Service Life Assessment Research Articles

Hypochlorous acid electrosynthesis and service life assessment of a Ti|Ti–Ru–Ir-oxides anode assembled in a flow electrolyzer: Understanding the influence of the concurrent O2 bubbling flow

This paper addresses the influence of bubbling flow and service life of the Ti|Ti–Ru–Ir-oxides anode during the electrosynthesis of HClO in a laboratory-scale filter-press-type electrolyzer. The electrolyzer was assembled in a flow plant in recirculation mode. Polarization curves in rotating disk electrode (RDE) revealed the coexistence of the oxygen evolution reaction (OER) during HClO electrosynthesis in diluted chloride solutions (containing 35 mM NaCl at pH 3). CFD simulations of the two-phase (O2–H2O) flow were obtained by solving simultaneously the Navier-Stokes and charge conservation equations using a finite element method code. The O2–H2O simulations show the efficient gas release in the electrolyzer provoked by the continuous phase (H2O) inertia and the well-engineered cell design. The moderated O2 dispersion caused a quasi-homogeneous current distribution along the anode. However, the current efficiency during HClO electrosynthesis gave values of ∼32% provoked by the OER on the anode. The HClO accumulations (from 3.02 to 6.64 mM) showed excellent agreement with CFD simulations. The accelerated life tests revealed that the Ti | Ti–Ru–Ir-oxides anode has a lifetime of at least 26 years during the HClO electrosynthesis in diluted chloride solutions.

Acceleration of Service Life Testing by Using Weibull Distribution on Fiber Optical Connectors

The service life assessment of previous fatigue stress has a fundamental role in estimating the reliability of products like fiber optical connectors, and should replicate use in severe environments in telecommunications systems. However, the vibration prediction models used in the literature present limitations in vibration life prediction. In this paper, we propose using the insertion loss fatigue life and including it in the Weibull distribution to determine the Weibull parameters ƞ and β to evaluate fiber optic connector reliability R(t) under environmental and mechanical testing stress. We analyzed the failure data of a standard telecommunication fiber optical connector under a program of service life stress testing against that of a fiber optical connector under only mechanical vibration stress testing. The fiber connectors were monitored during the vibration testing to review the transient change of the optical signal. Their results showed that the reliability of the fiber connectors submitted to the service life program was Rt=0.694, while that of the fiber connectors submitted to mechanical vibration only was Rt=0.970. In addition, the analysis showed that the service life testing consumed 70.2% of the product’s lifetime. We present in Numerical Validation the steps to determine the acceleration factors of the vibration test developed.

Deterioration Mechanism and Status Prediction of Hydrocarbon Lubricants under High Temperatures and Humid Environments

In practical engineering applications, high temperatures and water ingress seriously affect the service life of hydrocarbon lubricants. In this study, the deterioration process of hydrocarbon lubricants under high temperatures and humid environments was investigated, and a new health state prediction model was proposed. Simulation of hydrocarbon lubricant Polyalpha−olefin (PAO) molecules used the ReaxFF force field to analyse the high temperature thermal oxidation process of lubricants. The rheological properties of oil−water emulsions were determined by observing the morphology of oil−water two−phase mixtures with different water contents. A multiparameter fusion viscosity prediction model was proposed using a linear model of the viscosity of aqueous fluids, as affected by temperature and water content, and was fitted with the Andrade viscosity−temperature equation to predict lubricant viscosity changes under multiple parameters. Online validation tests were carried out on a compound planetary transmission system, and the surface topographical parameters of the transmission components were further discussed. Experimental results show that the linear correlation with the improved lubricant viscosity prediction model is 0.966, and the surface wear of transmission components is consistent with the trend of lubricant quality change. These findings provide a fundamental basis for the assessment of lubricant service life in high temperatures and humid environments.

