Brittle Materials Research Articles

Study on the groove geometry of pad in water dissolution polishing of soft brittle materials based on trajectory analysis

During the water dissolution polishing process of soft brittle materials, the pad's groove geometry plays a significant role in determining the performance. This not only affects the flow of the slurry but also directly impacts the overall distribution of the water core on the pad surface, thereby influencing the polishing effect. A trajectory model of the water core on the workpiece surface was established through kinematic analysis and the characteristics and effects of the pad's groove geometry in circular, radial, composite, and grid were studied combined with the trajectory analysis. The coefficient of variation and power spectral density were established to evaluate the trajectory uniformity. The trajectory density distribution was quantitatively analyzed to obtain a better understanding of the material removal uniformity. The simulation and experiment results indicated that the existence of groove geometry will greatly affect the flow of slurry and the surface quality. The grid groove had a better distribution of water core, which means better material removal. There exists a tradeoff between the number of grooves and their spacing. These insights offer a fresh perspective and serve as a valuable reference for further research and analysis into the groove characteristics of pads.

Bound-constrained optimization using Lagrange multiplier for a length scale insensitive phase field fracture model

The classical phase field model using the second-order geometric function α(φ)=φ2 (i.e., AT2 model), where φ∈0,1 is an auxiliary phase field variable representing material damage state, has wide applications in static and dynamic scenarios for brittle materials, but nonlinearity and inelasticity are found in its stress–strain curve. The phase field model using the linear geometric function α(φ)=φ (i.e., AT1 model), can avoid this, and a linear elastic threshold is available in its stress–strain curve. However, both AT2 and AT1 models are length scale sensitive phase field models, which could have difficulty in adjusting fracture strength and crack band simultaneously through a single parameter (the length scale). In this paper, a generalized quadratic geometric function (linear combination of AT1 and AT2 models) is used in the phase field model, where the extra parameter in this geometric function makes it a length scale insensitive phase field model. Similar to the AT1 model, negative phases can happen in the proposed generalized quadratic geometric function model. To solve this problem, a bound-constrained optimization using the Lagrange multiplier is derived, and the Karush–Kuhn–Tucker (KKT) conditions change from strain energy and maximum history strain energy (an indirect method acting on phase) to phase and Lagrange multiplier (a direct method acting on phase). Several simulations successfully validated the proposed model. A single element analysis and a bar under cyclic loading show the different stress–strain curves obtained from different models. A simulation of Mode I Brazilian test is compared with the experiment conducted by the authors, and two more simulations of Mode II shear test and mixed mode PMMA tensile test are compared with results from the literature.

Flexible All-Inorganic Thermoelectric Yarns.

Achieving both formability and functionality in thermoelectric materials remains a significant challenge due to their inherent brittleness. Previous approaches, such as polymer infiltration, often compromise thermoelectric efficiency, underscoring the need for flexible, all-inorganic alternatives. This study demonstrates that the extreme brittleness of thermoelectric bismuth telluride (Bi2Te3) bulk compounds can be overcome by harnessing the nanoscale flexibility of Bi2Te3 nanoribbons and twisting them into a yarn structure. The resulting Bi2Te3 yarn, with a Seebeck coefficient of -126.6µVK-1, exhibits remarkable deformability, enduring extreme bending curvatures (down to 0.5mm-1) and tensile strains of ≈5% through over 1000 cycles without significant resistance change. This breakthrough allows the yarn to be seamlessly integrated into various applications-wound around metallic pipes, embedded within life jackets, or woven into garments-demonstrating unprecedented adaptability and durability. Moreover, a simple 4-pair thermoelectric generator comprising Bi2Te3 yarns and metallic wires generates a maximum output voltage of 67.4mV, substantiating the effectiveness of thermoelectric yarns in waste heat harvesting. These advances not only challenge the traditional limitations posed by the brittleness of thermoelectric materials but also open new avenues for their application in wearable and structural electronics.

