M. Sabokrouh , M.r. Farahani ,
Volume 19, Issue 1 (1-2019)
Abstract
The weld residual stresses decrease the design stress in gas transportation pipelines. In this paper, two X70 steel pipes of 56 inch outside diameter were firstly girth welded. Experimental hole drilling test was conducted to evaluate the residual stress distribution in this joint. Then, the finite element simulation of the welding process was performed to evaluate the residual stress distribution precisely. The numerical results were verified by comparison with the obtained experimental measurements. The qualitative results achieved match properly with the experimental results. Simulation results (with a difference about 15% compared to experimental results) evaluated the maximum residual stress in hoop direction of pipe’s external weld metal. The experimental data showed that the maximum tensile residual stress was located on the center line of the weld gap on the pipe outer surface alongside with the pipe hoop direction. Moreover, the maximum compressive (hoop and axial) residual stresses occurred on the pipe inner surface in heat affected zone. The variations of the hoop residual stresses on the inner and outer surfaces of the pipe had similar trend with tensile distribution at the center line of the weld gap. However, these stresses showed different trends (tensile stress on the outer surface, and compressive stress on the inner surface) with distancing from the weld center line.
Mohammad-Ali Rezaei, H. Naffakh-Moosavy,
Volume 19, Issue 2 (2-2019)
Abstract
Inconel 718 is precipitation strengthened Ni-base superalloy that is strengthened by “γ″ precipitate with the Ni3Nb chemical composition, is widely used for medium and high temperature applications in many industries. The aim of this study is to evaluate the effects of pre-cold treatment on microstructure, geometry of weld, Weldability, and mechanism of HAZ liquation cracking in Inconel 718 superalloy by Nd:YAG pulsed laser welding. Microstructure was investigated, using optical microscope and scanning electron microscope and hardness test was used to investigate mechanical properties. The results of numerical calculations using Rosental relation showed that the length of different welding regions including Mushy Zone (MZ), Partially Melted Zone (PMZ), and Heat Affected Zone (HAZ) decreased by 46%, 46%, and 56%, respectively. The experimental calculations also indicated that the length of PMZ and HAZ, as well as the HAZ area decreased by 2.1, 2.5, and 2.5 times, respectively. Considering that grain boundary liquation was observed in all samples, the possible mechanism for HAZ liquation cracking is constitutional liquation of Nb-rich carbides and delta precipitates that encourages the formation of liquid films in the grain boundaries and causes HAZ liquation cracking in this region. Also, the hardness profile indicates that the hardness of the weld metal increased by using pre-cold conditions.
D. Rahmatabadi, A. Shahmirzaloo, M. Farahani, R. Hashemi,
Volume 19, Issue 2 (2-2019)
Abstract
The cold roll bonding (CRB) is a solid state welding process for bonding similar and dissimilar metals. The use of materials produced by the CRB method for different applications and the prediction of their behavior in simulation software requires the complete and accurate identification of their mechanical properties. Digital image correlation (DIC) is a powerful non-contact method for measuring the field of material deformation. Recently, the DIC method has been developed and widely used in various studies due to its advantages. In this research, two-layered aluminum alloy 1050 was produced via CRB process with applying 50% reduction of thickness at ambient temperature and then using the 2D-DIC system to extract distribution of the strain field during the uniaxial tensile test at rolling direction. Strain in two directions of length and width was calculated, using DIC and strain in terms of thickness, effective strain, and anisotropy coefficient, using plasticity relationships. Moreover, for the first time, using the virtual field methods (VFM), elastic and plastic parameters such as elastic modulus, Poisson ratio, strength coefficient, strain hardening exponent, and yield stress were calculated. The results showed that the strength and microhardness were significantly increased due to the work hardening and increasing the density of dislocations, and the elongation and strain hardening exponent were reduced. The strength for the two-layered aluminum was 113MPa, which improved more than three times of the initial aluminum. Also, changes in the elastic parameters were very small and the modulus of elasticity for the primary aluminum and two-layered aluminum was 69.3 and 70GPa, respectively.
