Design Service Life Research Articles

Basics of Operation of GTE Disks by the Technical Condition: the Way to Extend Their Design Service Life

The paper considers procedures for predicting safe damage to compressor and turbine disks in stationary and aircraft gas turbine engines at the stage of subcritical crack growth. The methods are proposed to evaluate inspection intervals and amounts of routine maintenance with consideration of the regularities underlying this type of crack growth. In this case, the features in the operation of materials are taken into consideration for stationary (peaking, semi-peaking, and steady-state modes) and aircraft (typical flight cycles) gas turbine engines. The crack propagation near various stress concentrators is analyzed with the help of the developed program using a stationary gas turbine disk as an example, which allows one to predict the crack growth life of the disk and the most probable location of its failure.

Minimal safe speed of the asymmetrically loaded combat airplane

Purpose – The purpose of this paper is to present a method for determining the safe flight boundaries of the asymmetrically loaded airplane in the terminal flight phases. The method is applicable to both, the inherent airplane asymmetries and those asymmetries resulting from the airplane use irregularities, asymmetric stores under the wing being one of the examples. The method is aimed to be used in the airplane design and combat airplane service life support. Design/methodology/approach – The analysis method is based on the comparison of demanded and structurally available flight control displacements. Control surface aerodynamic properties, structurally available flight control displacements and dynamic pressure define control surface authority as the capability of control surfaces to generate the forces and moments needed by the airplane to perform required maneuvers. Demanded flight control displacements are those related to the maneuvering requirements and to those needed to compensate lateral wind a...

Degree of saturation effect on the grout-soil interface shear strength of soil nailing

In the grouted soil nailing system, the bonding strength of cement grout-soil interface offers the required resistance to maintain the stability of whole structure. In practice, soil nailing applications are often placed at unsaturated conditions, such as soil slopes, shallow foundations, retaining walls and pavement structures. In these cases, the water content in the soil nail zone may increase or decrease due to rain water or dry weather, and even cannot become saturated during their design service life. In this study, the effect of water content (degree of saturation) on the shear strength of interface between cement grout and sand are experimentally investigated by means of direct shear test. Meanwhile the water retention curve was determined and interface microstructure was observed. Experimental results show that the shear strength of interface changes non-monotonously with degree of saturation when the interface was prepared, due to the non-monotonousness of the cohesiveness between soil particles. The less the cohesiveness between sand particles, the more grout was observed been penetrated into the voids, and thus the larger the interface shear stress.

Framework to Improve the Pavement ME Design Unbound Aggregate Rutting Model by Using Field Data

The AASHTOWare Pavement ME Design and the Guide for Mechanistic–Empirical Design of New and Rehabilitated Pavement Structures provide a methodology for analyzing response and predicting rutting performance of unbound granular pavement layers. However, this methodology has been reported to have low sensitivity to the properties of the base and subbase and the subgrade. The primary objective of this paper is to provide a framework for improving the prediction ability of the Pavement ME Design rutting model for unbound aggregate pavement layers. This goal was achieved by using accelerated testing data from full-scale pavement test sections constructed with different aggregate materials. These test sections were loaded to failure by using the accelerated transportation loading assembly at the University of Illinois. Nonlinear finite element solutions of the pavement test sections were studied so that stress-dependent modulus characterization models could be used for the anisotropic unbound aggregate base and isotropic subgrade. This approach enabled prediction of realistic stress states and accurate pavement responses. Realistic stress states and the use of a shear stress ratio concept were incorporated into the proposed framework needed to improve the rutting predictions of the Pavement ME Design damage model. Finally, a definite correlation appeared to exist between shear stress ratio values and the shift factors that were proposed for the adjustment of the model’s predicted rut depths so they would match the field-measured performance trends. The framework studied in this paper is applicable to the three-parameter Tseng–Lytton rutting model, the original version of the Pavement ME Design damage model, for the modifications needed to generate improved granular layer rut predictions throughout pavement design service life.

Estimation and Assurance of Machine Component Design Lifetime

The authors offer a kinetic model of machine components degradation failure development process by the material strength energy criterion at the stage of research and development. On the basis of this model, they developed an algorithm and a program, which will make it possible to estimate the design service life of the load element in various conditions of external loading. Theoretical results of the research work were verified and their practical application under production conditions was described.

