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Denting, a common geometric defect in oil and gas pipelines, can threaten the structural integrity and safety of pipelines. A pipeline dent is usually caused by the collision or extrusion of hard objects during the pipeline construction and service stages. Some rebound occurs in the dented zone when the external load is removed. In actual engineering, unconstrained dents tend to reround with increasing internal pressure of the pipeline. This study experimentally and numerically investigated the processes of springback and rerounding of a dented pipeline. First, full-scale testing was carried out to simulate the springback and rerounding processes, and the strain variations at the dent were measured. Then, a 3-dimensional numerical model was developed and then validated against the experimental results. According to the experimental and numerical results, the stress and strain responses of the pipeline during the springback and rerounding processes were studied in detail. Furthermore, the factors influencing the springback and rerounding coefficients were discussed. Finally, equations for predicting the springback and rerounding coefficients of dented pipelines were proposed on the basis of a nonlinear regression analysis. The results show that mainly elastic recovery occurs during springback. After a dent is unloaded, the elastic strain and von Mises stress of the pipeline decrease greatly, while the plastic strain remains unchanged. The elastic strain increases with increasing internal pressure. The springback and rerounding coefficients increase with increasing indenter diameter and diameter-to-wall thickness, while the loading depth has a negative effect on these coefficients. The proposed formulas can be used as a reference for estimating the ratios of dent springback and rerounding of dented pipelines. • Springback and re-rounding processes of a dented pipeline were experimentally and numerically investigated. • The variations in stress and strain in the processes of springback and re-rounding were analysed in detail. • Effects of dent and pipeline geometry on the springback and re-rounding behavior were examined. • New predictive formulas of springback and re-rounding coefficients for dented pipelines were derived. [ABSTRACT FROM AUTHOR]

• Model-based method to assess pipe dent due to external interference by excavators. • Numerical scheme for calculating excavator maximum force and kinetic energy. • Excavator-pipe interaction model suitable for static and dynamic contacts. • Dent charts for selecting the excavator to be employed to avoid damaging the pipe. • Preventive action that involve limiting the excavator workspace for risk mitigation. Despite the presence of numerous safety precautions, the primary cause of damage to underground pipes is often attributed to external interference from excavators during their operations. To address this issue, this paper introduces a model-based approach that incorporates both static and dynamic contact in assessing the damage caused by excavators on pipes. The objective of this method is to offer a practical tool that can assist in determining the appropriate excavator size for buried gas pipes. By identifying the maximum safe excavator size, the aim is to minimize the potential risks of mechanical damage to the pipe, to prevent hazards for operators and to protect the integrity of the pipeline. For this purpose, a comprehensive excavator model is constructed. Following this, a suitable damage model for the pipe is selected and the interaction between the bucket tooth and the pipe is modelled. To enhance accuracy, the excavator and pipe are interconnected through the solution of damped contact equations, which take into account the stiffnesses of both the pipe and excavator, as well as the damping effect resulting from pipe deformation. Results provide valuable insight into the potential damage caused to the pipe, which can be attributed to either static or dynamic contacts, depending on which excavator is being used. Failure is addressed by plastic dent, that can be avoided by selecting the most suitable excavator size. Moreover, the analysis of dent depth caused by various excavators on different pipes for gas transmission, opens to the possibility of mitigating the risk of failures by limiting the excavator workspace. [ABSTRACT FROM AUTHOR]

Comme pour tout traitement, la prescription d'inhibiteurs de la résorption osseuse (IRO) implique de mettre en balance les bénéfices et les risques attendus du traitement. Peu fréquente mais invalidante, l'ostéonécrose des mâchoires d'origine médicamenteuse (ONM) n'en reste pas moins l'effet indésirable le plus redouté des patients(e)s comme de certains professionnels de santé, possiblement en rapport avec une méconnaissance des éléments constituant cette balance bénéfices/risques. Une approche multidisciplinaire concertée, la prévention primaire via la réalisation systématique d'un bilan bucco-dentaire préthérapeutique dès lors que la situation clinique le permet, mais aussi l'instauration d'un suivi oral régulier permettent de considérablement limiter le risque d'ONM associé aux IRO, de faciliter l'adhérence au traitement et d'améliorer la qualité des soins. Prescription of bone resorption inhibitors implies a thorough evaluation of associated risks weighed against expected benefits. Although quite infrequent but highly debilitating, medication-related osteonecrosis of the jaw (MRONJ) is the most highly feared complication of such treatments, both by patients and some healthcare professionals. A concerted multiprofessional approach, primary prevention via systematic oral health examination as whenever possible, but also regular follow-up with an oral health professional, could all help limit the risk of MRONJ, increase patient adherence to treatment and improve the overall quality of care. [ABSTRACT FROM AUTHOR]

Although the first identification of an Asian spinosaurid theropod, Siamosaurus suteethorni from the Sao Khua Formation of Thailand, was published in 1986, what was in all likelihood a spinosaurid tooth was collected from the type section of the Sao Khua Formatio in the course of a stratigraphic survey of the Khorat Plateau (north-eastern Thailand) as early as 1962. The specimen, the present whereabouts of which are unknown, was described in 1963 as an ichthyosaur tooth, but apparently was the first dinosaur specimen to be reported from Thailand. On the basis of the description and figures, it is referred to the spinosaurid genus Siamosaurus. A purported plesiosaur tooth from the Phu Kradung Formation, described in the same paper, apparently belonged to a crocodile. The reasons for the initial misidentification of the spinosaurid tooth are reminiscent of those of other misinterpretations of similar teeth found in other parts of the world. [ABSTRACT FROM AUTHOR]

Much research has been conducted on circular hollow steel tubes subjected to indentation loads, but the response of a circular hollow steel tube when subjected to a combination of an indentation load (the load applied by an indenter) acting together with other loading conditions has received markedly less appraisal. An experimental study was conducted on two groups of circular hollow steel tubes that were either free-spanning or were base-supported. These tubes were first subjected to a uniform axial pre-compression, which is the most common service load across many tube applications, followed by the application of indentation loads while the magnitude of axial pre-compression was maintained. Strength, top surface and mid-height cross-sectional deformation, longitudinal and circumferential strains, and the failure mechanism of the tubes were compared, with a significant difference found between the response of the two groups of tests, and with this difference increasing as the magnitude of axial pre-compression and indenter displacement were increased. Additionally, it was identified that for the same level of absorbed energy, a deeper dent was produced for base-supported tubes than for free-spanning specimens. Moreover, analytical equations available in the literature were compared to the experimental results and good correlation was found between the experiments and the predictions. Bases-supported and free-spanning tubes are compared as below: • Both tube groups had similar indentation strength within the elastic range • Base-supported tubes had greater indentation strength within the inelastic range • A deeper dent formed in base-supported tubes for the same energy absorbed • Larger strains formed in the base-supported tubes • Modifications were made to analytical models to predict tubes indentation strength [ABSTRACT FROM AUTHOR]

