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Hareesh V Tippur - One of the best experts on this subject based on the ideXlab platform.
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effect of filler shape volume fraction and loading rate on Dynamic Fracture behavior of glass filled epoxy
Composites Part B-engineering, 2014Co-Authors: Vinod Kushvaha, Hareesh V TippurAbstract:Abstract The effect of filler shape and filler volume fraction on the Dynamic Fracture behavior of particulate polymer composites (PPC) has been studied. Mode-I Dynamic Fracture experiments were carried out on pre-notched glass-filled epoxy. An experimental setup comprising of a gas-gun and a long-bar was used to deliver one-point impact loading to unconstrained specimens. Pulse shapers were utilized to control the loading rate during impact loading. The Dynamic crack initiation and propagation events were captured using high-speed photography (∼300,000 frames per second). Digital Image Correlation (DIC) method was utilized to measure in-plane displacement fields around the crack-tip and extract Fracture parameters including stress intensity factor histories to examine the filler shape, volume fraction and loading rate effects. The results showed a pronounced improvement in crack initiation toughness for rod-shaped fillers producing ∼145% increase over unfilled epoxy at 15% V f with flakes and spherical fillers showing ∼97% and ∼67% improvement, respectively. For all three different volume fractions – 5%, 10%, and 15% – considered, the rod-shaped fillers produced the highest crack initiation toughness as well as post-initiation stress intensity factors followed by flakes and spheres, respectively. A linear relationship between crack initiation toughness and log of filler aspect ratio was also recorded. In addition, for 10% V f rod-shaped filler case, the effect of loading rate on Dynamic Fracture behavior has been examined. The loading rate study showed ∼113% and ∼50% increase in crack initiation toughness for the lowest and the highest loading rate cases, respectively, compared to that of neat epoxy.
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effect of filler particle shape on Dynamic Fracture behavior of glass filled epoxy
2013Co-Authors: Vinod Kushvaha, Hareesh V TippurAbstract:The effect of filler shape and filler volume fraction (micron sized rods, flakes and spheres) on Dynamic Fracture behavior of particulate polymer composites (PPC) is studied. The mode-I Dynamic Fracture experiments are carried out on pre-notched glass-filled epoxy specimens. An experimental set-up comprised of a long-bar apparatus to deliver one-point impact loading to an unconstrained specimen, is used in conjunction with a gas-gun. A controlled stress pulse is delivered to the specimen by impacting the long-bar by a striker launched using a gas-gun. A crack propagates into the specimen Dynamically and is captured using high-speed photography (~300,000 frames per second). Using the Digital Image Correlation (DIC) method, in-plane displacement fields around the crack tip are determined from the speckle images recorded during the Fracture event. With these, Dynamic Fracture toughness histories are evaluated to examine the filler shape effects. The results show pronounced improvement Fracture toughness for all filler types with rod-shaped fillers producing ~145% increase in crack initiation toughness over unfilled epoxy at 15% V f with flakes and spheres showing ~97% and ~67% improvement, respectively.
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Dynamic Fracture behavior of syntactic epoxy foams optical measurements using coherent gradient sensing
Optics and Lasers in Engineering, 2003Co-Authors: Medhat Awad Elhadek, Hareesh V TippurAbstract:Abstract Dynamic Fracture behavior of syntactic foams made of thin-walled microballoons dispersed in epoxy matrix is studied. Monotonically decreasing Dynamic Young's modulus with increasing volume fraction of microballoons is observed using ultrasonic pulse-echo and density measurements. The results are also in good agreement with the Hashin–Shtrikman lower-bound predictions for elastic porous solids. Dynamic crack initiation toughness and crack growth behaviors are examined using instrumented drop-tower tests and optical measurements. Crack initiation toughness shows a linear relationship with Young's modulus over the entire range of volume fraction of microballoons studied. A proposed model based on simple extension of micromechanics prediction agrees well with the measurements. The optical method of coherent gradient sensing (CGS) has been used along with high-speed photography to record crack tip deformation histories in syntactic foam samples subjected to impact loading. Pre- and post-crack initiation events have been successfully captured and apparent Dynamic stress intensity factor histories are extracted from the interferograms. Results suggest increasing crack speeds with volume fraction of microballoons. No significant dependence of Dynamic Fracture toughness on crack speed in any of the volume fractions is observed.
