نشریه علوم و فناوری کامپوزیت
سال یازدهم شماره 1 (پیاپی 39، بهار 1403)

Experts have always desired to obtain materials with the desired properties or required constituents. The optimization of microstructures is considered to ensure optimal mode and accurate calculations. Microstructures, as heterogeneous materials, undergo an optimization process to optimize their structure. In this article, we implement topology optimization design for multiphase elastic microstructure using a compensation factor and numerical homogenization method. During the study, numerical optimization is performed by applying calculations on design changes consisting of the volume percentage of each phase in each element. The technique used to solve the topology optimization problem involves dividing it into several series of two-phase subproblems, with a conventional two-phase operator used in the optimization space. In this research, we obtained values of 0.7264, 0.4447, and 0.3008 for shear modulus, bulk modulus, and axial stiffness, respectively. Generally, the calculation rate depends on the number of phases involved in the structure design process. Previous studies have addressed this question for symmetric, symmetrical, and two-phase microstructures. However, in this study, we address this design problem by creating tensors of material properties as a function of the volume percentage. This approach is achieved by defining a design space and establishing regular upper and lower boundaries for local features. These boundaries are maintained to ensure consistency and standardization in subsequent works related to multiphase microstructure design.

In this research, experimental and numerical studies have been conducted to investigate the performance of concrete beams reinforced with FRP materials using the Near Surface Mounted (NSM) reinforcement method. In this method, the separation of FRP is delayed, and these materials are less exposed to adverse environmental conditions. In this study, after achieving a suitable mix design for concrete and performing dimensional analysis for scaling laboratory samples, six concrete beam samples were constructed. These six samples were divided into two groups, one subjected to low-velocity impact loading and the other to static bending loading. In each group, a control sample without reinforcement was considered. Additionally, two of the beams were reinforced using GFRP rebars, and the other two were reinforced with CFRP composite plates. According to the results, the beams reinforced with CFRP plates and GFRP rebars experienced an increase in flexural strength by 15.3% and 24.7%, respectively, compared to the control sample under static bending loading. Furthermore, the maximum displacement of these samples at the mid-span under impact loading decreased by 23.36% and 40%, respectively. Also, due to the increased stiffness of the FRP-reinforced samples, the acceleration at the center of the span in these beams significantly increased compared to the control sample. Based on this, it can be concluded that concrete beams reinforced with FRP materials using the NSM method show satisfactory performance under static and dynamic loading.

In this article, the strength of the filament produced by the extrusion method has been investigated. For this purpose, testing samples were produced using ABS and carbon nanotubes as printable nanocomposite filaments in 3D printer. Carbon nanotubes were incorporated into ABS, and nanocomposite filaments were produced and their strengths were measured. In order to predict the strength of a nanocomposite filament, a suitable multi-scale model was developed. This model started from the microscale and after passing the in-between scale of meso, ended at the macroscale. For each scale, a suitable and separate representative volume element was defined, and its strength was predicted. Two parameters, CNT length and orientation, were captured at the microscale, and CNT agglomeration was taken into account at the mesoscale. Finally, at the macroscale, the strength of the nanocomposite filament was estimated using a genetic algorithm. In this study, the strength of the nanocomposite was calculated with two weight fractions of 0.1% and 0.5%, and it was observed that the final strength of the nanocomposite with weight fractions of 0.1% and 0.5% increased by 14% and 20%, respectively. The outputs of the modeling procedure were in very good agreement with experimental observations.

Cyanate esters are one the most suitable matrixes for production of high temperature composites with carbon fibers due to their excellent thermo-mechanical properties. Since the curing of this resin has a high heat release, applying a suitable curing cycle has the ability to control the heat release during the curing. Cyanate ester provides high adhesion to carbon fibers even in less resin content, so cyanate ester can be used as a matrix for preparing advanced composites. 2,2'-bis(4-cyanatophenyl)propane resin was synthesized by the reaction of cyanogen bromide and bisphenol A. The synthesized resin was characterized by FT-IR, 1H-NMR and 13C-NMR spectroscopies. The curing behavior of cyanate ester resin was determined by DSC and a suitable curing cycle was defined and it’s efficiency was monitored by FT-IR. Cyanate ester/carbon fiber composite with 30% and 44% resin contents was prepared and their ILSS was determined and thermal and mechanical properties were investigated by DMTA and TGA. The defined curing cycle for 2,2'-bis(4-cyanatophenyl)propane had the ability to control the high heat release of cuing reaction with the curing ability of the resin up to 95.6%. Cyanate ester has a high adhesion to carbon fibers in the composite even in the relatively low resin content 30%. Hence, the amount of ILSS was increased about 9% compared to the ILSS for composite with 44% resin content. At temperatures as high as 250 °C, composite had only 16% decrease in flexural modulus. The cyanate ester/carbon fiber composite had a char yeild of 82.6%.

In this paper, the effect of negative Poisson's ratio on the mechanical response and improving the damage behavior of carbon/epoxy composite laminates under low-velocity impact is studied. For this purpose, a MATLAB code is developed to determine the range of sequence angles to achieve both negative Poisson's ratio in-plane and through-thickness based on CLT. Also, the progressive damage model is written and implemented using the user-material subroutine-VUMAT consisting of Hashin and Puck failure criteria and the damage evolution model based on the equivalent-strain method to predict the initiation and evolution of damage for matrix and fiber. In the research process, the impact resistance performance of auxetic laminates is evaluated in comparison with composite laminates with positive Poisson's ratio with cross-ply and angle-ply sequences. The results showed that in some damage modes, auxetic behavior can lead to the improvement of composite laminate damage. Based on the analysis of the results, the highest damage amount of delamination, matrix tension, matrix compression, and fiber tension damage is observed in angle-ply, through-thickness auxetic, cross-ply, and through-thickness auxetic laminates, respectively. Meanwhile, cross-ply, angle-ply, and through-thickness auxetic laminates with characteristics such as high impact force, low impact time, low maximum displacement, and less dissipated energy than in-plane auxetic laminate are suitable for use in structures with hardwall design approach. Also, the in-plane auxetic laminate with features such as low impact force, high impact time, high displacement, and more dissipated energy than other composite laminates, is practical and operational for use in sacrificial structures.

Highly filled composites consist of two components of polymer matrix and different fillers with a weight fraction of more than 30%. There are different methods for studying the slurry flow behavior. In this article, the effect of pre-shear on the viscosity and homogeneity of the composite slurry and the final product has been investigated. The Viscosity of highly filled composite slurry with different shear rates in the temperature range of 40˚C after mixing in composites binder / aluminum / ammonium perchlorate and (binder / aluminum / ammonium perchlorate with Cross-linking agent) with the use of a Brookfield rotary viscometer was measured. It was observed that the viscosity and its dependence on the shear rate correspond to the behavior of the pseudoplastic fluid. Using the equation of power law, determining and analyzing the parameters of viscosity index (k) and pseudoplastic index (n), it was shown that the rheological behavior of highly filled composite depends significantly on the physical interactions between the filler and the matrix. it was observed that after adding the curing agent, the viscosity of the highly filled composite increases rapidly, and this increase in viscosity is due to smaller solid particles, an increase in molecular weight, and the formation of crosslinks in the prepolymer structure. Investigating the effect of mixing time on product homogeneity showed that the most homogeneous product was obtained during the entire mixing process of 135 minutes.

The authors requested to change the English name of the first author from “Amirreza, Amirirnejad” to “Amirreza Amirinejad” in the English section of the article reference, which is implemented in this amendment. It should be noted that this was done according to the written request of the authors.