Fracture Toughness (fracture + toughness)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Terms modified by Fracture Toughness

  • fracture toughness value

  • Selected Abstracts


    On the Fracture Toughness of Advanced Materials

    ADVANCED MATERIALS, Issue 20 2009
    Maximilien E. Launey
    Abstract Few engineering materials are limited by their strength; rather they are limited by their resistance to fracture or fracture toughness. It is not by accident that most critical structures, such as bridges, ships, nuclear pressure vessels and so forth, are manufactured from materials that are comparatively low in strength but high in toughness. Indeed, in many classes of materials, strength and toughness are almost mutually exclusive. From a fracture-mechanics perspective, the ability of a microstructure to develop toughening mechanisms acting either ahead or behind the crack tip can result in resistance-curve (R-curve) behavior where the fracture resistance actually increases with crack extension; the implication here is that toughness is often developed primarily during crack growth and not for crack initiation. Biological materials are perfect examples of this; moreover, they offer microstructural design strategies for the development of new materials for structural applications demanding combinations of both strength and toughness. [source]


    Effect of Heating Schedule on the Microstructure and Fracture Toughness of ,-SiAlON,Cause and Solution

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2002
    Misha Zenotchkine
    The effect of heating schedule on microstructure and fracture resistance has been investigated in single-phase Nd-, Y-, and Yb-,-SiAlON. Such effect is strongly system dependent, reflecting the strong influence of phase stability on ,-SiAON nucleation and the amount of transient/residual liquid during processing. The addition of 1% of ,-SiAlON seeds to the starting powders nearly completely obliterates such effect, while it simultaneously improves microstructure homogeneity and fracture resistance. SENB toughness of 7 MPam1/2 and peak R -curve toughness of ,11 MPam1/2 have been obtained for seeded Y-,-SiAlON ceramics using heating rates from 1C/min to 25C/min. [source]


    Relationship between Microstructure and Fracture Toughness of Toughened Silicon Carbide Ceramics

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2001
    Sung-Gu Lee
    Different microstructures in SiC ceramics containing Al2O3, Y2O3, and CaO as sintering additives were prepared by hot-pressing and subsequent annealing. The microstructures obtained were analyzed by image analysis. Crack deflection was frequently observed as the toughening mechanism in samples having elongated ,-SiC grains with aspect ratio >4, length >2 ,m, and grain thickness (t) <3 ,m (defined as key grains 1). Crack bridging was the dominant toughening mechanism observed in samples having grains with thickness of 1 ,m < t < 3 ,m and length >2 ,m (key grains 2). The values of fracture toughness varied from 5.4 to 8.7 MPam1/2 with respect to microstructural characteristics, characterized by mean grain thickness, mean aspect ratio, and total volume fraction of key grains. The difference in fracture toughness was mainly attributed to the amount of key grains participating in the toughening processes. [source]


    Comparison of Methods to Determine the Fracture Toughness of Three Glass-Ceramics at Elevated Temperatures

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2000
    Janet B. Quinn
    Two standardized methods for measuring kIc in ceramics are compared for use at high temperatures (precracked beam and surface crack in flexure). Results from a third technique involving the measurement of cracks around Vickers indentations are also presented. Three dental glass-ceramics, differing primarily in microstructure, were used as model materials in this study. They emphasized the importance of microstructure in determining high-temperature kIc values and the challenges in measuring them. The measured fracture toughnesses decreased with temperature and increased with imbedded grain size for all three methods. [source]