Ted Belytschko - One of the best experts on this subject based on the ideXlab platform.
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Cracking node method for Dynamic Fracture with finite elements
International Journal for Numerical Methods in Engineering, 2009Co-Authors: Jeong-hoon Song, Ted BelytschkoAbstract:A new method for modeling discrete cracks based on the extended finite element method is described. In the method, the growth of the actual crack is tracked and approximated with contiguous discrete crack segments that lie on finite element nodes and span only two adjacent elements. The method can deal with complicated Fracture patterns because it needs no explicit representation of the topology of the actual crack path. A set of effective rules for injection of crack segments is presented so that Fracture behavior beginning from arbitrary crack nucleations to macroscopic crack propagation is seamlessly modeled. The effectiveness of the method is demonstrated with several Dynamic Fracture problems that involve complicated crack patterns such as fragmentation and crack branching. Copyright © 2008 John Wiley & Sons, Ltd.
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element free galerkin methods for static and Dynamic Fracture
International Journal of Solids and Structures, 1995Co-Authors: Ted Belytschko, Mazen R TabbaraAbstract:Abstract Element-free Galerkin (EFG) methods are presented and applied to static and Dynamic Fracture problems. EFG methods, which are based on moving least-square (MLS) interpolants, require only nodal data; no element connectivity is needed. The description of the geometry and numerical model of the problem consists only of a set of nodes and a description of exterior boundaries and interior boundaries from any cracks. This makes the method particularly attractive for growing crack problems, since only minimal remeshing is needed to follow crack growth. In moving least-square interpolants, the dependent variable at any point is obtained by minimizing a function in terms of the nodal values of the dependent variable in the domain of influence of the point. Numerical examples involving fatigue crack growth and Dynamic crack propagation are presented to illustrate the performance and potential of this method.
Kenneth S Vecchio - One of the best experts on this subject based on the ideXlab platform.
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Hopkinson Bar Loaded Fracture Experimental Technique: A Critical Review of Dynamic Fracture Toughness Tests
Applied Mechanics Reviews, 2009Co-Authors: Fengchun Jiang, Kenneth S VecchioAbstract:Hopkinson bar experimental techniques have been extensively employed to investigate the mechanical response and Fracture behavior of engineering materials under high rate loading. Among these applications, the study of the Dynamic Fracture behavior of materials at stress-wave loading conditions (corresponding stress-intensity factor rate ∼106 MPam/s) has been an active research area in recent years. Various Hopkinson bar loading configurations and corresponding experimental methods have been proposed to date for measuring Dynamic Fracture toughness and investigating Fracture mechanisms of engineering materials. In this paper, advances in Hopkinson bar loaded Dynamic Fracture techniques over the past 30 years, focused on Dynamic Fracture toughness measurement, are presented. Various aspects of Hopkinson bar Fracture testing are reviewed, including (a) the analysis of advantages and disadvantages of loading systems and sample configurations; (b) a discussion of operating principles for determining Dynamic load and sample displacement in different loading configurations; (c) a comparison of various methods used for determining Dynamic Fracture parameters (load, displacement, Fracture time, and Fracture toughness), such as theoretical formula, optical gauges, and strain gauges; and (d) an update of modeling and simulation of loading configurations. Fundamental issues associated with stress-wave loading, such as stress-wave propagation along the elastic bars and in the sample, stress-state equilibrium validation, incident pulse-shaping effect, and the “loss-of-contact” phenomenon are also addressed in this review.
