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Magnesium alloys have a huge market and broad prospects due to their high specific strength, good ductility, and strong thermal conductivity. However, the active chemical properties of elemental magnesium and the negative standard electrode potential result in magnesium alloys being highly susceptible to corrosion and failure. Chemical conversion treatment of magnesium alloy can improve its corrosion resistance by preparing a chemical conversion film on its surface. Rare earth conversion treatment has the advantages of effortless process, moderate price, no pollution, good corrosion resistance, and synergistic effect with inorganic or organic additives, which is in line with the pursuit of “green chemical” in industrial production. At present, there is little research and application on lanthanum-based rare earth conversion coatings (La-RECC). This paper selects rare earth element lanthanum (La) to prepare La-RECC on the surface of AZ91D magnesium alloy through chemical conversion treatment. The microstructure, chemical composition, and protective properties of La-RECC were discovered, as well as their interrelationships, revealing the degradation process of La-RECC in 3.5% NaCl solution. La-RECC is composed of La(OH)3 and Mg(OH)2, exhibiting a crystal cluster structure with cracks, and there are a large number of needle-like crystals on the crystal cluster of La-RECC, with a thickness of 2.14 μm. The degradation process of La-RECC can be divided into three stages: Rapid degradation, slow degradation, and complete degradation. The complete degradation time of La-RECC in 3.5% NaCl solution is 82.5h. [ABSTRACT FROM AUTHOR]

Urban underground engineering is generally buried at a shallow depth and suffers long-term environmental water effects such as rainfall, rivers, underground pipeline leakage, and groundwater. The mechanical properties of the structures are affected by constant deterioration, which seriously hinders the safe, healthy, and sustainable development of the city. On the basis of on-site investigation of civil defense engineering, this article simulates the water environment conditions of mortar in underground engineering in the laboratory and conducts manual sample preparation in the laboratory. Then, water, H2CO3, NaCl, and Na2CO3 solution or wet–dry cycles are used to corrode the sample, respectively. A uniaxial compression test, Brazilian splitting test, analyses of the acoustic emission signals and electromagnetic signals, and magnetic imaging testing are performed, respectively. The results show that an increase in the action time of environmental water leads to a gradual increase in the uniaxial compressive strength, tensile strength, and elastic modulus of cement mortar, but it will decrease over a long period of time. Different environmental water components can also lead to a different performance of soaked mortar. The uniaxial compressive strength R, tensile strength σt, and elastic modulus E of mortar samples exhibit values in different solutions in the order of H2CO3 solution < NaCl solution < Na2CO3 solution < water. A moderate solution soak time can enhance the mechanical properties of the mortar, but this effect decreases at long time scales. The effect of wet–dry cycles on the mechanical properties and degradation process of mortar is significant. With the increase in wet–dry cycles, the porosity of mortar continuously increases. The cumulative ringing count, energy, amplitude, and impact number of acoustic emission signals always increase when the samples are loaded to failure. The uniaxial compressive strength, tensile strength, and elastic modulus first increase and then decrease. The experimental results lay the foundation for further investigating the performance changes in mortar under complex water environments in underground engineering. [ABSTRACT FROM AUTHOR]

A fundamental step in the best preservation of heritage materials is investigating their chemical and physical characteristics, and understanding how they interact with the surrounding environment. For this reason, the stone masonry of the monumental UNESCO site of Panamá Viejo was subjected to a thorough study to characterize the materials and evaluate their state of conservation. Additionally, potential outcrops were explored in order to identify sites for the supply of raw materials. The methodological approach encompassed mineralogical-petrographic investigations using stereomicroscopy, polarized light microscopy (PLM), X-ray powder diffraction (XRPD), scanning electron microscopy and energy dispersive X-ray spectrometry (ESEM-EDS) and X-ray fluorescence (XRF). The results revealed that the masonries primarily consists of polygenic breccia, basaltic andesite, rhyodacite, tuffite, and rhyolite. In addition, at the potential quarries, breccia and basaltic andesite were identified. The porous structure was studied using mercury intrusion porosimetry (MIP). Possible issues due to salt dissolution/crystallization cycles were considered. Consequently, ion chromatography (IC) was conducted on samples exhibiting alteration patinas to study the presence of soluble salts. In assessing the state of conservation, prevalent forms of deterioration included biological colonization, detachments, material loss, potential salt weathering, and chromatic alteration. In conclusion, the outcomes of this work provide a valuable resource for the current and future preservation of this site.

