Brittle Materials Research Articles

High pressure phase transition and its influence on structural, mechanical properties and elastic anisotropy of [formula omitted]: An ab-initio study

Lithium carbide (Li2C2), a promising tritium breeding material with potential applications in magnetic confinement-based fusion reactor blankets, has drawn significant attention due to its recent utilization in lithium-ion batteries. In the current study, we employed first-principles calculations with van der Waals (vdW) force correction to explore the structural and mechanical properties of Immm and Pnma phases of Li2C2 subjected to external hydrostatic pressure. It is demonstrated that inclusion of vdW effects accurately predicts Immm→Pnma phase transition at 16 GPa, aligning closely with experimental transition pressure. In contrast, PBE-GGA calculations underestimate the same by about 21%. Current paper is the first comprehensive study of pressure evolution of mechanical properties and strength determining parameters of Li2C2. Interestingly, this inherently brittle material exhibits ductile characteristics beyond 7.5 GPa. The paper also offers a quantitative comparison of its strength parameters with other prominent tritium breeding materials. Finally, the strong directional dependence due to the presence of C2 dimer is investigated by analyzing the pressure variation of elastic anisotropy. The study has its relevance in assessing structural integrity of Li2C2 during inadvertent buildup of tritium and helium that would generate stress in the solid breeder.

Fracturing behavior and mechanism of flawed disc specimens under compressive loading using geometry‐constraint‐based nonordinary state‐based peridynamics

AbstractA geometry‐constraint‐based nonordinary state‐based peridynamic (GC‐NOSBPD) model is developed to investigate the fracture characteristics of flawed brittle disc specimens under compressive loading as well as its fracturing mechanism. The bond‐associated horizon (BAH) size is directly defined based on the kinematic constraint (KC). This proposed model can well mitigate the numerical oscillation. The failure criteria based on the bond‐associated stress state are utilized to simulate the fracture of materials. Two stress effects can offer an insight into the fracturing mechanism of flawed specimens. The failure modes of flawed specimens are controlled by the tensile failure, and the crack growth trajectories acquired by the present numerical model are equivalent to those obtained by the experimental observations. The effects of size and crack inclination angles on the fracture toughness of brittle materials are assessed. The GC‐NOSBPD model is competent for evaluating the fracture damage of flawed brittle materials and understanding its failure mechanism.

Probing the Atomic Erosion Wear Characteristics of TiC-Coated Fe in Oil and Gas Drilling Environments.

The titanium carbide (TiC) coating is considered one of the key coating materials to resist erosion wear in oil and gas drilling environments due to its excellent impact and wear resistance. Based on molecular dynamics, the erosion wear resistance of TiC coatings and the pure Fe system in the simulation of nanoindentation, scratch, and particle impact was studied at the microscale. The results indicate that TiC coatings can effectively enhance the load-bearing capacity of the Fe substrate within the critical load range and exhibit low friction characteristics and erosion resistance. However, the protection is lost after the TiC coating cracks, leading to an increase in the tangential force. In addition, when TiC coatings and pure Fe systems exhibit typical erosion characteristics of brittle materials, the TiC coating will significantly reduce the erosion wear of the substrate.

Multicriteria-based optimization of roller compacted concrete pavement containing crumb rubber and nano-silica

