The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
R. O. Ritchie - One of the best experts on this subject based on the ideXlab platform.
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a novel approach to developing biomimetic nacre like metal compliant phase nickel alumina ceramics through coextrusion
Advanced Materials, 2016Co-Authors: R. O. Ritchie, Ryan P Wilkerson, Bernd Gludovatz, Jeremy Lee Watts, Antoni P Tomsia, Gregory E HilmasAbstract:: Bioinspired "brick-and-mortar" alumina ceramics containing a nickel compliant phase are synthesized by coextrusion of alumina and nickel oxide. Results show that these structures are coarser yet exhibit exceptional resistance-Curve Behavior with a fracture toughness three or more times higher than that of alumina, consistent with significant extrinsic toughening, from crack bridging and "brick" pull-out, in the image of natural nacre.
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fracture toughness and crack resistance Curve Behavior in metallic glass matrix composites
Applied Physics Letters, 2009Co-Authors: Maximilien Launey, Douglas C Hofmann, Jinyo Suh, Henry Kozachkov, William L Johnson, R. O. RitchieAbstract:Nonlinear-elastic fracture mechanics methods are used to assess the fracture toughness of bulk metallic glass (BMG) composites; results are compared with similar measurements for other monolithic and composite BMG alloys. Mechanistically, plastic shielding gives rise to characteristic resistance-Curve Behavior where the fracture resistance increases with crack extension. Specifically, confinement of damage by second-phase dendrites is shown to result in enhancement of the toughness by nearly an order of magnitude relative to unreinforced glass.
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crack growth resistance Curve Behavior in silicon carbide small versus long cracks
Journal of the American Ceramic Society, 2005Co-Authors: C J Gilbert, J J Cao, L C De Jonghe, R. O. RitchieAbstract:Crack-growth resistance-Curve (R-Curve) Behavior for small ( 3 mm) through-thickness cracks is examined in two silicon carbide (SiC) ceramics that have sharply contrasting fracture properties. The first, an in-situ toughened material designated ABC-SiC fails by intergranular fracture, whereas the second, a commercial SiC (Hexoloy SA), fails by transgranular cleavage. In the former microstructure, hot pressing with aluminum, boron, and carbon additives yields a network of plate-shaped grains, and the presence of an amorphous grain-boundary film that is {approximately}1 nm thick promotes debonding and crack deflection. The resultant grain bridging generates R-Curve toughening; in contrast, no evidence of crack-tip shielding is observed in Hexoloy SA. R-Curve Behavior has been evaluated using two techniques for the different crack-length regimes: a small-crack R-Curve has been deconvoluted from indentation-strength data and a long-crack R-Curve has been directly measured using fatigue-precracked, disk-shaped compact-tension specimens. Although Hexoloy SA fails catastrophically at <3 MPa{center_dot}m{sup 1/2}, ABC-SiC exhibits much-improved flaw tolerance with significant rising R-Curve Behavior and a steady-state fracture toughness of {approximately}9 MPa{center_dot}m{sup 1/2} after crack extension of {approximately}600 {micro}m. In ABC-SiC, however, differences in the Behavior of long and small cracks exist for crack sizes of less than {approximately}120 {micro}m, withmore » the small-crack measurements demonstrating much-reduced crack-growth resistance; this effect is not observed in Hexoloy SA. Microstructural sources of this Behavior are discussed.« less
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mechanistic aspects of fracture and r Curve Behavior in human cortical bone
Biomaterials, 2005Co-Authors: Ravi K Nalla, Jamie J. Kruzic, J H Kinney, R. O. RitchieAbstract:An understanding of the evolution of toughness is essential for the mechanistic interpretation of the fracture of cortical bone. In the present study, in vitro fracture experiments were conducted on human cortical bone in order to identify and quantitatively assess the salient toughening mechanisms. The fracture toughness was found to rise linearly with crack extension (i.e., rising resistance- or R-Curve Behavior) with a mean crack-initiation toughness, K0 of approximately 2 MPa square root m for crack growth in the proximal-distal direction. Uncracked ligament bridging, which was observed in the wake of the crack, was identified as the dominant toughening mechanism responsible for the observed R-Curve Behavior. The extent and nature of the bridging zone was examined quantitatively using multi-cutting compliance experiments in order to assess the bridging zone length and estimate the bridging stress distribution. Additionally, time-dependent cracking Behavior was observed at stress intensities well below those required for overload fracture; specifically, slow crack growth occurred at growth rates of approximately 2 x 10(-9) m/s at stress intensities approximately 35% below the crack-initiation toughness. In an attempt to measure slower growth rates, it was found that the Behavior switched to a regime dominated by time-dependent crack blunting, similar to that reported for dentin; however, such blunting was apparent over much slower time scales in bone, which permitted subcritical crack growth to readily take place at higher stress intensities.
