Initial Stacking Research Articles

Influence of thermal and acidic treatments on the morphology of a natural kaolinitic clay mineral

In this work, a natural kaolinitic clay mineral from Kribi in Cameroon is modified by thermal and acidic treatments. The influence of these treatments on the physicochemical properties of the clays is studied using X-ray diffraction, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption measurements, scanning electron microscopy, inductively coupled plasma–atomic emission spectroscopy and thermal analysis. Three calcination temperatures are explored: 600, 700 and 800 °C. The XRD pattern of the untreated clay showed that the natural clay mineral was mostly composed of kaolinite. Calcination at high temperatures allowed the amorphization of the natural kaolinitic clay mineral to obtain metakaolinite. This heat treatment of the natural clay mineral produced disintegration by rupture of the strong hydrogen bonds between the layers of the clay mineral. Heat treatment did not increase the specific surface area of the clay, which stayed around 20-30 m2/g. The acid treatment produced a high material texture modification giving microporous materials with a large surface area up to 315 m2/g with the sample previously calcined at 800 °C. The microporosity and mesoporosity increase is greater when the clay is calcined at high temperature. The morphology of the samples observed by SEM are modified by the acidic treatment. The initial two-dimensional stacking of particles evolves towards a narrower three-dimensional porous structure. These treatments open the way to produce highly porous clay materials that could be used as adsorbent materials for pollutant removal from water.

The Influence of Carbides on Atomic-Scale Mechanical Properties of Carbon Steel: A Molecular Dynamics Study

Pearlite is an important structure in carbon steel; however, the influence mechanism of carbides in pearlite on its mechanical properties and microstructure evolution has not yet been fully elucidated. In this work, a ferrite-carbide composite model with various carbide types was constructed to investigate the influence of carbide types via a uniaxial compression deformation using classical molecular dynamics simulations. It was found that the carbide type had little effect on the compressive elastic modulus, but a more obvious effect on the yield strain, yield stress, and flow stress. The maximum compressive elastic modulus was in the Fe2C model, with 300.32 GPa, while the minimum was found in the Fe4C model at 285.16 GPa; the error was 5.32%. There were significant differences in the yield stress, yield strain, and flow stress of the ferrite-carbide model according to the stress-strain curve. Secondly, the type of carbide used affected its elastic constant, especially the bulk modulus and Cauchy pressure. The maximum bulk modulus of the Fe4C model was 199.01 GPa, the minimum value of the Fe3C model was 146.03 GPa, and the difference was 52.98 GPa. The Cauchy pressure calculation results were consistent with the yield strain trend. Additionally, the effective elastic moduli of the composite system were used to verify the accuracy of the calculation results of this work. Thirdly, ferrite-carbide interfaces could act as a resource for dislocation emission. The initial stacking fault forms at ferrite-carbide interfaces and expands into ferrite. The dislocation type and segment in the ferrite-carbide model were significantly different due to the type of carbide used.

Dating fluid infiltration and deformation in the subducted ultramafic oceanic lithosphere by perovskite geochronology

Carbonated ultramafic rocks (i.e., ophicarbonates) form by peridotite serpentinization and carbonation at the seafloor. Their metamorphic evolution is linked to that of serpentinites, hence dating deformation and metamorphism in ophicarbonates will add constraints to the P-T-t history of the subducted ultramafic lithosphere. A potential, yet underexplored, suitable mineral for geochronology in ophicarbonates is perovskite (CaTiO3). We present trace element and geochronological data (LA-ICPMS and ID-TIMS) from perovskite in ophicarbonate rocks and calcite veins from two metamorphic terranes, Lanzo Massif and Val Malenco (Alps). Metamorphic perovskite in ophicarbonates is characterized by enrichment in heavy REE, and strong negative anomalies in Zr and Hf, as well as Sr and Pb, which are attributed to coexistence of a Zr-rich phase and mobilization of these elements by fluids, respectively. Other trace elements broadly reflect the composition of the protolith and allow the distinction of perovskite from mafic and ultramafic rocks.In the Lanzo Massif, the 49.6 ± 1.0 Ma age of perovskite in shear bands constrains H2-mediated carbonate reduction and abiotic methane and graphite formation at near peak metamorphic conditions during deformation. Perovskite from Val Malenco is found in calcite veins cutting across serpentinite shear foliation and its age of 48.9 ± 0.5 Ma coincides with a major thrusting and extension event that is distinct in age from the initial nappe stacking. The Val Malenco perovskite age can be reproduced by LA-ICPMS and ID-TIMS and is proposed as a suitable secondary reference material for metamorphic, low U perovskite. These results show that metamorphic perovskite geochronology yields geologically meaningful UPb ages and is a viable tool to date deformation and fluid flow in the subducted oceanic lithosphere.

