Showing papers on "Fracture toughness published in 2004"
TL;DR: In this article, a series of tests including upsetting tests, shear tests and tensile tests on 2024-T351 aluminum alloy providing clues to fracture ductility for a wide range of stress triaxiality was carried out.
1,644 citations
TL;DR: In this article, double-wall carbon nanotubes (DWCNTs) and an epoxy matrix were produced by a standard calandering technique and a very good dispersion of both DWCNT and carbon black (CB) was observed.
1,455 citations
TL;DR: Microscope investigation and X-ray diffraction revealed the important role played by the tetragonal to monoclinic phase transformation and by the relationship between the glassy matrix and the crystalline phase in the strengthening and toughening mechanisms of these ceramics.
828 citations
TL;DR: In this paper, the authors investigated the mechanics of protein-mineral nanocomposite structure and found that large aspect ratios and a staggered alignment of mineral platelets are the key factors contributing to the large stiffness of biomaterials.
Abstract: Natural biological materials such as bone, teeth and nacre are nanocomposites of protein and mineral with superior strength. It is quite a marvel that nature produces hard and tough materials out of protein as soft as human skin and mineral as brittle as classroom chalk. What are the secrets of nature? Can we learn from this to produce bio-inspired materials in the laboratory? These questions have motivated us to investigate the mechanics of protein–mineral nanocomposite structure. Large aspect ratios and a staggered alignment of mineral platelets are found to be the key factors contributing to the large stiffness of biomaterials. A tension–shear chain (TSC) model of biological nanostructure reveals that the strength of biomaterials hinges upon optimizing the tensile strength of the mineral crystals. As the size of the mineral crystals is reduced to nanoscale, they become insensitive to flaws with strength approaching the theoretical strength of atomic bonds. The optimized tensile strength of mineral crystals thus allows a large amount of fracture energy to be dissipated in protein via shear deformation and consequently enhances the fracture toughness of biocomposites. We derive viscoelastic properties of the protein–mineral nanostructure and show that the toughness of biocomposite can be further enhanced by the viscoelastic properties of protein.
817 citations
TL;DR: In this paper, Zirconium diboride and ZrB 2 ceramics containing 10, 20, and 30 vol% SiC particulates were prepared from commercially available powders by hot pressing.
Abstract: Zirconium diboride (ZrB 2 ) and ZrB 2 ceramics containing 10, 20, and 30 vol% SiC particulates were prepared from commercially available powders by hot pressing. Four-point bend strength, fracture toughness, elastic modulus, and hardness were measured. Modulus and hardness did not vary significantly with SiC content. In contrast, strength and toughness increased as SiC content increased. Strength increased from 565 MPa for ZrB 2 to >1000 MPa for samples containing 20 or 30 vol% SiC. The increase in strength was attributed to a decrease in grain size and the presence of WC.
731 citations
TL;DR: A major revision and update of a set of property charts for natural material published some 8 years ago by Ashby et al. as discussed by the authors with examples of their use to study mechanical efficiency in nature.
Abstract: The materials of nature, for example cellulose, lignin, keratin, chitin, collagen and hydroxyapatite, and the structures made from them, for example bamboo, wood, antler and bone, have a remarkable range of mechanical properties. These can be compared by presenting them as material property charts, well known for the materials of engineering. Material indices (significant combinations of properties) can be plotted on to the charts, identifying materials with extreme values of an index, suggesting that they have evolved to carry particular modes of loading, or to sustain large tensile or flexural deformations, without failure. This paper describes a major revision and update of a set of property charts for natural material published some 8 years ago by Ashby et al. with examples of their use to study mechanical efficiency in nature.
707 citations
TL;DR: In this paper, microencapsulated dicyclopentadiene (DCPD) healing agent and Grubbs' Ru catalyst are incorporated into an epoxy matrix to produce a polymer composite capable of self-healing.
