Estimation Of Service Life Research Articles

Crack Propagation in the Spur Gear of Tubler Gear Mechanism of Lathe Machine

An estimation of the spur gear service life and crack path analysisis proposed in this paper. Ip theory using numerical solution is used to find the fatigue crack propagation rate, service life, and crack path due to bending fatigue. A spur gear of tumbler gear mechanism of lathe machine, is implemented for this analysis. An experimental test on gear specimens was carried out to analyze the crack propagation due to fatigue. Besides, service life estimated by the theory was compared with the most common Paris law. Hence further, extended finite element approach (Ansys)is implemented for the simulation of gear crack propagation trajectory. The simulation results are verified with experimental test. The service life and crack trajectory of the gear is obtained with ‘Ip’ theory and found in good agreement with experiment.In overall, this study signifies the gear failure prediction methodology during crack propagation in respect of life cycles and trajectory path.

Resistance of phosphogypsum-based supersulfated cement to carbonation and chloride ingress

The search for cements with lower CO2 emissions and lower consumption of non-renewable materials has been a challenge for the cement industry. The aim of this study was to investigate the resistance of SSC concrete to carbonation and chloride ingress. Portland cements (CEM I and CEM III/B) were used as a comparison. The results showed that the carbonation was very advanced in the SSC concretes. This is related to the exclusive formation of C-S-H and ettringite as hydration products, which present a higher rate of carbonation than portlandite. The SSC concrete has a good performance in terms of chloride penetration, mainly due to the increased ability to combine chloride ions both physically and chemically. The service life estimation showed that SSC concretes could be suitable for rural and urban environments when low w/c ratios (0.40) are used. All SSC mixtures studied were suitable for chloride environments.

Experimental investigation on creep‐fatigue behaviours of as‐received and service‐exposed turbine blades: Mechanism and life evaluation

AbstractIn the present study, both the as‐received and the 600‐h‐serviced turbine blades were tested under the creep‐fatigue loading. The results showed that the service‐exposed blades exhibited a longer creep‐fatigue life than the as‐received ones due to the refinement of grain size and the increasing of hardness during the service process. Micro structural characterization revealed that there was no directional coarsening or rafting of γ′ precipitate after 600 h of service. Moreover, the as‐received blades exhibited initial cyclic hardening followed by saturation and softening, whereas the 600‐h‐serviced blades only exhibited continuous softening until fracture. A conservative service life prediction approach was proposed considering the experienced mission profile. This service life estimation method provides a new way to assess the durability of turbine blade.

Time to cracking in concrete cover length due to reinforcement corrosion via a simplified fracture mechanics approach

Determination of the concrete cover cracking time is one of the main parameters in estimating service life of concrete structures exposed to chloride-laden and other aggressive environmental conditions. The corrosion of reinforcing steel embedded in concrete occurs as a result of chloride attack or carbonation, and thus the increase in the volume of corroded reinforcing steel cracks the cover. In this paper, a theoretical model is proposed to calculate the cracking initiation and propagation time within the concrete cover. Increase in the volume of corroded reinforcing bar induces an internal pressure on the concrete around the bar, which brings on the cracking initiation and propagation through the cover. The internal pressure caused by corrosion is expressed in terms of steel mass loss, and then Faraday's law is implemented to account for the time in relationships. The time corresponding to creation of the first crack is obtained based on crack opening definition, and the crack propagation is approximated on the basis of fracture mechanics relationships. The merit of using fracture mechanics is that the crack propagation time can be calculated thru any desired length of the cover. In this model, the time required for corrosion products to fill the porous zone between concrete and steel bar, as well as the time needed to fill the void within the crack are also accounted for. Validity of the proposed model is investigated via comparing the results achieved in this model with those of experiments published in the literature.

Characterization of the fatigue behaviour for SAE 1045 steel without and with load-free sequences based on non-destructive, X-ray diffraction and transmission electron microscopic investigations

The change of mechanical stress-strain-hysteresis and different physical parameters during fatigue tests have been measured to demonstrate the fatigue behaviour and damage evolution processes of metallic materials. The electrical resistance e.g. can provide important information regarding the microstructural alteration by indicating the development of dislocation density. The states of such parameters of a fatigue specimen in a load-free sequence can represent the state of a component with a defined cyclic loading history. Therefore, conventional techniques measuring these parameters of common fatigue tests or even of service load tests with additional load-free sequences should have the application potential of remaining service life estimation and must be experimentally validated. In the scope of this paper, characteristic cycle-dependent changes of diverse physical parameters of fatigue specimens made from normalized SAE 1045 steel were determined and correlated with the residual stress state and dislocation density quantified by X-ray diffraction (XRD) and transmission electron microscopy (TEM) respectively.