A.a. Vaezi , H. Jafari ,
Volume 19, Issue 2 (2-2019)
Abstract
With regard to the industry demand for welding dissimilar metals, which are not possible to be welded by conventional welding, friction welding process can be a proper approach. In this study, friction welding of two stainless steels, martensitic 410 to austenitic 304, with variable parameters of friction time (40, 50, and 40 s), friction force (90, 100, and 120 kN), and forging force (130, 150, and 180 kN), under the constant rotating speed (850 RPM) and forge time (60 s), was investigated. Microscopic characterization using optical and scanning electron microscopes, and elemental analysis using energy dispersive X-ray spectroscopy were carried out on the welds. Soundness of the weld joints was evaluated using tensile and microhardness tests. Fracture surfaces of the tensile specimens were examined as well. The structure of the welded samples composed of acicular and rough martensite and elongated grains adjacent to 410 and 304 stainless steels, respectively. Tempering heat treatment locally caused converting rough martensite to lath martensite. The results showed that the tensile strength of the samples was in the range of 400-520 MPa, and the fractography revealed the occurrence of a brittle fracture. Microhardness measurement revealed that the highest hardness value was obtained in 410 stainless steel, at the heat-affected zone close to the interface. An appropriate friction weld joint with a tensile strength of 751 MPa was obtained after heat treatment of the weld location, and with the aid of selecting optimal parameters of 50 s friction time, 120 kN friction force, 180 kN forging force.
E. Mehrabi Gohari, M. Mohammadi, M. Nozari, H. Bagherpour,
Volume 19, Issue 6 (6-2019)
Abstract
Welding laser beams is one of the essential parts of in automobile manufacturing used for joining plates. In this paper, for the first time, simulation of of joining stainless steel to low carbon steel was carried out. For this purpose, at first, thermal analysis was carried out by finite element method and of temperature profile and the dimensions of the melting area was gained as results. This was followed by mechanical analysis. The thermal analysis results were stored in a mechanical element as history to obtain the thermal conditions of the material. As results of this analysis, the strain of elastic and plastic as well as the amount of residual stress The results show that low carbon steel passes through in , because of higher thermal conductivity. Also, low carbon steel saves more residual stress due to higher yield stress. For validation of simulated model, two plates of 304 stainless steel with similar parameters the simulated model by laser welding. Comparing the results obtained from the experimental model with the simulated model shows a very good agreement.
S. Yahya Abadi, M. Abbasi,
Volume 19, Issue 6 (6-2019)
Abstract
Al6061 alloy is widely used in the industry; so, its welding with reliable methods is of great importance. In the fusion welding of these alloys, imperfections such as cracks, cavities, and segregations of alloy element may occur that necessitates the application of solid state welding processes such as friction stir welding method. In spite of the many advantages of the friction stir welding, several attempts have been made to improve the properties of the resulting joints. In this study, the effect of increasing the cooling rate and the effect of vibration during the process on the microstructure and mechanical properties of Al6061 welds . Also, the simultaneous effect of water and vibration on the mechanical properties of the joints is evaluated The results showed that vibration due to increasing the strain and water due to increasing the cooling rate reduced the size in the stir zone. Investigations revealed that cooling rate increment decreased the dissolution of Mg2 precipitates significantly. The results of the tensile test showed that the strength of the due to the grain refinement as was applied or when increased. Also, when the vibration and coolant were applied simultaneously, the strength increased dramatically due to significant grain refinement and presence of Mg2 precipitates. On the other hand, with grain refinement, the volume fraction of grain boundaries increases and, thus, the growth of the cracks decreases and correspondingly elongation enhances.
M. Sabokrouh, M.r. Farahani,
Volume 19, Issue 7 (7-2019)
Abstract
In this paper, the analysis of variance (ANOVA) of weld residual stress distribution (using the hole drilling strain gage method according to ASTM 837 standard) was investigated (in the hoop and axial direction of the 56-inch gas transmission). The results of ANOVA show that the best distribution curve of residual stress is the third order function (3 degree of freedom) in the distribution diagram of hoop and axial residual stresses. In this order, the p value of the hoop and axial residual stress is 0.044 and 0.001, respectively. This indicates the high reliability of the third order function. Also, the value of F and coefficient of determination of this order has an appropriate value. In addition, due to the high p value and low reliability, the 5-order approximation function is not a suitable residual stress distribution curve compared to the third order function. Order approximation functions (2 and 4) have lower reliability (higher p value) and lower F value than odd order (3 and 5). Despite having the highest freedom with the highest p (lowest reliability), the lowest F, and the lowest coefficient of determination, the second-order function, is the most inappropriate approximation function. Despite the existence of residual stress with respect to the zero experimental residual stress compared to the approximation function, the use of strain test in points far from the weld one and the base metal is not essential.
