Life Prediction Of Structures Research Articles

Disk Brake Element Chatter Analysis and Strength Evaluation for Railway Vehicle System

Friction brake is still an absolutely necessary way of brake in high speed vehicle today. Complex nonlinear vibration phenomena appear in friction brake system because of dry friction between friction pairs. The resulted brake squeal and brake chatter may cause strength failure and fatigue damage of the disk brake element. Therefore, it is necessary to consider chatter in strength calculation and structure life prediction of disk brake element. In this paper, the finite element model of disk brake element is built. Vibration displacements and dynamic stresses are calculated for chatter character analysis and strength evaluation.

Experimental study on strength and deformation of plain concrete under triaxial compression after freeze-thaw cycles

The behavior of strength and deformation of plain concrete under triaxial compression after 0, 25, 50 and 75 cycles of freeze-thaw are experimentally studied using the static and dynamic triaxial experimental machine. The compressive strength, strain at the peak of stress and stress–strain relationship under triaxial compression were measured. The failure modes of concrete specimens are also described. The experimental results showed that the triaxial compressive strength decreased as the freeze-thaw cycles were repeated for plain concrete. The influence of the number of freeze-thaw cycles and the stress ratio on the principal compressive stresses σ 3 and corresponding strain ε 3 , stress–strain relationship was analyzed. On this basis, the failure criterion of concrete under triaxial compression after freeze-thaw cycles is proposed. It can serve as a reference for the maintenance, design and the life prediction of ocean structures, hydraulic structures, marine structures and offshore platform in cold regions.

Corrosion monitoring of reinforcing steel in cement mortar by EIS and ENA

Health degradation by corrosion of steel in civil engineering, especially in rough environment, is a persistent problem. Environment pollution and global warming will exacerbate this problem. The assessment of whole-life costing and residual service life prediction of structures is very important. Pitting corrosion is the most important factor which influences the service life of the reinforced concrete structures in many chloride included environments. Electrochemical impedance spectroscopy (EIS) method is used to study the corrosion process of reinforcing steel in cement mortar. According to the results of the experiments, dispersion and diffusing effect control the electrochemical process of carbon steel corrosion in the cement mortar. By fitting the results with EC, the parameters about CPE and Warburg impedance are calculated. The pitting corrosion behavior of reinforcing steel in cement mortar has been studied by electrochemical noise analysis (ENA) method, the wavelet transform has been employed to analyze the EN data of reinforcing steel in mortar, and the energy distribution plot (EDP) is plotted. The experimental results show that the change of EDP during the corrosion process can qualitatively reveal useful information on corrosion mechanisms.

Fatigue analysis of spot welds using a mesh-insensitive structural stress approach

This paper describes the application procedures of a nodal force based mesh-insensitive structural stress parameter for analysis of a comprehensive set of spot weld fatigue test data collected from a series of advanced high strength sheet steels. The structural stress parameter is calculated in an equilibrium sense in terms of bending and membrane components from nodal forces and moments at each grid point along the periphery of a weld nugget. Based on fracture mechanics considerations, an equivalent structural stress parameter is then used to take into account the effects of loading mode and sheet thickness on the fatigue of spot welded joints. The equivalent structural stress is proven effective in consolidating the large amount of fatigue data of spot welds for transformation induced plasticity (TRIP), dual-phase (DP), and high strength low alloy (HSLA) steels subjected to both tensile shear and coach peel loadings. As a result, a single master S–N can be established for fatigue design and life prediction of spot-welded structures.

Expert system for remnant life prediction of defected components under fatigue and creep–fatigue loadings

Life prediction and management of cracked high temperature structures is a matter of great importance for both economical and safe reasons. To implement such a task, many fields such as material science, structure engineering and mechanics science etc. are involved and expertise is generally required. In terms of the methodology of advanced time-dependent fracture mechanics, this paper developed an expert system to realize an appropriate combination of material database, condition database and knowledge database. Many assessment criteria including the multi-defects interaction and combination, invalidation criterion and creep-fatigue interaction are employed in the inference engine of expert system. The over-conservativeness of life prediction from traditional method is reduced reasonably and therefore the accuracy of predicted life is improved. Consequently, the intelligent and expert life management of cracked high temperature structures is realized which provides a powerful tool in practice.