Environmental and Economic Prioritization of Building Energy Refurbishment Strategies with Life-Cycle Approach

An increasing number of studies apply life-cycle assessment methodology to assess the impact of a new building or to prioritize between different building refurbishment strategies. Among the different hypotheses to consider during the application of this methodology, the selection of the impact indicator is critical, as this choice will completely change the interpretation of the results. This article proposes applying four indicators that allow analysing the results of a refurbishment project of a residential building with the life-cycle approach: non-renewable primary energy use reduction (NRPER), net energy ratio (NER), internal rate of return (IRR), and life-cycle payback (LC-PB). The combination of environmental and economic indicators when evaluating the results has allowed to prioritize among the different strategies defined for this case study. Furthermore, an extensive sensitivity assessment reflects the high uncertainty of some of the parameters and their high influence on the final results. To this end, new hypotheses related to the following parameters have been considered: reference service life of the building, estimated service life of material, operational energy use, conversion factor, energy price, and inflation rate. The results show that the NRPE use reduction value could vary up to −44%. The variation of the other indicators is also very relevant, reaching variation rates such as 100% in the NER, 450% in the IRR, and 300% in the LC-PB. Finally, the results allow to define the type of input or hypothesis that influences each indicator the most, which is relevant when calibrating the prioritization process for the refurbishment strategy.

Additively Manufactured NiTi and NiTiHf Alloys: Estimating Service Life in High-Temperature Oxidation.

In this study, the effect of the addition of Hf on the oxidation behavior of NiTi alloy, which was processed using additive manufacturing and casting, is studied. Thermogravimetric analyses (TGA) were performed at the temperature of 500, 800, and 900 °C to assess the isothermal and dynamic oxidation behavior of the Ni50.4Ti29.6Hf20 at.% alloys for 75 h in dry air. After oxidation, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used to analyze the oxide scale formed on the surface of the samples during the high-temperature oxidation. Two stages of oxidation were observed for the NiTiHf samples, an increasing oxidation rate during the early stage of oxidation followed by a lower oxidation rate after approximately 10 h. The isothermal oxidation curves were well matched with a logarithmic rate law in the initial stage and then by parabolic rate law for the next stage. The formation of multi-layered oxide was observed for NiTiHf, which consists of Ti oxide, Hf oxide, and NiTiO3. For the binary alloys, results show that by increasing the temperature, the oxidation rate increased significantly and fitted with parabolic rate law. Activation energy of 175.25 kJ/mol for additively manufactured (AM) NiTi and 60.634 kJ/mol for AM NiTiHf was obtained.

Service life estimation of heritage buildings: a case study

Service life estimation of heritage buildings: a case study

The Stochastic Annuity Method for Supporting Maintenance Costs Planning and Durability in the Construction Sector: A Simulation on a Building Component

Service life estimate is crucial for evaluating the economic and environmental sustainability of projects, by means—adopting a life cycle perspective—of the Life Cycle Cost Analysis (LCCA). Service life, in turn, is strictly correlated to maintenance investment and planning activities, in view of building/building component/system/infrastructure products’ durability requirements, and in line with the environmental-energy policies, transposed into EU guidelines and regulations. Focusing on the use-maintenance-adaptation stage in the constructions’ life cycle, the aim of this work is to propose a methodology for supporting the “optimal maintenance planning” in function of life cycle costs, assuming the presence of financial constraints. A first research step is proposed for testing the economic sustainability of different project options, at the component scale, which imply different cost items and different maintenance-replacement interventions over time. The methodology is based on the Annuity Method, or Equivalent Annual Cost approach, as defined by the norm EN 15459-1:2017. The method, poorly explored in the literature, is proposed here as an alternative to the Global Cost approach (illustrated in the norm as well). Due to the presence of uncertainty correlated to deterioration processes and market variability, the stochastic Annuity Method is modeled by introducing flexibility in input data. Thus, with the support of Probability Analysis and the Monte Carlo Method (MCM), the stochastic LCCA, solved through the stochastic Equivalent Annual Cost, is used for the economic assessment of different maintenance scenarios. Two different components of an office building project (a timber and an aluminum frame), are assumed as a case for the simulation. The methodology intends to support decisions not only in the design phases, but also in the post-construction ones. Furthermore, it opens to potential applications in reinforced concrete infrastructures’ stock, which is approaching, as a considerable portion of the building stock, its end-of-life stage.