무인항공기의 설계사용 수명판단을 위한 RAM-c 적용 연구

RAM (Reliability, Availability and Maintenance) has been applied to design and analysis tools which affects system's operational sustainability and its life cycle cost as RAM-c(2009 DoD). RAM-c plays also an important role to guarantee the system engineering for mission assurance. Reliability is highly related to the probability of system failure. Availability means mission capability or the condition of ready to mission. Maintenance includes both the repair to recover the system in the event of failure/unexpected breakdown and proactive maintenance to prolong the design service life of the system or machinery. It is the purpose that this paper is to analyze and conclude the objective service life of UAV. The more UAV is operated, the less the level of its reliability becomes. Repairing failures and supplying spare parts on time, system reliability could be improved up until the time over target. Applying statistical Weibull distributions, this paper suggests the analysis of the design service life and economic life of UAV based on RAM-c with operational data.

Investigation on the effect of supplementary cementitious materials on the critical chloride threshold of steel in concrete

Abstract The critical chloride threshold is a key parameter in the service life design of reinforced concrete structures exposed to chloride-bearing environments. This paper investigates the role of concrete composition, and particularly the effect of supplementary cementing materials, on the chloride threshold. To simulate real exposure conditions, ponding tests were carried out on reinforced concrete specimens with bars in free corrosion conditions and corrosion initiation was detected through corrosion potential and corrosion rate measurements. After two and a half years, the ponding was followed by an ageing period and the initiation of corrosion was further detected with anodic potentiostatic polarisation tests. Results of the tests showed several limitations of the approach based on chloride penetration and monitoring of free corrosion parameters to investigate the chloride threshold. In spite of this, a possible role of natural pozzolan and coal fly ash additions in leading to higher values of the chloride threshold and ground limestone in promoting lower values of the chloride threshold could be observed.

DOProC-based reliability assessment of steel structures exposed to fatigue

Summary Attention to the fatigue cracks in steel structures and bridges has been paid for a long time. In spite of efforts to eliminate the creation and propagation of fatigue cracks throughout the designed service life, cracks are still revealed during inspections. Fatigue crack damage depends on a number of stress range cycles. This is a time factor in the course of reliability for the entire designed service life. The failure rate increases in the course of time and the reliability decreased. If possible propagation of the fatigue crack is included into the failure rate, it is necessary to investigate into the fatigue crack and define the maximum acceptable degradation. Three sizes are important for the characteristics of the propagation of fatigue cracks. These are the initial size, detectable size and acceptable size. The theoretical model of fatigue crack progression is based on a linear fracture mechanics. A tension flange has been chosen for applications of the theoretical solution suggested in the studies. Depending on location of an initial crack, the crack may propagate from the edge or from the surface. Regarding the frequency, weight and stress concentration, those locations rank among those with the major hazard of fatigue cracks appearing in the steel structures and bridges. When determining the required degree of reliability, it is possible to specify the time of the first inspection of the construction which will focus on the fatigue damage. Using a conditional probability, times for subsequent inspections can be determined. For probabilistic calculation of fatigue crack progression was used the original and new probabilistic methods – the D irect O ptimized Pro babilistic C alculation (“DOProC”), which uses a purely numerical approach without any simulation techniques. This provides more accurate solutions to probabilistic tasks, and, in some cases, to considerably faster completion of computations. FCProbCalc code has been developed using the aforementioned techniques. By means of FCProbCalc (which stands for F atigue C rack Prob ability Calc ulation), it is possible to carry out the probabilistic modelling of propagation of fatigue cracks in a user friendly environment and to propose a system of regular inspections which should reveal damage to the structure, using the described computational procedures.

