Mechanical Properties

The rolling process is one of the common and widely used methods in manufacturing and forming various parts. The rolling process has a significant effect on the mechanical properties and microstructure of materials, which making it important in the manufacturing of products. 3D printing or additive manufacturing is a of the new method in producing parts that allows for the direct creation of parts from digital models. This process is based on creation parts layer by layer and can produce various parts quickly and with high precision. The unique features of additive manufacturing, such as design freedom, no need to dies and auxiliary equipment, and the ability to produce complex and integrated parts, have caught the attention of many industries such as aerospace, oil and gas, marine and automotive industries to use this method. In the other hand, problems such as microstructure defects, distortion, residual stress and anisotropy of mechanical properties are among the challenges in additive manufactured or 3D printed parts. Using the rolling process to modify 3D printed parts is one way to improve the microstructure and mechanical properties of materials. By combining the rolling process with additive manufacturing, hardness, strength, and elongation can be increased by homogenizing and refining grains of the structure. Also, this process can reduce distortion and residual stress in the additive manufactured parts.

The purpose of this paper is to investigate the manufacturing of a steel wall using gas metal arc welding (GMAW) process and to study its dimensional features, mechanical properties, and the microstructure. The selected parameters were the interpass dwell time, the welding speed, and the wire feeding speed. Based on the results, the average wall height and thickness decreases with increasing welding speed due to less weld deposition in the layer. A relationship between the wall thickness and height in terms of the welding speed and wire feeding speed was proposed. A longer interpass dwell time increased the wall height. The effective area percentage also increased with increasing welding speed. Tensile strength and elongation (%) were investigated based on the presence or absence of voids and microstructure. In high welding speed and long interpass dwell time, the microstructure included columnar grains with fine widmanstätten ferrite and intergranular pearlite. At low welding speed and short interpass dwell time, the microstructure consisted mostly of blocky ferrite and coarse pearlite. Both of these structures showed satisfactory strength and elongation. But in the other conditions, where the possibility of brittle phases in the heat-affected zone was higher, the strength and elongation decreased.

Production and aging environment moisture is one of the most important factors affecting solid composite propellant properties. In this research by designing necessary experiments, effect of production and aging environment moisture on the rheological, mechanical, ballistic and aging properties of solid composite propellant and also mechanism of moisture effects on the existent interactions in its structure were assessed. Experimental results showed that, producing propellant in the environment with up to 50 % humidity doesn’t have noticeable effect on its primary properties. But producing propellant in environment with 80-9o % humidity, decreased ultra tensile strength of 35 % and strain at ultra tensile strength of 17 % comparing the the base sample after fourteenth day of curing process. Aging of propellant in the environment with (50-70) % humidity during 5 months decreased ultra tensile strength of 49 % and strain at ultra tensile strength of 33 %. Burning rate determining experiment showed that aging of propellant in environment with saturated moisture for long time reduced the burning rate in the same pressures. Scanning electron microscopy (SEM) of the aged sample in environment with saturated moisture shows that the main reason of reducing mechanical properties are debonding of interaction between AP with binder matrix and intense abscission of AP from the sample

In this research, copper/silver-silicon carbide Cu-Ag-SiC composite was prepared by the friction stir processing (FSP). For this purpose, nanometer and micrometer SiC particles were used as reinforcing particles. In order to evaluate the microstructural properties, X-ray diffraction (XRD) analysis, scanning electron microscope and optical microscope were employed. Evaluation of mechanical properties through microhardness measurement, tensile test and pin on disc test were utilized to evaluate the wear behavior of the composite. The results of X-ray analysis revealed the presence of two phases of CuAg solid solution along with SiC particles, which indicated the formation of Cu-Ag-SiC composite. The addition of nano-particles led to a significant decrease in the intensity of peaks compared to micro-particles. This indicated a decrease in the grain size of the CuAg matrix. Using the FSP in the presence of reinforcing particles and without it led to a decrease in the crystal size and average grain size compared to the sample without FSP. So that the grain size of the sample without FSP and the FSPed sample without reinforcing particles and with nano-reinforcing particles were found to be about 46.3, 19.2 and 3.6 µm, respectively. The wear mechanism in the sample before FSP was adhesive wear due to its soft nature of the matrix, and after FSP in the sample without reinforcing particles, the adhesive wear decreased and due to the addition of silicon carbide micro and nano- particles reinforcement, the wear mechanism in entirely altered to abrasive wear. Overall, it can be stated that the addition of silicon carbide nanoparticles by FSP leads to the fabrication of  Cu-Ag-SiC composite with high mechanical properties.

In this research, the influence of friction stir welding parameters (tool traverse speed ranging from 50 to 150 mm/min, and tool rotational speed ranging from 300 to 1100 rpm) was investigated on the microstructure and mechanical properties of AA5052 aluminum/PP-Z30S polypropylene joint. Results showed that joint formation was accompanied by the formation of mechanical locks in the shape of anchor-like aluminum pieces. Decreasing the heat input (either by increasing the tool traverse speed or decreasing the tool rotational speed) resulted in the formation of larger anchors. The results of tensile-shear test showed that increasing the tool traverse speed from 50 to 100 mm/min led to an enhancement in the fracture load (by ~10%), while at higher traverse speeds, the fracture load decreased (from 235 to 181 N) due to the formation of defects and voids at the joint interface. An increase in the tool rotational speed from 300 to 900 rpm resulted in a superior fracture load (by 70%) due to the formation of anchors perpendicular to the polymer surface with greater penetration depth.