Fracture Of Materials Research Articles

Enhancing Reliability and Safety in Industrial Applications: Assessing the Applicability of Energy b-Value to Composites.

This study investigates the fracture behavior of glass fiber-reinforced plastic (GFRP) under various loading conditions using acoustic emission (AE) testing. Using fracture tests and time series analysis of AE signals, parameters such as b-value, improved b-value (Ib-value), and energy b-value (be-value) were examined to understand crack initiation, growth, and structural failure. The stress-strain curve revealed distinct responses during tensile and step loading, and time series analysis highlighted variations in amplitude, AE energy, and Kaiser and Felicity effects. Under tensile loading, the Ib-value exhibited a linear decrease, while step loading introduced complexities, including the Felicity effect. The be-value, incorporating energy considerations, fluctuated, providing insights into micro-cracks and macro-cracks. Statistical analysis demonstrated a consistent decrease in the be-value, emphasizing its potential for long-term monitoring. This study provides a comprehensive technique for assessing composite material fracture behavior, enhancing understanding for critical applications in hydrogen storage vessels and pressure pipes as well as advancing reliability and safety in industrial sectors.

Plasticity and ductile fracture of high-strength bolt materials under monotonic tension

The plasticity and fracture properties of high-strength bolts are crucial to the mechanical behaviours of bolted connections subjected to extreme loadings. However, the material properties of high-strength bolts have not been comprehensively studied. This paper presents a collaborative experimental and numerical investigation to characterise the material plasticity and fracture properties of normal high-strength bolts (NBs) and weathering high-strength bolts (WBs) under monotonic tension. Eighteen cylindrical tensile coupons, cut from M20, M24 and M30 grade 10.9 NBs and WBs, are tested to capture the full-range engineering stress-strain relationships. The combined Swift-Voce weighting model is modified to describe and calibrate the material true stress-strain relationship of NBs and WBs. Then, a void-growth model (VGM) incorporated with the calibrated true stress-strain relationship is used to simulate the ductile fracture of tensile coupons. The calibration process collaborating experimental results and finite element (FE) simulations to obtain material parameters of high-strength bolts is demonstrated in detail. This collaborating method is further employed to simulate the plasticity and fracture properties of normal bolts with various grades under tension, as well as grade 10.9 high-strength bolts subjected to monotonic tension at elevated temperatures in literature. FE simulation results show a high accuracy with experimental results across all specimens, proving the rationality of the proposed method for material plasticity and fracture properties of high-strength bolts.

Fracture Prediction of Hydrogel Using Machine Learning and Inhomogeneous Multiscale Network

AbstractHydrogels are soft polymeric materials with promising applications in biomedical fields. Understanding their fracture behavior is crucial for optimizing device design and performance. However, predicting hydrogel fracture is challenging due to the complex interplay between material properties and environmental factors. In this study, a machine learning (ML) approach to predict hydrogel fracture behavior is presented. A multiscale hydrogel fracture model is developed to generate simulation data, which is used to train a predictive neural network model. The ML model utilizes a hierarchical architecture of convolution long short‐term memory units to capture spatial and temporal dependencies in the data. Model predictions are found to closely match simulation results with high accuracy, demonstrating the ability to learn complex fracture processes. Comparison of crack lengths shows the model can generalize across different material parameters. This work highlights the potential of ML for advancing the understanding of hydrogel fracture and soft matter failure. The presented approach provides an efficient framework for predicting fracture in complex materials and systems.

Determination of Material and Fracture Properties of a Case-Hardened Planet Gear and Its Homogenisation Method to Obtain the Damage Mechanism Caused by Fragment Ingestion.

Before a new type of engine is introduced into civil aviation, it must comply with various safety regulations. These regulations include the analysis of secondary damage caused by the re-ingestion of a tooth fragment. The purpose is to prevent crack propagation through the gear rim, which would lead to catastrophic failure. In this context, identification of the initial crack location is crucial to determine the crack propagation path. Therefore, this paper presents a technique to determine and validate a constitutive material model and fracture locus for case-hardened spur gears. As the modelling of the surface-hardened layer is computationally intensive, it is necessary to homogenise the model. This paper comprehensively reviews and discusses the associated effects and errors. To determine the plastic behaviour of the case-hardened external gear (30CrNiMo8) and the nitrided internal gear (35CrAlNi7-10), the widely acknowledged Johnson-Cook material model is implemented using compression and Vickers indenter tests to define the necessary parameters. The fracture locus implementation is also based on the Johnson-Cook method and an axial shift of the fracture locus based on the hardness profile of the spur gears is determined by quasi-static pulsator tests. For validation, a project-specific gearbox test rig is used, enabling consistent ingestion of defined fragments. In addition, to check the likelihood of a tooth flank crack and to validate the results, a simplified ingestion experiment is performed.

