determining the boundary between RM and ES regions, has been deduced. Corresponding phase diagrams in the plane of soft and hard layer thickness have been obtained as a function of surface and interface anisotropies.