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Maintenance and repairing in actual engineering for long-term used structures, such as pipelines and bridges, make structural damage detection indispensable, as an unanticipated damage may give rise to a disaster, leading to huge economic loss. A new approach for detecting structural damage using transmissibility together with hierarchical clustering and similarity analysis is proposed in this study. Transmissibility is derived from the structural dynamic responses characterizing the structural state. First, for damage detection analysis, hierarchical clustering analysis is adopted to discriminate the damaged scenarios from an unsupervised perspective, taking transmissibility as feature for discriminating damaged patterns from undamaged ones. This is unlike directly predicting the structural damage from the indicators manifestation, as sometimes this can be vague due to the small difference between damaged scenarios and the intact baseline. For comparison reasons, cosine similarity measure and distance measure are also adopted to draw out sensitive indicators, and correspondingly, these indicators will manifest in recognizing damaged patterns from the intact baseline. Finally, for verification purposes, simulated results on a 10-floor structure and experimental tests on a free-free beam are undertaken to check the suitability of the raised approach. The results of both studies are indicative of a good performance in detecting damage that might suggest potential application in actual engineering real life.

Accurate and efficient damage detection in long-term health monitoring for structures still encounters many difficulties due to the effect of environment. Furthermore, recorded big data requires efficient damage detection algorithm. In this study, an efficient and effective damage detection algorithm is proposed using transmissibility along with Mahalanobis distance and Hotelling T-square. A numerically simulated beam and an experimentally tested laboratory structure are used to validate the proposed algorithm. Results demonstrate good performance of the proposed technique in damage detection.

Detecting structural damage in operational conditions still encounters some difficulties, especially in early-stage, as environmental varieties impose challenges in real engineering applications and may require large computational efforts in the structural health monitoring and potential maintenance. Unlike conventional strategies employing frequency response function or response data, a damage detection methodology is addressed in this study by employing transmissibility functions that retains a strong interrelation with structural damage or deterioration, in order to avoid the measurement of excitation, together with principal component analysis that leads to reduction in computational costs. In this procedure, transmissibility is extracted from the structural responses and main features are selected by principal component analysis for less computational costs. Then, via distance measures damage indicators are constructed for both intact and damaged states, and finally a numerical simulation with a clam...

We present a generalized shear deformation theory in combination with isogeometric (IGA) approach for nonlinear transient analysis of smart piezoelectric functionally graded material (FGM) plates. The nonlinear transient formulation for plates is formed in the total Lagrange approach based on the von Karman strains, which includes thermo-piezoelectric effects, and solved by Newmark time integration scheme. The electric potential through the thickness of each piezoelectric layer is assumed to be linear. The material properties vary through the thickness of FGM according to the rule of mixture and the Mori–Tanaka schemes. Various numerical examples are presented to demonstrate the effectiveness of the proposed method.

In this paper, the effect of a slight pitch difference between a bolt and nut is studied. Firstly, by varying the pitch difference, the prevailing torque required for the nut rotation, before the nut touches the clamped body, is measured experimentally. Secondly, the tightening torque is determined as a function of the axial force of the bolt after the nut touches the clamped body. The results show that a large value of pitch difference may provide large prevailing torque that causes an anti-loosening effect although a very large pitch difference may deteriorate the bolt axial force under a certain tightening torque. Thirdly, a suitable pitch difference is determined taking into account the anti-loosening and clamping abilities. Fourthly, fatigue experiments are conducted using three different values of pitch difference for various stress amplitudes. It is found that the fatigue life could be extended when a suitable pitch difference is considered Furthermore, the chamfered corners at nut thread ends are considered, and it is found that the finite element analysis with considering the chamfered nut threads has a good agreement with the experimental observation. Finally, the most desirable pitch difference required for improving both anti-loosening and fatigue life is proposed. Keywords: Bolt–nut connection, Pitch difference, Anti-loosening performance, Fatigue life, Finite element method

Fretting happens when there is an oscillatory displacement between two contact parts. In gross slip regime, wear is a dominant failure mode, which has a detrimental effect on the contact parts. To understand the wear behaviour in the fretting process, many experiments and simulations have been done. This phenomenal analysis is time-consuming, especially when fretting wear investigation is required under certain loading cases or during certain number of cycles. Under these conditions, fast prediction tools provide an alternative for this kind of problem. In this paper, a model reduction based on Proper Orthogonal Decomposition with Radial Basis Function (POD-RBF) is used to predict the wear characteristics of specimens under different slip amplitudes and at different fretting wear cycles based on simulation results. To demonstrate the advantages and disadvantages of POD-RBF, Grey Model and Curve Fitting are used to verify POD-RBF for one-parameter prediction, while Artificial Neural Network is applied to verify POD-RBF for three-parameter prediction. The results show that the approach of POD-RBF can predict the wear characteristics under different slip amplitudes and normal loads at different cycles with high accuracy and high computational efficiency.