A fundamental step in the best preservation of heritage materials is investigating their chemical and physical characteristics, and understanding how they interact with the surrounding environment. For this reason, the stone masonry of the monumental UNESCO site of Panamá Viejo was subjected to a thorough study to characterize the materials and evaluate their state of conservation. Additionally, potential outcrops were explored in order to identify sites for the supply of raw materials. The methodological approach encompassed mineralogical-petrographic investigations using stereomicroscopy, polarized light microscopy (PLM), X-ray powder diffraction (XRPD), scanning electron microscopy and energy dispersive X-ray spectrometry (ESEM-EDS) and X-ray fluorescence (XRF). The results revealed that the masonries primarily consists of polygenic breccia, basaltic andesite, rhyodacite, tuffite, and rhyolite. In addition, at the potential quarries, breccia and basaltic andesite were identified. The porous structure was studied using mercury intrusion porosimetry (MIP). Possible issues due to salt dissolution/crystallization cycles were considered. Consequently, ion chromatography (IC) was conducted on samples exhibiting alteration patinas to study the presence of soluble salts. In assessing the state of conservation, prevalent forms of deterioration included biological colonization, detachments, material loss, potential salt weathering, and chromatic alteration. In conclusion, the outcomes of this work provide a valuable resource for the current and future preservation of this site. [ABSTRACT FROM AUTHOR]

Maintenance cost contributes a large portion in total life-cycle cost of offshore wind systems and improves the efficiency of maintenance activities that has emerged as an effective solution in enhancing cost-effectiveness of offshore wind energy. This study proposes a mathematical model to determine the optimal maintenance schedules, by highlighting the deterioration process of offshore wind systems and accounting the optimal vessel routing of maintenance activities, maintenance cost therefore could be shifted to an optimal level. Firstly, reliability of each component is precisely analyzed with respect to the effect of previous maintenance activities. Then, an optimal individual maintenance schedule and a grouping maintenance schedule in daily manner are established based on reliability analysis and opportunity cost consideration. Finally, an optimal maintenance schedule approach accounting vessel routing is apparently presented to optimize the transportation cost of maintenance activities. Numerous influential factors such as system reliability, weather condition, maintenance resource, maintenance duration, production loss cost, and vessel related issues are deliberately examined to enhance the robustness and efficiency of the proposed approach. The experimental results investigating four different scenarios demonstrate that by applying the proposed approach, number of maintenance activity is lowered down, maintenance duration and vessel travelling distance are also significantly reduced in the range of 43.86% - 52.77%, and 52.90% - 58.35%, respectively. Therefore, the economic benefit on maintenance cost could be achieved in an interval of 15.15% - 23.25% by selecting the optimal maintenance schedule. [ABSTRACT FROM AUTHOR]

To reveal the deterioration process of magnesium oxychloride cement (MOC) in an outdoor, alternating dry–wet service environment, the evolution of the macro- and micro-structures of the surface layer and inner core of MOC samples as well as their mechanical properties and increasing dry–wet cycle numbers were investigated by using a scanning electron microscope (SEM), an X-ray diffractometer (XRD), a simultaneous thermal analyser (TG-DSC), a Fourier transform infrared spectrometer (FT-IR), and an microelectromechanical electrohydraulic servo pressure testing machine. The results show that as the number of dry–wet cycles increases, the water molecules gradually invade the interior of the samples, causing the hydrolysis of P 5 (5Mg(OH)2·MgCl2·8H2O) and hydration reactions of unreacted active MgO. After three dry–wet cycles, there are obvious cracks on the surface of the MOC samples, and they suffer from warped deformation. The microscopic morphology of the MOC samples changes from a gel state and a short, rod-like shape to a flake shape, which is a relatively loose structure. Meanwhile, the main phase composition of the samples becomes Mg(OH)2, and the Mg(OH)2 contents of the surface layer and inner core of the MOC samples are 54% and 56%, respectively, while the P 5 amounts are 12% and 15%, respectively. The compressive strength of the samples decreases from 93.2 MPa to 8.1 MPa and reduces by 91.3%, and their flexural strength declines from 16.4 MPa to 1.2 MPa. However, their deterioration process is delayed compared with the samples that were dipped in water continuously for 21 days whose compressive strength is 6.5 MPa. This is primarily ascribed to the fact that during the natural drying process, the water in the immersed samples evaporates, the decomposition of P 5 and the hydration reaction of unreacted active MgO both slow down, and the dried Mg(OH)2 may provide the partial mechanical properties, to some extent. [ABSTRACT FROM AUTHOR]

This study investigated the effect of layered double hydroxides (LDHs) on the deterioration process of cement paste in the sulfate environment. Cement pastes with the addition of original and calcined LDHs at 2.5 wt.% and 5.0 wt.% of cement were exposed to Na2SO4 solution for 360 days. The macroscopic performance of the cement paste was assessed based on mass variation, porosity, compressive strength, and content of sulfate ions. Furthermore, the microhardness, microstructures, and composition of the degraded pastes were examined using Vickers hardness (HV), mercury intrusion porosimetry (MIP), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The results indicate that cement paste incorporated with LDHs can mitigate the corrosion caused by sulfate effectively, especially in the case of calcined LDHs (C-LDHs), which primarily increase the adsorption of sulfate. Compared with the control specimen, the 180 d compressive strength loss ratio of specimens with 2.5 wt.% and 5.0 wt.% of C-LDHs decreased by 63.66% and 80.51%, respectively. Moreover, LDHs can reduce the amount of ettringite crystals, densify the microstructure, and refine the pore structure to mitigate the cement paste's sulfate corrosion significantly. Compared with the control specimen, the 180 d harmful pore volume fraction of specimens laced with 2.5 wt.% and 5.0 wt.% C-LDHs decreased by 43.77% and 54.51%, respectively. In terms of the content of C-LDHs, an optimal content of C-LDHs could ensure the dominant effect of adsorption, while excessive C-LDHs could refine pores. In addition, Vickers hardness has an excellent correlation with compressive strength, which could precisely predict the compressive strength. Moreover, by combining the Vickers hardness distribution and content distribution of sulfate ions, the cross-section of the paste could be classified into four regions to evaluate the deterioration process accurately: the degraded zone, the strengthened zone, the invaded zone, and the intact zone. [ABSTRACT FROM AUTHOR]