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Fracture toughness and R-Curve Behavior of laminated brittle-matrix composites
Metallurgical and Materials Transactions A, 1998Co-Authors: D. R. Bloyer, R. O. Ritchie, K. T. Venkateswara RaoAbstract:The fracture toughness and resistance-Curve Behavior of relatively coarse-scale, niobium/niobium aluminide (Nb/Nb_3Al) laminated composites have been examined and compared to other Nb/Nb_3Al composites with ( in situ ) Nb particulate or microlaminate reinforcements. The addition of high aspectratio Nb reinforcements, in the form of 20 vol. pct of 50- to 250-µm-thick layers, was seen to improve the toughness of the Nb_3Al intermetallic matrix by well over an order of magnitude, with the toughness increasing with Nb layer thickness. The orientation of the laminate had a small effect on crack-growth resistance with optimal properties being found in the crack arrester, as compared to the crack divider, orientation. The high fracture toughness of these laminates was primarily attributed to large (∼1- to 6-mm) crack-bridging zones formed by intact Nb layers in the crack wake; these zones were of sufficient size that large-scale bridging (LSB) conditions generally prevailed in the samples tested. Resistance-Curve modeling using weight function methods permitted the determination of simple approximations for the bridging tractions, which were then used to make smallscale bridging (SSB) predictions for the steady-state toughness of each laminate.
Jürgen Rödel - One of the best experts on this subject based on the ideXlab platform.
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temperature dependent r Curve Behavior of pb zr1 xtix o3
Acta Materialia, 2013Co-Authors: Yohan Seo, Jürgen Rödel, Emil Aulbach, Malte Vogler, Daniel Isaia, Kyle G WebberAbstract:The crack growth resistance Behavior of polycrystalline Pb(Zr1−xTix)O3 has been characterized in a novel experimental arrangement between 24 and 140 °C. Experimental measurements were carried out on compact tension specimens submerged in a temperature-controlled silicone oil bath. The results show a decrease in the observed shielding toughness, leading to an overall reduction in the maximum toughness. The temperature-dependent stress–strain Behavior and elastic properties were characterized, providing an insight into the effect of the changing ferroelastic properties on the temperature-dependent fracture Behavior.
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ferroelasticity and r Curve Behavior in bifeo3 pbtio3
Journal of the American Ceramic Society, 2006Co-Authors: A Kounga B Njiwa, Stuart L Turner, Jürgen Rödel, Timothy P. Comyn, Emil Aulbach, Andrew J BellAbstract:Stress–strain Curves of (1−x)BiFeO3–xPbTiO3 compositions with x=0.2, 0.3, and 0.35 were determined under uniaxial loading to assess the material's potential for domain switching. The composition with x=0.35 provides the highest remanent strain, with more than 0.2% coupled with a strong tendency to relaxation. This ferroelastic Behavior is in accordance with results from R-Curve measurements on the same compositions, where the material with the most remanent strain yields the highest toughening effect.
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effect of poling direction on r Curve Behavior in lead zirconate titanate
Journal of the American Ceramic Society, 2004Co-Authors: Sergio Luis Dos Santos E Lucato, Doru C Lupascu, Jürgen RödelAbstract:R-Curves of lead zirconate titanate (PZT) have been measured with compact tension (CT) specimens for different poling conditions and grain sizes. Depending on poling direction the plateau value of the R-Curves ranged from 1.13 to 1.54 MPa·m1/2 for a grain size of 6.4 μm and from 1.14 to 1.30 MPa·m1/2 for a grain size of 5.2 μm. Poling in the thickness direction yielded the material with the highest fracture toughness while the direction parallel to the loading direction led to the lowest fracture toughness.