Calculation of force parameters of workpiece machining process with end mill cutters

The aim is to develop and validate an operational methodology for calculating the force parameters and characteristics of the tool and the process of milling structural materials with end milling cutters. The structural schemes of machining and force models of oblique cutting processes in the modes of axial tool feed and continuous plastic deformation of the processed material were used when developing the method of preliminary calculation of the total axial force working on the cutting edge of end milling cutters. The rotating tool tests were conducted on a Hermle UWF 1202 H 3-axis machining center supplemented with a Kistler piezoelectric dynamometer (model 9272). Authors suggested, developed and tested the preliminary calculation method applied to the force characteristics of the machining process of workpieces by end milling cutters, considering how the energy power of ductile fracture of the machined material affects the process. Contact friction arising on the front and rear surfaces of the cutting tool does not reach the limiting value being subject to the Coulomb – Amonton law, that is, it is estimated by the dependence directly proportional to the normal pressure. After calculations, we defined the materials of the workpiece for milling, that is 45 steel (AISI 1045), and the end two-tooth cutter, uncoated T14K8 alloy, which was used to produce samples. The following milling modes were established: 4 mm boring depth; 50, 100 and 150 m/min cutting speeds; 0.05 and 0.1 mm/rev cutting tool feed. Deviation of the measured values of axial cutting force from the calculated values in the range of changing values of tool feed rate was found to be no more than 11%, and in the range of changing values of cutting speed no more than 15%. The developed calculation and analytical methodology for estimating force parameters of the machining process by end milling cutters provides an increase in the efficiency and reliability of the preliminary prognostic calculation of operating parameters and characteristics of cutting elements of end milling cutters.

A phase-field fatigue fracture model considering the thickness effect

Modern aero-engine turbine structures often have variable-thickness geometries (e.g., turbine structures with complex cooling systems) that pose a significant challenge to crack analysis. The phase-field fracture method is a numerical method that has recently received considerable attention. However, phase-field fatigue fracture models that consider the effect of thickness are still lacking. To address this problem, this paper proposes a modification of the fracture toughness in the phase-field fatigue model by introducing a relationship function between material fracture toughness and thickness (Gc-B curve). We use reference experimental data to fit the Gc-B curve of GH4169 and predict the fracture toughness of specimens with other thicknesses. The predictions of the proposed model agree well with the experimental results reported in the literature. This achievement contributes significantly to the structural safety design and life prediction of aero-engine components.

Application of a Closed-Form Model in Analyzing the Fracture of Quasi-Brittle Materials.

Fracture failure in quasi-brittle materials poses a persistent challenge in materials science and engineering. This study presents a thorough investigation of the Boundary Effect Model (BEM), offering a nuanced understanding of the size effect on fracture properties. The conceptual framework, evolutionary process, and applicability scope of BEM are elucidated, highlighting its accuracy and reliability in calculating fracture properties across various quasi-brittle materials. Through the integration of BEM with diverse fracture tests-such as three-point bending, four-point bending, and wedge-splitting-a linear correlation between maximum failure loads and material fracture properties is established. Notably, the study demonstrates that fracture properties, determined by BEM, can be regarded as consistent material constants across specimens of varying sizes, initial notch lengths, geometries, and microstructures. Validation of the BEM's reliability encompasses the analysis of 140 fracture test results involving concrete, hard rocks, and bamboo scrimber. The synergy of non-linear and linear BEM analyses emerges as a robust approach for accurately predicting the fracture behavior of quasi-brittle materials. This comprehensive exploration sheds light on the potential of the Boundary Effect Model as a valuable tool for predicting and understanding fracture mechanics in diverse materials and scenarios. This research serves as an effective approach to accurately evaluating the fracture properties of quasi-brittle materials, which is of great practical significance for material design, engineering construction, and various industrial applications.

