Fracture Toughness Of Materials Research Articles

High-temperature mechanical properties of ZrB2/SiC/Si3N4 ceramic tool materials with dual composite architectures

ZrB 2 /SiC ceramic granules with uniform a size and spherical shape were prepared by spray drying technology. ZrB 2 /SiC ceramic granules were added into ceramic matrix, and ZrB 2 /SiC/Si 3 N 4 ceramic tool materials with double composite architectures were prepared by spark plasma sintering technology. The mechanical properties from room temperature to 1100°C were measured. The hardness, flexural strength and fracture toughness at room temperature are 18.0 GPa, 589.0 MPa and 5.93 MPa m 1/2 , respectively. While the fracture toughness at 1100°C reach 6.1 MPa m 1/2 increase by 74.3% compared with the ceramic tool material without double composite architectures. At high temperature, the improvement of fracture toughness is due to the addition of ZrB 2 /SiC ceramic granules that deflect the cracks and propagates along the boundary between the granules and the matrix, which greatly increase the path during the crack propagation process, thereby improving the fracture toughness of the ceramic tool material.

The effects of the addition of tetragonal-ZrO2 on the mechanical properties of MgAl2O4 – ZrO2 composites

The effects of the addition of tetragonal 3mol% Y2O3 – ZrO2 into a MgAl2O4 spinel matrix were investigated. MgAl2O4 spinel's lacking mechanical properties prevent further utilization in many structural and refractory applications even though it has excellent chemical and thermal stability. The addition of tetragonal-ZrO2 was observed to improve the hardness, fracture toughness and biaxial flexural strength of MgAl2O4 materials. Moreover, the additions of 3mol% Y2O3 – ZrO2 resulted in a reduction of the mean grain size.

Investigation of Pop-in Formation Mechanism in Fracture Toughness Test of Welded Joint and Improvement of Acceptance Criteria

A pop-in is a small, arrested brittle crack that occurs during a fracture toughness test. This is one of the important factors of the CTOD assessment of a welded joint because the fracture toughness of material differs by the significance of the pop-in. The current standard of the pop-in is said to be too conservative because of the reasons below; the absence of the test methodology which ensures the generation of pop-ins, and the difference of the loading mode between the CTOD test and the real structures. The objective of this study is to investigate the mechanism of the pop-in formation and to improve the pop-in acceptance criteria. This study is aimed to come up with a new standard of pop-in significance determination with the idea of the local critical stress criterion and newly proposed crack propagation model incorporating energy consumption theory. That is, the CZM considering that the critical stress works as the local crack propagation criterion, and the fracture surface energy expressing plastic dissipation beneath the running crack wake is defined in each propagation, has been proposed. When the stress of the crack tip approaches the critical fracture stress, the cohesive strength is lost, and the fracture surface is created. When the cohesive strength is lost, it takes away the fracture surface energy. In the physical aspect, the fracture surface energy is increased as the fracture surface roughness increases. The Charpy test with the three-sided specimen is conducted to find the relationship between the fracture surface roughness and the fracture surface energy. The appropriate value or function of the fracture surface energy is determined by the roughness of the fracture surface and trial and error of the FEM analysis. The result of the FEM analysis is well validated with the experimental data. Finally, the authors calculate many extrapolated conditions of toughness distribution and LBZ width and conclude the current pop-in judgment criterion is too severe and propose a new rational one.

Effect of Addition of Previously-Synthesized Ce-TZP/Al2O3 Submicrometric Powder on the Properties of Al2O3-Based Ceramics