Properties Of High Performance Concrete:The Effect Of Cracks

The moisture transport and storage parameters of high performance concrete belong to the most critical parameters in designing and using complex reliability based models for service life prediction of concrete structures. However, mostly it is supposed that the material is compact without any significant cracks, which is not always true. In this paper, the effect of thermally induced cracks on the basic moisture transport and storage properties is analyzed. Experimental results show that the presence of cracks in hardened high performance concrete mixtures dramatically changes all measured hygric parameters. Also, the effects of both microsilica and the size and presence of aggregates on moisture transport and storage parameters are very important. The liquid water transport is found to be affected by cracks, microsilica and aggregates in a much more significant way than water vapour transport.

NDE corrosion metrics for life prediction of aircraft structures

have outlined the USAF shift towards an ‘Anticipate-and-manage’ approach to airframe corrosion control. The two approaches are essentially the same and are aimed at significantly reducing aircraft non-availability and at decreasing maintenance costs. The move from a ‘Find-and-fix’ approach requires a careful assessment of the effects of the corrosion on structural integrity of the aircraft. To achieve this, reliable models are needed which can be used to predict the long-term effects of corrosion on properties such as static strength and fatigue life. Significant progress has been made towards this goal through research being conducted in the US, Canada and Australia. Models allowing the effects of pitting and exfoliation corrosion on fatigue life and the role of corrosion on the degradation of lap joints are currently under development. Eventually these will allow the impact of different levels of corrosion on structural integrity to be assessed and will permit the time at which rectification must be carried out to be determined. The ‘Identify-and-manage’ or ‘Anticipate-and-manage’ approaches will only be possible if effective non-destructive evaluation (NDE) methods are available to detect, characterise and monitor the corrosion that is present within the airframe. The aim of the present project is to assess the capabilities of a range of NDE techniques for detecting and quantifying corrosion present in aircraft structures. As part of this programme, the initial step has been to establish the corrosion metrics that need to be determined so that the ‘Identify-and-manage’ approach can be followed. The metrics will depend on the particular models that are being employed to estimate the residual life of the structure. This paper presents the results of a review of the some of the models and tools that are currently under development and the basic corrosion data or corrosion metrics that are employed. The results from an initial feasibility study of pitting corrosion and crevice corrosion coupons are also presented.

Fatigue crack growth with overload under spectrum loading

Load cycle interactions can have a very significant effect in fatigue crack growth under variable amplitude loading. Studying of fatigue crack growth rate and fatigue life calculation under spectrum loading is very important for the reliable life prediction of engineering structures. In this paper, a fatigue life prediction model under various load spectra, using the strain energy density factor approach and the plastic zone size near crack tip as main parameters in calculating effective strain energy density factor, has been proposed. The present model is validated with fatigue crack growth test data provided by Ray under various variable amplitude and spectrum loading in 7075-T6 and 2024-T3 aluminum alloy, respectively. Predictions of present model are compared with those of the state-space model, FASTRN and AFGROW codes. The results show that the predicted results agree well with the test data.

