The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
R D K Misra - One of the best experts on this subject based on the ideXlab platform.
-
impact fracture behavior of clay reinforced polypropylene nanocomposites
Polymer, 2006Co-Authors: Q Yuan, R D K MisraAbstract:Abstract The micromechanism of plastic deformation during impact loading of polypropylene–clay nanocomposites is examined and compared with the unreinforced polypropylene under identical conditions of processing to underscore the determining role of clay. The addition of clay to polypropylene increases the impact strength in the temperature range of 0 to +70 °C. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM) techniques provided an understanding of the micromechanism of plastic deformation in terms of the response of the polymer matrix, nucleating capability of the reinforcement, crystal structure, percentage crystallinity, lamellae thickness, and particle–matrix interface. The enhancement of toughness on reinforcement of polypropylene with nanoclay is associated with change in the primary mechanism of plastic deformation from crazing and vein-type in neat polypropylene to microvoid-coalescence-fibrillation process in the nanocomposite.
-
reduced susceptibility to stress whitening during tensile deformation of calcium carbonate reinforced high density polyethylene composites
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006Co-Authors: M Tanniru, R D K MisraAbstract:Abstract The micromechanism of plastic deformation and susceptibility to stress whitening during tensile straining of 20% calcium carbonate-reinforced polyethylene micrometric composites is investigated and compared with the un-reinforced polyethylene under identical conditions of processing. The adoption of calcium carbonate in polyethylene has two mutually opposite effects: the reinforcement and the nucleating effect. The reinforcement effect increases the bulk crystallinity and modulus, while the nucleating effect decreases the spherulite size and has a negative influence on yield stress, neutralizing the positive influence of increase in percentage crystallinity. The effective reinforcement of polyethylene by calcium carbonate reduces the susceptibility to stress whitening, and is characterized by lower change in gray level in the plastically deformed stress whitened zone in comparison to neat polyethylene. Also, the reinforcement of polyethylene alters the primary micromechanism of plastic deformation and stress whitening from predominantly crazing–tearing in neat polyethylene to wedge/ridge tearing and fibrillation in calcium carbonate-reinforced polyethylene composites. This is related to the cumulative contribution of small spherulite size and the amorphous nature of the interface.
-
on significant retention of impact strength in clay reinforced high density polyethylene hdpe nanocomposites
Polymer, 2006Co-Authors: M Tanniru, Q Yuan, R D K MisraAbstract:Abstract The mechanical response of clay–reinforced polyethylene nanocomposite is investigated and the behavior compared with the un-reinforced polyethylene under identical conditions of processing. The micromechanism of plastic deformation during impact loading of neat polyethylene and clay–reinforced polyethylene nanocomposite are studied with scanning electron microscopy (SEM). The impact strength of composites is linked to structural studies by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM) and SEM observations. The addition of clay to polyethylene retains adequately high-impact strength in the investigated temperature range of −40 to +70 °C. The micromechanism of deformation is altered from a combination of craze and drawing of fibrils in neat polyethylene to microvoid coalescence-fibrillated process in the nanocomposite. The aspects related to micromechanism of deformation are discussed.
-
effect of wollastonite and talc on the Micromechanisms of tensile deformation in polypropylene composites
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004Co-Authors: R S Hadal, Aravind Dasari, Juergen Rohrmann, R D K MisraAbstract:Abstract The work presented here describes the effect of wollastonite and talc on the Micromechanisms of surface deformation and subsequent propagation into the bulk of low and high crystallinity polypropylenes during tensile straining. The potential of high resolution electron microscopy is utilized to examine deformation processes, and develop deformation mechanism maps. While mineral-reinforced polypropylenes exhibited an increase in tensile modulus, yield strength remained unaffected. Crystallization behavior indicated that the reinforcement minerals increase the rate of nucleation with consequent increase in percentage of bulk crystallinity. The reinforcement of polypropylene with wollastonite or talc alters the primary micromechanism of deformation from deformation bands/crazing in neat polypropylenes to wedge/ridge tearing in mineral-reinforced low crystallinity polypropylene composites. However, wedges were absent in high crystallinity polypropylene composites. The final fracture in reinforced polypropylene occurs by a mixed mode consisting of fibrillation and brittle mode, while crazing–tearing and brittle deformation are fracture modes for neat polypropylenes.
