Life Assessment Of Components Research Articles

Parameters related to building components’ life-cycle analysis in methods for buildings’ environmental performance assessment

In this study, the integration of factors related to life cycle analysis and assessment of building materials and components in the context of widely used methods applied for the evaluation of buildings’ environmental performance is examined. The reviewed assessment systems are BREEAM, LEED, CASBEE, DGNB, HQE and SBTool, with the analysis being focused on their versions referring to new office buildings. Issues related to the content and type of indicators and criteria used for the evaluation of factors referring to life cycle assessment, as well as to the way these rating elements are introduced into the structure and the evaluation process of the aforementioned methods, are examined. In this context, the relative standards and the appropriate –if any– databases and tools mentioned within each method are also demonstrated. The results of this work are systematically presented. The analysis is complemented by the examination of the inclusion of life cycle assessment-related factors in Level(s), a common European framework currently under trial. The present study aims at contributing to the identification of similarities and differences and at highlighting the current trends among widely used buildings’ environmental performance rating systems with regard to the approach they adopt considering building components’ life cycle assessment.

Oxidation of Ti–6Al–4V alloy between 450 and 600°C. Evolution of microstructure and mechanical properties

Titanium alloys are widely used in many applications thanks to their good corrosion resistance and to their high specific modulus. However, at temperatures above 450°C, oxidation must be taken into account to improve life assessment of components. Especially for long-term exposures, oxidation leads to an oxide scale along with an oxygen enrichment in the metal below this oxide scale. In this study, the oxidation behaviour of Ti– 6Al–4V is investigated between 450 and 600°C for a maximum duration of about 6800 h. Scanning electron microscope (SEM) and transmission electron microscopy (TEM) are used to characterize the oxide layer and the layer affected by oxygen uptake. The local oxygen content is quantified. Vibration tests are performed to determine elastic properties on thin specimens with different thicknesses affected by oxygen enrichment. Creep tests are also carried out to quantify the influence of this oxygen uptake on viscoplastic behaviour. An oxygen-enriched zone occupying 5% of the cross-section of a specimen is sufficient to induce detectable changes in its creep behaviour.

Microscopic Multiple Fatigue Crack Simulation and Macroscopic Damage Evolution of Concrete Beam

Microcracks in concrete can coalesce into larger cracks that further propagate under repetitive load cycles. Complex process of crack formation and growth are essentially involved in the failure mechanism of concrete. Understanding the crack formation and propagation is one of the core issues in fatigue damage evaluation of concrete materials and components. In this regard, a numerical model was formulated to simulate the thorough failure process, ranging from microcracks growth, crack coalescence, macrocrack formation and propagation, to the final rupture. This model is applied to simulate the fatigue rupture of three-point bending concrete beams at different stress levels. Numerical results are qualitatively consistent with the experimental observations published in literature. Furthermore, in the framework of damage mechanics, one damage variable is defined to reflect stiffness reduction caused by fatigue loading. S-N curve is subsequently computed and the macroscopic damage evolution of concrete beams are achieved. By employing the combined approaches of fracture mechanics and damage mechanics, made possible is the damage evolution of concrete beam as well as the microscopic multiple fatigue crack simulation. The proposed approach has the potential to be applied to the fatigue life assessment of materials and components at various scales in engineering practice.

Life of gas turbine engine components under corrosive exposure

Currently, operation of gas turbine engines takes place in the aggressive medium of the atmosphere of some climatic regions. As a consequence, this may cause fast degradation of the strength properties of parts of gas turbine equipment and their subsequent premature failure. The problem of determining the life of gas turbine engine components under corrosive exposure is vital. We present an analysis of the state of the art in the field of assessment of gas turbine engine component life under the influence of corrosive environment in Russia and abroad. UEC-Aviadvigatel, FSUE VIAM and NPO TSKTI JSC formulated approaches to the development of the lifing process for engine parts operating in corrosive environment.

