Resumo em Inglês:

Abstract The main goal of this study is to further expand the ES-MITC3 for analyzing the buckling characteristics of functionally graded porous (FGP) variable thickness (VT) plates with sinusoidal porous distribution. The ES-MITC3 was developed to improve the accuracy of classical triangular elements (Q3) and overcome the locking phenomenon while still ensuring flexibility in discretizing the structural domain of the Q3. The first-order shear deformation theory (FSDT) in combination with ES-MITC3 is used due to its simplicity and effectiveness. The Pasternak foundation (PF) is a two-parameter model with springer stiffness (k1) and shear stiffness (k2) that describes the foundation reaction as a function of the deflection and its Laplacian. The accuracy and performance of the proposed formulation are verified through comparative examples. Moreover, a comprehensive analysis has been undertaken to scrutinize the effects of geometric parameters and material properties on the buckling of FGP VT plates.

Resumo em Inglês:

Abstract This paper presents an investigation on the structural condition of a cable-stayed footbridge based on data collected in two dynamic tests, performed at different times. The natural frequencies and mode shapes were obtained by applying output only modal identification methods. At least four experimental mode shapes of the footbridge and stay cables were identified in Operational Modal Analysis. A 3D finite element model of the footbridge was calibrated by adjusting its dynamic properties to the experimentally identified in the first test. The procedure showed, besides an approximation of the dynamic behavior, an approximation of its static behavior, which was confronted to the structural design. The analysis found a discrepancy between the required reinforcement based on the updated model stresses and the existing steel reinforcement. The second test, performed one year later, provided different natural frequency values to those found in the first test and the spectrum presented inconsistency in one of its peaks. It was concluded that the structure presents conditioning problems, thus warning to future structural problems.

Resumo em Inglês:

Abstract This article aims to identify the presence of cracks in slender rotating beams (Euler Bernoulli) from the dynamic behaviour of cracked beams operating at low rotational speeds. For this purpose, the behavioural model of the cracked rotating beam developed by the authors in previous works is shown. The results of the mathematical model developed (natural frequencies) feed a novel meta-heuristic optimisation algorithm based on the survival tactics of rabbits against their predators: Artificial Rabbit Optimization (ARO). The application of this algorithm to the first two natural frequencies of vibration obtained with the analytical model and contrasted in previous works gives rise to the identification of the characteristic parameters of the crack contained in the beams. The estimation of the parameters: position along the beam and crack depth, show a high similarity with the initial data, which allows validating the application of the optimisation algorithm to the identification of cracks in this type of component as a first approach to a health monitoring method for more complex rotating cantilever beam structures.

Resumo em Inglês:

Abstract As an ideal impact energy absorber, the external inversion process of thin-walled metal tubes over circular dies has been studied theoretically since 1960s. However, in the most existing theoretical models, the curvature in the deformation area is a constant and only the steady inversion force is studied. Limited research has been conducted on the whole inversion process. In this study, from experimental and numerical results, the curvature is found to be varying and the whole inversion process can be divided into two stages by three states. Then a modified geometric model is proposed and the force displacement curves is derived. Next, it has been observed that current theoretical results exhibit greater conformity with experimental and numerical results. Finally, the effects of the tube wall thickness, tube average radius and die radius on crashworthiness indicators are studied theoretically by the verified theoretical model. These outcomes offer valuable reference for further research on tube inversion forming and energy absorption characteristics of external inversion mode.

Resumo em Inglês:

Abstract Based on the theory of solid porous media with pores, the dynamic response of layered saturated frozen soil under uniform moving load is studied. Firstly, the governing equation of saturated frozen soil is established. Then, the Fourier integral transform is used to decouple the governing equation of saturated frozen soil, and the general solution of the potential function is obtained, and the corresponding force and displacement of each layer of saturated frozen soil are derived. Finally, using the transfer matrix method, combined with the continuous condition, the semi-analytical solution of the layered saturated frozen soil medium in the frequency domain under the surface permeable condition is derived. After verifying the accuracy of the solution by comparing the model degradation with the existing literature, the effects of soil shear modulus, load moving speed, temperature, contact parameter and frequency on the dynamic response are analyzed in detail. The results show that the order of soft and hard soil layers is of great significance to accurately evaluate the dynamic response of saturated frozen soil.