Ferroelectric response to interlayer shifting and rotations in trilayer hexagonal Boron Nitride

From monolayers composed of different atoms, we can build structures with spontaneous vertical polarization by conveniently stacking multiple layers. We have studied, using first-principles methods and based on modern polarization theory, a system composed of three layers of hexagonal Boron-Nitride(h-BN) in all possible stackings. We obtain for each of the configurations how charge transfers between the layers and how it impacts on the polarization of the system. In addition, we studied a system of three layers, one of them rotated, and we found that not only did the magnitude of the polarization increase comparing with the bilayer but also, depending on the initial stacking and the rotated layer, we can create a variety of mosaic-like polarization arrangements, which are composed of regions with either triangular or hexagonal symmetry.

Nucleation of superlattice intrinsic stacking faults via cross-slip in nickel-based superalloys

Superlattice intrinsic stacking faults (SISF) are the main culprit for the low temperature creep deformation of modern nickel-based superalloys used in jet engines. While these faults were identified over fifty years ago, their nucleation mechanism remains unclear. This work provides the first ever experimental evidence, via transmission electron microscopy, of a SISF nucleating from a cross-slip event in a polycrystalline alloy. Such an instance was identified in a grain with a near-〈001〉 tensile loading orientation. In the nucleation mechanism proposed, cross-slip allows the two dissimilar a2〈110〉 dislocations required to form a SISF to meet on adjacent planes at a precipitate interface. The concept of a nascent fault is introduced: the initial stacking fault that forms on a crystallographic plane and the dislocations of which continue to form coplanar faults as they glide away. This nucleation mechanism and the subsequent dislocation evolution are detailed taking into consideration the shear stresses on the individual Shockley partials and the full dislocations involved, as well as the stress orientation dependence of the energy barrier for cross-slip. These findings will guide future characterisation efforts in the field and inform the modelling of more realistic predictive models of creep behaviour.

A three-dimensional sampling optimization method for buckling optimization of variable prestressed composite plates

A novel three-dimensional sampling optimization method (3DSO) is proposed for the stacking sequence design of variable prestressed composite plates. The lamination parameters (LPs) are used to determine the distances between stacking sequences and control their distribution in the design space of LPs allowing several good initial stacking sequences to be determined by uniform sampling. Then, local sampling optimization is conducted in the vicinity of the previous good initial points to refine the optimum. During the sampling procedure, dynamic distance constraints are applied to ensure that the stacking sequences are closest to the LPs. Lastly, the layerwise optimization approach (LOA) is employed as a local optimization solver to locate the final optimum. Ritz method is developed in terms of orthogonal polynomials to perform the prebuckling and buckling analyses for variable prestressed composite plates subjected to a variety of boundary conditions and a multiplicity of loading conditions. The performance of 3DSO is compared with that of two-dimensional sampling optimization (2DSO) method and genetic algorithm (GA). The optimization results indicate that the 3DSO method is efficient and robust for addressing the problem of stacking sequence optimization.

Preformado rápido para aplicaciones de automoción mediante instalaciones flexibles y automatizadas

The use of polymer matrix composites and, in particular, based on carbon fiber, is awakening more and more interest in the automotive sector, due to the great weight reduction potential they offer for the lightening of vehicle structures. The case of the BMW (with the i3, i8 and 7 Series) and some other manufacturers, represent the first cases of use of "large scale production" with these materials, with a growth perspective provided by the electric vehicle. To achieve a mass implementation of these new materials it is a key factor the development of processes and equipment that allow manufacturing with very short cycle times. Preforming is the key stage where the fiber stacking takes the form of the injection mold in which it will be introduced later. This stage of the process is the one that has a greater impact on the cost of the overall process, so it is especially necessary to develop optimization and automation techniques for rapid preforming. In this context, Fagor Arrasate, with the aim of offering its customers a competitive installation, has created and led a project in which it has collaborated with Tecnalia to develop pre-forming installations for the automotive sector.. A fast preforming process based on preheating and cold stamping has been developed combined with an automatic material feeding based on a transfer system and also completed with the automation of the initial stacking and the trimming of the final preform. The capabilities of this installation have been validated for an automotive demonstrator.