    Increase in the fracture toughness and bond energy of clay by a root exudate

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2008
    B. Zhang
    Summary Root exudates help drive the formation of the rhizosphere by binding soil particles, but the underlying physical mechanisms have not been quantified. This was addressed by measuring the impact of a major component of root exudates, polygalacturonic acid (PGA), on the interparticle bond energy and fracture toughness of clay. Pure kaolinite was mixed with 0, 1.2, 2.4, 4.9 or 12.2 g PGA kg,1 to form test specimens. Half of the specimens were washed repeatedly to remove unbound PGA and evaluate the persistence of the effects, similar to weathering in natural soils. Fracture toughness, KIC, increased exponentially with added PGA, with washing increasing this trend. In unwashed specimens KIC ranged from 54.3 2.5 kPa m,1/2 for 0 g PGA kg,1 to 86.9 4.7 kPa m,1/2 for 12.2 g PGA kg,1. Washing increased KIC to 61.3 1.2 kPa m,1/2 for 0 g PGA kg,1 and 132.1 4.9 kPa m,1/2 for 12.2 g PGA kg,1. The apparent bond energy, ,, of the fracture surface increased from 5.9 0.6 J m,2 for 0 g kg,1 to 12.0 1.1 J m,2 for 12.2 g kg,1 PGA in the unwashed specimens. The washed specimens had , of 13.0 1.9 J m,2 for 0 g kg,1 and 21.3 2.6 J m,2 for 12.2 g PGA kg,1. Thus PGA, a major component of root exudates, has a large impact on the fracture toughness and bond energy of clay, and is likely to be a major determinant in the formation of the rhizosphere. This quantification of the thermodynamics of fracture will be useful for modelling rhizosphere formation and stability. [source]


    Fracture behaviour of PC/ABS resin under mixed-mode loading

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 12 2001
    Husaini
    Fracture behaviour of polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) under mixed-mode loading conditions was studied for several weight fractions of PC and ABS. Mode I and mixed-mode fracture tests were carried out by using compact,tension,shear specimens. At a certain value of mixed-mode loading ratio KII,/KI, a crack of the shear type will initiates at the initial crack tip. Fracture toughness increases under mixed-mode loading with an increase in the mode II component, whereas it reduces with the appearance of a shear-type fracture. Fracture toughness and the appearance of a shear-type fracture depends on the blending ratio of PC and ABS. The transition to shear-type fracture occurs at lower value of KII,/KI for resins with higher fracture toughness. [source]


    Fracture toughness of modified dental resin systems

    JOURNAL OF ORAL REHABILITATION, Issue 8 2003
    R. E. Kerby
    summary This study compared the relative fracture toughness of a Bis-GMA//TEGDMA (50:50 wt%)-based resin system modified by 5, 10, and 15 wt% of a methacrylate-terminated poly(butadiene-acrylonitrile-acrylic acid) terpolymer toughening agent. After storage in distilled water at 37 2 C for 7 days, plane strain fracture toughness (KIC) was determined on an Instron testing machine at a 05-mm min,1 displacement rate. The glass transition temperature (Tg) in C was determined after 7 days (dry and wet) storage by thermomechanical analysis. The results of this study showed significantly improved fracture toughness and lowered water sorption with the modified resin systems which was indicated by higher wet glass transition temperatures. [source]


    Mechanical Properties of Monoclinic Zirconia

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2004
    Jens Eichler
    Fracture toughness and fracture strength data are presented for the first time for monoclinic zirconia. An undoped nanocrystalline zirconia powder was sintered at 1100C and yielded a theoretical density of more than 90% with a grain size of about 150 nm. The surface crack in flexure (SCF) technique was deemed most suitable for nanocrystalline materials. Measurements of Young's modulus and the determination of the fracture origin are also provided. [source]


    Solid-Solution Effects of a Small Amount of Nickel Oxide Addition on Phase Stability and Mechanical Properties of Yttria-Stabilized Tetragonal Zirconia Polycrystals

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2003
    Hiroki Kondo
    Stability and mechanical properties of the tetragonal phase were investigated for NiO-doped yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) systems. Only 0.3 mol% of NiO in solid solution could be added to the Y-TZP while maintaining the tetragonal phase. Fracture toughness improved remarkably on addition of a small amount of NiO. Raman spectroscopy analysis around cracks introduced by Vickers indentation revealed that the amount of monoclinic phase transformed from tetragonal phase was increased. It was confirmed that fracture toughness improvement was due not only to increased grain size, but also to Y-TZP destabilization by solid solution of NiO. [source]


    Simultaneous Synthesis and Densification of Titanium Nitride/ Titanium Diboride Composites by High Nitrogen Pressure Combustion