The addition of 0.1 wt% Zr in Al-Cu-Mg alloy contributes to the formation of a stronger Brass and weaker Goss textures during hot rolling. Aiming at this observation, the related texture formation mechanisms are discussed from the aspect of dynamic recrystallization (DRX) behavior and phase particle effect on grain rotation. This work demonstrates that the low degree of DRX and grain rotation behavior by S phases are essentially responsible for the enhanced Brass texture in Al-Cu-Mg-Zr alloy.

This paper addresses a damage detection method based on changes in modal curvature combined with Convolutional Neural Network (CNN). The use of modal curvature for damage detection is very well known. Some methods require modal data of healthy structures as a reference, others do not. Gapped Smoothing Method (GSM) is a vibration-based damage detection methodology, which makes use of modal curvature for identifying the location of structural damage and does not require information of the intact structure. The Bo Nghi bridge is used as an illustrative example. This bridge consists of four T-shaped concrete simply supported girders. One single beam with the same length and cross-section of the bridge girder is modeled and used to extract numerical data to train the CNN. A CNN is trained by using images from the damage index of the GSM to classify the damage location in the numerical beam model. Finally, the finite element model of the bridge is built and used to model damage scenarios to test the trained CNN. The results indicate that the combination of GSM and CNN can be used for damage detection and localization.

Recently, more attention has been paid to Artificial Neural Network (ANN) in the field of damage identification of engineering structures based on modal analysis. This paper proposes a new modified damage indicator, using transmissibility technique to improve Local Frequency Response Ratio (LFCR), combined with ANN. The main objective of the proposed damage indicator is to reduce the number of collected data for fast prediction and with higher accuracy instead of collecting all modal analysis data, i.e. natural frequencies, damping ratios, and mode shapes, or using inverse analysis for damage quantification. The suggested approach is tested using three layers laminated cross-ply [0°/90°/0°] composite beam and plate having single and multiple damage(s). The reliability and accuracy of the proposed application are demonstrated by predicting the severity of damages in the considered composite structures after analysing four damage scenarios.

A single variable shear deformation theory (SVSDT) is applied to free vibrations and harmonic response analysis of a multi-storey frame model considering flexibility of foundation. The column-foundation joints are modelled using three-spring approach instead of fixed support assumption to show the effects of soil-structure interaction (SSI) on the dynamic behaviour of frame model. The dynamic stiffness formulations are used for both free vibration and harmonic response analysis. The results that obtained using SVSDT and Timoshenko beam theory (TBT) are presented comparatively. The calculated natural frequencies are verified by finite element method (FEM). The convergence of FEM for the first three natural frequencies is presented for the fixed supported frame and frame considering SSI. The harmonic response curves are used to reveal the resonant and anti-resonant frequencies directly. It is seen that using a lateral displacement response for harmonic response curves may cause to miss natural frequencies of axial dominant modes of the frame model. However, all required natural frequency values of multi-storey frames considering foundation flexibility can be obtained via harmonic response curves that plotted by using a vertical displacement response of a node of model. Moreover, the proposed approach is validated by experimental data for scaled frame models, which are fixed supported and flexibly supported, respectively. The computation times for harmonic responses are tabulated for frame model on flexible foundation as well as fixed support assumption.

The friction of two bodies in relative motion is accompanied by several phenomena such as elevation of temperature. The aim of this work is to calculate the braking temperature of the brake disc of an aircraft during the landing phase, using a calculation code based on Finite Element Method (FEM) and the analytical method of Newcomb. This investigation uses two kinds of disc — full and real disc (original version mounted on the aircraft) — and three braking disc materials such as the cast irons FG15, FG20 and FG25. The result showed that the numbers of holes and slots existing in the real disc has no influence on the braking temperature compared to the full disc. On the other hand, all brake disc materials have almost the same thermal behavior. Both models, analytical and numerical, provided acceptable results.