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comparison of r Curves from single edge v notched beam sevnb and surface crack in flexure scf fracture toughness test methods on multilayered alumina zirconia composites
Journal of the American Ceramic Society, 2004Co-Authors: Robert J Moon, Keith J Bowman, Kevin P Trumble, Jürgen RödelAbstract:The single-edge V-notched-beam fracture testing method was used to measure the short-crack R-Curve Behavior of a 90-vol%-alumina–10-vol%-ceria-doped zirconia multilayered composite. The initiation and extension of short cracks from the V-notch tip were observed in situ via optical microscopy. Initial crack lengths of 15–50 μm were obtained repeatedly. The resulting R-Curve was similar to the R-Curve that was measured using the surface-crack-in-flexure testing method. The ability to control the position of the V-notch tip within a material permits study of the influence of specific microscopic features on the fracture Behavior.
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r Curve Behavior in alumina zirconia composites with repeating graded layers
Engineering Fracture Mechanics, 2002Co-Authors: Robert J Moon, Mark Hoffman, Jon Hilden, Keith J Bowman, Kevin P Trumble, Jürgen RödelAbstract:Abstract The single-edge-V-notched-beam testing geometry was used to measure the crack growth resistance (R-Curve) Behavior of multilayer graded alumina–zirconia composites for crack extensions parallel to the graded direction. Fracture mechanics weight function analysis was applied to explain the R-Curve Behavior of a compositional and grain-size graded microstructure. The results were then used to differentiate the influence of residual stress from other closure stresses, attributed to crack bridging, on the measured R-Curve Behavior.
M Heidarirarani - One of the best experts on this subject based on the ideXlab platform.
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delamination r Curve Behavior of Curved composite laminates
Composites Part B-engineering, 2019Co-Authors: A Ghadirdokht, M HeidariraraniAbstract:Abstract The effect of curvature on the delamination R-Curve Behavior of composite unidirectional laminates is investigated in both the experimental and numerical manners. The flat and Curved double cantilever beam specimens with different radii of curvatures are manufactured and tested subjected to mode I loading. A new data reduction method is developed for the Curved specimens by adopting the Timoshenko Curved beam theory. Experimental R-Curves indicate that curvature has no effect on the initiation toughness, while it significantly affects the steady-state toughness and fiber bridging length. Variation of the steady-state toughness and fiber bridging length vs. The different curvatures is formulated for the Curved specimens with R/h > 25 (R/h: the ratio of the radius of curvature to thickness). Finally, delamination propagation is simulated in the Curved double cantilever beam specimens in commercial finite element software, ABAQUS, by applying both the virtual crack closure technique and cohesive zone model.
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effect of interface fiber angle on the r Curve Behavior of e glass epoxy dcb specimens
Theoretical and Applied Fracture Mechanics, 2016Co-Authors: M M Shokrieh, Mazaher Salamattalab, M HeidariraraniAbstract:Abstract In this study, the effect of interface fiber angle on the R-Curve Behavior of double cantilever beam (DCB) specimens made of E-glass/epoxy under mode I loading is investigated experimentally. For this purpose, DCB specimens with stacking sequences of [0 11 /θ//0 12 ] and θ = 0, 30, 45, 90 are manufactured by hand lay-up method. These stacking sequences are chosen to eliminate the effect of remote ply orientation on the R-Curve Behavior of DCB specimens during the delamination propagation. In order to obtain the critical strain energy release rate, fracture tests are conducted on these specimens. Results show that DCB specimens with 0°//0° interface have the lowest initiation interlaminar fracture toughness and the greatest bridging zone length due to good penetration of two adjacent layers of the delamination interface. Moreover, results indicate that the interface fiber angle has significant effect on the steady-state interlaminar fracture toughness as well as the bridging zone length.
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finite element modeling of mode i delamination growth in laminated dcb specimens with r Curve effects
Composites Part B-engineering, 2013Co-Authors: M Heidarirarani, M M Shokrieh, P P CamanhoAbstract:This paper proposes a three-linear cohesive zone model (CZM) to capture the mode I delamination initiation and propagation Behavior of unidirectional DCB specimens under large-scale fiber bridging conditions (R-Curve Behavior). This CZM is produced by superposing two bilinear CZMs and the required parameters are obtained from the experimental R-Curve of a DCB specimen only knowing the initiation fracture toughness (Gi), the fiber bridging length (lFPZ) and the steady state toughness (Gss). The proposed method does not need the measurement of the crack tip opening displacement during the experiments and, therefore, it eliminates the current difficulties of the traditional CZMs in the simulation of delamination propagation under large-scale bridging.