In this work, a three-dimensional finite element-based mechanics-diffusion coupling model is developed to determine the stress/strain distribution and hydrogen (H) atom concentration at an unconstrained dent on an X52 steel pipe which is to be used for transport of high-pressure hydrogen gas. Both von Mises stress and equivalent plastic strain concentrations and a high hydrostatic stress gradient exist at the dent. The distribution of H atom concentration coincides with that of the hydrostatic stress. The maximum H atom concentration in the steel lattice locates at the dent bottom, while the distribution of the H atom concentration at metallurgical traps is consistent with that of the equivalent plastic strain. A competitive effect exists between the hydrostatic stress and the plastic strain on the H atom distribution. At low initial H atom concentrations (e.g., 0.001 mol/m3), the equivalent plastic strain dominates the distribution of H atoms. At high initial H atom concentrations (e.g., 0.1 and 1 mol/m3), the hydrostatic stress is more important to determine the distribution of H atom concentration. As the dent depth increases, both the von Mises stress and plastic strain at the dent increases, while the total H atom concentration decreases due to decreased hydrostatic stress. When the internal pressure increases from 5 MPa to 15 MPa, there are slightly increases in von Mises stress, equivalent plastic strain and the total H atom concentration. • A novel numerical model to determine the hydrogen atom distribution at a dent on pipelines. • The effect of internal pressure and dent depth on hydrogen atom accumulation at the dent. • The quantitative evaluation and location of hydrogen atom distribution at the dent. [ABSTRACT FROM AUTHOR]

• Failure indications were identified at the kinked dent location. • Micro-cracks related to the corrosion process was confirmed in the dent region. • FEM models date the crack indications to the pipe manufacturing process. • The crack indications were identified as laps. Pipeline failure causes can be divided in two groups: corrosion damage and mechanical damage. Mechanical damage usually includes dents, wrinkles, gouges, and combinations thereof. Dents can be considered the most common mechanical damage. In our study, a dent was located at the lower pipe region (5–7o'clock) as a consequence of indentation of the rocks on which the pipe was placed. The damaged pipe section was analyzed using visual, non-destructive testing (NDT), optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), hardness testing and transmission electron microscopy (TEM) analyses were performed to determine the origin, form, and mechanism of the crack indications at the dent location. Finite element method (FEM) was used for the creation and propagation cracks. The presence of micro-cracks in the dent region was confirmed, the formation of which on both pipe surfaces was related to the corrosion process. A deformation hardening was identified in the refined structure region in the kinked dent location. TEM analysis confirmed a higher concentration of dislocations in the deformed area compared to recrystallized area (undeformed area). The hardness and TEM analyses of the crack indications date them from to manufacturing process of the gas pipe. The FEM models of the pipe dent process supported this contention and confirm random presence of the crack indications in the dent location. The indications detected by NDT and the associated change in microstructure and mechanical properties occurred during the production process of the pipe. The dent, which included the mentioned indications, occurred during the operation of the pipeline. [ABSTRACT FROM AUTHOR]

The mechanically lined pipe, which consists of a carbon steel carrier and a thin-walled corrosion-resistant alloy liner, has proved to be a practical way to prevent the pipeline from internal corrosion. However, the local dent caused by third-party falling objects severely threatens the integrity of the lined pipe, especially the more fragile liner. This work investigates the influence of a local dent on the plastic responses and stability of a lined pipe system during bending. After validation of the numerical framework with the experimental results of a 12-inch lined pipe, the indentation and bending responses of two typical scenarios, namely, TDI and LDI, are examined. It is found that the liner could maintain a certain moment level after reaching the maximum instead of collapsing promptly. Furthermore, classic diamond buckling mode is observed in the TDI case, while the LDI case exhibits a twin triangular-shaped buckling mode. In addition, extensive parametric studies regarding important variables of the full-scale problem are performed. Amongst other findings, the buckling and collapse of the dented lined pipe are found to be affected by the orientation of the dent, which should be taken into account for practical dent evaluation. • Validation of the FE model with four-point bending experimental results of a 12-inch lined pipe. • Buckling and collapse analysis of dented mechanically lined pipes under bending, including two types of dents, namely TDI and LDI. • An extensive parametric study is investigated, including dent length, angle, depth, and key factors of the full-scale problem. [ABSTRACT FROM AUTHOR]

Because carbon fiber reinforced polymer (CFRP) laminated composites have electric conductivity, damage monitoring was performed using electrical resistance changes. The authors previously proposed an anisotropic electric-potential function method to calculate the electric-potential field of laminated CFRP composites. The method, however, did not deal with the effects of dents. The present study deals with the effects of dents on the anisotropic electric-potential function method. The dent causes an electric conductivity increase in the through-thickness direction. The increase was modeled and applied to a beam-type specimen. The results were compared with the finite-element method results, and the method using equivalent conductivity in the through-thickness direction was confirmed to be effective. [ABSTRACT FROM AUTHOR]

Numerical investigation is conducted in this paper on both intact and dented seamless metallic pipelines (diameter-to-thickness ratio D / t around 21), deploying nonlinear finite element method (FEM). A full numerical model is developed, capable of predicting the residual ultimate strength of pipes in terms of bending capacity ( M c r ) and critical curvature ( κ c r ). The simulation results are validated through test results by using the measured material properties and specimen geometry. An extensive parametric investigation is conducted on the influences of material anisotropy, initial imperfection, friction of the test set-up and dent parameters. It is found that the structural response is quite sensitive to the frictions that have been introduced by the test configuration. For a pipe with a considerable dent size, the effect of manufacturing induced initial imperfection is insignificant and can be neglected in the FEM simulation. The material yield stress in the pipe longitudinal direction dominates the bending capacity of structures. In the end, formulas are proposed to predict the residual ultimate strength of dented metallic pipes under pure bending moment, which can be used for practical purposes. A satisfying fit is obtained through the comparison between the formulas and FEM methods. [ABSTRACT FROM AUTHOR]