Fretting fatigue problems are common in the aerospace and automotive industries, which can seriously affect the fatigue response of the material and the stability of the overall structure. In this paper, the effect of the size, location of single critical micro-void on the fretting fatigue initiation life of heterogeneous materials is studied by numerical simulations and modified critical plane criterion. The theory of critical distance (TCD) is used to consider stress gradients near the crack initiation points. It is shown that when the critical micro-void is located at different positions inside the sample, there is a weakened area similar to the half butterfly wings. This means that when the micro-voids are located in this area, the crack initiation life will be less than that in the case of homogenous material. Furthermore, there are also two enhancement zones. When the micro-voids are located in these two zones, the fretting fatigue life can be increased, that is, at a certain depth below the contact edge and at a certain distance to the right of the contact edge.

We present, for the first time, an original experimental study on the effect of ageing process (seasoned in the aqueous environment) on the mechanical behaviour of adhesive tubular butt joints. In order to manufacture adhesive tubular butt joints, tubes with a diameter of 20 ± 1 mm, made of three different materials (polypropylene, carbon steel and galvanised steel) were considered. Two types of the adhesive epoxy compounds were used, namely a flexible adhesive (Epidian 57/PAC/100:80) and a stiff adhesive (Epidian 57/Z1/100:10). The ageing process, including the adhesive joint samples' seasoning in a specific environment, was conducted using three aqueous environments, namely mineral water, demineralised water and supply water. The specimens were aged for 3 months and 6 months. In addition, one reference sample subjected to the ageing process was considered. After ageing, the samples were subjected to tensile strength tests. These tests were carried out using the ZWICK/ROELL Z150 testing machine in accordance with the norm EN 15870. Based on the test results’ analysis, it was observed that the longer the seasoning time of the adhesive joint samples, the more negative effects on the adhesive joints (decreased strength regardless of the adhesive type or the material). For tubes made of both galvanised and carbon steel, the joints could work well in short-term exploitation as they would keep their strength for a certain period. Such joints could be less expensive in short-term exploitation than the widely used mechanical joints.

In this paper, non-destructive damage identification in beam-like and truss structures using Frequency Response (FR) data is presented. This approach is to formulate an inverse problem using Particle Swarm Optimization (PSO) and Finite Element Method (FEM) to identify the presence, location and quantification of the damage. PSO is one of the most efficient bio-inspired methods. It is used to minimize the objective function, which is based on FR data. The damage in structure is caused by loss of rigidity at a specific location. The capability and efficiency of this application to identify the location and severity of damage are demonstrated by means of several numerical examples. The results of the proposed approach show good accuracy.

In this study, free vibration analysis of Timoshenko beams is presented in order to determine the error in natural frequencies of a beam using experimental and numerical analysis based on Isogeometric analysis (IGA). Numerical modeling based on IGA has been updated using Cuckoo search algorithm according to the results found by experiments. NURBS order and sensitivity of discretization in the longitudinal and transversal directions are updated by Cuckoo search to identify the IGA best parameters. The results show that higher accuracy is achieved by using optimization technique for a beam structure to identify the best IGA parameters.

In this paper, the effect of local microstructural variation on the crack propagation is studied. The weldment sample is produced by bead-on-plate arc welding process. Resultant bead geometry and the equivalent heat source model are evaluated by the software SimWeld. Those data are imported to ABAQUS to regenerate the temperature field during welding. The volume fractions of product phases in the end are calculated at node using a well-known self-dependent metallurgical algorithm. Two tensile models using extended finite element method (XFEM) are established to analyze the crack growth. One model assumes uniform properties of base material in the whole weldment, while in the other model, the properties are obtained by interpolating with the local phase volume fractions. The power law is used to determine the crack opening. The differences in stress distribution and force-displacement curve demonstrate that the microstructure inhomogeneity does affect the crack propagation. Moreover, by interactively comparing the phase distribution and the crack path, it is found that the crack is incline to grow between the fusion zone (FZ) and heat affected zone (HAZ), where an abrupt change of microstructure happens.

This paper presents static bending behaviour of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) nanoplates with four types of distribution of carbon nanotubes. The NURBS based isogeometric analysis (IGA) is associated with refined plate theory (RPT) with four unknowns, in which, there is no need to use shear correction factors. To capture the size-dependent effect of plate, the modified couple stress theory is used with only one material length scale parameter. The accuracy and efficiency of proposed method are demonstrated through comparison with reference solutions. A number of numerical examples are presented to demonstrate the influence of the length scale on the bending behaviors of FG-CNTRC nanoplates.