Abstract Roller-compacted concrete pavement (RCCP) is a brittle material with low tensile strength that does not contain steel or dowel bars. This, in addition to the rigidity of the RCCP, causes degradation or cracking before the RCCP reaches its service life. To improve the performance of the RCCP, crumb rubber (CR) can be used as an aggregate. Hence, in this study, CR was used to replace 0, 10, 20, and 30% of the fine aggregate in the RCCP. To mitigate the adverse effect of the CR on the properties of the RCCP, nano-silica (NS) was added by weight of cement in proportions of 0, 1, 2, and 3%. To select an optimal mix based on various performance criteria, multicriteria-based optimization was carried out using techniques such as order of preference by similarity to ideal solution, evaluation based on distance from average solution, weighted sum model, and weighted product model techniques. During experimentation, CR improved the consistency and reduced the mechanical and durability properties of the RCCP, while NS reduced the consistency and improved the mechanical and durability performance of the RCCP. The M2 mix (mix containing 0% CR and 1% NS) is consistently ranked as the best choice for multi-criteria decision-making techniques and sensitivity analyses due to its exceptional physical, mechanical, and durability attributes, ensuring reliability across various decision-making scenarios. This study provides insights into the decision-making process for the choice of appropriate RCCP mix produced with CR and NS for improved performance in pavement applications and the importance of utilizing waste tire rubber in concrete pavements to promote sustainability.

A contactless energy transfer type of 3-DOF ultrasonic tool holder

The vibration form of the tool has a significant impact on the machining effect in rotary ultrasonic machining. Compared with 1DOF rotary ultrasonic machining, multi-DOF rotary ultrasonic machining have comprehensive advantages in the machining performance. However, the current multi-DOF rotary ultrasonic machining faces the challenges of miniaturization, multi-DOF vibration integration and high rotary speed. Therefore, a 3DOF ultrasonic vibration tool holder with decoupled three-channel contactless energy transfer was proposed, which realize 1DOF, 2DOF and 3DOF rotary ultrasonic machining with the same resonant frequency and the vibration conversion functions at high rotation speed. Structure design, principle analysis and simulation verification was carried out to determine the structure size and material. Through manufacturing and testing of prototype, the results show that under the performance of high speed, high transfer efficiency with 93 % and low temperature rise. The prototype of 3DOF ultrasonic vibration tool holder can not only integrate six vibration forms with high amplitude, but also has the function of replacing the milling tool for metal and grinding tool for brittle materials. Finally, through machining experiments with different vibration forms, two kinds of elliptical vibration produce regular textures with different shapes in the Ti-6Al-4V milling. In Al2O3 grinding, the surface roughness is the lowest under 2DOF vertical elliptical vibration grinding. While the 2DOF horizontal elliptical vibration grinding significantly improves the chip removal and prolongs the tool life. These findings provide guidance for machining performance under various vibration mode. It was proved that this tool holder integrated and switch with multiple vibration modes is of great value for high efficiency and high-quality multi-procedure machining.

Stress invariants and invariants of the failure envelope as a quadric surface: Their significances in the formulation of a rational failure criterion

When stress invariants up to the second order are employed to construct failure criterion for brittle materials, it involves three independent terms and therefore there are three coefficients to be determined. However, there are only two conditions available associated with the strengths under uniaxial tension and compression. Systematic examinations have given to the invariants of the failure envelope as a quadric surface according to analytic geometry. For the failure envelope to meet the basic assumptions, in particular, infinite strength under and only under hydrostatic compression, one of the coefficients can be eliminated based on rigorous mathematical inferences. As a result, it reproduces the Raghava-Caddell-Yeh criterion, which has never been rationally established before but is now in this paper. The failure envelope takes the form of circular paraboloid for brittle materials in general. The criterion degenerates to the von Mises criterion, giving a circular cylindrical failure envelope for ductile materials as a special case. It is as rational as the von Mises criterion in the sense that the assumptions made and the conditions available are logically sufficient for the complete establishment of the failure criterion without any ambiguity.