Investigation of influencing factors of wear in a sandblasting machine by CFD-DEM coupling

In order to study the effect of particle characteristics and operating conditions (particle diameter, density, shear modulus, initial stacking height and inlet pressure) on the wear of the sandblasting machine, the gas-solid two-phase flow inside a sandblasting machine under different operating conditions was simulated by coupling the CFD and DEM methods in this work. Combining with the Archard wear model, the erosion was calculated and the erosion distributions were obtained in different sandblasting machine parts, including the top cover, inlet pipe, cylindrical part, conical part and lower pipe. The simulation results demonstrate that severe erosion in the sandblasting machine occurs at the lower pipe near the outlet, the conical part and the joints between different parts. The erosion volume order for different parts from high to low is: the lower pipe, conical part, cylindrical part, inlet pipe and top cover. The erosion volume of the sandblasting machine increases with the increase of particle diameter, density, shear modulus, stacking height and inlet pressure. Comparatively, the initial stacking height and inlet pressure have more influence on the erosion, while the particle density and shear modulus have less influence.

Optimizing the Aerothermomechanical Behavior of Sandwich Panels Using Genetic Algorithm

A multi-objective optimization of a sandwich structure is presented to maximize the fundamental frequency and the critical buckling temperature while minimizing the cost of the laminate, alongside with keeping the weight lower than a preset value. The sandwich structure was chosen to be made of a high-stiffness, relatively expensive material (carbon/epoxy), and a low-stiffness, relatively low- cost material for the core (glass/epoxy). The governing equations are derived using the principle of virtual work, based on the first-order shear deformation plate theory. MATLAB Genetic Algorithm toolbox is used to find the optimum stacking sequence and ply thicknesses to achieve the optimal solution. The ground structure was used to set the initial ply stacking sequence and then the algorithm assumes the existence or absence of each ply and their thicknesses. The optimum buckling temperature and natural frequency values are introduced for different aerodynamic pressure values and under simply supported boundary condition.

Both Symmetric and Asymmetric Electro-Optic Dynamic Behavior with SSD (Smectic Single Domain) Liquid Crystals

SSD-liquid crystal panels’ retardation switching dynamic behaviors have been investigated from their in-plane and out-of-plane retardation switching behaviors. In-plane-only and a mixture between in-plane and out-of-plane retardation switching behaviors are highly related to the initial smectic liquid crystal molecular stacking configurations. With uniformly stacked configuration, a completely symmetric retardation switching, as well as light throughput behavior, was obtained. With a slight twisted stacking configuration, the retardation switching behavior is dependent on the applied electric field strength, which may change the initial molecular stacking configuration, resulting in either symmetric or asymmetric retardation switching. When the molecular stacking has twisted heavily, the obtained retardation switching showed asymmetric behavior regardless of the applied electric field strength.

Initial Deformation Behaviors in Lean Duplex Stainless Steel

The deformation behaviors of the austenite phase in lean duplex stainless steels were investigated through uniaxial tension tests with different amounts of deformation. Microstructural analysis showed that in the initial deformation stage the deformation in austenite grains had a predominant effect on the strain hardening behavior of the LDX-2101 steel. The initial deformation in the austenite grains was found to be mainly accommodated by the formation of stacking faults. As the deformation increased further, mechanical twins were generated by the initial stacking faults and sequentially interacted with dislocations to accommodate the strain. The analysis of dislocation behavior revealed that the deformation twinning process followed the three-layer twin formation mechanism.