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delamination r Curve as a material property of unidirectional glass epoxy composites
Materials & Design, 2012Co-Authors: M M Shokrieh, M Heidarirarani, M R AyatollahiAbstract:Abstract It is still questionable to think of delamination resistance of a double cantilever beam (DCB) as a material property independent of the specimen size and geometry. In this research, the effects of initial crack length and DCB specimen thickness on the mode I delamination resistance Curve ( R -Curve) Behavior of different unidirectional glass/epoxy DCB specimens are experimentally investigated. It is observed that the magnitudes of initiation and propagation delamination toughness ( G Ic-init and G Ic-prop ) as well as the fiber bridging length are constant in a specific range of the initial crack length to the DCB specimen thickness ratios of 8.5 a 0 / h I delamination Behavior (from the initiation to propagation) of E-glass/epoxy DCB specimens.
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effect of stacking sequence on r Curve Behavior of glass epoxy dcb laminates with 0 0 crack interface
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011Co-Authors: M M Shokrieh, M HeidariraraniAbstract:Abstract In this study, the influence of stacking sequence on mode I delamination resistance (R-Curve) Behavior of E-glass/epoxy laminated composites with an initial delamination between 0°//0° interface is experimentally investigated. To this end, symmetric double cantilever beam (DCB) specimens of stacking sequences; [0°12]s, [(0°/90°)3]2s and [0°/90°/ ± 45°/90°/0°]2s with two initial crack lengths are used. A pronounced R-Curve Behavior is observed on all stacking sequences due to locating delamination between two similar layers. Comparison of R-Curve Behavior of cross-ply and quasi-isotropic DCB specimens with unidirectional (UD) one reveals the significant effect of the non-dimensional coupling parameter, D c = D 12 2 / D 11 D 22 , on the R-Curves. Thus, three main outputs of R-Curves could be summarized as; (a) the initiation delamination toughness (GIc-init) of multidirectional (MD) laminates are much lower than that of UD one, (b) stacking sequence has no effect on the fiber bridging length in DCB specimens, and (c) the greater the Dc value of a laminate, the higher the steady-state propagation toughness (GIc-prop) is.
D K Shetty - One of the best experts on this subject based on the ideXlab platform.
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ζ ta4c3 x a high fracture toughness carbide with rising crack growth resistance r Curve Behavior
Journal of the American Ceramic Society, 2015Co-Authors: Michael Sygnatowicz, Raymond A Cutler, D K ShettyAbstract:The microstructures and mechanical properties of tantalum carbides containing predominantly the ζ-Ta4C3−x phase are compared with the properties of the monocarbide (γ-TaC) and the hemicarbide (α-Ta2C) and two-phase composites. It is shown that a Ta and γ-TaC powder mixture corresponding to a C/Ta at. ratio of 0.66 can be hot-pressed (1800°C, 2 h) to obtain ~95 wt% of ζ-Ta4C3−x with a density of 98% of theoretical. This material has an attractive combination of high fracture toughness (13.8 ± 0.2 MPa√m) and fracture strength (759 ± 24 MPa) with modest hardness (5.6 ± 0.5 GPa). The fracture toughness and strength measured for this material were the highest among all the materials with C/Ta ratio ranging from 0.5 (hemicarbide) to 1.0 (monocarbide). It is also shown that a material containing 86 wt% ζ-Ta4C3−x can be consolidated by pressureless sintering of a hydrogenated Ta and γ-TaC powder mixture without significant drop in density (97% of theoretical) or mechanical properties (13.4 ± 0.2 MPa√m, 700 ± 20 MPa, 6.0 ± 0.4 GPa). Materials containing high weight fraction of the ζ-Ta4C3−x phase exhibited rising crack-growth-resistance (R-Curve) Behavior. Optical and scanning electron microscope observations suggested crack-face bridging was the dominant toughening mechanism. The crack-bridging ligaments were lamellae of the basal planes of the ζ-Ta4C3−x phase produced by their easy cleavage. The thickness of the lamellae ranged from 40 to 2000 nm, significantly less than the grain size.
