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Fractional order models of viscoelastic polymeric solids undergoing large deformations
Get PDFWe present a fractional order model for nonlinear visco-hyperelastic solids taking into account large deformations. A three-field form of the Hu-Washizu principle is introduced to create a stable finite element method in the context of nearly incompressible dynamics. The β-method (a generalized midpoint rule) for time discretization is implemented into a variational finite element framework for efficient computing of numerical approximations to the initial boundary-value problem for hyperbolic equation of motion. Finally, a 2-D cantilever beam problem with a step end load is considered in order to demonstrate the algorithm
Properties of cement screeds using recycled fine aggregates with respect to cement percentage
Get PDFThis article deals with the effect of 100% replacement of natural aggregate by recycled aggregate and at the same time the effect of cement percentage on the observed properties of cement screeds. For these purposes, concrete and brick recycled aggregate is used in combination with CEM I 42.5R Portland cement, constituting 10 %, 15 %, 20 % and 25 % of the mixtures weight. To determine the properties of the cement screeds, test intervals of 3, 7, 14, 21 and 28 days are set, during which changes in bulk density are monitored. Simultaneously, destructive tests are carried out on test beams of 4 × 4 × 16 cm in size. The results found that the use of recycled fine aggregates allows the production of lighter cement screeds, for example, for reconstruction. Potentially usable mixes appear to be those containing 15 %, 20 % and 25 % cement compared to recycled aggregate. For the contaminated recyclate fine fraction, the flexural strength has been shown to improve. However, this improvement is not reflected in an increase in compressive strength
Validation of geotechnical laboratory tests data obtained from various sources
Get PDFData validation is a critical step in every data analysis. It is a well-known fact that the results of any data analysis are directly dependent on the input values. This paper works with a worldwide database of laboratory tests collected during four year operation of web calibration application ExCalibre and elaborates on the data correctness. ExCalibre application enables automatic calibration of three critical state models based on data from standard laboratory tests. The paper presents the rules and overall methodology for checking the validity of laboratory tests data and summarises the obtained results
Transforming point cloud data into 3D BIM models: a case study on slabs
Get PDFWe explore the automatized transition of point cloud data into a Building Information Model (BIM), an essential task for reconstructions, demolition plans, or auditing. In this study, we use point cloud data generated by 3D laser scanning. The research elaborates on the process of segregating and segmenting floor slabs from point clouds and the developed algorithms categorize point cloud subsets based on different height parameters (z-coordinates). Once slabs are identified, a function is applied to create envelopes for each slab level, accommodating any convex or concave shape. The resulting geometry, along with relevant auxiliary data, is exported in the Industry Foundation Classes (IFC) format, a standard for BIM data exchange. The exported entities can then be further processed using prevalent software such as Revit or ArchiCAD
Instability of dust-lower-hybrid mode in irradiated streaming dusty plasma with dust charge fluctuation
Get PDFA theoretical investigation of the photoelectric effect through dust charge fluctuation on the low frequency dust-lower-hybrid (DLH) mode has been done using fluid model of plasma. In this study collisional effects between charged and neutral particles and lighter particles streaming along the both external magnetic and electric fields are considered. It is assumed that dust grains are negatively charged. It has been observed that the DLH mode becomes unstable significantly due to photoelectric effect compared to the streaming and collisional effects
Effect of geometry on homogenised properties of selected auxetic metamaterials
Get PDFOur study investigates the influence of geometrical parameters of two types of auxetic metamaterials on their effective properties. In particular, we focus on three-dimensional lattice structures, which we represent with discrete beam models of their respective Periodic Unit Cells (PUCs). Limiting the scope of the study to linear elasticity, we compute the effective response of PUCs by plugging the kinematic ansatz of the first-order numerical homogenisation into the strain energy expression arising from the Direct Stiffness Method and minimising the energy with respect to the periodic fluctuation field. The obtained effective stiffness matrices are post-processed to arrive at elastic parameters as Poisson’s ratios coefficients, that are reported in different directions with respect to the key geometrical parameters
Numerical modeling of concrete beams subjected to partial wetting and drying cycles
Get PDFConcrete structures are commonly subjected to cycles of wetting and drying, which can have a significant impact on their behavior. However, experimental data on the effects of wetting and drying on concrete beams are scarce. This study presents the results of a 4-year experimental program on 2.5 m span concrete beams with heights of 100 mm, 150 mm, and 200 mm subjected to one-sided wetting and drying cycles. Vertical deflection of the beams was monitored throughout the experiment, and moisture mass balance was measured on companion specimens.The behavior of the specimens was experimentally assessed, and subsequently numerical models using coupled hygromechanical finite element simulations were developed. The purpose of the simulations was to verify the prediction capabilities of the established constitutive models for moisture transport and creep and shrinkage of concrete and, if needed, to propose necessary corrections to the constitutive models
Multi-parameter optimization of layered WS2-polymer nanocomposite under mechanical loading
Get PDFThe aim of the study is to determine the optimal geometry and magnitude of the applied load to ensure safety and prevent delamination in a three-layered nanocomposite structure under axial mechanical loading. The structure consists of a layer of the nanomaterial tungsten disulfide (WS2) and a substrate layer of poly(methyl methacrylate) (PMMA), which are adhesively bonded using SU-8 glue. To achieve this aim, a multi-parameter optimization problem (MOP) is formulated. It includes a two-dimensional stress function model that describes stress transfer in the considered three-layer structure. Two types of analytical solutions for the interface shear stress (ISS) are derived, featuring real and complex roots. The decision variables in MOP include the external load, layer thicknesses, and structure length. The optimization criterion is defined as the minimization of the difference between the model ISS and ultimate shear stress (USS) in the adhesive layer to assure no delamination occurs in the nanocomposite structure. A genetic algorithm and alternative optimization approach developed within the framework of “Mathematica” are implemented for the optimization of both model solutions. As a result, optimal values for the given external load, layer thicknesses, and structure length are obtained for considered nanostructure. For the case of an ISS model solution with real roots, the optimization procedures ensure optimal geometries that physically correspond to thinner structural layers, but they are limited at lower possible loads. In contrast, for the case of a model solution for the ISS with complex roots, solutions for the optimal geometries of the nanostructures were obtained with thicker layers requiring higher loads, than thinner ones, but delamination does not occur
Experimental dynamic analysis of the footbridge across Jizera River in Mladá Boleslav
Get PDFThe text of this submitted paper is devoted to the experimental dynamic analysis of the newly designed footbridge across the Jizera River in Mladá Boleslav. Theoretical modal analysis has shown potential risk that some of the natural frequencies of the bridge deck will belong to the range which is typical for pacing frequencies induced by pedestrians. The resonance behaviour of this structure should be reduced by Tuned Mass Dampers (TMD), which would be tuned for separate natural frequencies of this structure. Therefore, the experimental dynamic analysis was performed on the footbridge in order to assess the effectiveness of installed TMDs. The experiment was divided into two stages, the first one was realized at the footbridge when TMDs were not yet installed, and the second one was carried out on the footbridge with installed and activated TMDs. Moreover, the authors have performed an experimental modal analysis in order to verify the aptness of the computational model and its results
Reconstruction of concrete morphology using deep learning
Get PDFIn this contribution, the concrete morphology is reconstructed with a simple algorithm selecting a pixel value based on the small set of surrounding pixels. A deep neural network (DNN) is used as a classifier, and the authors focus on studying different DNN architectures. The performance of the proposed algorithm is evaluated on several statistical descriptors and the grain size distributioncurve