-
the role of micrometric wollastonite particles on stress whitening behavior of polypropylene composites
Acta Materialia, 2004Co-Authors: Aravind Dasari, R D K MisraAbstract:The micromechanism and susceptibility to stress whitening during tensile straining of micrometric wollastonite mineral-reinforced polypropylenes is studied by electron microscopy and compared with unreinforced neat polypropylenes. Mineral-reinforced polypropylene composite exhibit significantly reduced susceptibility to stress whitening, and are characterized by lower gray level in the plastically deformed stress whitened zone. This behavior is attributed to the effective reinforcement of polypropylene by wollastonite that acts in concert increasing the tensile modulus of the composite and restricts plastic deformation of the matrix. The increase in tensile modulus is explained in terms of a three-phase model involving matrix, particle, and interface zone. Furthermore, isothermal crystallization indicated that the reinforcement mineral increases the rate of nucleation with consequent increase in % bulk crystallinity. The reinforcement of polypropylene alters the primary micromechanism of stress whitening from deformation bands/crazing in neat polypropylenes to wedge/ridge-tearing in mineral-reinforced polypropylene composites. The final fracture in reinforced polypropylene occurs by a mixed mode consisting of fibrillation and brittle mode, while crazing-tearing and brittle deformation are fracture modes for neat polypropylene.
J Llorca - One of the best experts on this subject based on the ideXlab platform.
-
mechanical behavior and deformation Micromechanisms of polypropylene nonwoven fabrics as a function of temperature and strain rate
Mechanics of Materials, 2014Co-Authors: R Jubera, Alvaro Ridruejo, Carlos Gonzalez, J LlorcaAbstract:Abstract The mechanical behavior and the deformation and failure Micromechanisms of a thermally-bonded polypropylene nonwoven fabric were studied as a function of temperature and strain rate. Mechanical tests were carried out from 248 K (below the glass transition temperature) up to 383 K at strain rates in the range ≈10−3 s−1 to 10−1 s−1. In addition, individual fibers extracted from the nonwoven fabric were tested under the same conditions. Micromechanisms of deformation and failure at the fiber level were ascertained by means of mechanical tests within the scanning electron microscope while the strain distribution at the macroscopic level upon loading was determined by means of digital image correlation. It was found that the nonwoven behavior was mainly controlled by the properties of the fibers and of the interfiber bonds. Fiber properties determined the nonlinear behavior before the peak load while the interfiber bonds controlled the localization of damage after the peak load. The influence of these properties on the strength, ductility and energy absorbed during deformation is discussed from the experimental observations.
-
Micromechanisms of deformation and fracture of polypropylene nonwoven fabrics
International Journal of Solids and Structures, 2011Co-Authors: Alvaro Ridruejo, Carlos Gonzalez, J LlorcaAbstract:The Micromechanisms of deformation and fracture in tension were analyzed in a commercial polypropylene nonwoven geotextile material in a wide range of strain rates. Two different loading scenarios (smooth and notched specimens) were considered to study how these mechanisms are modified in presence of a stress concentration. The nonwoven fabric presented significant deformability and energy-absorption capability, which decreased with the strain rate, together with a high level of strength, which increased with strain rate. In addition, the material was notch-insensitive as the stress concentration around the crack tip was relieved by marked nonlinear behavior, which induced crack blunting. Different experimental techniques (standard mechanical tests, in situ testing within the scanning electron microscope, digital image correlation, etc.) were used to establish the sequence of deformation and failure processes and to link these Micromechanisms with the macroscopic behavior.
-
fatigue of particle and whisker reinforced metal matrix composites
Progress in Materials Science, 2002Co-Authors: J LlorcaAbstract:Abstract The reinforcement of metallic alloys with ceramic particles or whiskers has generated a new family of composite materials. They have matured during the last 20 years, and are currently used in structural components subjected to cyclic loads. This was partially possible thanks to a large research effort aimed at characterizing their behavior in fatigue. The results of this activity constitute a fairly coherent body which relates the Micromechanisms of cyclic deformation to the overall fatigue performance. They are presented in this review, which is divided in seven sections. After the introduction, the microstructural changes induced by the dispersion of the ceramic reinforcements are described. This is followed by two sections devoted to an analysis of the Micromechanisms of cyclic deformation from the microstructural and mechanical viewpoints. The next two sections are focused on the origins of crack nucleation and the kinetics of crack propagation upon cyclic loads. The overall fatigue performance of these composites is examined in the last part, which emphasizes their advantages and limitations as compared to the unreinforced counterparts. The effects of the processing, thermo-mechanical treatments, microstructural features, environmental factors and loading conditions are included in each section to provide a comprehensive picture of the fatigue performance of these composites.