In this study, indentation responses of high strength steel pipe with local wall thinning (gouge) under internal pressure have been studied through experimental procedure and numerical analysis. The experimental study was carried out on laboratory scale specimens from API 5 L X80 steel. Dent produced by a hemi-spherical indenter with diameter of 20 mm and axial gouge introduced to the pipe’s outer surface. In experimental work, the influence of some parameters such as depth of dent, axial gouges of different sizes and presence of the internal pressure have been investigated. A numerical modeling approach has also been employed. The current numerical simulation has first been validated by experimental results previously conducted by the authors. The numerical results show well agreement with the experimental results. Effects of internal pressure level, boundary condition and D/t ratio on the response of pipelines subjected to lateral impacts numerically studied and the results have then been compared with analytical equations provided in some design codes. The results show that the analytical relations estimate greater lateral resistance than numerical results. Validated model were then used to derive a semi-empirical equation for predicting structural behavior of locally damaged tubes as a function of internal pressure. Furthermore, the elastic-plastic finite element analyses were performed to estimate the variations of failure depth with several internal pressures and gouge sizes. [ABSTRACT FROM AUTHOR]

A 3D scanning method is proposed for the measurement of surface damage on aircraft structural panels. Dent depth measurements were shown to be within 0.04 ± 0.06 mm (95%) of those taken using a Starrett 643J dial depth gauge based on 54 flat panel dents, and 0.04 ± 0.05 mm (95%) based on 74 curved panel dents. Dent depths were quantified by the difference between a point cloud rendering of the damaged surface and a surface fit approximating the original, undamaged surface. Convergence studies were used to evaluate the accuracy of the surface fit, enabling this technique to be used as a stand-alone inspection method. Image processing was used to measure dent length and area, and the results showed that this method is more efficient and reliable compared to manual methods. This novel non-destructive evaluation technique thus demonstrates potential to enable the timely extraction of surface dent measurements during on-site aircraft inspections. [ABSTRACT FROM AUTHOR]

Ground explosions are one of the threats to the structural integrities of buried pipelines. To investigate failure modes of buried pipelines subjected to ground explosions, numerical calculation models of buried pipelines in soil and rock layers were established. The stress, strain, plastic deformation and failure modes of the buried pipeline were investigated. The effects of the explosion magnitude, diameter-thickness ratio, burial depth, explosion height and explosion offset on the failure behaviour of the pipeline in the rock layer were studied. The results showed that the pipeline deformation process only lasted for 0.03 s. The high stress zone and plastic strain zone were present in the upper part of the pipeline, and a dent appears. A buried pipeline in a rock layer is more dangerous than that in a soil layer due to the reflection of the explosion wave in the rock layer. The deformation, plastic strain and total energy of the pipeline increase gradually in the rock layer with increasing explosion magnitudes or diameter-thickness ratios, but these indices decrease with the increased burial depths, explosion heights and explosion distances. Empirical formulas can be used to predict the strain and dent rates of the buried pipeline. These results can provide the theoretical basis and references for laying pipeline, as well as for their safety evaluations and maintenance, etc. [ABSTRACT FROM AUTHOR]

Ground explosions are one of the threats to the structural integrities of buried pipelines. To investigate failure modes of buried pipelines subjected to ground explosions, numerical calculation models of buried pipelines in soil and rock layers were established. The stress, strain, plastic deformation and failure modes of the buried pipeline were investigated. The effects of the explosion magnitude, diameter-thickness ratio, burial depth, explosion height and explosion offset on the failure behaviour of the pipeline in the rock layer were studied. The results showed that the pipeline deformation process only lasted for 0.03 s. The high stress zone and plastic strain zone were present in the upper part of the pipeline, and a dent appears. A buried pipeline in a rock layer is more dangerous than that in a soil layer due to the reflection of the explosion wave in the rock layer. The deformation, plastic strain and total energy of the pipeline increase gradually in the rock layer with increasing explosion magnitudes or diameter-thickness ratios, but these indices decrease with the increased burial depths, explosion heights and explosion distances. Empirical formulas can be used to predict the strain and dent rates of the buried pipeline. These results can provide the theoretical basis and references for laying pipeline, as well as for their safety evaluations and maintenance, etc. [ABSTRACT FROM AUTHOR]

Pipelines, especially existing natural gas pipelines, provide an efficient and economical means for hydrogen transport, accelerating realization of a full-scale hydrogen economy. However, the existing aged pipelines usually contain dents, which serve as effective traps to accumulate hydrogen atoms, potentially causing hydrogen embrittlement and pipeline failures. To date, there has been a strong interest in development techniques for assessment of hydrogen atom distribution at a dent on pipelines. In this work, a three-dimensional nonlinear finite element-based model was developed to investigate the hydrogen atom diffusion and distribution at a constrained dent on an X52 steel pipe. Parametric effects, including dent depth and internal pressure, were determined. The presence of a dent on pipelines drastically changes the local stress and strain distributions, facilitating diffusion and accumulation of hydrogen atoms at the dent. The minimum hydrogen atom concentration at the crystalline lattice sites, (i.e., 3.8 mol/m3) is located on the outer surface of the dent center, and the maximum hydrogen atom concentration (i.e., 12.1 mol/m3) is found on both sides of the dent with 103 mm from the dent center in the circumferential direction. The hydrogen atom concentration at trap sites at the dent is much lower than that at the lattice sites. The diffusion and accumulation of hydrogen atoms at the dent area is affected by two competitive mechanisms, i.e., hydrostatic stress and plastic strain, depending on the initial concentration of hydrogen atoms entering the interior of the pipe steel. At a low initial concentration such as 0.001 mol/m3, the equivalent plastic strain dominates the distribution of hydrogen atoms at the dent, and the hydrogen atom concentration at the lattice sites is much lower than the concentration at the trap sites. At high initial hydrogen atom concentrations such as 0.1 and 1 mol/m3, the hydrostatic stress is the dominant factor to determine the distribution of hydrogen atoms, which mainly accumulate at the lattice sites. With an increased depth of the dent, both the von Mises stress and plastic strain concentrations increase, and so is the hydrogen atom concentration. The increase of internal pressure from 5 MPa to 15 MPa only slightly elevates the von Mises stress, equivalent plastic strain and the hydrogen atom concentration. • Developed a finite element model to determine hydrogen atom distribution at a dent on existing pipelines. • The hydrogen atoms mainly accumulate at the lattice site, rather than trap sites, of the dent. • The hydrogen atom distribution is affected by hydrostatic stress or plastic strain. [ABSTRACT FROM AUTHOR]

