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The paper is focused on investigation of an influence of William series expansion and the maximum tangential stress criterion. In the paper, is almoust mixed mode I/II crack growth path of an angled crack plate subjected to biaxial far field loading is investigated. It is shown, then account the higher order terms of the Williams series expansion a very good agreement is observed between the experimental and mixed mode fracture paths in the angled crack problem. [ABSTRACT FROM AUTHOR]

There are various models out there, both theoretical and experimental, which are used to predict the fatigue crack growth in metals. Machine learning based computational models have been recently developed to predict such crack growth rate in a more comprehensive manner. This paper presents a supervised machine learning model with a better accuracy than the existing machine learning models. The experimental data obtained from the fatigue test carried out on CT specimen of material SA516Gr70 is used to test and train the model. The machine learning model XGBoost, which is implemented in this paper, is not only more accurate but also less likely to over fit when exposed to unseen data. Three alternative algorithms are investigated and by the process of elimination, best one is chosen. The paper shows the results received from some of those models, which were important in order to select the best one. The metrics used to filter and tune the model's performance are R2 score and mean squared error. The procedure for finding the optimal model and its results have been discussed. [ABSTRACT FROM AUTHOR]

This paper presents investigated results from Finite Element (FE) linear static analyses of the solid riveted metallic lap joints with and without corrugated plate edges. The main objective is to study the impact of corrugated edge of single rowed riveted single shear metallic lap joint on edge failure occurrences such as edge wrinkling, edge shear out, and edge split. A solid riveted lap joint is simplest and mostly used permanent joint type in the aerospace industries. During any aircraft development, a detailed analysis of every design parameter of all the riveted joints is a significant part in reporting riveted joint strengths and weights. There are many studies reported on importance of design parameters of solid riveted metallic lap joints. However, the impact of edge margin's geometrical shape on the edge failure modes in the riveted metallic lap joints were very rarely carried out. Hence, the influence of edge margin's geometrical shape on stress distribution along the edge margin direction was not reported in the literature. As an initial part of this paper, the geometrical shape of the edge margins has been optimized to corrugated shapes in order to reduce the normal stresses along the edge margin directions. The next part of the study describes FE investigation of three varieties of solid riveted single shear metallic lap single rowed joints. Investigated samples are of 2024-T3 aluminum alloy, manufactured from a thickness of 2mm sheet and the solid rivet NAS1097AD6-7 made of 2117-T4 aluminum alloy. Metallic lap joints with one, two and four rivets in a single row cases are investigated. FE linear static analyses have been performed with edge margin of 1.5D and 2D on straight and corrugated shapes by keeping all other design parameters of the joint as constant. An average possible weight reduction per joint due to introduction of corrugated edge margins over straight edges has also been reported. Reduction in normal stresses along the corrugated edge margins compare to straight edge margins are presented as the main outcome of the study. [ABSTRACT FROM AUTHOR]

Many automobile components which are subjected to high stresses are manufactured by the forging process. Many trials are going on to improve the life of H13 die steel material. Main aim of the study is to evaluate the effect of stress distribution in forging dies and forging materials due to the application of different impact energies to reduce the chances of failure of the job materials. The main properties required for the forging material are high thermal resistance, high fracture toughness and high hot hardness. In this paper, the stress distribution and deformation is studied due to the application of varying impact energies with the Von mises stresses distribution in the job by using LS Dyna. It was evaluated that with the application of impact energies in the increasing order the deformation of job was increased along with the increase in Von mises stresses distribution across the section and which suggest the safe value range which the job and die can bear without failing. [ABSTRACT FROM AUTHOR]

Current transport infrastructure in Europe depends on numerous steel and concrete-steel bridges, often from high-strength steel. One of the main engineering challenges related to such bridges is to ensure their reliability during their whole lifespan. It is not easy as load by automotive or rail transport typically induces fatigue effects, especially on steel parts. It is usually necessary to execute periodic inspections which should make possible timely detection of issues (cracks) which would make effective repairs possible. Thus, it is important to be able to plan these inspections in right times and to inspect the critical details with focusing on their fatigue damage. The paper discusses some challenges related to this approach. The Direct Optimized Probabilistic Computation method (DOProC) is combined with linear fracture mechanics analytical solution to find the time of the first inspection. Then it is assumed that modified solution can be used to find times of further inspections. In the paper there are discussed issues related to the speed of the DOProC in such application and the approaches to limit the computational time without a loss of precision. [ABSTRACT FROM AUTHOR]

