مجله مهندسی ساخت و تولید ایران
سال هفتم شماره 5 (امرداد 1399)

Severe plastic deformation has been attracted the attention of researchers during the last couple of decades as a method to produce fine grain materials with high strength. In this study a new technique, called hydro assisted tube pressing (HATP), is proposed for severe plastic deformation of tubular materials. In this technique, unlike conventional methods, the fluid pressure is employed instead of die and mandrel, to maintain the geometry of the tube, and also to eliminate the die and tube surface contacts, making the required force in this process independent of the length of the tube. Each pass of the HATP process involves two half-cycles that by passing the tube through the deformation channel during the first and second half-cycle, respectively, the tube’s diameter increases and decreases and imposing a plastic strain on the tube. Finite element simulation results showed that the force required in this technique is 60% less than that in the PTCAP technique for AL1050 with the specified dimensions. In this proposed technique, by increasing the length of the tube, the force will not increase, which is one of the advantages of this method for producing high strength tubes with large dimensions. The experiments on AA1050 tubular specimens showed that the yield and ultimate tensile strengths increase from 51 and 65 MPa to 78 and 96 MPa, respectively, after two passes of HATP. Moreover, the micro-hardness tests on the samples after three half-cycles showed an increase in the hardness from 28 to 35 HV.

In this study, the effect of processing parameters on the shape memory properties of 3D-printed PLA products, in the fused deposition modeling (FDM) method, was investigated. The FDM is one of the most widely used additive manufacturing methods due to its low cost and high process capability in fabricating components with complex geometries. Manufacture of shape-memory materials in a 3D printing process is also called 4D printing. Utilizing the three-point bending test, the shape memory behaviors of the printed specimens, with infill percentages of 50% and 100% and printing angles of 0, ±45, and 90 degrees, were measured. To evaluate and compare the effects of the 3D printing process parameters on the shape memory properties, similar specimens with the same geometry were produced using the compression molding process. According to the results, the force recovery of the samples with 100% and 50% fill percentages were 61.6% and 68.9%, respectively, compared to 60.8% for the counterpart samples produced via compression molding. Also, the shape recovery of the FDM process and the compression molding were recorded as 86.3% and 95%, respectively. Assumingly, the higher density and the lack of porosity of the samples produced via the compression molding process increased the initial programming force and the recovered force, accordingly.

Pulse thermography is used in various industries to inspect and monitor certain parts and assemblies. Corrosion in steel structures and components is one of the most important defects that impose huge costs on industries each year, which can be partially reduced by timely detection. There are many ways to diagnose corrosion, but the high speed of testing, the need to not sample, the inspection of large surfaces in low time, and the ability to perform it on many materials, are the advantages of pulse thermography. In this paper, from non-destructive testing methods, pulsed thermography is used to detect corrosion defects in metal sheets. The samples tested in this paper are made of low carbon steel and alloy steel which have many applications in various industries. The aim of this study was to simulate and identify corrosion defects in steel parts. Various defects were designed and fabricated to evaluate the strength of this non-destructive testing in determining the minimum diameter and maximum depth. The effects of excitation sources distance, radiation angle, material of samples and duration of excitation on the tests were investigated. The ability to detect defects without the need for image processing has been exploited to the advantage of the employed method. From the pattern of defects created in the samples, the smallest detected defect in the low carbon steel specimen was 4 mm in diameter at 1 mm depth and in the alloy steel specimen the smallest detected defect was 3 mm in diameter at 1 mm depth.

Different definitions of nano-technology prove this truth that nano-technology includes wide range of various scientific fields. In fact, nano-technology is an interdisciplinary science and a new approach to the all domains. In Nanomanipulation process by utilizing Atomic Force Microscope, contact models play important role for determining critical force and time which constituent the first phase of this process. In current study, two contact stages in Nanomanipulation of gold cylindrical micro/nano particles are investigated. First stage is the contact of micro/nanoparticles and substrate and the second one is the contact between cantilever tip and micro/nanoparticles. For the first stage, five significant contact models including Hertz, Lundeberg, Dawson, Nikpour and Heoprich have been used. Also in the second stage, contact models of Hertz and JKR have been applied. Dawson model predicts maximum and Nikpour model predicts the least amounts of deformation and penetration depth for the contact of the first stage of deformation between substrate and gold cylindrical micro/nanoparticles. Also the deformation between cylindrical particles and spherical tip apex has the minimum amount in Hertz model and the highest amount of deformation and penetration depth have been showed in JKR model due to regarding adhesion forces. Generally, the results indicate increasing the angle of tip apex along the z axis leads to decrease of penetration depth and the amount of deformation between particles and substrate which Lundeberg model has been demonstrated the least amount and Nikpour model has been showed the highest amount of decrease.

Due to the need of some industries for the direct bonding of metal and composite layers to each other and its special applications in the industry, this paper examines the solution for adhesive bonding between steel and carbon-phenolic composite. Since this composite layer does not inherently have a good adhesion to the steel surface, steel substrate surface preparation is inevitable in order to create a resistant bonding. In this research, for the preparation of steel surfaces, the knurling process with four types of knurl wheels with different geometries and pitches was used and then, by applying the adhesion tensile test, the strength of adhesive bonding of the composite layer to their surface was investigated. The results showed that in about 50% of all samples, the knurling operation was able to increase the adhesive bond strength compared to the sample with smooth metal surface. In Comparison of adhesive bond strength for two cross and straight knurl patterns, the tensile bond strength created by straight knurl shape was reported about 5 times greater than the cross knurl shape in the case of equal tensile and at pitch equal 0.6 mm. Also, the highest value for adhesive bond strength was reported in 12.62 MPa for preparated surface by using of straight knurl shape at pitch equal 0.6 mm which increased by 76% compared to machined smooth surface.

In this research, the surface of aluminum 7075-T6 was reinforced by pumice micro and nanoparticles using the friction stir process (FSP). First, optimum parameters of pass number (1 & 4 pass), travel speed (40 & 80 mm/min) and tool rotation rate (800 & 1200 rpm) considering the microstructure, hardness and resistance to wear were selected. Results showed that with increasing the pass number, decreasing the travel speed and increasing the tool rotation rate, the grain size in stirred zone (according to the microscopy images) decreased, while the hardness (according to the Vickers micro-hardness test results) and resistance to wear (according to the pin on disk test results) increased. Under conditions of single pass, travel speed of 80 mm/min and tool rotation rate of 800 rpm, average grain size in stirred zone was 10 micron; while under conditions of four passes, travel speed of 40 mm/min and tool rotation rate of 1200 rpm it was reduced to 5 micron that led to an increase in average micro-hardness from 80.2 to 94.6 Vickers and a decrease in wear amount from 33 to 27 mg after a sliding distance of 1000 m. By addition of pumice micro and nanoparticles, average micro-hardness was increased to 99.6 and 107.8 Vickers and wear amount was decreased to 24 and 20 mg, respectively.