Laser fiber cleave: Modeling and fundamentals

In the laser-assisted fiber cleaving process, an ultrashort, high-energy laser is used to introduce a flaw on the optical fiber surface, and then the fiber is cleaved under a tension or bending load. The quality of the cleaved end depends on the crack propagation from the artificial flaw. To understand the cleaving process and the effects of flaw parameters on cleaving quality, crack propagation is modeled by considering a pre-existing surface flaw using a graph-based finite element method (GraFEA). GraFEA is based on the nonlocal multiple cracking simulation framework for brittle and quasi-brittle materials. First, a three-point bending test is conducted to calibrate material parameters in GraFEA for commercial fused silica glass. Subsequently, the model is validated by four-point bending and ring-on-ring tests. After validation, the fiber cleaving process is investigated by parametric simulations in which different loading types (bending or tension) are considered. Finally, a beneficial process window is obtained and recommended for improved cleaving quality.

An Additive Manufacturing MicroFactory: Overcoming Brittle Material Failure and Improving Product Performance through Tablet Micro-Structure Control for an Immediate Release Dose Form.

Additive manufacturing of pharmaceutical formulations offers advanced micro-structure control of oral solid dose (OSD) forms targeting not only customised dosing of an active pharmaceutical ingredient (API) but also custom-made drug release profiles. Traditionally, material extrusion 3D printing manufacturing was performed in a two-step manufacturing process via an intermediate feedstock filament. This process was often limited in the material space due to unsuitable (brittle) material properties, which required additional time to develop complex formulations to overcome. The objective of this study was to develop an additive manufacturing MicroFactory process to produce an immediate release (IR) OSD form containing 250 mg of mefenamic acid (MFA) with consistent drug release. In this study, we present a single-step additive manufacturing process employing a novel, filament-free melt extrusion 3D printer, the MicroFactory, to successfully print a previously 'non-printable' brittle Soluplus®-based formulation of MFA, resulting in targeted IR dissolution profiles. The physico-chemical properties of 3D printed MFA-Soluplus®-D-sorbitol formulation was characterised by thermal analysis, Fourier Transform Infrared spectroscopy (FTIR), and X-ray Diffraction Powder (XRPD) analysis, confirming the crystalline state of mefenamic acid as polymorphic form I. Oscillatory temperature and frequency rheology sweeps were related to the processability of the formulation in the MicroFactory. 3D printed, micro-structure controlled, OSDs showed good uniformity of mass and content and exhibited an IR profile with good consistency. Fitting a mathematical model to the dissolution data correlated rate parameters and release exponents with tablet porosity. This study illustrates how additive manufacturing via melt extrusion using this MicroFactory not only streamlines the manufacturing process (one-step vs. two-step) but also enables the processing of (brittle) pharmaceutical immediate-release polymers/polymer formulations, improving and facilitating targeted in vitro drug dissolution profiles.

First principles investigation for the hydrogen storage properties of novel lithium-based XLiH3 (X=K, Rb) perovskite-type hydrides for advance hydrogen storage system

In this work, the density functional theory is used to investigate the structural, mechanical, electronic, dynamic, thermodynamic, optical and hydrogen storage properties of XLiH3 (X = K, Rb) for the first time. Both KLiH3 and RbLiH3 materials exhibit dynamic, mechanical and thermodynamic stability. The lattice parameters of KLiH3 and RbLiH3 are 3.908 and 4.070 Å, respectively. The investigation of Cauchy pressure, Poisson's ratio and B/G ratio shows that KLiH3 and RbLiH3 are brittle materials. Moreover, the electronic properties of XLiH3 hydrides demonstrate that KLiH3 and RbLiH3 show metallic nature. Optical properties of these compounds are studied and reveal that they have very high refractive indexes and dielectric functions. The thermodynamic properties, including heat capacity, entropy, enthalpy, and free energy of XLiH3, are investigated as well. The hydrogen storage capacities of KLiH3 and RbLiH3 are 5.805 and 3.071 wt%, respectively, confirming that KLiH3 has a high hydrogen storage capacity and is more suitable as a hydrogen storage material. Our study opens up a new-pathway for designing novel hydrogen storage materials.