A new algorithm for fatigue life assessment of automotive safety components based on the probabilistic approach: The case of the steering knuckle

In the present paper, the author has attempted to examine fatigue life of automotive safety components under axial variable amplitude loading conditions. To this end, the time components of stress tensor in the critical area of the knuckle and Liu-Zenner criterion were used to calculate the time history of equivalent stress. Then, the probability distribution function (PDF) of stress was extracted by applying the stress level counting technique. The Fourier curve fitting method was employed in order to formulate the PDF. Subsequently, the fatigue life of the component was estimated using the probabilistic approach. Finally, the results of the higher order of Fourier curve fitting and different counting ranges were compared with the experimental results. Thus, the best algorithm for precisely determining fatigue life of automotive components was obtained.

Determination of fracture toughness from the small punch test using circular notched specimens

The small punch (SP) test method is an innovative technique which shows potential for residual life assessment of components in service. The main tasks of the technique are to derive standard material properties with a limited amount of material, including strength/toughness, creep and fatigue behaviour. In order to achieve the objective, many methods have been put forward since early 1980’s but even in the new EN standard in preparation no common acceptable methods are available yet for fracture mechanics testing of notched SP specimens.An investigation is carried out to exploit new approaches to determine fracture toughness from small punch tests, including a new type of notched specimen and a new analytic approach. The new type of specimen is a circular notched disc with thickness of 1 mm, and the diameter of the circular notch is 2.5 mm with depth of 0.5 mm which has been proposed and tested by JRC Petten, European Commission. The advantage of the circular notched specimen is that a plane strain condition is built around the crack tip which makes determination of the elastic fracture toughness KIC possible if the condition of small scale yielding is met. In comparing the volume of the new type specimen with the standard fracture specimens, it is only 1/5000 of that of the three point bending specimen (TPB) and 1/2000 of that of the compact tension specimen (CT).In this paper, a method based on fracture energy is proposed to estimate the J-integral for the circular notched specimen, and the procedure to determine the fracture toughness JIC is also addressed. In order to verify the proposed approach, a so-called “Local approach” analytical simulation has been performed to determine the J-R resistant curve and the fracture toughness JIC by using standard small punch tests. In comparison of the J-integral predicted in this paper with the literatures data and the master curve, a good agreement is also found.

Mixed mode I/II crack growth investigation for bi-metal FSW aluminum alloy AA7075-T6/pure copper joints

Over the past two decades, a large number of papers have been published for investigating mechanical properties and microstructure of Friction Stir Weld (FSW) joints made of several similar and dissimilar alloys. Crack growth resistance of such joints is an important design parameter for integrity and life assessment of FSW components. In practice, propagation of cracks in structures fabricated by the FSW technique, which initiate in the welding region, can occur under multiaxial and complex tensile-shear loadings. However, review of the literature shows that there are only limited research works regarding mixed mode I/II (i.e. tensile-shear) fracture resistance study of FSW weldments. Thus, to fill this research gap in this paper, mixed mode I/II fracture resistance of dissimilar aluminum alloy AA7075-T6 / pure copper butt joints welded by the FSW is investigated both experimentally and theoretically. First, a novel semi-circular bend shape specimen is proposed for conducting mixed mode I/II fracture tests. Then, due to ductile behavior of the cracked specimens, the experimentally obtained load-carrying capacity (LCC) of the tested specimens is predicted theoretically using the maximum tangential stress (MTS) and mean stress (MS) criteria in conjunction with the Equivalent Material Concept (EMC). It is revealed that both EMC-MTS and EMC-MS combined criteria can predict quite well the experimental results.

Accelerated Creep Life Assessment of In-Service Power Plant Components

Structural metals used in plant components are subject to aging from a combination of fatigue, creep, and corrosion. Exposure to elevated temperatures promotes creep. Aged metals lose toughness, or the ability to absorb energy at stress above the yield point and cannot endure an occasional high load without fracturing. Creep is one of the most critical factors for determining the structural integrity of components. The main objective of the current study is to assess the remaining creep life of various 20-year old power plant engineering components such as the high temperature fasteners. Due to time constraints, the approach followed in this study was to utilize the accelerated high temperature creep testing in addition to Scanning Electron Microscopy (SEM) analysis to assess the remaining life of 4 different samples. The accelerated high temperature creep tests were conducted at a stress level of 61 MPa and at a temperature of 1000°C for samples Sample 1 (original), Sample 2, Sample 3 and Sample 4; these samples were collected from different parts of the power plant. SEM analysis was carried out for all the samples. The results of the accelerated high temperature tests were compared to similar materials’ theoretical creep data using Larson Miller curve. The Larson Miller actual creep lives of the tested samples were much higher than the experimental ones, which suggest that the samples are critically aged. SEM analysis on the other hand, showed that all samples have high percentage of creep voids