The excavation of buried pipelines shows that combined dent and scratch defects exist at the bottom of the pipe due to the extrusion and scraping action of rocks, which is likely to decrease its pressure bearing capacity. This paper experimentally investigates the tensile strength of CT80 steel plates with dent and scratch defects. Results show that the tensile strength is affected to varying degrees by dent depth, scratch depth and the indenter diameter. Finite element analysis (FEA) is then carried out to propose the failure criterion by comparing with experimental results. It is thought that failure happens when the equivalent stress of the intermediate node in the direction of the remaining thickness of the defect center of the model reaches the true tensile strength of the material. With this criterion, large numbers of finite element calculations can be developed to study the failure pressure of buried pipelines with combined dent and scratch defects. [ABSTRACT FROM AUTHOR]

The present study was undertaken to evaluate rutting, fracture and thermal cracking resistance behavior of asphalt mastic containing inert and active fillers. A control neat binder (AC-30) along with basalt (B) as an inert filler and hydrated lime (HL) as active filler were selected in this study. The asphalt mastics were prepared for different percentages of HL (5, 10, 15 and 20%) filler, in such a way that Filler to Binder (F/B) ratio becomes 0.8. A total of five combinations of asphalt mastic were prepared such as: AC-30 + 80% B + 0% HL, AC-30 + 75% B + 5%HL, AC-30 + 70% B + 10%HL, AC-30 + 65% B + 15%HL, and AC-30 + 60% B + 20%HL. The rutting, fracture and thermal cracking resistance of asphalt mastics was evaluated using Superpave rutting factor parameter, Double Edge Notched Tension (DENT) and Bending Beam Rheometer (BBR), respectively. Influence of HL on the performance of neat asphalt mastic was observed to be predominant in high-temperature range as obtained from the G ∗ /Sinδ value. The aging resistivity of asphalt mastic increased with the inclusion of HL, indicating a better rutting performance of asphalt mastic. The intermediate-temperature performance of asphalt mastic with HL was found to be higher compared to neat asphalt mastic from Critical Tip Opening Displacement (CTOD) results, implying better resistance to fracture. The addition of HL increased the low-temperature performance of asphalt mastic obtained from S(t) and m(t) values with S(t) and E(t) master curve, indicating enhanced resistance to thermal cracking. The combined effect of B and HL filler on the G ∗ /Sinδ, CTOD, S(t), m(t) and E(t) parameters are presented in this study. In addition, ranking of asphalt mastics based on various parameters (i.e. CTOD and m(t)) is discussed in this paper. [ABSTRACT FROM AUTHOR]

• Defined pipeline monitoring threshold and pipeline repairing threshold. • Investigated the effects of indenter and pressure on the pipeline thresholds. • Proposed a dent evaluation method based on pipeline threshold. Dent is the most common defect on natural gas pipelines, leading to pipe leakage or rupture. Since the dent depth-based failure criterion is unreasonable, this work proposed a new ductile damage-based evaluation method for dented natural gas pipelines. The new method was proposed by finite element analysis combined with Oyane ductile damage criterion. Specifically, a finite element-based model was developed to model the formation process of an unconstrained dent, and its accuracy was verified by comparison with test data. A new parameter called the pipeline defect parameter was defined as the ratio of the dent depth to the pipeline diameter to illustrate the dimensionless of dent depth. Then, two safety indicators based on pipeline defect parameter, i.e., monitoring and repairing thresholds, of dented pipelines were determined considering the dent springback. The parameter effects, i.e., indenter geometries and size, as well as internal pressure, were determined. Finally, the proposed method's adaptability and reasonable were demonstrated by case studies. It is expected to provide a useful method for operating dented natural gas pipelines safely. [ABSTRACT FROM AUTHOR]

Pipelines are major structures for transporting the liquid or gaseous products and their safe operation is dependent upon the maintenance of structural integrity of the system. Leaks in natural gas pipelines can cause significant harm to people, property, and the environment. Pipelines are damaged mechanically when they subjected to external interferences. In pipes, mechanical defects such as dents, cracks, gouges, and scratches are prevalent. These damages can sometimes occur close to one another, resulting in a single defect in the pipe wall. Individual defects have been demonstrated to be less harmful than compounded defects. A crack in a dent, also known as a dent-crack defect, is one of the pipeline's combined defects. As a result of the damage, the pipeline's capacity may be reduced, and a reliable evaluation of the defect is critical for the pipeline's continued safe operation. At present several assessment methods are available, but there is a need to evaluate these methods against test results. This paper discusses on (i) pipeline failures (ii) defects in pipeline (iii) dents & assessment of dents (iv) cracks (v) dents combined with cracks (vi) monitoring of defects (vii) fatigue life assessment models for the pipes containing mechanical defects. • Review of causes of pipe line failures, various defects in pipelines and their significance. • Monitoring and assessment procedures of dents, cracks and dents combined with cracks in pipelines. • Fatigue life assessment models for the pipes containing mechanical defects subjected to internal pressure. [ABSTRACT FROM AUTHOR]

• The model can simulate the initiation and propagation of fatigue cracks under rolling contact. • The crack evolution and fatigue life of the model including surface topography with different dents and roughness are analyzed. • Simulation results of crack evolution for the model with dent are consistent with experimental results. • The effects of roughness amplitude and wavelength on surface-originated pitting and subsurface-originated spalling are analyzed. A peridynamic(PD) fatigue simulation model is developed to study the effect of surface topography on rolling contact fatigue(RCF). Based on the PD fatigue damage-cumulative model proposed and verified in a previous study, a two-dimensional PD numerical model of the contact area of the rolling bearing is established, and the crack evolution and fatigue life of the model including surface topography with different dents and roughness are analyzed. The results show that cracks initiate from the shoulders of the dent, and then form spalling at the trailing edge, which is consistent with the experimental observations. Simulation of the model with sinusoidal and random rough profiles shows that there is competition between surface and subsurface crack nucleation. The larger the roughness amplitude or wavelength, the more prone to surface nucleation. Finally, the effects of roughness amplitude and wavelength on surface-originated pitting, subsurface-originated spalling and fatigue life are analyzed. [ABSTRACT FROM AUTHOR]