This paper evaluates the behavior of non-structural masonry built with horizontal hollow clay bricks. The aims of the study are to reduce the structural vulnerability of houses built with this type of bricks in seismic zones of Latin America, especially Colombia and Ecuador. The tested specimens were 50 centimeters wide, approximately 10 centimeters thick and 1 meter high. The retrofitting methods consisted of two types of reinforcement: the first one with a 3:1 sand:cement ratio. (S:C) mortar overlay with 2.5 centimeters thick for overlay the welded wire mesh (WWM) (ϕ4mm/15cm) adhered to the masonry with plastic anchors on each face of the wall. The second one with the use of mortar overlay reinforced with steel fibers (SF20) using a dosage of 20 kg/m3, with an average thickness of 2.5 centimeters and a 3:1 S:C ratio. The experimental program included the testing of 13 axial compression specimens, 4 prisms for compression with WWM reinforcement, 4 prisms for compression with SF20 reinforcement, 4 with plain mortar overlay and 1 control masonry without any type of reinforcement, only with hollow bricks. Each type of reinforcement was assessed using a monotonic quasi-static axial compression test and 3 quasi-static cyclic tests. The results showed that SF20 reinforcement increases the compressive strength, controls crack growth, but the failure mode is fragile. On the other hand, the WWM reinforcement shows a lower compressive strength, but a less fragile failure mode since the more cracks are visualized and their size increases as the load increases in the test. This is also evident in the load-deformation curves. The WWM reinforcement does contribute to life safety, by holding the collapsed clay block fragments between the mortar diaphragms. In addition, it was observed in the experimental tests that the resistance can be increased by ensuring a continuous anchorage that holds the WWM on both faces of the horizontally drilled bricks. Finally, as a conclusion, the increase of resistance by SF20 reinforcement generates stiffer prisms for compression, but it would not guarantee life protection in case of cracking or collapse of masonry walls; on the other hand, WWM does allow greater deformations, despite not having a similar resistance as the walls reinforced by SF20. [ABSTRACT FROM AUTHOR]

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 development of fundamental ideas about the inelastic deformation and fracture of materials is of great practical importance. This is substantiated by the need for a macroscopic theory suitable for solving engineering problems and taking into account real physical processes occurring in a deformed material. Such a theory can be efficiently used in problems of computer-aided design of materials with required mechanical properties. This paper is devoted to the formulation of the principles of the macroscopic theory of inelastic deformation, which couples the mechanical and physical aspects. The theory combines two macroscopic theories: the classical theory of elasticity and the continuum theory of translational defects. The proposed theory uses the Lagrangian formalism in combination with the gauge field method. The latter allows introducing defects of the translational type. The application of the principle of least action to the Lagrangian with gauge fields made it possible to obtain the equations of motion for both elastic displacements and defects. The adequacy of the proposed theory is confirmed by several classical examples. [ABSTRACT FROM AUTHOR]

The paper is focused on the crack growth in the manganese cast steel under static and dynamic loading. Crack extension is simulated by means of element extinction algorithms. Determination of micro-mechanical parameters is based on the combination of static tests, microscopic observation and numerical calibration procedures. The attention is paid on the influence of initial value of J-integral and the slope of R curve which is modelled by 3D FEM. Standard CT and SENB bodies were used for static tests and for dynamic tests Charpy body with V-notch. The commercial Abaqus software system, its explicit and implicit variant with a programmed user procedure, was verified by the WARP3D system. [ABSTRACT FROM AUTHOR]