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2002
    Masachika Shibuya
    Composites of TiN/TiB2 were synthesized by a combustion process of BN, Ti in a nitrogen atmosphere. The effect of the BN/Ti ratio and the nitrogen gas pressure on the synthesis of these composites was investigated. Dense TiN/TiB2 composites with relatively high hardness and toughness were fabricated by combustion synthesis from Ti and BN under a nitrogen pressure of 4.0 MPa. The Vickers microhardness of the products obtained from reactants with a BN/Ti mole ratio of 0.11 increased with an increase in nitrogen pressure and had a maximum value of ,25 GPa. Fracture toughness, KIC, of the products increased from 3.1 to 5.9 MPam1/2 as the BN/Ti ratio increased from 0.11 to 0.20. However, products formed under nitrogen pressures higher than 6.0 MPa exhibited circumferential macrocracks due to thermal shock. [source]


    Effects of rubber-rich domains and the rubber-plasticized matrix on the fracture behavior of liquid rubber-modified araldite-F epoxies

    POLYMER ENGINEERING & SCIENCE, Issue 11 2000
    Keqin Xiao
    The fracture behavior of a bisphenol A diglycidylether (DGEBA) epoxy, Araldite F, modified using carboxyl-terminated copolymer of butadiene and acrylonitrile (CTBN) rubber up to 30 wt%, is studied at various crosshead rates. Fracture toughness, KIC, measured using compact tension (CT) specimens, is significantly improved by adding rubber to the pure epoxy. Dynamic mechanical analysis (DMA) was applied to analyze dissolution behavior of the epoxy resin and rubber, and their effects on the fracture toughness and toughening mechanisms of the modified epoxies were investigated. Scanning electron microscopy (SEM) observation and DMA results show that epoxy resides in rubber-rich domains and the structure of the rubber-rich domains changes with variation of the rubber content. Existence of an optimum rubber content for toughening the epoxy resin is ascribed to coherent contributions from the epoxy-residing dispersed rubber phase and the rubber-dissolved epoxy continuous phase. No rubber cavitation in the fracture process is found, the absence of which is explained as a result of dissolution of the epoxy resin into the rubber phase domains, which has a negative effect on the improvement of fracture toughness of the materials. Plastic deformation banding at the front of precrack tip, formed as a result of stable crack propagation, is identified as the major toughening process. [source]


    Effect of Decrease of Hydride-Induced Embrittlement in Nanocrystalline Titanium,

    ADVANCED ENGINEERING MATERIALS, Issue 8 2010
    M.A. Murzinova
    Abstract The room-temperature impact toughness, strength and ductility of nanocrystalline (NC) and microcrystalline (MC) titanium with hydrogen content ranging from 0.1 to 16,at.-% (0.002 to 0.450,wt.-%) are studied. NC titanium has higher strength and lower sensitivity to hydride-induced brittle fracture than the MC material. In contrast to MC titanium, the elongation and impact toughness in the NC material does not decrease dramatically with increasing hydrogen content. Moreover, the fracture toughness in hydrogenated NC condition is found to be higher than that in MC titanium. This unusual result may be associated with the precipitation of equiaxial nanoscale hydrides in the interior of ,-grains in the NC material, while platelet hydrides are formed in MC titanium. One can expect that the risk of hydride-induced embrittlement is lower in NC than in MC titanium, making the NC material attractive for potential application under conditions that may cause hydrogen saturation above the permissible level for MC titanium. [source]


    Three-Dimensional Printing of Complex-Shaped Alumina/Glass Composites,

    ADVANCED ENGINEERING MATERIALS, Issue 12 2009
    Wei Zhang
    Abstract Alumina/glass composites were fabricated by three-dimensional printing (3DP) and pressureless infiltration of lanthanum-alumino-silicate glass into sintered porous alumina preforms. The preforms were printed using an alumina/dextrin powder blend as a precursor material. They were sintered at 1600,C for 2,h prior to glass infiltration at 1100,C for 2,h. The influence of layer thickness and sample orientation within the building chamber of the 3D-printer on microstructure, porosity, and mechanical properties of the preforms and final composites was investigated. The increase of the layer thickness from 90 to 150,m resulted in an increase of the total porosity from ,19 to ,39,vol% and thus, in a decrease of the mechanical properties of the sintered preforms. Bending strength and elastic modulus of sintered preforms were found to attain significantly higher values for samples orientated along the Y -axis of the 3D-printer compared to those orientated along the X - or the Z -axis, respectively. Fabricated Al2O3/glass composites exhibit improved fracture toughness, bending strength, Young's modulus, and Vickers hardness up to 3.6,MPa m1/2, 175,MPa, 228,GPa, and 12,GPa, respectively. Prototypes were fabricated on the basis of computer tomography data and computer aided design data to show geometric capability of the process. [source]