This work deals with the ultimate compressive strength of highly damaged plating resulting from dropping objects, grounding or collision. Extensive static nonlinear finite element analyses are conducted, where several governing parameters are considered. The effect of dent depth as well as dent size is studied. Different dent shapes are considered in order to cover different possible damage scenarios. The toughness modulus is used to measure the capacity of the plate to withstand the applied load with permanent deformation. An expression to estimate the average reduction of ultimate strength of highly damaged steel plates, subjected to compressive loading as a function of the residual breadth ratio is also developed. [ABSTRACT FROM AUTHOR]

As a cost-effective solution for transporting corrosive hydrocarbons, mechanically lined pipe has been used in many offshore and onshore projects. The bonding between the carbon steel carrier and the non-corrosive liner is commonly achieved by mechanical expansion. As typical pipeline damage, the local dent brings deformation to the bimetallic composite, which is expected to undermine the structural integrity. This work investigates the influence of a local dent on the plastic responses and stability of a lined pipe system during bending. Part I presents the results of the experiments and numerical analysis involving a set of small-scale lined tubes. The lined tubes, made of carbon steel Grade GB45 (AISI 1045) and copper Grade T2, are manufactured using a custom hydraulic expansion facility. The products have finished diameters of 50 mm and an overall D / t of 16.5, with 1.0 mm thickness for the liner. A minor transverse dent is introduced to the specimen using a cylindrical indenter. The dented tube is subsequently bent to collapse in a four-point bending facility. It is found that the local dent tends to induce early collapse of both the outer tube and the liner, resulting in a noteworthy reduction of the bending capacity of the composite. Initially, the local dent grows stably instead of collapsing right away. With increasing bending, the liner develops a major buckle and several satellite dimples around it. Subsequently, the manufacture, indentation, and the succeeding bending to collapse are simulated using a custom numerical framework, and the experimental results are reproduced reasonably well. Part II will use the validated numerical model to conduct an extensive parametric study of the important variables of the problem for full-scale lined pipes. [ABSTRACT FROM AUTHOR]

This work developed a new finite element (FE)-based method to perform pressure capacity assessment on a corroded X80 steel pipe containing a dent, where their mutual interaction and the effect on further corrosion growth were defined. Parametric effects including corrosion depth, dent depth, corrosion length and service time were determined. The presence of a dent at corrosion defect remarkably changes the local stress distribution, elevating stress to plastic range. The mutual interaction between the dent and the corrosion defect depends on both the initial corrosion depth and the initial dent depth. The interaction remarkably changes the local stress level at the dent and must be included in pipeline burst failure assessment. • Developed a new assessment method for pressure capacity of corroded X80 steel pipelines containing a dent. • Determined the mutual interaction of corrosion defect and dent on failure pressure. • Determined the corrosion defect growth rate in the presence of dent on pipelines. [ABSTRACT FROM AUTHOR]

The aim of this work is to analyse the local and the global structural behaviour of rectangular steel plates with a local dent. Nonlinear finite element analyses have been performed to explore the effect of different dent depths on the ultimate strength and the post-collapse behaviour. The post-collapse modes are discussed and the change of the buckling mode for different plate thickness ranges is categorized. The behaviour in post-collapse regime is analysed using the defined stress–strain rate. Two relationships have been developed to estimate the ultimate strength reduction as a function of the plate slenderness and dent ratio. Based on the existing ultimate strength design formula and a new developed factor, a new formulation for ultimate strength of damaged plate has been introduced accounting for the effect of local dent. The new developed formulation is capable to account for an initial global imperfection, residual stresses, openings, corrosion deterioration and existence of dents. [ABSTRACT FROM AUTHOR]

The present study evaluates the influence of initial residual stresses surrounding scratch or dent type surface anomalies on the fatigue crack growth of Direct Aged (DA) Inconel 718 alloy. A heat treatment has been used to at least partly relax these residual stresses in order to evaluate their effect on the fatigue crack initiation and propagation starting from scratches and dents. In the presence of compressive residual stresses under the surface anomaly, the first stages of crack propagation are slowed down. The evolution of the crack front shape is also strongly influenced by the residual stress field and leads to the formation of an “ear-shaped” crack front for dents and initiation in the corners for scratches. The initiation fatigue life is short for both type of surface anomalies and a competition between the stress concentration and the initial microstructural state was noted for the control of this stage of the fatigue life. These results highlight the need to characterize the residual stress field resulting from the introduction of the surface anomaly in order to predict accurately the fatigue life of DA Inconel 718 alloy components containing scratches and dents. A preliminary finite element simulation is developed in this study to address this issue. [ABSTRACT FROM AUTHOR]

This paper studies the effect of a central dented imperfection on the load carrying capacity of stiffened panels considering the residual stress caused by the indentation, and identifying the type of boundary conditions to adopt for a model to be used in an experimental programme for damaged panels. A quasi-static nonlinear finite element analysis is used to simulate the production of the local dent, followed by an ultimate strength analysis of the stiffened panels under uniaxial compressive load. The structural plastic strain causes the residual stress and the dent, which are included in the ultimate strength analysis of the stiffened panels under compressive load. To prescribe appropriately the boundary conditions for the central span of stiffened panels, two and three spans models are adopted in the FE analyses. The effects of residual stress, geometric range and dent depth on the ultimate strength of the stiffened panels with a central dented imperfection are investigated using nonlinear quasi-static finite-element analysis. [ABSTRACT FROM AUTHOR]

Guided elastic waves have been anticipated as a rapid screening technique for pipe inspection. Dents occurring in pipes are a severe problem which may lead to the possibility of pipe failure. A study of the reflection characteristics of guided waves from dents of varying geometrical profile in pipes is investigated through experiments. Dented region is represented by a series of circumferential cross-sections and its geometric parameters are described by axial length and the maximum and minimum outer diameters. Both single and double sided dents are mechanically simulated in hollow aluminum pipes and then experimentally tested by exciting the longitudinal L(0,2) mode. A quantitative parameter, so-called deformation rate relating to the maximum and minimum outer diameters of the dents is defined to evaluate the effect of the extent of the deformation on the reflection. For both types of dents, it is shown that the reflection coefficients of the L(0,2) mode are all approximately a linear function of their respective deformation rates. Mode conversion occurs at the dents and reflections of the F(1,3) mode are identified. The results show that the amplitude of the reflected F(1,3) mode is generally higher when the dent has stronger non-axisymmetric features. [ABSTRACT FROM AUTHOR]