Analytical model for material removal rate in rotary tool micro-ultrasonic machining of hard and brittle materials

The rotary tool micro-ultrasonic machining (RT-MUSM) process is a newly developed variant of conventional micro-USM. It is preferred over conventional micro-USM due to its ability to remove material at a faster rate and with better accuracy than the machined microfeatures. Some experimental investigations have been conducted on the RT-MUSM process for the machining of hard and brittle materials. However, the theoretical model of the material removal rate (MRR) for the RT-MUSM process has not been discussed in the literature. Thus, the present research work reports on developing a predictive model of the MRR for the RT-MUSM process during glass machining. Pure brittle fracture mode was considered to be the material removal mechanism during the model's development. The developed model was verified through experiments. The estimated results were compared with the experimental results and found to be in good agreement with each other. Additionally, statistical analysis was carried out for the prediction accuracy of the developed model. The results revealed that the model is adequate, with a correlation coefficient of 0.9976 and a mean absolute percentage error of 2.45%. Hence, the developed model can be used to estimate the MRR for the RT-MUSM process of hard and brittle materials such as ceramics.

Resistance of CAD/CAM composite resin and ceramic occlusal veneers to fatigue and fracture in worn posterior teeth: A systematic review.

Severe tooth wear is related to substantial loss of tooth structure, with dentin exposure and significant loss (≥1/3) of the clinical crown. The objective of this systematic review was to summarize and analyze the scientific evidence regarding the mechanical performance of computer-aided design/computer-aided manufacturing (CAD/CAM) composite resin and CAD/CAM lithium disilicate ceramic occlusal veneers, in terms of fatigue and fracture resistance, on severely worn posterior teeth. Currently, occlusal veneers are an alternative for treating worn posterior teeth. Although scientific evidence demonstrates the good performance of lithium disilicate occlusal veneers, there are less brittle materials with a modulus of elasticity more similar to dentin than ceramics, such as resin CAD/CAM blocks. Therefore, it is important to identify which type of material is best for restoring teeth with occlusal wear defects and which material can provide better clinical performance. This review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A comprehensive search of the PubMed, Embase, Web of Science, Scopus, Cochrane, OpenGrey, Redalyc, DSpace, and Grey Literature Report databases was conducted and supplemented by a manual search, with no time or language limitations, until January 2022. We aimed to identify studies evaluating the fatigue and fracture resistance of CAD/CAM composite resin and ceramic occlusal veneers. The quality of the full-text articles was evaluated according to the modified Consolidated Standards of Reporting Trials (CONSORT) criteria for in vitro studies, and 400 articles were initially identified. After removing duplicates and applying the selection criteria, 6 studies were included in the review. The results demonstrated that the mechanical performance of CAD/CAM composite resin occlusal veneers is comparable to that of CAD/CAM lithium disilicate occlusal veneers in terms of fatigue and fracture resistance.

Effect of laser-assisted heat treatment on material removal behavior of sapphire in indentation and scratching

Sapphire is widely used in aerospace, microelectronics and defense applications. Due to its high hardness and low fracture toughness, it is difficult to achieve high efficiency and low damage machining. Laser-assisted machining is an effective method for machining hard and brittle materials and has been explored in many experimental and theoretical studies. In this paper, the mechanical property of sapphire and the variation of the coefficient of friction assisted by different laser powers are investigated in detail. Meanwhile, Raman spectroscopy was employed to reveal the residual stress characteristics in the deformation zone of the scratch grooves, and to analyse the changes in the depth of plastic-brittle transition of sapphire after heat treatment with different laser powers. Comparing the material removal behavior of sapphire in indentation and scratching experiments with and without laser-assisted heat treatment (LAHT), and exploring their material removal mechanisms. Experimental results show that LAHT can improve the ductility and workability of sapphire by reducing the hardness and improving the fracture behavior of the material. Hardness and elasticity modulus decrease with increasing power, and the distribution of residual stress changes from compressive to tensile with increasing power. Laser treated surface was found to possess shorter crack length, no significant localized chipping and spalling in indentation, and its scratch grooves were deeper with no radial cracks observed, the scratching force ratio was higher, the critical load for brittle-plastic transition became larger, and plastic flow lines and lumpy spalling debris appeared in the scratch areas. Nearly zero cracks were observed in material subsurface under the LAHT. With LAHT, the material is removed at a higher rate and in a more plastic way, fracture behavior of the material is improved, surface and subsurface damage is reduced, and the machining efficiency is enhanced. This study has important implications and benefits for the machining of sapphire in ensuring surface quality and achieving high efficiency.