This work investigated the effect of a composite of tetragonal zirconia with alumina-reinforced Ceria (ATZ) previously synthesized, on the properties of alumina-based ceramics (Al2O3). Monolithic alumina powder and Al2O3 powder mixtures containing 5, 10, 15 and 20 wt.% of Ce-TZP/Al2O3 were processed by high energy milling, compacted and then sintered at 1600 °C - 2 h. Sintered pure alumina and composites were characterized by relative density, scanning electron microscopy, X-ray diffraction and surface roughness. Then, the elastic modulus, the Vickers hardness, the fracture toughness and the 4-point flexural strength were evaluated. The results indicated an increase in relative density as a function of the addition of ATZ, with values ​​between 94.3 ± 0.8% and 98.9 ± 0.7%. The observed microstructure after sintering showed tetragonal ZrO2 grains with average sizes of 0.6 μm well dispersed in the Al2O3 matrix, which presents average grain sizes of around 1.5 μm. The crystalline phases identified in the composites were ZrO2-tetragonal and Al2O3 hexagonal. The addition of the composite (ATZ) in the alumina matrix generates a gradual reduction in the elastic modulus (398 ± 15 GPa ~366 ± 34 GPa) and in the hardness (20.5 ± 1 GPa ~17.3 ± 0.7 GPa) of the sintered ceramics. On the other hand, the addition of this same composite (ATZ) in the alumina matrix considerably increases the materials fracture toughness, reaching values of approximately 6.7 ± 0.9 MPa.m1/2. The same trend was observed in the flexural strength results which ranged from 258 MPa (5wt.% Ce-TZP/Al2O3) to 316 MPa (20wt.% Ce,Y-TZP/Al2O3). The Ce-TZP reinforcement acts as a toughening agent of the Al2O3 matrix due to the coupled mechanisms of toughening by zirconia phase transformation, residual stresses due to the difference in thermal expansion of the crystalline phases and differences in microstructural morphologies.

Numerical analysis of fracture toughness in tessellated materials by continuous distributed dislocation technique

In this study, a plane-packed tessellated structure that models the natural structure of living organisms is investigated to find an alternative material that is tougher than currently used materials such as ceramic matrix composites. We generalize a method for generating a plane-packed tessellated structure of a regular polygon with n tips, and develop a numerical procedure for analyzing the stress field in the tessellated structure based on the continuous distributed dislocation (CDD) method. The effects of n and the loading direction, which is defined as the azimuthal angle measured from the side of the polygon, on the fracture toughness values are examined using the fractal dimension D. It is revealed that the crack propagation path deflects significantly as the loading angle approaches the value of 2-nπ/2n. The deflected crack shape is also characterized using D. It is discovered that D and the fracture toughness value vary with similar trends with the loading angle. The relationship between the polygon shape and loading angle shows that the fracture toughness increases with D, which characterizes the complexity of the crack path, and the number of vertices in the polygon. Therefore, it can be concluded that controlling D and the plane geometry can effectively improve the fracture toughness of materials.

Experimental study on fracture toughness of quenched and tempered and TMCP high strength steels

In this study, the fracture toughness of five kinds of high strength steel (HSS) with the nominal yield strength of 550 MPa, 690 MPa and 890 MPa were experimentally studied. Two steel delivery conditions, i.e., quenched and tempered HSS and thermo-mechanical control process HSS, were included and compared. The effect of heat input on the fracture toughness of HSS was investigated. A comparative study was organized for the fracture toughness of base material (BM), heat-affected zone (HAZ) and weld metal (WM). Results indict that the fracture toughness of the heat-affected zone of QT steels (QT550 and QT690) first increases and then decreases slightly with the increase of heat input. There is an optimal heat input for quenched and tempered HSS welding to achieve satisfactory fracture toughness. Either too small or large heat input is not beneficial to the resistance to crack propagation. With increase of steel strength, it seems the optimal heat input for quenched and tempered HSS becomes smaller. The effect of heat input on fracture toughness of TMCP HSS is different with quenched and tempered HSS: higher heat input would normally produce higher fracture toughness for HSS TMCP550. With the increase of yield strength, the fracture resistance increases for both quenched and tempered HSS and TMCP HSS.

Unveiling the brittleness of hybrid organic–inorganic 0-D histammonium zinc chlorometallate by nanoindentation

Hybrid organic–inorganic halometallates, with different organic and inorganic components, can provide a wide array of tunable physical properties. While many optoelectronic phenomena are being explored, research on the mechanical properties of this class of materials, especially fracture toughness, is lacking, resulting in conclusions on material flexibility being drawn from their elastic modulus and hardness alone with an implicit assumption that these properties correlate with material flexibility. In this Letter, we report nanoindentation results on the elastic modulus, hardness, and fracture toughness of single crystal samples of hybrid organic–inorganic histammonium chlorozincate, HistZnCl4 along the [001] axis. We find that the elastic modulus is 12.078 ± 1.034 GPa, and the hardness is 0.611 ± 0.089 GPa. Moreover, the fracture toughness of this sample is measured to be 0.098 MPa m12. Although these materials have a hardness to modulus ratio similar to that of metals, they fracture like brittle materials, demonstrating the importance of conducting studies on a material fracture toughness before determining their applicability in flexible device applications.