Moslem Valaee Tale, Yousef Mazaheri, M. Sheikhi, F. Malek Ghaini, Gh.r. Usefifar,
Volume 19, Issue 7 (7-2019)
Abstract
During the process of Resistance spot welding (RSW), some of the molten metal comes out of the interface of the two sheets, which causes contamination on the body of the cars. This named as expulsion and disrupts the staining process and reduces the safety of the workshop. In this study, by numerical and Experimental investigation, effect of welding current and electrode force on expulsion in RSW of galvanized and non-galvanized steel sheets the prediction of expulsion for both sheets was performed. Experimental results showed that with increasing the welding current, nugget diameter and weld strength increased continuously until expulsion occurrence. The resultant nugget in both types of sheets have almost similar diameter at the similar welding current however in the galvanized sheet, expulsion occurred at a larger nugget diameter. Increasing the electrode force before the occurrence of expulsion increased the nugget diameter, but then reduced the nugget diameter. The results of the investigation were found to be consistent with a modified numerical model. In this model, increase in the nugget diameter increased the force from within the nugget and accelerated the expulsion, while the electrode force was a hindrance to the expulsion. Zinc coated on galvanized steel sheets with low contact resistance and friction coefficient between zinc-zinc metal resulted in a good fit between two sheets during the welding process which according to the numerical model, causes expulsion to occur at a larger nugget diameter for galvanized steel sheets.
A. Torabi, F. Kolahan,
Volume 19, Issue 8 (8-2019)
Abstract
Pulsed laser welding have a wide application in welding of thin sheet because of high intensity of its localized heat source. In the current study, 3 experimental tests with low, medium, and large level of energy and also, the 3D finite element simulation of Nd:YAG pulsed laser welding in thin sheet AISI316L have been done. Thermal analyzes were done with ABAQUS software in transient heat transfer. In order to increase the accuracy of thermal model, heat losses were considered as convection, radiation, and thermal conduction. 3 thermal models with different heat flux distribution as Gaussian surface, Gaussian volume, and conical volume were used. The main aim of this study is the selection of best thermal model between 3 mentioned thermal models to estimate the melt pool geometry with high accuracy. In addition, with defining and applying the shape factor in 3 thermal models, the finite element analyses were carried out in order to enhance the precision of estimated melt pool geometry. After thermal analysis, the melt pool geometry dimensions are extracted for each of the mentioned thermal models and compared with experimental results. Results show that thermal analysis with Gaussian surface model have the melt pool geometry accurately just in welding with low energy. Also, the conical model could estimate the melt pool geometry in all levels of energy with acceptable accuracy. Therefore, the pyramidal thermal model can be selected as the most suitable model for simulating pulsed laser welding in thin steel sheets.
P. Khoshrooz, M. Farahani, M. Safarabadi Farahani, S. Zohoori ,
Volume 19, Issue 9 (9-2019)
Abstract
Curing process of composites results in the formation of residual stress and distortion. According to costs of composites fabrication, simulation of the fabrication process in order to avoid wasting investment is important. A common and simple method of composite fabrication is hand lay-up. In this research plane stress due to temperature change of composite laminates has been investigated and its resultant curvature has been analyzed. So, two symmetric and un-symmetric laminates with eight plies are subjected to 100-degree centigrade temperature change and normal and shear stresses have been calculated. First, by classical lamination theory which is the most important theory in stress analysis of composites, mechanical properties of glass/epoxy composite with 70 percent volume fraction, temperature change and stacking sequence are input variables of the written program. Three in-plane stress component is read and the amount of curvature has achieved that shows it is negligible for the symmetric sample. To validate the residual stress field, finite element simulation for both samples has been done that resulted in finding the same results with negligible errors. Assumptions are considered in finite element modeling and classical lamination theory which result in deviation of outputs from reality. In spite of these assumptions, the thermal simulation of composite laminations in ABAQUS software can have the desired prediction of reality. The innovation of the research is the use of this software and the verification of code.