Sea defenses are constructed to protect coastlines, embankments and artificial constructions from erosion and destruction of water actions such as wave, storm, tide and so on. However, these structures are destroyed yearly because the climate change and rising sea level induce storms, flood or even drought. The reasons of sea defense system failure can also be the out-of-date structure, which cannot withstand the rising level of water any more. Therefore, the aim of this study is to develop a new type of concrete block for interlocking revetment using topology optimization method in ANSYS 18.0, which saves about 70% of material compared to regular solid block. Topology optimization analysis cannot provide the exact solution of the concrete block shape for manufacturing, but it can be a great reference for engineering design practice.

Fluid-Structure Interaction (FSI) is one of the interesting subjects in coastal construction. In this study, Smoothed Particle Hydrodynamic (SPH) method is utilized to model the fluid domain. Finite Element Method (FEM) is used to model the solid structure. SPH is a mesh-free method, which is flexible to model and analyze complicated problem domains. The interaction between a thin-walled concrete block and wave under different initial conditions is modeled by ABAQUS. The SPH-FEM model is validated by interaction of elastic gate with water pressure, the results are compared with previous research and show very good agreement. It is found that SPH-FEM model can capture the entire FSI process deformation of a complex geometry. As expected, the present approach performs well with a suitable geometry for thin-walled concrete blocks to protect coastal areas from climate change.

Rock cutting in various forms is used in mining and civil engineering area such as oil & gas drilling, tunneling etc. The dieted understand of the rock cutting mechanism is quite essential to the bit design and parameters selection. This study constructed the finite element model of rock cutting to investigate the crack initiation and propagation, chips formation and cutting force, and the effect of cutting depth on rock breaking mechanism is also analyzed. The results show that cutting depth plays an important role in the rock failure behavior, when the cutting depth is shallow, the ductile failure mode is dominated and brittle failure mode is dominated at the larger depth of cut. The cutting force increases linearly with the depth increase of cut when cutting depth is shallow; however, the nonlinearity of cutting force increase appeared when the depth of cut exceeds the threshold value. The magnitude of MSE tends to decrease with the depth increase of cut and tends to stabilize when the depth of cut reaches a certain value. The results obtained in this study can lead to an enhanced understanding of rock breaking mechanisms in rock cutting.

In this paper, a six-variable quasi-3D model is developed for laminated composite plate subjected to thermal and mechanical loadings. With higher-order terms in the displacement fields, the plate model can capture both shear deformation and thickness stretching effects. Consequently, it enables us to achieve more accurate results in deflection, shear stress distributions, which are satisfied with traction free and interlaminate continuity conditions. The governing equation is derived from Galerkin weak form and then discretized by isogeometric analysis (IGA), which utilized NURBS basis function to fulfill C1-continuity requirement without additional variables.

This paper, instead of using the popular numerical methods such as Finite Element Method, Finite Volume Method, etc. that are applied for fluid computation with the advantages of simplicity, introduces a new method named Polygonal Finite Element Method (PFEM). Based on the stability of mixed finite element, discretization is governed by the so-called inf-sup condition, which, in this case, depends on the choice of the discrete velocity and pressure spaces. We put forward a new choice of these spaces defined over convex polygonal partitions of the domain. Within each element, the pressure field is represented by the polygonal basis functions and the velocity is controlled by richer polygonal bubble functions.

In this study, we investigate a new design of interlocking revetment that is constructed by precast hollow concrete blocks. The defense structure is to protect the estuary from complex water actions at a river mouth in Vietnam. The hollow concrete block of the structure is designed to be hollow inside for material saving and construction efficiency. Then, the block will be filled by sand onsite. However, the structure performance under the effects of external loads should be investigated since its design is the first time of implementation in coastline protecting system in Vietnam. The block is modeled in ANSYS 18.0 for the calculation of deformation and stresses induced by the action of wave on the block surfaces. The conventional finite element method is used for solving the unknowns of studied models. The investigated results are the displacements of the hollow concrete block in various directions and the equivalent von-Mises stress generated within the structure. The calculation also shows that there are some sharp points of the structure experiencing stress singularity, which should be considered in design.

Seawalls have been implemented for coastal protection for centuries. The gravity type vertical seawalls made of plain concrete is the most common one used widely because of its advantages such as competitive construction cost, little maintenance requirement, etc. In this work, a novel three dimensional precast thin-walled concrete block forming seawall has been simulated by using finite element software. Unlike the traditional gravity type seawalls, such as hollow block, is low self-weight structure and can be damaged under exceed load. Therefore, load-bearing capacity of block itself under wave attack is necessarily evaluated. Of course, stability of seawall structure against sliding, overturning or bearing capacity of soil foundation are important factors and should not be overlooked. Theoretical aspects and computational modelling procedures are presented in detail. ABAQUS commercial software is adopted for this study.