Machine learning coupled with acoustic emission signal features for tool wear estimation during ultrasonic machining of Inconel 718

The material removal in the ultrasonic machining process is due to the fracture of the workpiece material. The fracture is due to energy transfer by vibrating abrasive particles. The vibration energy is induced by a tool oscillating at a frequency of more than 20 kHz. The vibrating particles not only impact the workpiece surface but also impact the oscillating tool, and it leads to the fracture of the tool, which is of interest to understand to guarantee efficient machining with accuracy and precision. In the current investigation, the tool wear during the ultrasonic machining of Inconel 718 super alloy is attempted. An acoustic emission sensor is integrated with the machining setup, and signal information is extracted in the time and time-frequency domains. The features and process parameters are input to a support vector regression model to estimate tool wear. The model developed for tool wear prediction yields an accuracy of 96.13% compared to the model developed with only process parameters, which delivers an accuracy of 84.89%. The developed model can be beneficial for the real-time monitoring of tool wear during the ultrasonic machining process for industrial and remote applications.

A Non-Intrusive Stochastic Phase-Field for Fatigue Fracture in Brittle Materials with Uncertainty in Geometry and Material Properties

A Non-Intrusive Stochastic Phase-Field for Fatigue Fracture in Brittle Materials with Uncertainty in Geometry and Material Properties

Experimental and Numerical Analysis of Ductile Fracture of Polymeric Materials

Experimental and Numerical Analysis of Ductile Fracture of Polymeric Materials

Influence of material microstructure on fracture development in deformable bodies

The problem of predicting the location and direction of local fracture and estimating the ultimate load of composite material is one of the practically important problems of fracture mechanics. With a wide variety of composite materials, it is natural to expect the presence of a large number of failure criteria, each of which should be valid for a certain class of materials and reflect most completely its physical and mechanical properties, structural defects, operating conditions, etc. The choice of effective assessment of the bearing capacity of modern composite material under extreme conditions is at present the main task of researchers. In this paper, the criterion of fracture of composite materials based on simple and quite effective theory of macrostresses by M.Ya. Leonov and K.M. Rusynka is preferred. The macrostress theory effectiveness is shown in the papers by V.V. Panasiuk, L.T. Berezhnytskyi, S.Ya. Yarema, L.V. Ratych, and M.H. Stashchuk. In our paper, we clarify and extend the advantages of macrostress concept criterion in comparison with other fracture criteria in deformable bodies. Examples of crack propagation in the process of body tension are given in this paper.

Structural Reliability of pressure tube of a PHWR with volumetric flaws

The volumetric flaws can get generated in the pressure tubes (PT) of PHWR (made of Zr-2.5Nb material) during the operation of the reactor. The PT material has hydrogen present during the fabrication. Additionally, the zirconium material has a tendency to pick up hydrogen from the surrounding environment and can cause initiation of a crack through delayed hydride cracking (DHC) mechanism. This crack can grow due to the DHC and has the potential to cause leakage or break of the PT. The crack formation occurs only when a set of conditions are met. The model for the crack initiation ahead of the tip of a volumetric flaws is prescribed by the CSA Standard N285.8-15. The formation of the crack is dependent of the geometry of PT, geometry of the flaw (length, depth and root radius), applied loading (due to internal pressure, residual stresses), hydrogen concentration in the material and the material tensile and fracture properties. Most of these parameters are well defined. However, some of them like flaw geometry and material properties are not known with certainty. The structural reliability based methods quantify the uncertainty using probability distributions and present results in form of probability estimates. In this work, the probability of initiation of DHC ahead of a volumetric flaw and its subsequent growth is reported. Monte Carlo based simulation method along with variance reduction techniques is used to predict the probability. This study is useful to establish the Leak-Before-Break behaviour of the PT.

Linking local microstructure to fracture location in a two-dimensional amorphous solid under isotropic strain.