Stochastic Measure of Fatigue Crack Damage for Health Monitoring of Ductile Alloy Structures

This paper models a stochastic measure of fatigue crack damage in ductile alloys that are commonly encountered in structures and machinery components of complex mechanical systems such as land, air, ocean, and space vehicles. The constitutive equations of the damage measure are built upon the physics of fracture mechanics and are substantiated by Karhunen-Loe` ve decomposition of fatigue test data where statistical orthogonality of the estimated measure and the resulting estimation error is demonstrated in a Hilbert space setting. The non-stationary probability distribution (PDF) function of the damage estimate is generated in a closed form without numerically solving stochastic differential equations in the Wiener integral or It integral setting. The model of crack damage measure allows real-time execution of decision algorithms for health monitoring, risk assessment, and life prediction of mechanical structures on inexpensive platforms such as a Pentium processor. The stochastic model of fatigue crack damage measure is in good agreement with experimental data sets for 2024-T3 and 7075-T6 aluminum alloys.

A Software Framework for Probabilistic Fatigue Life Assessment of Gas Turbine Engine Rotors

Abstract An enhanced life management process based on probabilistic damage tolerance methods has been developed to address material anomalies in titanium rotating components of gas turbine engines. Related methods are being used as tools to investigate the impact of engine monitoring and usage variability on prognosis for field readiness and life management. This paper begins with an overview of the process of probabilistic damage tolerant design, using the DARWIN® computer program to illustrate the interplay between various random variables and the conventional elements of structural design and life prediction. Special attention is then given to the initial distribution of material anomalies, scatter in fatigue crack growth data, and variability in complex mission histories. The significance of each source of variability for different applications is discussed.

The application of p-version finite-element methods to fracture-dominated problems encountered in engineering practice

This paper details experience applying higher-order ( p-version) finite-element methods to highly specialized and difficult problems in structural life predictions, namely in predictions of aircraft structural fatigue life using crack growth analyses. Crack growth analyses require reliable estimates of the Mode I stress intensity factors (SIFs) for given load, boundary conditions, and geometry. Fortunately, accurate and reliable stresses and stress intensity factors, obtained quickly and efficiently from finite-element simulations performed with higher-order methods, enable basic procedures to be successfully applied to the development of advanced life prediction methods. Many FEA software packages could have been used to obtain engineering data such as SIFs and stresses. However, advanced numerical methods incorporated into higher-order finite-element methods allow the engineering analyst to have confidence in the results. This confidence comes from being able to obtain more accurate and reliable results using convenient error checking and numerical convergence of engineering data such as maximum stress and strain and SIFs, stress contours, and deformations. In addition, greatly shortened analysis schedules are realized through the use of procedures such as the automatic extraction of SIF parameters using the contour integral method (CIM). The versatility of higher-order methods is demonstrated by some examples encountered in engineering practice—multisite damage scenarios and corroded plates.

Development of novel NDE techniques and their significance in the COE program on the physics and chemistry of fracture and failure prevention

Development of novel NDE techniques and their significance in the COE program on the physics and chemistry of fracture and failure prevention

Chloride threshold dependence of pitting potential of reinforcements

Chloride threshold is one of the key parameters needed for service life prediction of concrete structures. The main difficulty that the determination of this parameter encounters is that the chloride threshold inducing active corrosion is not a unique value and depends on several variables. Among them the electrical potential exhibited by the rebar surface is the one less experimentally studied, even though it was identified some decades ago as the most comprehensive controlling parameter for the disruption of passivity. In the present paper the influence of the potential of reinforcements embedded in mortar on the chloride threshold has been studied for the first time in a region from +250 to −650 mV with respect to SCE. Identical samples have been tested in order to perform a statistical treatment and so mean values are given. The chloride thresholds found are expressed as total and free chloride as well as chloride/hydroxide (Cl −/OH −) ratio. The results show that chloride threshold is independent of the potential for values more anodic than −200±50 mV (SCE) being this region the typical potentials exhibited by passive reinforcements in atmospheric conditions. For potentials more cathodic than −200±50 mV (SCE), the threshold progressively increases and a linear fitting is possible. The dependence of chloride threshold with the potential approaches to the understanding why in previous works researchers have found significant differences.