Wellbore instability problem is one of the key problems in drilling highly deviated, extended reach wells, particularly in high temperature, high-pressure formations (HPHT). However, many researches are focus on the vertical wellbore, and few studies have investigated on the three-dimensional inclined wellbore instability analysis which considering the influence of thermo-poroelastoplasticity. In this paper, a three-dimensional fully coupled thermo-poroelastoplasticity inclined wellbore stability model is presented by using finite element method, besides, this model can be used for the wells with any deviation angle and azimuth angle just by changing the far field stresses and boundary conditions. The distribution of pore pressure, wellbore stresses under the conditions of various deviation angle, consolidation times and temperatures have been analyzed. The research results show that, the stability problems are generally serious in deviated wells. The wellbore has more instability while the consolidation time increases and it has more instability in the heating cases than in cooling cases. The conclusions achieved in this paper will help the drilling engineers to understand the inclined wellbore instability problems correctly.

The first two steps in Structural Health Monitoring (SHM) are to detect and localize damage in a structure. Transmissibility uses only output signals to extract the structural dynamic parameter and very sensitive to damage. In this paper, a simply supported beam is analyzed using a transmissibility-based damage detection methodology combined with Auto-Associative Neural Network (AANN). Firstly, the transmissibility is calculated between two points in the examined beam. Then a transmissibility indicator is taken as input for the neural network, which accounts only for the response data and is sensitive to damage. The target of AANN is the location and the severity of the damage. It is found that the network, after being trained, show good results and can be used to detect and localize damage.

(1) Background: Irregular and non-standard work arrangements have become a serious determinant to the health and safety of workers. The aim of this study is to investigate the relationship between shift work and occupational accident absence. A representative Belgian sample considering several sociodemographic and work characteristics is used. (2) Methods: This study is based on the data of the sixth European Working Condition Survey (EWCS). The sample is restricted to 2169 respondents from Belgium. By using multivariate logistic regression modeling techniques and adjusting several confounders, the associations between shift work and occupational accident absence are studied. (3) Results: It is found that about 11.1% of the workers undergo an occupational accident absence. A multivariate regression model demonstrates an increased occupational accident absence risk for workers who have shift work (odds ratio, or OR, 1.92, 95% CI 1.06&ndash, 3.46). Also, gender and biomechanical exposure were significantly associated with occupational accident absence ((OR 2.07, 95% CI 1.16&ndash, 3.69) and (OR 2.03, 95% CI 1.14&ndash, 3.63), respectively). No significant interaction effects are found with gender and age variables. 4) Conclusion: This study confirms that doing shift work is significantly associated with occupational accidents. In order to reduce the significance of occupational accidents, shift work should be limited through national-level policies.

This paper discusses the issues concerning the strength of PE–HD 500 polyethylene adhesive joints depending on the applied variable structural and technological factors. The variable structural factor was joint geometry: the samples were single-lap joints and butt adhesive joints. As far as the technological factors are concerned, two types of cyanoacrylate adhesives were used (Loctite 401 and Loctite 406), different surface preparation methods were employed (with and without the application of a primer) and different primer-application techniques were used (the primer was applied to one or both adherend surfaces). The primer was selected with respect to the adherend and adhesive types. The samples of the produced adhesive joints were subjected to dimensional analysis followed by destructive testing. The strength tests were performed on the Zwick Roell Z150 testing machine in accordance with the DIN EN 1465 standard. Following the destructive tests, the adhesive joints were examined with respect to failure patterns based on visual valuation and the standard PN-EN ISO 10365. The statistical analysis was performed by the F-Snedecor and T-Student tests, the Cochrane-Cox test as well as relevant statistical models, taking into account the first error type of α = 0.05. The results demonstrate that the adhesive joint strength of elements made of polyethylene is affected by both surface preparation method (including the use of the primer) and the type of adhesive used. It is observed that the strength of adhesive joints increases with increasing the amount of the primer.

The numerical prediction of fretting fatigue lives has been an important research topic over the past few decades. Generally, those predictions are based on the addition of an initiation life, e.g. computed by Continuum Damage Mechanics, and a propagation life, calculated from the analysis of the growth of an initial crack until final rupture of the material. The propagation life prediction often relies on an empirical description of the crack growth rate. Normally, regardless the size of grains in the microstructure, a Paris growth law for long cracks is used. In this paper, our goal is to incorporate the behavior of short cracks on the growth law and analyze its impact on the predictions of fretting lives. Our results show that short cracks have a considerable impact on the predictions of fretting fatigue at low stresses (higher lives), but for relatively high stresses (shorter lives), it has almost no influence and a simple Paris law provides good estimates.