Using foam polyurethane sealers for strengthening of soils of a road bed of transport constructions

The article presents an overview of the methods of producing alternative building materials by strengthening soils with organic binders based on synthetic resins. Their use in road construction would meet the needs of construction organizations in high-quality building materials and ensure reliable operation of soil masses of subgrade road transport structures throughout estimated service life. The authors proposed a new, alternative method for soil stabilization using urethane foam sealants, which have proven themselves in civil engineering in the form of mounting foams. The paper describes a method for strengthening soil with sealants, its labor production technology, properties and physical and mechanical characteristics. The results of the trial experience of soil strengthening with polyurethane foam sealant are described and conclusions are made based on the work.

Chloride Diffusivity, Fatigue Life, and Service Life Analysis of RC Beams under Chloride Exposure

This study investigates the combined actions of flexural fatigue loading and chloride exposure by an experimental examination of the initial fatigue loading cycles (0.2, 0.4, 0.8, and 1.2 million), chloride exposure duration (0, 3, and 6 months), and modeling estimating service life. The results show the following: (1) at the initial fatigue loading cycles of 0.4, 0.8, and 1.2 million, (a) the chloride diffusivity of tensile concrete is similar, which are greater than the specimens initially fatigue loaded with 0.2 million cycles; (b) the chloride diffusivity of compressive concrete increases as the initial fatigue loading cycles increase; and (c) specimens present similar values of fatigue life and service life, which are shorter than the specimens initially fatigue loaded with 0.2 million cycles. (2) As the chloride exposure duration increases from 3 to 6 months, (a) chloride contents of tensile concrete increases more than that of compressive concrete, but both diffusion coefficients decrease; and (b) the fatigue life decreases by ~25%–75% and service life decreases by ~28%–55%. (3) There is an exponential correlation between the fatigue life and service life of beams.

Incorporation of glass powder and metakaolin as cement partial replacement to improve concrete mechanical properties and increase service life

The search for the application of alternative materials, that can partially replace cement and increase the service life of concrete structures, is necessary from the environmental and technological point of view. In this context, the partial substitution of cement in concretes by pozzolanic additions can be performed as ternary mixtures, such as the combined incorporation of glass powder and metakaolin, enabling the reduction of cement consumption and the minimisation of the CO2 emissions and the natural resources consumption. Therefore, this research evaluated the incorporation of glass powder and metakaolin in an isolated and combined way, as partial substitutes for cement in concretes. The compressive strength and the chloride penetration resistance were evaluated by means of electrical resistivity, chloride permeability, steady-state chloride migration test and chloride diffusion test, obtaining the diffusivity and chloride contaminated depth by the colorimetric method. The alkali–silica reactivity test was also conducted, because of the alkali content of the waste glass being higher than the standard requirements. It was concluded that the combined use of ground glass powder and metakaolin in concrete allowed the replacement of up to 20% of the cement, promoting microstructural improvements and increasing properties related to durability and compressive strength already available at 28 days. Furthermore, it increased the estimated service life up to five times, working as an alternative for the reduction of cement use and concrete properties' improvement.

An investigation of the airport pavement management system (APMS)

The research aims to discuss and investigate the process of airport pavement management system (APMS). The methodology of the research is based on previous studies that describe the major elements of the APMS to gain more solutions from the previous different case studies. The investigate includes various subjects such as components and cost approach of the APMS. The methodology used in the research is a descriptive method based on previous studies and from different books by using pavement management system (PMS). The study describes the typical distress types of the asphalt-surfaced pavements and the Portland cement concrete pavements of airports. Additionally, the research clarifies the test methods of the airport pavement, such as the ASTM D5340 and ASTM D6433. Research investigates that the software used in the APMS like PAVER and Road-SIT, Airport PMS that are used by the airport agencies to collect information about the situation of the runway pavement. The APMS still needs more research and new studies due to a lack of information and studies in different airports around the world. The airports shall use the service life estimation (SLT) for the pavement in the runways and parking. In recent studies, the method is not used, whereas including a quantitative methodology which demonstrates results to facilitate the clarity of the results to illustrate the advantage of the SLT.