Brittle fracturing of materials is common in natural and industrial processes over a variety of length scales. Knowledge of individual particle dynamics is vital to obtain deeper insight into the atomistic processes governing crack propagation in such materials, yet it is challenging to obtain these details in experiments. We propose an experimental approach where isotropic dilational strain is applied to a densely packed monolayer of attractive colloidal microspheres, resulting in fracture. Using brightfield microscopy and particle tracking, we examine the microstructural evolution of the monolayer during fracturing. Furthermore, we propose and test a parameter termed Weakness that estimates the likelihood for particles to be on a crack line, based on a quantified representation of the microstructure in combination with a machine learning algorithm. Regions that are more prone to fracture exhibit an increased Weakness value, however the exact location of a crack depends on the nucleation site, which cannot be predicted a priori. An analysis of the microstructural features that most contribute to increased Weakness values suggests that local density is more important than orientational order. Our methodology and results provide a basis for further research on microscopic processes during the fracturing process.

Структура и прочность пористых материалов на основе порошков карбида титана разной дисперсности

Materials with porosity from 67.5 to 82.5 % were obtained from mixtures of titanium carbide powders and ammonium bicarbonate blowing agent by sintering in vacuum at temperatures of 1300 – 1500 °C. X-ray phase analysis of porous materials found that the crystal lattice parameter decreases with increasing sintering temperature. This indicates a decrease in the content of bound carbon C/Ti in titanium carbide. As a result of a comparative study of the obtained according to bending test strength characteristics of materials synthesized from nano- and submicron titanium carbide powders, it was found that the strength have close values. Ultimate bending strength are in the range of 2.6 – 18.1 MPa. As the porosity of the material increases, the tensile strength decreases. Fracture is brittle. In the fracture of materials obtained from titanium carbide nanopowder, destruction is observed both along the body and along the grain boundaries regardless of the sintering temperature. In materials obtained by sintering submicron titanium carbide powder at 1500 °C, the destruction occurs predominantly along the body of the grains. It has been found that under the same sintering conditions, the density of the porous material made of titanium carbide nanopowder is higher than that of the material made of submicron powder.

Micro-Mechanism Relations Between Deformation and Damage Behavior of Materials at Elevated Temperature

Deformation of metallic materials at elevated temperatures occurs by the movement of atoms either individually or in a group by diffusion, grain boundary sliding, and the slip processes as facilitated by vacancy, dislocations, and grain boundaries. The constitutive relationship for deformation is developed based on the contributions of external test conditions like temperature and strain rate or stress applied and the internal conditions like chemical composition, phases present, and the length scale of microstructures. Deformation can occur coherently by synergisms of all participating mechanisms, failing to which becomes a source for initiating the damage in the material. The same mechanisms that were initially responsible for deformation to occur then become the facilitators for void nucleation and its growth, which then go through cavity coalescence, and crack formation on the way to cause ultimate fracture of materials. The constitutive relationships for damage mechanisms then take the form that promotes the removal of atoms from the damaged part to a farther site, which further enhances the act of material damage. In the present work, the micro-mechanisms responsible for deformation and failure will be examined to evolve a relationship towards establishing connectivity between these two processes by integrating the effects of internal and external variables for a range of materials.

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Topicality. A large number of light polymerization materials used in dentistry for the restoration of both anterior and canine teeth due to their aesthetic and mechanical properties determine the relevance of their comparative studies. Any restorative dental material, similarly to natural teeth, must possess sufficient mechanical durability in order to function in the oral cavity over an extensive period of time. In view of this, investigation of mechanical properties of such materials is the clinical task of paramount importance. The objective of the research is to analyse strength characteristics and features of destructive processes of lighthardening composite materials under three-point pressure with the application of the acoustic emission method (AE). Materials and methods. Samples were made from composite filling materials Latelux, Tetric N-Ceram, Charisma Classic, Filtek Z250, which were afterwards pressed until their complete destruction on the CBP-5 machine. In the process of fracture initiation and development signals were recorded by a portable eight-channel SKOP-8M measuring system. Flexural strength and elastic modulus were determined, in addition to dynamics of material fracture being studied by the acoustic emission method. Results. It has been established that the nature of the destruction of Latelux, Tetric N-Ceram and Charisma Classic materials is elastic and plastic at the initial stage of pressure, with the transition to brittle during its further growth, whereas the destruction of the Filtek Z250 material is brittle. Conclusion. The signals accompanying the destruction of the Tetric N-Ceram composite appear to have the highest amplitude and energy, while those accompanying the destruction of Latelux demonstrate the lowest amplitude and energy. Tetric N-Ceram nanohybrid composite shows the highest resistance to destruction. Key words: composite materials, strength, elasticity, pressure, destruction, acoustic emission.