An applied method for fatigue life assessment of engineering components using rigid-insert crack closure model

The purpose of this paper is to provide a new method for analyzing and evaluating the fatigue crack closure load and estimating the life of engineering components using RICC (Rigid-Insert Crack Closure Model), non-destructive replica technique, and a new sample. For this purpose, first, the method of solving the RICC model has been changed from linear approximation to nonlinear state and therefore, a significant improvement in the accuracy of the model results has been achieved. Then, using the model, a new formulation for the influence line in the points of sample is obtained, which has a significant accuracy. The formulation of the RICC model results in a set of equations that can help to determine the closure load and the characteristics of the load-displacement diagram using the residual crack mouth opening displacement in zero load (residual CMOD), which is the only empirical input parameter of Model. The new formulation method has been applied to a standard sample that has the same conditions as a real instance. The amount of residual crack openness in zero load (crack residual displacement) was measured using the replica technique and COD-gage simultaneously on a standard sample and were investigated using the obtained relationships and the accuracy of the outcomes. To prove the reliability, model results have been investigated through doing the experimental tests on aluminum alloys. Finally, the results obtained from the proposed relationship for the analysis and evaluation of the crack closure load and fatigue life were compared with the experimental results, which showed acceptable results.

Durability Analysis for Coil Spring Suspension Based on Strain Signal Characterisation

This paper aims to predict the durability of an automobile coil spring by characterising the captured strain data. The load histories collected at coil spring are often presented in time domain but time domain cannot provide sufficient information for fatigue life prediction. The objective of this study was to characterise the strain signal in time domain, frequency domain and time-frequency domain for fatigue life prediction. The signal obtained in time domain was used to predict the fatigue life of the coil spring through Rainflow cycle counting technique and models of strain-life relationships. In frequency domain, fast Fourier transform revealed that the frequency components in the strain signal ranged between 0-5 Hz. The frequencies can be further categorised into two ranges: 0-0.3 Hz and 1-2 Hz. Power spectral density confirmed that the frequencies with high energy content were 0-5 Hz and the total energy content in the signal is 4.0872x103 µɛ2. Short time Fourier transform can identify the local time and frequency properties of the signal but it has a limitation in time-frequency resolutions. Wavelet transform can provide a better time-frequency resolutions and it confirmed that the transients in the time domain had frequency range of 1-2 Hz. In summary, this study revealed different possible approaches of signal processing in fatigue life assessment of automotive components as guidance for the selection of suitable approach based on the type of information needed for the analysis.

Optimization for Upgradation of Small Hydropower Plant in Nepal: A Case Study of Sundarijal Hydropower Plant

Efficiencies of electro-mechanical components of the Sundarijal Hydropower Plant in Nepal has been decreased and the plant has been generating less energy than design generation. The study shows that the plant can be upgraded to 1.1 MW capacity at Q60 design with rehabilitation. Main objective of the plant rehabilitation is to improve operational stability and reliability of power supply by increasing capacity, efficiency, and safety of the plant. The research is based on the Residual Life Assessment of hydro-mechanical components. Minimum thickness of existing penstock obtained from measurement is six mm which is sufficient for upgradation at Q60 design. Mechanical and chemical properties of penstock is found to be acceptable for upgradation. Machine foundations are tested to be safe for upgradation. Upgradation can be carried out for two scenarios: i) using two generating units system ii) using three generating units system. Energy generation per annum from two generating units system is 65.92 MWh lower than three generating units system. The difference in annual revenue between two systems is 3.93 thousand USD. Capital cost estimation shows that cost for three generating three generating units system is higher than two generating units system by 152 thousands USD. Cash flow analysis shows that IRR ratio for two generating units system is higher than three generating units system by three percentage. Upgradation with two generating units system is more suitable and beneficial than three generating units system. Optimization of turbine units is also carried out using nonlinear gradient reduction method in excel solver. Journal of the Institute of Engineering, 2018, 14(1): 82-95

Use of time-of-flight secondary ion mass spectrometry for the investigation of hydrogen-induced effects in austenitic steel AISI 304L

