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Fretting fatigue is a combination of two complex mechanical phenomena. Fretting appears between components that are subjected to small relative oscillatory motions. Once these connected components undergo cyclic fatigue load, fretting fatigue occurs. In general, fretting fatigue failure process can be divided into two main portions, namely crack initiation and crack propagation. Fretting fatigue crack initiation characteristics are very difficult to detect because damages such as micro-cracks are always hidden between two contact surfaces. In this paper Continuum Damage Mechanics (CDM) approach in conjunction with Finite Element Analyses (FEA) is used to find a predictor tool for fretting fatigue crack initiation lifetime. For this purpose an uncoupled damage evolution law is developed to model fretting fatigue crack initiation lifetime at various fretting condition such as contact geometry, axial stress, normal load and tangential load. The predicted results are validated with published experimental data from literature.

Fretting is a phenomenon that occurs at the contacts of surfaces that are subjected to oscillatory relative movement of small amplitudes. Depending on service conditions, fretting may significantly reduce the service life of a component due to fretting fatigue. In this regard, the analysis of stresses at contact is of great importance for predicting the lifetime of components. However, due to the complexity of the fretting phenomenon, analytical solutions are available for very selective situations and finite element (FE) analysis has become an attractive tool to evaluate stresses and to study fretting problems. Recent laboratory studies in fretting fatigue suggested the presence of stress singularities in the stick-slip zone. In this paper, we constructed finite element models, with different element sizes, in order to verify the existence of stress singularity under fretting conditions. Based on our results, we did not find any singularity for the considered loading conditions and coefficients of friction. Since no singularity was found, the present paper also provides some comments regarding the convergence rate. Our analyses showed that the convergence rate in stress components depends on coefficient of friction, implying that this rate also depends on the loading condition. It was also observed that errors can be relatively high for cases with a high coefficient of friction, suggesting the importance of mesh refinement in these situations. Although the accuracy of the FE analysis is very important for satisfactory predictions, most of the studies in the literature rarely provide information regarding the level of error in simulations. Thus, some recommendations of mesh sizes for those who wish to perform FE analysis of fretting problems are provided for different levels of accuracy.

This paper presents an approach of inverse damage detection and localization based on model reduction. The problem is formulated as an inverse problem where an optimization algorithm is used to minimize the cost function expressed as the normalized difference between a frequency vector of the tested structure and its numerical model. A finite element model of bi-dimensional monolithic composite beam reinforced by a graphite-epoxy is used to define a numerical model of the tested structure in which different scenarios of damage are considered by stiffness reduction. Then, calculations are made on a reduced model built by the technique of proper orthogonal decomposition coupled by radial basis functions. The accuracy of the method is verified through different damage configurations. The results show that the developed algorithm is a feasible methodology of predicting damage in short computing time and with high accuracy. The effect of noise on the accuracy of the results is investigated in some cases for the structure under consideration. DOI: http://dx.doi.org/10.5755/j01.mech.21.6.12526

Fretting wear is the material damage of two contact surfaces caused by micro relative displacement. Its characteristic is that debris is trapped on the contact surfaces. Depending on the material properties, the shapes of the debris, and the dominant wear mechanisms, debris can play different roles that either protect or harm interfaces. Due to the micro scale of the debris, it is difficult to obtain instantaneous information and investigate debris behavior in experiments. The Finite Element Method (FEM) has been used to model the process of fretting wear and calculate contact variables, such as contact stress and relative slip during the fretting wear process. In this research, a 2D fretting wear model with a debris layer was developed to investigate the influence of debris on fretting wear. Effects of different factors such as thickness of the debris layer, Young's modulus of the debris layer, and the time of importing the layer into the FE model were considered in this study. Based on FE results, here we report that: (a) the effect of Young's modulus of the debris layer on the contact pressure is not significant; (b) the contact pressure between the debris layer and the flat specimen decreases with increasing thickness of the layer and (c) by importing the debris layer in different fretting wear cycles, the debris layer shows different roles in the wear process. At the beginning of the wear cycle, the debris layer protects the contact surfaces of the first bodies (cylindrical pad and flat specimen). However, in the final cycle, the wear volumes of the debris layers exhibit slightly higher damage compared to the model without the debris layer in all considered cases.