Abstract: Microencapsulated dicyclopentadiene (DCPD) healing agent and Grubbs' Ru catalyst are incorporated into an epoxy matrix to produce a polymer composite capable of self-healing. The fracture toughness and healing efficiency of this composite are measured using a tapered double-cantilever beam (TDCB) specimen. Both the virgin and healed fracture toughness depend strongly on the size and concentration of microcapsules added to the epoxy. Fracture of the neat epoxy is brittle, exhibiting a mirror fracture surface. Addition of DCPD-filled urea-formaldehyde (UF) microcapsules yields up to 127% increase in fracture toughness and induces a change in the fracture plane morphology to hackle markings. The fracture toughness of epoxy with embedded microcapsules is much greater than epoxy samples with similar concentrations of silica microspheres or solid UF polymer particles. The increased toughening associated with fluid-filled microcapsules is attributed to increased hackle markings as well as subsurface microcracking not observed for solid particle fillers. Overall the embedded microcapsules provide two independent effects: the increase in virgin fracture toughness from general toughening and the ability to self-heal the virgin fracture event.
702 citations
TL;DR: Comparing three hot-pressed glass-ceramics and alumina glass-infiltrated ceramics, processed by both slip casting and dry pressing, revealed the relationship between the glass matrix and the crystalline phase and the characteristics of the latter were correlated to the strengthening and toughening mechanisms of these glass- Aceramics.
451 citations
TL;DR: The results of triaxial extension experiments on Carrara marble are presented that show a continuous transition from extension fracture to shear fracture with an increase in compressive stress.
Abstract: Fracture is a fundamental mechanism of material failure. Two basic types of brittle fractures are commonly observed in rock deformation experiments--extension (opening mode) fractures and shear fractures. For nearly half a century it has been hypothesized that extension and shear fractures represent end-members of a continuous spectrum of brittle fracture types. However, observations of transitional fractures that display both opening and shear modes (hybrids) in naturally deformed rock have often remained ambiguous, and a clear demonstration of hybrid fracture formation has not been provided by experiments. Here we present the results of triaxial extension experiments on Carrara marble that show a continuous transition from extension fracture to shear fracture with an increase in compressive stress. Hybrid fractures form under mixed tensile and compressive stress states at acute angles to the maximum principal compressive stress. Fracture angles are greater than those observed for extension fractures and less than those observed for shear fractures. Fracture surfaces also display a progressive change from an extension to shear fracture morphology.
291 citations
TL;DR: The mechanical properties discussed include the deformation behavior of UHMWPE, the yielding associated with quasi-static tension and compression, fracture toughness, cyclic loading, and fatigue resistance.
277 citations
TL;DR: In this paper, a flattened Brazilian disc specimen is used for determination of the elastic modulus E, tensile strength σ t and opening mode fracture toughness K IC for brittle rocks in just one test.
TL;DR: In this paper, the effect of welding cycle on the fracture toughness properties of high-strength low alloy (HSLA) steels is examined by means of thermal simulation of heat-affected zone (HAZ) microstructures.
Abstract: The effect of the welding cycle on the fracture toughness properties of high-strength low alloy (HSLA) steels is examined by means of thermal simulation of heat-affected zone (HAZ) microstructures. Tensile tests on notched bars and fracture toughness tests at various temperatures are performed together with fracture surface observations and cross-sectional analyses. The influence of martensite-austenite (M-A) constituents and of “crystallographic” bainite packets on cleavage fracture micromechanisms is, thus, evidenced as a function of temperature. Three weakest-link probabilistic models (the “Master-curve” (MC) approach, the Beremin model, and a “double-barrier” (DB) model) are applied to account for the ductile-to-brittle transition (DBT) fracture toughness curve. Some analogy, but also differences, are found between the MC approach and the Beremin model. The DB model, having nonfitted, physically based scatter parameters, is applied to the martensite-containing HAZ microstructures and gives promising results.
TL;DR: The successful use of linear elastic fracture mechanics theory in predicting brittle fracture in isotropic domains with cracks is attributed to the successful correlation of a single parameter, namely the stress intensity factor, with experimental observations for the determination of failure initiation or crack propagation as mentioned in this paper.
Abstract: The successful use of linear elastic fracture mechanics theory in predicting brittle fracture in isotropic domains with cracks is attributed to the successful correlation of a single parameter, namely the stress intensity factor, with experimental observations for the determination of failure initiation or crack propagation.