Research on the mechanism of tool-workpiece coupling contact and theoretical modeling of surface roughness in turning brittle materials

Research on the mechanism of tool-workpiece coupling contact and theoretical modeling of surface roughness in turning brittle materials

Cracking in semiconductor devices–effect of plasticity under triaxial constraint

A semiconductor device integrates dissimilar materials of small sizes and complex geometries. During fabrication, the materials are deposited at various temperatures. Both deposition and change in temperature cause stresses in the materials. Under the stresses, ductile materials may deform plastically, and brittle materials may crack. Here we focus on how plastic deformation in the ductile materials affects cracking in nearby brittle materials. We study a model structure in which a metal line is encased by a silicon substrate and a brittle oxide layer. In the triaxially constrained metal, the stresses readily exceed the yield strength of the metal. Such high stresses in the metal elevate the stresses in the oxide. The degree of triaxial constraint varies with the aspect ratio of the metal. We compute the stress in the oxide, as well as the energy release rate of an edge crack and a long channel crack. We discuss strategies to avert cracking in the oxide.

SEDIMENTATION IN HYDROELECTRIC POWER TURBINES

The primary cause of erosive wear and energy loss is friction, and reportedly, one-third of the world’s energy resources go to overcome friction by several methods. The presence of deposits in water is a common problem in mountainous regions and some Ukrainian hydroelectric power stations. Hydro turbines face serious issues related to erosion from deposits during operation. Erosive wear occurs due to the impact of solid particles against a solid surface. The current environment contains particles whose velocity is sufficient to damage metal surfaces. Various researchers have conducted numerous studies to minimise the effect of deposit erosion in multiple locations of Francis turbine components (FT). For this purpose, they performed field investigations, experimental measurements, empirical modelling, computational fluid dynamics (CFD) work, and other methods. Various empirical models have been used to describe erosive wear in terms of material and fluid properties. They established that, for ductile materials, maximum erosion occurs at an impact angle of 30°, whereas for brittle materials, it occurs in the range of 80–90°. In the literature, various experimental methods are available to quantitatively assess slurry erosion, such as the rotating disk apparatus (RDA), slurry tank testing, jet erosion testing, and rotating drum testing. Due to manufacturing technologies used in mechanical processing processes, the exposed surface has a certain absolute roughness that increases during machine operation due to abrasion or erosion. Therefore, surface texture leads to increased energy efficiency losses during operation. Technological advancements have facilitated the widespread use of computational tools to address deposit erosion issues. In recent decades, numerical methodology has been a widely used and effective tool, yielding tangible and reliable results. This study examines potential methods for detecting and reducing deposits. This type of erosion depends on flow characteristics, surface properties, and properties of the eroding material. The article provides comprehensive information on sedimentation (deposits) causing wear in hydraulic turbines. Keywords: hydroelectric turbine, sedimentation erosion, computational fluid dynamics, fluid-structure interaction.

Optimization of the Femtosecond Laser Machining Process for Single Crystal Diamond Using Response Surface Methodology

Femtosecond laser machining offers high precision and minimal thermal impact, making it a promising technique for processing hard and brittle materials like single-crystal diamonds (SCDs). In this study, the femtosecond laser machining process for SCD material was systematically optimized to improve both machining efficiency and quality. Initial single-factor experiments were conducted to explore the effects of key process parameters—laser power, scanning speed, and number of scans—on machining performance. Subsequently, response surface methodology (RSM)-based experiments designed using the Box–Behnken method were employed to comprehensively refine the process. A regression model was developed to analyze the data, and the interaction effects of the parameters were thoroughly evaluated. The validated model identified an optimal set of parameters, resulting in a significant improvement in machining performance. This research provides a comprehensive framework for optimizing femtosecond laser machining processes, offering valuable insights critical for the production of advanced lightweight components in industries such as aerospace, optical instruments, and high-performance electronics.

