Reza Bagheri - Academia.edu (original) (raw)

Papers by Reza Bagheri

Research paper thumbnail of PP/GF/EPR Composites I: Deformation Mechanism

Research paper thumbnail of Toughening mechanism in Polypropylene/EPR blends

Research paper thumbnail of Hybrid PP/EPR/GF Composites I: Deformation Mechanisms

Research paper thumbnail of Role of different compatibilizing approaches on the microstructure and mechanical properties of polypropylene/talc composites

AIP Conference Proceedings, 2014

Effect of reprocessing cycles on the degradation of polypropylene copolymer filled with talc or m... more Effect of reprocessing cycles on the degradation of polypropylene copolymer filled with talc or montmorillonite during injection molding process

Research paper thumbnail of Dilatational shear bands in rubber-modified isotactic polypropylene

Materials & Design, 2004

The main goal of this study is to further understanding of the role of rubber particles on deform... more The main goal of this study is to further understanding of the role of rubber particles on deformation mechanisms in PP/EPR blend. For doing this standard tensile specimens were produced using injection molding. The results of microscopic evaluation of tensile specimen after some stretching show that damage forms in some points and then propagates in different directions. Also some elongated voids are observed, those are probably formed due to cavitation of rubber particles or debonding at the interface. With regard to achieved micrographs one may conclude that the deformation mechanism in PP/EPR blend can be massive dilatational shear banding due to repeated cavitation.

Research paper thumbnail of Paper: DILATATIONAL SHEAR BANDS IN RUBBER-MODIFIED ISOTACTIC POLYPROPYLENE

Research paper thumbnail of Paper: FRACTURE MECHANISM UNDER DYNAMIC LOADING OF ELASTOMER-MODIFIED POLYPROPYLENE

Research paper thumbnail of Paper: HYBRID PP-EPR-GF COMPOSITES PART 1-DEFORMATION MECHANISMS

Research paper thumbnail of Influence of spherulitic microstructure on deformation mechanism in isotactic polypropylene

Research paper thumbnail of Deformation, yield and fracture of elastomer-modified polypropylene

Journal of Applied Polymer Science, 2003

In recent decades, great attention has been devoted to the toughening of isotactic poly(propylene... more In recent decades, great attention has been devoted to the toughening of isotactic poly(propylene) (PP) with elastomers such as ethylene-propylene rubber (EPR). The most important reasons for this interest are the moderate cost and favorable properties of PP. This article is focused on the role of EPR in the deformation and fracture mechanism of PP/EPR blends with different volume fractions of elastomer phase. Differential scanning calorimetry (DSC), tensile tests, and microscopy techniques were used in this study. The fracture mechanism of isotactic PP toughened by EPR (PP/EPR) has also been studied by three point bending (3-PB) and four point bending (4-PB) tests. Rubber particle cavitation appears to be the main mechanism of microvoid formation, although some matrix/particle debonding was observed. The investigation of the toughening mechanism shows that a wide damage zone spreads in front of the pre-crack. Optical microscopy (OM) illustrates that, in pure PP, crazing is the only fracture mechanism, and no evidence of shear yielding is found, while in PP blends craze-like features associated with shear yielding are observed, which have been identified as high shear localized dilatational bands. This type of deformation pattern supports a model previously proposed by Lazzeri 1 to explain the interparticle distance effect on the basis of the stabilization effect on dilatational band propagation exerted by stretched rubber particles.