During the energy transformation from fossil fuels to renewable energy sources, the use of hydrogen as fuel and energy storage can play a key role. This presents new challenges to industry and the scientific community alike. The storage and transport of hydrogen, which is nowadays mainly realized by austenitic stainless steels, remains problematic [L. Zhang et al., Int. J. Hydrogen Energy 39, 20578 (2014)], which is due to the degradation of mechanical properties and the possibility of phase transformation by hydrogen diffusion and accumulation [P. Rozenak, Metall. Mater. Trans. A 45, 162 (2014)]. The development of materials and technologies requires a fundamental understanding of these degradation processes. Therefore, studying the behavior of hydrogen in austenitic steel contributes to an understanding of the damage processes, which is crucial for both life assessment and safe use of components in industry and transportation. As one of the few tools that is capable of depicting the distribution of hydrogen in steels, time-of-flight secondary ion mass spectrometry was conducted after electrochemical charging [O. Sobol et al., Surf. Interface Anal. 48, 474 (2016)]. To obtain further information about the structural composition and cracking behavior, electron-backscattered diffraction and scanning electron microscopy were performed. Gathered data of chemical composition and topography were treated employing data fusion, thus creating a comprehensive portrait of hydrogen-induced effects in the austenite grade AISI 304L. Specimens were electrochemically charged with deuterium instead of hydrogen. This arises from the difficulties to distinguish between artificially charged hydrogen and traces existing in the material or the rest gas in the analysis chamber. Similar diffusion and permeation behavior, as well as solubility, allow nonetheless to draw conclusions from the experiments [Y. Fukai and H. Sugimoto, Adv. Phys. 34, 263 (1985)].

Surface machining condition and fatigue life on Inconel 718

Life assessment of components working in aero-engines at elevated temperatures is critical. Machining has a serious effect on these nickel-based alloys, for example in turbine discs, affecting their life in service. Machining (turning, broaching…) modifies surface roughness, thickness of the affected substrate layer (including the effect of possible broken carbides) and residual stress distribution near the component surface. On top of that, it is possible to shot-peen or not the component, which again modifies its surface integrity. The aim of this work is to discern among the effect of the different parameter: roughness, damage and residual stresses on fatigue performance and optimum machining conditions.

The B Life Assessment of Auto Chassis Components and Application Based on Weibull Distribution

The reliability life of auto chassis components is the important part of auto safety, and B life is theuniversal evaluation index. The essay established a method of fatigue reliability B life based on weibull theory. The method have been used in the actual test and got the B life, which give the reference to the reliability life of auto chassis components.

A stress gradient approach for fretting fatigue assessment of metallic structural components

In the present paper, the fretting fatigue life assessment of metallic structural components under cylindrical contacts is performed by applying a critical plane-based multiaxial fatigue criterion. Such a criterion is formulated by using the so-called critical point method: a material point located at a certain distance from the hot-spot on the contact surface is assumed to be the critical point where to perform the above assessment. The above distance, function of the material properties, is measured along three alternative paths (a normal path, an inclined path and a principal stress oriented path) and, using such three different paths to determine the critical point location, the effectiveness of the criterion is evaluated by means of experimental data related to aluminium alloy specimens under cylindrical contacts. Further, in order to improve the accuracy of the critical plane-based criterion in terms of fretting fatigue lifetime evaluation, a new approach involving a critical distance also function of the stress gradient in the contact zone is proposed and experimentally validated.

Fatigue life assessment of large scale T-jointed steel truss bridge components

Among current approaches for fatigue strength assessment, the effective notch stress method is widely employed by practising engineers designing welded joints. This is particularly important in the situation where the nominal stress and structural stress cannot be easily quantified. In this paper, the applicability of the so called effective notch stress approach on large-size T-joints in truss bridges is investigated through a comprehensive experimental programme supported by numerical analysis. A series of large-scale fatigue tests on prototype large-size T-joints with cope holes were conducted. These types of joints are normally used in fully welded truss bridges. Furthermore, a simple parametric study was conducted using finite element analysis to investigate the effect of plate thickness and cope-hole radius on effective notch stress. Comparison of the results with commonly used design guidance documents reveals that the effective notch stress approach provides a conservative estimate of the fatigue strength of the specimens tested in this experimental programme.

