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An understanding of the failure mechanisms induced by seepage flow is important from both a practical and a theoretical perspective. Conventionally, failure arising from seepage flow is considered a consequence of piping (internal erosion), according to seepage theory, at a critical hydraulic gradient of around 1. However, failures arising from seepage flow are more complex and might involve different mechanisms than originally suspected. This research paper reviews the published literature and identifies the most up-to-date findings to make recommendations for future research. We present experimental evidence that indicates that internal fluidisation in granular soil can occur in many unseen situations when subjected to localized flow that does not necessarily adhere to Darcy's law. Ultimately, we conclude that while there has been substantial research to investigate and explain the mechanism(s) of failure of granular materials subject to vertical seepage flow, to the best of our knowledge, no research studies have simulated the potential failure mechanism of a granular bed triggered by lateral seepage flow, which might arise, for instance, in the case of leakage via a defect in an earth dam or a sheet pile retaining wall. Therefore, further research is needed to improve our understanding of failure mechanisms associated with lateral seepage flow. [ABSTRACT FROM AUTHOR]

Natural fiber reinforced sandwich composites have been of keen interests to researchers as a result of their low cost, moderately good mechanical properties, and biodegradability. The main attention of the present work lies on the eco-friendly honeycomb structures for sandwich panels. This paper investigates the mechanical characteristics of flexural and fracture strengths of the sandwich panels involving polypropylene as its core and treated flax fabric fiber reinforced polymer matrix composites as face sheets. Taguchi's design of experiments is implemented in the experimental analysis. The influence of fabric orientation and surface treatment on the properties is reconnoitered. Analysis of Variance (ANOVA) is employed to study the influences of different parameters on flexural and fracture strengths of sandwich panels. [ABSTRACT FROM AUTHOR]

The objective of this work is to find out the stress intensity and load confrontation of the axially cracked ASME pressure vessels so that the condition of the vessel will be branded how much more the life of the vessel wall would come if the crack is generated during operating conditions. The background of this work is based on the failures often occurring in the oil, gas and chemical plant industries. Process equipments are having its own standard design procedures and operating life's according to its material properties. Some of the equipments need frequent refurbishment as well as proper maintenance during operations due to the various working conditions. The code practices that process equipments need to be designed for time span of 20 to 25 years. However failures occurring during operations are unpredictable but it is diagnosable. It may be due to various reasons such as malfunctioning of components and wrong operations. In this paper the work is such that if the crack is generated axially inside due to load or corrosion, how much more operation the vessel would sustain. If the cracks grow continuously due to frequent loads how long the un-cracked thicknesses would withstand the internal pressure loads. ASME based designed pressure vessel has been considered for this study. The typical pressure vessel crack has been modeled internally in axial directions. The operating load has been applied and the behavior of cracks and its load confrontations were simulated using finite element technology and the results were presented. [ABSTRACT FROM AUTHOR]

Packaging-related internal failure such as solder fatigue or wire crack has been acknowledged as one of the principal root causes of IGBT power module failures. Condition monitoring is needed by power electronic system operator as a cost-effective means of improving IGBT reliability. In this paper, an approach is presented to monitor internal failure inside a IGBT power module by identifying the increase of external case temperature due to internal failure, In this method, an IGBT power module is regarded as a black box system without considering any internal factors or models associated with the heat sink as well as the power loss module, all electrical factors at certain working points are classified as the inputs, meanwhile the case temperature is considered as the output of the black box system respectively, in which any device power loss model or heat sink model is not established to estimate the internal thermal resistance. Firstly, case temperature is predicted based on the GA-BP artificial neural network, after that, a monitoring method are presented based on the predicted look-up table or model and a threshold for the difference between the measured and the predicted case temperature is set reasonably. It is because that the total loss in the module increases as junction temperature rises generated from internal failure, causing an increase in case temperature rise, the external characteristic of IGBT is the reflection of internal condition, once the measured case temperature is higher than the predicted temperature at a certain working point, taking account of the masking effect of measuring accuracy and errors, then a conclusion can be get that the IGBT condition is abnormal. At last, experiment has validated and demonstrated the concept and characterized the proposed method. [ABSTRACT FROM AUTHOR]