Resumo em Inglês:

Abstract In this work, a corotational finite element formulation is suggested for spatial beams with geometrically nonlinear behavior subjected to static loads. We returned to the three successive rotation angle procedure, mainly the Tait-Bryan angles. By carefully defining the trigonometric rules for all rotation angles, the singularity problem, that had limited the use of these angles, is avoided. Three different types of coordinate systems are used: a fixed global coordinate system that stays fixed throughout the analysis, a fixed local coordinate system that is fixed and precisely attached to each element, and a corotational local frame for each element that moves and rotates together with the element throughout the analysis. The rigid body motion can easily be separated from the overall deformation since the deformation is always tiny relative to the corotational frame. An incremental-iterative method is used for the solution based upon the Newton-Raphson method. Different examples are solved to demonstrate the practicality, correctness, and accuracy of the proposed method. The solutions converge at a relatively quick rate.

Resumo em Inglês:

Abstract A general geometric model of the elliptical cross-section double-ogive-nose projectile (ECDP) was established, and the expression of penetration resistance was obtained. Based on the special shape and penetration process characteristics of the ECDP, a three-stage penetration model was constructed, and closed-form penetration equations were derived. Three ECDPs with the major–minor axis ratio of 1.5 were launched by a 130 mm gas-gun to impact the plain concrete targets with the oblique angle of 10° at a nominal striking velocity of 650 m/s, the experimental data such as the penetration depth of the ECDPs and the failure characteristic parameter of the targets was obtained. The initial posture of the ECDP had little effect on the penetration depth and trajectory deflection under the condition of the target with 10° oblique angle, but it had obvious influence on the structural response. The theoretical model was verified by experimental data, the calculated result of the penetration depth was in good agreement with the experimental data, the deviation was within the range of -13.5% ~ -8.5%.

Resumo em Inglês:

Abstract This article presents a parametric numerical study of the pullout behavior of headed bars embedded in concrete elements. The finite element model was developed using Abaqus software and validated to simulate the behavior of four pullout tests. The numerical results were validated against the experimental results and showed excellent agreement with the load-slip response and failure modes. Furthermore, a parametric numerical study with 23 simulations was planned to explore the influence of several variables on concrete cone failure, including concrete strength, flexural reinforcement ratio, geometry and head size, shaft diameter, and edge and group effects. The ultimate load results, failure modes, and influence on ultimate load are discussed.

Resumo em Inglês:

Abstract Slender reed straws in nature can withstand heavy weight of reed spikes and lateral wind force, and thus show good mechanical properties, especially compression resistance and shear resistance. In the paper, the quasi-static and dynamic mechanical properties of reed straws were studied. Three influencing factors of the straws were set according to the nodes (node-containing, node-free), location section (location 1, 2, 3, 4, 5), and moisture content (low, medium, high). The tensile strength of node-free reed straws with low moisture content ranged from 55.40 to 68.14 MPa at different locations. The axial compressive strength of node-containing straws was higher than that of node-free straws, and the influence of moisture content on the axial compressive strength was more obvious. The radial compressive strength of node-containing straws is 13.00 times higher than that of node-free straws in the corresponding part. The bending strength of straws gradually increases from the top to the root, and it is further enhanced with higher moisture content. The axial impact peak load of node-containing straws is up to 1.27 times that of node-free straws, and the axial impact peak load of straws with high moisture content is 1.40 times higher than that of straws with low moisture content in the corresponding part. The radial impact strength of reed straws gradually increases from the top to the root. In terms of bending impact strength, the impact toughness of reed straws ranges from 0.030 to 0.14 J·cm2, and the specific energy absorption ranges from 1.09 to 4.35 J/kg. Because of the excellent mechanical properties, reed straws provide important material performance data for the engineering field and inspire the design of new engineering materials or structures by improving strength and reducing weight.

Resumo em Inglês:

Abstract This work introduces a new family of strain tensors based on the hyperbolic sine function: The Generalized Hyperbolic Sine (GHS). This family is obtained by using any given strain measure as an argument in a normalized hyperbolic sine function. Particularly, this paper adopts the Seth-Hill family as an argument and shows how some drawbacks of the classical strain measures can be overcome by means of the proposed strain family. A broad analytical study of pure deformation modes (simple axial extension, equi-biaxial loading and simple shear) is presented to show the behavior of the proposed strain family and investigate the physical coherence of their responses. Obtained results are promising as the GHS family proved itself capable of enhancing the physical behavior of the Seth-Hill strain measures and providing versatility with the addition of just one material constant with clear physical meaning. Materials investigated in the article are isotropic and homogeneous. The proposed Hookean-type hyperelastic models can be applied for both incompressible and compressible materials without additional strain energy density function changes.