Effect of constraint on creep crack initiation time in test specimens in ASTM-E1457 standard

The creep crack initiation (CCI) time of six specimen geometries in ASTM E1457 standard has been predicted by using numerical simulations, and the constraint effect on CCI time was analyzed. The results show the specimens with different geometries, size ranges and side-grooves recommended by ASTM-E1457 produce different CCI time data due to different constraint levels. With increasing constraint levels in specimens, the CCI time is reduced. The quantitative correlation formulas of CCI time with creep constraint parameters have been established, and they may be applied in CCI life assessment of high-temperature components for accounting for constraint effect and improving accuracy.

Fatigue assessment of a notched member under combined LCF and HCF loading

Steam turbine last stage blades can experience a wide range of load spectra during their lifetime, which involves both Low Cycle Fatigue (LCF) and High Cycle Fatigue (HCF) phenomena.In the paper a numerical model is proposed for considering this specific load spectrum in the fatigue life assessment of turbine blade components made of high strength precipitation-hardening steels.The method is based on cyclic isothermal stress and strain controlled fatigue test results of notched and un-notch specimen up to the HCF-regime. Moreover, stress controlled tests on notched specimens with different stress ratios were performed in order to evaluate the influence of mean stress and to derive a local Haigh diagram. The Highly Stressed Volume (HSV) has been used to transfer characteristic fatigue properties from specimens to a critical area (notched part) of a turbine blade. Furthermore, the real operating conditions of the component were used to allow the application of Palmgren-Miner damage rule.An ad-hoc MATLAB® software has been developed for the post-process of Finite Element Analysis (FEA) results, in particular for the automatic calculation of the HSV on the critical areas of the component. The proposed fatigue model has been finally applied on a real case study (blade dovetail) using appropriate safety margins for reliable design assessment.

Improvement of predicting mechanical properties from spherical indentation test

Although nowadays the Instrumented Indentation Test (IIT) can be applied to the fields from nano- micro- to macroscopic scale, this paper only addresses its application in the area of life assessment of components in industry, such as power and/or petroleum chemistry plants. In comparison of IIT with other miniature specimen techniques, such as the small punch test, impression test, micro-tensile or small ring tests etc., the relative advantages of the IIT technique are: non-destructive test could be performed on site, no sample machine is needed to cut out material, thus no sample processing is necessary. Therefore, the IIT method has potential for residual life assessment of components in service. A portable IIT indenter has been developed to measure both load and displacement, from which actual material properties of components can be evaluated.In order to develop analytical software for a new portable IIT instrument, authors reviewed several existing analytical methods, such as the representative stress-strain method, dimensional analysis method, and inverse finite element method. This paper first gives an overview of these analytical methods, their advantage and disadvantage, and then put forward ideas to improve them. Finally, the so-called Neural Network (NN) is introduced as the NN method. This method, can deliver evaluation on site without time-consuming finite element analysis.Experimental results for IIT are provided by DNV KEMA. First verifications are carried out for elastic-plastic properties, such as yield strength, tensile strength, Young's modulus and Brinell hardness. A good agreement is found between the conventional test results and the analytical prediction from IIT results. More validation and tests are needed and planned for the near future.

Advanced Methodologies for Fracture Analysis and Damage Tolerant Evaluation

The objective of the paper is to present the advanced methodologies for fracture analysis and damage tolerant evaluation of metallic structural components for efficient and safe design of structural systems meeting the functional criteria. An efficient and novel Numerically Integrated-Modified Virtual Crack Closure Integral (NI-MVCCI) technique has been demonstrated for 4-noded bilinear, 8-noded (regular & quarter-point), 9-noded Lagrangian and 12-noded cubic isoparametric family of finite elements. Another advanced numerical method, Extended Finite Element Method (XFEM) for fracture analysis of cracked stiffened panels has been discussed. Methodologies for crack growth and remaining life assessment of structural components under constant and variable amplitude loading have been presented. Brief description on residual strength evaluation has been provided. Numerical studies on fracture analysis to compute Strain Energy Release Rate (SERR), G and stress intensity factor (SIF) and remaining life assessment and residual strength evaluation have been conducted and the results are compared with the respective analytical/experimental results.