Papers by Mahmood Shokrieh
International Symposium on Algorithms and Computation, May 14, 2013
International Journal of Advanced Design …, 2011
Theoretical and Applied Fracture Mechanics, 2021
This work aims at studying the loading rate dependency of mode I delamination growth in CFRPs, us... more This work aims at studying the loading rate dependency of mode I delamination growth in CFRPs, using typical fracture toughness analysis through both the R-curve and the crack tip opening rate. The average SERR is a method of data reduction based on energy balance which has been previously introduced to characterize delamination growth under different types of loading conditions in a similar manner. In the present research, the application of this method was extended to further analyze the results of delamination experiments at different loading rates. Mode I delamination tests on double cantilever beam specimens were performed at displacement rates varying from standard quasi-static testing up to 400 mm/s. A clear decrease in the propagation fracture toughness as well as in the average SERR was observed at high loading rates. The reduced fracture resistance at elevated rates was physically explained in correlation with fiber bridging, fiber breakage, and matrix cleavage observed in fracture surfaces via scanning electron microscopy.
Mechanics of Composite Materials, 2015
In order to improve the mechanical properties and decrease the manufacturing costs of traditional... more In order to improve the mechanical properties and decrease the manufacturing costs of traditional polymer concrete, a new concrete mix is presented, where fine silica sand is used instead of common large and small aggregates. In addition, to decrease manufacturing costs, a polyester resin is employed instead of epoxy matrix. By performing compression and three-point bending tests, it was found that the new polymer concrete had a higher compression strength than the traditional polymer concrete and a similar bending strength. Also, a two-phase micromechanical model was used to analytically estimate the compressive strength of the new material, and a rather good agreement between experimental data and theoretical calculations was found to exist.
Iranian Polymer Journal, 2016
Polymeric materials have wide applications; therefore, it is necessary to develop a dynamic const... more Polymeric materials have wide applications; therefore, it is necessary to develop a dynamic constitutive model to investigate their strain rate-dependent mechanical behavior. In this study, mechanical behavior of neat epoxy and carbon nanofiber (CNF)/epoxy nanocomposites were studied experimentally and analytically. For this purpose, the Johnson–Cook material model has been modified to develop a generalized strain rate-dependent constitutive model to simulate the tensile and shear mechanical behaviors of the neat epoxy at a wide range of applied loading rates. The present model includes three main components: the first component expresses the elastic behavior of polymers using an empirical equation. The second component models the nonlinear behavior of polymers using the modified Johnson–Cook model. Finally, the third component predicts the ultimate strength of polymers under dynamic loading conditions using another empirical equation. Furthermore, by combining the generalized strain rate-dependent constitutive model and the modified Halpin–Tsai micromechanical model, a dynamic constitutive-micromechanical model is presented to predict the strain rate-dependent mechanical behavior of CNF/epoxy nanocomposites. To evaluate the present model, predicted results for the pure epoxy and CNF/epoxy nanocomposites were compared with conducted and available experimental data. It is shown that the present model predicts the strain rate-dependent mechanical behavior of polymeric materials with a good accuracy.
Experimental Mechanics, 2020
Background The slitting method is a widely used destructive technique for the determination of re... more Background The slitting method is a widely used destructive technique for the determination of residual stresses. Because of the rich data content of the full-field methods, optical techniques such as digital image correlation (DIC) are replacing strain gages for surface measurements. Objective The objective of the current paper is to overcome the difficulties that arise in using the DIC technique combined with the slitting method. The present noise, low signal-to-noise ratio, and systematic errors are the main impediments to the use of DIC in the slitting method. Methods An approach based on the eigenstrain concept was exploited to ascertain the optimum region of interest (ROI) for the analysis. After that, a robust procedure was implemented to utilize the DIC method while excluding the rigid body motion and rotation artifacts from the obtained displacements. Results Different slitting steps may cause dissimilar rigid body motions and rotations of the specimen. The proposed method was able to eliminate all of these different shears and stretches in the images simultaneously. The slitting experiment was conducted on a symmetric cross-ply composite specimen, and the slit progressed down to half the thickness. Although some rigid body motions were large, the method managed to exclude all of them for eight slitting steps. Conclusion A comparison made between the results of the current method and those of the strain gage technique shows that they are in acceptable agreement with each other, and this full-field method can be extended to smaller scales or other destructive techniques.
Mechanics of Composite Materials, 2015
The Taguchi method was used to determine the optimum content of a four-parameters cellulose fiber... more The Taguchi method was used to determine the optimum content of a four-parameters cellulose fiber pulp, polyvinyl alcohol (PVA) fibers, a silica fume, and bentonite for cement-based composite sheets. Then cement composite sheets from the hybrid of PVA and the cellulose fiber pulp were manufactured, and their moduli of rapture were determined experimentally. The result obtained showed that cement composites with a hybrid of PVA and cellulose fiber pulp had a higher flexural strength than cellulose-fiber- reinforced cement ones, but this strength was rather similar to that of asbestos-fiber-reinforced cement composites. Also, using the results of flexural tests and an analytical method, the tensile and compressive moduli of the hybrid of PVA and cement sheet were calculated. The hybrid of PVA and cellulose fiber pulp is proposed as an appropriate alternative for substituting asbestos in the Hatschek process.