This paper investigates the low velocity impact response of cotton, flax/cotton and glass/cotton hybrid composites. The composites were prepared by compression moulding and cut to dimensions specified by the Boeing impact test specification. All the specimens were impacted at 17, 26, 44, 62 and 77J energy levels on an Instron dynatup 9250HV drop weight impact tower by a hemispherical impactor head. Impulse software was used in data acquisition and analysis of results. The cotton and flax/cotton composites mainly failed through cracking, tensile fracture and delamination, while glass/cotton hybrid composites failed by deflecting and delamination. The glass/cotton composites were not penetrated and did not fracture even at high impact energy levels. [ABSTRACT FROM AUTHOR]

The majority of structures contain singularities that cause a high stress concentration on the root of defect which affect the mechanical properties. In this regard, it's important to take into account that the development process of fracture phenomenon requires a physical volume of elaboration of failure process. The concept of determination of this volume forces us to defineits diameter that called the effective distance. In order to settle this issue, the current paper proposes a new method such as stress triaxiality to define the fracture process zonecaused by all-notch in a volumetric approach that's examined under a mixed mode I+II. The bend specimens are computed by finite element method (FEM) and the local stress distribution was calculated by the Abaqus/CAE. The study shows a credibility of the criteria (y stress gradient and (3 parameter of triaxiality) to determine the effective distance along the notch. The comparison between the various values shows a good agreement. [ABSTRACT FROM AUTHOR]

Recently, a new method, called X-FEM. has been proposed to models without remeshing the material and /or geometrical evaluative discontinuities (cracks, voids, inclusions, bimaterials...). The advantage of the method is that the element topology need not conform to the surfaces of the discontinuities. It has obtained so promising results that some authors have immediately foreseen the opportunities of applying X-FEM to many types of engineering problems in complex domains. However, due to its complexity, the implementation of the X-FEM method in commercial software is still very limited. This paper covers the formulation and implementation of this recent method, and discusses various aspects of the approach. Numerical experiments show the effectiveness and robustness of the XFEM implementation in the in-house software XFr. [ABSTRACT FROM AUTHOR]

Using the metal structure of TLJ900 bridge erecting machine as an example, this paper takes its natural frequency and vibration model as indexes of damage detection, the frequency variation and the vibration model are analyzed in different damage positions and different damage degree. The simulation results demonstrate that the first ten order vibration models under different damage positions are no less than those of undamaged positions, therefore, the vibration model is difficult to identify the damage of structure, but the damage positions and damage degree can be evaluated according to the frequency variation. The frequency variation is small when the damage is slight for the single crack damage, and vice versa. Moreover, the frequency can be obtained quickly and accurately. So, the frequency variation can be used to identify damage even the damage is serious. [ABSTRACT FROM AUTHOR]

AISI 1045 steel is used extensively by most industry sectors mainly in automotive for applications requiring more strength and wear resistance such as connecting rods. Connecting rods are widely used in variety of car engines. It is subjected to forces generated by mass and fuel combustion, thus, it must be capable to transmitting axial tension and compression. In this paper, connecting rod was used as a research material. This article discusses the analysis on strain signal of fatigued material using a new method called Integrated Kurtosis-based Algorithm for Z- filter (I-kaz) approach. Fatigue tests were performed according to the ASTM E466-96 standard with the attachment of astrain gauge to the tested specimen. Fatigue test was carried out using variable amplitude loading (VAL) at frequency 8 Hz. A data acquisition system was used to collect those fatigue strain signals. Fatigue damage characteristics were observed through the signals and analysis was performed by using I-kaz approach. I-kaz parameter was determined to relate with fatigue failure assessment which will describe the fatigue life. [ABSTRACT FROM AUTHOR]