Damage detection and localization in civil engineering constructions using dynamic analysis has become an important topic in recent years. This paper presents a methodology based on non-destructive detection, localization and quantification of multiple damages in simple and continuous beams, and a more complex structure, namely two-dimensional frame structure. The proposed methodology makes used of Firefly Algorithm and Genetic Algorithm as optimization tools and the Coordinate Modal Assurance Criterion as an objective function. The results show that the proposed combination of Coordinate Modal Assurance Criterion and Firefly Algorithm or Genetic Algorithm can be easily used to identify multiple local structural damages in complex structures. However, the convergence rate becomes slower for the case of multiple damages compared to the case of single damage. The effect of noise on the algorithm is further investigated. It is found that the proposed technique is able to detect the damage location and its severity with high accuracy in the presence of noise, although the convergence rate became slower than in the case when no noise is present. It is also found that the convergence rate of Firefly Algorithm is much faster than that of Genetic Algorithm.

In this paper, a review of some techniques proposed in the literature for modelling crackinitiation in adhesively bonded joints is presented. The techniques reviewed are: a) the singular intensityfactor, b) the inherent flaw size, c) Cohesive-zone model (CZM) and d) Continuum Damage Mechanics(CDM). The singular intensity factor characterizes the stress singularity at the corner point and can beused as a failure criterion to predict crack initiation. The inherent flaw method technique assumes that asmall crack having a fraction of millimetres is initiated at the singular point in order to develop a fracturemechanics criterion for crack initiation. The strain energy release rate for an un-cracked specimen is usedto determine the size of the inherent flaw. The cohesive zone model (CZM) technique is based ondefining parameters from fracture mechanics test specimens and using them to model failure of the joints.Continuum Damage Mechanics makes use of thermodynamics principles in order to derive a damageevolution law. In this damage evolution law the damage variable (D) is expressed as a function of numberof cycles, applied stress range and triaxiality function. Furthermore, the possibility of using the eXtendedFinite Element Method (XFEM) to predict crack initiation is elaborated.

In the surgical process of total knee replacement (TKR), it is well known that the three types of failureswhich are; a) unable to reproduce normal knee function, b) bone-implant interface failure c) wear duringuse. These failures are certainly due to the motion and the load that influence the prosthesis components.In this study, the modelling questions of the human knee joint will be discussed in relation only to themultibody dynamics models. Firstly, a summary is presented about the relevant literature, where themodels with their different features are presented and evaluated. The existing models are mainly focusedon the investigation of the ligaments (linear of non-linear properties), the description of the contact path,and contact forces during the motion, kinematics (rotation, abduction and adduction) and even the wearmechanism of the knee joint. The primal advantages of the multibody dynamics models are the easyadaptability in the mechanical parameters to carry out simulations and the connection with CAE programsthat helps the design of new prostheses. A new multibody model is also presented by the authors.

Fretting fatigue is a combination of two complex mechanical phenomena, namely, fretting and fatigue. Fretting appears between components that are subjected to small relative oscillatory motion. Onc...

Fretting fatigue is a phenomenon in which two contact surfaces undergo a small relative oscillatory motion due to cyclic loading. There is a need to analyze the effects of contact geometry on crack propagation under fretting fatigue conditions. In this investigation, a finite element modeling method was used to study the effects of different contact geometries along with crack–contact interaction on crack propagation lifetime. Different contacts geometries—that is, cylindrical on flat and flat on flat—along with different contact span widths were analyzed. In addition, the effects of different contact spans on stress distribution at the contact interface were investigated. The computed crack propagation life was compared with experimental results. It was found that the crack initiated near the contact trailing edge for all contact geometries, which agreed with experimental observations. In terms of crack propagation for different contact spans, the fretting fatigue life for a two-based cylindrical pad was...

Fretting fatigue damage occurs in contacting parts when they are subjected to fluctuating loadings and sliding movements at the same time. This phenomenon may occur in many applications such as bearings/ shafts, bolted and riveted connections, steel cables, and steam and gas turbines. In this paper, the effect of elevated temperature on fretting fatigue life of Al7075-T6 is investigated using a new device for fretting fatigue tests with variable crank shaft mechanism. Also a finite element modeling method was used to estimate crack propagation lifetime in aluminum alloy, Al7075-T6 specimens at elevated temperature under fretting condition. In this method, shear and normal stresses that are caused by contact load are updated at each crack growth increment. Finally, a comparison between the experimental and numerical results is done in order to evaluate the FE simulation. Department of mechanical engineering, Islamic Azad University, Takestan Branch, Takestan, Iran The experimental results show that: (i) fretting fatigue life of the material increases with temperature up to 350°C by 180% for low stresses and decreases by 40% for high stresses, (ii) this fashion of variation of fretting fatigue life versus temperature is believed to be due to degradation of material properties which occurs by overaging and wear resistance increase due to oxidation of aluminum alloy. While overaging gives rise to degradation of mechanical strength of material and hence the reduction of its fretting fatigue life, surface oxidation of the specimens brings some improvement of fatigue behavior of the material. Metallurgical examination of the specimens reveals that temperature results in precipitation of impurities of al-7075-T6. The size of precipitated impurities and their distances gets bigger as temperature increases. This could be a reason for material degradation of specimens which are exposed to heating for longer time duration.