Techno-Press, 2020
In the present paper, changes in the residual stress of carbon/epoxy laminated composites as a re... more In the present paper, changes in the residual stress of carbon/epoxy laminated composites as a result of adding graphene nanoparticles (GNPs) content were studied theoretically and experimentally. Three dissimilar weight fractions of GNPs, i.e., 0.1%, 0.25% and 0.5%, were added into an epoxy matrix. Unidirectional carbon fibers (CFs) were used as reinforcement to fabricate cross-ply laminated composites. Mechanical and thermal properties of the GNP/epoxy nanocomposites were then characterized via tensile tests as well as thermomechanical analysis (TMA). Based on experimental observations, adding even small fractions of GNP to epoxy matrix caused to decrease in the coefficient of thermal expansion (CTE) significantly while the epoxy resin Young's modulus increases moderately. The measurements of residual stresses in cross-ply CF/epoxy and GNP-CF/epoxy laminated composites were performed using the slitting method. The results of experiments show 11.7%, 14.3% and 16.52% reductions in residual stresses as a result of adding 0.1%, 0.25% and 0.5% GNP to the matrix of the cross-ply CF/epoxy laminated composites, respectively. This is conclusive evidence that GNP can reduce CTE and decrease residual stresses significantly.
علوم و تکنولوژی پلیمر, 2008
Applications of thermoplastic composites have developed extensively. The thermoplastic composites... more Applications of thermoplastic composites have developed extensively. The thermoplastic composites in comparison with the thermoset composites have many advantages. Thermoplastic composites can be melted and remolded many times. The duration of manufacturing process of these composites is short, producing very tough material, and the welding ability and multiple recyclings are their further advantages. The lack of knowledge in this group of composites is the main obstacle in their development. In this review the research works in the field of residual stresses in thermoplastic composites is presented. First, a literature survey on the available research on residual stresses on thermoplastics and thermoplastic composites reinforced with short fibers is compiled. Moreover a review on the available research on residual stresses on thermoplastic composites reinforced with long fibers is presented as well. The effects of the residual stresses on these composites are discussed. Experimenta...
علوم و تکنولوژی پلیمر, 2007
Nanocomposite materials have recently attracted increasing interests in the field of modelling. F... more Nanocomposite materials have recently attracted increasing interests in the field of modelling. Finite element modelling can be used for computation of bulk properties of polymer/clay nanocomposites. In this study, by considering the structure of a nano-composite material, a quasi real model is proposed. The model has been used to predict the elastic constants by selection of suitable elements and boundary conditions. The effects of nano-structural parameters on the mechanical properties of a polymer/clay nano-composite are studied. The geometrical overlap of particles, horizontal distance between particles, length of particles and nano-clay volume fraction are defined as functions of the nano-structural parameters and their effects on mechanical properties of nano-composites are studied by a finite element modelling technique.
علوم و تکنولوژی پلیمر, 2013
The effects of physical, thermal and mechanical parameters on curing microthermal residual stress... more The effects of physical, thermal and mechanical parameters on curing microthermal residual stresses are studied, based on the energy method, to present a theoretical solution for prediction of residual stress felds. A fnite element analysis is developed to compare the theoretical and numerical results together. There is found to be a good agreement between the results of the two methods. However, due to the edge effect, the fnite element method is not able to satisfy the boundary conditions at the composite ends. An increase in the fber length leads to a signifcant increase in axial and shear stresses. In addition, for long fber composites the axial and shear residual stresses distribution become more uniform along the fber length and suddenly decrease to zero at the composite edge. The results of the two methods demonstrate that besides the physical characteristics of composites, the order of mismatch in thermal and mechanical properties of the fber and matrix has a considerable in...
علوم و تکنولوژی پلیمر, 2008
Vacuum assisted resin transfer molding, as a sub-branch of RTM is a method of manufacturing compo... more Vacuum assisted resin transfer molding, as a sub-branch of RTM is a method of manufacturing composite specimens. Considering the industrial development of this method, different modified techniques are designed to improve its performance. Among these techniques, using a half flexible mold is regarded as an important method. In this work, dominant equations of resin flow through the mold in polar coordinates are solved analytically. Based on this approach, closed-form solutions have been presented for different parameters such as thickness variation of preformed fiber, resin pressure, resin velocity and fiber volume fraction as functions of two variables, namely, time and the distance from injection port. After verification of the approach employed in this work, the results are presented. Important parameters influencing the quality and the rate production are studied in detail.
fatigue behavior, displacement control, epoxy resin, frequency effect, mechanical properties T he... more fatigue behavior, displacement control, epoxy resin, frequency effect, mechanical properties T he mechanical properties of epoxy resin including tensile and flexural modulus, tensile and flexural strength for static conditions are currently studied. The frequency effect as significant parameter at room temperature is investigated and fatigue behavior of the epoxy resin in tension-tension loading conditions for different frequencies of 2, 3 and 5 Hz are obtained. The epoxy resin has been taken under flexural bending fatigue loading and fatigue life is investigated. The results of the experiments show the values of 2.5 and 3 GPa of tensile and flexural modules and 59.98 and 110.02 MPa of tensile and flexural strengths for the resin, respectively. To achieve a linear load-deflection relationship in a three-point bending experiment, a maximum allowable deflection of 5 mm is acquired. The relationship between the frequency and fatigue life shows higher frequency results in lower fatigue ...