A Modified Semi-Probabilistic Approach for the Assessment of the Residual Service Life of Reinforced Concrete Structures Subjected to Carbonation

This paper presents a modification of an existing semi-probabilistic model that is used for estimating the residual service life of reinforced concrete structures subjected to carbonation. Generated MATLAB codes are used for the estimation of the residual service life for cases where the parameters considered are not necessarily normally distributed through the application of the theory of reliability. Monte Carlo simulation is also performed to validate the results of the modified model and to introduce a practical approach that can be used for the estimation of the residual service life of deteriorated reinforced concrete structures due to carbonation. The modified model is validated using existing data available in literature and is expected to serve as an efficient and user-friendly design tool that is able to deliver an estimation of the residual service life of deteriorated reinforced concrete structures due to carbonation.

Synthesis and Studies on Partially Stabilized Zirconia and Rare-Earth Zirconate Pyrochlore Structured Multilayered Coatings

Abstract This work is focused on the thermal fatigue behaviour studies of ceramic coatings, as TBC (Thermal Barrier Coating) system, its importance in determining the thermo-mechanical properties and service-life estimation of the coatings when exposed to elevated operating temperatures. Commercial 6-8%Yttria stabilized zirconia (YSZ) top coat (TC) and NiCrAlY bond coat (BC) in (a) conventional YSZ (BC and TC), (b) multi-layered functionally graded materials (FGM) i.e., BC - blend (50BC+50TC)-(TC) configuration and (c) lab synthesized Zirconia based pyrochlore (Lanthanum Zirconate-LZ) were the coating materials involved. Nickel based super alloy Inconel 718 substrates were coated by using Atmosphere Plasma Spray (APS) system with three different (varying power) plasma spray parameters. All the sides of the 25mm x 10mm x 5mm thick substrates were completely covered with the bond coat and ceramic coating. FGM configuration was spray coated only on one side of the Inconel flat plates. Thermal shock cycle tests were performed on the coated specimen by following the ASTM B214-07 guidelines which comprised of introducing the coated specimen in a muffle furnace at 1150°C, held in it for 2 minutes before removing from furnace followed by forced fan air cooling (one shock cycle). The specimen were periodically subjected to visual inspection for faults, before continuing the shock cycles, until the coating flaked off or cracked or detached from substrate. Cross section metallographic samples were prepared and analysed under SEM (Scanning Electron Microscope) and Energy Dispersive spectroscope (EDS) to study the as-sprayed coating morphology and interface quality, measure coating thickness, study defects characteristics and the chemical composition. Crystal structural phases were analysed using X-Ray Diffraction (XRD).

Engineering behaviour of lime- and waste ceramic dust-stabilized expansive soil under continuous leaching

Numerous distresses in pavement structures on chemically stabilized expansive soils have raised considerable debate regarding the long-term performance of lime-stabilized subgrades. Therefore, this paper examines the effects of continuous leaching on the durability of lime- and waste ceramic dust (WCD)-stabilized expansive subgrades. The tests were performed with different percentages of quicklime (3.5, 4.5, 5 and 10%), while the combined effects of lime and WCD were evaluated by adding 1.5% of WCD to the mixtures containing 3.5 and 4.5% lime. Geotechnical tests such as Atterberg limits, compaction and California bearing ratio (CBR), in addition to microstructural and leachate analyses, were used to evaluate the engineering properties of the stabilized soils. The CBR result shows that early strength development occurred in the soils mixed with lime and WCD. However, at longer curing periods, the beneficial effect of lime on the engineering properties of the soil increased with an increase in lime content. Results of the leaching tests show considerable changes in the physicochemical properties of the soil mixtures, while the estimated service life of the stabilized soils increased from 3.4 to 9.2 years, as lime content increased from 3.5 to 10%. Microstructural analysis results reveal that the flocculated nature of the soil fabric and the density of the fibrous cementitious compounds increased with an increase in lime content. This study clearly indicates that electrical conductivity, pH and pore-water cation concentrations can be used in combination with geotechnical tests, to correctly evaluate the durability of lime- and lime-WCD-stabilized expansive soils.

