Constrained Groove Pressing Process Research Articles

Constrained groove uniform pressing process for achieving homogeneously improved properties in copper

Constrained groove pressing (CGP) is a popular method to produce an ultrafine-grained microstructure and thus enhanced mechanical properties in the metal sheet. CGP is a severe plastic deformation technique that simultaneously presses the metal sheet with flat and grooved dies to subject it to large shear strain without changing the dimensions. The inherent inhomogeneity of the processed sheet may be a drawback of the CGP process. According to published research, this is caused by the sharp edges of the grooved dies responsible for additional bending strain along with shear strain. Moreover, even if the grooves are made circular, it can impart constant bending strain, but the shear strain varies. In this research, a new die has been designed to impart constant combined bending and shear strain in the metal sheet using constrained groove uniform pressing. Hence, the process is changed as the number of presses required for 1 pass are changed and named constrained groove unform pressing. C101 was used as the material for the new process. Properties of the copper sheet observed to be improved homogeneously as it was processed through the new die and process. The uniformity of the imposed strain was verified by theoretical, experimental, and simulation results.

Optimal Constrained Groove Pressing Process Parameters Applying Modified Taguchi Technique and Multi-Objective Optimization

Most engineering problems are complicated, and developing mathematical models for such problems requires understanding the phenomena through experiments. It is well known that as processing parameters with assigned levels increase, so does the number of experiments. By minimizing the number of experiments, Taguchi’s method of experimental design will help to furnish the idea of full factorial experimental design. Taguchi’s method is more appropriate for single-objective optimization problems and needs modifications while dealing with multi-objective optimization problems. Aluminum alloys are in great demand in today’s automotive and aerospace sectors due to their low density, good corrosion resistance, and excellent machinability. The material is subjected to a constrained groove pressing (CGP) process to obtain microstructural grain refinement with enhanced mechanical behavior. This paper considers AA6061 material having major alloys such as silicon and magnesium. For this work, 3 CGP process parameters (viz., displacement rate, plate thickness and number of passes) are assigned 3 levels to each parameter, acquired the test data, viz., grain size (gs), micro hardness (hs), and tensile strength (ult) based on L9 orthogonal array of Taguchi. Using a modified version of Taguchi’s methodology, it is possible to estimate the range of grain size (gs), micro hardness (hs), and tensile strength (σult) for effective combinations of the CGP processing parameters and validate the results with existing test data. A more dependable and simpler multi-objective optimization procedure is used to choose the optimal CGP processing parameters.

Constrained Constant Radius Pressing (CCRP) process to improve mechanical properties and microstructural homogeneity of pure copper sheet

Constrained groove pressing (CGP) is a well-known severe plastic deformation (SPD) process used to improve the mechanical properties of metallic sheets by forming the ultrafine grain (UFG) structure. The conventional CGP process employs 45° grooved dies to impart good amount of plastic strain on the specimen without altering the specimen's initial dimensions. The literature indicates that conventional CGP-processed sheets have inherent strain inhomogeneity. In the present investigation, an effort was made to minimize the inherent strain inhomogeneity by modifying conventional CGP dies into symmetric constrained constant radius pressing (CCRP) dies. Three distinct CCRP dies with varying radius of curvature and die parameters were designed to attain the optimal combination of mechanical properties. It was found that metal sheets processed by new modified dies (CCRP) exhibit improved ductility and significantly enhanced toughness, in contrast to the sheets processed by conventional CGP dies. The improvement in mechanical properties could be attributed primarily to homogeneous grain refinement. In addition, the finite element analysis (FEA) was used to simulate the influence of different die designs on the strain distribution across the sheet, and it showed that lower die angle of CCRP lead to more homogeneous distribution of strain across the arc of the CCRP die.