    Increase in the fracture toughness and bond energy of clay by a root exudate

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2008
    B. Zhang
    Summary Root exudates help drive the formation of the rhizosphere by binding soil particles, but the underlying physical mechanisms have not been quantified. This was addressed by measuring the impact of a major component of root exudates, polygalacturonic acid (PGA), on the interparticle bond energy and fracture toughness of clay. Pure kaolinite was mixed with 0, 1.2, 2.4, 4.9 or 12.2 g PGA kg,1 to form test specimens. Half of the specimens were washed repeatedly to remove unbound PGA and evaluate the persistence of the effects, similar to weathering in natural soils. Fracture toughness, KIC, increased exponentially with added PGA, with washing increasing this trend. In unwashed specimens KIC ranged from 54.3 2.5 kPa m,1/2 for 0 g PGA kg,1 to 86.9 4.7 kPa m,1/2 for 12.2 g PGA kg,1. Washing increased KIC to 61.3 1.2 kPa m,1/2 for 0 g PGA kg,1 and 132.1 4.9 kPa m,1/2 for 12.2 g PGA kg,1. The apparent bond energy, ,, of the fracture surface increased from 5.9 0.6 J m,2 for 0 g kg,1 to 12.0 1.1 J m,2 for 12.2 g kg,1 PGA in the unwashed specimens. The washed specimens had , of 13.0 1.9 J m,2 for 0 g kg,1 and 21.3 2.6 J m,2 for 12.2 g PGA kg,1. Thus PGA, a major component of root exudates, has a large impact on the fracture toughness and bond energy of clay, and is likely to be a major determinant in the formation of the rhizosphere. This quantification of the thermodynamics of fracture will be useful for modelling rhizosphere formation and stability. [source]


    Microstructures and Mechanical Properties of Hot-Pressed ZrB2 -Based Ceramics from Synthesized ZrB2 and ZrB2 -ZrC Powders,

    ADVANCED ENGINEERING MATERIALS, Issue 3 2009
    Wei-Ming Guo
    The influence of ZrC on the microstructure and mechanical properties of ZrB2 -SiC ceramics was investigated. SEM observation showed that the presence of ZrC greatly inhibited the grain growth of ZrB2 and SiC phases. With the introduction of ZrC, the Vickers' hardness, fracture toughness, and bending strength of the sintered ceramics increased significantly. [source]


    Properties of ZrB2 -Reinforced Ternary Composites,

    ADVANCED ENGINEERING MATERIALS, Issue 9 2004
    D. Sciti
    Different amounts of ZrB2 particles are added to a matrix constituted by AlN+SiC for the production of novel electro-conductive composites by hot pressing. The presence of ZrB2 particles makes the composites electro-conductive and improves many relevant mechanical properties, such as toughness, hardness and strength. The new materials can reach a fracture toughness of 4 MPa.m1/2 and strength of 504 MPa at 1400C. [source]


    Microstructure and Properties of an HfB2 -SiC Composite for Ultra High Temperature Applications,

    ADVANCED ENGINEERING MATERIALS, Issue 5 2004
    F. Monteverde
    An ultra-high-temperature ceramic (UHTC) based on HfB2 was produced. The microstructure consisted of fine and regular diboride grains (2 ,m average size), with SiC particulate distributed intergranularly, not rarely in clustered formation, and low levels of secondary phases were identified. The resulting thermo-mechanical properties proved interesting results for microhardness and fracture toughness. The microstructural alteration experienced within the explored temperature range renders the material unsuitable for service in extreme conditions of temperature and pressure. [source]


    Determination of the Gurson,Tvergaard damage model parameters for simulating small punch tests

