Mechanical Behavior Of Structures Research Articles

On decision-theoretic model assessment for structural deterioration monitoring

As data from monitored structures become more available, the demand for its efficient use in structural operation and management grows. This can be achieved by using structural response measurements to assess the usefulness of models describing deterioration processes and the mechanical behaviour of structures. This work aims to frame Structural Health Monitoring as a Bayesian model updating problem, where the quantities of inferential interest characterise the deterioration process and/or structural state. Using posterior estimates of these quantities, a decision-theoretic definition is proposed to assess the models based on (a) their ability to explain the data and (b) their performance in decision support tasks. The framework is demonstrated on strain response data from a test specimen subjected to three-point bending and accelerated corrosion, leading to thickness loss. Results indicate that a priori domain knowledge of the deterioration form is critical.

Experimental and numerical investigations on the thermal and moisture transfer in green dual layer wall for building

This study presents a numerical and experimental investigations of coupled temperature and humidity transfer through bio-sourced dual layer for building. Two types of materials are used as a low-density insulating material and a high-density structural material characterized by its mechanical structural behavior. The hygrothermal properties were measured and introduced in the developed dynamic model based on the Kunzel and Mendes models. The finite difference method was applied to solve the coupled heat and moisture transfer for one and dual layer building walls. Comparison of the Kunzel and Mendes models suggest that experimental tests offer accurate solutions. The study further explores a numerical transient simulation of hygrothermal response in real scenarios of a multi-layer building wall exposed to winter and summer climatic conditions. Building energy efficiency was investigated for the case where the biosourced insulating material was in the external or in the internal side of the building wall.

Assessment of minimum allowable thickness of advanced steel (FeCrAl) cladding for accident tolerant fuel

The ferritic iron-chromium-aluminum (FeCrAl) alloy cladding is considered to be the most promising for near-term application in the ATF framework to replace existing zirconium alloy cladding. Although FeCrAl cladding presents several advantages, it is well known that there are at least two main drawbacks, one is the increased thermal neutron absorption cross-section compared to the current Zr-based cladding resulting in a neutronic penalty and another is tritium higher permeation. In the present study, the minimum allowable thickness of cladding is addressed considering neutronic penalty reduction and the mechanical-structural behavior under the LOCA accident condition. The neutronic penalty assessment was performed using the Monte Carlo code and mechanical-structural performance of the FeCrAl cladding using the TRANSURANUS fuel code, which was modified to consider properly the FeCrAl cladding.

Mechanical Behavior of Composite Beams Considering Nonlinear Shear Stiffness of Clustered Studs

Clustered studs are suitable for use in prefabricated steel-concrete composite beams. As a kind of shear connector, clustered studs have a non-negligible influence on the mechanical behavior of structures. Based on the theory of elasticity, prefabricated composite beams investigated via laminated plane stress problem. The load-slip curves of the shear connectors are linearly processed, and through iterative calculations, the displacement and stress distribution functions of prefabricated composite beams are obtained. Then, a model test is carried out on the positive bending moment section of prefabricated composite beams. A sampling method with front segments controlled by the load and back segments controlled by the slip is adopted. This method provides a better rate of convergence and higher accuracy than those of other methods. The test results show that when the load is small and the composite beam is in the elastic stage, the slope of the load-slip curve can be used as the shear stiffness of the clustered studs. When the load is large and the composite beam enters the plastic stage, the nonlinear shear stiffness of the studs must be considered to obtain a high-precision solution.

Multi-Objective Optimization for Curvilinearly Stiffened Porous Sandwich Plates Reinforced with Graphene Nanoplatelets

With the development of innovative manufacturing technology, multi-objective optimization algorithms for optimal design of advanced composite structures have gained increasing attention. An effective and high-accurate prediction on the mechanical behavior of structures is the basic core of optimization algorithms. Thus, a novel refined sinusoidal higher-order theory (NRSHT) combined with isogeometric analysis (IGA) is developed as the high-precision solver. A novel curvilinearly stiffened porous sandwich plate reinforced with graphene nanoplatelets (CSP-GPL) is proposed as the research object. Compared with previous higher-order theories, the proposed NRSHT can more accurately forecast the natural frequencies of CSP-GPL through several numerical and experimental tests. Subsequently, the shape and material distribution design of CSP-GPL are studied with multi-objective optimization. The random forest regression (RFR) is utilized as the high-fidelity surrogate model to construct the objective function in the improved Nondominated Sorting Genetic Algorithm (NSGA-II), which can significantly accelerate the integration of NRSHT-IGA and NSGA-II. Finally, the Pareto-optimal solutions, optimizing for fundamental frequency and total mass of CSP-GPL, are obtained from the present platform, which can give effective suggestions for the future designer to meet specific requirements.