Optimal Design of Wire Sheave Used in Offshore Drilling Operations

This paper presents optimized design geometries of wire sheaves that are used in offshore drilling operations. Seven different design geometries of wire sheaves are considered for this study. The criteria considered in this comparison are utilization ratios of yield and buckling capacities and fatigue life. The constrained used are the self-weight and rotational inertia. The obtained utilization ratios of yield capacity, buckling capacity, and fatigue life against the weight and rotational moment of inertia are finally compared. The comparisons reveal that currently used lightest sheave geometry has very good yield and buckling capacities than all other geometries. But it has high self-weight and rotational inertia. Finally, the web with decreasing thickness which has a lowest rotational inertia is proposed as the most suitable design geometry, if the expected design life is limited to 20 years. Different sheave geometries are also proposed depending on the required design service life.

Stochastic Analysis of Flexural Strength of RC Beams Subjected to Chloride Induced Corrosion

Importance of consideration of chloride induced corrosion in service life design of reinforced concrete (RC) structures situated in marine environment is well known. This paper attempts to provide, within the framework of Monte Carlo Simulation, methodologies for durability based service life design of RC members. A methodology using fragility curves is proposed to assist in the service life design of freely degrading RC flexural beams. For maintained RC beams, a methodology is developed, that incorporates the concepts of virtual aging, failure rate approach and time-variant reliability analysis. By addressing maintenance at the design stage itself, the methodology developed would help in sustainability based service life design. The use of both the methodologies is demonstrated by considering an example of T-beam. From the results of the example problem considered, it has been found that corrosion initiation time would govern the service life. 30% replacement of cement with pulverized fuel ash is considered as a sustainable alternative for construction of durable structures satisfying the service life performance targets with lesser number of repairs.

Maritime vessel obsolescence, life cycle cost and design service life

Maritime vessels have long service life and great costs of building, manning, operating, maintaining and repairing throughout their life. Major actions are needed to repair, renovate, sometime built or even replace those scrapped when technology or demand changes determine obsolescence. It is regarded as a concern throughout vessel's entire life cycle and reflects changes in expectation regarding performances in functioning, safety and environmental effects. While service live may differ from physical lives, expectations about physical lives is the main factors that determines design service life. Performance and failure are illustrated conceptually and represented in a simplified form considering the evolution of vessels parameters during its service life. In the proposed methodology an accumulated vessel lifecycle cost is analyzed and obsolescence is characterized from ship's design, performances, maintenance and management parameters point of view. Romanian ports feeding Black Sea are investigated in order to provide comprehensive information on: number and types of vessels, transport capacity and life cycle length. Recommendations are to be made in order to insure a best practice in lifecycle management in order to reduce costs.

Mechanical Analysis and Finite Element Simulation of Scissor Transmission Mechanism under Partial Load

Partial load has great impact on both service life and security design of scissor transmission mechanism. A mechanical model has been established, on the assumption that the scissor units are rigid bodies and the connecting rods are elastic bodies, for the research on the scissor transmission mechanism considering partial load. The recursive matrix used to calculate the node force of multi-unit transmission mechanism has been obtained. And based on the recursive matrix, the method has been deduced to calculate the node force of the scissor transmission mechanism in the unbalanced loading condition after the connecting rods were replaced by equivalent models—the springs. The finite element model carried out with SAP84 was established to measure the accuracy of the equations obtained by theory derivation, and the results proved the correctness of the theoretical formula because of the little difference between theoretical results and simulation results. The conclusion obtained could serve as theoretical guidance for mechanical analysis and optimal design on scissor transmission mechanism in the unbalanced loading condition and reference for elastomeric scissor unit research.

Towards Practical Carbonation Prediction and Modelling for Service Life Design of Reinforced Concrete Structures

Amongst the scientific community, the interest in durability of concrete structures has been high for quite a long time of over 40 years. Of the various causes of degradation of concrete structures, corrosion is the most widespread durability problem and carbonation is one of the two causes of steel reinforcement corrosion. While much scientific understanding has been gained from the numerous carbonation studies undertaken over the past years, it is still presently not possible to accurately predict carbonation and apply it in design of structures. This underscores the complex nature of the mechanisms as influenced by several interactive factors. Based on critical literature and some experience of the author, it is found that there still exist major challenges in establishing a mathematical constitutive relation for realistic carbonation prediction. While most current models employ permeability /diffusion as the main model property, analysis shows that the most practical material property would be compressive strength, which has a low coefficient of variation of 20% compared to 30 to 50% for permeability. This important characteristic of compressive strength, combined with its merit of simplicity and data availability at all stages of a structure's life, promote its potential use in modelling over permeability. By using compressive strength in carbonation prediction, the need for accelerated testing and permeability measurement can be avoided.This paper attempts to examine the issues associated with carbonation prediction, which could underlie the current lack of a sound established prediction method. Suggestions are then made for possible employment of different or alternative approaches.