Investigation of neighboring grain effects on load shedding in titanium alloys under cold dwell fatigue

Load shedding under cold dwell fatigue in titanium alloys has been a threat to the safety of the aero-engine since it is responsible for crack formation. The strain incompatibility between the soft-hard grain pair arises from the significant creep in the soft grain during the dwell period, which is fundamentally related to the load shedding. Such deformational heterogeneity is not only affected by the soft-hard grain itself but also by its neighboring grains, but the effect of the latter is rarely reported. In this paper, the effect of neighboring grains, including location, crystal orientation, texture, etc., on load shedding is quantitatively investigated using a three-dimensional rate-dependent crystal plasticity model by controlling the microstructural morphology of the grains. In particular, the mechanism that the dwell fatigue cracks tend to nucleate from the sample's interior rather than the free surface is revealed. Restriction of rigid body rotation from neighboring grains can further enhance load shedding. The crystal orientation of individual and group neighboring grains sitting at different locations with respect to the soft-hard grain pair is evaluated. The grain directly attached to the hard grain has the strongest influence. The statistics of load shedding are analyzed by conducting hundreds of simulations with different textures. Stronger textures are found to be able to enhance load shedding and thus deteriorate the service lifetime. The change of locations showing the highest stress during the dwell period arising from plastic deformation in neighboring grain may lead to the phenomenon of reverse load shedding. Understanding the neighboring grain effects from both the mechanistic basis and the statistical point of view is important in integrity evaluations and service life assessments of titanium components in aero-engines.

Service life modelling of carbonated reinforced concrete with supplementary cementitious materials considering early corrosion propagation

The importance of considering corrosion propagation in service life design of carbonated concrete with supplementary cementitious materials (SCMs) has been highlighted by the decline in carbonation resistance caused by partial replacement of ordinary Portland cement (OPC) with SCMs. This study proposes a novel Carbonation-induced Early Corrosion Propagation based Service-life Assessment Model (CECP-SAM) for carbonated SCM concrete, which is characterized by the considerations of semi-carbonation zone and macrocell corrosion in corrosion propagation with an incipient crack as end of service life. Experimental and field data were used to verify CECP-SAM. The effects of exposure conditions, SCM replacements, water/binder ratio, cover thickness, rebar diameter, semi-carbonation zone and macrocell corrosion on service life are presented. Results indicate that the partial replacement of OPC with pulverized fuel ash (PFA) and ground granulated blast furnace slag (GGBS) can significantly decrease service life from 66 years to 8 years and 17 years, respectively. Corrosion propagation can result in a 91% reduction in service life but service life can be extended from less than 20 years to more than 90 years by considering early corrosion propagation. Practical equations are proposed to facilitate performance-based service life design. Prescriptive limits are also provided for service lives of 50 and 100 years.

Thermal and structural response of a pavement solar collector prototype

Thermal and structural response of a pavement solar collector prototype

Determination of reference service life for reinforced concrete multistorey residential buildings: case study of Akure, Nigeria

The Service life of a building is the period from commencement of service to the time just before costly maintenance becomes necessary for continued meeting of minimum performance requirements. Knowledge of service life determines whether to demolish and replace a building or major repairs are required and the absence of information on this has led to many building failures. This research therefore aimed to determine the Reference Service Life (RSL); a parameter required for the evaluation of a building’s Service Life. Twenty reinforced concrete multistorey residential buildings around the Federal University of Technology Akure (Nigeria) were assessed via visual inspection, material testing, and structural analysis. Information obtained from the assessment was used to develop a comprehensive open-ended service life database. Non-destructive tests were conducted on the buildings’ structural elements and the results used to determine the service life of each of the buildings with the aid of Life 365 Software. Weighted factors which depend on the quality characteristics, operational conditions and the environment of the buildings were used as a grading system for the assignment of sub-factors for the adjustment of the Life 365 service life values, leading to a value of 29 years as the Reference Service Life (RSL) for the study area. The result obtained will benefit construction professionals and appropriate regulatory authorities in the study area while the procedure can be adopted for service life assessment in other locations lacking appropriate database.

A Lifetime Prediction Method of Pressured Gas Polyethylene Pipes by Strain-Hardening Modulus and Tensile Test