This study presents an intermediate step in prosthesis design, by introducing a newly developedtwo-dimensional mathematical, and a three-dimensional computational knee model. The analytical model isderived from Newton’s law with respect to the equilibrium equations, thus based on theoreticalassumptions, and experimentally obtained parameter. The numeric model is built from an existingprosthesis, involving three parts as patella, femur and tibia, and currently it is under development. Themodels are capable to predict – with their standard deviation – the patellofemoral (numerically tibiofemoralas well) forces in the knee joint during squatting motion. The reason why the squatting is investigated is dueto its relative simplicity and the fact, that during the movement the forces reach extremity in the knee joint.The obtained forces – as a function of flexion angle – are used firstly as fundaments to the knee designmethod, and secondly to extend the results related to the existing isometric kinetics, where one of the newlyobtained functions appears as an essential – and so far missing – input function. Most results arecompared and validated to the ones found in the relevant literature and put into a dimensionless form inorder to have more general meaning.

Fretting fatigue occurs when two contact bodies undergo small oscillatory relative motion due to cyclic loading. It leads to fretting damage, which reduces the service life of the bodies in contact. This can be explained by the high stresses generated at the contact surface between the two bodies. Therefore, numerical analysis, such as Finite Element Analysis (FEA), would be useful to understand the fretting fatigue phenomenon and to investigate techniques to reduce its effect on fatigue lifetime of mechanical components. In this paper, FEA of fretting fatigue Aluminum specimen is carried out in order to study the stress distribution and crack initiation location. Two commercial FEA packages, namely ANSYS and ABAQUS are used to analyze the specimen. The stress distribution along the contact surface between the two bodies obtained using both codes is compared and analyzed.

The excursion of the center of gravity (COG) line is often examined in terms of balance control, standing, walking or running locomotion, etc. Although these examinations are carried out on multiple human subjects, the obtained results are not bound to any “human-like” quantity such as the anatomically well-defined and widely accepted angle of flexion. This paper is meant to prove the following hypotheses: the horizontal excursion of the COG line changes its position during squatting in contrary with steady-state assumption and it can be derived as a single empirical function of flexion angle. A test setup was developed for the experiments, alongside with an experiment protocol and a special construction method to obtain the results. During the experiments, 16 healthy, male and female participants’ data were used as a basis for the dimensionless λfunctions. The results showed common characteristics between the subjects’ data, and suggested that the general relationship between the squatting and the excursion of COG can be described with linear, dimensionless functions. As a final goal of this study, the obtained dimensionless functions will be used in a mathematical model, which is being developed.

Welds unavoidably show defects, which can negatively affect the integrity of the entire structureand, worst case, result in a failure. Defects of a considerable size should therefore be detected, assessedand, if necessary, repaired. The assessment of a defect requires a procedure which allows a conservativeestimation of the acceptability of the defect. To develop such procedure, both experimental and numericalresearch is performed. This paper describes the inherent possibilities and limitations of numerical researchthrough finite element modelling, as compared to experimental research. Summarizing all arguments, itbecomes clear that numerical research is a highly powerful tool, but a thorough experimental validation is ofparamount importance. Moreover, some specific weld-related problems are highly difficult to address,namely the presence of stable crack growth and material heterogeneity. More research is needed toachieve a description of these phenomena, under a set of conservative assumptions.

This paper presents the application of the Finite Element Method (FEM) to a wide range of physical engineering problems and analysis types. It summarises some of the research works carried out by the author using FEM. The types of analysis, which are coved in this paper, include linear and non-linear stress analysis, heat transfer analysis, diffusion analysis, coupled thermal-stress and coupled diffusionstress analysis, fracture mechanics analysis and modelling of macro-cracks, fatigue damage initiation and crack propagation analysis, modal analysis, transient dynamics analysis and traffic flow analysis.

