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The paper investigates the fracture of the target plate under shock-wave loading. The material of the target plate is orthotropic organic plastic. The compression wave was generated on organic plastic using an aluminum striker plate. The velocity of interaction varied from 100 to 400 m/s. The study is carried out numerically by the finite element method in a three-dimensional statement using the author's software EFES. An elastic-brittle model is proposed to describe the behavior of the composite. A tensor-polynomial criterion of the second degree is used as a criterion of the fracture of the composite. A two-stage model is proposed to describe the fracture of the orthotropic material of the target plate. The model of the behavior of the composite takes into account the different modulus of strength properties in compression and tension. The behavior of the material of the striker is described by an elastoplastic medium, for the fracture of which a deformation criterion is proposed according to the limiting value of plastic deformation. The influence of the direction of reinforcement of the composite on the fracture of the target plate was studied. [ABSTRACT FROM AUTHOR]

The paper deals with investigations of a crack propagating in a semi-circular concrete disc loaded in bending. Various crack inclination angles ensure different degrees of I+II mixed-mode conditions. Generally, concrete material exhibits quasi-brittle fracture behavior, which is difficult to describe. It has been shown that fracture in this kind of material occurs in a larger zone around the crack tip. Thus, the multi-parameter fracture mechanics concept can help to understand the facture response better. Particularly, the Williams power expansion with a selected number of its initial terms is used for approximation of the crack-tip stress/displacement field. The over-deterministic method together with a finite element analysis of the problem is used for calculation of the coefficients of the series. The deflection angle of the initial crack is then assessed via generalized/multi-parameter form of Maximum Tangential Stress (MTS) criterion in dependence on various parameters. The theoretical results are compared to experimentally obtained data. The results prove that the multi-parameter description of the crack-tip fields can bring more accurate assessment of the fracture response of a crack under mixed-mode loading. [ABSTRACT FROM AUTHOR]

In this paper, presents the stress intensity factor in linear elastic fracture mechanics. A simple model was created in the program Abaqus. Two variants were compared, namely the solution using the finite element method and the extended finite element method. The stress intensity factor is then used in both methods, where there are many criteria for crack propagation decisions, which is further used in these methods. [ABSTRACT FROM AUTHOR]

Computer simulation is widely used in the design and development of technical products. Multiscale nature of deformation and fracture of novel materials requires to use for this purpose not only the conventional finite element method but particle methods at different spatial scales as well. This paper presents a computer code aimed for discrete-continuum simulation of friction based on coupling finite elements (as a continuum method) with movable cellular automata (discrete particle method). Two computer codes based on finite elements and written in different programming languages are used: commercial and in-house. Peculiarities of the application program interfaces of the particle code for coupling with both finite element codes are described and analyzed. It is shown that the code developed takes the advantages of both cases and promises to be very efficient for simulating various contact problems including friction. [ABSTRACT FROM AUTHOR]

Our existing Ultrasonic Broken Rail Detection system detects complete breaks and primarily uses a propagating mode with energy concentrated in the head of the rail. Previous experimental studies have demonstrated that a mode with energy concentrated in the head of the rail, is capable of detecting weld reflections at long distances. Exploiting a mode with energy concentrated in the web of the rail would allow us to effectively detect defects in the web of the rail and could also help to distinguish between reflections from welds and cracks. In this paper, we will demonstrate the analysis of a piezoelectric transducer attached to the rail web. The forced response at different frequencies is computed by the Semi-Analytical Finite Element (SAFE) method and compared to a full three-dimensional finite element method using ABAQUS. The SAFE method only requires the rail track cross-section to be meshed using two-dimensional elements. The ABAQUS model in turn requires a full three-dimensional discretisation of the rail track. The SAFE approach can yield poor predictions at cut-on frequencies associated with other modes in the rail. Problematic frequencies are identified and a suitable frequency range identified for transducer design. The forced response results of the two methods were found to be in good agreement with each other. We then use a previously developed SAFE-3D method to analyse a practical transducer over the selected frequency range. The results obtained from the SAFE-3D method are in good agreement with experimental measurements. [ABSTRACT FROM AUTHOR]

For evaluating functionally graded materials, fracture mechanics methods offer significant reliability and performance in predicting crack propagation. To determine the ability two-dimensional finite element model for evaluating crack propagation routes and SIF values is being used to estimate crack propagation path and stress intensity values under LEF investigation. the stress intensity factor (SIF) for different types of crack propagation has been developed. The (DET) displacement extrapolation technique has been used to predict the crack and crack propagation movements that will occur as a result of stress intensity variables. In this paper, different geometric shapes have been used, which is a rectangular plate with a double-edged notch hole (DENT) from the materials has been used, for the purpose of reliability analysis of this model to showing crack propagation in fracture mechanics. Moreover, the model source code was developed to use MATLAB software. Functionally graded materials are a challenging and complex task engineering material that has continuous or steady changes in the composition and microstructure across its thickness. Functionally graded materials (Nickel – Aluminum) with varying percentages for each layer have been used. The results of two-dimensional finite elements showed a significant prediction of the crack path and SIF value. [ABSTRACT FROM AUTHOR]