Distortion induced fatigue of deck plate at rib intersection with diaphragm in orthotropic steel deck

Toe-deck (TD) fatigue due to wheel induced distortion of orthotropic steel decks (OSDs) was reported by laboratory tests. The existing OSDs could probably suffer the TD fatigue and is evaluated using the hot spot stress (HSS) method. The wheel induced stresses of the trough-deck welded joint are analyzed using the shell model. The influences of HSS with mesh size, stress extrapolation, element shape function and the hot spot location variation are checked. TD fatigue durability using the monitored traffic data and the design specifications are discussed. Results demonstrate that the weld toe of the joint suffers wheel induced stress concentration and frequent stress cycles. The refined shell model using the 4-node-shell elements results in nearly constant HSS. TD fatigue durability of the 12mm deck with 50mm asphalt pavement falls below the designed service life that might explain the observed fatigue cracks in the vicinity of the deck toe by laboratory tests and the in-site observation. The TD fatigue evaluation using the HSS method may be utilized to get a conservative OSD design.

Effect of metakaolin on the chloride ingress properties of concrete

Research and practical experience have shown that partial replacement of cement by metakaolin improves concrete durability as a result of the refinement of the pore structure. While much research has been presented on concrete performance with metakaolin, it is scarce concerning the transport properties of chlorides in concrete with metakaolin, in natural conditions (i.e., un-accelerated). This study determines the chloride diffusion coefficients for several concretes with vary levels of cement replacement with metakaolin, and compares these results with chloride migration coefficients obtained from accelerated laboratory testing. In this study, two cement types (CEM I 42,5R and CEM IV/A 42,5) and two cement contents levels where used with metakaolin replacement levels varying from 10-20%. Concretes where tested for fresh properties, compressive strength, electrical resistivity, chloride ingress characteristics (natural diffusion and migration), and mercury intrusion porosimetry. The results show improved strength, durability properties and chloride penetration resistance of concretes with metakaolin. Furthermore, the use of metakaolin in fly ash concrete improves the early age performance of the concrete (<90 days), counteracting the delay in strength and durability gain typically associated with fly ash concrete. The results obtained from this study fulfil the lack of critical input for service life design models of reinforced concrete structures in chloride environments, with emphasis on concretes with metakaolin replacement.

Single-Point Power-Mooring Composite Cables for Wave Energy Converters

This paper presents the analysis and design of single-point power-mooring cables applied to wave energy converters (WECs). A mooring cable design process is suggested, and effects of cable cross-sectional layout, material selection, and conductor design on cable properties are investigated. The study focuses on cable design and structural material for a long service life. Six designs and four structural materials were studied for a total of 18 different configurations. The materials used for the study included Vectran HS, Kevlar 49, carbon fibers in a vinyl ester matrix, and MP35N alloy. Cable design had minimal impact on cable properties. Material used and component helical angle exhibited significant impact on cable mechanical properties. Synthetic fiber designs exhibited more desirable mechanical properties and fatigue performance than both carbon fibers in a vinyl ester matrix and MP35N alloy. Wave device heave and cable tension were not affected by cable material.

Durability characteristics of steel fibre reinforced geopolymer concrete

Escalation in the cost of repair and rehabilitation of concrete structures which develop distress much earlier than the design service life has turned the focus on the durability aspect of concrete. This paper presents the result of an experimental study conducted to evaluate the durability characteristics of plain and fibre reinforced geopolymer concrete and its comparison with Portland cement based conventional concrete. The durability parameters considered in this study include water absorption, abrasion resistance, resistance to chemical attack, effect of alternate wetting and drying and resistance against chloride ions. Test results revealed that plain and fibre reinforced geopolymer concrete possesses superior durability characteristics than conventional concrete of the same grade with respect to most of the durability parameters.