In this paper, a finite element sub-modelling method is used to estimate the stress distribution and the crack propagation lifetime in Aluminium alloy, Al7075-T6 specimens. Different contact geometries, i.e. cylinder-on-flat and flat-on-flat, and different contact span width’s with different pad’s compression forces are analysed. It is found that fretting fatigue life for two based cylindrical pads is shorter than that for two based flat pads and in two based flat pads is shorter than that for perfectly flat pads. In the case of two based flat pads, stress distribution in the pad with width of 3.1 mm is about 14% higher than that in the pad with the width of 6.2 mm and about 21% higher than that in the pad with the width of 9.3 mm. Similarly, stress in cylindrical pads with width of 3.1 mm is 36% higher than that in the pad with width of 6.2 mm and 130% higher than that in the pad with width of 9.3 mm. Stresses increased by 21% for pad force of 1800 N and around 40% for pad force 2400 N compared with 1200 N pad force. Also it is observed that by increasing pad width for both flat and cylindrical pads, crack propagation lifetime increased. Furthermore, fretting fatigue crack growth rate raises when pads compression force increases.

The analysis of fretting fatigue plays an important role in many engineering fields. The presence of heterogeneity may affect the performance of a machine or a structure, including its lifetime and stability. In this paper, the effect of randomly distributed micro inclusions on the fretting fatigue behaviour of heterogeneous materials is analysed using the finite element method (FEM) for different sizes, shape and properties of inclusions. The effect of micro inclusions on macroscopic material properties is also considered by representative volume element (RVE). It is shown that the influence of micro inclusions on macroscopic material properties cannot be ignored, and the shape and size of the inclusions have less effect on the macroscopic material properties as compared to the material properties of inclusion and volume ratio. In addition, various parameters of inclusions have little effect on the peak tensile stress, which remains almost the same as homogeneous material. Peak shear stress occurs at many places inside the specimen, which can result in multiple cracking points inside the specimen, as well as at the contact surface. Moreover, the stress band formed by the stress coupling between adjacent inclusions may have an important influence on the direction of crack growth.

To assemble pipelines and tubular structures, threaded couplings can be used. In service these couplings are often subjected to dynamic loads. To maintain a secure connection, they are generally preloaded. The combination of preload and external dynamic loads results in a multiaxial stress distribution over the connection, where the coupling’s threads act as stress raisers, initiating fatigue cracks. The fatigue life of the connection depends on its global geometry, local thread geometry, interface and material properties. In this study the fatigue life of standard API Line Pipe couplings and two modified coupling configurations is determined experimentally. The influence of the coupling’s global geometry on the connection’s fatigue life was studied. Threaded pipe samples with a nominal size of 1” were tested on a four-point bending fatigue test setup. A sample was considered to be failed when a through thickness crack appeared. This was detected by pressurizing the tube samples. When a pressure drop was recorded, the test was stopped. The number of elapsed load cycles defines the fatigue life of the connection. Using this methodology, S-N curves were obtained for the standard API Line Pipe connection and two modified coupling configurations. Both configurations exhibited an improved fatigue life relative to the standard connection. In the final part of this paper, these experimental observations are explained by a combination of a damage evolution law and a finite element model.

The damage parameters for crack initiation in a single lap joint (SLJ) are determined by combining continuous damage mechanics, finite element analysis (FEA) and experimental fatigue data. Even though a SLJ has a simple configuration, the stresses in the adhesive region are quite complex and exhibit multi-axial states. Such a condition leads to the need to introduce a general value for the triaxiality function in the damage evolution law rather than using a triaxiality function which equals unity, as in the case of a uni-axial stress state, e.g., the bulk adhesive test specimen presented in Part 1 of this paper. The effect of stress singularity, due to the presence of corners at edges, also contributes to the complex state of stress and to the variability of the triaxiality function along the adhesive layer in a SLJ. The damage parameters A and β determined in Part 1 for bulk adhesive are now extended to take into account the multi-axial stress state in the adhesive layer, as calculated from FEA.

A mesh-independent continuum damage model has been proposed to predict the residual strength of adhesively bonded joints by introducing a displacement-based damage parameter into the constitutive equation of damaged materials. Joints bonded with a ductile adhesive EA9321 were studied for a range of environmental degradation. The moisture-dependent damage parameter for EA9321 was calibrated using an aged, mixed-mode flexure (MMF) test. The parameter was then used without further modification to model failure in aluminium and composite single-lap joints (SLJ) bonded with the same adhesive. The finite element analysis (FEA) package ABAQUS was used to implement the coupled mechanical-diffusion analyses required. The elastic–plastic response of the adhesive and the substrates, both obtained from the bulk tensile tests, were incorporated. A von Mises yield model was considered and both 2D and 3D modelling were undertaken and the results compared. The predicted joint residual strengths agreed well with the corresponding experimental data and the damage propagation pattern in the adhesive was also predicted correctly. The mesh independence of the model was demonstrated. This continuum damage model provides a means of predicting environmental degradation in ductile adhesive-bonded joints, where failure is predominantly within the adhesive layer.