Mechanical and microstructural characterization of Nimonic 263 superalloy after constrained groove pressing at elevated temperatures

Nimonic 263 superalloy is primarily being used in gas turbines, high-pressure pipelines, steam heaters, etc. due to its capability to withstand high temperatures and pressure for a longer duration. In this work, an experimental investigation on Nimonic 263 alloy has been carried out to improve its mechanical and microstructural properties using constrained groove pressing (CGP) at various temperatures. CGPed specimens have been characterized through mechanical tests (tensile test and hardness test) and microstructural studies (XRD, SEM fractography, and optical microscope). The results demonstrated that the CGP process had a significant impact on the alloy's properties. Compared to the as-received material, the CGPed specimens exhibited substantial improvements in yield strength (YS), ultimate tensile strength (UTS), and micro hardness, with average values of 234.58%, 43.79%, and 110.31%, respectively. The average grain size gets reduced due to CGP from 220.70 μm for the as-received material to 106.02 μm, 117.09 μm and 94.01 μm for CGP at room temperature, 250o C, and 450o C, respectively. An increase in the peak intensity is observed in the XRD after the CGP process due to a decrease in crystal size and an improvement in dislocation density with an average value of 31.68%. Fractography studies have revealed a mixed-mode (ductile and brittle) failure for the CGPed specimens compared to the ductile failure mode in the as-received material. Using Abaqus 6.14 software, the finite element analysis of the CGP process has been performed and the results have been found in good agreement with the analytical results. Thus, the CGP process can effectively improve the mechanical and microstructural properties of Nimonic 263 alloy for high-temperature applications.

Superior combined strength and elongation by conducting elevated temperature constrained groove pressing on Al–Mg–Mn sheets

Al 5083 alloy has widely been employed in marine and offshore engineering as well as production of various types of superplastically formed parts in aerospace and automotive industries. The constrained groove pressing (CGP) is also one of important sheet severe plastic deformation (SPD) technique. In this study, The CGP process has been performed on Al 5083 sheets at an elevated temperature and up to three cycles. Complementary experiments, namely metallography, precipitation evolution, hardness and tensile tests as well as fractography were conducted for various deformed and undeformed sheets. The 1-passed workpiece represented the minimum average grain size (AGS) 8 μm due to huge strain induction. By computing the inhomogeneity factor (IF), it was also found that the 2-passed sample was the most inhomogeneous worksheet with an IF of 6.3. By performing three CGP cycles, superior elongation of 56.2% combined with UTS of 309 MPa were achieved for the 3-passed sample, making this workpiece very suitable for conducting any subsequent metal forming process. This was mainly due to the precipitation evolutions of Al6(Fe,Mn) and Al3Mg2 particles. Moreover, fractography of various specimens showed that by performing greater number of CGP cycles, the fracture mechanisms changed to a ductile mode due to creation of tiny and deep dimples.

Strength enhancement and uniform strain distribution through cross route-constrained groove pressing

Constrained groove pressing (CGP) is one of the severe plastic deformation techniques for sheet metals to impose large plastic strain and produce ultrafine-grained (UFG) structures without any change in dimensions. Cross route-constrained groove pressing (Cross-CGP), an advanced version of the conventional CGP process, involves two CGP cycles with an equivalent strain of 2.32 per cycle where the square sample is rotated by 90° after performing every cycle of CGP. The strain path in the sheet during conventional CGP and cross-CGP significantly affects the homogenization of mechanical properties. Sheets of low carbon steel are processed through conventional-CGP and cross-CGP routes. The ability to sustain the maximum strain has been increased in the cross-CGP process due to uniform strain distribution. The tensile strength and hardness in the sheet processed through cross-CGP are higher than that of conventional CGP, especially at higher pass numbers. Tensile behavior and hardness in two different orientations (parallel and perpendicular to the groove direction) have been found to be almost the same in the cross-CGP processed sheet.