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2010
    I. I. CUESTA
    ABSTRACT The objective of the final small punch test (SPT) is to determine the fracture properties of materials, such as fracture toughness, when not enough material is available for the conduct of conventional fracture tests. The damage model developed by Gurson, and subsequently modified by Tvergaard and Needleman (GTN), allows for the numerical simulation of the elastic-plastic behaviour until fracture. This model is based on several constitutive material parameters that must be calibrated if the model is to be properly applied. In this paper, we develop a consistent methodology for the identification of the GTN damage parameters based on the adjustment of the load-displacement curve obtained in the SPTs. The methodology presented is applicable to simulating other different SPTs with different thicknesses and test temperatures. Also, the three-dimensional modelling developed will be useful in the future for analysing the possible anisotropy exhibited by some materials. The next step in the simulation will be to determine its validity in other stress fields with different triaxiality ratios, like the one present in CT specimens, the ultimate goal being to allow for the estimation of the material fracture toughness. [source]


    Study of influence of notch root radius on fracture behaviour of extra deep drawn steel sheets

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 12 2009
    V. V. CHAUDHARI
    ABSTRACT Fracture tests are carried out on extra deep drawn steel CT specimens containing notches with different values of notch root radius (,= 0.07,0.75 mm). Experimental findings clearly show a critical notch root radius (,c) below which the fracture toughness remains independent of , and above which it varies linearly with ,. The 3D finite element analysis shows that the location of maximum stress level causing crack initiation is in the vicinity of notch tip. The maximum stress level is independent of ,; however, its location is shifted away from notch tip along unbroken ligament length with increase in ,. [source]


    Strength recovery of machined Al2O3/SiC composite ceramics by crack healing

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 12 2007
    M. ONO
    ABSTRACT Alumina is used in various fields as a machine component. However, it has a low fracture toughness, which is a weakness. Thus, countless cracks may be initiated randomly by machining, and these cracks decrease the component's mechanical properties and reliability. To overcome this problem, a crack-healing ability could be a very useful technology. In this study, Al2O3/SiC composite was sintered. This alumina exhibits excellent crack-healing ability. Small specimens for a bending test were made from the Al2O3/SiC. A semicircular groove was machined using a diamond ball-drill. The machining reduced the local fracture stress from approximately 820,300 MPa. The machined specimens were crack-healed under various conditions. The fracture stress of these specimens after crack healing was evaluated systematically from room temperature (RT) to 1573 K. It was found that the local fracture stress of the machined specimen recovered almost completely after crack healing. Therefore, it was concluded that crack healing could be an effective method for improving the structural integrity of machined alumina and reducing machining costs. [source]


    Predicting the J integral fracture toughness of Al 6061 using the small punch test

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9 2007
    E. BUDZAKOSKA
    ABSTRACT The 6000 series aluminium alloys (Al,Mg,Si systems) are commonly used as medium-strength structural materials; in particular, the 6061 (Al,1Mg,0.6Si) alloy is widely utilized as a general-purpose structural material due to its excellent formability and corrosion-resisting capabilities. The objective of this study was to obtain a correlation between the small punch (SP) test estimated equivalent fracture strain (,qf) and fracture toughness (J1C) property for 6061 aluminium, and determine its viability as a non-destructive fracture toughness test technique for remaining life assessment of in-service components. Samples of 6061-T6 aluminium were cut from bulk plate, in both the longitudinal and transverse directions, for the as-received condition as well as subjected to three different over-ageing heat-treatment schedules. A strong linear correlation between valid J1C and SP estimated biaxial fracture strain ,qf is presented for aluminium 6061 at room temperature. [source]


    The effect of gentamicin sulphate on the fracture properties of a manually mixed bone cement

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 6 2007
    M. BALEANI
    ABSTRACT This work investigates the effect of adding gentamicin, an antibiotic, on the fracture properties of bone cement. Endurance limit, fatigue crack propagation and fracture toughness were determined for a polymethylmethacrylate-based cement, containing 10% w/w of barium sulphate as radiopacifying agent, and the same formulation modified by the addition of 4.22% w/w of gentamicin sulphate. The antibiotic does not affect the endurance limit nor the fracture toughness of the material. There are significant differences in the parameters of the Paris' law fitting the crack growth data: once the main crack is nucleated, it initially propagates at a lower rate but thereafter accelerates faster in gentamicin loaded bone cement. Despite this difference, the growth rate for the same stress intensity factor remains of the same order of magnitude in both formulations. The addition of 4.22% w/w of gentamicin sulphate to radiopaque bone cement has a negligible total effect on the fracture properties of the material. [source]