The eXtended isogeometric analysis (X-IGA) combined with Particle swarm optimization (PSO) is used for crack identification in two-dimensional linear elastic problems based on inverse problem. The application of fracture mechanics test under mode II loading is performed. The X-IGA possesses the advantages of the combination between eXtended Finite Element Method (X-FEM) and the Isogeometric Analysis (IGA). The objective function minimizes the gap between the calculated and measured displacements. Convergence studies at various positions of crack on the plate are calculated and the results shows that the proposed technique can detect damage with minimum accuracy 95% for the position and maximum accuracy 98%.

The importance of revetment slope (RS) structures for protecting coastal is indisputable. RS structures not only can maintain stability of embankment, but also can reduce sea wave energy by its optimized geometric features. For years, civil engineers have developed numerous solutions of RS structures based on theoretical aspects, experiments, and numerical analysis. Due to the lack of analysis criterion, design codes, and experimental facilities, numerical analysis methods significantly become of interest. One of the most challenges is that to perform the interactions between concrete blocks, which form RS structure, and water, i.e. dynamic fluid–structure interaction (FSI). Also, interaction between RS structures and embankment or foundation slope stability must be investigated carefully. Analysis of inter-locking block interactions is one of our missions in the VLIR-OUS TEAM 2017 project that we are running. In addition, due to the limitation of existing RS structures, e.g., heavy and dense materials, optimizations of RS structure are concerned. This paper is to overview the development of RS structures and approaches for analyzing contact problems. Theoretical aspects and computational modeling procedures are mentioned. ABAQUS commercial software is adopted. Hence, novel efficient RS structures could be developed and applied in the real world.

Mechanics is a branch of physics that describes the theoretical aspects related to the response of objects to external forces and displacements [...]

In this paper, a transmissibility based damage detection methodology using artificial intelligence is proposed. Structural health monitoring requires accurate damage detection in real engineering while the environmental uncertain-ties make this a challenge. In order to reduce this effect, artificial intelligence, such as artificial neural networks might be a possible strategy for achieving a better interpretation of the monitored data during operational condition. In this study, transmissibility is taken into account as damage sensitive feature because it accounts for the response data only. Then, auto-associative neural network is employed for detecting the structural damage and predicting its severity. In order to validate our proposed technique, a ten-floor structure is simulated and studied. The results show good perfor-mance in detecting damages. DOI: http://dx.doi.org/10.5755/j01.mech.23.5.15339

This paper presents a methodology for damage detection and localization in composite beams using vibration data, Particle Swarm Optimization (PSO) and Genetic Algorithm (GA). The data was acquired by developing a software that performs dynamic analysis of composite beams based on the Finite Element Method (FEM). The objective function makes use of natural frequencies and Modal Assurance Criterion. After validating the effectiveness of the proposed method, a comparative study between the performances of PSO and GA in detecting multiple and single damage scenarios is carried out. Then, the effect of noise is investigated by taking different noise levels in the modal data. It appears that the noise has a negligible effect on the performance of the presented approaches.DOI: http://dx.doi.org/10.5755/j01.mech.23.4.15254

Floating is a dangerous phenomenon for aircrafts and usually ends with plane rupture. It can be used to characterize a dynamic instability of the structure. Floating phenomenon is usually due to an interaction between aerodynamics, elasticity and inertial forces. It appears at a determinate speed of flight called critical floating speed. The aim of the present study is to determine the floating critical speed of an aircraft wing in a subsonic fan by means of experimental tests and numerical simulations using the commercial Finite Element Analysis package ANSYS CFX. The obtained experimental results are in good agreement with those obtained using the numerical approach.DOI: http://dx.doi.org/10.5755/j01.mech.23.4.15175