Re-examination and comparison of activation volume, strain rate sensitivity, and dislocation density for coarse grain and CGP-processed UFG materials

The frequently used metallurgical parameters such as activation volume, internal stress, strain rate sensitivity, and dislocation density are identified in ultrafine-grained (UFG) materials through erudite analytical relations. It is difficult to analyze such parameters optically since the material consists of highly distorted and inhomogeneous microstructure due to the large strain imposed during the constrained groove pressing (CGP) process. Hence, transient tests like stress relaxation tests are advantageous over the optical to use. Apart from the identification of parameters in low-carbon steel materials using uniaxial loading and stress relaxation tests, the relationship between the parameters is nobly investigated in as-received and UFG structure samples produced through the CGP process. In the relationship, the exponential-power law constitutive to describe the accurate stress–strain curves, identification of mobile and forest dislocation density during strain hardening, and exponential variation between grain size and activation volume are proposed. The replenishment or exhaustion of mobile and forest dislocation density significantly affects the metallurgical parameters during uniaxial tensile loading followed by stress relaxation testing. In this experimental and analytical work, the CGP process produces a UFG material that has lower activation volume and higher stress drop, mobile dislocation density, forest dislocations density, strain rate sensitivity, and internal stress.

Developing methods of constrained groove pressing technique: A review

Among various severe plastic deformation (SPD) techniques, constrained groove pressing (CGP) has arisen as a famous technique for fabricating ultrafine-grained sheet metals and alloys in recent times. The severe strain is applied to improve the mechanical performance and properties. However, inhomogeneous grain refinement, lower formability, surface unevenness, and microcracks are the common limitations of conventional CGP-processed samples. Therefore, this review inspects the latest progress through modifications of the CGP process and compares the process efficacy with the conventional process. Advanced CGP processing techniques, such as modification of die design, annealing of the processed sample, cross CGP, ring CGP, hybrid SPD, covered sheet casing CGP, and rubber pad CGP, are emerging techniques to up-scale the procedure and improve the grain refinement and thereby produce superior mechanical properties. In this review paper, the historic research of conventional CGP and its effect on grain refinement and mechanical properties is initially briefed and then recent progress through different advanced techniques is highlighted, especially in alloys. Albeit significant progress has been observed in CGP, the future scope and successful usage of CGP-processed samples in actual practice are discussed in the last stage.

Numerical-experimental study of die geometry in the constrained groove pressing of 6061 aluminum sheets

Nowadays, in line with the need of different industries to the materials with high strength to weight ratio, researchers have drawn attention to the processes of severe plastic deformation. The constrained groove pressing (CGP) is one of the most effective methods of severe plastic deformation to produce high-strength sheet metal using two dies with different shapes (grooved and flat). Despite the advantages of CGP in creating high accumulative plastic strain, this process leads to non-uniformity in mechanical properties of the sheet. This non-uniformity is one of the limitations of the CGP process which is considered in this study. Experimental and numerical studies were performed to investigate CGP process on 6061 aluminum alloy sheet up to two complete passes and the mechanical properties of the sheets were studied. Hardness testing was conducted on the worked material and the increase in the hardness of tested material in both longitudinal and thickness directions were observed. Also, it was shown that the non-uniformity in hardness distribution is correlated to the non-uniformity in the strain distribution. So, validated numerical model was used to develop the response surface method (RSM) and consequently to investigate the effect of geometric parameters in the grooved die on the strain uniformity. Finally, die geometry was optimized using the developed RSM model to produce a sample with more uniformity in strain and hardness distribution.

The study of mechanical and microstructural properties of the AZ31 magnesium alloy using constrained groove pressing at elevated temperature: A review

AZ31 magnesium alloy is used in different industries such as defence, aerospace, and biomedical applications, due to its high strength-to-weight ratio and it has a capability to expand its applications by improving its characteristics. Constrained groove Pressing (CGP) has a capability to produce ultrafine grained sheet (UFG) metals primarily based totally on severe plastic deformation, which can improve mechanical properties. Study on CGP of AZ31 magnesium alloy, which has poor formability and low ductility at room temperature (RT) is still difficult. The goal of this paper is to analysis the effects of constrained groove pressing (CGP) on the characteristics and applications of the AZ31 magnesium alloy at high temperatures. After the CGP process, most of the specimens mechanical properties like strength and hardness had improved. Microstructural changes and mechanical properties are also varying with the number of passes.