The paper deals with a problem of rock finite element modelling and simulation. The main intention of authors was to present possibilities of different approaches in case of rock constitutive modelling. For this purpose granite rock was selected, due to its wide mechanical properties recognition and prevalence in literature. Two significantly different constitutive material models were implemented to simulate the granite fracture in various configurations: Johnson - Holmquist ceramic model which is very often used for predicting rock and other brittle materials behavior, and a simple linear elastic model with a brittle failure which can be used for simulating glass fracturing. Four cases with different loading conditions were chosen to compare the aforementioned constitutive models: uniaxial compression test, notched three-point-bending test, copper ball impacting a block test and small scale blasting test. [ABSTRACT FROM AUTHOR]

The paper deals with numerical analysis of the DCB test configuration together with the data reduction scheme described in the ASTM D 5528 Standard for determination of the mode I fracture toughness in case of the laminated composites with mechanical couplings. Numerical analysis based on the FEM approach was performed with the Abaqus software exploiting the VCCT technique. The experiments on the DCB beams made of coupled laminates were also performed. The results show, that the distribution of the Strain Energy Release Rate can be asymmetric. A need for appropriate data reduction schemes has been revealed. [ABSTRACT FROM AUTHOR]

We showed our work on modeling turbine blade crack detection in Sonic Infrared (IR) Imaging with a method of creating flat crack surface in finite element analysis (FEA) in last year's QNDE paper. This modeling has been carried out continuously as part of model-assisted study on crack detection in aircraft engine turbine blades. We have presented that Sonic IR Imaging NDE is a viable method to detect defects in various structures. It combines ultrasound excitation for frictional heating in defects and infrared imaging to sense this heating, and thus to identify the defects. It is a fast wide-area imaging technology. It only takes a second to image a large area of a target sample. When an aircraft is in flight, the turbine engine blades operate under high temperature and high cyclic stresses. Thus, fatigue cracks can form after many hours of operation. Sonic IR Imaging can be used to detect such cracks. However, we still need to better understand contributions of parameters/factors in the crack detection process with Sonic IR Imaging. FEA modeling can help us to reveal certain aspects through the data it produces where experimental work cannot achieve. Upon the model we presented last year, a two-step simulation process was designed to simulate the important aspects in our experiments. These include a newly designed model for the ultrasound transducer which delivers mechanical energy to the sample and the implementation of static force while engaging the transducer to the sample. In this paper, we present the ideas and the results from the new model. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HAP-Ca10(PO4)6 (OH)2), which exhibits excellent biocompatibility in the body, is one of the most widely used bioactive ceramics for biomedical applications. Along with the ability to carry the load, one of the most important properties of materials used for bone replacement is biocompatibility. In fact, HAP is a bioactive material and it can incorporate into bone structures, supporting bone in-growth without breaking down or dissolving, and it interacts with the living tissue due to the presence of free calcium and phosphate compounds. Generally, Al2O3 powder is added to HAP powder in order to obtain high fracture toughness. Al2O3 has good mechanical properties as compared with HAP, and exhibits extremely high stability with human tissues [1-6]. In this paper, the effect of microwave sintering temperature on the relative density, hardness, and phase purity of compacted bovine Hydroxyapatite (BHA) powder was reported. This research is a comprehensive attempt to develop Hydroxyapatite bio composite ceramics reinforced with alumina-Al2O3, pure titanium and pure pulverised boron powder. A Finite Element (FEM) analysis is also used for modelling to simulate the macroscopic behaviour of this material, taking into account the relevant microscopic scales. [ABSTRACT FROM AUTHOR]

This work was focused on the experimental testing and finite element analysis (FEA) of timber beams with and without flaws (different types of cracks and hole). The aim was analysing the effect of flaws on their load-carrying capacity. This topic is important for designers of timber constructions, since even today there is still a lack of knowledge in the field of fracture mechanics of wood. The results from experimental testing and numerical simulations were discussed in this paper. Two wood products were analysed, namely, sawn and glued laminated beams (glulam beams) and three types of flaws were considered for both products i.e. a vertical crack, an oblique crack and a circular hole. In addition for glulam beams the horizontal crack in the glue line was considered. Four-point bending test was created for experimental testing considering quasi-brittle characteristic of wood. 4 samples for each type of beam, 36 in total. XFEM (Extended Finite Element Method) was used for finite element analysis of beams with considering orthotropic-elastic properties for glulam beams were considered and The results of mechanical tests and FEA gave us an overview on how different types of flaws influence the load-carrying capacity of sawn and glulam beams and with what accuracy we can simulate cracks in wood using computational method. [ABSTRACT FROM AUTHOR]