TL;DR: The ex vivo crack-initiation and crack-growth toughness are determined and are found to deteriorate with age; the initiation toughness decreases some 40% over 6 decades from 40 to 100 years, while the growth toughness is effectively eliminated over the same age range.
TL;DR: In this paper, the elastic moduli, biaxial strength and fracture toughness of unreduced (NiO-YSZ) and reduced (Ni-YSZ) anode were determined as functions of porosity.
TL;DR: In this article, the authors presented experimental evidence supporting crack bridging, rather than microcracking, as the most significant mechanism of toughening in cortical bone and dentin.
01 Jan 2004
TL;DR: In this paper, the authors presented experimental evidence supporting crack bridging, rather than microcracking, as the most significant mechanism of toughening in cortical bone and dentin.
Abstract: Two major mechanisms that could potentially be responsible for toughening in mineralized tissues, such as bone and dentin, have been identified—microcracking and crack bridging. While evidence has been reported for both mechanisms, there has been no consensus thus far on which mechanism plays the dominant role in toughening these materials. In the present study, we seek to present definitive experimental evidence supporting crack bridging, rather than microcracking, as the most significant mechanism of toughening in cortical bone and dentin. In vitro fracture toughness experiments were conducted to measure the variation of the fracture resistance with crack extension [resistance– curve (R-curve) behavior] for both materials with special attention paid to changes in the sample compliance. Because these two toughening mechanisms induce opposite effects on the sample compliance, such experiments allow for the definitive determination of the dominant toughening mechanism, which in the present study was found to be crack bridging for microstructurally large crack sizes. The results of this work are of relevance from the perspective of developing a micromechanistic framework for understanding fracture behavior of mineralized tissue and in predicting failure in vivo.
25 Nov 2004-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a convergent lens is used to deliver 1.2-J, 8-ns laser pulses by a Q-switch Nd:YAG laser, operating at 10-Hz.
Abstract: Laser shock processing (LSP) or laser shock peening is a new technique for strengthening metals. This process induces a compressive residual stress field which increases fatigue crack initiation life and reduces fatigue crack growth rate. Specimens of 6061-T6 aluminum alloy are used in this investigation. A convergent lens is used to deliver 1.2 J, 8 ns laser pulses by a Q-switch Nd:YAG laser, operating at 10 Hz. The pulses are focused to a diameter of 1.5 mm onto a water-immersed type aluminum samples. Effect of pulse density in the residual stress field is evaluated. Residual stress distribution as a function of depth is assessed by the hole drilling method. It is observed that the higher the pulse density the larger the zone size with compressive residual stress. Densities of 900, 1350 and 2500 pulses/cm 2 with infrared (1064 nm) radiation are used. Pre-cracked compact tension specimens were subjected to LSP process and then tested under cyclic loading with R = 0.1. Fatigue crack growth rate is determined and the effect of LSP process parameters is evaluated. Fatigue crack growth rate is compared in specimens with and without LSP process. In addition fracture toughness is determined in specimens with and without LSP treatment. It is observed that LSP reduces fatigue crack growth and increases fracture toughness in the 6061-T6 aluminum alloy.
TL;DR: In this article, the concept of effective grain size (d EFF ) is applied to ductile-to-brittle transition temperature, DBTT, for ultrafine ferrite/cementite (Uf-F/C), ferrite-pearlite (F/P), quenched (Q), and quench-and-tempered (QT) microstructures in a low carbon steel.
Abstract: To analyze the good toughness of ultrafine ferrite/cementite steels, the concept of effective grain size (d EFF ) is applied to ductile-to-brittle transition temperature, DBTT, for ultrafine ferrite/cementite (Uf-F/C), ferrite/pearlite (F/P), quenched (Q), and quench-and-tempered (QT) microstructures in a low carbon steel. The d EFF is determined to be 8, 20, 100, and 25 μm for Uf-F/C, F/P, Q, and QT, respectively. In F/P and Q, it is in accordance with the ferrite grain size and the prior austenite grain size, respectively. In QT, the d EFF fits the martensite packet size. In Uf-F/C, the ferrite grain size has a bimodal distribution and the larger grain size corresponds to the d EFF , which is the smallest among the four microstructures. In terms of the relationship between d EFF and DBTT, the Uf-F/C, Q, and QT microstructures can be placed into the same group and the F/P to a different one. Furthermore, the Uf-F/C has the highest estimated fracture stress among the four microstructures. These might be the result of the difference in the surface energy of fracture, namely the former is estimated to have a surface energy of 34.6 J/m 2 and latter a surface energy of 7.7 J/m 2 . Thus, the excellent toughness of the ultrafine ferrite/cementite steel can be attributed to the small d EFF and the high surface energy of fracture.