A method using meso-scopic parameter is established to describe the damage evolution of refractories in this paper. According to the complex nonlinear mechanical behavior of refractories, based on micromechanics, relations between effective elastic modulus and meso-scopic parameter for refractories are derived in terms of the interphase model. The damage evolution is divided into three stages: the initial damage, the damage of the matrix and the damage of the interface. Based on the analytic method of the interphase model, relation between macro-scopic damage variable and the strain for refractories is fitted as cubic polynomial under uniaxial compression test. The results show a generally good agreement between the predicted value and the experimental data, which proves the validation of the proposed method. [ABSTRACT FROM AUTHOR]

Sandwich beams subjected to three points bending may fail in several ways, including tension or compression failure of the facing; face yielding and face wrinkling. In this paper three face sheets materials were used to study the effect of the fibre orientation on static failure of composite sandwich beams carbon/epoxy, kevlar/epoxy, glass/epoxy of stacking sequence [+θ/-θ] 3s, [0°/90°] 3s and [45°/-45°] 3s. The stresses in the face were calculated using maximum stress criterion and the simple beam theory, including transverse shear effect. The obtained different results show that the sandwich beams with carbon/epoxy, and glass/epoxy face sheets are the best materials, in return the kevlar /epoxy facing characterised by a low mechanical resistance in compressive and tensile. The critical failure loads, depends on the properties of the face sheets materials and the fibre orientation. [ABSTRACT FROM AUTHOR]

This paper deals with a new scheme for the diagnosis of localized defects in ball bearings based on the multi-scale principal component analysis (MSPCA), Power quality distribution and a pattern Probabilistic Neural-Network Classifier (PNNC). Vibration signals for normal and defect bearings were acquired from an experimental system. The DWT coefficients and Power quality distribution were used to provide an efficient method for generating feature vectors. A pattern Probabilistic Neural-Network Classifier was trained and used as a diagnostic classifier. The simulation results demonstrate that the developed diagnostic method can reliably detect and separate different level faults [1], [2]. [ABSTRACT FROM AUTHOR]

This paper presents scattering of fatigue time series data to develop a relationship between the fatigue damage and the Morlet wavelet coefficient. In order to achieve the purpose, the SAESUS strain signal was inputted into a segmentation algorithm based on the wavelet coefficient amplitude level which produces 49 segments that each has an overall fatigue damage. Observation of the fatigue damage and the wavelet coefficient was made on each segment. In the end of process, this algorithm produced a more reliable and suitable method of fatigue stain signal segmentation and segment by segment analysis to identify any improvements in the data scattering for fatigue data clustering prospects. Scatter plot was produced based on the relationship between segmental fatigue damage and its corresponding wavelet coefficient value. As the result, the relationship between the fatigue damage and the Morlet wavelet coefficient is strong and parallel, since the higher wavelet coefficient presents the higher fatigue damage, otherwise, it is the lower fatigue damage. [ABSTRACT FROM AUTHOR]

Stress corrosion cracking (SCC) has been acknowledged as a trigger phenomenon which can cause a failure especially in welded pipeline installations. By the name, three factors must be involved in SCC failure: stress, corrosive environment and an initial crack. This article observes the effect of grain orientation to the SCC failure in ASTM A36 plate. The results show that with lower grain orientation the precracked plate withstands longer in a certain corrosive surroundings and stress load. From microstructure observation the finer grains in lower orientation are believed to increase the SCC resilience. The microstructure at fracture region shows that the lower orientation tends to develop intergranular crack growth whilst at higher orientation transgranular is exhibited. This phenomenon also explains why the lower grain orientation can hold SCC failure longer. [ABSTRACT FROM AUTHOR]

Bi-material interfaces exist in many advanced materials or engineering structures. It has been established that because of the presence of stress concentration/singularity at interface corner, failure may initiate from the interface corner. In order to characterize the interface properties, it is necessary to determine the bonding strength of interface accurately by eliminating the stress singularity. This paper presents a review on the researches done so for covering the stress singularity analysis at bi-material interface, determination of the order of stress singularity, stress singularity elimination techniques and measurement of interface strength. It is suggested that more researches are needed in effective technique to eliminate interface stress singularity. More accurate and realistic experimental method for determination of interface bonding strength may be developed based on improved design of specimens that stress singularity at the interface corner can be effectively eliminated. [ABSTRACT FROM AUTHOR]