The paper deals with the interaction of reinforced concrete slab with subsoil. The subject of the paper was the processing of nonlinear analysis of the performed experiment. The specifics of the solved task include that it connects the design of concrete structures and geotechnical tasks. It was necessary to take into account the actual behavior of the concrete structure and subsoil. The experiment includes a reinforced concrete slab by dimensions 2000 x 2000 mm, 150 mm thickness. Reinforcement was used netting steel bar ⊘ 8 / 100 mm. For the research task is important, that due to cracking in the reinforced concrete slab, its stiffness bending changes. This change affects the life of the structure due to its degradation. The paper focuses on the comparison of the experiment with the numerical model in two selected load cases. For numerical modeling was used the deformation variant of the finite element method and the 30 computational model. In the computational model, the fracture-plastic material model was chosen for concrete. The Newton-Rapson method was chosen for nonlinear calculation. [ABSTRACT FROM AUTHOR]

In this paper, series of FEM analyses were performed to define stress intensity factors in 42CrMo4 steel lug joint and predict cycling crack growth. An eXtended Finite Element Method were used in computations to investigate influence of different types of boundary conditions. Crack geometry was assumed as through - thickness. The Results of stress intensity factors for stationary cracks were compared with Newman and Schijve analytical solutions. Crack paths were obtained for 2D by implementing Paris Law coupled with crack propagation criterion and direct cycling algorithm for three different hardness of steel (28,42,54 HRC). All the studies were computed an pre-processed in ABAQUS environment. [ABSTRACT FROM AUTHOR]

Pipe strings (such as drill pipe, tube, pipeline, riser) are critical facilities in oil & gas industry, which are highly susceptible to cracks caused by stress corrosion and fatigue damage. The most common defects are longitudinal and transverse surface cracks on pipe strings in oil & gas industry. Conventional nondestructive testing (NDT) methods are inadequate for these surface cracks on pipe strings. In this paper, a full 360° circumferential current induced by a coaxial excitation coil is present for inspection of longitudinal and transverse surface cracks on pipe strings. The finite element method (FEM) is employed to obtain characteristics signals by analyzing the distorted electromagnetic field above the cracks. The induced circumferential current test system is set up and crack inspection experiments are carried out. The results show that both longitudinal and transverse surface cracks can be detected effectively at one pass scanning on pipe string using the induced circumferential current. [ABSTRACT FROM AUTHOR]

This paper investigates the crack propagation and fracture failure of the gas turbine compressor blades on the vibrator rig. The blades used in the investigation were the newly qualified specimen from gas turbine factory, without any preliminary cracks or corrosion pits. The casting blades made of titanium alloy were entered into the transverse vibration in the resonant condition during the experiment. During the high cycle fatigue test, the growth of the crack was monitored and measured with the method of dye penetration. In the second part of work, finite element method (FEM) was utilized to calculate the stress distribution of the blade during vibration, and the first mode of transverse vibration was considered in the analysis. The maximum principal stress zone of the finite element model in the resonance condition was at the place where the crack occurred. [ABSTRACT FROM AUTHOR]

The paper presents easy-to-use and accurate numerical procedures determining the level of damage to structures subjected to fatigue load. The main goal of the research was the implementation in the finite element analysis program of fatigue analysis procedures for selected multiaxial fatigue criteria, taking into account the exact fatigue characteristics of materials and the certain pattern of cumulative summation the fatigue damages. Selections of three types of criteria were selected for the study: invariant criterion, criterion using the mean values in the elementary volume and the criterion defined in the critical plane. Moreover, tests were carried out for Michell's problem of the topology optimization, which showed the impact of the criteria on the shape of optimal structures. [ABSTRACT FROM AUTHOR]

The paper presents results of applying various approaches to simulation of contact surfaces fracture under high velocity interaction of solid bodies. Three basic methods have been distinguished having the difference in the algorithms of mass distribution after elements fracture at contact boundaries. Authors own finite element computer software program EFES has been used for the calculations. The calculation was carried out in a complete three-dimensional formulation. The obtained results using all three algorithms have been compared to the experimental results. [ABSTRACT FROM AUTHOR]