A modified bond-based peridynamic approach for rigid projectile perforation on concrete slabs

Peridynamic (PD) has a unique advantage in describing the crack growth and fragmentation of brittle materials. Concerning the dynamic behaviors and failure patterns of concrete slabs under projectile perforations, a modified bond-based PD approach maintaining both the easy implementation and computational stability characteristics was firstly developed from the following three aspects, (i) a rate-dependent PD constitutive model was proposed for describing the dynamic behaviors of concrete; (ii) a progressive damage criterion considering the tension-compression anisotropy, softening behavior, and strain rate effect of concrete was incorporated to more accurately reproduce the damage and failure of concrete; (iii) an improved micro-modulus function related to bond length was introduced to reveal the internal length effect of bond force. Then, numerical simulations of projectile perforation on concrete slabs by utilizing the developed modified bond-based PD approach, as well as the corresponding sensitivity analyses of discretization parameters including horizon size and particle spacing were performed. Based on the recommended horizon size and particle spacing, the predicted residual velocity of projectile and failure patterns of concrete slabs exhibited an excellent agreement with the test data. Furthermore, by comparisons of the traditional bond-based PD and classical finite element methods, the superiority of developed approach in describing the perforation damage of concrete targets against projectile impact was demonstrated. Finally, the modified bond-based PD approach was employed to blind simulate the projectile normal and oblique perforating multi-layered spaced concrete target plates. It was found that the modified PD model reasonably predicted the terminal ballistic trajectory, deflection angle, and residual velocity of projectile, as well as the failure patterns of target plates. The present work provides a new way to predict the terminal ballistic effect of projectile and dynamic behaviors of concrete slabs.

Fabrication of microchannels on silica glass by femtosecond laser multi-scan: From surface generation mechanism to morphology control

Femtosecond laser processing has become a critical technique for the microfabrication of hard and brittle materials, particularly in microfluidic device applications. This study focuses on the fabrication of microchannels with controllable cross-sectional profiles in silica glass, a material known for its excellent physical and chemical properties. Through a combination of experimental research and theoretical analysis, the surface generation mechanisms governing microchannel morphology are investigated, alongside the influence of various processing parameters on the surface roughness at the microchannel bottom. A comprehensive optimization method is developed to control sidewall taper and surface roughness by adjusting laser scanning paths and modes. Utilizing a composite scanning approach, the study achieves near-rectangular microchannels with average sidewall taper angles below 5° and surface roughness (Sa) of 2.53 μm. These results provide a new strategy for precise control of microchannel morphology in silica glass, offering significant potential to enhance the efficiency and precision of microfluidic device fabrication, with broad applications in both industrial and research settings.

First Principle Study of Structural, Electronic, Mechanical and Optical Properties of Bulk Niobium Dichalcogenide NbX2 (X=S, SE) within a Visible Phonon Energy Range

An intensive study on structural, electronic mechanical and optical properties of bulk Niobium Dichalcogenides NbX2 (X=S, Se) was carried out using the first principle. The structural parameters such as Equilibrium Lattice Parameters, Volume, Bulk Modulus, and FirstDerivative Modulus were calculated to determine if the materials are energetically stable. Elastic constants were further obtained from which mechanical properties i.e. bulk, Young's and shear moduli and consequently Poisson's ratio were obtained. Based on the well-known Born stability conditions Bulk-NbS2 is most likely mechanically anisotropic ductile material. While Bulk-NbSe2 for the predicted B/G ratio in all three methods is less than a critical value of 1.75, hence this shows that NbSe2 is a brittle material exploring its electronic and optical properties whose motivation was to find out the most stable phase and ascertain if these materials could be used in various fields that suit their mechanical and optical properties. Furthermore, from the calculated optical spectra, plasma frequencies were analyzed which indicated the possibility of applying the material in plasmonic-related fields.