A multilayer model of a solder joint is presented in this paper capable to simulate the stress/strain distribution in such connections after deformations. Finite Element methods are applied to obtain more expressive results compared to approximate calculations in elasticity/plasticity. The proposed layer structure, including intermetalic layers, is justified by relevant examples on lead-free material in the recent research work. Simulated deformations after displacement steps are compared to the behavior of loaded joints in shear tests. Statements on stability are supported by various strain plots in critical regions. Especially the solder volume at the ends of the joints close to the metallization shows a disadvantageous stress concentration that indicates centers of possible structural failures. An important extension of the model is the inclusion of different sized pores in the solder joint. Modeling, visualization and the properties of pores are discussed sufficiently. The multilayer model contributes to increase the quality of solder joints and moreover its flexibility enables an easy adaptation to future tasks in research and electronic engineering. [ABSTRACT FROM AUTHOR]

This paper presents analyse of crack origin and stress distribution of bonded steel-concrete composite beam by numerical method. A three-dimensional finite element model has been developed in this work. Before the stress analysis, results obtained via finite element model on deflexion and strain evaluations with increase of applied load are compared with those obtained by experimental test. The numerical model developed allows knowing the crack origin of the composite beam and the direction of crack propagation. The results show that compared with the other kinds of stresses, the local tensile stress in the concrete slab is the closest to the ultimate strength and causes the initial cracking in the concrete slab. Particularly, it is found that the variation of applied load width plays an important role in the determination of location and value of the maximal tensile stress in the concrete slab. However, the effect of variation of the adhesive thickness, from 3mm to 15mm, on the deflexion and the shear stress is not important, Based on the obtained results, it is concluded that the ruin of the bonded steel-concrete composite beam is not situated at the steel-concrete interface and the bonded composite beam is applicable in practice. [ABSTRACT FROM AUTHOR]

Finite Element Analysis (FEA) combining with the concepts of Linear Elastic Fracture Mechanics (LEFM) provides a practical and convenient means to study the fracture and crack growth of the materials. 2-D finite element model is developed for two different geometries; a rectangular plate with cracks emanating from a circular hole and Double Edge Notched Plate (DENT). Both geometries are in tensile loading and under mode I conditions. In this paper, a displacement extrapolation technique is employed particularly, to predict the crack propagations directions and to, calculate the Stress Intensity Factors (SIFs). Therefore, verification of the predicted SIF and crack trajectory are validated, with the relevant numerical and analytical results obtained by other researchers. [ABSTRACT FROM AUTHOR]

In this paper, we present a new numerical schema to model the crack growth without remeshing. We proposed an algorithm that couples the level set method with the double degenerated finite element DQPE to solve the elastic-static fatigue crack problem: The LSM is used to represent the crack location, including the location of crack tips. The DQ-FEM is used to compute the stress and displacement fields necessary for determining the rate of crack growth. The results obtained are compared to reference solutions and show excellent agreement. [ABSTRACT FROM AUTHOR]

Logarithmic and quadratic models are proposed for determination of fracture toughness (KIC), based on experimental values of Charpy impact energy (CVN) and first ply failure load of laminated composites (σFPF), both at room and at low temperatures. Most published correlations, which are obtained for steels, are based on ultimate strength. For composites, determination of ultimate yield strength needs costly experimental tests or complicated numerical simulations. In this study, first ply failure load (σFPF) is used instead of ultimate strength which can be simple determined analytically or experimentally. In order to this, a considerable number of experiments have been conducted to augment the necessary data. Values of KIC, CVN, and σFPF of glass/epoxy composites have been collected through standard test methods at different test temperatures in the range of 23 °C to -30 °C. Good agreement was found between estimated fracture toughness by the presented method for tested temperature range and available experimental data. [ABSTRACT FROM AUTHOR]