Strain gage techniques have been successfully but sparsely used for the determination of stress intensity factors (SIFs) of orthotropic materials. For mode I cases, few works have been reported on the strain gage based determination of mode I SIF of orthotropic materials. However, for mixed mode (I/II) cases, neither a theoretical development of a strain gage based technique nor any recommended guidelines for minimum number of strain gages and their locations were reported in the literature for determination of mixed mode SIFs. The authors for the first time came up with a theoretical proposition to successfully use strain gages for determination of mixed mode SIFs of orthotropic materials [1]. Based on these formulations, the present paper discusses a finite element (FE) based numerical simulation of the proposed strain gage technique employing [902/0]10S carbon-epoxy laminates with a slant edge crack. An FE based procedure has also been presented for determination of the optimal radial locations of the strain gages apriori to actual experiments. To substantiate the efficacy of the proposed technique, numerical simulations for strain gage based determination of mixed mode SIFs have been conducted. Results show that it is possible to accurately determine the mixed mode SIFs of orthotropic laminates when the strain gages are placed within the optimal radial locations estimated using the present formulation. [ABSTRACT FROM AUTHOR]

Sonic Infrared (IR) Imaging Nondestructive Evaluation (NDE) technology has shown inherent advantages for defect detection in aircraft structures. It can image a wide area within a second or two for metal material targets. Due to high stresses aircraft engine turbine blades bear during their operation, fatigue cracks can form after a number of hours of service. Sonic IR imaging shows its great potential for this application. However, interaction of the sonic excitation and subsequent crack heating requires fundamental understanding of physical and thermal processes in complex geometries such as turbine blades. Simulation modeling can provide results to better understand contributions of some parameters where experimental arrangements are hard to produce. Because of the irregular shapes of turbine blades, their finite element analysis (FEA) models are always dominated by tetra elements. In the usual procedure of using tetra elements, it is very difficult to create flat crack surface in such complex shapes. A new method to create a flat crack surface is designed for an actual blade. In this paper, we will present data of modeling turbine blade crack detection with external ultrasound excitation as the results of applying this new method, guided by our experimental Sonic IR imaging study on the blade. [ABSTRACT FROM AUTHOR]

A new model is developed for the hydraulic fractured well in coalbed, by considering the following aspects: methane desorption phenomena, finite conductivity vertical fracture, and asymmetry of the fracture about the well. A new parameter is introduced to describe the storage of the fracture, which is named combined fracture storage. Another new concept called fracture asymmetry coefficient is used to define the asymmetry of the fracture about the well. FEM is used to solve the new mathematic model. Both well test type curve and seepage field are got and analyzed. The effects of combined fracture storage, desorption factor, the fracture conductivity, fracture asymmetry coefficient, etc. on type curve are all discussed in detail in this paper. [ABSTRACT FROM AUTHOR]

Two previously proposed formulations to simulate nondestructive inspection by guided waves (GW) are extended to deal with (possibly multiple) scattering by several discontinuities or defects. They hybridize models for transducer diffraction effect (radiation, reception), for scattering by local discontinuities (by a finite element technique with specific boundary conditions minimizing the mesh size) and semi analytic finite elements for the guided propagation in homogeneous guides in between. The paper derives the formulations; examples illustrate their interest in NDT simulation. [ABSTRACT FROM AUTHOR]

In production of passenger cars, geometry complexity of deep drawn body panels increases constantly. For that reason, sheet metal components are analyzed within finite element analysis (FEA) with regard to their feasibility in production and expected quality before production equipment, such as drawing dies, is manufactured. Main criteria for characterizing component quality are cracks and sidewall wrinkles. In particular, cracks occur due to local overload in sheet metal plane caused by inadequate process parameters such as too high friction or forming forces. In contrast, sidewall wrinkles are caused by an inadequate level of compressive stress in component areas without contact between sheet metal component and drawing die. In FEA, failure by cracks can be analyzed evaluating scalar values of thinning or strain distribution in forming limit diagram with regard to forming limit curve. In contrast, detecting sidewall wrinkles often requires a manual and visual inspection of simulation results by the user. Therefore, a procedure to detect sidewall wrinkles in an automated manner is presented in this paper. The presented method determines occurrence of sidewall wrinkles based on strain distribution in forming limit diagram. Utilization of the disclosed calculation strategy allows estimation of cracks and sidewall wrinkles simultaneously after one run of simulation code. The presented approach for automated detection of sidewall wrinkles in combination with multivariate statistics shows a tool for virtual engineering to optimize deep drawing processes. Prior to die manufacturing, optimization with regard to both sides of the process window is possible. Hence, an increase in design efficiency, design space and reduction of development time and costs can be achieved at the same time. [ABSTRACT FROM AUTHOR]