In recent years, polyethylene (PE) pipes have been widely utilized for urban natural gas transmission. However, as the use of high-density polyethylene (HDPE) pipes increases, their service life and long-term performance assessment have become one of the most significant issues to be addressed. There has been a ton of studies on PE pipe life prediction techniques both domestically and internationally, but very little has been carried out on PE pipe life prediction in actual gas working environments with varying acid and alkaline levels. This experiment accelerates the aging of PE pipes using acid and alkaline corrosion immersion experiments to determine the lifespan of PE pipes. This study aims to investigate the performance changes of HDPE under strong, weak, and neutral corrosion conditions using corrosion solutions with PH values of 1, 5, and 8, to propose the impact of corrosion caused by various acids and alkalies on the HDPE aging life for natural gas, and to develop a mathematical model between the aging life of polyethylene and the PH values of acid and alkali corrosion solutions. The studies involved soaking and corroding HDPE pipes with various acidity and alkalinity chemicals to speed up the aging process, and then the tensile test was used to determine the mechanical characteristics of the aged PE pipes. Based on our findings, the empirical equation between acidity and service life of PE pipes is obtained by the mathematical fitting method, and a life prediction model of buried city gas HDPE pipes is proposed. The actual life of the aged pipes is determined by the relationship between strain-hardening (SH) modulus and aging time. The findings demonstrate that the service life of PE pipes changes with different levels of acidity and alkalinity: 1.872 days, 1060.507 days, and 1128.58 days following corrosive solution-accelerated aging with solution acidities of PH1, PH5, and PH8, respectively. The life prediction method applies to various plastic pipes in comparable environments as well as HDPE city gas pipes that are subject to acid and alkali corrosion forces.

Service life assessment of yttria stabilized zirconia (YSZ) based thermal barrier coating through wear behaviour

Countless research has suggested Yttria-stabilized Zirconia (YSZ) to be a top candidate for being implemented as thermal barrier coatings (TBC). However, when exposed to prolonged service, temperature and stress variations succeed in initiating a catastrophic phase transformation from tetragonal to monoclinic structure in Zirconia. Hence, the estimation of endurance for YSZ-based TBC is necessary to minimize failure in such situations. The main purpose of this research was to determine the relationship between tribological investigations and the estimated lifespan of YSZ coatings accurately. The study used various methods such as wear resistance testing, optical profilometry, specific wear rate, and coefficient of friction to estimate the maximum durability of TBCs. The research also provided insights into the composition and microstructure of the TBC system and found the optimized concentration of Yttrium doping to be 3.5 wt %. The study discovered that erosion was the main cause of roughness depreciation from SN to S1000. The estimation of the service life was primarily made based on optical profilometry, specific wear rate (SWR), coefficient of friction (COF) and wear resistance values which were further supported by the results of chemical characterization of the samples through electron dispersive spectroscopy (EDS), wavelength dispersive spectroscopy (WDS) and X-Ray Diffraction (XRD) analysis. The results were reliable and accurate and suggested future areas of investigation, such as 3D profilometry for surface roughness and thermal conductivity evaluation using laser-assisted infrared thermometers.

Service-life assessment of aircraft integral structures based on incremental fatigue damage modeling

The Ottosen–Stenström–Ristinmaa (OSR) incremental fatigue damage model is adapted for fatigue-life assessment of integral airframes milled from 7050-T7451 aluminum plates. For validation, variable-amplitude high-cycle fatigue experiments are conducted for circumferentially notched, axisymmetric specimens, and for a geometry similar to an aircraft fuselage frame, with flanges, stiffeners, and web panels. We also describe how the parameters of the OSR model can be modified to account for surface roughness, and for setting acceptable failure probability.

Survival Analysis of Concrete Overlays on Low-Volume Roads in Iowa

Concrete overlays are an important component of Iowa’s rural road network. More than 2,000 centerline miles of concrete overlays have been paved in Iowa over the last few decades, including many overlays on low-volume roads serving 400 vehicles per day or less. In this study, a survival analysis was performed using automated pavement condition data collected on Iowa’s concrete overlays to obtain a probabilistic assessment of concrete overlay service life, paying particular attention to the performance of overlays on low-volume roads. Concrete overlays were found to perform very well, with a 30-year survival probability of 85.3% for all projects to rehabilitation or reconstruction, and 76.6% for overlays only on low-volume roads. Survival life was reduced when the survival condition was changed to performance thresholds based on a pavement condition index (PCI) of 60/100 and an International Roughness Index (IRI) value of 170 in./mi, but was still good overall. Overlays tended to reach the failure condition for PCI before IRI, indicating that cracking is a more common distress than surface roughness. Another important finding was that concrete on asphalt overlays had a longer median survival life and a greater 30-year survival probability than concrete on concrete-unbonded overlays. Overall, concrete overlays have performed well in Iowa and are well suited to low-volume roads and rural county highways.

