Search

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]

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]

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]

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]

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]

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]

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]

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]

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]