TL;DR: In this article, the authors used an indentation method to determine the hardness and fracture toughness of coarse-grained, single-phase intermetallics, such as Ag3Sn, AuSn4, Cu3sn, Cu6Sn5 (η and η`), Ni3sn4, Ni3Sn4 and γ-Cu5Zn8, respectively.
Abstract: Many intermetallics, such as Ag3Sn, AuSn4, Cu3Sn, Cu6Sn5 (η and η`), Ni3Sn4, and γ–Cu5Zn8 are present in modern solder interconnects as a result of solder chemistry and/or due to the interfacial reaction between solder and metallization scheme. Coarse-grained, single-phase intermetallics are produced by conventional casting followed by annealing for long time. Ambient temperature isotropic elastic moduli (bulk, Young’s, shear, and Poisson’s ratio) and selected plastic properties (hardness and indentation fracture toughness) of these intermetallics are presented. The isotropic elastic moduli of these intermetallics are determined by the pulse-echo technique. The measured bulk, Young’s and shear moduli lie in the range of 6.3 to 11.4 × 1010 N/m2, 7.1 to 12.3 × 1010 N/m2 and 2.7 to 4.5 × 1010 N/m2, respectively. The hardness and fracture toughness are determined by an indentation method. The loads used for indentation experiments were: 100–10,000 g for Ag3Sn and γ–Cu5Zn8, 10–50 g for AuSn4, 200–1000 g for Cu3Sn, 50–100 g for Cu6Sn5, and 100–200 g for Ni3Sn4. The measured Vickers hardness lies in the range of 50 to 470 Kg/mm2, and the measured indentation fracture toughness lies in the range of 2.5 to 5.7 MPa m1/2. Due to coarse grain size of the specimens, the indentation cracks were contained within one grain. In Cu3Sn, Cu6Sn5 (η and η`) and Ni3Sn4 intermetallics, the indentation cracks were found to be nearly straight and run along the indent diagonal. However, the cracks in AuSn4 showed significant zig-zag and branching phenomena, and they seemed to propagate along particular cleavage plane(s). The presence of slip bands are also observed in AuSn4, Ag3Sn, Cu3Sn, γ-Cu5Zn8, and Ni3Sn4. In the case of Ag3Sn and γ–Cu5Zn8, indentation cracks cannot be induced by applying loads up to 10 kg. Rather, extensive plastic deformation occurs resulting in the formation of a large number of shear/kink bands, and possibly twins, that spread across several grains. At a load of 5000 g or higher, Ag3Sn exhibits grain boundary decohesion near the indents. Among the intermetallics studied, Ag3Sn is shown to be the most ductile.
TL;DR: In this article, a critical review has been performed of the published experimental research concerning delamination onset and growth in composite laminate interfaces of different lay-ups under single-mode loadings, and it was found that the traditional fracture toughness characterization by unidirectionally reinforced composite tests can lead to marked under- or overestimation of material resistance to crack growth.
TL;DR: In this paper, the densification behavior and mechanical properties of B4C hot-pressed at 2000°C for 1 h with additions of Al2O3 up to 10 vol% were investigated.
Abstract: The densification behavior and mechanical properties of B4C hot-pressed at 2000°C for 1 h with additions of Al2O3 up to 10 vol% were investigated. Sinterability was greatly improved by the addition of a small amount of Al2O3. The improvement was attributed to the enhanced mobility of elements through the Al2O3 near the melting temperature or a reaction product formed at the grain boundaries. As a result of this improvement in the density, mechanical properties, such as hardness, elastic modulus, strength, and fracture toughness, increased remarkably. However, when the amount of Al2O3 exceeded 5 vol%, the level of improvement in the mechanical properties, except for fracture toughness, was reduced presumably because of the high thermal mismatch between B4C and Al2O3.