Durability against Wetting–Drying Cycles of Water Treatment Sludge–Fly Ash Geopolymer and Water Treatment Sludge–Cement and Silty Clay–Cement Systems

AbstractThe viability of using two waste materials, water treatment sludge (WTS) and fly ash (FA), for developing sustainable masonry units has been previously investigated in terms of strength but the important aspect of durability against wetting–drying (w–d) cycles has yet to be studied. A study on durability against w–d cycles, an important parameter for service life design of the sustainable masonry units, is investigated in this paper. The liquid alkaline activator (L) was a mixture of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH), and a high calcium fly ash (FA) was used as a precursor. The results of cyclic w–d test indicate that the WTS–FA geopolymer manufactured with an optimum ingredient (L:FA=1.6, Na2SiO3:NaOH=90∶10) and at an optimum heat condition of 85°C for 72 h can be used as durable bearing masonry units; i.e., the compressive strength is greater than 12 MPa after 12 w–d cycles. For this optimum ingredient, the w–d cycle strength, qu(w−d) at heat temperatures between 65 and 95°C ...

Upgrading the SPP-500-1 moisture separators-steam reheaters used in the Leningrad NPP turbine units

The specific features of existing designs of moisture separators-steam reheaters (MSRs) and experience gained with using them at nuclear power plants are considered. Main factors causing damage to and failures of MSRs are described: nonuniform distribution of wet steam flow among the separation modules, breakthrough of moisture through the separator (and sometimes also through the steam reheater), which may lead to the occurrence of additional thermal stresses and, hence, to thermal-fatigue damage to or stress corrosion cracking of metal. MSR failure results in a less efficient operation of the turbine unit as a whole and have an adverse effect on the reliability of the low-pressure cylinder’s last-stage blades. By the time the design service life of the SPP-500-1 MSRs had been exhausted in power units equipped with RBMK-1000 reactors, the number of damages inflicted to both the separation part and to the pipework and heating surface tubes was so large, that a considerable drop of MSR effectiveness and turbine unit efficiency as a whole occurred. The design of the upgraded separation part used in the SPP-500-1 MSR at the Leningrad NPP is described and its effectiveness is shown, which was confirmed by tests. First, efforts taken to achieve more uniform distribution of moisture content over the perimeter and height of steam space downstream of the separation modules and to bring it to values close to the design ones were met with success. Second, no noticeable effect of the individual specific features of separation modules on the moisture content was revealed. Recommendations on elaborating advanced designs of moisture separators-steam reheaters are given: an MSR arrangement in which the separator is placed under or on the side from the steam reheater; axial admission of wet steam for ensuring its uniform distribution among the separation modules; inlet chambers with an extended preliminary separation system and devices for uniformly distributing steam flows in the separator; separated layout of the of the separator and steam reheater; and use of transversely finned tube bundles for organizing cross flow of steam over the tubes.

Service life extension program for aircraft structures

Performance of aircraft in general, its systems and airframe materials, can be significantly reduced by environmental conditions in which the aircraft operates during the service life. Material performance of steel and aluminum alloys can be greatly degraded because of the environmental conditions (temperature, humidity, UV radiation, pollutants, etc.), which severely affect the integrity and safety of aircraft structure. Apart from the other severe environmental conditions, the effect of the corrosion on structural integrity is a critical issue for damage tolerance design and analysis and needs to be carefully investigated. The corrosion and corrosion fatigue failure process of an aircraft structure are directly concerned with many factors, such as load, material characteristics, and corrosive environment and so on. Attention in this paper is focused on the application of the Nondestructive Inspection (NDI) methods in the process of extension of service life of aircraft structures. The NDI methods were used as a part of service life extension program for the extension of the operation life of the G-4 Super Galeb aircraft structures that have been in service in air force for more than 25 years. The computation and experimental NDI methods and practice steps that diminish the negative effects of corrosion process were shown in this paper. Special attention in this paper is focused to the use of the NDI methods. These steps enable to extend the service life of aircraft structures beyond its designed service life with the accurate prediction of the further service reliability.