Francesco Iacoviello - One of the best experts on this subject based on the ideXlab platform.
-
damage Micromechanisms in a hot dip galvanized steel
Procedia structural integrity, 2017Co-Authors: Vittorio Di Cocco, Francesco Iacoviello, Laura Dagostino, S NataliAbstract:Abstract: Hot-dip galvanizing is one of the most used methods to apply zinc-based coatings on steels in order to provide sacrificial protection against corrosion over all the steel surface. The aim of this work is the analysis of the hot dip zinc coated steel plates mechanical properties by means of a non-standardized bending test performed minimizing both the bending moment differences along the bending axis and the interactions between the clamping system and the specimen coating. Bending tests are performed both on non-coated and on hot dip zinc coated plates, correlating the measured variables (applied load and crosshead displacement) with the bending moment and the specimen bending angle. Tests are characterised by a good repeatability. Results show that the main damaging mechanisms depend on the different mechanical behaviour of the intermetallic phases and on their thickness. For all the investigated coating conditions, radial cracks are observed. They initiate corresponding to the Γ phase and propagate up to the ζ-η interface. The coating thickness increase implies both an increase of the importance of the cracks in δ and ζ phases and the presence of cracks at ζ-η interfaces.
-
Damaging Micromechanisms in an as cast ferritic and a ferritized ductile cast iron
Procedia Structural Integrity, 2017Co-Authors: Laura D'agostino, Vittorio Di Cocco, Diego Omar Fernandino, Francesco IacovielloAbstract:Abstract: Mechanical behavior and damaging Micromechanisms in Ductile Cast Irons (DCIs) are strongly effected by matrix microstructure (e.g., phases volume fraction, grains size and grain distribution) and graphite nodules morphology peculiarities (e.g., nodularity level, nodule size, nodule count, etc.). The influence of the graphite nodules depends on both the matrix microstructure and the loading conditions (e.g., quasi-static, dynamic or cyclic loadings). According to the most recent results, these graphite nodules show a mechanical properties gradient inside the graphite nodules, with the graphite elements – matrix debonding as only one of the possible damaging Micromechanisms. In this work, two different ferritic DCIs were investigated (a ferritic matrix obtained from as-cast condition and a ferritized matrix) focusing on the damaging Micromechanisms in graphite nodules due to tensile stress. Specimens lateral surfaces were observed using a Scanning Electron Microscope (SEM) during the tests following a step by step procedure.
-
fatigue crack propagation and overload damaging Micromechanisms in a ferritic pearlitic ductile cast iron
Fatigue & Fracture of Engineering Materials & Structures, 2016Co-Authors: Francesco Iacoviello, Vittorio Di Cocco, M CavalliniAbstract:Recently discovered (1948), ductile cast irons (DCIs) are able to combine the good castability of grey irons with the interesting mechanical properties, both static and cyclic, of carbon steels, allowing to directly produce components with complex shape that are requested to be characterized by high mechanical performances, especially considering toughness and fatigue resistance. DCIs mechanical properties and damaging Micromechanisms depend on the matrix (ferritic, pearlitic, ferrite pearlitic, ausferritic, etc.) and on the graphite nodules morphological peculiarities (shape, dimension, distribution, etc.). In this work, the fatigue-crack propagation Micromechanisms in a ferritic–pearlitic DCI were investigated, focusing both the role played by the microstructure and the contribution of the graphite nodules. In addition, the overload effects on the composite microstructure of the investigated ferritic–pearlitic DCI were analysed.