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Dynamic Fracture of bovine bone
Materials Science and Engineering: C, 2006Co-Authors: Raghavendra R Adharapurapu, Fengchun Jiang, Kenneth S VecchioAbstract:Abstract True clinical Fracture of bones in bovine, race horses or humans occur predominantly during impact loading (e.g. car accidents, falls or physical violence). Although static Fracture tests provide an estimate of Fracture toughness or R-curve behavior in bones, the static toughness values may be ill suited for predicting failure under Dynamic loading conditions due to the visco-elastic response of bone (i.e. strain rate dependent properties). Despite decades of the study on deformation rate dependency of bone properties such as compression and Fracture toughness, high-quality Dynamic Fracture data remain limited. Preliminary tests (compression and Fracture toughness) have been conducted on dry and wet bovine bone under both static and Dynamic loading conditions. While compression tests have been conducted with loading direction parallel and perpendicular to the bone axis (longitudinal and transverse, respectively), Fracture tests were performed only in the transverse direction. The strain rate in compression tests varied between 10− 3 and 103 s− 1, and the stress intensity rate varied between ∼10− 3 and 105 MPa√m/s. While low strain rate tests were conducted on conventional mechanical testing machines, high strain rate experiments were conducted on a split-Hopkinson bar under compression and a novel three-point bend configuration. The Fracture morphology and the extent of damage of bone in each case were characterized using SEM, and an attempt is made to relate these to the rate dependent Fracture toughness of the bone. It is believed that such understanding is crucial for mechanistic interpretation of bone Fracture phenomenon and eventually for predicting bone failure reliably.
Jay Fineberg - One of the best experts on this subject based on the ideXlab platform.
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instability in Dynamic Fracture
Physics Reports, 1999Co-Authors: Jay Fineberg, Michael P MarderAbstract:Abstract The Fracture of brittle amorphous materials is an especially challenging problem, because the way a large object shatters is intimately tied to details of cohesion at microscopic scales. This subject has been plagued by conceptual puzzles, and to make matters worse, experiments seemed to contradict the most firmly established theories. In this review, we will show that the theory and experiments fit within a coherent picture where Dynamic instabilities of a crack tip play a crucial role. To accomplish this task, we first summarize the central results of linear elastic Dynamic Fracture mechanics, an elegant and powerful description of crack motion from the continuum perspective. We point out that this theory is unable to make predictions without additional input, information that must come either from experiment, or from other types of theories. We then proceed to discuss some of the most important experimental observations, and the methods that were used to obtain the them. Once the flux of energy to a crack tip passes a critical value, the crack becomes unstable, and it propagates in increasingly complicated ways. As a result, the crack cannot travel as quickly as theory had supposed, Fracture surfaces become rough, it begins to branch and radiate sound, and the energy cost for crack motion increases considerably. All these phenomena are perfectly consistent with the continuum theory, but are not described by it. Therefore, we close the review with an account of theoretical and numerical work that attempts to explain the instabilities. Currently, the experimental understanding of crack tip instabilities in brittle amorphous materials is fairly detailed. We also have a detailed theoretical understanding of crack tip instabilities in crystals, reproducing qualitatively many features of the experiments, while numerical work is beginning to make the missing connections between experiment and theory.
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microbranching instability and the Dynamic Fracture of brittle materials
Physical Review B, 1996Co-Authors: Eran Sharon, Jay FinebergAbstract:We describe experiments on the Dynamic Fracture of the brittle plastic, PMMA. The results suggest a view of the Fracture process that is based on the existence and subsequent evolution of an instability, which causes a single crack to become unstable to frustrated microscopic branching events. We demonstrate that a number of long-standing questions in the Dynamic Fracture of amorphous, brittle materials may be understood in this picture. Among these are the transition to crack branching, ``roughness'' and the origin of nontrivial Fracture surface, oscillations in the velocity of a moving crack, the origin of the large increase in the energy dissipation of a crack with its velocity, and the large discrepancy between the theoretically predicted asymptotic velocity of a crack and its observed maximal value. Also presented are data describing both microbranch distribution and evidence of a new three-dimensional to two-dimensional transition as the ``correlation width'' of a microbranch diverges at high propagation velocities. \textcopyright{} 1996 The American Physical Society.