Objectives: The main objective of this study is to examine the relationship between indicators of nonstandard work arrangements, including precarious contract, long working hours, multiple jobs, shift work, and work-related accident absence, using a representative Belgian sample and considering several sociodemographic and work characteristics. Methods: This study was based on the data of the fifth European Working Conditions Survey (EWCS) . For the analysis, the sample was restricted to 3343 respondents from Belgium who were all employed workers. The associations between non-standard work arrangements and workrelated accident absence were studied with multivariate logistic regression modeling techniques while adjusting for several confounders. Results : During the last 12 months, about 11.7% of workers were absent from work because of work-related accident. A multivariate regression model showed an increased injury risk for those performing shift work (OR 1.546, 95% CI 1.074-2.224). The relationship between contract type and occupational injuries was not significant (OR 1.163, 95% CI 0.739-1.831). Furthermore, no statistically significant differences were observed for those performing long working hours (OR 1.217, 95% CI 0.638-2.321) and those performing multiple jobs (OR 1.361, 95% CI 0.827-2.240) in relation to work-related accident absence. Those who rated their health as bad, low educated workers, workers from the construction sector, and those exposed to biomechanical exposure (BM) were more frequent victims of workrelated accident absence. No significant gender difference was observed. Conclusion : Indicators of nonstandard work arrangements under this study, except shift work, were not significantly associated with workrelated accident absence. To reduce the burden of occupational injuries, not only risk reduction strategies and interventions are needed but also policy efforts are to be undertaken to limit shift work. In general, preventive measures and more training on the job are needed to ensure the safety and well-being of all workers.

A fretting fatigue failure scenario can be explained by accumulation of damage, which leads to formation of initial macro-cracks at the contact interface and propagation of macro-cracks to sudden rupture of bulk material. The main aim of this study is estimating these two portions by means of a numerical modelling approach. For this purpose, an uncoupled damage model based on a thermodynamic potential function is used to model the crack initiation lifetime. In order to model crack propagation part a linear-elastic fracture mechanics approach under mixed-mode loading conditions has been considered. The crack propagation direction is defined based on experimental observation and compared with some available criteria in the literature, which are usually used for proportional loading conditions. The estimated results are compared with observed experimental lifetime and show good agreement.

Fretting fatigue is a mechanical failure process, which consists of two complex failure mechanisms. Fretting is caused by small relative movement between connected parts and fatigue is due to alternating bulk load. Fretting fatigue is highly non-linear and subjected to non-proportional loading condition. The multiaxial nature of stress at contact interface can be highly influenced by different phase difference between axial, tangential and contact load. In this study, the effect of different phase difference between axial and tangential load on fretting fatigue behaviour is investigated. Moreover, by applying cyclic contact load instead of constant contact load, its effect on fretting fatigue response and crack initiation lifetime is investigated. It was found that the phase difference affects the maximum location of dissipated energy along with fretting fatigue crack initiation lifetime.

A simple, yet powerful, new technique based on Artificial Neural Network (ANN) combined with Particle Swarm Optimization (PSO) for damage quantification in laminated composite plates using Cornwell indicator (CI) is proposed. The analysis is performed in two stages. In the first stage, IsoGeometric Analysis (IGA) is formulated for square laminated composite plates having three layers [ 0 ° / 90 ° / 0 ° ] . In the second stage, IGA model is coupled with PSO for damage quantification using an inverse problem approach and CI as an objective function to minimize the difference between calculated and measured values. This paper aims to assess the application of ANN-PSO for damage quantification in composite structures in order to achieve efficient computational time. IGA is used as modelling technique, CI is used as input data, whereas damage locations and severities are used as output data. The result indicates that high accuracy of damage quantification is achieved using ANN-PSO-IGA-CI. Furthermore, it is demonstrated that huge saving in computational time is achieved when using ANN-PSO-IGA-CI compared with PSO-IGA-CI.

In this article, a refined modified couple stress theory based on isogeomeric analysis to capture the small-scale effect on laminated composite micro-plates is developed for the first time. Based on Hamilton's principle, the weak form for composite plate is established by using the Reddy's third order shear deformation theory without shear correction factor and the refined modified couple stress theory. Unlike the modified couple stress theory, which contains only one material length scale parameter, the proposed theory contains three material length scale parameters. To confirm the accuracy of the proposed method, several examples are presented, discussed and compared to references' solutions. In addition, cut-out complicated shapes are analyzed to show the influences of the small-scale effect on free vibration behaviors of laminated micro-plates. An increase in the material length scale parameter leads to decrease in the deflection, stresses and increase in frequencies and critical buckling load factor. The presented numerical results show the great efficiency of the NURBS-based isogeometric analysis for capturing the small-scale effect of the composite laminated micro-plates.

In this paper, a novel Three-Dimensional (3D) prefabricated Hollow Concrete Block (HCB), which can form seawall structures, is numerically investigated. Unlike the traditional gravity-type seawalls, this is a lightweight structure in comparison with the conventional ones, but it possesses advantageous features under complex loading conditions. The load bearing capacity of HCB itself under the wave loading has been examined. The highly complicated soil-structure interaction is taken into account so that the underlying simulation may predict realistic behaviors of seawall structures. The results indicate that this novel seawall model requires fewer concrete materials, but is adequate under sea wave attacks. For instance, stresses induced on seawall blocks are smaller than the allowed stresses of concrete. By adding sand into the HCB components to increase its weight and using supported-piles system, the stability of the seawall structure is enhanced and its settlement is reduced. The results obtained are evaluated using reference studies, from literature, regarding the elastic settlement of foundation. The techniques proposed in this paper, therefore, may provide an important pathway for further studies aiming to achieve optimal and reliable coastal designs taking into account the impacts of climate change.