-
fatigue crack tip damaging Micromechanisms in pearlitic ductile cast irons
Fatigue & Fracture of Engineering Materials & Structures, 2015Co-Authors: Francesco Iacoviello, Vittorio Di Cocco, Alessandra Rossi, M CavalliniAbstract:In the last years, damaging Micromechanisms in ductile cast irons (DCIs) were widely investigated: DCI microstructure (ranging from ferritic–pearlitic DCIs to austempered ones), graphite elements morphology (shape, dimension and distributions) and loading conditions were the main investigated parameters. Focusing on the role played by the graphite nodules, they were considered merely as voids embedded in a metal matrix. Recent analysis underlined that the nodules role in the DCIs damage evolution is more complicated and is influenced by the matrix microstructure. In this work, the crack tip damaging Micromechanisms in a pearlitic DCI is investigated considering both fatigue loading conditions and the effects of overloads, focusing the interaction between the crack and the investigated DCI microstructure (pearlitic matrix and graphite nodules). On the basis of experimental results, the applicability of ASTM E399 standard on the characterization of fatigue crack propagation resistance in pearlitic DCIs is critically re-analyzed.
-
stress triaxiality influence on damaging Micromechanisms in a pearlitic ductile cast iron
Fracture and Structural Integrity, 2014Co-Authors: Vittorio Di Cocco, Francesco Iacoviello, Alessandra Rossi, M CavalliniAbstract:In the last decades, damaging Micromechanisms in ductile cast irons (DCIs) have been widely investigated, considering both the matrix microstructure and the loading conditions influence. Considering the graphite nodules, they were initially considered as voids embedded and growing in a ductile metal matrix (especially considering ferritic ductile cast irons). Recent experimental results allowed to identify a more complex role played by the graphite nodules, depending on the matrix microstructure. In this work, damaging Micromechanisms in a pearlitic DCI were investigated by means of tensile tests performed on notched specimen, mainly focusing the role played by graphite elements and considering the stress triaxiality influence.
Vittorio Di Cocco - One of the best experts on this subject based on the ideXlab platform.
-
Damaging Micromechanisms in an as cast ferritic and a ferritized ductile cast iron
Procedia Structural Integrity, 2017Co-Authors: Laura D'agostino, Vittorio Di Cocco, Diego Omar Fernandino, Francesco IacovielloAbstract:Abstract: Mechanical behavior and damaging Micromechanisms in Ductile Cast Irons (DCIs) are strongly effected by matrix microstructure (e.g., phases volume fraction, grains size and grain distribution) and graphite nodules morphology peculiarities (e.g., nodularity level, nodule size, nodule count, etc.). The influence of the graphite nodules depends on both the matrix microstructure and the loading conditions (e.g., quasi-static, dynamic or cyclic loadings). According to the most recent results, these graphite nodules show a mechanical properties gradient inside the graphite nodules, with the graphite elements – matrix debonding as only one of the possible damaging Micromechanisms. In this work, two different ferritic DCIs were investigated (a ferritic matrix obtained from as-cast condition and a ferritized matrix) focusing on the damaging Micromechanisms in graphite nodules due to tensile stress. Specimens lateral surfaces were observed using a Scanning Electron Microscope (SEM) during the tests following a step by step procedure.
-
damage Micromechanisms in a hot dip galvanized steel
Procedia structural integrity, 2017Co-Authors: Vittorio Di Cocco, Francesco Iacoviello, Laura Dagostino, S NataliAbstract:Abstract: Hot-dip galvanizing is one of the most used methods to apply zinc-based coatings on steels in order to provide sacrificial protection against corrosion over all the steel surface. The aim of this work is the analysis of the hot dip zinc coated steel plates mechanical properties by means of a non-standardized bending test performed minimizing both the bending moment differences along the bending axis and the interactions between the clamping system and the specimen coating. Bending tests are performed both on non-coated and on hot dip zinc coated plates, correlating the measured variables (applied load and crosshead displacement) with the bending moment and the specimen bending angle. Tests are characterised by a good repeatability. Results show that the main damaging mechanisms depend on the different mechanical behaviour of the intermetallic phases and on their thickness. For all the investigated coating conditions, radial cracks are observed. They initiate corresponding to the Γ phase and propagate up to the ζ-η interface. The coating thickness increase implies both an increase of the importance of the cracks in δ and ζ phases and the presence of cracks at ζ-η interfaces.