Research paper thumbnail of Toughness prediction in functionally graded Al6061/SiCp composites produced by roll-bonding

Ceramics International, 2014

Functionally graded aluminum matrix composites (FGAMC) are new advanced materials with promising ... more Functionally graded aluminum matrix composites (FGAMC) are new advanced materials with promising applications due to their unique characteristics in which composite nature combined with graded structure. 22 different architectures of Al6061/SiC p composite laminates were fabricated by successive hot roll-bonding. For FGAMCs, two composite layers as outer strips and a layer of Al1050 as interlayer were applied. To investigate laminate toughness, quasi-static three-point bending test was conducted in the crack divider orientation. Genetic programming as a soft computing technique was implemented to find mathematical correlations between architectural parameters and experimentally obtained results. Doing this, 75 sets of reliable data achieved and randomly divided into 63 and 12 as training and testing sets, respectively. Input parameters of "specimen thickness", "SiC content in composite layers", "rolling strain", "maximum achieved stress", and "strain in utmost stress", as well as, "total strain of specimen" were utilized for modeling. 21 models of different types each used 8 independent parameters, wholly and/or partially, were proposed. In order to introduce the best model, four criteria of "higher regression", "minimum errors", "minimum subtraction of errors summation" and "minimum sum of absolute subtractions of predicted and experimented toughness" were considered. Based on different evaluations, a model which used 5 inputs, as well as, 30 chromosomes, 8 head sizes, 2 genes, addition as linking function, RRSE as fitness function while implemented 5 different mathematical operators was selected. The study showed that predicted results and experimented data had good conformity while all models had reliable applicability for predicting fracture tolerance of aluminum matrix composites with graded structures under quasi-static bending condition.

Research paper thumbnail of Incorporating Aspect Ratio in a New Modeling Approach for Strengthening of MMCs and its Extension from Micro to Nano Scale

Advanced Composite Materials, 2010

The strengthening behavior of particle reinforced metal-matrix composites is primarily attributed... more The strengthening behavior of particle reinforced metal-matrix composites is primarily attributed to the dislocation strengthening effect and the load transfer effect. To account for these two effects in a unified way, a new multi-scale approach is developed in this paper incorporating the aspect ratio effect into the geometrically necessary dislocation strengthening relationships. By making use of this multi-scale approach, the deformation behavior of metal-matrix composites (MMCs) and metal-matrix nanocomposites (MMNCs) as a function of size, volume fraction, aspect ratio, etc. of the particles has been investigated. Comparison with the previously proposed models and the available experimental results reported in the literature for both MMCs and MMNCs systems demonstrates the superiority of the proposed model.

Research paper thumbnail of Fracture behaviour of isotactic polypropylene under static loading condition

Materials & Design, 2003

The fracture mechanism of isotactic polypropylene has been studied by three-and four-point bendin... more The fracture mechanism of isotactic polypropylene has been studied by three-and four-point bending tests. The result of threepoint bending test shows that a wide spread damage zone is present in front of the notch. Looking in more detail via crosspolarised light shows the evidence of birefringence in the stress-whitened zone. Increasing the applied load causes it to spread out the stress-whitened zone. Then the craze-like features are nucleated inside the stress-whitened region. The result of four-point bending test shows that craze-like damage appears in front of pre-crack and its propagation is dictated by spherulite microstructure.

Research paper thumbnail of Controlling the rheological behavior of nucleated polypropylene via incorporating dimethylbenzylidene sorbitol (DMDBS) masterbatch

Polyolefins Journal, Jan 1, 2023

Dimethylbenzylidene sorbitol (DMDBS) is a common nucleating/clarifier agent used in polypropylene... more Dimethylbenzylidene sorbitol (DMDBS) is a common nucleating/clarifier agent used in polypropylene (PP). So many researchers have looked at different aspects of incorporating this additive on the crystallization behavior of PP. The current study is focused on a rather new topic and that is the role of the carrier resin of DMDBS masterbatch on the rheological behaviour of polypropylene. This objective has been achieved through studying the role of the carrier resin on the phase separation behavior of DMDBS upon cooling. It has been shown that a permanent bond is formed between the molecules of carrier resin and DMDBS in the masterbatch and this bond slows down the crystallization kinetics of DMDBS in the final blend which in turn, influences its rheological behavior. Frequency sweep experiments conducted on a block copolypropylene showed that lower values of storage shear modulus (G¢), loss shear modulus (G²), and complex shear viscosity (ɳ*) are observed if DMDBS is incorporated as a masterbatch. Interestingly, a different effect was observed when the masterbatch constituents were employed directly into polypropylene, illustrating the importance of the mentioned bond between DMDBS and the carrier resin in the masterbatch.