Stability coefficient of interlocking compressed earth block masonry under axial compression

To investigate the effects of the height–thickness ratio (β) on the mechanical properties and stability coefficients ([Formula: see text]) of interlocking compressed earth block (ICEB) masonry members under axial compression, four groups of specimens with different β of 3.75, 6.75, 11.25, and 14.25 were tested, thereby assessing their stress process, failure mode, compressive strength, and in- and out-of-plane deformations. All the specimens underwent brittle failure under axial compression: the compressive strength was found to decrease in a range from 5.6% to 43% with increasing β, whereas the initial stacking defects and the in- and out-of-plane deformations increased. The specimens became less stable, and we noticed that the overall damage was caused by strength failure and not instability failures. Because the stability coefficient of ICEB-based masonry components cannot be calculated as those of more conventional brickwork, we combined our results with well-established masonry design guidelines and derived an interlocking improvement coefficient. Finally, we proposed a formula for calculating the axial compression stability coefficient of ICEB masonry that can provide a useful reference for subsequent research on ICEB walls.

Investigation of curing deformation behavior of curved fiber metal laminates

To keep the size and shape accuracy of fiber metal laminates (FMLs) with an initial curvature during manufacturing, curing deformation behavior is investigated by using analytical, numerical and experimental methods. Based on Eckstein’s theory, an analytical model considering slippage effect between metal layer and fiber layer is developed to study the warping deformation modes of curved FMLs after curing process. The warping displacements of the curved FMLs predicted by the analytical method are in good agreement with the finite element results and experimental data. The final equilibrium configurations of the curved FMLs can be captured by using the analytical method, which can guide the size and shape control for FMLs. The effect of the side length, initial curvature radius and stacking sequence on the curing deformation characteristics of curved FMLs is studied. The curing deformation mechanisms of the curved FMLs with [Al/0/90/Al] and [Al/90/0/Al] stacking sequences are also illustrated from the perspectives of force and total strain energy.

Using path optimum algorithm to solve slot selection problems for outbound containers of different attributes in container terminals

The outbound container slot selection problem (OCSSP) is a hot topic in the field of port research and of great significance to improving the operational efficiency of container yards. With the initial stacking state and extractive sequence of containers being known, the goal is to accomplish the task of extracting all containers in the container block with a minimum number of container relocations. OCSSP is an NP-hard problem. To obtain more practical research results, this paper proposes an improvement to the existing model and presents an improved version of the path optimum algorithm that considers container attributes. With the objective of improving the overall operational efficiency of container terminal yards, this study analyzed some practical issues related to container extraction by taking into consideration the influences of extraction priority levels, movements of obstruct containers, the Manhattan distances of gantry crane, and other factors on the model. Finally, the paper distills some scheduling strategies applicable to OCSSP in the hope of providing a theoretical basis and practical guidance to container port operators for the better allocation and optimization of coastal container ports resources.

Stacking- and chirality-dependent collapse of single-walled carbon nanotubes: A large-scale density-functional study

Using density functional theory with van der Waals (vdW) corrections, we study the collapse of free-standing single-walled carbon nanotubes (also called ``dogbone'' nanotubes). Their thermodynamic stability is strongly influenced by the initial stacking sequence, with lateral shear allowing registry change with turbostratic stacking predominant. The electronic structure of collapsed zigzag and armchair carbon nanotubes is investigated, demonstrating sensitivity to the lattice registry. The opening of small (meV) band gaps is shown for both armchair and zigzag collapsed nanotubes, arising from quantum confinement and charge transfer between the bilayer graphenelike central region and nanotubelike edges. Different scaling rules for the band gaps of collapsed carbon nanotubes are obtained as a function of their widths taking stacking and chirality into account. We reconcile a complete understanding of electronic properties in these deformed tubes with literature theoretical and experimental results, suggesting collapsed nanotubes can be promising candidates as conductive nanoribbons in electronic and spintronic device applications.

Wide Range Morphological Transition of Silver Nanoprisms by Selective Interaction with As(III): Tuning–Detuning of Surface Plasmon Offers To Decode the Mechanism

Polyvinylpyrrolidone (PVP)-based silver nanoprisms (AgNPrs) show an initial stacking geometry because of their low zeta potential and electrostatic interaction between face-to-face energetically stable {111} surface-bound pyrrolidone groups through the Na+-ion-induced cation−π interaction. Congested interplanar space between AgNPrs allows As(III) to react differentially with silver atoms from facial {111} and peripheral {110} facets to result in smaller stackings and finally nanoseeds. Above this critical concentration of As(III), PVP leached out from nanoparticles to form nanoseed-engulfed emulsions and induced controlled aggregation. This entire morphological transition has been decoded by recording their surface plasmon and surface-enhanced Raman scattering tuning and confirmed by the transmission electron microscopy study. Strong affinity and selectivity of As(III) toward the Ag atom (verified and estimated by the HF/3-21g* level of density functional theory calculation) coupled with low-cost colorime...