For concrete used in severely cold regions such as the Qinghai-Tibet Plateau, the Northeast China, and the Arctic region, it will inevitably be subjected to the freeze-thaw (FT) cycles close to -40 ℃. However, the lowest temperatures of the conventional concrete FT cycle tests are not lower than -20 ℃. To investigate the differences in concrete damage between the conventional FT cycle circumstance and the severely cold FT cycle circumstance, there are two kinds of the FT cycle test circumstances in this study: -18 ℃ ∼ +5 ℃ (FTC-18) and -40 ℃ ∼ +5 ℃ (FTC-40). The results indicate that, under both FT cycle circumstances, the deterioration rate of concrete escalates as the increase in the FT cycle number. Based on numerical simulation, after the same FT cycle number and under the same stress, the quantity of cracks formed by the load inside the concrete under FTC-40 exceeds that under FTC-18. The results from multi-scale experiments and numerical simulation consistently show that the damage effect of FTC-40 on concrete is more significant than that of FTC-18. The reason for this is that at -40 ℃, more pore water freezes compared to -18 ℃. In addition, the FT damage constitutive models for concrete exposed to both FTC-18 and FTC-40 are developed. The stress-strain curves obtained from the theoretical models exhibit good alignment with the experimental stress-strain curves, thereby confirming the validity and accuracy of the established models. • The freeze-thaw cycles of −18 °C ∼ +5 °C and − 40 °C ∼ +5 °C were conducted on the concrete. • The damage of freeze-thaw cycles to concrete increases with the cycle number. • The discrete element numerical model of concrete was established. • The freeze-thaw damage constitutive model of concrete was derived. [ABSTRACT FROM AUTHOR]

Taking the dolomite with anhydrite interlayer at the bottom of Huangcaoshan Tunnel in Shanghai-Wuhan-Chengdu high-speed railway as the research object, the wetting deterioration and uniaxial compression tests were performed to study the influence of different interlayer orientations on the hygroscopic deterioration characteristics of rock and to analyze the process of rock deterioration. The wetting cracking and deformation characteristics of dolomite with interlayer in different directions were analyzed respectively from the time effect of rock micro-expansion and the change of ultrasonic longitudinal wave velocity, and the uniaxial compression evolution process of samples with different moisture absorption conditions and interlayer directions was analyzed respectively from the aspects of crack volume strain and energy dissipation. The results show that the direction of interlayer had a significant effect on the wetting and deterioration of the rock. The sample with vertical interlayer cracked obviously during wetting, resulting in volume expansion along the axial and radial directions of the sample; However, the sample with horizontal interlayer had almost only axial volume expansion, and the expansion rate was small. After the rock was wet and deteriorated, the propagation velocity of ultrasonic longitudinal wave in the rock decreased, and the decrease amplitude in the sample with vertical interlayer was greater than that in the sample with horizontal interlayer. After rock wetting, its uniaxial compressive strength, crack initiation level, expansion level, and the threshold value of elastic strain energy density for failure decreased, while the radial peak strain, the energy conversion rate of dissipation increased, and the plastic characteristics of the sample were enhanced, and the sample with vertical interlayer changed significantly compared with the sample with horizontal interlayer.

Given the flexible and configurable characteristics of smart manufacturing systems with a limited time per manufacturing task, the assumption of infinite time for prostems is no longer applicable to the joint-control strategy. Consequently, a joint-control model that considers production, inspection, and maintenance within a finite-time scenario for smart manufacturing systems is proposed in this paper. The objective is to optimize overall production and maintenance functions to minimize the total system cost. Comparing the joint strategy under infinite time with the proposed finite-time approach reveals significant differences in unit costs between the two scenarios. To enhance the effectiveness of the model, a discrete iterative algorithm with multiple loops was developed. Through a case study, it was observed that 1) joint strategies implemented within a finite time horizon were more cost-effective than those under infinite time, thus emphasizing the need for business managers to develop strategies within a finite time frame; 2) different production planning and efficiency levels had varying effects on the final joint strategy, necessitating customized strategies based on different production durations. Overall, the research gap regarding joint strategies within a finite-time context was addressed in this research, serving as a methodological foundation for practitioners to develop various strategies that minimize total costs across diverse real-world scenarios. [ABSTRACT FROM AUTHOR]