Titanium and its alloys are an important class of materials, especially for aerospace applications, due to their excellent combination of strength and fracture toughness as well as low density. However, these materials are generally regarded as difficult to machine because of their low thermal conductivity and high chemical reactivity with cutting tool materials. Moreover, the low thermal conductivity of Titanium inhibits dissipation of heat within the workpiece causing an higher temperature at the cutting edge and generating for higher cutting speed a rapid chipping at the cutting edge which leads to catastrophic failure. In addition, chip morphology significantly influences the thermo-mechanical behaviour at the workpiece/tool interface, which also affects the tool life. In this paper a finite element analysis of machining of TiAl6V4 is presented. In particular, cutting force, chip morphology and segmentation are taken into account due to their predominant roles to determine machinability and tool wear during the machining of these alloys. Results in terms of residual stresses are also presented. Moreover, the numerical results are compared with experimental ones. [ABSTRACT FROM AUTHOR]

In this paper, a finite element method based on nonhomogeneous elements is used to study crack problems in three-dimensional (3D) functionally graded materials (FGMs). Since the actual material properties at each integral point are employed in the integration during formation of the element stiffness matrix, each element can have nonhomogeneous material properties. By this method, the number of elements is reduced and the meshing effort for the structure is simplified. Therefore, the modeling process for numerical simulation of fracture behavior in 3D FGMs is greatly simplified. The crack front characteristics of Mode-I edge penetrable crack in 3D FGM specimens are studied under uniform tension loading. The influence of material nonhomogeneity constant and geometric parameters on the stress intensity factors (SIFs) of the 3D FGM specimens are investigated. [ABSTRACT FROM AUTHOR]

Probabilistic fracture analysis is performed for predicting uncertain fracture responses of Functionally Graded Material (FGM) structures. The uncertainties in material properties including Young's modulus and fracture toughness are considered. The limit state function for a crack initiation event is defined in terms of the J-integral for FGMs. The First-Order-Reliability-Method (FORM) is used in conjunction with a finite element code that computes the J-integral with high accuracy. A two-step probabilistic analysis procedure is proposed to investigate the effects of the uncertainties in the spatial distribution of Young's modulus on the probability of crack initiation in FGMs. First, we investigate the effects of the uncertainties in the shape of the spatial distribution by considering the slope and the location of the inflection point of a spatial distribution profile as random quantities. Second, we investigate the effects of the spatial fluctuations of Young's modulus by making use of a discretized random field. The companion paper (Part II) implements this method into a finite element fracture analysis code and presents numerical examples. [ABSTRACT FROM AUTHOR]

Apart from the calculation of the plastic formability of metals the prediction of ductile cracks in cold forming processes is very important in order to design these processes efficiently. Therefore, many crack criteria have been developed and implemented in several FEM Programs. These criteria scale the crack prediction down to one value and they are qualified to detect the most endangered areas occurring cracks during the forming process quite well. All these criteria have two significant disadvantages: on one hand none of these criteria consider the whole forming history and on the other hand the detected critical value is not applicable to other forming processes. Therefore a new method to predict ductile fracture in cold forming processes has been developed. Various upsetting, bending and extrusion tests were designed in order to provoke a failure during the forming process. All these processes were modelled by means of the Finite Element Method to acquire the whole forming history (including the first principle stress, the equivalent stress and the equivalent strain starting with the first deformation to the first crack occurrence) for the area where the first fracture occurs. Basal in the results way a database with forming histories which all will lead to an failure during a forming process was built up. This database is used to train an artificial neural network. The artificial neural network will be able to predict a failure for new forming histories. The paper gives an overview over the use of the artificial neural network, the calculation of the forming histories and the used forming processes as well as the interaction between the Finite Element Method and the artificial neural network. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The paper deals with the development of fracture models for polydisperse inhomogeneous media with random arrangement of inclusions. An extended finite element method (X-FEM) is used, according to which crack growth is described by special enriched functions in combination with additional degrees of freedom. Modeling of crack development is performed in the Abaqus software. The influence of stress concentrators in the form of peculiarities of a heterogeneous structure on the process of crack propagation is investigated, particular cases of representative volume elements are considered. [ABSTRACT FROM AUTHOR]

Linear elastic fracture mechanics (LEFM) concept is generally used to study the influence of crack on the performance of structures. In order to study the LEFM concept on damaged structure, the usage of finite element analysis software is implemented to do the simulation of the structure. Mesh generation is one of the most crucial procedures in finite element method. For the structure that crack or damaged, it is very important to determine the accurate local meshing size at the crack tip of the crack itself in order to get the accurate value of stress intensity factor, KI. Pre crack will be introduced to the lag screw based on the von mise's stress result that had been performed in previous research. This paper shows the influence of local mesh arrangement on numerical value of the stress intensity factor, KI obtained by the displacement method. This study aims to simulate the effect of local meshing which is the singularity region on stress intensity factor, KI to the critical point of failure in screw. Five different set of wedges meshing size are introduced during the simulation of finite element analysis. The number of wedges used to simulate this research is 8, 10, 14, 16 and 20. There are three set of numerical equations used to validate the results which are brown and srawley, gross and brown and Tada equation. The result obtained from the finite element software (ANSYS APDL) has a positive agreement with the numerical analysis which is Brown and Srawley compared to other numerical formula. Radius of first row size of 0.014 and singularity element with 14 numbers of wedges is proved to be the best local meshing for this study. [ABSTRACT FROM AUTHOR]