Mechanical behavior of bilayer structures of Ti64 alloy and its composites with TiC or TiB under quasi-static and dynamic compression

Bilayer structures of titanium alloy Ti-6Al-4V (Ti64) and metal matrix composites (MMC) on the base of this alloy reinforced with 5, and 10 % (vol.) of TiC or TiB particles were made using press-and-sinter Blended Elemental Powder Metallurgy (BEPM). The mechanical behavior of these structures was studied under quasi-static and high strain rate compression. Dynamic tests with compression velocity in the range 4–15 m/s (820–2880 s−1) were done using the split Hopkinson pressure bar (SHPB), whereas the quasi-static tests were performed with compression velocity of 0.0005 m/s (10−3 s−1). Stress–strain curves were obtained and the effect of phase composition, microstructure, and strain rate was analyzed and discussed. Current results were compared with previous studies conducted on homogeneous MMCs and Ti64 alloy tested in similar conditions. The deformation mechanism evaluated from the microstructure analysis of the samples was verified using in-situ high-speed camera recordings. Numerical simulation based on Finite Element Analysis was conducted to further investigate the behavior of the samples during the SHPB trials. Generalized scheme of the deformation and damage process of two-layer alloy/composites hybrids as a function of compression rate was proposed.

Mechanical behavior of Ti6Al4V lattice structures; numerical and experimental analysis

This study deals with the mechanical behavior of lattice structures produced by the Laser Powder Bed Fusion process experimentally and numerically for four different topologies of Body-Centered Cubic, Body-Centered Cubic with struts along Z-direction, Face-Centered Cubic and Face-Centered Cubic with struts along Z-direction. To study the effect of cross-section geometry of the struts on the mechanical behavior of the structure, three circular, rectangular and I-shaped cross-sections with the same surface area were manufactured and tested. Their simulations were done using Abaqus software and the simulation results were in great agreement with the test results. Numerical and experimental investigations showed that samples with the I-shaped cross-section of the strut exhibit more stiffness and strength.

Research on Mechanical–Structural and Oil Yield Properties during Xanthoceras sorbifolium Seed Oil Extraction

Products from Xanthoceras sorbifolium Bunge seed have gained extensive attention for various applications, especially in the fields of edible oils and industrial applications. In order to study seed kernel mechanical–structural behavior and oil yield mechanisms during extrusion, we set up a self-developed texture analyzer with in situ microscope observation. Test results indicated that seed kernel oil yield and pressing energy showed an approximately parabolic shape under pressing strain, and maximum oil yield reached 25.7%. Only local tissue damage occurred on seed kernels at strain 45–85%, cracks formed from the kernel edge to the inside zone and small cracks obviously increased in number, corresponding with the oil yield and energy–strain curve. The effect of speed on oil yield showed an opposite trend to strain effect; high pressing speed led to lower oil yield due to the short time for oil precipitation and lower pressing energy. Dwell time obviously promoted oil output within 600 s. Drying temperature had a negative effect due to structural change. Oil yield was almost zero at temperatures below 120 °C. The oil yield and pressing energy relation curve was obtained by polynomial fitting; optimal seed kernel oil pressing conditions were strain 95%, 0.1 mm/s, 20 °C, dwell time 600 s. The research provides in-depth theoretical guidance for Xanthoceras sorbifolium Bunge oil production.

Development of load-temporal model to predict the further mechanical behaviors of tunnel structure under various boundary conditions

Prediction of the further mechanical behaviors is vitally important for tunnel engineering to prevent disasters and maintain stability. It is a challenge for most existing researches to couple multiple influence factors. This study aims to develop a novel Load-Temporal (LT) model to predict the further mechanical behaviors of structure using machine learning method, which considers the effect of both historical performance and external loads. As a case study, the developed model is employed in an underwater shield tunnel, in which a Structural Health Monitoring System (SHMS) is installed. Based on the monitoring data obtained from SHMS, plenty of data experiments are conducted to develop model and determine the optimal parameters. Also, the comparison analysis is adopted to indicate the prediction accuracy of proposed model is higher than that of the classical models. The predicted ability of LT model is discussed via experiments of different time scale in further. As promising applications, LT model is used to predict the mechanical behaviors under various boundary conditions, based on which to determine the dangerous states and the structural performance under these conditions.