To reveal the deterioration process of magnesium oxychloride cement (MOC) in an outdoor, alternating dry–wet service environment, the evolution of the macro- and micro-structures of the surface layer and inner core of MOC samples as well as their mechanical properties and increasing dry–wet cycle numbers were investigated by using a scanning electron microscope (SEM), an X-ray diffractometer (XRD), a simultaneous thermal analyser (TG-DSC), a Fourier transform infrared spectrometer (FT-IR), and an microelectromechanical electrohydraulic servo pressure testing machine. The results show that as the number of dry–wet cycles increases, the water molecules gradually invade the interior of the samples, causing the hydrolysis of P 5 (5Mg(OH)2·MgCl2·8H2O) and hydration reactions of unreacted active MgO. After three dry–wet cycles, there are obvious cracks on the surface of the MOC samples, and they suffer from warped deformation. The microscopic morphology of the MOC samples changes from a gel state and a short, rod-like shape to a flake shape, which is a relatively loose structure. Meanwhile, the main phase composition of the samples becomes Mg(OH)2, and the Mg(OH)2 contents of the surface layer and inner core of the MOC samples are 54% and 56%, respectively, while the P 5 amounts are 12% and 15%, respectively. The compressive strength of the samples decreases from 93.2 MPa to 8.1 MPa and reduces by 91.3%, and their flexural strength declines from 16.4 MPa to 1.2 MPa. However, their deterioration process is delayed compared with the samples that were dipped in water continuously for 21 days whose compressive strength is 6.5 MPa. This is primarily ascribed to the fact that during the natural drying process, the water in the immersed samples evaporates, the decomposition of P 5 and the hydration reaction of unreacted active MgO both slow down, and the dried Mg(OH)2 may provide the partial mechanical properties, to some extent.

This study investigated the effect of layered double hydroxides (LDHs) on the deterioration process of cement paste in the sulfate environment. Cement pastes with the addition of original and calcined LDHs at 2.5 wt.% and 5.0 wt.% of cement were exposed to Na2SO4 solution for 360 days. The macroscopic performance of the cement paste was assessed based on mass variation, porosity, compressive strength, and content of sulfate ions. Furthermore, the microhardness, microstructures, and composition of the degraded pastes were examined using Vickers hardness (HV), mercury intrusion porosimetry (MIP), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The results indicate that cement paste incorporated with LDHs can mitigate the corrosion caused by sulfate effectively, especially in the case of calcined LDHs (C-LDHs), which primarily increase the adsorption of sulfate. Compared with the control specimen, the 180 d compressive strength loss ratio of specimens with 2.5 wt.% and 5.0 wt.% of C-LDHs decreased by 63.66% and 80.51%, respectively. Moreover, LDHs can reduce the amount of ettringite crystals, densify the microstructure, and refine the pore structure to mitigate the cement paste’s sulfate corrosion significantly. Compared with the control specimen, the 180 d harmful pore volume fraction of specimens laced with 2.5 wt.% and 5.0 wt.% C-LDHs decreased by 43.77% and 54.51%, respectively. In terms of the content of C-LDHs, an optimal content of C-LDHs could ensure the dominant effect of adsorption, while excessive C-LDHs could refine pores. In addition, Vickers hardness has an excellent correlation with compressive strength, which could precisely predict the compressive strength. Moreover, by combining the Vickers hardness distribution and content distribution of sulfate ions, the cross-section of the paste could be classified into four regions to evaluate the deterioration process accurately: the degraded zone, the strengthened zone, the invaded zone, and the intact zone.

In mountainous regions, protection infrastructures designed to mitigate the impacts of torrential floods often consist of a complex system of several structural components (check dams). Over time, the efficacy of this system in protecting downstream assets diminishes as the structural components deteriorate. The extent of deterioration is influenced by the interdependencies between the failure modes of individual components, as well as those between multiple components of the system. Understanding and quantifying the chain of failure events, known as cascading effects, is a critical scientific challenge that remains largely unexplored. In this study, we propose a novel approach that employs physics-based models to examine the deterioration of a series of check dams over time, while considering failure dependencies and bidirectional interactions between consecutive dams. The results obtained from this approach reveals that the absence of a downstream dam accelerates the deterioration rate of upstream dams, while its presence serves to stabilize them. We further incorporate stochastic deterioration and maintenance processes using Stochastic Petri nets to support decision-making regarding maintenance actions for each dam, while also considering economic factors. Strategies involving minor operations achieved cost-effectiveness and prolonged satisfactory performance of the dams, with notable impacts from upstream and downstream dam presence on maintenance costs. We illustrate our approach using a case study of the Faucon torrent in France, where we model the deterioration of three consecutive check dams subjected to torrential floods over a period of 100 years. • Improved understanding of check dam deterioration and maintenance strategies. • Quantitative modeling and analysis of interdependencies between check dams. • Investigating the influence of cascading effects on check dam performance. • Cost-effectiveness analysis of different maintenance strategies. • Robust modeling approach using stochastic processes and simulations. [ABSTRACT FROM AUTHOR]

Formaldehyde is a carcinogenic compound that harmful to health and often misused as a food preservative in Indonesia. However, in most of the foods including fish, formaldehyde can be formed endogenously or naturally during storage. Recently, Moonfish (Lampris guttatus) from Indonesia has been exported. Meanwhile, during delayed transportation to importing countries, moonfish need to be kept frozen up to several months This condition leads to the formation of formaldehyde. The aim of this research is to study the pattern of endogenous formaldehyde formation in moonfish during the frozen storage period. The study was conducted by observing the formation of endogenous formaldehyde as well as the formation of DMA (dimethylamine), TVB (total volatile base), TMA (trimethylamine), and TMAO as parameters related to the formation of endogenous formaldehyde in moonfish. The parameters were observed periodically shortly after the fish died until six months in frozen storage. The results showed that the content of formaldehyde, TVB, TMA, and DMA in moonfish during six months of frozen storage increased every month. The formation of natural formaldehyde in the moonfish was inline with quality degradation. Moonfish is still suitable for consumption based on its freshness level up to one month in frozen storage, but based on the formation of formaldehyde, the level of consumption should consider the calculation of maximum daily intake based on specified reference dose. [ABSTRACT FROM AUTHOR]