The general formula proposed by Landes and Begeley [1], which has been modified for years, among which more or less complicated approaches can be distinguished for determining the J-integral in laboratory conditions. One of them is the ASTM standard [2], according to which the energy required to calculate the J-integral should be decomposed into elastic and plastic parts, and thus the factor η depending on the shape of the specimen used in laboratory tests. Some approaches, e.g. the Polish standard [3], indicate that the J-integral should be calculated without decomposing into elastic and plastic parts. The normative documents mentioned do not usually mention the dependence of the η factor on the geometrical dimensions of the specimen (except for the shape of the specimen) or the dependence on the material characteristics. As shown in [4-7], the value of the coefficient η depends on the crack length and the material characteristics, however, the influence of material constants is usually discussed in a strictly defined range. It should be noted that papers [4-7] are based on the decomposition of the coefficient η value into elastic and plastic parts. The hybrid method presented in [8] for assessing selected parameters of fracture mechanics, referring to EPRI procedures [9], allows to evaluate them without the need for tedious numerical calculations, however, unlike EPRI procedures, it does not introduce the need to decompose these parameters into elastic and plastic components. In view of this fact, in this study it was decided to assess on the basis of numerical calculations carried out for the dominance of plane strain, the effect of crack length and material constants (expressed in yield strength and strain hardening exponent in R-O law) on the value of the coefficient η which is required to estimate the value of the J-integral in accordance with by Landes and Begeley [1]. The discussion presented in [10] was the inspiration to undertake this topic. In this paper, based on a comprehensive numerical analysis of SEN(B) specimens dominated by a plane strain state, for four different crack lengths and sixteen hypothetical elastic-plastic materials (characterized by different yield strength and different level of stain hardening exponent), the values of the J-integral were estimated, the impact of the crack length and material constants on the value of J-integral was assessed, an analysis of the P=f(u) curves and discussion on the effect of crack length and material constants on the value of the factor η were presented. Using the approach given in [4-7], simplification was made in the analysis and the value of the coefficient η was determined for each analysed specimen. The analysis showed a strong dependence of the coefficient η on the crack length and the strain hardening exponent n. It turned out that the coefficient η does not depend on the yield strength of the specimen material. The results were summarized in tabular form and approximated using the Table Curve 3D program. The measurable effect of the paper is a summary of numerical results – values of the coefficient η for 64 SEN(B) specimens and a new form of the function η=f(a/W, n) which was proposed, and which allowing to take into account in the process of determining the J-integral by the factor η the geometry of the specimen (relative crack length a/W) and material characteristics (n – strain hardening exponent in R-O law). [ABSTRACT FROM AUTHOR]

This paper studies the effect of ZnO filler content on the mechanical properties of PLA/ZnO. Fused Deposition Modelling (FDM) was used to print the samples. Polylactic Acid (PLA) was used in this project and the ZnO powder was added during the printing process. The speed of the dispenser (low speed=1000 RPM, medium speed = 1400 RPM and high speed=1800 RPM) is the parameter that was varied to control the filler content of the composite. All the samples underwent a tensile test to determine the mechanical properties and followed by the SEM test to analyse the surface changes and fracture mechanics of the tensile test. Tensile test results reveal that as the dispenser's speed is increased from 1400 RPM to 1800 RPM, the tensile strength decreases from 23.664 MPa to 22.046 MPa. However, pure PLA has the lowest tensile strength at 21.963MPa. This tensile strength corresponds to the percentage of break elongation, with samples at the low dispenser speed of 1000 RPM having the greatest percentage of elongation with 4.04% due to the high tensile strength. SEM analysis reveals that pure PLA has a smooth and flat appearance morphology, whereas the PLA/ZnO composite has a rougher surface and many voids. [ABSTRACT FROM AUTHOR]

In recent years, the use of new advanced materials plays an ever-more significant role in modern structures and machine components. In comparison with conventional metallurgy procedures, sintering, also known as powder metallurgy, presents significant advantages. However, the porosity of the sintered materials causes stress concentration, strain localization and damage accumulation in a material microstructure, which can lead to the material failure. Therefore, fracture modelling on the material microscale level is necessary for the reliable behaviour assessment and life-time determination of sintered materials on the macroscale. During recent years, the phase-field (P-F) method has gained huge popularity within the computational fracture mechanics field. It is a diffusive method that regularizes the sharp crack discontinuity within a volume, which is often controlled by some length-scale parameter. In the present paper, a 2D P-F formulation is used for modelling microcrack propagation in heterogeneous and homogeneous materials. Different porous models are extracted from metallographic images. The heterogeneous materials consist of two constituents: ferrite and bainite. Elasto-plastic material properties of ferrite and bainite are obtained by the sharp instrumented indentation. The numerical results are compared with metallographic images after uniaxial test to observe intra-or transgranular crack formation. [ABSTRACT FROM AUTHOR]