Using fractal voids to understand Mode I compressive fracture in brittle materials – A two-dimensional analysis

Unlike cases of direct or indirect tensile loading, analysis of Mode I fracture in cases of compressive loading must necessarily consider two-dimensional flaw geometries. The consequent analytical complications have resulted in little theoretical evolution towards understanding Mode I fracture in compressive loading. Researchers have recently observed that the linear elastic (LE) stress fields surrounding two-dimensional flaws in compression appear to have indicative value regarding Mode I fracture, but no rational framework has yet been proposed for their interpretation. Herein it is demonstrated that by idealizing void surfaces as fractal, and using what will be called the “small flaw assumption,” LE stress fields can be interpreted to obtain significant insight regarding brittle Mode I compressive fracture. Using fractal voids, a rational and consistent explanation for the satisfaction of the stress and energy criteria at the surface of two-dimensional flaws is presented. The discussion resolves many typical theoretical issues in the literature in a manner consistent with fundamental Griffith theory, and accounts for size and shape effects. The framework further enables the computationally efficient prediction of peak KI values associated with the propagation of line cracks from two-dimensional flaws from a brittle medium subject to macroscopic uniaxial compression via LE stress fields.

Experimental investigation of permeability evolution and progressive damage of sandstone in the complete process of direct shear

Permeability evolution and damage behavior under shearing conditions are critical for reliable predictions of rock seepage characteristics during excavation and a correct assessment of their impacts on the occurrence of natural or induced hazards. However, publications concerned with this problem have been poorly issued so far. The primary objective of this study is to innovatively investigate permeability evolution and damage behaviors of sandstone in the complete process of direct shear. Several groups of red sandstone specimens are deformed in direct shearing using a newly modified servo-controlled direct shear apparatus to measure permeability evolution and monitor acoustic emission (AE) activities with damage under various normal stress conditions. The morphology of the rupture surfaces is scanned using a 3D laser scanner after tests. According to our experimental results, the locus of the shear stress-displacement curve is found to be closely associated with microcrack progressivity. The initial permeability in advance of shearing test and the peak permeability appearing after the peak shear stress decrease with the increasing normal stress. The minimal and maximum permeability values exhibit a lag-effect with respect to the turning and the peak points on the shear stress-displacement curve. Furthermore, a palpable surge is found in the interevent time function during shearing, which can be a potential indicator for early warning of catastrophic rupture of brittle rock materials under shearing or compression. The joint roughness coefficient (JRC) values in the direction of shearing deformation for each normal stress case are more significant than those in the direction perpendicular to the shear displacement. The impacts of our obtained results are potential ramifications for permeability control in rock engineering projects.

On the microscale deformation of the oxide layer formed on a Zr-2.5 Nb alloy: A micropillar compression study

Oxides are prone to brittle failure, leading to passivity loss and exposing the underlying metal during service. Thus, understanding the mechanical response of oxides is crucial for evaluating metal passivity. The present study examines the oxide layer on a Zr-2.5 Nb alloy used in CANDU® reactors after different exposure times. Micropillar compression tests on the oxide layer revealed that the mean failure stress and strain remain unchanged (are within the error) for both samples. Post-deformation characterization confirms that the failure of the oxide layer is brittle and could be pseudo-shear, which is consistent with the critical failure mode for brittle materials.

Material Removal Mechanisms of Polycrystalline Silicon Carbide Ceramic Cut by a Diamond Wire Saw.