The long-term durability of adhesively bonded aluminium, composite and dissimilar substrate joints exposed to humid environments has been investigated. Failure of the joints was modelled with a cohesive zone model (CZM) approach where the governing parameters were determined from fracture mechanics test specimens saturated in a range of humid environments. The reduction in residual strength of an aluminium single lap joints (SLJ) immersed in de-ionised water was successfully predicted. For joints submerged in tap water the degradation was faster than predicted and there were signs of corrosion. XPS analysis carried out on the failure surfaces indicated that the more severe degradation might have been due to cathodic delamination. There was some discrepancy between the experimental and the predicted results of the aged composite SLJ. Composite failure might have contributed to this, which was not included in the modelling. Large residual stresses were induced in the dissimilar substrate joints due to the mismatch of coefficients of expansion of the substrates. The evolution of the total residual strains (thermal and swelling) was modelled. The residual stresses were seen to relax but were still significant even after exposure for a year. The predicted degradation overestimated the residual strength of the double lap joints (DLJ). It is suggested that this may be due to a residual stress-enhanced degradation mechanism.

This paper describes a dynamic test carried out on intact and damaged FRP composite beams with fixed-fixed boundary condition. Hammer excitation is used to excite the beam at fixed locations. The modal parameters are extracted from the time response using a time domain analysis, i.e. the stochastic subspace identification technique. In order to introduce damage, two sections of the beam are bonded together using an epoxy adhesive, and then a static test is carried out. For the static test, a 3-point bending -configuration is used, i.e. the beam is fixed at both ends and a static load is gradually applied in the middle of the beam using a screw jack. Different static load steps, and in turn different damage stages, are considered. After each load step, dynamic measurements are carried out. The results obtained from both tests are presented and analysed.

The associations between several measures of low employment quality and some specific health and safety outcomes have become the subject of more recent investigation. The main objective of our study is to examine the relationships between irregular work arrangements indicators including contract type, long working hours, multiple jobs, shift work, and occupational injuries, taking into account several sociodemographic and work characteristics.

The use of a cohesive zone model (CZM) to predict the long-term durability of adhesively bonded structures exposed to humid environments has been investigated. The joints were exposed to high relative humidity (RH) environments and immersion in both tap and deionised water for up to a year before quasi-static testing to failure. Both stressed and unstressed conditions during aging were considered. The degradation was faster for the stressed joints and for those joints immersed in the more corrosive environments. Two mechanisms were suggested to explain this behaviour: cathodic delamination and stress-enhanced degradation. In the model, the cohesive zone parameters determine the residual strength of the joints. The degradation of these parameters was, in the first instance, related directly to the moisture concentration. The model was then extended to include degradation due to stress and more corrosive environments. Good correlation between the numerical modelling and the experimental results was obtained.

A cohesive zone model (CZM) has been used in conjunction with both elastic and elasto– plastic continuum behaviour to predict the response of a mixed mode flexure and three different lap shear joints, all manufactured with the same adhesive. It was found that, for a specific dissipated CZM energy (Γ0) there was a range of CZM tripping tractions (σu) that gave a fairly constant failure load. A value of σu below this range gave rise to global damage throughout the bonded region before any crack propagation initiated. A value above this range gave rise to a discontinuous process zone, which resulted in failure loads that were strongly dependent on σu. A discontinuous process zone gives rise to mesh dependent results. The CZM parameters used in the predictions were determined from the experimental fracture mechanics specimen test data. When damage initiated, a deviation from the linear load–displacement curve was observed. The value for σ uwas determined by identifying the magnitude that gave rise to the experimentally observed deviation. The CZM energy (Γ 0) was then obtained by correlating the simulated load-crack length response with corresponding experimental data. The R-curve behaviour seen with increasing crack length was successfully simulated when adhesive plasticity was included in the constitutive model of the adhesive layer. This was also seen to enhance the prediction of the lap shear specimens. Excellent correlation was found between the experimental and predicted joint strengths.

A cohesive zone model used to predict the residual strength of degraded adhesively bonded lap joints is presented in this paper. Interfacial failure of adhesive joints for a range of degradation was studied. A mixed mode interfacial rupture element was proposed with a traction-separation law. The two moisture dependent fracture parameters, fracture energy and tripping traction, were calibrated using a mixed mode flexure (MMF) test and finite element analyses. These parameters were used to model the thick adherend shear test (TAST) and single lap joint (SLJ) configurations without further modification. The ABAQUS FEA package was used to implement the coupled mechanical-diffusion analyses. The plasticity of the substrates was incorporated successfully and the predicted joint residual strengths agree well with the corresponding experimental data.