SPECIFIC ENERGY CAPACITY OF PROCESSING AND ENERGY EFFICIENCY FOR PROCESS OF GRINDING WITH WHEELS FROM SUPERHARD MATERIALS

The analysis of modern research shows that when evaluating the specific energy intensity of the abrasive processing process, one should pay attention not only to the indicators of grinding power and material removal rate, but also to the indicator of the wear of the abrasive tool, which we will show below for the grinding tool made of superhard materials. It is shown that the traditional method of estimating the specific energy capacity based on the ratio of the grinding power to the processing productivity does not provide an adequate solution, since with it the specific heat capacity of processing exceeds the specific heat capacity of melting of the processing material by almost an order of magnitude. Therefore, it is the application of a new approach to the assessment of the specific energy intensity of diamond grinding, taking into account the wear of the working layer of the diamond wheel, and makes it possible to estimate the indicators of the specific energy intensity of grinding and the energy efficiency coefficient. It has been proven that when estimating the specific energy capacity of grinding metal-ceramic composite materials consisting of a low-melting and refractory component, the latent heat capacity of melting of the low-melting component should be taken as the basis. It is shown that the plastic mode of grinding occurs precisely when the specific energy capacity of grinding, taking into account the wear of the wheel, becomes close to the specific heat capacity of melting of a brittle material.

Critical cutting thickness model considering subsurface damage of zirconia grinding and friction–wear performance evaluation applied in simulated oral environment

Ductile mode removal is always a popular topic in zirconia ceramic cutting and grinding. The completely undamaged ductile mode grinding is extremely inefficient and difficult to control, which limits the clinical application of dental zirconia ceramics. Hence, considering the effect of subsurface damage, this paper redefines the ductile mode grinding removal of ceramic materials and establishes a critical cutting thickness model for zirconia ceramic grinding. Results show that the better the lubrication condition, the smaller the subsurface damage degree and the larger the removal range of ductile zone. To verify the model, grinding experiments of zirconia ceramic under different lubrication conditions are conducted. The results show that grinding under nanofluid minimum quantity lubrication obtains the lowest friction coefficient, which is reduced by 58.54 % and 18 % compared with dry grinding and minimum quantity lubrication (MQL), respectively. Under nanofluid minimum quantity lubrication (NMQL) condition, the critical cutting thickness is 2.27 µm, which is 160.92 % larger than that under dry grinding. The error between the theoretical model and the experimental results is 10.67 %, which verifies the correctness of the theoretical model. Furthermore, using the workpiece material obtained from grinding experiments, friction–wear experiments are conducted on dental zirconia ceramics under different loads in a simulated oral environment. The results show that zirconia ceramics obtained by NMQL grinding achieve better anti-friction and anti-wear performance than that of MQL. When the maximum cutting thickness of zirconia ceramics processed by NMQL grinding is 2.27 µm, the wear rate of the workpiece is 3.06 × 10−5 mm3/N·m, and at 2.6418 µm, the wear rate of the workpiece is 2.01 × 10−3 mm3/N·m. This paper aims to provide theoretical guidance and technical support for the ductile mode removal of hard, brittle materials.

A macro-scale constitutive model of low-density cellular concrete for blast simulation