Nano-scale fracture toughness of fly ash incorporated hydrating cementitious composites using experimental nanoindentation technique

Instrumented nanoindentation technique has proven its strength by providing incredible insight into the material microstructure of homogeneous materials. Its success has led to its implementation in heterogenous materials such as cementitious composites. The implementation of instrumented nanoindentation on cement paste composites has proven to be very fruitful as it has enabled the evaluation of fundamental properties including Young’s modulus, hardness, creep at multiscales. However, there are more complex properties like fracture toughness which are crucial to characterize the material at macro scales. This characterisation would be benefitted by studies at micro-, nano- scales of the complex properties; but they are seldom reported. Cement-based materials have extremely complex, multiscale structures that are initiated from the chemical reactions of the hydration process and then continue to evolve with time. Also, preparing the surface of hydrating cementitious composites requires special consideration as it can greatly affect the indentation results. To explore the microstructural composition and its fracture toughness, an experimental grid nanoindentation protocol has been put forward. This experimental protocol has been implemented on three cement pastes, i.e., plain Ordinary Portland Cement (OPC), OPC + 20% fly ash, and OPC + 40% fly ash during their early stages as well as near complete stages of hydration. Since measuring the micro cracks around the indent is virtually near impossible, the load vs. displacement curves recorded by the indentations have been utilized in an energy-based method to evaluate the energy release rate and fracture toughness. The evaluated values of fracture toughness property of the individual microstructural phases will help in shedding a light on the development and spread of fracture toughness in cement-based materials. In this study the different methods for fracture toughness evaluation at the micro scales using nanoindentation technique are reported on and the method suitable for cementitious materials is implemented to evaluate fracture toughness of the microstructural phases.

A suitable mixed mode I/II test specimen for fracture toughness study of polyurethane foam with different cell densities

Rigid foam materials are among the low strength structural components that can be failed catastrophically under mechanical loads. Low fracture toughness is therefore a major failure mode in these materials and researchers try to find suitable testing methods for determining the fracture toughness of foam materials. In this research a suitable test specimen that is an edge notch disc bend specimen subjected to asymmetric three-point bending and called Asymmetric Edge Notch Disc Bend (AENDB) is proposed for conducting mixed mode I/II fracture experiments on polyurethane (PUR) foam with different cell densities. The geometry factors of the specimen that are required for determining the stress intensity factors were determined by means of the finite element analyses for different mode mixities. The mixed mode I/II fracture toughness envelope and fracture initiation angle were obtained for the (AENDB) specimen made of three foam densities ranging from 100 to 300 kg/m3. For example, KIc and KIIc values were varied in the ranges 0.08–0.31 MPa.m0.5 and 0.09–0.34 MPa.m0.5, respectively. It was observed that the fracture toughness data are increased for all mode mixities by increasing the foam density. However, the mixed mode fracture curve and fracture initiation directions obtained from the AENDB specimen were lower than the corresponding curves of other mixed mode I/II test samples such as asymmetric semi-circular bend (ASCB) specimen. This can be attributed to the plane strain condition that is obtained at the mid-section of the AENDB specimen, since the crack front length in the AENDB specimen is significantly greater than the ASCB specimen. Finally, the experimental results obtained from the AENDB specimen were predicted using two fracture criterions. The results of this research indicate that the suggested AENDB specimen is a good candidate mixed mode I/II fracture configuration for investigating foam and other similar cellular materials.