Research paper thumbnail of Fracture toughness of a hybrid-rubber-modified epoxy. I. Synergistic toughening

Journal of Applied Polymer Science, 2012

Effect of loading rate on toughness characteristics of hybrid rubber-modified epoxy was investiga... more Effect of loading rate on toughness characteristics of hybrid rubber-modified epoxy was investigated. Epoxy was modified by amine-terminated butadiene acrylonitrile (ATBN) and recycled tire. Samples were tested at various loading rates of 1-1000 mm/ min. Fracture toughness measurements revealed synergistic toughening in hybrid system at low loading rates (1-10 mm/min); hybrid system exhibited higher fracture toughness value in comparison with the ATBN-modified resin with same modifier content. However, synergistic toughening was eliminated by increasing the loading rate. At higher loading rates (10-1000), the fracture toughness of hybrid system decreased gradually to the level lower than that of ATBN-modified epoxy. Fractography of the damage zones showed the toughening mechanisms of ATBN-modified system was less affected by increasing the loading rate compared to that of hybrid system. V

Research paper thumbnail of Improved wear, mechanical, and biological behavior of UHMWPE-HAp-zirconia hybrid nanocomposites with a prospective application in total hip joint replacement

Journal of Materials Science

Research paper thumbnail of The simultaneous effect of silica nanoparticles and rubber particles on the toughness of epoxy polymer

International Journal of Nanomanufacturing, 2010

The objective of this study is to investigate the effects of both rubbery phase and nanosilica on... more The objective of this study is to investigate the effects of both rubbery phase and nanosilica on mechanical properties of epoxy. Three series of formulations based on epoxy including nanosilica, rubber and rubber/nanosilica were prepared. Transmission electron microscopy showed that nanoparticles were homogeneously dispersed throughout the epoxy matrix. Compression and fracture toughness tests along with scanning electron microscopy and transmission optical microscopy were also done to evaluate the properties of the compounds. Although the results of compression tests indicate that addition of nanosilica could not change elastic modulus and yield strength of neat resin significantly, nanosilica has a considerable effect on fracture toughness of nanocomposites as well as hybrid compounds. Moreover, for the first time, the synergistic effect of nanosilica on rubber-toughened epoxy is explored via studying the toughening mechanisms acting at the crack-tip. The results indicate that debonding of nanosilica aggregates which leads to void formation in the matrix promote matrix shear yielding.

Research paper thumbnail of Characterization of polyamide 6/carbon nanotube composites prepared by melt mixing-effect of matrix molecular weight and structure

Composites Part B: Engineering, 2015

ABSTRACT Effects of molecular weight and structure of polyamide 6 (PA6) on morphology and propert... more ABSTRACT Effects of molecular weight and structure of polyamide 6 (PA6) on morphology and properties of PA6/MWCNT prepared by melt mixing were investigated. Microscopic analysis showed fine dispersion of MWCNT within low viscosity PA6s due to domination of melt infiltration into MWCNT agglomerate at low viscosity matrices with linear structure. Rheological data indicated good interfacial interaction with no percolation of MWCNT up to 2 wt% loading. DSC thermograms showed nucleating role of MWCNT on crystallization of PA6s with marginal effect on crystallinity. Experimental data supported with micromechanical model showed limited improvement on mechanical properties, but it was closely consistent with degree of dispersion of MWCNT.