    Cleavage fracture of RPV steel following warm pre-stressing: micromechanical analysis and interpretation through a new model

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9-10 2006
    S. R. BORDET
    ABSTRACT In this paper, the warm pre-stress (WPS) effect on the cleavage fracture of an 18MND5 (A533B) RPV steel is investigated. This effect, which describes the effective enhancement of the cleavage fracture toughness at low temperature following a prior loading at high temperature, has received great interest in light of its significance in the integrity assessment of structures, such as nuclear pressure vessels, subjected to thermal transients. Several loading cycles between room temperature (RT) and ,150 C are considered: Load-Unload-Cool-Fracture (LUCF), Load-Cool-Fracture (LCF) and Load-Cool with Increasing K-Fracture (LCIKF). All experiments complied with the conservative principle, which states that no fracture will occur if the applied stress intensity factor (SIF) decreases (or is held constant) while the temperature at the crack-tip decreases, even if the fracture toughness of the virgin material is exceeded. The experimental results indicate that an effective WPS effect is present even at small pre-load (Kwps= 40 MPa,m), and that a minimum critical slope (,,K/,T) in the LCIKF cycle has to be exceeded to induce cleavage fracture between RT and ,150 C. Numerical modelling was performed using mixed isotropic and kinematic hardening laws identified on notched tensile (NT) specimens, tested in tension to large strains (up to 40%), followed by large compressive strains. Detailed microstructural investigations on compact tensile (CT) and NT fracture test specimens were performed so as to determine the nature of the cleavage initiation sites, as well as the local mechanical conditions at fracture. Based on this local information, a new cleavage model was calibrated and applied to predict the probability of cleavage fracture after WPS: it is shown that the predictions are in good agreement with the experimental results. [source]


    Theoretical crack path prediction

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1-2 2005
    H. A. RICHARD
    ABSTRACT In many practical cases, the crack growth leads to abrupt failure of components and structures. For reasons of a reliable quantification of the endangerment due to sudden fracture of a component, therefore, it is of enormous importance to know the threshold values, the crack paths and the growth rates for the fatigue crack growth as well as the limiting values for the beginning of unstable crack growth (fracture toughness). This contribution deals with the complex problem of a,however initiated,crack, that is subjected to a mixed-mode loading. It will present the hypotheses and concepts, which describe the superposition of Mode I and Mode II (plane mixed mode) as well as the superposition of all three modes (Mode I, II and III) for spatial loading conditions. Those concepts admit a quantitative appraisal of such crack situations and a characterization of possible crack paths. [source]


    Modelling ductile fracture behaviour from deformation parameters in HSLA steels

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2004
    S. SIVAPRASAD
    ABSTRACT In this work, an attempt is made to model the ductile fracture behaviour of two Cu-strengthened high strength low alloy (HSLA) steels through the understanding of their deformation behaviour. The variations in deformation behaviour are imparted by prior deformation of steels to various predetermined strains. The variations in parameters such as yield strength and true uniform elongation with prior deformation is studied and was found to be analogous to that of initiation fracture toughness determined by independent method. A unique method is used to measure the crack tip deformation characterized by stretch zone depth that also depicted a similar trend. Fracture toughness values derived from the stretch zone depth measurements were found to vary in the same fashion as the experimental values. A semiempirical relationship for obtaining ductile fracture toughness from basic deformation parameters is derived and model is demonstrated to estimate initiation ductile fracture toughness accurately. [source]


    Enhancement of fracture toughness due to energy screening effectin the early stages of non-elastic failure

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2003
    M. P. WNUK
    ABSTRACT A triaxiality-dependent cohesive zone model for a stationary and a quasistatic crack is proposed. The model is rooted in the mesomechanical approach to Fracture Mechanics and is inspired by the quantum law concerning emission of light, which was postulated by Max Planck at the end of the 19th century. The model provides an extension of the early concepts of Barenblatt, Dugdale and the Bilby,Cotrell,Swinden team. It also incorporates the experimental observations of the pre-fracture states due to Panin and his school in Tomsk. Relations between micro- and macroparameters that characterize the deformation and fracture processes in dissipative media are described in detail. The analysis suggests that the ratio of the ,true' work of fracture to the total energy dissipated during the course of the irreversible deformation contained within the end zone can be used as a measure of material resistance to a quasistatically propagating fracture. [source]