The microcontact model of joint surfaces with waviness and asperity interaction

The joint surfaces have a significant effect on the behavior of mechanical structures. Strong demand exists for the development of a model that can include the contact characteristics of joint surfaces. In this article, a new contact model considering asperity interaction and surface waviness is proposed. The roughness and waviness of the surface are separated by the Fourier series, and a contact model for an asperity is first established to obtain the displacement caused by asperity interaction. The joint surface is then treated as the contact between a rough surface and a smooth waviness to obtain a new model which considers asperity interaction and surface waviness. Simulation results show that when the normal load is fixed, the contact deformation decreases with the increasing radius of the waviness peak, but increases with the increasing surface roughness. In addition, asperity interaction will lead to a lower contact stiffness and a larger real contact area. Compared with other models, the results obtained from the proposed model are closer to the experimental results.

Effects of thermo-magneto-electro nonlinearity characteristics on the stability of functionally graded piezoelectric beam

Due to the increasing interests in using functionally graded piezoelectric materials (FGPMs) in the design of advanced micro-electro-mechanical systems, it is important to understand the stability behaviors of the FGPM beams. In this study, considering the effects of geometrical nonlinearity, temperature, and electricity in the constitutive relations and the effect of the magnetic field on the FGPM beam, the Euler-Bernoulli beam model is adopted, and the nonlinear governing equation of motion is derived via Hamilton’s principle. A perturbation method, which can decompose the deflection into static and dynamic components, is utilized to linearize the nonlinear governing equation. Then, a dynamic stability analysis is carried out, and the approximate analytical solutions for the nonlinear frequency and boundary frequencies of the unstable region are obtained. Numerical examples are performed to verify the present analysis. The effects of the static deflection, the static load factor, the temperature change, and the magnetic field flux on the stability behaviors of the FGPM beam are discussed. From the proposed analytical solutions and numerical results, one can easily and clearly find the effects of various controlled parameters, such as geometric and physical properties of the system, on the mechanical behaviors of structures, and the conclusions are very important and useful for the design of micro-devices.

Computational multi-scale analysis of simultaneous processes of delamination and damage accumulation in laminated composites

When studying mechanical behavior of structures made of laminated polymer composite materials, issues related to their relatively high susceptibility to damage, such as delamination, fiber breakage and matrix failure, play significant role. Key aspects are also related to accurate description of the internal structures and heterogeneity of the material. This work is aimed at a numerical study of the processes of damage accumulation in plies as well as development of delamination in laminated polymer composite L-shaped specimen taking into account microstructural parameters. The influence of contact conditions between the plies on the model’s behavior has been studied. It was established that the delamination processes inside the specimen can initiate at the early stages of deformation, which is reflected in the difference of the results obtained using models with various numbers of separated plies. Comparison of the results of modelled elastic behavior of the specimen and models with the developed delamination leads to conclusions about influence of a number of model parameters on the results obtained before and after propagation of delamination. In particular, such factors as the geometry and mechanical properties of models, the number and conditions for specifying contact pairs in the model were analyzed.

Connections Between Topology and Macroscopic Mechanical Properties of Three-Dimensional Open-Pore Materials

This work addresses a number of fundamental questions regarding the topological description of materials characterized by a highly porous three-dimensional structure with bending as the major deformation mechanism. Highly efficient finite-element beam models were used for generating data on the mechanical behavior of structures with different topologies, ranging from highly coordinated bcc to Gibson–Ashby structures. Random cutting enabled a continuous modification of average coordination numbers ranging from the maximum connectivity to the percolation-cluster transition of the 3D network. The computed macroscopic mechanical properties – Young’s modulus, yield strength, and Poisson’s ratio – combined with the cut fraction, average coordination number, and statistical information on the local coordination numbers formed a database consisting of more than 100 different structures. Via data mining, the interdependencies of topological parameters and relationships between topological parameters with mechanical properties were discovered. A scaled genus density could be identified, which assumes a linear dependency on the average coordination number. Feeding statistical information about the local coordination numbers of detectable junctions with coordination number of 3 and higher to an artificial neural network enables the determination the average coordination number without any knowledge of the fully connected structure. This parameter serves as a common key for determining the cut fraction, the scaled genus density, and the macroscopic mechanical properties. The dependencies of macroscopic Young’s modulus, yield strength, and Poisson’s ratio on the cut fraction (or average coordination number) could be represented as master curves, covering a large range of structures from a coordination number of 8 (bcc reference) to 1.5, close to the percolation-cluster transition. The suggested fit functions with a single adjustable parameter agree with the numerical data within a few percent error. Artificial neural networks allow a further reduction of the error by at least a factor of 2. All data for macroscopic Young’s modulus and yield strength are covered by a single master curve. This leads to the important conclusion that the relative loss of macroscopic strength due to pinching-off of ligaments corresponds to that of macroscopic Young’s modulus. Experimental data in literature support this unexpected finding.

