نشریه علوم و فناوری کامپوزیت
سال دهم شماره 4 (پیاپی 38، زمستان 1402)

This research was conducted with the aim of investigating the compatibilizer of methyl diphenyl diisocyanate and maleic anhydride polypropylene on the morphology and physical-mechanical properties of wood-plastic composite containing nanosilica and nanoclay, high density polyethylene, wood flour. For this purpose, 3% compatibilizer along with nano particles at 3 levels of 0%, 2%, 4% were mixed with an internal mixer and test samples were prepared using the injection molding method. Then, the physical and mechanical properties of the samples such as water absorption and thickness swelling, modulus and tensile and bending resistances and impact resistance were performed on the samples. The results showed that the increase of nano particles had a positive effect on the physical and mechanical properties except impact resistance and improved them. However, the presence of nano-silica has led to an increase in the water absorption of composites. Examining the FTIR spectra and XRD patterns, the distribution of nanoclay in the field of polymer is of interlayer type, and in nanosilica, there is the accumulation of nano particles and the increase in the dimensions of the crystals in the composite. The results of bending and tensile strength were confirmed by scanning electric microscope.

In this research, short carbon fibers are used as reinforcement with percentages of two, four, six and eight percent in aluminum 5083 by hot pressing method, with a pressure of 100 MPa, a temperature of 500 degrees Celsius, for one hour and in an argon gas environment. used. A low-energy mill was used to mix powdered raw materials in optimized milling times. Then the density of the resulting composite samples was calculated and mechanical tests such as hardness measurement, tensile stress and bending stress were investigated and finally the fracture sections of the tensile samples were studied. The best results for the composite sample with four percent by volume of reinforcement with a relative density of 98.4 in the optimal mixing time of four hours, tensile strength 360.28 MPa, bending strength 423.77 MPa and hardness 6.101 Vickers with the failure mechanism of pulling out the fibers and the bridging of the cracks on the fibers was obtained. Came.

In this research, the use of composites based on bismuth oxide with impurities of Gadolinium, titanium, yttrium, tungsten, zirconium and zinc as a protective material for effective protection has been discussed. In here, the evaluation of X-ray and gamma ray shielding for selected composites has been done using the simulation tool based on Monte Carlo method of Geant4, in the photon energy range of 15 keV to 15 MeV. To investigate the performance of these selected composites, effective quantities in gamma ray attenuation such as: attenuation coefficients (total, linear and mass), mean free distance, one-tenth and half-value layers, the ratio of Compton scattering to the total attenuation coefficient have been calculated. To verify the simulation results, the simulation results are compared with the data extracted from the NIST-XCOM database, and the data extracted from the NIST-XCOM database and the simulation results are in good agreement with each other. Also, the percentage deviation (RD) between the calculated results is less than 2% in most cases. Due to the high atomic number of bismuth and Gadolinium, compound of bismuth oxide containing Gadolinium absorb and attenuate high-energy photons with higher efficiency than lead and are less toxic. Bismuth oxide compound shields with Gadolinium element can be used as absorbers of high-energy photons for various jobs in the field of medical radiation, such as doctors, dental hygienists, operating room workers, and radiologists, and can improve the health and safety of workers.

In this study, the modal analysis of sandwich conical shells with a composite lattice core was presented using experimental and numerical methods. For this purpose, samples of such sandwich were made of two identical Kevlar-fabric face sheets and a composite (glass-carbon fibers) lattice core with regular hexagonal cells. Next, modal tests were carried out to extract the natural frequencies and the mode shapes by collecting frequency responses using a laser accelerometer. Also, ABAQUS FE simulations were performed using three-dimensional elements and were validated with the results obtained from modal tests. According to the experimental results, the difference in the natural frequencies of samples is less than 3% for the first mode shape (m,n)=(1,2) and 6% for the second mode shape (m,n)=(1,3). Therefore, it can be concluded that there is the least possible error in the conceptual design and the implementation of various manufacturing processes. In addition, there is good agreement between the results obtained from modal tests and ABAQUS finite element method, i.e. the maximum difference in natural frequencies of the first four mode shape is approximately 16%.

As components of the car's dashboard, there is a support structure which is called cross-car beam (CCB). This beam bears the loads and respond to crash forces. Cross-car beam is essential, because its functions include safety, structural support of the instrument panel and passing sound, vibration and harshness (NVH) standards. If the natural frequencies of the cross-car beam overlap with one of the excitement frequencies, a phenomenon known as resonance occurs. According to the low stiffness of the cross-car beam, the modal response of the cross-car beam should be studied and modified to avoid this destructive phenomenon. In this article, by changing the material of the cross-car beam from steel to polymer-based composite, the beam was redesigned and its vibration performance and stress analysis were performed. The simulations showed that changing the material of the metal beam to glass-epoxy composite, carbon-epoxy composite and fiber in metal laminate (FML) increased the natural frequency by 18%. In order to avoid resonance, more increasing is required for natural frequency amount. Therefore, several supports were added to connect beam to car body and reduce degree of freedom. Changing the material and increasing supports at the same time resulted 460% increasing for natural frequency. Because excessive increase of natural frequency will lead to increasing structure rigidity and as a result stress concentration, so numerical stress analysis was done and finally a suitable laminated composite was suggested for cross-car beam.

Fiber Metal Laminates are new composite structures in which several thin metal sheets and composite layers are connected together. These structures have properties such as high fatigue resistance, high impact resistance and high energy absorption, which have led to a growing use of them in various industries. In this study, damage in FMLs under tensile static loading, including matrix cracking, delamination induced by matrix cracking and plasticity in metal layers, was examined. Using the analytical model, stress distribution and energy release rate were extracted in FML containing matrix cracking and delamination. Numerical modeling of FML containing such damages was also performed. The stress distribution results obtained from the analytical and numerical models were compared, and good agreement between the results was observed. Furthermore, the FML samples were subjected to tensile test and the damages that occurred in them were displayed. By using the analytical model and calculating energy release rate, the matrix crack saturation and the initiation of delamination at the crack density of 0.38 (the distance between two cracks is 2.7 mm) were extracted. By observing the experimental samples, this crack density was observed in most of the length of the sample, but due to various reasons such as manufacturing defects, in some areas the distance between the cracks was larger than the mentioned value.