Engineering materials fail below their yield strength due to the application of loads resulting in fracture. These fractures of materials are observed due to the grain structure or micro voids or discontinuities in grain structure. In order to improve the mechanical properties and modify the grain structure, investigations have been followed with different material processing operations. In this paper AISI EN 19 tool steel mechanical properties were studied. To enhance the properties of tool steel, the material have been austenized for a period of time and quenched in water. Few of the specimens have been treated with cryogenic treatment for duration of hours and later tempered. The effect of this process has made a change in the tool steel microstructure specimens and has improved their strengths. [ABSTRACT FROM AUTHOR]

The paper deals with time dependent probability analysis of the failure of a steel bridge. The theoretical model of fatigue crack propagation is based on linear fracture mechanics. The statistical Monte Carlo method is applied to the analysis of failure probability. The results of probability analysis are elaborated applying the calibration curves processed, based on experimental research. Some aspects of the random sampling methods are discussed. [ABSTRACT FROM AUTHOR]

The present paper discusses the experimental results obtained testing some curved specimens strengthened using Fiber Reinforced Polymer (FRP) composite materials. The experimental investigation has been aimed at characterizing the influence of normal stresses induced by curved supports on the stress-transfer mechanism of FRP composites. To this scope some single lap shear tests performed at the University of Florence on FRP strengthened curved prisms with two different curvature radii (1500 and 3000 mm) have been analyzed. The numerical model, implemented in the FE code Abaqus, is a sophisticated micro-modeling (heterogeneous) approach, where bricks and mortar are simulated separately with 4-noded plane strain elements with damage in tension and compression, FRP is assumed elastic and an elastic uncoupled cohesive layer is placed between FRP reinforcement and the masonry support. Numerical results obtained are in satisfactory agreement with the experimental ones in terms of peak loads, collapse mechanisms and damage patterns at collapse. A detailed investigation of the effect of FRP-masonry normal stresses is also present in the proposed paper. [ABSTRACT FROM AUTHOR]

The paper presents a first attempt to calculate fatigue life for random loading with single overloads with the use of the spectral method of fatigue life assessment. The proposed modification of the fatigue life assessment algorithm is based on the transformation of the power spectral density of the loading signal with the use of the correction factor using the information obtained from the spectral kurtosis. The procedure is explained and verified on the basis of comparison of calculation results with the results obtained with the rainflow cycle counting method. The same damage degree hypothesis is used in both cases, it is the well-known linear Palmgren-Miner model. The obtained results confirm that there is a need to perform a correction in terms of the influence of the overloading amplitudes in the spectral method of fatigue life assessment. [ABSTRACT FROM AUTHOR]

Among Non-Destructive Diagnostic Techniques (NDTs), Acoustic Emission (AE) is particularly useful to evaluate and/or monitor the material properties of structures and their degradation over time. For instance, this method permits identify early micro-fractures by depicting the release of mechanical energy of an elastic wave radially propagating through the material from the fracture zone, obtaining the possibility to localize the damage of the investigated specimen. Despite the large number of localization strategies that have been examined in the literature, there are nowadays no specific and standard guidelines. Within this framework, in this paper, the results of an AE experimental test performed on a prestressed reinforced concrete joist subjected to a four-point bending load are presented. The data collected during the test will be analysed focusing in particular on the hits cumulative curves and hits energies for each channel, showing how the overall behaviour of these parameters provides interesting insights into the specimen response. Finally the linear localization of the events produced during the test will be reported and correlated with the theoretical expectations, in terms of tensile and shear cracks. The results will confirm the expectations, reporting the main events in the central region of the specimen, that experiences the maximum constant bending momentum. All the findings of this test will show a setup for the early detection of micro-fractures in prestressed reinforced concrete elements, providing an interesting base for the extension of the technique to buildings and general structures. [ABSTRACT FROM AUTHOR]

The paper presents the results of a factual study of the fracture surface of a high-pressure turbine rotor blade with a fatigue crack. The study of the fracture relief showed that on the fracture surface of the blade near the trailing edge there is a zone of brittle transcrystalline and intergranular fracture, surrounded by an intragranular fracture with a developed microrelief. Further crack growth in the direction of the leading edge was carried out by a fatigue mechanism. As a result, it was found that the main cause of blade failure is the formation and development of a fatigue crack in the direction from the trailing edge of the airfoil to the leading edge. [ABSTRACT FROM AUTHOR]