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r Curve Behavior and flaw insensitivity of ce tzp al2o3 composite
Journal of the American Ceramic Society, 1993Co-Authors: Nageswaran Ramachandran, Luen Yuan Chao, D K ShettyAbstract:A ceria-partially-stabilized zirconia-aiumina (Ce-TZP/Al2O3) composite optimized for transformation toughening was used to demonstrate its flaw insensitivity due to R-Curve Behavior. Four-point bend specimens fabricated with a controlled distribution of spherical pores showed nearly the same characteristic strength and strength variability (Weibull modulus) as specimens fabricated without the artificial pores. In situ observations confirmed stable growth of cracks initiated at pores and the crack lengths at fracture instability were much greater than the pore sizes, thus resulting in fracture strengths insensitive to the pores. The small variability in the fracture strength was found to be associated with variability in the R-Curve and the instability crack lengths. An analysis based on the fracture instability criterion for rising crack growth resistance accounted for the strength variability due to variability in the R-Curve. Comparable four-point bend experiments were also conducted on a sintered yttria-partially-stabilized zirconia (2Y-TZP) ceramic. This ceramic showed significant degradation of strength due to the presence of the pores. This flaw sensitivity is attributed to its steep rising R-Curve over short crack lengths.
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rising crack growth resistance r Curve Behavior of toughened alumina and silicon nitride
Journal of the American Ceramic Society, 1991Co-Authors: Nageswaran Ramachandran, D K ShettyAbstract:R-Curves for a sinter/HIPed SiC(whisker)-reinforced alumina and a sintered silicon nitride were assessed by direct measurements of lengths of cracks associated with Vickers indentation flaws. The fracture toughness measurements based on (a) initial (as-indented) crack lengths, (b) equilibrium growth of cracks during increasing far-field loading, and (c) crack lengths corresponding to unstable fracture showed definitive trends of R-Curves for both materials. The fracture mechanics analyses employed an indenter-material constant that was independently estimated using a physical model for the residual driving force and a free surface correction factor that accounted for the effects of size and shape of the cracks on stress intensity. It is shown that R-Curve estimations based on crack length measurements have the intrinsic advantage that crack length dependence of fracture toughness is not assumed a priori as is done in conventional analysis based on strength. The measured fracture toughness of SiC(whisker)-reinforced alumina was in agreement with the prediction of a toughening model based on crack bridging by partially debonded whiskers.
Jamie J. Kruzic - One of the best experts on this subject based on the ideXlab platform.
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fatigue threshold r Curve Behavior of grain bridging ceramics role of grain size and grain boundary adhesion
Journal of the American Ceramic Society, 2011Co-Authors: Sarah Gallops, Theo Fett, Jamie J. KruzicAbstract:To better understand the role of grain size and grain-boundary adhesion on the fatigue threshold R-Curve Behavior of grain bridging ceramics, a study was conducted on the fatigue threshold Behavior of 99.5% pure polycrystalline alumina with two different microstructures (fine and coarse) and in two different environments (moist air and dry N2). The fine-grained microstructure showed higher fatigue thresholds at short crack sizes, while the coarse-grained microstructure demonstrated higher fatigue thresholds at long crack sizes. The former effect lead to slightly higher calculated fatigue strengths and was attributed to the crack stalling process that leads to earlier elastic bridge formation in that microstructure. The latter effect is attributed to toughening that is dominated by frictional and mechanical interlocking bridges at longer crack sizes where the larger grains are able to give more bridging. By testing the coarse microstructure in a dry environment, a higher K0 was achieved for the glassy grain boundaries giving a higher R-Curve at short crack sizes and higher calculated fatigue strengths.