The Necropolis of Carmona, which has more than 600 tombs carved in calcarenites, is among the most important Roman burial sites preserved in southern Spain. The tombs in the Necropolis show severe alteration and multiple weathering processes after being excavated at the end of the nineteenth century without a preventive conservation plan. The archaeological site shows strong anthropic modifications related to different excavation stages and in relation to the construction of facilities for the visiting public. In particular, the exposure of the buried tombs to meteoric conditions and anthropic modification of natural drainage have led to an important acceleration of the deterioration of the tombs. The conservation status of the Necropolis was defined through a comprehensive geo‐environmental study that combined field observations and laboratory data, modelling and digital mapping and environmental monitoring. Results allow a methodology to be developed providing guidelines to minimize potential risks when excavating new tombs (now buried) in the future. Moreover, the most suitable prospective areas can be defined inside the Necropolis in terms of the environmental, geological and geomorphological conditions which will enhance the preservation of newly exhumed tombs. Geo‐environmental preventive conservation methods that we propose can be entirely applied to other large archaeological sites completely exposed to open‐air atmospheric conditions. [ABSTRACT FROM AUTHOR]

The purpose of this study is to integrate a conventional production-inventory management approach and a process-quality design approach so as to promote quality and reduce costs. Because the integration of these two approaches into a single system is conducted under the influence of a deterioration process, estimated costs of production must be modified. Only then can these various costs be presented as a total cost for the present integrated system. This total cost includes: a setup cost for production reordering and process resetting, quality-related costs stemming from the loss of product quality along with a tolerance-related production process cost and a failure cost for product defects, backorder costs for production shortage, carrying costs generated by the storing and handling of inventory, and material costs for determining the process mean. The Taguchi quality loss function is introduced to assess quality loss in the system. The decision variables include the initial setting (process mean), process tolerance, and production order quantity. These variables need to be determined simultaneously to minimise the average total cost for a cycle time. An example is presented to demonstrate the proposed approach. [ABSTRACT FROM AUTHOR]

• An approach for discretizing continuous-time continuous-state deterioration processes is provided. • The gamma process is considered as an example and an implementation is provided. • Matrix algebra is used to optimize a condition-based maintenance policy. We present an approach for discretizing stationary continuous-time continuous-state non-decreasing deterioration processes. This results in a discrete-time Markov chain that is represented by its transition probability matrix. Based on this approach, the easier specification of the more realistic continuous-time continuous-state models can be combined with the better analytical tractability of the discrete-time discrete-state models. We consider the gamma deterioration process as a special case and use the discretization approach combined with matrix algebra to optimize condition-based maintenance for a continuously monitored single-unit system. [ABSTRACT FROM AUTHOR]

Extra high‐voltage converter transformer resin impregnated paper (RIP) bushing is used as the outlet device of the converter transformer, its safe operation is directly related to the reliability of the power system. Under the long‐term effects of high current, strong mechanical stress and abrasion, the contact resistance of connection structure inside the bushing is prone to deteriorate. When the local overheating increases to a certain level, the insulation performance of bushing will decline and may lead to penetrating discharge. Therefore, it is vital to develop strategies for predicting the overheating fault of RIP bushings. In this study, firstly, one typical overheating fault of RIP bushing induced by the contact deterioration was diagnosed according to the fretting corrosive model and SF6 decomposition process. Secondly, using the three‐dimensional electromagnetic‐thermal‐fluid finite element method, the temperature distributions of RIP bushing under the different overheating degrees were simulated. Finally, based on the maintenance experience and simulation results, the diagnosis strategies were proposed. The diagnosis principle and prediction strategies were successfully helped to maintain the faulted RIP bushings and wall bushings before a destructive overheating accident could occur, which provide a basic reference for the fault prediction and improvements of relative standards. [ABSTRACT FROM AUTHOR]

This paper aims to integrate a two-period condition-based preventive maintenance (TP-CBM) into a pull production system by using Kanban control policy. The pull system is subject to continuous degradation and random failures. It is assumed that the system's degradation can be divided into several stages, where the hazard rate increasing factor is introduced to describe the failure rate at each stage. Meanwhile, quality of products is also considered. Markov chain is used to formulate the process of degradation and periodic inspection policy is adopted to trigger the preventive maintenance. A mathematical model is proposed to obtain the optimal production control and maintenance policies, i.e. the inspection rate, the amount of Kanban and the preventive maintenance threshold. A genetic algorithm combined with integer programming is proposed to solve the problem. Numerical instances indicate that the proposed TP-CBM policy is effective and efficient. [ABSTRACT FROM AUTHOR]

Achieving optimal production cycle time for improving manufacturing processes is one of the common problems in production planning. During recent years, different approaches have been developed for solving this problem, but most of them assume that mean quality characteristic is constant over production run length and sets it on customer’s target value. However, the process mean may drift from an in-control to an out-of-control at a random point in time. This study aims to select the production cycle time and the initial setting of mean quality characteristic, so that the expected total cost, consisting of quality loss and maintenance costs as well as ordering and holding costs, already considered in the classic models is minimized. To investigate the effect of mean process setting, a computational analysis on a real world example is performed. Results show the superiority of the proposed approach compared to the classical economic production quantity model.