M. Salavati, Y. Mazaheri, M. Sheikhi,
Volume 19, Issue 10 (10-2019)
Abstract
The Nd: YAG pulsed laser welding process with different speed and shielding gas was applied on 2205 duplex stainless steel. The effects of different parameters on the microstructural evolutions and mechanical properties were investigated. Four different zones with different secondary austenite contents were observed in the weld microstructure. By changing the shielding gas from argon to nitrogen, the secondary austenite percentage was not significantly varied. The secondary austenite fraction was showed about 38% reduction with increasing the welding speed. The weld penetration depth decreased with changing the shielding gas from argon to nitrogen (about 26% and 14% reduction at speed of 3.8 and 8.3 mm/s, respectively) and increasing the welding speed (about 43% and 34% reduction under shielding gas of argon and nitrogen, respectively). The variations in microhardness values along the weld line were correlated to the microstructural characterizations. Changing the welding speed had no significant effect on the microhardness variations, but changing the shielding gas from argon to nitrogen caused a significant increase of microhardness.
J. Mohamadi Gangaraj, S. Nourouzi, H. Jamshidi Aval,
Volume 20, Issue 1 (1-2020)
Abstract
In the conventional casting process, the presence of porosity in the structure is inevitable. Compocasting method is one of the processes for composite production. Performing friction stir processing as a complementary process will modify the microstructure and good distribution of reinforcing particles in the matrix. Therefore, in this study, friction stir processing was used to improve the composite properties of A390 / 10wt% SiC composites. The FSP process was performed at rotational and traveling speeds of 800rpm and 40 mm / min, respectively. Three ratios of shoulder diameter to pin diameter (D/d) of 2, 2.5 and 3 were used, each of them was processed in one to three passes. An optical microscope (OM) was used to examine the microstructure of the processed samples. Microstructural data and its association with the results of the hardness and tensile test yielded the desired parameter. The results showed that FSP modifies the microstructure including resizing and distribution of SiC particles, primary silicon as well as changes the grain size of aluminum. The uniform distribution of particles on one side and the reduction of the grain size of aluminum, on the other hand, is effective in determining the desired parameter. The highest strength and toughness in the D/d ratio was 2.5 and in the third pass were 260MPa and 10.8M J/m3, respectively. Also, the average particle size of SiC, silicon and aluminum grains in the optimum parameter were 2.98, 14.98 and 16.3 μm, respectively.
H. Mohammadnia, S.m. Mousavizade, H.r. Ezatpour,
Volume 20, Issue 1 (1-2020)
Abstract
In this research, the effect of tool rotation speed and dwelling time on the strength of the welds produced by protrusion friction stir spot welding (PFSSW) was investigated. This simple novel technique involves the use of a designed circular protrusion on the backing anvil. Welding was performed by pinless tools on the AA5053 sheets with a thickness of 1 mm at tool rotation speeds of 630-2000 rpm and dwelling times of 6 s, 12 s, and 18 s. Appearance surface of produced welds was the smooth and free keyhole in comparison with conventional friction stir spot welding. Tensile-shear test results showed that all welds were failed in circumferential failure mode. Maximum and minimum peak loads were obtained at 1600 rpm, 18 s (4.9 kN) and 1000 rpm, 12 s (3.5 kN), respectively. Maximum and minimum elongations were obtained at 2000 rpm, 18 s (5 mm) and 2000 rpm, 6 s (2.3 mm), respectively. Maximum and minimum failure energies were obtained at 2000 rpm, 18 s (12.3 J) and 1000 rpm, 12 s (3.1 J), respectively.
S.a.a. Akbari Mousavi , Gh. Faghani, H.r. Sheivani,
Volume 20, Issue 2 (1-2020)
Abstract
One of the emerging methods of joining various metals is the use of laser beam welding in a variety of industries such as transportation, aerospace, radar, and marine construction, which reduces fuel consumption and thus reduces environmental pollution. In this study, the microstructure and mechanical properties of similar joints of aluminum alloy 6061 with a thickness of 2 millimeters have been investigated by the laser beam welding method with a high power of 5000 watts. Examined items include the effect of laser welding parameters such as power, frequency, and welding speed on microstructural and mechanical properties. Microstructural analysis results using an optical and scanning electron microscope show that in the process, the microstructure of the weld in the base metal to the center of the weld region changed from the dendritic column to the parallel dendritic zone and eventually reached the equiaxed dendritic area, due to the higher input temperature and consequently less cooling rate. Energy-dispersive X-ray spectroscopy (EDS) showed no significant change in the chemical composition. Investigating the mechanical properties using hardness measurement, and the tensile testing showed that the hardness in the fusion zone was lower than other base metal zones, and the optimized sample was failed in the weld zone. The tensile strength of the optimum welding sample is approximately equal to half the tensile strength of the base metal.