This paper outlines a framework for evaluating the asymptotic crack tip field solution incorporating Tz parameter in three-dimensional crack problems. Assessment was done based on the comparisons with analytical solutions and results from three-dimensional crack-tip finite element analysis. Fully plastic asymptotic crack tip stress field solutions were provided by carrying out detailed full field finite element analysis on single edge deeply cracked bar subjected to bending load based on a non-hardening material response. Two out-of-plane specimen thicknesses were considered for the bar to evaluate the effect of out-of-plane constraint on the distribution of crack tip stress field. The asymptotic solutions of thick bend bars were found to be contained within a Prandtl crack tip field at the center of the specimen. At the free surface of the specimen, a corner field develops, causing deviation of the J-Q-Tz solution from the three-dimensional surface crack-tip field. The results also showed that the three dimensional asymptotic crack tip solution, J-Q-Tz has limited capabilities in characterizing the crack tip fields for thin specimen. [ABSTRACT FROM AUTHOR]

In the present paper, Thomason's criterion is coupled with the well-known Gurson-Tvergaard-Needleman (GTN) damage model and used for the determination of the critical void volume fraction ƒc, which marks the initiation of the coalescence stage. The onset of void coalescence predicted by Thomason's criterion is compared to that obtained by using a predefined ƒc, which is usually fitted on the basis of experimental results, as originally proposed in the GTN model. Comparisons are made in terms of both single finite element simulations and numerical results of deep drawing of a cup. [ABSTRACT FROM AUTHOR]

Micro-forming refers to the application of conventional forming processes to manufacture products from ultra-thin sheet materials. While attempting to meet the increasing demand for cost-effective manufacturing of micro-formed components, it is very important to reduce the defects in the products. In this paper, we report a number of Finite Element (FE) simulations of the micro-deep drawing process with various sample thicknesses and eccentric distances. The simulations indicated that when the sample thickness is nearly equal to the gap between the plunger and the die, the sample is likely to develop fractures at the bottom corner. When the sample thickness is much smaller than the gap, wrinkling appears in the sample. If the sheet thickness is reduced, the wrinkles approach the bending zone. If the punch-die eccentricity is increased, the pressing process results in a defective product. The simulation results compared well with experimental results. This suggests that the computer simulations can be used to design future experiments. [ABSTRACT FROM AUTHOR]

In wire drawing of high strength steel wire for the application in tier cords, the inclusion plays the key role resulting in wire fractures. The effects of inclusion size, position and shape on wire drawing is investigated via finite element analysis in this paper. A 3D finite element model is developed to analyze the effect of inclusion position on the risk of fracture, and a 2D axisymmetrical finite element model for an inclusion at the wire center is established to investigate the effects of inclusion size and shape on wire fracture. A damage model with the consideration of stress status and plastic strain increment is used to characterize the risk of wire fracture. Finite element analysis results indicate that wire fracture is very critical to the inclusion located at wire core, and inclusion with an elliptical shape and its long axis lining well with the wire axis. Finite element analysis also proves that with the use of 7 degree die instead of 9 degree die is able to reduce the risk of fractures by about 28%. [ABSTRACT FROM AUTHOR]

The paper presents recent progress to model process compensated resonant testing (PCRT) for silicon nitride balls. An analytical model was developed that accurately describes the series of surface acoustic wave (SAW) and intermediate Whispering Gallery (WG) modes. A finite element method model of an elastic sphere was also developed to study the effect of surface flaws on the modal response. Using the numerical model, it was shown that the higher frequency SAW modes will degenerate in most cases as shifts lower in frequency with increasing crack dimensions. [ABSTRACT FROM AUTHOR]

The idea of this paper is to discuss some problems in coupling of analytical solutions and the finite element method for boundary value problems with a singularity. As an example we consider a problem from fracture mechanics in the plane. [ABSTRACT FROM AUTHOR]