Comprehensive Evaluation of Pavement Waterproofing Layer Materials for Bridge and Tunnel Projects

In order to achieve the preferential selection of pavement waterproofing layer materials, so that the waterproofing layer material selection is more scientific and objective, eliminating the impact of subjective factors, this paper uses hierarchical analysis to build a hierarchical evaluation model of pavement waterproofing layer. Based on the literature review method, a two-tier evaluation index of the layered evaluation model of pavement waterproofing layer materials was constructed, mainly three first-tier indexes of performance assessment, service life assessment, and cost assessment, under which the second-tier indexes of waterproofing performance, durability, weather resistance, impermeability, crack resistance, thermal stability, aging resistance, low temperature crack resistance, fatigue resistance, material cost, construction cost, and maintenance cost were established. And through the hierarchical analysis method of calculation, test the consistency by deriving the weight of each indicator, where the most important first layer of indicators for performance, the weight of 0.5390, the second layer of indicators is more important for waterproof performance (0.5303), thermal stability (0.3550), low-temperature crack resistance (0.3550), material cost (0.6333). The study provides a scientific and objective evaluation model for the preferential selection of pavement waterproofing layer materials.

The Development of Comprehensive Technology for Non-Destructive Testing of Implicit Defects and Service Life Assessment of Polymer Composite Materials

The Development of Comprehensive Technology for Non-Destructive Testing of Implicit Defects and Service Life Assessment of Polymer Composite Materials

A viscoelastic constitutive model considering deformation and environmental-induced damages for solid propellants

Realistically representing the constitutive response of solid propellants is crucial for industrial use and service life assessment of solid rocket motors (SRMs), as they are generally stored for a long time and exposed to complex loadings and environmental conditions, resulting in the possible loss of the grain structural integrity of SRMs and consequently the failure in the motor. This contribution develops a three-dimensional viscoelastic constitutive model that considers the effects of damages caused by environmental factors and large deformation. Environmental-induced damages are represented by introducing normalized crosslinking density (CLD) and micropore evolution, which is assumed to be the coupled results of oxidation, hydrolysis, degradation, migration, etc. Deformation-induced damages are attributed to interface debonding or failure in the binder as well as cyclic loadings. An ABAQUS subroutine based on the current model is then applied for numerical analysis. The effects of strain rate, temperature, confining pressure, cyclic loadings, and environmental aging on the stress response are presented. The predicted results match reasonably well the experiments. As the model takes into account the microstructural changes both due to mechanical loadings and environmental effects, it applies to the stress analysis of solid rocket motors, whether new or stored for years.

Prediction of chloride resistance level of concrete using machine learning for durability and service life assessment of building structures

The resistance of concrete to chloride penetration determines the durability and service life of reinforced concrete building structures in coastal or chloride-laden environments. This work adopted five machine learning algorithms, naïve bayes, k-nearest neighbors, decision trees, support vector machine, and random forests, to predict the chloride resistance level of concrete based on its ingredients, considering two scenarios. The first scenario considers all features describing the mix components, whereas the second scenario considers only a subset of the features. All models are validated by performing intensive evaluation matrices using unseen data. The validation results confirm that the developed models predict the level of chloride resistance of concrete with high accuracy. Of all the algorithms, the support vector machine performed best, with 89% and 88% accuracy in the first and second scenarios, respectively.

Modeling carbonation depth of recycled aggregate concrete using novel automatic regression technique

Waste from concrete demolition is a sustainability concern that can be mitigated when used as recycled aggregate in concrete instead of virgin natural aggregates. However, the durability of recycled aggregate concrete (RAC), including concrete carbonation, needs to be investigated before the widespread applications of RAs in construction. Developing artificial intelligence-based predictive models for estimating the carbonation depth of RAC using the available data can reduce the need for experimental studies to generate reliable models for the service life assessment of concrete structures. In this study, artificial bee colony expression programming (ABCEP), as a novel branch of automatic regression technique, was used to predict the carbonation depth of RAC from a large dataset consisting of 655 data samples. Several ABCEP architectures were developed, different analyses were conducted, and a comparison study between the best ABCEP model and previous models published in the literature was conducted. The findings show that the best structure of the ABCEP model could estimate the carbonation depth of RAC with a reasonable root mean square error of 3.33 mm. The exposure time was the most influential parameter affecting the carbonation depth of RAC. Furthermore, the ABCEP model could outperform the previous models, despite the larger unknown dataset used to test its performance.