One of the common failure modes of thin cylindrical shells subjected to external pressure is buckling. The critical buckling pressures of these shell structures are mainly affected by the geometrical imperfections present in the cylindrical shell which are very difficult to alleviate during manufacturing process. Dent is one of the common geometrical imperfections present in thin shell structures which may be formed due to mechanical damage caused by accidental loading or impact. In this work, numerical parametric study is carried out to study the influence of dent parameters of centrally located dent (dent length, dent width, dent depth and angle of orientation of the dent), cylindrical shell parameters ( L / R ratio and R / t ratio) and yield stress on the critical buckling pressure of externally pressurized thin dented cylindrical shells with simply supported boundary conditions at both top and bottom edges using non-linear static finite-element analysis of ANSYS. [ABSTRACT FROM AUTHOR]

Local dent is a typical damage of aircraft, however, very few studies have investigated the effect of dents on the residual ultimate strength of the aluminum plate under different loading conditions, especially under tensions. In this study, drop-weight impact tests were conducted on the 2024-T3 aluminum alloy plate to generate 5 types of dents, and then tension tests were performed on the dented specimens to investigate the effects of the dents on the residual ultimate strength. Results show that the residual ultimate strength and the fracture displacement of the plate are significantly affected by the local dents. With increase in the depths of spherical, V-shape, and elliptical dents, the ultimate strengths decrease in quadratic trend. Whereas, for the conical and U-shape dent, linear relationships were observed between dent depth and the ultimate strength. The mathematical formulas between the ultimate strength reduction rate and the dent depth reduction factors were derived through regression analysis on the experimental results. [ABSTRACT FROM AUTHOR]

The context of this paper is the German research project KESS (Konfigurierbares Elektronisches Schadensidentifikationssystem) funded by the Federal Ministry of Education and Research. In this Project, an entire system from sensing structure-borne sound up to Car-2-Infrastructure communication for the minor damage detection of car sharing vehicles is under development. Therefore, the suppression of noise signals is essential for the further algorithms to classify minor damages. Minor damages in vehicle body parts create structure-borne sound which overlaps with additional oscillations of the vehicle. In the ordinary usage of vehicles, those additional oscillations are mainly caused by road and engine noise. Within this paper the differences of such noise signals and signals of structure damages will be described. Therefore, an analysis method to calculate spectrally decomposed envelope signals of structure-borne sound signals is given and the analysis results will be presented. A digital filter method to attenuate the majority of noise signals and to preserve the useful signals for the detection of minor damages will be given at the end of this paper. This digital filter method has been successfully designed and implemented into the algorithm of the sensor by using model based design techniques. [ABSTRACT FROM AUTHOR]

The paper presents an approach for fully-automatic detection and recognition of minor vehicle body damages in a scenario of frequently changing drivers, such as in the car rental or car sharing businesses. It utilizes a sensor network integrated into the vehicle body. The algorithmically contribution is the multi sensor-data fusion of the signals from these sensors and the subsequent reasoning framework stage. The present research assignment is the inclusion of additional information from the network of the vehicle's electronic control units. This additional information about the vehicle state (e.g. closed or opened door status, speed, changing fuel level) is used to verify the calculated damage events. The efficiency of a structural damage detection directly depends on the acoustical vehicle noise level. Additional structure-borne sound sources also introduce oscillations into the vehicle body (e.g. road and engine noise, opening and closing doors). Some of this information uses a central electronic unit for adaptive sensor data processing of the damage detection system. The higher confidence of correctly identified damages increases the credibility of the system. [ABSTRACT FROM AUTHOR]

Changes in the internal pressure and the temperature in a steel pipeline generates cycles of high axial compression/relaxing in the line. This makes the line vulnerable to cyclic creep and progressive plastic straining (ratcheting). On the other hand, offshore pipelines are usually laid unburied, so they might become disposed to heavy accidental transverse loads, such as those caused by impacts from trawl gears, anchors or other dropped objects. This paper deals with the ratcheting behavior of dented steel offshore pipelines under uniaxial cyclic loading. The experimental study were conducted on small scale specimens from X80 steel pipes with an outer diameter of D=44mm and D/t of 22. Effects of some key parameters such as the initial pre-strain, the cyclic stress amplitude and the dent depth magnitude were investigated. It was found that while the initial pre-strain and the cyclic stress amplitude had strong effects on the ratcheting response of both dented and intact tubes, the strain ratcheting rate was radically increasing by the presence of a dent. The dent was also significantly affecting the number of stress cycles which could be tolerated by the pipe. When the initial pre-strain was low the changes in the ratcheting behavior of the dented pipes and the intact pipe were less significant. With higher initial pre-strains, even very small dents were resulting in remarkable degradation of the pipe ratcheting response. [ABSTRACT FROM AUTHOR]

Abstract: Sensitivity to initial imperfections under compressive loading has been extensively studied in shell structures. However, due to the existence of a wide range of imperfections with various shapes and amplitudes, the real behavior of such structures needs to be further investigated when they face with a damaged area. This study presents an experimental program in which buckling and failure response of damaged shell specimens are analyzed. The results of this study can be generalized for many kinds of cylindrical shells to full scale of applications with similar D/t ratios. [Copyright &y& Elsevier]

Highlights: [•] Modeling of cutting forces while applying a slicing motion to the push-cutting process. [•] Analysis of state of stress at the cutting edge. [•] Stress Intensity Factors for cutting with a symmetrical and asymmetrical cutting knife. [•] Fracture toughness of the paper sheet material is determined through DENT test. [•] The new model is verified by sideways push-slice cutting stacked thin paper material. [Copyright &y& Elsevier]

Highlights: [•] Experimental burst tests have been performed on vessels containing a dent+gouge defect. [•] The gouge dimensions were identical for all the vessels. [•] The influence of the dent depth on burst pressure was analysed. [•] The most of time, failure occured on other place than that of the defect. [•] A criterion based on stress triaxiality was proposed to evaluate the burst pressure and failure location. [Copyright &y& Elsevier]