In this paper the Scaled Boundary Finite Element Method (SBFEM) is applied for the simulation of Lamb waves in cracked plates. This method is highly advantageous to study the interaction of different Lamb wave modes with cracks as the crack is not discretized and no refinement is required around the crack tip. Numerical examples are presented for the reflection of the fundamental symmetric and antisymmetric modes from cracks of different depth. The spatial Fourier transformation is employed to calculate the amplitudes of reflected Lamb wave modes. The results reveal possibilities to obtain details of the crack geometry in non-destructive testing and structural health monitoring applications. [ABSTRACT FROM AUTHOR]

Taylor impact test presented in a previous study on a commercial high strength and super hard aluminum alloy 7A04-T6 are numerically evaluated using the finite element code ABAQUS/Explicit. In the present study, the influence of fracture criterion in numerical simulations of the deformation and fracture behavior of Taylor rod has been studied. Included in the paper are a modified version of Johnson-Cook, the Cockcroft-Latham(C-L), the constant fracture strain, the maximum shear stress and the maximum principle stress fracture models. Model constants for each criterion are calibrated from material tests. The modified version of Johnson-Cook fracture criterion with the stress triaxiality cut off idea is found to give good prediction of the Taylor impact fracture behavior. However, this study will also show that the C-L fracture criterion where only one simple material test is required for calibration is found to give reasonable predictions. Unfortunately, the other three criteria are not able to repeat the experimentally obtained fracture behavior. The study indicates that the stress triaxiality cut off idea is necessary to predict the Taylor impact fracture. [ABSTRACT FROM AUTHOR]

In the deep drawing process, determination of the drawing depth and prediction of the time and the place that fracture occurs has been one of the important case studies which engineers tend to take into account. Because of a drastic reduction in design and manufacturing expenditures, numerical methods are extended to calculate the drawing depth during the process. In this paper, ductile damage model in which the stress triaxiality and equivalent strain are the most effective parameters on the damage growth and fracture of the material is used to predict fracture. For prediction the place and time of ductile fracture, according to ductile damage criteria, the fracture strain for various stress triaxiality values should be determined. To obtain the parameters of ductile damage model for St12 steel, some tensile tests have been performed on the notched specimens. Numerical simulation of deep drawing was performed using commercial finite element ABAQUS. Results obtained from simulation are in good agreement with the experimental ones and emphasize that using ductile damage model is appropriate to anticipate the place and time of the fracture during the deep drawing process. [ABSTRACT FROM AUTHOR]

In the plastic deformation of damaged materials, the influence of distribution of voids on the mechanical properties is an important issue. Therefore, it is necessary to control the void growth. As various sizes of voids are actually distributed in a damaged material, we have to evaluate the local damage state. The influence of clustering of multi-size voids is also serious concern. In the present paper, aluminum sheets which contain multi-size holes have been treated as simple models of damaged materials. These models have two pairs of holes of two different sizes. The diameter of larger holes is described as da and the diameter of smaller ones is db. The angle θa is defined as the inclined angle of line segments on each center of larger holes against horizontal line. Similarly, the angle θb is the array angle for smaller ones. The angle θa and θb are chosen to cover 0° through 60°. The behavior of plastic deformation and the interference between holes in these models under the uniaxial tensile load have been evaluated by FEM analysis. When the ratio of hole diameters db/da is 0.5 and the array angle of larger holes θa is 0°, the stress in the close area of hole decreases as the angle θb increases. It is assumed that local plastic deformation is affected by the interference between a larger hole and a smaller hole. When the array angle θa is 0°, the stress in the close area of smaller holes is high regardless of the array angle θb. In the case of θa = θb = 30°, the interference with holes is strong. It is indicated that the relationship between the array angle of larger holes and the development of the shear band have an influence on the local plastic deformation. As these results, it is shown that the size of distributed holes, the array pattern of holes against the loading direction and the development of the share band are mutually related to the local plastic deformation. [ABSTRACT FROM AUTHOR]

Induction thermography is a non-contacting, non-destructive evaluation method with a wide range of applications. A deeper understanding of the detectability of cracks requires fundamental knowledge about the induced current density distribution in the component under test. A calculation of the current distribution provides information how much current is flowing at which location of the component, how a crack disturbs the current density, how much heat is produced at which location of the component, and how the heat diffuses to the surface. The heating process depends on the type of crack. On the one hand there are cracks which can be detected mainly by direct observation of the heating process due to an increased current density, and on the other hand there are cracks which can be detected mainly because of a modification of the heat diffusion. This paper presents an analytical model for the calculation of the current distribution, including the back-flow current along with finite-element calculations. Furthermore, two new crack models are presented for a better description of real cracks. [ABSTRACT FROM AUTHOR]