Nondestructive Evaluation (NDE) and Structural Health Monitoring (SHM) simulation tools capable of modeling three-dimensional (3D) realistic energy-damage interactions are needed for aerospace composites. Current practice in NDE/SHM simulation for composites commonly involves over-simplification of the material parameters and/or a simplified two-dimensional (2D) approach. The unique damage types that occur in composite materials (delamination, microcracking, etc) develop as complex 3D geometry features. This paper discusses the application of 3D custom ultrasonic simulation tools to study wave interaction with multilayer delamination damage in carbon-fiber reinforced polymer (CFRP) composites. In particular, simulation based studies of ultrasonic guided wave energy trapping due to multilayer delamination damage were performed. The simulation results show changes in energy trapping at the composite surface as additional delaminations are added through the composite thickness. The results demonstrate a potential approach for identifying the presence of hidden multilayer delamination damage in applications where only single-sided access to a component is available. The paper also describes recent advancements in optimizing the custom ultrasonic simulation code for increases in computation speed. [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]

Residual fatigue lifetime assessment of a cracked structure is a common task for engineering and scientific community. Fatigue crack may appear on the surface or in the initial defect, e.g. pores in weldments. Such a structure needs to be examined, whether is it safe to be operated. Various assessment methods of different difficulties exist. In this paper, numerical and experimental study on fatigue crack propagation is presented. Propagation of a fatigue crack starting from an initial surface defect of semi-elliptical shape through the flat specimen is considered. Two load ratios were employed in order to compare their effects, as loading at low asymmetry R = 0.1 ensures presence of a plasticity induced crack closure, while at load ratio R = 0.6 fatigue crack growth without premature closure is expected. Beach marks were created on the fracture surface in order to study the fatigue crack evolution, number of cycles spent for fatigue growth and also the influence of premature closure on the crack front evolution. One of the well-known methods was applied for numerical fatigue lifetime evaluation and estimated number of cycles required for crack growth through the body was compared to the experimentally measured data. Second part of the paper deals with fatigue crack front curvature, which is always affected at the vicinity of the free surface due to the corner singularity of the stress field. However, when crack closure appears, fatigue crack propagation is retarded and furthermore, crack front is curved even more at the free surface as a result of earlier closure than in the middle of the body. Separation of these two effects allows direct comparison of their impact on fatigue crack front propagation. [ABSTRACT FROM AUTHOR]

The paper presents the results of fatigue crack growth simulation of the transition joint for S235JR steel and A5083 aluminum with the Grade 1 titanium interlayer coat and A1050 aluminum. Calculations were performed using ANSYS software. The publication presents the crack growth phenomena observed during fatigue testing. Additionally, calculations of residual stresses distributions induced by the process of joining materials during welding were carried out. Results of crack length calculations were comparable with experimantal data. [ABSTRACT FROM AUTHOR]

In the paper, we theoretically studied the dynamics of mode II crack propagation in brittle solids with taking into account the finite duration of incubation of local fracture. The study was carried out by computer simulation using the movable cellular automaton method. We analyzed the influence of the magnitude of fracture incubation time on the fulfillment of the scale-invariance condition of dynamic crack propagation. We proposed a definition of this condition in terms of fracture incubation time and introduced a new physically based criterion to classify structural levels of fracture in brittle materials. [ABSTRACT FROM AUTHOR]

The fracture toughness of materials is a fundamental parameter in assessing the structural integrity of crack-containing structures. Issues relating to economic demands in the availability of materials for testing and imposing strict rules to structures that exhibit enhanced toughness due to geometries and loading conditions caused the need to consider the application of fracture toughness measurement with small-scale specimens. The current small-scale testing and fracture toughness characterization still need to fully fulfil the fracture toughness data transferability from the laboratory test specimens to real structures influenced by unavoidable defects. This paper outlines the conventional elastoplastic fracture toughness approaches and how they apply to small-scale specimen fracture toughness testing. Recent techniques to characterize three-dimensional elastoplastic stress-strain fields around the crack tip were highlighted, as an extension to the current two-parameter fracture toughness assessment was proposed. Explicit expressions were given to develop an analytical formulation for small-scale fracture toughness measurement and characterization. [ABSTRACT FROM AUTHOR]