A progressive cohesive failure model has been proposed to predict the residual strength of adhesively bonded joints using a moisture-dependent critical equivalent plastic strain for the adhesive. Joints bonded with a ductile adhesive (EA9321) were studied for a range of environmental degradations. A single, moisture-dependent failure parameter, the critical strain, was calibrated using an aged, mixed-mode flexure (MMF) test. The mesh dependence of this parameter was also investigated. The parameter was then used without further modification to model failure in aluminum and composite single-lap joints (SLJ) bonded with the same adhesive. The FEA package ABAQUS was used to implement the coupled mechanical-diffusion analyses required. The elastic–plastic response of the adhesive and the substrates, both obtained from the bulk tensile tests, were incorporated. Both two-dimensional and three-dimensional modelling was undertaken and the results compared. The predicted joint residual strengths agreed we...

This work is concerned with developing numerical modelling techniques for predicting the environmental degradation of adhesively-bonded joints. Associated experimental data are also reported. The moisture-dependent mechanical properties of the adhesive were obtained by testing bulk specimens also exposed to various moisture contents. The diffusion parameters for moisture in the adhesive were determined by carrying out gravimetric experiments on bulk adhesive samples. The moisture-dependent interfacial bond strength of the adhesive system investigated has been determined by testing a mixed mode flexure (MMF) specimen, exposed to obtain various levels of moisture content at the interface. Progressive damage in the joints was modelled with a two-parameter cohesive zone model (CZM). The CZM parameters were determined by correlating the experimental data obtained from the MMF test with results from the numerical simulation. The parameters were then used to predict the response of another configuration, the not...

A comparison of the different methods used to calculate strain energy release rate in bonded DCB joints has been made. The standard beam theory method has been shown to be in error and models with a compliant crack front have been evaluated in search of a more reliable analytical method. It is found that in fatigue testing, a beam on elastic foundation (BEF) model gives excellent results and a simple form of the BEF equation is proposed.

Adhesive bonding has become a powerful joining technique during the last few decades. It has many applications in aerospace, automotive and other industries. One of the major advantages of adhesive bonding, compared to riveting or welding, lies in its superior fatigue resistance. In this paper, fatigue crack propagation in adhesively bonded joints is analysed and discussed. Three different bonded joints are considered in this study, namely Double Cantilever Beams, Single Lap Joints and Double Lap Joints. Experimental samples were made from carbon fibre composite substrates bonded with an epoxy adhesive. The joints were tested in constant amplitude fatigue at different loads and plots of load against number of cycles to failure were obtained. A crack propagation law was then derived from the experimental results of the Double Cantilever Beam and implemented in a finite element based predictive tool in order to predict the number of cycles to failure for Single Lap and Double Lap joints subjected to cyclic fatigue loading. The prediction technique is based on numerically integrating the crack growth law along the bonding line from an initial crack length to a final crack length. A comparison of mode I strain energy release (G(I)) and total strain energy release rate (G(T)) as failure criteria in the prediction procedures is presented.

The fast growth of non-standard employment in developed countries highlights the importance of studying the influence of contract type on worker's safety and health.The main purpose of our study is to investigate whether non-standard workers are more injured than standard workers or not. Additionally, other risk factors for occupational accidents are investigated.Data from the Belgian surveys on work ability in 2009 and 2011 are used. During their annual occupational health examination, workers were asked to fill in a self-administered questionnaire. In total, 1886 complete responses are collected and analyzed using logistic regression.Temporary workers did not have higher injury rates than permanent workers [OR 0.5, 95% confidence interval 0.2-1.2]. Low-educated, less-experienced workers and those exposed to dangerous conditions are more frequent victims of occupational accidents.The present data do not support the hypothesis that non-standard workers have more injuries than standard workers. Our results about occupational accidents derived from a non-representative sample of the Belgian workforce and cannot be generalized due to the heterogeneity in job organization and labor regulations between countries. Further research is needed to extend our findings and to seek other factors that may be associated with work accidents.

Experimental studies have been undertaken that provide the fracture energy of an epoxy-steel interface that has been exposed to various uptake levels of moisture. The test configuration used for these studies is the mixed mode flexure (MMF) test. The specimens have been exposed to the moist environment as open-faced specimens. The results provided by the test show a steady degradation in the interface fracture energy with increasing moisture content. Surface characterisation techniques such as X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to characterise the nature of the failure surfaces. Both of these analyses show a reduction of adhesive fragments and carbon overlayer thickness on the steel fracture surface with increasing moisture levels. The variation of carbon overlayer thickness with moisture exhibits a similar trend as the fracture energy, indicating that the two may be related.