TL;DR: In this article, a miniaturized own nanoindentation and nanoscratch device for use inside a scanning electron microscope is presented, where the indentation axis is operated at an inclined angle with respect to the SEM column.
TL;DR: In this paper, the effects of increasing temperature and confining pressure on the fracture toughness of clay bearing rock, fracture toughness experiments were carried out at temperatures elevated from room temperature up to 200°C using single edge-notched round bar in bending (SENRBB) and semi-circular bend (SCB) specimens of Kimachi sandstone and Tage tuff.
05 Feb 2004-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a Virtual-Internal-Bond (VIB) model was used to model deformation and failure in the nanostructured biocomposite, which incorporated an atomic cohesive force law into the constitutive model of materials.
Abstract: As organic–inorganic hybrid composites, natural biological materials exhibit superior mechanical properties such as toughness and strength in comparison with their constituent phases: the organic phase is usually very soft and the inorganic phase very brittle. Understanding the mechanisms by which nature designs strong composites with weak materials could provide helpful insight and guidance for the development and synthesis of novel materials for industrial applications. In our recent studies on nanostructure of biological materials (Proc. Natl. Acad. Sci. U.S.A. 100 (2003) 5597; Eng. Fract. Mech. 70 (2003) 1777), the nanometer size of mineral platelets is interpreted as a result of strength optimization, in that an intrinsically brittle material reaches the theoretical strength at the nanoscale despite of crack-like flaws. The mineral nanoparticles are embedded in a soft protein matrix, resulting in an organic–inorganic composite with high toughness and strength. The present study is focused on the effects of protein and protein–mineral interface. A Virtual-Internal-Bond (VIB) model, which incorporates an atomic cohesive force law into the constitutive model of materials, is adapted to model deformation and failure in the nanostructured biocomposite. We show that the protein layer can effectively enhance the toughness of biocomposites through crack shielding and impact protection.
TL;DR: In this paper, a 3D finite element analysis was performed to define appropriate stacking sequences for end-notched flexure (ENF) specimens with starter delaminations on θ /− θ and 0°/ θ interfaces.
TL;DR: In this article, the concept of composite construction simultaneously at nano-and macroscopic length scales was explored, and a model system was identified that allows us to test this concept by combining molecular level hybridization using a silsesquioxane epoxy nanocomposite with microscopic modification using core−shell rubber particles.
Abstract: This study explores the concept of composite construction simultaneously at nano- and macroscopic length scales. This approach promises to allow improvement of multiple properties coincidentally but independently. A model system was identified that allows us to test this concept by combining molecular level hybridization using a silsesquioxane epoxy nanocomposite with macroscopic modification using core−shell rubber particles (CSR). The objective here was to form an epoxy resin system with enhanced thermal stability, elastic modulus, and fracture toughness. The nanocomposite was made by reacting octa(dimethylsiloxyethylcyclohexyl epoxide)silsesquioxane (OC, 1.3 nm diameter) with diaminodiphenylmethane (DDM). This resin offers excellent elastic moduli and thermal stabilities at the expense of poor fracture toughness. OC/DDM is a “single phase” hybrid nanocomposite that is used here as a matrix for ≈100 nm diameter CSR reinforcing particles. Characterization of OC/DDM/CSR composites shows that fracture toug...
TL;DR: Post hoc analyses of data from previously tested bovine and antler cortical bone compact specimens demonstrates that, in contrast to crack initiation approach, the crack propagation approach successfully identifies the superior toughness properties of red deer's antlers cortical bone.
TL;DR: In this article, the impact toughness of the cladded metals at a given test temperature is found significantly higher than that of parent plate alone because of the high impact-toughness of 316L austenitic stainless steel layer.
TL;DR: In this article, the authors used nanometer-sized Al2O3 particles (15 nm average diameter) as reinforcements to enhance the fracture toughness of a highly crosslinked, nominally brittle, thermosetting-unsaturated polyester resin.