In this study, the effect of the pavement maintenance cycle on the fatigue reliability of simply-supported steel I-girder bridges under dynamic vehicle loading is studied. The bridge model and the fatigue load model are both adopted from the Load and Resistance Factor Design (LRFD) Bridge Design Specifications of the American Association of State Highways and Transportation Officials (AASHTO). A three-dimensional vehicle-bridge coupled model is developed to simulate the vehicle-bridge interaction and used to obtain the stress ranges of the steel bridge girders under the dynamic vehicle loading. Numerical simulations are carried out to study the influence of three important parameters, including the road surface condition, bridge span length and vehicle speed, on the fatigue damage induced by the fatigue truck. The results from this study show that the bridge fatigue reliability decreases dramatically under repeated dynamic vehicle loads when the road surface condition is very poor and that the pavement maintenance cycle has a significant influence on the bridge fatigue reliability. A procedure for determining the desired pavement maintenance cycle to achieve the target fatigue reliability of steel bridge girders is developed. An example is also provided for demonstrating the proposed procedure. [ABSTRACT FROM AUTHOR]

To ensure the safety in seaport terminal, many maintenance activities should be done every year. However, frequent and delayed maintenance activities would cause low service quality and require large sums of money. Therefore, a study of maintenance scheduling in seaport is needed to be carried out. The aim of this paper is the study and the design of a maintenance module based on Petri nets (PNs) for container handling equipment. In this context, we propose a new P-time Petri net for maintenance (PTPNM). This tool includes spare parts, maintenance group and deterioration process. The PTPNM can give a true expression of the system operation process by introducing time, which is suitable for process indexes calculation and evaluation such as equipment maintenance, support resources utilization, mission success rate and average waiting time. [ABSTRACT FROM AUTHOR]

The current practice for bridge-fatigue design may have underestimated the effect of dynamic vehicle loading and truck overloading on the fatigue life of steel bridges. In this study, a new approach for fatigue design of steel bridges was proposed that considers the effect of these two factors more rationally. A three-dimensional vehicle-bridge coupled model was developed to simulate the interaction between the bridge and vehicle. A simply supported steel I-girder bridge was used as an example for illustration of the proposed approach. The fatigue vehicle model was adopted from the AASHTO LRFD code, and overloading was considered by increasing the gross weight of the truck model. Numerical simulations were conducted to study the influence of three important parameters--road surface condition (RSC), vehicle speed, and truck gross weight--on the fatigue damage of the bridge considered. The results show that the RSC and truck gross weight both have a significant impact on the bridge-fatigue damage. By considering the cumulative fatigue damage caused by each truck passage under different RSCs and the deterioration process of the RSC during its whole lifecycle, a simple and reasonable expression was proposed for bridge-fatigue design. The proposed approach improves the current bridge-fatigue design method in that it rationally considers the vehicle dynamic effect, the influence of overloaded trucks, and the deterioration of RSC, which have a large influence on bridges' fatigue life. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to evaluate the impact factor (IM) in LRFD bridge design specifications for fatigue design and to propose a method for determining reasonable IMs for the fatigue design of steel I-girder bridges that can more rationally consider the effect of the deterioration of the road surface condition (RSC) during its whole lifecycle. The deterioration process of the RSC was investigated under the given traffic and environmental conditions, and the number of truck passages taken for the RSC to deteriorate from one class to the next was investigated. A three-dimensional coupled vehicle-bridge model was developed to simulate the interaction between the bridge and vehicle, with both the bridge and fatigue load models adopted from an existing LRFD code. The IM of the stress range (IM-SR), which is calculated using the stress range instead of the maximum stress used traditionally, was used for the fatigue analysis of steel girders. Numerical simulations were performed to study the IM-SR of steel I-girder bridges under different RSCs while taking into consideration the effect of two other important parameters: bridge span length and vehicle speed. Results show that the RSC has a greater impact on the IM-SR than on the traditional IM, and the IM-SR is greater than the traditional IM calculated using the maximum stress. By considering the cumulative fatigue damage caused by the passage of each truck under different RSCs and the deterioration process of the RSC during its whole lifecycle, simple and reasonable expressions were proposed for the IMs for fatigue design of steel I-girder bridges under the given traffic and environmental conditions. [ABSTRACT FROM AUTHOR]