The aim of this work is to predict the fatigue life of a heat exchanger tube subjected to variable thermo-mechanical loading. In order to achieve this objective, this study has been based on two fracture mechanics models, i.e. the global approach and the continuous damage one. These models take into account the geometrical non-linearity introduced by the presence of a semielliptic crack and also the thermo-mechanical cyclic loading type. The component investigated in this study is a 316L steel tube with a semi-elliptical crack. Then the 14 mm thick tube is induction heated to 300-550 °C. The experimental results have been compared with the numerical computations of these models carried out using a finite element code. From these results, the number of cycles before the damage to the simplified structural model of the heat exchanger can be predicted. [ABSTRACT FROM AUTHOR]

The current study addresses the mechanical and fracture behaviors of extruded ZK60A magnesium alloy. This material has numerous potential structural applications, and its characteristics need to be determined for it to be used as a structural material. Tensile, hardness, and Charpy impact tests were performed as per American Society for Testing and Materials standards to determine the mechanical behavior of the material. Its fracture behavior was determined using plane-strain fracture toughness, stable crack growth, and fractographic tests. The fracture toughness was calculated from the fracture toughness-thickness curve obtained from fracture tests on single-edge notch bend specimens with fatigue pre-cracks. The stable crack growth studies were conducted using three-point bend specimens to determine the initiation and maximum loads and the range of stable crack growth for both mode I and mixed-mode loading cases. X-ray diffraction analysis of the alloy was also conducted. Scanning electron microscopy was used to observe the fracture surface morphologies of the specimens. This study addresses the structural analysis, advanced materials, and safety and reliability aspects of aerospace research. [ABSTRACT FROM AUTHOR]

Crack-tip opening displacement (CTOD) has been widely used to measure the fracture toughness of materials. Based on the energy partitioned work of fracture concept, CTOD behavior is able to describe in more depth the characteristics of mechanical fracture of materials. This study aims to investigate the CTOD behavior in the ultraviolet (UV) irradiated zeolite-HDPE composites. The annealed double-edge notched tension (DENT) shape composite was exposed in UV radiation environment for 50, 100, 150 and 200 hours at a constant temperature of 60°C and atmospheric pressure. The DENT specimens are subjected tensile loaded according to ESIS protocol. CTOD was analyzed based on the concept of partitioned work of fracture. The results show that at the yielding and crack initiation stage, the CTOD value begins to increase when the displacement has passed the 0.5 mm value. At the crack propagation stage, the range of CTOD and displacement values are shorter with increasing duration of UV radiation. At the same crack extension, the CTOD value decreases by increasing the duration of UV radiation. [ABSTRACT FROM AUTHOR]

A series of investigations is carried out to understand the crack growth behaviour under various stress ratios and amplitudes of cyclic load, respectively, on fibre metal laminates (FML) composites. The results of the investigation show that the increase of the stress ratio reduces the fatigue life and increases the crack growth rate of the composite. These relate to the displacement on every material forming the composite and to the delamination in the zone nearby the crack tip when the composite was cycled under constant cyclic load. Besides this, fibre-epoxy bridging contributes to lower the crack growth rate. The bridging occurs if the displacement between the monolithic aluminium and the fibre-epoxy is not too different. [ABSTRACT FROM AUTHOR]

The fracture behavior of annealed composites of zeolite-filled high density polyethylene has been investigated using the essential work of fracture concept. The crack opening displacement (COD) was estimated starting from the essential work of fracture value. The morphology of the fracture surface was examined using the scanning electron microscopy and the fracture mechanisms were discussed. The results showed that the composite with a 5 wt.% zeolite concentration has a unique fracture behavior characterized by the highest resistance to crack initiation in accordance with COD but a low resistance to crack propagation. The non-essential work of fracture as the resistance to the stable crack propagation has shown a maximum of 2.5 wt.% of zeolite followed by a sharp drop at[ ]a higher content of zeolite indicating a zeolite induced ductile-to-brittle transition. The fractured surface morphology revealed that the zeolite particle clusters arrested the plastic crack growth, which was more effective at 5 wt.% zeolite concentration. At a higher zeolite content, the amount of particle clusters rose, leading to a decrease in the average distance between them. Consequently, a large-scale plastic deformation of the matrix effectively favored the small strain damage and the fracture eventually occurred in the ductile-to-brittle transition. [ABSTRACT FROM AUTHOR]