Polycrystalline silicon carbide (SiC) is a highly valuable material with crucial applications across various industries. Despite its benefits, processing this brittle material efficiently and with high quality presents significant challenges. A thorough understanding of the mechanisms involved in processing and removing SiC is essential for optimizing its production. In this study, we investigated the sawing characteristics and material removal mechanisms of polycrystalline silicon carbide (SiC) ceramic using a diamond wire saw. Experiments were conducted with high wire speeds of 30 m/s and a maximum feed rate of 2.0 mm/min. The coarseness value (Ra) increased slightly with the feed rate. Changes in the diamond wire during the grinding process and their effects on the grinding surface were analyzed using scanning electron microscopy (SEM), laser confocal microscopy, and focused ion beam (FIB)-transmission electron microscopy (TEM). The findings provide insights into the grinding mechanisms. The presence of ductile grinding zones and brittle fracture areas on the ground surface reveals that external forces induce dislocation and amorphization within the grain structure, which are key factors in material removal during grinding.

Numerical investigation on the impact resistance of ceramic-based composite structure with hybrid architecture

As known, ceramics possess desirable strength, hardness and low density, which have been extensively applied in engineering fields. However, the inherent brittleness makes the ceramics present poor toughness and consequently impact resistance as well. In recent decades, some ingenious architectures of biomaterials employed to improve the mechanical properties of brittle bulk materials, such as laminate and brick-mud, have become increasingly popular. Here, in order to further enhance the impact resistance of ceramics, a kind of hybrid ceramic-based composite structure is designed according to the gradient feature in dactyl club of mantis shrimp. The impact resistance performances of bulk, laminate, brick-mud and hybrid structures are investigated by finite element simulation. The results show that the hybrid structure can effectively avoid catastrophic failure, thereby having large scope of deformation area to store energy. Moreover, the damage mass of impactor for the hybrid plate is the largest due to the beginning hard collision between impactor and target plate and long cumulative damaging time of impactor. As a result, with the highest internal energy and eroding kinetic energy of impactor simultaneously, the hybrid structure dissipates the most energy of impactor. Further, under extreme working conditions of oblique and high velocity impact, the hybrid structure still exhibits optical impact resistance performance.

Phase-field modeling of crack growth under coupled creep-fatigue

Crack growth under coupled creep-fatigue strongly influences service life of metallic components operating at high temperatures. However, there lack numerical models that enable direct simulations of crack growth and plasticity development under coupled creep-fatigue. In this study, a unified phase-field model is developed for simulating crack growth under fatigue, creep, and coupled creep-fatigue. This model is able to reproduce the Paris laws for both brittle and ductile materials in pure fatigue mode, which shows that the degradation rate due to cyclic stress in ductile materials is generally larger than that in brittle materials. Fatigue simulations with different yield strengths demonstrate that plasticity facilitates crack growth in typical ductile materials. High-throughput simulations are performed under coupled creep-fatigue conditions, with varying hold-stress levels and hold-time. By analyzing crack growth rate under different hold-time, a creep-fatigue interaction term is obtained. Simulation results demonstrate that the creep-fatigue interaction is caused by smaller stress gradient and enhanced degradation rate ahead of the crack tips under coupled creep-fatigue, compared to the situation of pure fatigue. This work reveals the origin of different Paris-law exponents in brittle and ductile materials and demonstrates how the interplay between creep and fatigue affects crack growth.

Fracture failure analysis of traction transformer oil pump flange

A flange fracture occurred during the installation of a traction transformer oil pump. The causes of the flange fracture were analyzed using physical, chemical, and finite element methods. The fracture surface shows expanded edges and a linear fracture source, indicating an overload fracture. No significant defects such as pinholes, looseness, or cracks were found in the internal structure, which contains elongated Si phases. The Si, Ti, and Zn content in the failure part does not meet standard specifications. The hardness of the failure part is HBW107.8, meeting standards, but the elongation at break is at the lower limit, suggesting higher material brittleness. Finite element analysis revealed a maximum tensile stress of 241.5 MPa on the flange, close to the yield strength, indicating a small safety margin. The flange fracture is related to high material brittleness and potential assembly anomalies. To prevent similar incidents, strict control of raw material quality, regular inspection of mechanical properties, and finite element analysis for structural optimization are necessary.