RILEM TC 160-MLN 'Methodology for life prediction of concrete structures in nuclear power plants' Probabilistic methods for assessing current and future performance of concrete structures in nuclear power plants

RILEM TC 160-MLN 'Methodology for life prediction of concrete structures in nuclear power plants' Probabilistic methods for assessing current and future performance of concrete structures in nuclear power plants

Special Issue on Challenges and Resolutions in Structural Life Prediction

Special Issue on Challenges and Resolutions in Structural Life Prediction

Measuring the membrane potential across cement-based materials

Cement-based materials tend to self-establish an electric field when exposed to an ionic concentration gradient. This is of importance in several areas of cement technology, particularly where the prediction of ion transport is required, such as in service life prediction of concrete structures and cement-based solidification of hazardous waste. Measurement of the membrane potential across a specimen is the most direct method of quantifying the field. The outcome of research directed at developing a sound method of measuring membrane potentials is reported. Theory important to measure and interpret membrane potentials is presented. The main variables involved in measuring membrane potential are then considered, including specimen configuration, electrolytes and reference electrodes. The greatest obstacle to accurate membrane potential determination is the presence of junction potentials in the test set up. Methods of minimizing and estimating junction potentials are presented. An example is presented involving measuring the potential across 10-mm-thick OPC mortar specimens housed between 0.5 M NaCl and simulated pore solutions, using calomel electrodes and KNO3 salt bridges. The total junction potential involved was calculated to be around 2.2 mV. The corrected membrane potential started at around −23 mV on first exposure, increasing to a value of around +30 mV by 38 days.

Software complex ‘strength’ of the decision support system for strength accompaniment of structures safe operation

Software complex (SC) ‘strength’ of the decision support system (DSS) has been developed for strength accompaniment of structures safe operation, (pressure vessels, pipelines, storage tanks, etc.) during their life cycle, (beginning with engineering designing and ending with taking a decision to remove them from service), including the cases when defects of different origin are detected. Basic principles of the DSS SC ‘strength’ functioning afford structural strength assessment and life prediction for a defect-free or defected structural element, taking into account the diversity of service conditions. Strength accompaniment of the object of the diagnostics has been oriented to multilevel representation of the life cycle of the defect growth (defect history) from its nucleation, to the consequences assessment of possible failure, caused by the propagation of this defect.

膜構造建築物用膜材料の屋外ばくろによる耐久性能評価に関する研究

Performance overtime of membrane materials for membrane structure has prominent important role as a front line of defence barrier between inner and outer space of the structure. This paper deals with the results of ten years out door exposure tests for PVC coated polyester fabrics, intended to obtain much practical and applicable performance data for design for durability or service life prediction of membrane structure. It could be conducted that behaviour of degradation in time, especially, tensile and tear strength are comparatively critical in view of structural safety aspect and this could be applicable as performance based test data for setting service life of the membrane structures and also setting some measures for maintenance operation.

On the estimation of the fatigue cycle distribution from spectral density data

This paper deals with the fatigue life prediction of components and structures subjected to random fatigue, i.e. to cyclic loading whose amplitude varies in an essentially random manner. In particular, this study concentrates on the general problem of directly relating fatigue cycle distribution to the power spectral density (PSD) by means of closed-form expressions that avoid expensive digital simulations of the stress process. At present, all the methods proposed to achieve this objective are based on the use of a single parameter of the PSD. In this work, by numerical simulations and theoretical considerations, it is shown that the statistical distribution of fatigue cycles depends on four parameters of the PSD and the methods proposed in the literature provide reliable results only in particular cases. The proposed approach lays the foundation for a more accurate evaluation of the fatigue cycle distribution. As a first result, a closed-form solution for the case of broad-band processes with narrow-band time derivative has been obtained in this paper.

Plant aging and life prediction of corrodible structures. Proceedings of the International Symposium, Sapporo, Japan, May 15–18, 1995

Plant aging and life prediction of corrodible structures. Proceedings of the International Symposium, Sapporo, Japan, May 15–18, 1995