Kajian Umur Jalan Rel Berdasarkan Keausan dengan Metode dari AREA dan Perjana

Penentuan usia layan rel merupakan hal yang penting untuk dilakukan untuk menghindari terjadinya kerusakan rel yang fatal. Estimasi usia layan komponen rel dapat ditinjau berdasarkan faktor keausan. Tulisan ini mencoba menghitung dan membandingkan usia layan rel berdasarkan rumus perhitungan keausan rel dengan metode AREMA yang menggunakan formula empiris dari Hay dan menggunakan metode PT KAI. Hasil menunjukkan nilai yang bervariasi untuk berbagai koridor yang ada pada lintas wilayah operasi Madiun, sesuai dengan spesifikasi jalan rel, beban lintas, dan geometri jalan rel. Namun demikian, perbandingan terhadap kondisi eksisting jalan rel belum bisa dilakukan karena adanya keterbatasan data hasil pengujian terhadap jalan rel yang dioperasikan.

The Impact of Two-Layer Lubrication Parameters on the Service Life of Railway Rails

The prerequisites, basic hypotheses and sequence of creation of a mathematical model for estimation of service life of railway rails in conditions of two-layer lubrication are given in the article. The created mathematical model is presented in the final form. The model takes into account the geometry of the wheel-rail contact, the initial and constant surface roughness, actual loads on the rail, speed of the rolling stock, strength characteristics of steels and the antifriction additive, as well as the basic parameters of two-layer lubrication. The main parameters of lubrication include the concentration of solid antifriction additives in oil which is sufficient to fill irregularities of the contact surface; the boundary molecular oil film thickness. The results of calculations using the developed mathematical model are presented. The performed calculations reveal the positive effect of the parameters of a two-layer lubricant on the resource of rails. The anti-wear effect of the lubricant increases as the concentration of graphite in the oil increases and the weight of the carriage decreases. Based on the performed calculations, conclusions and recommendations were obtained regarding further experimental verification of the mathematical model, as well as the influence of the parameters of two-layer spray lubrication on wear and service life of transport rails.

Freeze-thaw Damage Dependence on Wind-driven Rain of Outdoor Exposed Concrete – A Case Study

Abstract It has been shown in previous studies that the existing precast concrete element building stock in Finland has quality issues, especially with freeze-thaw durability and reinforcement corrosion. In addition, it has been presented that deterioration rate is the fastest in coastal area and decreases towards north which has been supposed to be a reason of lower amount of wind-driven rain (WDR). The aim of this study was to examine the connection between the amount of WDR on structures and the freeze-thaw damage more comprehensively. Condition investigation reports of 472 precast concrete element buildings were reanalysed to study the relation and the results were compared to climate data of the same time period to study the correlation between condition investigation observations and the amount of WDR. In addition, the observations made in a condition investigations and their relation to climate load at the same building were studied as a case study. The results show that there is a significant connection between the WDR related climate load and the freeze-thaw damage occurrence. The results can be used to plan protective methods and be a base for service life estimations.

Application of the factor method to the service life prediction of window frames

Window frames present an important role in the energy efficiency of the buildings. The deterioration of window frames strongly influences their water and air tightness, thus comprising the buildings performance. In this sense, the service life of window frames should be carefully analysed, identifying the factors that influence the deterioration of these components, to improve their durability over the buildings’ life cycle. In this study, the service life of window frames is estimated through the application of the factor method. For this purpose, a sample of 173 aluminium and 41 wooden window frames are analysed, collected through a visual inspection campaign, in order to characterise these elements and their state of degradation. In this study, three scenarios are proposed for the quantification of the durability factors, intending to obtain an optimised model for the service life prediction of window frames. Using the optimised scenario, an estimated service life ranging between 37 and 41 years was obtained for aluminium frames, while an estimated service life around 28 years was obtained for wooden frames. The results obtained are consistent with similar studies and the empirical knowledge related with the durability and service life of window frames.