On the role of fracture process zone size in specifying fracturing mechanism under dominant mode [formula omitted] loading

The double-edge notched Brazilian disk (DNBD) test is used to investigate the failure mechanism of the polymeric material of polymethyl-methacrylate (PMMA) under dominant shear loading. It has previously been shown that DNBD is a simple and efficient test for measuring shear fracture toughness of rock materials. However, the results in this study show that a tension-based fracturing type prevails in the DNBD samples of PMMA. To predict the type of failure, the previously proposed fracture type (FT) criterion was employed. It is shown that the FT criterion is able to accurately predict the fracturing type, the fracture initiation load and the kink angle of the DNBD specimens. In addition, a comparison made between the results of the DNBD tests of PMMA and rock samples demonstrates the main reason for the different observed fracturing types. Thanks to a large fracture process zone in rocks, DNBD samples of rock materials fail with self-planar extension of cracks due to shear stresses. In contrast, due to small fracture process zone in PMMA, the DNBD samples of PMMA show tension-based failure mechanism with the formations of kinks. As the final discussion, an incremental finite element simulation is used to justify the reason behind the stable tension-based crack growth in the DNBD specimens of PMMA, and to predict the crack propagation trajectory.

Development of Mode I and Mode II fracture toughness of cemented paste backfill: Experimental results of the effect of mix proportion, temperature and chemistry of the pore water

Despite the comprehensive understanding of the development of the modes I & II fracture toughness of brittle materials, the evolution of the fracture toughness of cemented paste backfill (CPB) under different conditions remains unknown. Given the importance of modes I & II fracture toughness in analyzing the fracture initiation and propagation, many semi-circular CPB samples (with different water-cement (w/c = 6.5, 7.35, 8) ratios, cement contents (3%, 4.5%, 6%), curing temperatures (2 °C, 20 °C, 35 °C) and sulphate contents (0 ppm, 5000 ppm, 15000 ppm, 25000 ppm)) are prepared and subjected to semi-circular bending (SCB) test after being cured for 3 days, 7, 14, and 28 days. Irrespective of the mixing recipe or the curing conditions, all samples for mode I fracture toughness measurement generally experience a sudden failure, while the cracks in the samples for measuring the mode II fracture toughness propagate gradually. The obtained results show that a decrease of w/c ratio contributes to the modes I & II fracture toughness acquisition. Besides, owing to the acceleration effect of temperature on the cement hydration and the self-desiccation, the modes I & II fracture toughness of CPB increases with temperature as well. However, the effects of sulphate ions on the growth of the modes I & II fracture toughness of CPB depend on the initial sulphate content and the curing age. In other words, there is a competition effect between the factors contributing to the fracture toughness increase (refinement of the capillary structure by cement hydration products) and decrease (inhibition of the cement hydration by sulphate ions). The findings of this study provide critical information in the stability assessment of CPB structures, which is beneficial to the improvement of the mining safety.

Effect of build orientation and raster pattern on the fracture behavior of carbon fiber reinforced polymer composites fabricated by additive manufacturing

Additive manufacturing (AM) process parameters highly affect the mechanical and fracture properties of additively manufactured carbon fiber reinforced polymer (CFRP) composites. In this work, we study the effect of two process parameters, including build orientation (XYZ, XZY, and ZXY) and raster pattern ( ± 45º and 0º/90º), on the fracture behavior of the CFRP composites fabricated by fused filament fabrication (FFF). The mode I fracture toughness and effective fracture energy of the CFRP composite materials are measured on compact tension samples. The crack growth direction in the FFF-fabricated CFRP composites is found to be controlled by both build orientation and raster pattern. The fracture toughness of the examined CFRP material is sensitive to build orientation, while the effective fracture energy reveals significant dependence on both build orientation and raster pattern. The samples fabricated with the XYZ and ZXY build orientations exhibit 5-fold greater effective fracture energy than the ones with the XZY build orientation. A wide range of fracture energy dissipation mechanisms, including fiber-bridging and fiber pull-out, are identified depending on the process parameters. The reported fracture trends in this study have the potential to provide guidelines for the development of FFF-fabricated CFRP composites with high fracture resistance.

