نشریه علوم و فناوری کامپوزیت
سال دهم شماره 1 (پیاپی 35، بهار 1402)

Polyvinyl chloride owns a special place in various industries as the third most used polymer worldwide. Due to the widespread usage of synthetic leather, one of the research gaps in this field is the study and optimization of curing conditions. The present research aims to investigate the effects of temperature and time of curing on the mechanical properties of synthetic leather to establish the optimal temperature and time of curing. To this end, synthetic leather films were prepared using the knife coating technique (KCT). Then specimens were placed at different temperatures and times to perform the curing process. Thermal degradation was determined by checking the color of the samples. Also, to investigate the effect of curing conditions on the mechanical behavior of synthetic leather, dumbbell-shaped samples were prepared and subjected to uniaxial tensile tests. The results showed that due to the high molecular motions of the particles at 190°C, the plasticizer penetrates well into the chains of emulsion PVC and thus increases its mechanical properties. Additionally, the mechanical properties of the synthetic leather were enhanced by increasing the cure time at constant temperatures. Afterward, thermal degradation occurred due to the long-term curing process, reducing mechanical properties. According to the obtained results, the curing conditions can significantly affect the mechanical properties of synthetic leather. Likewise, identifying the optimal temperature and time of curing in the artificial leather industry allows the development of products with high mechanical properties without special fillers.

Friction stir process (FSP) was used to improve hardness and tribological properties of Al-5083 aluminum alloy through formation of metal matrix composite (MMC) material. The process involved the use of titanium diboride powder (TiB2) and carbon nanotubes reinforcing materials. The number of passes during the process was varied. Observations of the microstructure of the composite materials were made using scanning electron microscopy (SEM), while the composited surface layers were examined using microhardness testing. After conducting four passes using FSP, the surface nanocomposite obtained from carbon nanotubes and TiB2 yielded a maximum increase in hardness of 32.3%, and 21.6% compared to the base alloy respectively. Moreover, the samples produced with four passes, containing carbon nanotubes, showed a hardness 8% greater than the samples produced with the same number of passes, but with TiB2. Additionally, the highest wear resistance was also obtained using four passes. The wear resistance exhibited by the carbon nanotube-reinforced composite was approximately 45% greater than the TiB2 powder-reinforced composite. Hence, the use of FSP can potentially increase the working life of the part in wear conditions by up to 3.5 times.

With the development and expansion of 3D printing and upgrading to 4D printing, it became possible for static 3D printed structures to turn them into a dynamic structure over time by applying one or more stimuli simultaneously. 4D printing was able to transform a simple geometry into a complex geometry without the need for printing the entire geometry from the beginning. Also, 4D printing reduced production costs, wasted fewer materials, increased production speed, and added features such as self-assembly, self-compatibility, and self-healing to the features related to 3D printed structures. In this study, first, different types of smart materials (such as shape memory polymers, shape memory alloys, hydrogels, etc.) and activation mechanisms (such as water, heat, pH, etc.) used in 4D printing were evaluated. Then, focusing on polymers and polymer composites, the properties and characteristics of 4D printing were described. In the following, the types of 3D printing methods utilized in the 4D printing of polymers were explained, and in a separate section, the effect of the printing process parameters using an FDM printer on the response of the materials used to the applied stimulus is discussed. Furthermore, the expansion of 4D printing in various industries such as medicine, aerospace, sensors, robotics, and other fields of application in which 4D printing entered was discussed and at the end of this study, the existing challenges and future opportunities were profoundly discussed.

In this research, a method based on the vacuum infusion process is proposed for making sandwich panels used in the marine industry. The mechanical properties of the product made with this method have been significantly improved compared to the adhesive bonding method, and also from an economic point of view, it’s cost-effective to use this method. In this method, the construction of face-sheets and their adhesion to the core is done in a single step, which results in some benefits such as reducing construction costs, increasing the production speed and improving the quality of the face-sheets adhesion to the core. According to the intended application, i.e. application in the marine industry, the core is made of grooved Polyvinyl Chloride (PVC) foam and the face-sheets are made of glass/vinylester, which are well-known materials in the marine industry. The mechanical properties of the sandwich panel made by the proposed method have been investigated in both bending and compression loading. The results indicate that in the product made with the proposed method, the bending strength has increased by 78%, the compressive strength has increased by 92%, and the energy absorption has increased by 101% compared to the sandwich panel made by adhesive bonding method. The main factor in improving the mechanical properties of this product is the creation of a network of resin in the empty space of the grooves, which creates a structure similar to the foam filled honeycomb cores and strengthens the core, especially in the thickness direction.

Composites of continuous fibers have higher mechanical performance than short fibers, which is why they are produced and used significantly in the aviation industry. One of the new methods of joining composites is ultrasonic welding. In this process, by applying high power (100 to 2000 watts) and high frequency (15 to 100 kHz) vibrations to the joint of two parts, heat is generated in the joint and causes the two parts to stick together. In this research, the parameters of the ultrasonic welding of polyamide 6 glass composite, the effect of the interlayer film, and the direction of the fibers on the strength of the connection have been investigated. Ultimately, the ultrasonic welding connection has been compared with the adhesive bond. In examining the connection as an edge-to-edge connection, the samples were cut according to ASTM D5868 standard and subjected to a tensile-shear test after ultrasonic welding. Considering the average input parameters for time, pressure, and power, it was observed that using a pure polymer film layer as the interlayer film increases the welding strength. By changing the direction of the fibers of all layers by 90 degrees, the welding strength decreased a little. The amount of polymer and fiber protrusion increased, and the appearance quality decreased. In comparing the welding connection with the adhesive bond, the value of the welding strength was higher than the strength of the adhesive connection. Also, the time spent on the welding connection was much less than on the adhesive bonding.

Fabricating Metal matrix composites (MMCs) reinforced by fibers is one of the biggest issues in the engineering in various industries, due to having production limitations. In this research has been tried to fabricate aluminum matrix composites reinforced by fibers through thixomixing as novel method in semi-solid state and by helping shear force. For doing this, the basalt fibers (with the volume fraction of 2, 4, and 6) were dispersed into the molten A356 aluminum and by creating the shear mixing in the range of semi-solid temperature of aluminum, the composites were fabricated. For investigating the mechanical behavior of fabricated composites, the Brinell hardness and shear punch tests were used. Also, microstructural investigations and elemental analysis by scanning electron microscope were performed. The obtained results showed that by increasing the fibers content, the hardness and shear strength were simultaneously improved, which resulted to improve the ultimate strength of composite. The shear strength from 119.1 MPa (for without fibers sample) to 132.3 MPa (in reinforced composite by 6 vol.% basalt fibers) was increased. Also, the hardness test results showed an increase in Brinell hardness from 62.3 to 70.8 Hb in the sample with 6 vol.% of basalt fibers. The ultimate tensile strength in this sample also showed the 10.9% improvement. Microstructural investigations depicted that the formation of intermetallic compounds at the interface caused to improve the mechanical properties.