M. Sabokrouh,
Volume 20, Issue 4 (4-2020)
Abstract
The effects of tempering heat treatment on girth weld containing titanium oxide and titanium carbide nanoparticles (X-65 grade of the gas pipeline) were evaluated. The Charpy results show that it has been respectively increased by 26% and 15% in the tempered sample containing titanium oxide and titanium carbide nanoparticles compared to the no heat treatment sample (containing titanium carbide and titanium carbide nanoparticles). Also, the ultimate strength tempered sample containing titanium oxide nanoparticles and titanium carbide nanoparticles compared to the no heat treatment sample (containing titanium oxide and titanium carbide nanoparticles) has been respectively decreased by 6% and 4%. The results show that the fatigue life in both tempered nano-alloy samples has been increased. The fatigue life in the tempered sample of titanium carbide nanoparticles has increased more than the fatigue life in titanium oxide nanoparticles. The fatigue test results show that in the tempered sample containing titanium carbide nanoparticles compared to the tempered sample containing titanium oxide nanoparticles, fatigue life (150-N force) has been increased by 30%. In this loading, the fatigue life (tempered sample containing titanium carbide nanoparticles compared to the no heat treatment sample) has been increased by 19%. The hole drilling strain gage results show that in the tempered sample containing titanium oxide nanoparticles and titanium carbide nanoparticles, hoop residual stresses have been respectively decreased by 48% and 45% compared to the no heat treatment sample (containing titanium oxide and titanium carbide nanoparticles).
M. Sabokrouh ,
Volume 20, Issue 5 (5-2020)
Abstract
In this article, the effects of normalization heat treatment on girth weld with containing titanium oxide and titanium carbide microparticles (X-65 grade of the gas pipeline) were evaluated. The Charpy test results show that in the normalized sample containing titanium oxide microparticles and titanium carbide microparticles compared to the no heat treatment sample (containing titanium carbide microparticles and titanium carbide microparticles), has been respectively increased by 33% and 18%. Also, the ultimate strength of normalized samples containing titanium oxide microparticles and titanium carbide microparticles compared to the no heat treatment sample (containing titanium oxide microparticles and titanium carbide microparticles) has been increased by 9% and 11%, respectively. The results show that the fatigue life in both normalized micro-alloy samples has been increased. The fatigue life in the normalized sample of titanium carbide microparticles has increased more than the titanium oxide microparticles. The fatigue test results show that the fatigue life (150-N force) has been increased by 36% in the normalized sample containing titanium carbide microparticles compared to the normalized sample containing titanium oxide microparticles. In this loading, the fatigue life (normalized sample containing titanium carbide microparticles compared to the no heat treatment sample) has been increased by 27%. The hole-drilling strain-gage results show that in the normalized sample containing titanium oxide and titanium carbide microparticles, hoop residual stresses have been respectively decreased by 12% and 8%compared to the no heat treatment sample (containing titanium oxide microparticles and titanium carbide microparticles).
M. Sabokrouh , M. Farahani,
Volume 20, Issue 5 (5-2020)
Abstract
Titanium is one of the most important microalloy elements used in the gas transmission industry. In this paper, titanium nano-oxide and titanium nano-carbide were added to two separate samples. Then the shielded metal arc welding (SMAW) was performed on high-strength low alloy steel according to welding procedure specification of the national Iranian gas company. The effects of annealing heat treatment on girth weld with containing titanium oxide and titanium carbide nanoparticles (X-65 grade of gas transmission pipeline) were evaluated. The Charpy test results show that in the annealed sample containing titanium oxide nanoparticles and titanium carbide nanoparticles compared to the no heat treatment sample (Containing titanium carbide nanoparticles and titanium carbide nanoparticles), energy absorbed has been respectively increased by %13 and %9. Also, the ultimate strength of the annealed sample containing titanium oxide nanoparticles and titanium carbide nanoparticles compared to the non-heat treated sample has been respectively decreased by %8 and %3. The fatigue life in both annealed nano-alloy samples has been increased. Also, the fatigue life in the annealed sample of titanium carbide nanoparticles has increased more than fatigue life in the titanium oxide nanoparticles. The fatigue life (Annealed sample containing titanium carbide nanoparticles compared to the no heat treatment sample) has been increased by %16. The hole drilling strain gage results show that in the annealed sample containing titanium oxide nanoparticles and titanium carbide nanoparticles compared to the non-heat treated sample, hoop residual stresses has been respectively decreased by %31 and %19.