Research paper thumbnail of Dielectric and piezoelectric properties of porous PZT–PCN ceramics sintered at different temperatures

Research paper thumbnail of Paper: LOADING RATE-INDUCED TRANSITION IN TOUGHENING MECHANISM OF RUBBER-MODIFIED EPOXY

Research paper thumbnail of PP/GF/EPR Composites I: Deformation Mechanism

Research paper thumbnail of Toughening mechanism in Polypropylene/EPR blends

Research paper thumbnail of Hybrid PP/EPR/GF Composites I: Deformation Mechanisms

Research paper thumbnail of Role of different compatibilizing approaches on the microstructure and mechanical properties of polypropylene/talc composites

AIP Conference Proceedings, 2014

Effect of reprocessing cycles on the degradation of polypropylene copolymer filled with talc or m... more Effect of reprocessing cycles on the degradation of polypropylene copolymer filled with talc or montmorillonite during injection molding process

Research paper thumbnail of Dilatational shear bands in rubber-modified isotactic polypropylene

Materials & Design, 2004

The main goal of this study is to further understanding of the role of rubber particles on deform... more The main goal of this study is to further understanding of the role of rubber particles on deformation mechanisms in PP/EPR blend. For doing this standard tensile specimens were produced using injection molding. The results of microscopic evaluation of tensile specimen after some stretching show that damage forms in some points and then propagates in different directions. Also some elongated voids are observed, those are probably formed due to cavitation of rubber particles or debonding at the interface. With regard to achieved micrographs one may conclude that the deformation mechanism in PP/EPR blend can be massive dilatational shear banding due to repeated cavitation.

Research paper thumbnail of Paper: DILATATIONAL SHEAR BANDS IN RUBBER-MODIFIED ISOTACTIC POLYPROPYLENE

Research paper thumbnail of Paper: FRACTURE MECHANISM UNDER DYNAMIC LOADING OF ELASTOMER-MODIFIED POLYPROPYLENE

Research paper thumbnail of Paper: HYBRID PP-EPR-GF COMPOSITES PART 1-DEFORMATION MECHANISMS

Research paper thumbnail of Influence of spherulitic microstructure on deformation mechanism in isotactic polypropylene

Research paper thumbnail of Deformation, yield and fracture of elastomer-modified polypropylene

Journal of Applied Polymer Science, 2003

In recent decades, great attention has been devoted to the toughening of isotactic poly(propylene... more In recent decades, great attention has been devoted to the toughening of isotactic poly(propylene) (PP) with elastomers such as ethylene-propylene rubber (EPR). The most important reasons for this interest are the moderate cost and favorable properties of PP. This article is focused on the role of EPR in the deformation and fracture mechanism of PP/EPR blends with different volume fractions of elastomer phase. Differential scanning calorimetry (DSC), tensile tests, and microscopy techniques were used in this study. The fracture mechanism of isotactic PP toughened by EPR (PP/EPR) has also been studied by three point bending (3-PB) and four point bending (4-PB) tests. Rubber particle cavitation appears to be the main mechanism of microvoid formation, although some matrix/particle debonding was observed. The investigation of the toughening mechanism shows that a wide damage zone spreads in front of the pre-crack. Optical microscopy (OM) illustrates that, in pure PP, crazing is the only fracture mechanism, and no evidence of shear yielding is found, while in PP blends craze-like features associated with shear yielding are observed, which have been identified as high shear localized dilatational bands. This type of deformation pattern supports a model previously proposed by Lazzeri 1 to explain the interparticle distance effect on the basis of the stabilization effect on dilatational band propagation exerted by stretched rubber particles.