Mechanical behaviour of additively-manufactured polymeric octet-truss lattice structures under quasi-static and dynamic compressive loading

Two different polymer resins were used to create three different octet-truss lattice structures of different densities. The mechanical behaviour of these structures has been examined under both quasi-static and dynamic compressive loading. The structures were printed using stereolithography (SLA) additive manufacturing. The basic building octet unit has a fixed strut length of L=10mm, with the designed strut radius varying from R=0.7mm to 1.3mm to provide structures of different densities. It has been found that the mechanical behaviour of the printed octet structures depends on both the relative density and the intrinsic material properties. Higher density structures show larger effective yield and compressive strengths, while the basic printing material fundamentally determines its macroscopic properties: one material provides a brittle mechanical response under compression while the other provides a tough response. The former lattice structures behaved in a brittle manner at all relative densities, fracturing at small strains. For the latter resin lattice structures, on the other hand, under quasi-static compression, the stress-strain curves changed from a slightly stress oscillating mode at low relative density (i.e. ρ¯=0.13) to a stable stress plateau mode at high relative density (i.e. ρ¯=0.41). The Specific Energy Absorption (SEA) of both lattice structures had a monotonically increasing relationship with relative density, the SEA of the brittle resin specimen is higher than that of the tough resin specimen, while the tough resin specimen exhibits its excellent energy absorption under a wide displacement range. For the dynamic compressive tests, the tougher resin structures displayed strain-rate effects, while the more brittle ones did not. The numerically predicted response of both lattice structures agreed closely with the experimental results.

Tecnologia de processos e sistemas construtivos

O terceiro número do Volume 9 de 2018 da PARC Pesquisa em Arquitetura e Construção é composto por artigos de pesquisa e de revisões sistemáticas da literatura. Em especial, destaca-se a seção de Tecnologia de Processos e Sistemas Construtivos com artigos expandidos do 1º WORKSHOP DO GRUPO DE TRABALHO DE TECNOLOGIA DE PROCESSOS E SISTEMAS CONSTRUTIVOS (TECSIC) da Associação Nacional de Tecnologia no Ambiente Construído. Ao todo, os estudos foram desenvolvidos por pesquisadores dos estados brasileiros de Minas Gerais, São Paulo e Paraná. As instituições de ensino e pesquisa envolvidas nos estudos apresentados são: Pontifícia Universidade Católica do Paraná, Universidade de São Paulo, Universidade Estadual de Campinas, Universidade Federal de Minas Gerais, Universidade Federal do Paraná e Universidade Federal de São Carlos. As áreas de formação dos autores concentram-se em Engenharia Civil, na maioria, incluindo Arquitetura e Urbanismo e Engenharia Mecatrônica. A temática de tecnologia de processo e sistemas construtivos foi abordada com enfoque em componentes de piso e de fechamento estrutural, ambos em concreto, e automação do processo industrial de aço cortado e dobrado. Os artigos de pesquisa tiveram enfoque no ensino do comportamento mecânico das estruturas e de topografia, em ambos os casos, para estudantes de Arquitetura e Urbanismo. As revisões sistemáticas da literatura abordam pesquisas em Modelagem da Informação da Construção integrada ao planejamento de obras com painéis pré-fabricados e a Internet das Coisas.