Fracture Toughness of Layered Materials with a Hardened Surface Layer

Fracture Toughness of Layered Materials with a Hardened Surface Layer

Mode I fracture toughness of Carbon/glass hybrid comopsite

Mode I fracture toughness of carbon/ glass reinforced polyster hybrid composite was invesitigated expermrntally and numerically by using the cosmos)/m 2.6 finite element software (fms) by utulizing the hand laup techniqe)(HLU). The single edge notch bending (SENB) test was developed to evalute the mode l fracture toughness of carbon composites, glass composite and hybrid compodite materials at varuos fiber configurations. Scaning electron microscope (SEM) was used to examine the fracture surface of the hybrid composite material under the effect of mode l loading. the expermental result showed the maximum stress intensity (sif) factor 882mpa. mm1/2. obtained in the hybrid composite with stacking dequencess (c/g/g/c) during the mode l loading compared to other stacking sequences. this is attributed to the goid interfical between the carbon and glass fibers and matrix face. From the resukts, it was suggested that the expermental results is a goid a gremnent with the finite element modelling

A comparative study on the comminution behavior of diorite rocks

In this article factors that affect the comminution behavior of heterogeneous diorite rocks obtained from two quarry locations in Botswana were investigated. Diorite rocks are in great abundance in Botswana and they are increasingly viewed as a relatively inexpensive and reliable alternative construction material to sustain the infrastructure growth in Botswana. The diorite rock samples collected from both the Central and North-Eastern districts were studied for structural similarities and mineral composition. These two are the main factors that influence material hardness, fracture toughness and particle size distribution (PSD) following breakage, which are important material properties in construction applications (Barry & James, 2016). The aim of the investigation was to comminute and compare the behavior of the rock sample types, under similar experimental conditions in a laboratory jaw crusher as well as in a planetary ball mill. The product PSD was used to theoretically determine and compare power requirements. The experimental results show that the diorite rock sample collected from the central region required 41.58 KWht-1 while the one collected from the north-eastern region required 38.33KWht-1 to fragment from a particle feed in the -50 + 40 mm size range to a product in the -11.2 + 6.3 mm size range, which is a typical construction aggregate size range. The diorite sample collected from the central district was largely characterized by amorphous phase constituents and high silicate/quartz content (12.4%) while the north-eastern diorite was characterized by a high crystalline phase percentage and lower silicate/quartz composition (6.94%). The experimental results show that inherent diorite rock properties play a significant role in determining cost of production and product application in the quarry industry of Botswana.

Fracture and strength of single-atom-thick hexagonal materials

The fracture toughness has been theoretically and experimentally estimated for few of various two-dimensional (2D) materials. Relationship between the fracture toughness and other mechanical properties of 2D hexagonal materials is extremely needed for a quick estimation in engineering applications, as well as for a better comprehension of their fracture properties. The present work investigates through molecular dynamics simulations at room temperature the mode-I fracture of 25 single-atom-thick hexagonal materials with the buckling height-bond length ratio in the range from 0 through ∼0.6, including 6 planar sheets (graphene, boronitrene, SiC, GeC, AlN and InN) and 19 buckled sheets (silicene, InP, SiGe, SnSi, SnGe, SnO, GeO, SiO, blue-P, arsenene, GeS, SnS, antimonene, bismuthene, SiTe, SnSe, SiSe, GeTe and SnTe). Fracture mechanism is considered. With this large data set and based on dimensional analysis, an empirical formula is established to estimate the mode-I fracture toughness from the elastic modulus, intrinsic tensile strength, bond length and buckling height of a single-atom-thick hexagonal material with reasonable accuracy. This simple formula provides quick estimation of the fracture toughness and is useful for engineering applications.

Effect of erbium doping on phase composition, mechanical and thermal properties of ZrO2-based ceramics