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local crack branching as a mechanism for instability in Dynamic Fracture
Physical Review Letters, 1995Co-Authors: Eran Sharon, Steven P Gross, Jay FinebergAbstract:The motion of a crack in Dynamic Fracture has been shown to be governed by a Dynamical instability causing oscillations in its velocity and structure on the Fracture surface. We present experimental evidence indicating that the mechanism for instability is attempted local crack branching. At the instability onset, a crack will locally change its topology and sprout small, microscopic side branches. The trajectories of these local branches are independent of the crack velocity and exhibit scaling behavior. A connection between microscopic and macroscopic crack branching is established.
T. Kobayashi - One of the best experts on this subject based on the ideXlab platform.
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Evaluation method of Dynamic Fracture toughness by the computer-aided instrumented Charpy impact testing system☆
International Journal of Pressure Vessels and Piping, 2003Co-Authors: Isamu Yamamoto, T. KobayashiAbstract:Abstract The instrumented Charpy impact test has been widely used as a simple method semi-empirically evaluating the material impact toughness. The authors have developed a new Dynamic Fracture tougness evaluation system using a instrumented Charpy impact testing machine aided with a personal computer, which has been called the ‘CAI (Computer-Aided instrumented Charpy Impact testing)’ system. Using the CAI system, Dynamic Fracture toughness such as K d , J d , T mat and various energies can be obtained from the load-deflection curve of a single pre-cracked specimen. In this paper, in addition to the detail of the CAI system, the elastic deformation behaviour of the Charpy testing machine and its correspondence in the CAI system are described.
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Dynamic Fracture toughness of 6061al composites reinforced with sic particulates
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2001Co-Authors: T. Kobayashi, Lihe Qian, Hiroyuki Toda, Zhongguang WangAbstract:Abstract Dynamic Fracture toughness experiments were conducted at room temperature on 6061Al alloy reinforced with 15 and 25% volume fractions of 9.5μm SiC particulates. The Fracture properties were evaluated in terms of crack initiation toughness, crack propagation energy and total absorbed energy. The Dynamic Fracture of the unreinforced 6061Al alloy was also studied as a comparison. The results of Dynamic tests for both composites and matrix alloy are compared with their respective quasi-static cases. It is found that addition of SiC particles can drastically decrease Fracture toughness of 6061Al alloy at both quasi-static and Dynamic loading rates. 15%SiC P composite shows a considerable increase in crack initiation toughness and a much greater increment of crack propagation energy in Dynamic loading case compared with static loading case, whereas 25%SiC P composite exhibits a negligible increment of crack propagation energy and a reduced increase of crack initiation energy in Dynamic case in contrast to 15%SiC P composite. Detailed SEM examination of the Fracture surfaces and optical observation of microstructures beneath the Fracture surfaces of both composites, combined with an in-situ SEM observation, were made to investigate the Fracture processes of the composites.
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introduction of a new Dynamic Fracture toughness evaluation system
Journal of Testing and Evaluation, 1993Co-Authors: T. Kobayashi, Isamu Yamamoto, Mitsuo NiinomiAbstract:Instrumented Charpy impact test has been widely used as a simple method for semi-empirically evaluating material impact toughness. The authors have developed a new instrumented Charpy impact testing system, which is called CAI (Computer Aided instrumented Charpy Impact testing) system. Using the CAI system, Dynamic Fracture toughness parameters such as Kd, Jd, Tmat, and various absorbed energies can be obtained from the load-deflection curve of a single precracked specimen for both ductile and brittle materials. It has been already put into practical use in Japan. This paper introduces the details of the toughness evaluation procedures in the CAI system.