-
fatigue crack propagation and overload damaging Micromechanisms in a ferritic pearlitic ductile cast iron
Fatigue & Fracture of Engineering Materials & Structures, 2016Co-Authors: Francesco Iacoviello, Vittorio Di Cocco, M CavalliniAbstract:Recently discovered (1948), ductile cast irons (DCIs) are able to combine the good castability of grey irons with the interesting mechanical properties, both static and cyclic, of carbon steels, allowing to directly produce components with complex shape that are requested to be characterized by high mechanical performances, especially considering toughness and fatigue resistance. DCIs mechanical properties and damaging Micromechanisms depend on the matrix (ferritic, pearlitic, ferrite pearlitic, ausferritic, etc.) and on the graphite nodules morphological peculiarities (shape, dimension, distribution, etc.). In this work, the fatigue-crack propagation Micromechanisms in a ferritic–pearlitic DCI were investigated, focusing both the role played by the microstructure and the contribution of the graphite nodules. In addition, the overload effects on the composite microstructure of the investigated ferritic–pearlitic DCI were analysed.
-
fatigue crack tip damaging Micromechanisms in pearlitic ductile cast irons
Fatigue & Fracture of Engineering Materials & Structures, 2015Co-Authors: Francesco Iacoviello, Vittorio Di Cocco, Alessandra Rossi, M CavalliniAbstract:In the last years, damaging Micromechanisms in ductile cast irons (DCIs) were widely investigated: DCI microstructure (ranging from ferritic–pearlitic DCIs to austempered ones), graphite elements morphology (shape, dimension and distributions) and loading conditions were the main investigated parameters. Focusing on the role played by the graphite nodules, they were considered merely as voids embedded in a metal matrix. Recent analysis underlined that the nodules role in the DCIs damage evolution is more complicated and is influenced by the matrix microstructure. In this work, the crack tip damaging Micromechanisms in a pearlitic DCI is investigated considering both fatigue loading conditions and the effects of overloads, focusing the interaction between the crack and the investigated DCI microstructure (pearlitic matrix and graphite nodules). On the basis of experimental results, the applicability of ASTM E399 standard on the characterization of fatigue crack propagation resistance in pearlitic DCIs is critically re-analyzed.
-
stress triaxiality influence on damaging Micromechanisms in a pearlitic ductile cast iron
Fracture and Structural Integrity, 2014Co-Authors: Vittorio Di Cocco, Francesco Iacoviello, Alessandra Rossi, M CavalliniAbstract:In the last decades, damaging Micromechanisms in ductile cast irons (DCIs) have been widely investigated, considering both the matrix microstructure and the loading conditions influence. Considering the graphite nodules, they were initially considered as voids embedded and growing in a ductile metal matrix (especially considering ferritic ductile cast irons). Recent experimental results allowed to identify a more complex role played by the graphite nodules, depending on the matrix microstructure. In this work, damaging Micromechanisms in a pearlitic DCI were investigated by means of tensile tests performed on notched specimen, mainly focusing the role played by graphite elements and considering the stress triaxiality influence.
Thilo F. Morgeneyer - One of the best experts on this subject based on the ideXlab platform.
-
On deformation and damage Micromechanisms in strong work hardening 2198 T3 aluminium alloy
Acta Materialia, 2018Co-Authors: Ante Buljac, François Hild, Lukas Helfen, Thilo F. MorgeneyerAbstract:Abstract The deformation and damage Micromechanisms ahead of a notch in a large flat specimen have been assessed using in situ synchrotron laminography combined with digital volume correlation for the strain evaluation in the material bulk. Despite the enhanced work hardening of the naturally aged Al-Cu-Li alloy several slanted strained bands were found from very early loading onward in the slanted fracture region. The final slanted crack followed one of the strained bands without significant ductile damage growth. In the high stress triaxiality region, close to the notch that underwent substantial local necking, two damage Micromechanisms were observed, namely, i) limited void nucleation and growth from intermetallic particles, and ii) slanted shear cracks, even starting from the specimen surface and also located in single grains as shown by post mortem EBSD analyses. In the intermediate region a new deformation mechanism of flip-flopping strain bands and resulting flip-flopping cracks have been revealed using “projection DIC” measurements.