Output-based structural damage detection is becoming increasingly appealing due to its potential in real engineering applications without any restriction regarding excitation measurements. A new transmissibility-based damage detection approach is presented in this study by combining transmissibility with correlation analysis in order to strengthen its performance in discriminating damaged from undamaged scenarios. From this perspective, damage detection strategies are hereafter established by constructing damage-sensitive indicators from a derived transmissibility. A cantilever beam is numerically analyzed to verify the feasibility of the proposed damage detection procedure, and an ASCE (American Society of Civil Engineers) benchmark is henceforth used in the validation for its application in engineering structures. The results of both studies reveal a good performance of the proposed methodology in identifying damaged states from intact states. The comparison between the proposed indicator and the existing indicator also affirms its applicability in damage detection, which might be adopted in further structural health monitoring systems as a discrimination criterion. This study contributed an alternative criterion for transmissibility-based damage detection in addition to the conventional ones.

A three-dimensional metallo-thermo-mechanical analysis of bead on plate welding is performed in this work. This coupled model enables to capture the microstructural development and temperature history at local region. As a result, the residual stress is evaluated based on the temperature-dependent mechanical properties computed by the mixture of individual phase. Isotropic hardening is assumed in the finite element (FE) analysis. At the same time, the distribution of residual stress is also predicted by treating the mechanical properties as integral values of sheet metal. The two simulated fields of stress and strain after welding are analysed and compared. Moreover, as it is known that welding changes the mechanical properties of the original material, especially in fusion zone (FZ) and heat affected zone (HAZ), the stress and strain data at interested areas (HAZ and FZ) are subtracted for comparison. The predicted stress and strain fields are imported to subsequent simulation of standard tensile test. The stress-strain curves are compared with the one of base material. It is found that residual stress has significant influence on the structural performance of weld joints.

Fretting is a small oscillatory relative motion between two normal loaded contact surfaces. It may cause fretting fatigue, fretting wear and/or fretting corrosion damage depending on various fretting couples and working conditions. Fretting fatigue usually occurs at partial slip condition, and results in catastrophic failure at the stress levels below the fatigue limit of the material. Many parameters may affect fretting behaviour, including the applied normal load and displacement, material properties, roughness of the contact surfaces, frequency, etc. Since fretting damage is undesirable due to contacting, the effect of rough contact surfaces on fretting damage has been studied by many researchers. Experimental method on this topic is usually focusing on rough surface effects by finishing treatment and random rough surface effects in order to increase fretting fatigue life. However, most of numerical models on roughness are based on random surface. This paper reviewed both experimental and numerical methodology on the rough surface effects on fretting fatigue.

System identification performs as a core issue in structural dynamic analysis. In this study, transmissibility coherence is introduced for system identification with recalling the existing techniques based on transmissibility. Unlike previous approaches that require four-point measurement, the proposed methodology in this study only requires two-point measurement. The merit behind this approach is that the transmissibility coherence can be employed to estimate the subtraction of transmissibility between two reference points, by using auto- and cross-spectrum analysis. Verification using experimental data proves the feasibility of the proposed technique.

Los modelos analiticos disponibles para calcular las fuerzas patelofemorales de la rodilla estan limitados al movimiento estandar de cuclillas cuando el centro de gravedad es fijo horizontalmente. En este articulo se presenta un modelo para calcular con exactitud las fuerzas patelofemorales, teniendo en cuenta el cambio de posicion del centro de gravedad del tronco durante una sentadilla profunda (posicion de sentadilla modificada). Se valida la exactitud del modelo desarrollado mediante comparaciones con resultados de la tecnica de dinamica inversa.

Vibration-based damage detection techniques use the change in modal data as an indicator to assess damages in the structure. Knowing the structural dynamic characteristics of the healthy and damaged structure, the estimation of the damage location and severity is possible by solving an inverse problem. This paper presents a mathematical expression relating damage location and depth to the frequency shifts of the bending vibration modes. This expression permits the extraction of a series of coefficients that characterize each damage location and are independent of the damage severity. The vector aggregating these coefficients for a given location constitutes a Damage Location Indicator (DLI) that unambiguously characterizes the position of a geometrical discontinuity in the beam. A set of vectors typifying all locations along the beam may be used as patters opposable to the damage signature found by measurements. The similarity between the signature and one of the patterns indicates the location of damage.