In this investigation, we present a comparative study on finite elements for capturing discontinuities by means of standard finite elements (FEM) or extended finite elements (X-FEM). For this purpose, several specimens containing geometrical and material discontinuities have been analyzed. The analysis covered different basic geometrical configurations, namely propagation of single crack-tip, propagation of double crack-tip, void and inclusion growth. The basic idea is to determine numerically values of certain fracture parameters, and to compare them with the results given by analytical solution. These main characteristics constitute the key to every fracture mechanics analysis. They are the base for the majority of failure criteria. Hence, determining these characteristics must be assessed as accurately as possible. [ABSTRACT FROM AUTHOR]

This study presents a numerical investigation on the stress intensity factors (SIF) obtained under pure torsion loadings or mode III. ANSYS finite element analysis (FEA) was used to determine the SIFs along the crack front of surface cracks embedded in the solid circular bars. 20-node isoparametric singular elements were used around the crack tip by shifting the mid-side node 1/4-position close to a crack tip. Different crack aspect ratio, a/b were used ranging between 0.0 to 1.2 and relative crack depth, a/D were ranged between 0.1 to 0.6. Mode I SIF, KI obtained under bending moment was used to validate the proposed model and it was assumed that this proposed model was validated for analyzing mode III problems. It was found that, the FII and FIII were dependent on the crack geometries and the behavior of crack growth were also dependent on a/b and a/D. [ABSTRACT FROM AUTHOR]

Thin-walled tubes have been studied and applied in many engineering industries. Most of the investigations are based on experimental methods to consider the amount of absorbed energy by the structure. The production cost and the time taken to manufacture a component can be reduced by defining the shape and thickness of the structure, and result prediction. In this study the energy absorption characteristics of cylinder tubes with aluminum, magnesium and steel materials has been simulated by ABAQUS software with finite element method to predict the probable crush on the component. The obtained results from simulation, such as absorbed energy, specific energy absorption (SEA) and reaction force have been expressed for simple circular tube and Tailor-Made Tube (TMT), and then the energy absorption and SEA of two tubes with three different applied materials are compared. Lastly the results show that the capacity of Tailor-made tube in both energy absorption and specific energy absorption is higher than simple tube. Moreover, steel can absorb more energy than aluminum, and in the other hand magnesium has the highest specific energy absorption in comparison to aluminum and steel. [ABSTRACT FROM AUTHOR]

In this work, we introduce an implementation of the X-FEM method for discontinuity problems within the finite element software XFr. The proposed implantation approach overcomes a number of difficulties associated with the use of standard finite element method. Several numerical examples illustrating the main features and the computational efficiency of the XFr program for discontinuity propagation are presented. [ABSTRACT FROM AUTHOR]

This work is devoted to the development of material model in order to characterize the complex nonlinear behavior of real refractory material. According to the complex nonlinear mechanical behavior and the damage mechanisms of refractory materials, damage model of refractory materials was put forward based on the interphase model by the method of micro-mechanics. The model was considered as three elastic stages. The initial stage was linear and the other two were nonlinear according to the change of Young's modulus. Moreover, the damage of the model was defined by the change of Young's modulus. Utilizing the model proposed, a subroutine was developed through the commercial software ABAQUS. The numerical simulation of the behavior of the magnesium carbon refractory under compression was carried out using the subroutine. The results show the function of secondary development to well describe the damage of the refractory. A good agreement of the numerical and experimental results is obtained. [ABSTRACT FROM AUTHOR]