Contribution to the formability improvement in sheet metal stamping by a novel technique to control press kinetics

The thickness variation during sheet deep drawing process has an impact on the quality of the final product and can lead to local material fractures. To minimize this phenomenon caused by varying degrees of stretching in different areas of the sheet, various methods can be employed. This research paper introduces a novel technique for metal sheet deep drawing, specifically designed for parts with complex geometric shapes that exhibit significant variations in deformation levels across different areas. The objective of this method is to enhance the quality of the deep drawing process by reducing thickness variations in the final part. In this proposed approach, the vertical movement of the punch is accomplished through two vertical rotational movements. This increases the flexibility of the deformation process, ensuring that the active tools elements occupy the most advantageous positions determined by the material flow in the die. As a result, the material's deformability is improved, allowing for a higher degree of deformation. Additionally, this new method offers a relatively simple design and kinematics solutions for the press and eliminates the need for lengthy assembly-disassembly times.

The development of laser cutting and drilling processes for thick Lithium Niobate wafers for electronic sensor applications

Lithium Niobate (LiNbO3) is a CVD grown synthetic salt having a trigonal crystal structure consisting of niobium, lithium, and oxygen. Due to its variety of mechanical and optical properties, single crystal LiNbO3 finds end use applications in optical waveguides, piezoelectric sensors, optical modulators, and electronic oscillators.LiNbO3 wafers are traditionally mechanically processed using abrasive disks and wire saws, and as a result of the inherently low fracture toughness cut-edge chipping and fracture occur lowering process yields. This study aimed to develop a laser process for the cutting, profiling and drilling of thick whole LiNbO3 wafers, using a femtosecond pulsed 515 nm wavelength source. The stresses induced during processing were controlled through a combination of wafer annealing, crystallographic (012) and (010) cleavage plane orientation. Process generated thermal gradients were controlled using beam manipulation and a water spray liquid flow process. The developed processes substantially reduced material fracture and significantly enhanced cut-edge quality, elevating yields above 80%.

Study on the Relationship between Crack Initiation and Crack Bifurcation in Walnut Shells Based on Energy

Clarifying the dissipated energy required for crack expansion is an effective way to control material crushing. Therefore, based on the material fracture probability model and fractal theory, the energy range required for crack extension was determined, and the morphology of the cracks was quantified. This study investigates the influence of walnut size on crack propagation characteristics; this includes its effects on the crack initiation threshold energy, representing resistance to crack initiation, and the crack bifurcation threshold energy, representing resistance to crack bifurcation. The results show that crack extension has a well-defined threshold energy below which cracks do not initiate or bifurcate. The size of walnuts significantly impacts crack propagation characteristics, showing that both crack initiation threshold energy and crack bifurcation threshold energy decrease with increasing walnut sizes. In addition, there is a positive correlation function between the crack initiation threshold energy and the crack bifurcation threshold energy. The experimental results can offer fresh insights into material fracture prediction and serve as a reference for numerical simulations.

Utilizing X-ray Computed Tomography for Lithium Slag: A Guide to Analyzing Microstructure and Its Potential Influence on Liberation

Slag containing lithium aluminate is analyzed for its microstructure. This refers to the mineralogical composition, shape and size of the target and matrix phase, orientation of the target phase, and porosity. To investigate the microstructure of the target phase, a representative sample is taken from the block and measured using the XCT. With the help of the two- and three-dimensional analysis, an insight into the complex structure can be gained. The target phase, in this case, lithium aluminate, has a dendritic structure with different orientations and thus also influences the microstructure of the matrix phase. This is composed of a mix of several minerals and amorphous components. Fine pores with a radius of 10–100 µm are found throughout the sample volume. The fracture behavior of the slag is estimated on the basis of the influencing factors that can initiate fracture in brittle materials or divert the path of the fracture. Since the mineralogical and thus also mechanical properties of the slag can be influenced by its production process, suggestions are given as to how slags should be structured in order to ensure a non-random fracture, which is required for the efficient liberation of the target phase in mechanical processing.