Abstract: Effects of soil–pipe interaction on the response of continuously supported offshore pipelines subjected to transverse impacts caused by dropped objects are studied. For this, the impact on an internally pressurized pipeline resting on a flexible bed has been numerically simulated. The numerical model has first been validated against different sets of experimental data from the authors and a number of researches. A relatively extensive parametric study has then been carried out to examine effects from variations in the pipe geometry, internal pressure, boundary conditions, indentor shape and orientation, embedment depth of the pipe into the soil bed and subsoil mechanical properties on the pipeline response. It has been noticed that the presence of internal pressure results in substantial increase in the impact force. It, however, reduces the denting length, causing the deformation to become spatially more localized. It has also been shown that the flexibility of pipe bed plays an important role in the impact energy dissipation. This effect becomes more pronounced when the internal pressure is relatively low. [Copyright &y& Elsevier]

Abstract: The work described in this paper forms part of a closed analytical solution for the quasi-static response of flexibly supported pressurized pipes against lateral impacts. The results can be used, for example, in an analytical study of offshore oil/gas pipelines subjected to impacts from falling anchors, trawl boards or other dropped objects. The solution is based on the principles of virtual velocities. It employs a simplified three dimensional analytical model to provide a closed-form relationship for the denting force in terms of the dent depth. A rigid-perfectly plastic behavior is considered for the tube wall resistance. The flexibility of the soil, existing around and underneath the pipe, is modeled using a subgrade reaction modulus. This work can be regarded as a continuation of previous works reported by one of the authors. It is now extended to take into account the bed flexibility. Predictions from the proposed mathematical solution are also examined against those from numerical finite element simulations. Various states of end condition, internal pressure, soil stiffness and the pipe embedment into the soil are considered. The comparisons show a good agreement between the results from the analytical model and finite element analyses. [Copyright &y& Elsevier]

Abstract: Series of low velocity impact tests were carried out on different types of fibre metal laminates (GLARE®) with varying material constituents. Impact damages in the laminates and their extent were analysed. Relationship between the configuration as well as the properties of the laminates with different material constituents and the impact response in terms of indent was derived. This relationship resulted in an empirical method predicting the dent depth under low velocity impact in laminates with different configurations. The method is valid as long as there is reference impact data obtained on a composite material with the same constituents and identical boundary conditions. [Copyright &y& Elsevier]

Abstract: The aim of the present paper is to study the influence of a local dent on the collapse behaviour of stiffened panels. A quasi-static nonlinear finite element analysis is used to simulate the production of the local dent which will model the residual stress and the springback effect of the stiffened panels. The effect of residual stress caused by the local dent on the collapse behaviour of stiffened panels is investigated. The material properties used in the finite element analysis have been evaluated by tensile tests. Stiffened panel models with three and two bays in the longitudinal direction are used to prescribe appropriately boundary conditions for the middle bay. The relationship of the maximum indentation load and length of plate are almost linear and the springback displacements converge to a constant with increasing final depth of the dent. The residual stress caused by the indentation affects slightly the ultimate strength of the dented stiffened panels under consideration. [Copyright &y& Elsevier]

Abstract: Thin steel plates are widely used in many structural applications because of its high load carrying capacity with less weight. The load carrying capacity of thin plates mainly depends on its buckling behavior which in turn is affected by the imperfections present in it. Dent is one of the common geometrical imperfections present in thin shell structures which may be formed due to mechanical damage caused by accidental loading or impact. In this work, influence of various dent parameters (dent length, dent width, dent depth and angle of orientation of the dent) on the static ultimate strength of thin square plates of different thicknesses under uniaxial compressive loading is studied. The dent is modeled on the FE surface of perfect thin square plate of size 1000mm (of different thickness) for different sizes and angles of orientation of the dent at the center of the plate. These dented plates are analyzed using non-linear static buckling analysis of general purpose FE software ANSYS V12. From the results obtained, it is found that both shorter and longer dents reduce the ultimate strength drastically. But in case of shorter dents, variation of ultimate strength of dented plates due to variation of size and angle of orientation of dents is insignificant, whereas in the case of longer dents, size and angle of orientation of dents have significant effect. It is also found that the reduction in ultimate strength of thin plates with a dent of same size and orientation increases with increase in shell thickness. [Copyright &y& Elsevier]

Abstract: The objective of this study was to investigate the effect of the dent magnitude on the collapse behavior of a dented pipe subjected to a combined internal pressure and in-plane bending. The plastic collapse behavior and bending moment of the dented pipe containing several dent dimensions were evaluated using elastic–plastic finite element (FE) analyses. The indenters used to manufacture the dents on the API 5L X65 pipe were hemispherical rods with diameters of 40, 80, 160 and 320mm. Dent depths of 19, 38, 76, 114 and 152mm were introduced to the pipe with a diameter of 762mm and a wall thickness of 17.5mm. A closing or opening in-plane bending load was applied to the dented pipes pressurized under an internal pressure equivalent to atmospheric pressure as well as pressures of 4, 8, and 16MPa. The FE analyses results showed that the plastic collapse behavior of the dented pipes was significantly governed by the bending mode and the dent geometry. Moment-bending angle curves for the dented pipe were obtained from computer simulations and evaluated with a variety of factors in the FE analyses. The load bearing capacity of the dented pipes under the combined load was evaluated by TES (Twice Elastic Slope) moments. The load bearing capacity of the pipe containing up to a 5% dent depth of the outer diameter was not reduced in comparison to that of the plain pipe. The opening bending mode had a higher load bearing capacity than the closing bending mode under the combined load regardless of dent depth. The TES moment decreased with increasing dent depth and internal pressure regardless of the bending modes. [Copyright &y& Elsevier]

Abstract: The origin of more than 90% in service pipeline failures is attributed to the presence of stress concentration areas such as defects in forms of gouges, dents, or when these defects are present together. These defects are provoked by external factors interferences, for instance by excavation machines. The influence of the dent depth on the burst pressure of the pipeline was evaluated. An approach based on a simple local strain criterion has been proposed to predict the damage and the failure of evaluated dented pipe. To validate a purely empirical rule, which specifies that a critical depth dent is equal to 10% of outside diameter of the pipeline, a series of mechanical tests (denting tests and burst tests) were conducted. Finite element analysis used in order to compare the numerical and experimental results. Experimental results showed that a single dent did not affect the burst pressure of the investigated specimens; therefore the rule of a critical depth of dent equal to 10% was found very conservative. [Copyright &y& Elsevier]