The number of stress cycles ( NSC ) specified in the AASHTO LRFD bridge design specifications for the fatigue design of steel bridges is evaluated in this paper. A new approach for determining the reasonable number of stress cycles for the fatigue design ( NSC_ FD ) of simply-supported steel I-girder bridges is proposed which takes the dynamic effect of vehicle loading into account. A three-dimensional vehicle–bridge coupled model is developed to simulate the interaction between the bridge and vehicle, in which both the bridge and fatigue load models are adopted from the LRFD code. The equivalent number of stress cycles ( ENSC ), which is calculated based on the fatigue damage accumulation from the dynamic stress time history due to each truck passage, is used for the fatigue analysis of steel girders. Numerical simulations are conducted to study the influence of three important parameters, including the road surface condition (RSC), bridge span length and vehicle speed, on the ENSC of simply-supported steel I-girder bridges. Results show that the RSC has a great impact on the ENSC . By considering the cumulative fatigue damage caused by each truck passage under different RSCs and the deterioration process of the RSC during its whole life cycle, simple and reasonable expressions are proposed for calculating the NSC_ FD of simply-supported steel I-girder bridges under the given traffic and environmental condition. [ABSTRACT FROM AUTHOR]

Optimized maintenance and management strategies are often emphasized in infrastructure management. Although such strategies serve to facilitate decision making, it is important to recognize that revolutions in asset management can come from improvements to hardware performance rather than managerial techniques. Underlying the managerial solutions, this study focused on the utility of various pavement materials and a special layer to support a performance-oriented asset management plan. This study compared the life expectancy and uncertainties of Stone Mastic Asphalt (SMA), Polymer Modified Asphalt (PMA), Rut-resistant Asphalt (RRA), Porous Asphalt (PA), and conventional hot-mix asphalt (HMA), which are widely introduced in field maintenance works. Problems associated with insufficient data due to short elapsed time and insufficient time-series performance data were mitigated by employing an advanced statistical method, the Markov mixture hazard model applying hierarchical Bayesian estimation. Empirical studies were conducted using historical performance data covering a period of 5 years (2002-2007) from 150 special monitoring sections in the K-Network. The results provide useful information for developing improved specifications for maintenance design and performance-based contracts that may lead to radical reform of infrastructure asset management. The Markov mixture hazard model with hierarchical Bayesian estimation is also a powerful tool for solving critical limitations in the post-evaluation of short-term projects. [ABSTRACT FROM AUTHOR]

The objective of this study is to examine the influence of cation type on deterioration process of cement paste exposed to external sulfate attack. The experiment was carried out by micro-hardness test (Vickers hardness), compressive strength test and expansion test. Solutions respectively containing Na 2 SO 4 , K 2 SO 4 , (NH 4 ) 2 SO 4 and MgSO 4 with sulfate concentration of 5.0 wt% were chosen as the sources of sulfate to attack the cement paste. The pH values of solutions containing different sulfate salts were measured to support the analysis. The deterioration process of the cement paste specimens immersed in different attacking solutions was analyzed. The results shown that, the reducing rate of Vickers hardness of cement paste samples immersed in solutions containing different sulfate salts were generally sequenced as Na 2 SO 4 ≈ K 2 SO 4 > MgSO 4 > (NH 4 ) 2 SO 4 . With the addition of exposure time, the deterioration process exerted at different rate with the variation of sulfate salts. The expansion of specimens immersed in solutions containing Na 2 SO 4 , K 2 SO 4 , MgSO 4 and (NH 4 ) 2 SO 4 occurred in two stages within a certain range of exposure time. Besides, compressive strength appeared to be well correlated with Vickers hardness for different kinds of sulfate salts. [ABSTRACT FROM AUTHOR]

Joint reliability importance (JRI) evaluates the interaction of two components in contributing to the system reliability in a system. Traditional JRI measures mainly concern the change of the system reliability caused by the interactive change of the reliabilities of the two components and seldom consider the probability distributions, transition rates of the object component states, and system performance. This article extends the JRI concept of two components from multi-state systems to multi-state transition systems and mainly focuses on the joint integrated importance measure (JIIM) which considers the transition rates of component states. Firstly, the concept and physical meaning of JIIM in binary systems are described. Secondly, the JIIM for deterioration process (JIIMDP) and the JIIM for maintenance process (JIIMMP) in multi-state systems are studied respectively. The corresponding characteristics of JIIMDP and JIIMMP for series and parallel systems are also analyzed. Finally, an application to an offshore electrical power generation system is given to demonstrate the proposed JIIM. [ABSTRACT FROM AUTHOR]

The article explores a problem of loss measures and setup determination for a process under performance deterioration. An integration method is presented to determine the probability function sojourning in each state at some point in time for this deterioration process. Several performance-evaluation methods are first presented based on probability functions of states. After which, a general class of loss functions is integrated to construct loss measures.