In this paper, the size effect on elastic properties of single-walled nanotubes is evaluated via ... more In this paper, the size effect on elastic properties of single-walled nanotubes is evaluated via the strain gradient elasticity approach. For this purpose, rod, torsion bar and Euler-Bernoulli beam models are used. The tension rod model is developed in the present study. The Euler-Bernoulli beam model is utilized and the boundary conditions are modified in the present research. In addition, a model for the rod under torsion is developed. Afterwards, by using the constitutive relation in strain gradient elasticity, the size-dependent elastic properties of carbon nanotube are achieved effectively. The results show that the length of the carbon nanotube is more effective on the Young modulus in comparison with that of on shear modulus and when the length of nanotube decreases, the Young modulus decreases similarly.
polymer concrete, compressive strength, flexural strength, estimation of strength, micromechanics... more polymer concrete, compressive strength, flexural strength, estimation of strength, micromechanics I n comparison with conventional concrete, the polymer concrete has considerably better mechanical properties. Meanwhile, polymer concrete is more expensive than traditional cement concretes. Considering the good mechanical properties of polymer concrete, its applications can be developed by reducing manufacturing costs. In this study, in order to improve the mechanical properties and reduce the manufacturing costs of polymer concrete, a new formulation is presented. In this formulation, the more common mixture of large and small aggregates was replaced by silica sand. In addition, in order to reduce the manufacturing costs, polyester resin was used instead of epoxy resin as the base material. The compressive and three-point bending tests showed that the polyester-based concrete had a higher compressive strength (20%) in comparison with the epoxy-based concrete, while their bending stre...
The main objective of this research is to predict Young’s modulus and Poisson’s ratio of carbon n... more The main objective of this research is to predict Young’s modulus and Poisson’s ratio of carbon nanotube reinforced polymer (CNTRP). A full stochastic multi-scale modeling technique is developed to consider all effected parameters of all nano, micro, meso and macro-scales. The length, orientation, agglomeration, curvature and dispersion of the CNTs are taken into account as random parameters. Comparing results of simulation with experimental observations, it is shown that developed method is an efficient tool to predict elastic properties of CNTRP.
دییامن هدافتسا لیذ ترابع زا هلاقم نیا هب عاجرا يارب : Please cite this article using: M. M. Shokr... more دییامن هدافتسا لیذ ترابع زا هلاقم نیا هب عاجرا يارب : Please cite this article using: M. M. Shokrieh, A. R. Shamaei Kashani, R. Mosalmani, A dynamic-micromechanical constitutive model to predict the strain rate dependent shear behavior of neat and reinforced polymers with carbon nanofibers, Modares Mechanical Engineering, Vol. 15, No. 7, pp. 13-21, 2015 (In Persian) هئارا لدم کی يراتخاس یکیمانید تهج یکیناکمورکیام شیپ ینیب راتفر یشرب اهرمیلپ و ياهرمیلپ تیوقت هدش نبرک فایلاونان اب
Aerospace Mechanics Journal, 2009
Resin transfer molding, that is a sub-branch of liquid composite molding, is one of the manufactu... more Resin transfer molding, that is a sub-branch of liquid composite molding, is one of the manufacturing methods of polymeric composites. Various modification has been presented to improve this proces ...
This study aims to obtain mechanical properties of multi-phase composite materials with high volu... more This study aims to obtain mechanical properties of multi-phase composite materials with high volume fraction of inclusion. For this purpose, a new method is presented for the homogenization of multi-phase composites. A new homogenization method was developed based on a combination of the Mori-Tanaka model and the differential model. The new homogenization method was named MT-DS model which consists of four stages. In the first stage, average strain created in the inclusion is calculated. Then, based on the modified differential scheme, the stiffness tensor for the homogenized material is calculated. In the third stage, based on the Mori-Tanaka model as well as Eshelby equations, the strain concentration tensor is calculated. Finally, in the fourth stage, using the MT-DS model, the strain concentration and stiffness tensors for the homogenized material are calculated. For homogenization, according to shape of the inclusion as well as its volume fraction, the strain concentration tensor is calculated and the homogenized material is used in order to calculate the stiffness tensor. Using this method, in each stage, instead of properties of the raw matrix material, properties of the homogenized matrix material are included in the calculations. The effect of other inclusions on the adjacent inclusions is also considered. This procedure is continuously repeated until the equivalent stiffness tensor is obtained. To validate the new proposed model, obtained results were evaluated in a comparison with the results of the experiments.
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Papers by Mahmood Shokrieh