This paper describes different experimental techniques for obtaining modal parameters of structures. Attention is focused on those techniques that may be applicable to in situ concrete structures (e.g. bridges). In a first stage, experiments are made on reinforced concrete beams of 6 meters length. The beams are excited using three types of excitation methods: impact hammer excitation and two different electromagnetic shaker signals: pseudo-random and swept-sine signals. The modal parameters are determined either by performing curve-fitting procedures on series of measured frequency response functions or by applying the stochastic subspace identification technique to the time response signals of the structure. The influence of the non-linear behaviour of the concrete beams is investigated by performing measurements at different excitation amplitudes. It appears that modal parameter estimates are affected by excitation techniques, data acquisition parameters and processing methods. The main cause of this is the non-linear behaviour which is observed even at very low vibration amplitudes. However, the influence on resonant frequencies and mode shapes is negligible. This is not the case for the modal damping ratios, so that the estimation of these parameters is unreliable.

Damage detection in civil engineering structures using the change in dynamic system parameters has gained a lot of scientific interest during the last decade. By repeating a dynamic test on a structure after a certain time of use, the change in modal parameters can be used to quantify and qualify damages. To be able to use the modal parameters confidentially for damage evaluation, the effect of other parameters such as excitation type, ambient conditions,... should be considered. In this paper, the influence of excitation type on the dynamic system parameters of a highway prestressed concrete bridge is investigated. The bridge, B13, lies between the villages Vilvoorde and Melsbroek and crosses the highway E19 between Brussels and Antwerpen in Belgium. A drop weight and ambient vibration are used to excite the bridge and the response at selected points is recorded. A finite element model is constructed to support and verify the dynamic measurements. It is found that the difference between the natural frequencies measured using impact weight and ambient vibration is in general less than 1%.

For the purpose of damage evaluation, this paper studies the effect of temperature variations on modal parameters recorded at two different times in a prestressed concrete highway bridge. A drop weight and ambient vibration were used to excite the bridge. A finite element model was developed to support and verify the dynamic measurements. The effects of temperature change on the structure's natural frequencies are analyzed and interpreted. (A)

Damage assessment based on the vibration response of structures has been, in the last decades, an important research area in various engineering branches. It integrates knowledge from a variety of disciplines, such as mechanical and structural engineering, material science, computer science and signal processing, and data management. This special issue is dedicated to fundamental understanding of the vibrational behavior of damaged structures and to the development of methods and techniques that are able to tackle these specific problems. A number of 23 papers have been submitted, from which a total of 7 papers have been finally selected to integrate the present issue. Two among them are focused on failures in machineries: W. Wen et al. in the paper “Planetary Gearbox Fault Diagnosis Using Envelope Manifold Demodulation” extract fault characteristics from the vibration signals, since in “Undecimated Lifting Wavelet Packet Transform with Boundary Treatment for Machinery Incipient Fault Diagnosis” by L. Duan et al. a Volterra series assisted undecimated lifting wavelet packet transform is investigated for machinery incipient fault diagnosis. The presented approaches dramatically enhance the weak defect feature extraction. Damages in structural elements are the target of research presented in “Development of a Vehicle-Bridge-Soil Dynamic Interaction Model for Scour Damage Modelling” by L. Prendergast et al., “Feature Recognition forMine HoistingWire Rope Based on Magnetic Flux Leakage Signals” by Z. Zhao et al., and “Experimental Study on Progressive Collapse Performance of Frame with Specially Shaped Columns Subjected to Middle Column Removal” by T. Wang et al. A model updating strategy for bolt-ball joint stiffness characterization for health monitoring is presented in “Finite Element Model Fractional Steps Updating Strategy for Spatial Lattice Structures Based on Generalized Regression Neural Network” by C. Liu et al. An interesting method to perform efficient fatigue tests is proposed by Y. Jiang et al. in the paper “Experimental Design and Validation of an Accelerated Random Vibration Fatigue Testing Methodology.” They succeed to significantly reduce the test time and the sample size. The papers reflect, without doubt, significant researches and developments of this subject. We hope that readers will find all articles of the special issue useful and exciting and that the articles will stimulate further research activities in the area of damage assessment.

Threaded pipe connections are used to connect well casing, well tubing, drill pipes and risers.For many of these applications fatigue resistance plays an important role. In this study the fatigueproperties of threaded connections are studied using a combination of finite element modelling andexperimental testing. Using 2D axisymmetric FE analysis several connections are compared. It is shownthat the load distribution over the engaged threads is an important feature. Experimental tests are carriedout on three setups. A small scale four-point bending setup is used to develop S-N curves. An S-N curve fora standard API Line Pipe connection is compared to an S-N curve for a connection that showed animproved load distribution over the engaged threads in the FE analysis. On a medium scale four-pointbending setup, strains together with crack opening are measured. The strain measurements are comparedwith the strains obtained by the numerical model. Finally a full scale resonant bending fatigue setup ispresented, which will be used in future testing of pipe connections ranging from 168 mm (6”) to 508 mm(20”) in diameter.