The influence of loading rates on hardening effects in elasto/viscoplastic strain-hardening materials

In this paper the influence of increasing loading rates on hardening effects is analyzed for rate-dependent elastoplastic materials. The effects of different loading rates on hardening rules are discussed with regard to the constitutive behavior of strain-hardening materials in elasto/viscoplasticity. A suitable procedure for the numerical simulation of rate-sensitive material behavior is illustrated. A comparative analysis is presented on constitutive relations in strain-hardening plasticity without rate effects and with rate effects in order to show the different role played by hardening rules in the rate-sensitivity analysis of elasto/viscoplastic strain-hardening materials. By reporting suitable numerical simulations for the adopted constitutive relations it is shown that when the rate of application of the loading is increased the influence of hardening has a different effect in the mechanical behavior of structures. Computational results and applications are finally illustrated in order to show numerically the different role played by hardening on the plastic strains when the loading rates are incremented for elasto/viscoplastic strain-hardening materials and structures.

Motivation in mechanics of materials classes: An experimental approach

This work presents a novel didactic methodology for the approximation of the students to the subject of Mechanics of Materials, with the aim of improving the understanding of the inertia moment, and its relevance on the mechanical behaviour of structures. The students have grouped on groups of two to three persons. The work consisted in designing the most efficient beam having in mind several design constraints. Tensile tests were performed to determine the relevant material properties. Those were used for the analytic dimensioning of the beams. The aim of the work is to obtain the highest efficiency possible, since it results in the best mark, as possible. The efficiency was measured by the maximum load on experimental bending testing, divided by the mass of the beam. The results, as well as the interest of the methodology are discussed. It is proved that this methodology can be useful for the students to apply theoretical concepts and, at the same time, to give a deeper understanding of real experimental tests.

A refined model of longitudinally reinforced metal composite wall-beams under steady creep conditions

This paper provides equations describing, to a different degree of accuracy, the bending behavior of longitudinally reinforced metal-composite beams-walls, working under conditions of the steady creep of materials of all phases of composition. From these equations, as partial cases, the correlations of the Bernoulli theory and two versions of the Timoshenko theory are obtained. For statistically definable beams, a simplified version of the specified theory has been developed. Based on the cases of the study of the flexural deformation of hinge-based beam-walls, it is demonstrated that there are such metal compositions, which when used, means that neither classical theory, nor either of the two variants of Timoshenko’s theory can guarantee reliable results regarding amenability even within a 20% level of accuracy, thought of as accessible in the study of the mechanical behavior of structures under the conditions of a steady creep. However, to make reliable calculations, the use of specified theories is needed, allowing for the calculation of the edge effects arising in phase materials in the neighborhood of supporting cross sections.

Numerical analysis on mechanical behaviors of hierarchical cellular structures with negative Poisson’s ratio

Two-dimensional hierarchical re-entrant honeycomb structures were designed and the mechanical behaviors of the structures were studied using a finite element method. Hierarchical re-entrant structure of order n (n ≥ 1) was constructed by replacing each vertex of a lower order (n − 1) hierarchical re-entrant structure with a smaller re-entrant hexagon with identical strut aspect ratio. The Poisson’s ratio and energy absorption capacity of re-entrant structures of different hierarchical orders were studied under different compression velocities. The results showed that the Poisson’s ratio of the first and second order hierarchical structures can reach −1.36 and −1.33 with appropriate aspect ratio, 13.8% and 12.1% lower than that of the zeroth order hierarchical structure. The energy absorption capacity of the three models increased with an increasing compression velocity; the second order hierarchical structure exhibited the highest rate of increase in energy absorption capacity with an increasing compression velocity. The plateau stresses of the first and second order hierarchical structures were slightly lower than that of the zeroth order hierarchical structure; however the second order hierarchical structure exhibited the highest energy absorption capacity at high compression velocity (60 m s−1).

A BEM formulation applied in the mechanical material modelling of viscoelastic cracked structures

The present study aims at performing a mechanical analysis of 2D viscoelastic cracked structural materials using the Boundary Element Method (BEM). The mesh dimensionality reduction provided by the BEM and its accuracy in representing high gradient fields make this numerical method robust to solve fracture mechanics problems. Viscoelastic models address phenomena that provide changes on the mechanical material properties along time. Well-established viscoelastic models such as Maxwell, Kelvin–Voigt and Boltzmann are used in this study. The numerical viscoelastic scheme, which is based on algebraic BEM equations, utilizes the Euler method for time derivative evaluation. Therefore, the unknown variables at the structural boundary and its variations along time are determined through an ordinary linear system of equations. Moreover, time-dependent boundary conditions may be considered, which represent loading phases. The dual BEM formulation is adopted for modelling the mechanical structural behaviour of cracks bodies. Three examples are considered to illustrate the robustness of the adopted formulation. The results achieved by the BEM are in good agreement with reported data and numerical stability is observed.