Supersonic nonlinear flutter of cross-ply laminated shallow shells

The aim of this paper is to investigate the geometrical nonlinear flutter of cross-ply laminated shallow shell with rectangular boundary and strong nonlinearity. The classical laminate plate and piston aerodynamic theories are employed to obtain the governing equation of the systems. The Galerkin method and approximate-analytical homotopy perturbation method are used to predict the flutter boundary of the laminated shallow shell. In this study, the effects of shell geometric dimensions, stacking sequence, and initial deflection on critical flutter pressure are investigated. According to the results, the initial deflection and stacking sequence of the laminated shells can change the nonlinear behavior of shells. The method presented in this study is more accurate than usual perturbation methods in predicting the nondimensional flutter pressure of laminated shallow shell subjected to large initial deflections.

Stacking sequence optimization and blending design of laminated composite structures

The stacking sequence optimization problem for multi-region composite structures is studied in this work by considering both blending and design constraints. Starting from an initial stacking sequence design, unnecessary plies can be removed from this initial design and layer thicknesses of necessary plies are optimally determined. The existence of each ply is represented with discrete 0/1 variables and ply thicknesses are treated as continuous variables. A first-level approximate problem is constructed with branched multipoint approximate functions to replace the primal problem. To solve this approximate problem, genetic algorithm is firstly used to optimize discrete variables, and meanwhile, a blending design scheme is proposed to generate a blended structure. Starting from the thinnest region, this scheme shares all layers of current thinnest region with its adjacent regions. For non-shared layers in the adjacent regions, local mutation is implemented to add or delete plies to make them efficient designs. The whole process is repeated until the blending rule is satisfied. After that, a second-level approximate problem is built to optimize the continuous variables of ply thicknesses for retained layers. Those procedures are repeated until the optimal solution is obtained. Numerical applications, including a two-patch panel and a corrugated central cylinder in a satellite, are conducted to demonstrate the efficacy of the optimization strategy.

Multi-objective optimal design of hybrid composite laminates for minimum cost and maximum fundamental frequency and frequency gaps

The design of hybrid composite laminates made of high-stiffness skin and low-stiffness core layers is presented. By considering vibration characteristics, the objective is the simultaneous maximization of fundamental frequency (or the gap between two consecutive frequencies) and minimization of cost by seeking the optimal stacking sequences of both skin and core layers. By introducing the concept of ground structure in laminate design, an initial stacking sequence consisting of high-stiffness skin and low-stiffness core layers is firstly given, and the design problem is then formulated with mixed discrete and continuous variables by defining a weighted min-max objective function and determining the minimum, where discrete variables represent the existence of each ply in the initial stacking sequence, and continuous variables are used for ply thicknesses. The problem is made explicit with branched multipoint approximate functions, and genetic algorithm (GA) is adopted to optimize discrete variables so that necessary/unnecessary layers from the initial stacking sequence are retained/suppressed. For fitness calculation in GA, a second-level approximation is built with the convex linearization to optimize continuous ply thicknesses of the retained layers. Using that approach, optimal stacking sequences are found for hybrid graphite/epoxy-glass/epoxy laminated plates with different aspect ratios, by considering free vibration.

Concurrent optimization of stacking sequence and stiffener layout of a composite stiffened panel

ABSTRACTThis article is to optimally design laminated composite stiffened panels by optimizing both stacking sequences of the panel skin and stiffeners as well as the layout of stiffeners. Starting from initial designs of stiffener layout and stacking sequences for each stiffener and the panel skin, the problem is formulated with discrete and continuous variables, where discrete 0/1 variables represent the absence/presence of each layer in initial stacking sequences, and continuous variables represent layer thicknesses. A first-level approximate problem is established to make the problem explicit. Genetic algorithm is used to determine the existence of each layer in the laminates. When the number of retained layers in stiffener becomes zero, that stiffener can be seen as unnecessary and removed. For individual fitness calculation, a second-level approximate problem is constructed to optimize continuous ply thicknesses of retained layers. Correspondingly, laminated stacking sequences and stiffener layout are concurrently optimized.