ErxTi0.1Zr0.9–xO2–1.5x (x = 0.04, 0.05, 0.06, 0.07, 0.08) ceramics were synthesized by a solid-state reaction method. The influence of the Er3+ addition on the phase composition, Vickers hardness, fracture toughness, and thermal conductivity of this ceramic material was investigated. The X-ray diffraction results reveal that the c-ZrO2 content increases from 1.85 vol% to 33.89 vol%, and the percentage of t-ZrO2 decreases from 98.15 vol% to 66.11 vol% with the increase in Er3+ content from 4 mol% to 8 mol%. Moreover, the addition of Er3+ is beneficial to the volume expansion of the unit cell. At the same time, the incorporation of Er3+ weakens the coordination of oxygen ions around the metal cations, resulting in a corresponding decrease in the tetragonality of the t-ZrO2. The Vickers hardness and fracture toughness of the ErxTi0.1Zr0.9–xO2–1.5x ceramics show increasing and decreasing trends, respectively. The thermal conductivity has a significant decline due to point defects caused by the Er3+ doping. The 8ETZ ceramic exhibits the highest Vickers hardness (12.7 GPa), the lowest fracture toughness (7.6 MPa⋅m1/2), and the lowest average thermal conductivity (1.85 W/(m·K)) in the temperature range of 200–1000 °C. All of the above properties are higher than those of the Y2O3-stabilized ZrO2 ceramic.

Prediction of fracture toughness of metallic materials

Fracture toughness is a measurement of fracture resistance and is a crucial parameter in designing and manufacturing structural engineering components, including the components of ships and offshore structures. However, accurate measurement of fracture toughness requires a fatigue pre-cracked specimen which can be challenging to prepare in extremely brittle materials. Moreover, specimen thickness is another requirement which can be challenging to achieve as well, particularly in very tough materials. Therefore, a physics-based closed-form analytical expression is proposed to determine fracture toughness of isotropic materials simply by utilizing a uniaxial tensile test specimen. The expression naturally introduces a length scale parameter, consistent with non-local applications, such as peridynamics, as well. Fracture toughness of various metallic materials, including both brittle and ductile, are predicted and compared to the experimental results in the literature. Predicted fracture toughness values are in good agreement with the experimentally measured ones.

Experimental study on Mode-I fracture toughness using Chevron Straight-notched Semi-circular Bend (CSNSCB) method

Rock fracture toughness is an important parameter for the engineering geological design. In this present study, chevron straight-notched semi-circular bend (CSNSCB) specimens with wide-flat liner chevron ligament (Type-A) and long-narrow liner chevron ligament (Type-B) were designed and prepared using wire cutting method. Mode-I fracture toughness KIC values and dimensionless stress intensity factor Y* were calculated. Moreover, these two types rock failure properties and KIC values variation features were both analyzed. The obtained results indicate that the width of precast artificial crack is small which can ensure the flatness and symmetry of cutting plane and then the tested Stress Intensity Factor (SIF) which has smaller deviation is more accurate and reliable. The Y* values for each type of configuration were calculated using Finite Element Method (FEM) and Slice Synthesis Method (SSM) and they firstly had a decreased trend and then an increased trend with the increasing of normalized crack length α, which represent the transition from stable crack propagation (α > αm) to unstable crack propagation (α < αm). Compared to Type-A specimens, Type-B specimens had the calculated minimum dimensionless stress intensity factor Y*min with smaller deviation and average KIC values with smaller variation coefficients. Moreover, Type-A specimen has the average fractal dimension D value of 1.2209 which is 4.79% larger than that of 1.1651 for Type-B specimen, indicating its more complex crack generation and rougher fracture surfaces. That is to say, Type-B specimen has the advantages of small crack FPZ and crack propagation without deviation as well as smooth fracture surface. Since it can offset the harmful influence of rock anisotropy and good crack guided effect, its KIC value is much satisfactory and closer to the true fracture toughness of rock-like materials.

A Modified Compact Tension Test for Characterization of the Intralaminar Fracture Toughness of Tri-Axial Braided Composites.

The application of braided composite materials in the automotive industry requires an in-depth understanding of the mechanical properties. To date, the intralaminar fracture toughness of braided composite materials, typically used for describing post-failure behavior, has not been well-characterized experimentally. In this paper, a modified compact tension test, utilizing a relatively large specimen and a metallic loading frame, is used to measure the transverse intralaminar fracture toughness of a tri-axial braided composite. During testing, a relatively long fracture process zone ahead of the crack tip was observed. Crack propagation could be correlated to the failure of individual unit cells, which required failure of bias-yarns. The transverse interlaminar fracture toughness was found to be two orders of magnitude higher than the reference interlaminar fracture toughness of the same material. This is due to the fact, that intralaminar crack propagation requires breaking of fibers, which is not the case for interlaminar testing.