    Experimental techniques for fracture instability toughness determination of unidirectional fibre metal laminates

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2002
    E. M. CASTRODEZA
    ABSTRACT The aim of this work is to propose procedures for the measurement of the fracture toughness of fibre metal laminates (FMLs) reinforced with unidirectional fibres of aramid or glass. Experimental techniques for fracture toughness evaluation by using Compact (C(T)) and Single-Edge Bend (SE(B)) specimens obeying ASTM standards are introduced. Procedures from the standard for thick metallic materials were modified in order to overcome problems, which can arise when testing FMLs , that is, specimen buckling, indentations and crack growth in planes other than the plane of the fatigue pre-crack or notch. The methodology proposed was experimentally tested leading to satisfactory results. [source]


    Mechanical and microstructural investigations into the crack arrest behaviour of a modern 2Cr-1 Mo pressure vessel steel

    FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2001
    E. Bouyne
    Tests were performed on a 2 Cr,1 Mo steel to measure the fracture toughness at initiation, KIc and at arrest, KIa,. The results were compared with those obtained on another pressure vessel steel (A508) of similar strength. Two techniques were used to measure KIa,: (i) isothermal compact crack arrest (CCA) tests, and (ii) specially designed thermal shock experiments using an externally notched ring. These specimens were cooled to ,196 C and then heated by induction in the centre of the ring to produce very steep thermal gradients. This caused crack initiation from the notch. The crack propagates very rapidly (,500 m s,1,) and stopped when it reached the warmer region of the specimen. The specimens were analysed using an elastic,plastic finite element method to determine KIa values. These tests reveal a greater temperature shift (,100 C) between KIc and KIa in 2 Cr,1 Mo steel than in A508 steel. Detailed metallographical examinations of the micromechanisms of crack propagation and arrest in the 2 Cr,1 Mo steel showed that this involves the nucleation of a three-dimensional network of cleavage microcracks which change their direction at bainitic packet boundaries. The remaining uncracked ligaments between the cleavage microcracks break by ductile rupture mechanism [source]


    Nanostructure Fracturing: Brittle-to-Ductile Transition in Uniaxial Compression of Silicon Pillars at Room Temperature (Adv. Funct.

    ADVANCED FUNCTIONAL MATERIALS, Issue 15 2009
    Mater.
    On page 2439, F. stlund et al. report on an interesting effect observed during the compression of sub-micrometer silicon pillars; a critical diameter separates pillars that are observed to crack from pillars that exhibit metal-like ductility. This observation allows for the development of a quantitative method for measuring the fracture toughness of such structures, which can be used to predict and explain small-volume fracture behavior. [source]


    Brittle-to-Ductile Transition in Uniaxial Compression of Silicon Pillars at Room Temperature

    ADVANCED FUNCTIONAL MATERIALS, Issue 15 2009
    Fredrik stlund
    Abstract Robust nanostructures for future devices will depend increasingly on their reliability. While great strides have been achieved for precisely evaluating electronic, magnetic, photonic, elasticity and strength properties, the same levels for fracture resistance have been lacking. Additionally, one of the self-limiting features of materials by computational design is the knowledge that the atomistic potential is an appropriate one. A key property in establishing both of these goals is an experimentally-determined effective surface energy or the work per unit fracture area. The difficulty with this property, which depends on extended defects such as dislocations, is measuring it accurately at the sub-micrometer scale. In this Full Paper the discovery of an interesting size effect in compression tests on silicon pillars with sub-micrometer diameters is presented: in uniaxial compression tests, pillars having a diameter exceeding a critical value develop cracks, whereas smaller pillars show ductility comparable to that of metals. The critical diameter is between 310 and 400,nm. To explain this transition a model based on dislocation shielding is proposed. For the first time, a quantitative method for evaluating the fracture toughness of such nanostructures is developed. This leads to the ability to propose plausible mechanisms for dislocation-mediated fracture behavior in such small volumes. [source]