Cellular concrete is a building material with highly porous structure in the matrix. Due to its excellent thermal and sound insulation performance, low-density cellular concrete (≤600 kg/m3) is often used in the construction of non-structural elements in residential and industrial buildings. During service, low-density cellular concrete elements may be subjected to blast loads induced by chemical or gas explosions. Therefore, a material model that can accurately describe the mechanical behavior of low-density cellular concrete is essential to investigate the damage and dynamic response of cellular concrete elements subjected to blast loading. Previous study indicated that low-density cellular concrete exhibits a cap-shaped compressive meridian. However, the commonly used brittle material models adopt the basis of a monotonical increase in the deviatoric strength with increasing hydrostatic pressure, which is contradictory to the experimental observations of low-density cellular concrete. Therefore, this study aims at developing a material model for predicting the dynamic response of low-density cellular concrete elements subjected to blast loads. Firstly, a series of laboratory tests were conducted to study the mechanical properties of low-density cellular concrete. The quasi-static, triaxial and dynamic properties, including the damage evolution modes, the compressive meridian, the hydrostatic pressure-volumetric strain relationship, and the strain rate effects were identified. Secondly, a plastic-damage material model of low-density cellular concrete was proposed and the material parameters were calibrated by the laboratory test results. To verify the feasibility of the model, single element simulations were carried out and results indicated that the model can accurately describe the complex behavior of low-density cellular concrete. Thirdly, numerical simulations were conducted to validate the proposed model by comparing predictions with blast test results from the literature. The numerical model accurately predicted the displacement responses and failure processes of low-density cellular concrete elements, with a maximum difference of 21 mm for maximum displacement and only 2 mm for residual displacement. The results demonstrate the high accuracy of the developed model in predicting the dynamic response and damage of low-density cellular concrete elements under various blast loading scenarios.

Compressive Properties of Basalt Fibers and Polypropylene Fiber-Reinforced Lightweight Concrete.

With the development of high-rise and large-scale modern structures, traditional concrete has become a design limitation due to its excessive dead weight. High-strength lightweight concrete is being emphasized. Lightweight concrete has low density and the characteristics of a brittle material. This is an important factor affecting the strength and ductility of the lightweight concrete. To improve these shortcomings and proffer solutions, a three-phase composite lightweight concrete was prepared using a combination of tumbling and molding methods. This paper investigates the various influencing factors such as the stacking volume fraction of GFR-EMS, the type of fiber, and the content and length of fiber in the matrix. Studies have shown that the addition of fibers significantly increases the compressive strength of the concrete. The compressive strength of concrete with a 12 mm basalt fiber (BF) (1.5%) admixture is 9.08 MPa, which is 62.43% higher than that of concrete without the fiber admixture. The compressive strength was increased by 27.53 and 21.88% compared to concrete containing 3 mm BF (1.5%) and 0.5% BF (12 mm), respectively. Fibers can fill the pore defects within the matrix. Mutually overlapping fibers easily form a network structure to improve the bond between the cement matrix and the aggregate particles. The compressive strength of lightweight concrete with the addition of BF was 16.71% higher than that with the addition of polypropylene fiber (PPF) with the same length and content of fibers. BF has been shown to be more effective in improving the mechanical properties of concrete. In this work, the compressive mechanism and optimum preparation parameters of a three-phase composite lightweight concrete were analyzed through compression tests. This provides some insights into the development of lightweight concrete.

Linear and Nonlinear Formulation of Phase Field Model with Generalized Polynomial Degradation Functions for Brittle Fractures

The classical phase field model has wide applications for brittle materials, but nonlinearity and inelasticity are found in its stress–strain curve. The degradation function in the classical phase field model makes it a linear formulation of phase field and computationally attractive, but stiffness reduction happens even at low strain. In this paper, generalized polynomial degradation functions are investigated to solve this problem. The first derivative of degradation function at zero phase is added as an extra constraint, which renders higher-order polynomial degradation function and nonlinear formulation of phase field. Compared with other degradation functions (like algebraic fraction function, exponential function, and trigonometric function), this polynomial degradation function enables phase in [0, 1] (should still avoid the first derivative of degradation function at zero phase to be 0), so there is no Γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Gamma $$\\end{document} convergence problem. The good and meaningful finding is that, under the same fracture strength, the proposed phase field model has a larger length scale, which means larger element size and better computational efficiency. This proposed phase field model is implemented in LS-DYNA user-defined element and user-defined material and solved by the Newton–Raphson method. A tensile test shows that the first derivative of degradation function at zero phase does impact stress–strain curve. Mode I, mode II, and mixed-mode examples show the feasibility of the proposed phase field model in simulating brittle fracture.