Stress intensity factor (SIF) calculations for semi-elliptical surface crack in round bars subjected to a combined loading using a three-dimensional finite element (FE) model was numerically presented. Different crack aspect ratio, a/b ranging between 0.0 to 1.2 and relative crack depth, a/D is in between 0.1 to 0.6 were considered. Firstly, the SIF obtained from bending loading (Mode I) was compared with available literature results to validate the proposed model. Since the loading is non-symmetrical, the whole finite element model was constructed and both bending and torsion loading were remotely applied to the model. The effective SIF technique was used to combine the individual SIF. Then, the combined SIFs were compared with the SIF obtained using finite element analysis (FEA) under combined loadings. It was found that the calculated SIF using the effective SIF technique was higher than the combined SIF predicted numerically using FEA. The discrepancies may due to the interaction of crack surfaces especially under the loading of pure torsion. [ABSTRACT FROM AUTHOR]

Yield criteria for aeolotropic behavior are postulated and solutions for the plastic bending of circular plates with different types of plastic anisotropy are obtained under simple support conditions. Load cases considered are partial or total uniformly distributed loads, and loading by a rigid punch. Results are extended to include the condition of a concentrated load at the centre of the plate in each case. [ABSTRACT FROM AUTHOR]

The results of analytical and experimental researches concerning predicting of fatigue crack growth in the operating conditions are presented. Main conditions causing a fatigue crack growth at the complex spectrum of loading are analyzed and divided to two groups. Theory of fatigue crack growth indication and the crack growth indicator (CGI) are developed. The fatigue tests with aluminium alloy flat specimen and CGI at constant and variable amplitude of loading was carried out. It is shown the estimate of mean value of constant C" of CGI both cases closes to that one of flat specimen. There is planned and executed a flight experiment using CGI located on two aircraft An-24 and An-26. The combination of CGI technology with fractography of a fatigue crack surface allows to decreases number of necessary tests, terms of their carrying out, and increases accuracy and reliability of results. Results of crack growth in CGI at operational load allowed to evaluate the parameters of generalized Paris- Erdogan law and statistical properties of crack increment per flight. It is shown the Kolmogorov-Smirnov test shows the hypothesis about normal distribution of log increment in flight is significant at the 5% level. [ABSTRACT FROM AUTHOR]

Blade failures are observed ever since Frank Whittle faced problems with his W2 jet engine development during the II World War. They continue to happen even now with advances in engine designs. Stress based and Strain based life estimation help in design stage; however a failure always has a tell-tale story of Fracture with Crack Initiation and Propagation that embeds all the clues of how the failure occurred. A study of this fracture surface helps in understanding the underlying phenomena in the machine causing the failure. Here a case study is described in understanding a blade fracture through a process driven tool "TurboManager" developed with several modules as a turbine life estimation work bench for the rotating machine components. It is shown how such a tool helps in blade failure investigation. [ABSTRACT FROM AUTHOR]

A new finite element model has been developed to predict fatigue crack growth in arbitrary 2D geometries under constant amplitude loading. The purpose of this model is on the determination of 2D crack paths and surfaces as well as on the evaluation of components Lifetimes as a part of the damage tolerant assessment. Throughout the simulation of crack propagation an automatic adaptive mesh is carried out in the vicinity of the crack front nodes and in the elements which represent the higher stresses distribution. The fatigue crack direction and the corresponding stress-intensity factors are estimated at each small crack increment by employing the displacement correlation technique under facilitation of singular crack tip elements. The propagation is modeled by successive linear extensions, which are determined by the stress intensity factors under linear elastic fracture mechanics (LEFM) assumption. The stress intensity factors range history has to be recorded along the small crack increments. Upon completion of the stress intensity factors range history recording, fatigue crack propagation life of the examined specimen is predicted. Verification of the predicted fatigue life is validated with relevant experimental data and numerical results obtained by other researchers. The comparisons show that this model is capable of demonstrating the fatigue life prediction results as well as the fatigue crack path satisfactorily. [ABSTRACT FROM AUTHOR]

On the basis of fracture mechanics, a numerical study has been considered in order to study the effect of size of degenerated finite element in modeling the singularity near the crack tip. It allows to numerically estimating of the stress intensity factors, for Central Notched specimen, by using two techniques of modeling (finite element standard and degenerated finite elements). This work makes it possible to confirm the aptitude of the degenerated finite elements to model the singularity accurately existing in the vicinity of the cracks. [ABSTRACT FROM AUTHOR]