The article deals with development of a new generation of a URM [Universal Rotation Module]. Current generation showed us deficiency in the design, which needed to be resolved in new generation. Overall, the current assembly is requiring many parts, which is increasing difficulty on a supply chain as well as increasing time for the overall assembly and disassembly. This is especially important, when the current generation is still in prototype phase, and often reassembly and testing is required. In this paper we are going to reduce the number of parts necessary to build new generation, as well as describe design changes for the new generation of the URM. For that we are going to use simulation as well as manufacturing some parts with FDM techniques. For simulation we will be looking at points with highest stress, overall factor of safety to look for material failure and deviation under load to achieve higher accuracy of positioning. [ABSTRACT FROM AUTHOR]

The paper presents the results of studying the characteristics of fracture resistance of promising 26KhMFA pipe steel in the range of climatic operating temperatures. It was found that the steel under the study has high indicators of both mechanical strength and resistance to fatigue crack propagation in the temperature range from +20 to −70°C. Studies of the phenomena accompanying the crack growth on the lateral surface of CT-specimens have been carried out. It is shown that with a drop in the test temperature, the area of the localized plastic deformation zone at the fatigue crack tip decreases with a simultaneous microhardness increase within this zone. [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]

The paper deals with development, verification and application in simulations of an efficient non-hypersingular traction boundary integral equation method (BIEM) for solution of boundary-value problem (BVP) describing time-harmonic SH-wave scattering by two impermeable nanocracks in an exponentially graded anisotropic piezoelectric plane. The modeling approach is based on the surface elasticity continuum model proposed by Gurtin and Murdoch and linear fracture mechanics. The sensitivity of the stress and electric concentration factors to the electromechanical coupling, to the characteristics of the incident wave, to the position-dependent material properties, to the surface elasticity and to the dynamic cracks interactions is presented and discussed. [ABSTRACT FROM AUTHOR]

This paper deals with the problem of calculation of Stress Intensity Factor in two ways: theoretically and numerically with two methods: Virtual Crack Closure Technique and J – Integral method. Three types of geometries were considered: plates with central/boundary crack and notch bending specimen. Numerical simulations covered a mesh sensitivity study for three mesh sizes and linear/nonlinear material model. Good correlation between exact solution and numerical tests was achieved. [ABSTRACT FROM AUTHOR]

The paper deals with the investigation of plastic deformation localization in mechanical tension tests of low carbon samples in the initial state and after 25 years of operation in thermal and power equipment. It was established in the tests long before the global loss of stability that stable localized deformation zones are formed in the area of further fracture. In the material after operation, these zones are seen earlier than in the initial steel. A parameter defining the degree of homogeneous material without localized deformations is proposed; this parameter can be used to predict the condition of long-term operated thermal and power equipment. [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]

In this paper, the seismic vulnerability assessment of the ruins of the ancient church of St Francis of Assisi in Amantea, in the province of Cosenza, is investigated. The survey campaign highlighted the geometrical and mechanical characteristics of the 13th century church necessary for the suitable structural analysis. The result of this first processing was the creation of a simplified geometric model used for the definition of the numerical model with the FE code Abaqus CAE. The most widely used damage models in the literature have been implemented in the code to take into account the mechanical behavior of the constituent masonry. In particular, the aim of this work is to highlight two aspects about the seismic-resistant behavior of the building: the trigger of local failure mechanisms and the efficiency of the strengthening already carried out in the past. [ABSTRACT FROM AUTHOR]