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Abstract: Purpose: Manual delineation of dental structures is too time-consuming to be feasible in routine practice. Information on dose risk levels is crucial for dentists following irradiation of the head and neck to avoid postextraction osteoradionecrosis based on empirical dose-effects data established on bidimensional radiation therapy plans. Material and methods: We present an automatic atlas-based segmentation framework of the dental structures, called Dentalmaps, constructed from a patient image-segmentation database. Results: This framework is accurate (within 2Gy accuracy) and relevant for the routine use. It has the potential to guide dental care in the context of new irradiation techniques. Conclusion: This tool provides a user-friendly interface for dentists and radiation oncologists in the context of irradiated head and neck cancer patients. It will likely improve the knowledge of dose-effect correlations for dental complications and osteoradionecrosis. [Copyright &y& Elsevier]

Abstract: A new mechanistic approach is used to characterize resistance of polyethylene to deformation and fracture in double-edge-notched tensile test. The new approach considers all three mechanisms involved in the fracture process, i.e. for fracture surface formation, shear plastic deformation, and necking, and can be used to determine values of specific energy consumption for each mechanism. This is different from the conventional approach, known as essential work of fracture (EWF), which does not consider the difference between shear plastic deformation and necking. Results from the new approach for a polyethylene copolymer show that specific energy density for fracture surface formation is about half of that determined from the EWF approach, and specific energy density for necking is very close to that determined from simple tensile test. The latter provides some support for validity of the new approach in characterizing fracture behaviour of polyethylene when accompanied by large deformation and necking. The paper also points out crack growth conditions that have to be met for valid application of the EWF approach and shows that such conditions are not met when deformation and necking occur in polyethylene. [ABSTRACT FROM AUTHOR]

Abstract: The steady laminar subsonic flow past a flat plate having a stretch of an elastic membrane, the pressure on the other side of which is adjustable, is studied within the framework of the triple deck theory. The resulting lower deck problem is supplemented with a membrane equation relating the pressure difference across the membrane to its curvature. By pressurizing or depressurizing the membrane, it assumes the form of a hump or a dent that alters the flow characteristics. Numerical solutions obtained, in either case, give plausible account of the interaction between the membrane and the flow. [Copyright &y& Elsevier]

The transverse impact resistance behaviour of pipe-in-pipe submarine pipelines after 15 years of service is studied experimentally and numerically. From drop hammer impact tests of 4 full-scale specimens, the influence of specimens' span, corrosion and dent defect on the transverse impact resistance is studied in terms of failure mode, impact force-time history curves, displacement-time history curves, strain-time history curves and impact force-displacement curves. The experimental results indicate that the dynamic failure process consists of four stages, including primary vibration stage, secondary vibration stage, stable stage and unloading stage. As the suspension span of the specimen increases, the primary failure mode changes from local indentation to global bending deformation. The corrosion and the dent defect impair the impact resistance. Finite element (FE) models are then established and verified through comparison with experimental results. Numerical analyses indicate that the total impact energy is mainly dissipated by the outer pipe and the inner pipe according to the energy dissipation analysis for each component of the pipe-in-pipe specimens under transverse impact load. Parametric study is implemented finally to disclose the influence of the dimensions of pre-existing corrosion and dent defect on the transverse impact behavior of pipe-in-pipe submarine pipelines. • Impact tests were carried out on 4 full-scale serviced submarine pipe-in-pipe specimens. • Dynamic failure process of submarine pipe-in-pipes under transverse impact is analyzed. • Energy dissipation of specimens under transverse impact is quantified. • Effects of pre-existing corrosion and dent defect on transverse impact resistance are investigated. [ABSTRACT FROM AUTHOR]

Abstract: Application of the crack compliance method to the analysis of thin-walled rings with a radial crack has two features: a crack is considered as a concentrated angular compliance and the deformation of all other sections of the rings is calculated as for a curvilinear beam. The latter can be most conveniently found by the method of initial parameters where the values of generalized forces and displacements at the end of some zone are determined as a linear combination of their values at the beginning of the zone. The goal of the study is to derive and apply the method of initial parameters equations taking into account the influence of circumferential stresses on the ring curvature. As far as the authors know, this is the first time that the stress intensity factor has been derived for an elastic thin-walled pipe with a radial crack in a geometrically nonlinear formulation. Here, an increase in pressure leads to a somewhat slowed increase in the stress intensity factor. In addition, a number of problems for dents are considered. The effect of the dent shape on the stress–strain state is analyzed. An expression for the stress intensity factor for a complex defect, a crack emanating from the dent apex, is presented. [Copyright &y& Elsevier]

Abstract: In this review, we will present the recent works, which shows a link between arterial lesions, particularly in coronary arteries, and periodontal disease. The pathways are those of chronic infection, and several studies have revealed a relationship between arterial lesions and buccal bacteraemia. Though the mechanism that links them is still unclear, the first hypotheses suggest that the presence of the bacteria in the bloodstream triggers a direct reaction (bacteria on the target organ), and/or an indirect immune reaction. This immune response could be induced by an increase in the secretion of pro-inflammatory cytokines (IL1, IL6, TNF), which are also involved in atherogenesis. Indeed, these cytokines have been found in higher concentrations in patients with periodontal disease, whereas reduced levels have been found in patients who have had deep gum pockets thoroughly cleaned. Cardiologists need to have access to such information not only because of the similarity of the populations, but also because of the therapeutic consequences. The future development of simple dental scores will provide an important tool for epidemiological studies of primary and secondary prevention. [Copyright &y& Elsevier]

Abstract: Mechanical damage in the form of dents and gouges is recognised as a severe and common form of mechanical damage to pipelines. In general terms, dents and gouges reduce both the static and cyclic strength of a pipeline. The severity of a dent depends on a number of factors, including: the size and shape of the dent; whether it affects the curvature of a girth or seam weld; and whether it contains other defects, such as a gouge or a crack. An understanding of the issues that influence the severity of mechanical damage is required to ensure that the appropriate action is taken on finding such damage, and that all of the necessary information is gathered for conducting an assessment. For example, what inspection method(s) are appropriate, and when is it better to repair such damage, rather than assess it? This paper discusses some of the issues that may arise during the assessment of mechanical damage, such as: when is a feature really a dent; when does a superficial scrape become classified as a gouge; and the limitations of existing assessment methods. These issues are illustrated with two recent case studies of damage to offshore gas transmissions pipelines. [Copyright &y& Elsevier]