An Evaluation of the Hydrolytic Stability of Selected Experimental Dental Matrices and Composites.

Materials with potential use as dental restoration should be evaluated in an aggressive environment. Such accelerated aging is widely used in other industries and allows the assessment of service life. In the presented study, three neat resins (UDMA/Bis-GMA/TEGDMA 70/10/20 wt.%, UDMA/Bis-GMA/TEGDMA 40/40/20 wt.% and UDMA/Bis-EMA/TEGDMA 40/40/20 wt.%) and three composites based on these matrices were tested before and after aging protocols (I-7500 cycles, 5 °C and 55 °C, water and 7 days, 60 °C, 0.1 M NaOH; II-5 days, 55 °C, water and 7 days, 60 °C, 0.1 M NaOH). Flexural strength (FS), diametral tensile strength (DTS) and hardness (HV) were determined. Applied aging protocols resulted in a decrease in the value of the FS, DTS and HV. Larger changes were noticed for the neat resins. Materials in which the content of bis-GMA was lower or substituted by bis-EMA showed better resistance to degradation. The choice of mixtures with monomers characterized by lower sorption values may favorably affect hydrolytic stability. It was shown that for composites there was a drastic decrease in hardness, which suggests a more superficial effect of the used protocols. However, degradation of the surface layer can result in a growing problem over time given that the mastication processes are an inherent element in the oral environment.

ANALYSIS OF THE MOST COMMON DAMAGES IN REINFORCED CONCRETE STRUCTURES: A REVIEW

Reinforced concrete structures are often subjected to various negative environmental influences, reducing their reliability and durability. Main engineering tasks include extension of their life cycle, assessment of durability, reliability and residual service life. This requires reliable assessment of existing damages due to negative environmental impacts. Deterioration of RC structures is complex issue, which should be considered with the account of various factors. Damages and defects should be assessed, according to different criteria: degradation degree, type, time and cause of formation, etc. Article provides detailed analysis of the most common damages in RC structures on the basis of thorough literature review of this issue. Also, the classification of reasons for decrease of bearing capacity is proposed. Additionally, are discussed corrosion mechanisms and specifics of stress-strain state in corroded RC structures.

Remaining Service Life (RSL ) Assessment of Engine Oil in Rock Excavators

The quality of lubricant oil plays a central role in the performance of machineries. Aggressive working environment of industry, particularly in mining industry, remains a dominant point in faster rate of degradation. The colossal consumption of oil is a factor to an inflated maintenance cost which can be averted by optimizing the lubricant oil consumption using scientific and methodical approaches. At present the schedule drain-off interval is accomplished at a regular interval of operation hour recommended by manufacturers. This is a conservative approach and results in loss of useful life. This work aims to determine the Remaining Service life (RSL) of the engine oil in Excavators. The oil properties are measured at regular intervals. Kinematic Viscosity, Viscosity Index (VI), Total Acid Number (TAN) and Total Base Number (TBN) are measured. The measured values suggest the degradation level of oil before filling fresh oil. The remaining service life (RSL) is determined by juxtaposing Parameter Profile Approach (PPA), Analytical Hierarchy Process (AHP) and Vector Projection Approach (VPA). The approach will be a precursor to the excavator maintenance personnel to drain-off the oil at right time despite of manufacturer’s recommendation.

Quality Control Method for the Service Life and Reliability of Concrete Structures

In the past few years, there has been an increasing societal and industrial demand for the reliable assessment and design of structural systems with service-life criteria of at least several decades. The life cycle characterisation of engineering structures in terms of an anticipated service life remains a significant aspect of sustainability in the construction industry. This requires special attention to the definition of structural performance under various actions, and to the implemented engineering materials and methods as well as to the inverse identification and monitoring of structural conditions. Subsequently, the focus remains on the development of a holistic performance-based design approach for new and existing structures and infrastructures. This paper presents the fundamental reliability concepts of performance-based design, with a focus on lifetime assessment. Case studies from actual structural components’ design are used to verify the proposed methodology and indicate the significance of quality assurance in the lifetime assessment of engineering structures. We also confirmed that reliability and quality assurance criteria are strongly connected. Therefore, a methodology for quality-based service life assessment is presented and elaborated in the case studies.