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r Curve Behavior and micromechanisms of fracture in resin based dental restorative composites
Journal of The Mechanical Behavior of Biomedical Materials, 2009Co-Authors: M B Shah, Jack L Ferracane, Jamie J. KruzicAbstract:Abstract The fracture properties and micromechanisms of fracture for two commercial dental composites, one microhybrid (Filtek™Z250) and one nanofill (Filtek™Supreme Plus), were studied by measuring fracture resistance Curves ( R -Curves) using pre-cracked compact-tension specimens and by conducting both unnotched and double notched four point beam bending experiments. Four point bending experiments showed about 20% higher mean flexural strength of the microhybrid composite compared to the nanofill. Rising fracture resistance was observed over ∼1 mm of crack extension for both composites, and higher overall fracture resistance was observed for the microhybrid composite. Such fracture Behavior was attributed to crack deflection and crack bridging toughening mechanisms that developed with crack extension, causing the toughness to increase. Despite the lower strength and toughness of the present nanofill composite, based on micromechanics observations, large nanoparticle clusters appear to be as effective at deflecting cracks and imparting toughening as solid particles. Thus, with further microstructural refinement, it should be possible to achieve a superior combination of aesthetic and mechanical performance using the nanocluster approach for dental composites.
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r Curve Behavior and toughening mechanisms of resin based dental composites effects of hydration and post cure heat treatment
Dental Materials, 2009Co-Authors: M B Shah, Jack L Ferracane, Jamie J. KruzicAbstract:Abstract Objectives To test the hypothesis that the fracture resistance of two different particulate resin composites degrade after water hydration and improve after post-cure heat treatment, and to correlate those changes with salient failure micromechanisms. Methods Two composites with different filler morphology were selected, denoted microhybrid (Filtek™ Z250) and nanofill (Filtek™ Supreme plus). Following initial light curing, hydrated samples were aged in water for 60 days at room temperature while post-cured samples were heat treated at 120 °C for 90 min. Fracture resistance was assessed using fracture resistance Curves ( R -Curves) utilizing pre-cracked compact tension, C(T), specimens. The flexural strength of the hydrated composites also was evaluated in four-point bending using unnotched beams. Scanning electron microscopy (SEM) of crack paths and fracture surfaces was performed to determine the micromechanisms of fracture and toughening. The results were compared by two-way ANOVA and Tukey's multiple comparison test ( p ≤ 0.05). Results SEM observations revealed a predominantly interparticle matrix crack path for all cases except the hydrated nanofill composite, which showed evidence of particle matrix debonding. Hydration lowered the strength for both composites and the peak toughness for the nanofill composite. The strength decrease was attributed to resin matrix plasticization and hydrolytic degradation in both cases, with additional interfacial degradation causing a larger strength decline and concomitant peak toughness decrease in the nanofill composite. The post-cure heat treatment noticeably changed the R -Curve shape causing the peak toughness to be reached after shorter amounts of crack extension. Such changes help explain the increases in strength reported in other studies and is attributed to improved resin matrix properties. Significance Results from this study provide new insight into the micromechanisms of fracture in resin-based dental composites which should aid the future development and improvement of these materials.
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mechanistic aspects of fracture and r Curve Behavior in human cortical bone
Biomaterials, 2005Co-Authors: Ravi K Nalla, Jamie J. Kruzic, J H Kinney, R. O. RitchieAbstract:An understanding of the evolution of toughness is essential for the mechanistic interpretation of the fracture of cortical bone. In the present study, in vitro fracture experiments were conducted on human cortical bone in order to identify and quantitatively assess the salient toughening mechanisms. The fracture toughness was found to rise linearly with crack extension (i.e., rising resistance- or R-Curve Behavior) with a mean crack-initiation toughness, K0 of approximately 2 MPa square root m for crack growth in the proximal-distal direction. Uncracked ligament bridging, which was observed in the wake of the crack, was identified as the dominant toughening mechanism responsible for the observed R-Curve Behavior. The extent and nature of the bridging zone was examined quantitatively using multi-cutting compliance experiments in order to assess the bridging zone length and estimate the bridging stress distribution. Additionally, time-dependent cracking Behavior was observed at stress intensities well below those required for overload fracture; specifically, slow crack growth occurred at growth rates of approximately 2 x 10(-9) m/s at stress intensities approximately 35% below the crack-initiation toughness. In an attempt to measure slower growth rates, it was found that the Behavior switched to a regime dominated by time-dependent crack blunting, similar to that reported for dentin; however, such blunting was apparent over much slower time scales in bone, which permitted subcritical crack growth to readily take place at higher stress intensities.