Tough and Ductile Architected Nacre‐Like Cementitious Composites

AbstractEnhancing fracture toughness and ductility of brittle materials such as concrete remains a challenge. Nature offers numerous mechanisms to enhance fracture toughness using purposeful designs of materials’ architecture. Natural nacre exhibits high fracture toughness by promoting inelastic deformation and hierarchical toughening mechanisms. Here, “nacre‐like‐separated” and “nacre‐like‐grooved” cementitious composites inspired by brick‐and‐mortar arrangement of mollusk shells are proposed. These nacre‐like composites are engineered by laser processing cement paste into individual tablets and grooved patterns (as intentional defects) and laminating them with limited amounts of suitable elastomeric (polyvinyl siloxane) interlayers. It is found that interlayer deformation, tortuous crack propagation guided by the defects, and crack bridging are the main toughening mechanisms in these composites that lead to rising resistance curves. The study hypothesizes tablet sliding as an additional toughening mechanism in “nacre‐like‐separated”, preventing tablet failure and leading to the postponed onset of bulk composite failure. These mechanisms significantly enhance both fracture toughness and ductility by 17.1 and 19 folds, compared to constituent hardened cement paste, respectively. By engineering laser‐induced defects into tabulated cementitious‐elastomeric material at meso‐scale, a class of tough and ductile cementitious composites is introduced, resulting in significantly high fracture toughness values (73.68 MPa.mm1/2), comparable to Ultra‐high‐performance‐concrete without sacrificing the strength.

Experimental and theoretical investigation of the influence of post-curing on mixed mode fracture properties of 3d-printed polymer samples

This study explores the mechanical properties and fracture characteristics of additively manufactured acrylonitrile butadiene styrene specimens, focusing on the impact of raster angle and post-process heat treatment. To this end, a large number of tensile and semi-circular bending samples with three distinct raster angles of 0/90°, 22/ − 68°, and 45/ − 45° were prepared and exposed to four types of heat treatments with different temperature and pressure conditions. Simultaneously, theoretical models of maximum tangential stress (MTS) and generalized MTS (GMTS) were developed to estimate the onset of specimen fracture under mixed-mode in-plane loading conditions. Recognizing the non-linear behavior within the stress–strain curve of tensile test samples, particularly in the annealed samples, an effort was undertaken to transform the original ductile material into a virtual brittle material through the application of the equivalent material concept (EMC). This approach serves the dual purpose of bypassing intricate and tedious elastoplastic analysis, while concurrently enhancing the precision of the GMTS criterion. The experimental findings have revealed that while the annealing process has a minimal effect on the yield strength, it considerably enhances energy absorption capacity, increases fracture toughness, and reduces the anisotropy. Additionally, the combined EMC-GMTS criterion has demonstrated its capability to predict the failure of the additively manufactured parts with an acceptable level of accuracy.

Cracking behavior of brittle materials under eccentric decoupled charge blasting

The decoupled charge structure is often used in controlled blasting. However, in actual engineering scenarios, boreholes are typically horizontal or inclined. The explosive is close to the borehole wall because of gravity action, resulting in an eccentric charge structure. In this study, concentric and eccentric decoupled charge blasting tests were conducted on 250 mm × 250 mm × 150 mm cuboid concrete specimens. The blast-induced fracture propagation behavior was evaluated using digital image correlation (DIC) technology, and surface fracture networks were extracted by image processing to investigate the fractal characteristics. A three-dimensional finite element model was established and verified using experimental data to reveal the influencing mechanism of the coupling medium and eccentricity coefficient on concrete fractures from the energy perspective. Finally, the borehole wall pressure (BWP) and displacement distribution with different charge structures and coupling media are analyzed theoretically, and the application of an eccentric charge structure in smooth blasting is discussed. The results reveal that nonequivalent BWP and displacement are produced in eccentric charge blasting, with a more evident crushed zone appearing on the coupled side owing to the higher energy utilization efficiency of the explosive. Sand had the largest fracture volume fraction ratio between the coupled and decoupled sides, effectively controlling the damage level on the decoupled side. The proposed eccentric decoupled charge-blasting scheme produced directional damage effects in the field test, maximizing the failure of the excavation rock while reducing the damage level to the reserved rock.