The connection pipes of technological apparatuses are an integral constructural element, as they serve for the input, output of raw materials and products through the pipelines connected to them. In the process of repair and operation, the formation of extended linear, most dangerous, defects are possible on the surface of the nozzles. Technical standards have established norms for the size of such defects, according to which the defect is considered acceptable or unacceptable, depending on the operating conditions of the device. In case of exceeding the permissible dimensions of the detected defect, the device is subject to decommissioning and repair. In exceptional cases, temporary operation with defects exceeding the permissible norms is allowed when calculating and justifying from the point of view of fracture mechanics by a specialized scientific and technical organization specializing in such calculations. Linear defects are the most unfavourable from the point of stress concentration and can be places of premature failure under certain conditions. The presence of such defects on the branch pipes of the fittings, especially on their inner side under the influence of aggressive working media, can accelerate the transition of the apparatus to the limiting state. Also, the form of a linear defect and its location on the surface of the branch pipe can have a significant impact on the resource and safe operation of the apparatus. At present, research on numerical modelling and assessment of the stress-deformed state of objects and elements under various conditions is relevant and effective. This paper investigates the relationship between the shape and location of a longitudinal extended linear defect on the inner. [ABSTRACT FROM AUTHOR]

Alternative current field measurement (ACFM) and eddy current thermography are both induced by eddy currents, and it is a commonality between them. The commonality has laid a good foundation for the combination of the two testing techniques. In this paper, a numerical study on distribution law of magnetic field and temperature field around the crack using eddy current excitation is carried out. The feasibility of the combination of ACFM and eddy current thermography is discussed as well. A specimen made of ferromagnetic material is tested by a U-shaped inducer, and a semielliptical crack is built on the specimen. The distribution law of magnetic field and temperature field is both studied using the same eddy current excitation. The relationship between the crack size and distribution of magnetic field and temperature field is identified by altering the length and depth of the crack. Through comparisons, the magnetic distribution law around the crack in this paper is consistent with that of ACFM, and the maximum temperature difference around the crack meets the inspection requirement of a thermal imager. These findings might make it possible to eventually combine ACFM and eddy current thermography. [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]

The results of 2D and 3D modelling of damage accumulation in rock mass elements are represented in the paper. The estimations of the initial (general) and set steps of roof caving are obtained for the lava conditions of Alardinskaya mine, OAS "YuzhKuzbassUgol". The results of modelling give a good agreement with empirical estimations of roof caving steps for the flat-dipping coal seams. [ABSTRACT FROM AUTHOR]

The Total Focusing Method is an ultrasonic array post-processing technique which synthetically focuses at every pixel in an image space in both transmission and reception. The Half-Skip Total Focusing Method is a modification to the method in which either the transmitting or receiving ray path contains one reflection from the back surface of the component being inspected. When an array is placed on a parallel-sided component on the opposite side to that from which surface-breaking cracks initiate, the Half-Skip method enables specular reflections to be captured from the faces of the crack. In this paper, the Half-Skip method is applied to experimental array data from notches in a titanium component of 6 mm thickness and from fatigue cracks in a titanium component of 3 mm thickness. An ultrasonic array with a center frequency of 18 MHz is used. The HSTFM is found to be advantageous over the TFM for measuring the depth of the smaller notches and cracks, and vice-versa. The HSTFM is also successfully applied to simulated array data from a real stress corrosion crack shape. [ABSTRACT FROM AUTHOR]

In the paper, experimental results of fatigue crack growth were presented. The main object of authors' investigation was a fatigue crack path determined under mixed mode (I+II) loading condition. For this purpose the CTS (compact tension shear) specimens were used. The tests were performed under the load ratio R = 0.1 and constant amplitude loading for a different mixity level. An experimental results were described using ΔK stress intensity factor range. In the paper, the experimental procedure was described and the kinetic fatigue fracture diagrams were constructed. After the fatigue tests the fractal dimension for the fracture surface was determined. According to the obtained results, the fractal dimension is not sensitive for different mixity level of loading (I+II) for structural steel S355J0. [ABSTRACT FROM AUTHOR]

Penetration of sand has been analyzed in a Poncelet framework. Published data from several sources have been analyzed. Threshold velocities associated with grain fracture and transition from friction-dominated resistance to inertiadominated resistance have been identified. Values for Poncelet drag and threshold velocities are found to be consistent for all of the papers on dry sand that were examined. [ABSTRACT FROM AUTHOR]

This paper focuses on developement of multi-scale micromechanical damage model for the prediction of compressive strength of cement pastes. The main purpose is to identify and quantify phenomena causing drop of strength between the nanoscale and the micro-scale. The model upscales material strength, Young modulus and fracture energy considering the volume fractions of individual chemical phases at each scale; starting with C-S-H globules at the nano-scale, going up to cement paste at the micro-scale. [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]