Research paper thumbnail of Toughness prediction in functionally graded Al6061/SiCp composites produced by roll-bonding

Ceramics International, 2014

Functionally graded aluminum matrix composites (FGAMC) are new advanced materials with promising ... more Functionally graded aluminum matrix composites (FGAMC) are new advanced materials with promising applications due to their unique characteristics in which composite nature combined with graded structure. 22 different architectures of Al6061/SiC p composite laminates were fabricated by successive hot roll-bonding. For FGAMCs, two composite layers as outer strips and a layer of Al1050 as interlayer were applied. To investigate laminate toughness, quasi-static three-point bending test was conducted in the crack divider orientation. Genetic programming as a soft computing technique was implemented to find mathematical correlations between architectural parameters and experimentally obtained results. Doing this, 75 sets of reliable data achieved and randomly divided into 63 and 12 as training and testing sets, respectively. Input parameters of "specimen thickness", "SiC content in composite layers", "rolling strain", "maximum achieved stress", and "strain in utmost stress", as well as, "total strain of specimen" were utilized for modeling. 21 models of different types each used 8 independent parameters, wholly and/or partially, were proposed. In order to introduce the best model, four criteria of "higher regression", "minimum errors", "minimum subtraction of errors summation" and "minimum sum of absolute subtractions of predicted and experimented toughness" were considered. Based on different evaluations, a model which used 5 inputs, as well as, 30 chromosomes, 8 head sizes, 2 genes, addition as linking function, RRSE as fitness function while implemented 5 different mathematical operators was selected. The study showed that predicted results and experimented data had good conformity while all models had reliable applicability for predicting fracture tolerance of aluminum matrix composites with graded structures under quasi-static bending condition.

Research paper thumbnail of Incorporating Aspect Ratio in a New Modeling Approach for Strengthening of MMCs and its Extension from Micro to Nano Scale

Advanced Composite Materials, 2010

The strengthening behavior of particle reinforced metal-matrix composites is primarily attributed... more The strengthening behavior of particle reinforced metal-matrix composites is primarily attributed to the dislocation strengthening effect and the load transfer effect. To account for these two effects in a unified way, a new multi-scale approach is developed in this paper incorporating the aspect ratio effect into the geometrically necessary dislocation strengthening relationships. By making use of this multi-scale approach, the deformation behavior of metal-matrix composites (MMCs) and metal-matrix nanocomposites (MMNCs) as a function of size, volume fraction, aspect ratio, etc. of the particles has been investigated. Comparison with the previously proposed models and the available experimental results reported in the literature for both MMCs and MMNCs systems demonstrates the superiority of the proposed model.

Research paper thumbnail of Fracture behaviour of isotactic polypropylene under static loading condition

Materials & Design, 2003

The fracture mechanism of isotactic polypropylene has been studied by three-and four-point bendin... more The fracture mechanism of isotactic polypropylene has been studied by three-and four-point bending tests. The result of threepoint bending test shows that a wide spread damage zone is present in front of the notch. Looking in more detail via crosspolarised light shows the evidence of birefringence in the stress-whitened zone. Increasing the applied load causes it to spread out the stress-whitened zone. Then the craze-like features are nucleated inside the stress-whitened region. The result of four-point bending test shows that craze-like damage appears in front of pre-crack and its propagation is dictated by spherulite microstructure.

Research paper thumbnail of Controlling the rheological behavior of nucleated polypropylene via incorporating dimethylbenzylidene sorbitol (DMDBS) masterbatch

Polyolefins Journal, Jan 1, 2023

Dimethylbenzylidene sorbitol (DMDBS) is a common nucleating/clarifier agent used in polypropylene... more Dimethylbenzylidene sorbitol (DMDBS) is a common nucleating/clarifier agent used in polypropylene (PP). So many researchers have looked at different aspects of incorporating this additive on the crystallization behavior of PP. The current study is focused on a rather new topic and that is the role of the carrier resin of DMDBS masterbatch on the rheological behaviour of polypropylene. This objective has been achieved through studying the role of the carrier resin on the phase separation behavior of DMDBS upon cooling. It has been shown that a permanent bond is formed between the molecules of carrier resin and DMDBS in the masterbatch and this bond slows down the crystallization kinetics of DMDBS in the final blend which in turn, influences its rheological behavior. Frequency sweep experiments conducted on a block copolypropylene showed that lower values of storage shear modulus (G¢), loss shear modulus (G²), and complex shear viscosity (ɳ*) are observed if DMDBS is incorporated as a masterbatch. Interestingly, a different effect was observed when the masterbatch constituents were employed directly into polypropylene, illustrating the importance of the mentioned bond between DMDBS and the carrier resin in the masterbatch.