M. Mamourian, S.a. Naghedifar , M. Mohammadi Neyshaburi ,
Volume 20, Issue 8 (8-2020)
Abstract
Residual stress is one of the most substantial defects of welded parts caused by intensive thermal gradient. In this study, different mechanical and thermal techniques for reducing residual stresses have been investigated and the effectiveness of contributing parameters has been discussed afterwards. Subsequently, some equations have been proposed for welding energy and exergy efficiency and the effects of parallel flame heating, vibration method, and hammer working method on reducing welding residual stresses are expressed. The results show that by using parallel heating technique, the enhancement of flame power would result in reducing both energy and exergy efficiencies. However, the decremental rate of the two efficiencies would slow down and they approach to an asymptotic value. Increasing the speed of welding improves two efficiencies more than 2 times. On the other hand, the normalized entropy is reduced by increasing the heat input of the flames. This fact is an indicator of a reduction in welding residual stress. This reduction is more at high speeds. Eventually, the ratio of the two efficiencies shows that in this study, economical power was about 1800j/s. The reduction of normalized entropy for the vibration, hammering, and parallel flame methods are 0.001, 0.1, and 10, respectively. Overall, it is expected that thermal methods are more efficient than mechanical methods in reducing residual stresses.
H. Hashemi, S.h. Hashemi,
Volume 20, Issue 9 (9-2020)
Abstract
Because of the inherent structure of welded pipelines, the seam weld can be a potential source for initiation and propagation of crack that can eventually lead to failure of the structure. Due to the critical conditions in the welding region, the investigation of failure energy in gas transportation pipeline is very important for engineers and line designers. In this paper, the three-point bending test (according to the standard specimen of drop-weight tear test) was performed quasi-statically on the seam weld pipe and base metal of spiral seam weld pipe of API X65 steel from which force diagrams were extracted. The presence of sudden load drops in the force-displacement diagram of the specimen in the weld indicated the inhomogeneous structure of the weld. The diagrams of force-displacement, yield and ultimate force, amount of steady crack growth and fracture energy of the metal and seam weld specimens including initiation and propagation energy of crack were investigated and compared. Also, the ratio of the force drop to the ultimate force at the same displacement rate was investigated. The results showed that in seam weld compared to the base metal specimen, the yield force was higher and the ultimate force, the amount of steady crack, initiation and propagation energy of crack were lower. In addition, the lower ratio of force to ultimate force (at the same displacement) in the base metal also indicated a high resistance of the base to the crack propagation.
S. Nazaralizadeh , M. Vaseghi, M. Sameezadeh ,
Volume 20, Issue 9 (9-2020)
Abstract
P91 steel is widely used in the construction of power plant components and the wider use of this steel is in the future planning of power plants in Iran. The preheating, the temperature control between the welding passes and the post-welding heat treatment, are required to obtain optimum toughness and creep resistance. Preheating, and most importantly post-heating are essential to prevent hydrogen remaining and the cracking problem. In this study, the effect of post-welding heat treatment (PWHT) and electrode drying on microstructure and mechanical properties of SMAW multi-pass weldment of P91 steel plate was studied by changing post-heating and baking processes. The optical microscope and FESEM microstructural studies, as well as ambient tensile tests, were done on a variety of different conditions from wet electrodes to post heated specimens that were used in order to evaluate the welding characteristics of SMAW process on the mentioned material. It was seen that utilizing wet electrodes with no immediate subsequent post-heating caused a noticeable decrease in tensile, and yield strength. On the other hand, post-heating treatment increases the number of precipitates in the weld metal and HAZ and the size of the primary austenite grains in the weld metal and HAZ becomes more homogeneous.