Application of non-destructive testing methods for assessing fracture resistance in dental ceramics: the sound harvesting test

IntroductionEvaluating the fracture resistance of dental ceramics such as monolithic zirconia crowns is crucial for assessing their durability. Conventional destructive laboratory tests often fail to accurately evaluate the timing and failing crack formation of these brittle materials. Non-destructive testing methods, such as acoustic emission testing (AET), offers an alternative by providing valuable data on material properties without causing damage to the samples.The in vitro study aimed to evaluate the sensitivity of a sound harvesting modified acoustic emission testing by comparing the fracture resistance of posterior monolithic zirconia crowns (MZCs) measured via the modified set up with that of a conventional fracture toughness test.Material and methodsA modified acoustic emission set up, the sound harvesting test (SHT), featuring a condenser microphone, an amplifier, a custom audio chipset and a cut-off switch integrated into a universal testing machine, was compared to a conventional fracture toughness test to measure fracture loads on 50 posterior monolithic zirconia crowns divided in two groups.ResultsThe sound harvesting test recorded a mean fracture load of 1,108.99 N, significantly less than the 1,292.52 N measured with the conventional test, indicating a more sensitive detection of fractures. Statistically significant differences (p < 0.05) were observed between the two groups.ConclusionDespite its limitations, the study suggests considering sound harvesting testing as an potential alternative for fracture load testing of dental brittle materials due to its ability to identify failures at lower loads enhancing therefore a more accurate evaluation of the behavior of dental materials. However, further testing on a broader range of dental materials is warranted to improve result accuracy and applicability.

Length Scale Insensitive Phase-Field Fracture Methodology for Brittle and Ductile Materials

We present length scale insensitive phase-field fracture models for brittle and ductile fracture to address the deficiencies of widely implemented models which over-estimate crack dissipation. An approach is proposed to attain a regularization length scale insensitive mechanical response, which considers a continuous approximation of a crack boundary with a function of infinite support. This is in contrast to previous approaches to attain a length scale insensitive response which exploited approximations of the crack boundary with functions of finite support. The choice of these functions with finite support creates implementational challenges which are avoided in the presented quasi-brittle and ductile fracture models with infinite support of the phase-field. The capability of these models is demonstrated in several benchmarks with attention given to the sensitivity of the structural response with respect to the choice of regularization length scale. The models are validated against a three-point bending test on a concrete specimen and an in-plane shear test on a steel specimen.

Surface characteristics of precision as-cut NdFeB magnet considering diamond wire wear

NdFeB is the highest output value permanent magnet material at present, which has extremely high magnetic properties and is widely used. In the production process of NdFeB, cutting is an indispensable process, and high precision as-cut surface characteristics can reduce the cost of subsequent processes. In this paper, the single factor sawing experiment of NdFeB was carried out by using the range of processing parameters in industrial production. The effects of workpiece feed speed, saw wire speed, workpiece processing size and diamond saw wire wear on sawing surface morphology, surface material brittleness removal ratio, roughness and waviness were studied. The research shows that the surface characteristics of the workpiece sawed in the stable wear stage of the diamond saw wire are the best. In all service stages of the saw wire, reducing the feed speed and workpiece processing size, and increasing the wire speed will reduce the surface roughness and waviness, reduce the number and size of pits, and reduce the proportion of brittle removal areas. The research results provide an experimental reference for the optimization of diamond wire saw cutting parameters of NdFeB.