Research paper thumbnail of Fracture toughness of a hybrid-rubber-modified epoxy. I. Synergistic toughening

Journal of Applied Polymer Science, 2012

Effect of loading rate on toughness characteristics of hybrid rubber-modified epoxy was investiga... more Effect of loading rate on toughness characteristics of hybrid rubber-modified epoxy was investigated. Epoxy was modified by amine-terminated butadiene acrylonitrile (ATBN) and recycled tire. Samples were tested at various loading rates of 1-1000 mm/ min. Fracture toughness measurements revealed synergistic toughening in hybrid system at low loading rates (1-10 mm/min); hybrid system exhibited higher fracture toughness value in comparison with the ATBN-modified resin with same modifier content. However, synergistic toughening was eliminated by increasing the loading rate. At higher loading rates (10-1000), the fracture toughness of hybrid system decreased gradually to the level lower than that of ATBN-modified epoxy. Fractography of the damage zones showed the toughening mechanisms of ATBN-modified system was less affected by increasing the loading rate compared to that of hybrid system. V

Research paper thumbnail of Improved wear, mechanical, and biological behavior of UHMWPE-HAp-zirconia hybrid nanocomposites with a prospective application in total hip joint replacement

Journal of Materials Science

Research paper thumbnail of The simultaneous effect of silica nanoparticles and rubber particles on the toughness of epoxy polymer

International Journal of Nanomanufacturing, 2010

The objective of this study is to investigate the effects of both rubbery phase and nanosilica on... more The objective of this study is to investigate the effects of both rubbery phase and nanosilica on mechanical properties of epoxy. Three series of formulations based on epoxy including nanosilica, rubber and rubber/nanosilica were prepared. Transmission electron microscopy showed that nanoparticles were homogeneously dispersed throughout the epoxy matrix. Compression and fracture toughness tests along with scanning electron microscopy and transmission optical microscopy were also done to evaluate the properties of the compounds. Although the results of compression tests indicate that addition of nanosilica could not change elastic modulus and yield strength of neat resin significantly, nanosilica has a considerable effect on fracture toughness of nanocomposites as well as hybrid compounds. Moreover, for the first time, the synergistic effect of nanosilica on rubber-toughened epoxy is explored via studying the toughening mechanisms acting at the crack-tip. The results indicate that debonding of nanosilica aggregates which leads to void formation in the matrix promote matrix shear yielding.

Research paper thumbnail of Characterization of polyamide 6/carbon nanotube composites prepared by melt mixing-effect of matrix molecular weight and structure

Composites Part B: Engineering, 2015

ABSTRACT Effects of molecular weight and structure of polyamide 6 (PA6) on morphology and propert... more ABSTRACT Effects of molecular weight and structure of polyamide 6 (PA6) on morphology and properties of PA6/MWCNT prepared by melt mixing were investigated. Microscopic analysis showed fine dispersion of MWCNT within low viscosity PA6s due to domination of melt infiltration into MWCNT agglomerate at low viscosity matrices with linear structure. Rheological data indicated good interfacial interaction with no percolation of MWCNT up to 2 wt% loading. DSC thermograms showed nucleating role of MWCNT on crystallization of PA6s with marginal effect on crystallinity. Experimental data supported with micromechanical model showed limited improvement on mechanical properties, but it was closely consistent with degree of dispersion of MWCNT.

Research paper thumbnail of Dielectric and piezoelectric properties of porous PZT–PCN ceramics sintered at different temperatures

Research paper thumbnail of Paper: LOADING RATE-INDUCED TRANSITION IN TOUGHENING MECHANISM OF RUBBER-MODIFIED EPOXY