Abstract: In this paper a replacement-repair model is developed to study a renewing free replacement warranty (RFRW) for a class of multi-state deteriorating repairable products. After a replacement, the product warranty is renewed. Two parameters affect the manufacturer’s decision to minimally repair or replace a failed item: the product deterioration level at the time of failure and the remaining warranty time. We derive an optimal replacement-repair policy to minimise the expected warranty servicing cost per item sold. In the case of a product with two different working states, we are able to explicitly find the optimal values of the replacement-repair parameters using the Adomian decomposition method. In general, for , it is impossible to find the optimal parameter values analytically. Hence, a computational procedure for finding these optimal values is proposed. For more clarification, numerical examples are also presented. [Copyright &y& Elsevier]

Many manufacturing processes and production systems suffer from progressive degradation with usage and age and are subject to random failures resulting from such deterioration. Traditional models for evaluating the reliability and performance of a process/system use binary-state models, with working success or failure, to classify the states of the process/system that are unrealistic. This article proposes the classification of discrete multiple states of the deterioration process. A nonhomogeneous continuous-time Markov process is employed for modelling the process deterioration because we assume that the time for which a process stays in certain state depends not only on the current state but also on the time for which the process has been in the current state. For major and minor deteriorations, we present symbolic solutions of several differential equations by using MATLAB to estimate the probability of the process being in each state at time t. We contribute dynamic performance and cost measures for the state-age-dependent process deterioration to assess the severity of the deterioration at some point in time as well as the total severity that it causes over the entire process. The optimal setup time is determined in order to estimate the minimum total expected cost during the production period. A practical application of the proposed methodology is illustrated throughout this article. [ABSTRACT FROM AUTHOR]

In the conventional production-inventory management approach, the production order quantity is determined by referring to costs such as the ordering cost and inventory cost. However, the quality level being produced may change during the production process owing to process deterioration. Thus, under process deterioration, a production order quantity based solely on the conventional production-inventory management system may be overproduced, due to a lack of consideration of varied quality costs at different points of time, along with the production run length. Hence, for cyclical quality promotion and cost reduction, there is a motivation to extend the conventional production-inventory management approach by adding the process-quality design approach which considers the varied quality-related costs as a function of time. The decision variables include the initial setting, process tolerance, and production order quantity, which have to be determined simultaneously for true optimization so that the average total cost, which includes the setup cost for production reordering and process resetting, quality loss, and tolerance cost for process quality, and the inventory cost for production inventory, is minimized. An example of a production process subject to process deterioration is presented for illustrating the possible application of the proposed model. [ABSTRACT FROM AUTHOR]

This paper considers a problem of reliability assessment and determination of optimal replacement time for a machine tool under wear deterioration. Traditional models classifying a tool’s condition use binary states, with working (success) or failure (1 or 0), to evaluate its reliability and decide its optimal replacement time; however, as most machine tools deteriorate over time, a multi-state discrete model is reported as a more realistic classification for quantifying the tool wear condition. In this paper, we propose a nonhomogeneous continuous-time Markov process (NHCTMP) for modeling the tool wear process, representing the length of time the tool stays in a certain state, which depends not only on its current state but also on how long it has remained in the current state. According to this model, we first develop reliability assessment for the tool with the multi-state deterioration. Then, we derive an average expected cost function of the tool operating over the manufacturing period and optimize it to find the optimal replacement time of the tool. The optimization of the average value of the expected cost over tool replacement time emerges as a classical tradeoff idea, balancing between increasing the average cost of tool replacement and decreasing the average cost of tool deterioration. A real application is illustrated throughout the paper. [ABSTRACT FROM AUTHOR]

As a common used injection in China, the ‘Qing Kai Ling’ injection is holding the extensive attention. However, the injections made from different manufactures may cause different curative effects due to their unstable qualities. Thus an evaluation method is needed. Fourier transform infrared (FTIR) spectroscopy has several advantages, such as fast, accurate, and easy to handle, in the analysis. So it is chosen as the integrity identification to the injections. Furthermore, two-dimensional (2D) correlation analysis was used to enhance the IR information, that is, more detail could be gained. Using 2D IR method ‘Qing Kai Ling’ injections from different pharmaceutical factories could be identified easily. Also, the different batches of the injection in the same factory could be differentiated. In a conclusion, FTIR spectroscopy combined with 2D correlation analysis provides a powerful method for the quality control of the traditional Chinese medicine injections. [Copyright &y& Elsevier]

The traditional Chinese medicine ‘Qing Kai Ling’ injection after deterioration is distinguished from the original formulation using Fourier-transform infrared spectroscopy (FTIR) and two-dimensional correlation infrared spectroscopy (2D-IR). The IR spectra of the injections before and after deterioration are so similar, that it is very difficult to distinguish them by using the conventional approach. However, the higher spectral resolution and more structural information provided by 2D-IR analysis makes the identification possible. According to the results of 2D correlation analysis, the band at 1611 cm−1 in IR spectra, in fact, consists of the overlap of three bands at 1572, 1667 and 1729 cm−1, which are assigned to the alkaloids (heterocyclic compounds), flavone derivatives, and carbonyl compounds in the injection, respectively. Interestingly, the autopeak at 1667 cm−1 disappears in synchronous spectrum of the deteriorated ‘Qing Kai Ling’ injection. It is suggested that the deterioration of the injection in air at room temperature be due to the oxidation of the flavone compounds mainly. As all intensities of the correlation peaks involved with the band in 1059 cm−1 decrease greatly, it is assigned to the thermal decomposition of the glucoside components. Hence, it can conclude that the oxidation of the flavone compounds and the decomposition of the glucoside components are some of the main causes concerning to the deterioration of ‘Qing Kai Ling’ injection at ambient temperature. Thus, the 2D-correlation analysis provides a powerful method for the quality control of the traditional Chinese medicine injection. [Copyright &y& Elsevier]