In previous conferences, we have described Sonic Infrared (IR) Imaging, and presented both experimental and theoretical work using induced chaotic sound within aircraft parts and structures. We have demonstrated that induced chaotic sound is much more effective in producing heat in defects than is single-frequency sound, thus resulting in stronger IR signals. Therefore, for the same defect, the probability of detection with chaotic sound is much higher than with non-chaotic sound. In this paper, we present a finite-element study of the vibration and heating in aluminum and titanium to investigate the effects of their different material properties. We allow both friction and plastic deformation as sources of heating in our models. [ABSTRACT FROM AUTHOR]

This paper presents a Cohesive Zone Model (CZM) approach for investigating dynamic crack propagation in homogeneous and Functionally Graded Materials (FGMs). The failure criterion is incorporated in the CZM using both a finite cohesive strength and work to fracture in the material description. A novel CZM for FGMs is explored and incorporated into a finite element framework. The material gradation is approximated at the element level using a graded element formulation. A numerical example is provided to demonstrate the efficacy of the CZM approach, in which the influence of the material gradation on the crack growth pattern is studied. [ABSTRACT FROM AUTHOR]

Sonic IR imaging, which combines infrared imaging and ultrasound excitation, as a relative new member of the NDE family, has been drawing wider and wider attention due to its fast, wide area inspection capability. In our previous presentations and publications, we have described the application of acoustic chaos to Sonic IR imaging and have provided experimental illustrations as well. In addition, we have described realistic finite-element models that simulate the heating of cracks in metals by both chaotic and non-chaotic sound. These models allow for both friction and plastic deformation as sources of heating. In this paper, we present our further study on the physical mechanisms that are responsible for the advantages of chaotic sound for Sonic IR crack detection. Using finite-element analysis, here we will present theoretical explanations, both for the origin of the chaos, and for the mechanisms responsible for the chaotic enhancement of crack detection. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this paper, the basic principle and application of extended finite element method (XFEM) are expounded based on the model of plate structure crack. Simulating crack location by level set method; the discontinuity of crack can be supplemented through introducing Heaviside functions and crack tip reinforcement function .On this basis, the damage model of edge crack and center crack under the same boundary condition are established. The displacements of each node in the two Situations are given and explained the application of damage model in two aspects. [ABSTRACT FROM AUTHOR]

Models which simulate the interaction of ultrasound with cracks can be used to optimize ultrasonic array inspections, but this approach can be time-consuming. To overcome this issue an efficient hybrid model is implemented which includes a finite element method that requires only a single layer of elements around the crack shape. Scattering Matrices are used to capture the scattering behavior of the individual cracks and a discussion on the angular degrees of freedom of elastodynamic scatterers is included. Real crack shapes are obtained from X-ray Computed Tomography images of cracked parts and these shapes are inputted into the hybrid model. The effect of using real crack shapes instead of straight notch shapes is demonstrated. An array optimization methodology which incorporates the hybrid model, an approximate single-scattering relative noise model and the real crack shapes is then described. [ABSTRACT FROM AUTHOR]

This paper presents an application of the peridynamic method to predict a viscoelastic behavior. The peridynamic theory is a nonlocal continuum theory that shows an inherent crack initiation and crack growth criterion when it is applied on elastic material. This method is developed in order to resolve the problem of conventional finite element method (FEM) which is unable to predict singularities such as crack and failure. In this work, peridynamic is specifically applied to viscoelastic material in order to enhance the method. It is shown in the result that peridynamic method is able to predict linear viscoelasticity with acceptable accuracy regarding to an experimental data. [ABSTRACT FROM AUTHOR]

Stress fracture is a type of biomechanical failure of bone caused by loads during intense physical training. This failure is very important for aged persons and athletics. Because of cell death, in some cases after emergency surgery the injured person may suffer from lifelong disability. In this research, a three-dimensional finite element model of human femur has been created and analyzed under single, expanded and partial expanded loads. Analysis has been performed using commercially available software. The material is assumed to have isotropic elastic characteristics. The results indicated that the maximum stress occurred at the inferior root of the femoral neck. The magnitude of the strain shows good agreement with the published experimental results. This verifies the finite element modeling and the simplified model used. [ABSTRACT FROM AUTHOR]

Edge cracking in advanced high strength steels (AHSS) is a significant failure mode in many sheet metal stamping processes. Edge pre-forming into a wave (or scallop) shape is a common technique used in conventional steels to gather material in high edge stretch regions in preparation for the subsequent edge stretch process. The pre-forms designed for mild steels do not always apply to AHSS because the properties of AHSS can differ greatly from those of conventional steels. This work has studied the effects of pre-forming on AHSS edge cracking. Experiments have been conducted to stretch pre-formed steel strips to failure. Strain distributions of pre-forms with various levels of stretch have been measured using digital image correlation (DIC) technology. Finite element analyses have been performed and compared with the experimental results. Different failure criteria have also been evaluated for use in this type of application. [ABSTRACT FROM AUTHOR]