In this paper, a creative and intelligent approach based on an inverse problem that accurately predicts crack location in plate structures is presented. The eXtended Finite Element (XFEM) and the eXtended IsoGeometric Analysis (XIGA) are combined with two optimization techniques, namely Particle Swarm Optimization (PSO) and Jaya algorithm to predict the crack location. The superiority of XIGA is demonstrated by using various NURBS orders to reduce the number of elements, provide fast simulation and achieve best convergence compared with XFEM. Four numerical-optimization techniques are considered in this paper, namely XFEM-Jaya, XIGA-Jaya, XFEM-PSO and XIGA-PSO. In the optimization techniques, the objective function minimizes the difference between the calculated and measured displacements and strains. Convergence studies for various positions of a crack and a hole in plates are performed and the results show that Jaya algorithm significantly performs more accurate and faster than PSO. In addition, the proposed techniques are validated using experimental data and another numerical-optimization technique, i.e. XFEM coupled with Genetic Algorithm (GA), presented in literature. The comparisons show that XIGA-Jaya performs the best of all considered techniques.

Fretting fatigue is a complex tribological phenomenon that can cause premature failure of connected components that have small relative oscillatory movement. The fraction of fretting fatigue lifetime spent in crack initiation and in crack propagation depends on many factors, e.g., contact stresses, amount of slip, frequency, environmental conditions, etc., and varies from one application to another. Therefore, both crack initiation and propagation phases are important in analysing fretting fatigue. In this investigation, a numerical approach is used to predict these two portions and estimate fretting fatigue failure lifetime under a conformal contact configuration. For this purpose, an uncoupled damage evolution law based on principles of continuum damage mechanics is developed for modelling crack initiation. The extended finite element method approach is used for calculating crack propagation lifetimes. The estimated results are validated with previously reported experimental data and compared with other available methods in the literature., The authors wish to thank the Ghent University for the financial support received by the Special Funding of Ghent University, BOF (Bijzonder Onderzoeksfonds), in the framework of project (BOF 01N02410) and gratefully acknowledge the financial support provided by the Spanish Ministry of Economics and Competitiveness through the project DPI2010-20990.

In this paper, Continuum Damage Mechanics (CDM) theory is applied to low cycle and high cycle fatigue problems. Damage evolution laws are derived from thermodynamic principles and the fatigue number of cycles to crack initiation is expressed in terms of the range of applied stresses, triaxiality function and material constants termed as damage parameters. Low cycle fatigue damage evolution law is applied to adhesively bonded single lap joint. Damage parameters as function of stress are extracted from the fatigue tests and the damage model. High cycle fatigue damage model is applied to fretting fatigue test specimens and is integrated within a Finite Element Analysis (FEA) code in order to predict the number of cycles to crack initiation. Fretting fatigue problems involve two types of analyses; namely contact mechanics and damage/fracture mechanics. The high cycle fatigue damage evolution law takes into account the effect of different parameters such as contact geometry, axial stress, normal load and tangential load.

This paper investigates the three-dimensional thermo-elastic deformation of cylindrical shells on two-parameter elastic foundations with continuously graded of volume fraction, subjected to thermal load. Suitable temperature and displacement functions that identically satisfy boundary conditions at the edges are used to reduce the equilibrium equations to a set of coupled ordinary differential equations with variable coefficients, which are solved by Generalized Differential Quadrature (GDQ) method. Results are presented for two-constituent isotropic and fiber-reinforced functionally graded cylindrical shells that have a smooth variation of volume fractions through the radial direction. Symmetric and asymmetric volume fraction profiles are presented in this paper. The fast rate of convergence of the method is demonstrated and comparison studies are carried out to establish its very high accuracy and versatility. Effects of stiffness of the foundation and variations of different parameters of generalized power-law distribution on steady-state responses of the functionally graded cylindrical shell resting on elastic foundation are discussed. In addition, the effects of the FGM configuration are studied by considering the mechanical entities of different FGM fiber-reinforced cylindrical shells resting on elastic foundation. Some results are presented for the first time and some important conclusions are drawn.