Microstructure and Mechanical Properties of Dual‐Phase Steels by Combining Adjusted Initial Microstructures and Severe Plastic Deformation

Herein, the effects of initial microstructure in combination with the severe plastic deformation on the developed microstructures and mechanical properties of dual‐phase (DP) steels are investigated. DP steels are produced by an intercritical annealing from the preliminarily heat‐treated samples with different initial microstructures. The constrained groove pressing (CGP) process is additionally applied before the final intercritical annealing step. It is found that the martensitic and tempered martensitic microstructures lead to DP steels with a good balance of strength and elongation because of finer and more uniformly dispersed martensitic islands. The ferrite/pearlite banded initial microstructure is not a proper choice for intercritical annealing as all mechanical properties become worse. The CGP can be employed before intercritical annealing for refining microstructure and enhancing damage tolerance of DP steels. Nevertheless, the impacts of the CGP process on the resulted strength of DP steels are obviously different depending on the initial microstructures. The amounts, sizes, and distributions of dimples and cleavage facets on the fracture surfaces of DP steels correlate well with the corresponding microstructures and tensile characteristics.

A new approach of the constrained groove pressing process on Al5083-O alloy using PMMA polymer, without die non-friction coefficient: nanostructure, mechanical Properties and hardness

The Constrained Groove Pressing (CGP) on annealed Al5083 (Al5083-O) alloy sheets by means of Polymethyl Methacrylate (PMMA) polymer is investigated in this research. Input parameters include Traverse Speed (1, 2, and 3 mm/min), Pass Number (1, 2, 3, and 4), and Lubricants (Grease, Oil, and without lubricants). Reciprocally, output parameters consist of Nanostructure (SEM and EBSD images), Hardness (HV), and Mechanical Properties – Impact Strength (kJ/m2), Tensile Strength (MPa), Young's Modulus (MPa), and Elongation (%). Revealed by the results, the impact strength is gradually improved in the 1st, 2nd, 3rd, and 4th passes by respectively adding oil and grease, compared to the state of using no lubricant. The impact strength results demonstrated that the addition of grease has a significant effect on the impact strength of composite samples. In order to build a high-quality product through the CGP process, it is very important for the mechanical properties to be based on the input parameters. In CGP processes, the Continuous Dynamic Recrystallization (CDRX) is considered as the ultrafine-grained mechanism. To predict the grain size evolution and the plastic deformation rate, the combination of Finite Element (FE) method and the ETMB model is utilized. Indicating the high generalizability and reliability as compared to other modeling methods, both the experimental test results and the ETMB model data, which have a higher degree of accuracy, are presented.

Effects of constrained groove pressing on mechanical properties of a TWIP steel

The evolution of mechanical properties and microstructure of a twinning induced plasticity (TWIP) steel sheet during constrained groove pressing (CGP) was investigated. It was found that by imposing CGP, the volume fraction of twins, hardness and yield strength increase significantly, while ductility decreases. The results of the pin-on-disk wear test showed that the CGP process improves the wear resistance of the TWIP steel, where oxidation is the main wear mechanism. The effect of annealing treatment at various temperatures on the hardness evolution of the CGP-treated samples was also investigated. Moreover, a modified work-hardening model was applied to predict the flow behaviour of TWIP steel during the severe plastic deformation. The model successfully predicts the flow curve and measured dislocation density and twin evolution.

Microstructural characterization and electrochemical behavior of nano/ ultrafine grained pure copper through constrained groove pressing (CGP)

This study presents microstructural, electrochemical, and mechanical characterizations on pure copper fabricated using constrained groove pressing (CGP) in quiescent phosphate buffer solution (pH = 11.73). We tested the effect of surface modifications on electrochemical features using electrochemical impedance spectroscopy (EIS) and Mott–Schottky analysis. A three-dimensional simulation via finite element modeling evaluates the CGP effects on the maximum principal stress and the plastic strain distribution. The transmission electron microscopy (TEM) micrographs confirm that the increasing CGP cycles result in a nano/ultrafine grain microstructure. Our electrochemical study showed that the CGP process can positively impact the passive behavior of pure copper. Mott–Schottky analyses illustrated that the point defect densities decline in the p-type semiconducting passive layer upon receiving CGP. Besides, increasing the CGP cycles lowers the corrosion current density and produces less defective passive films.

An experimental investigation on the influence of elevated-temperature constrained groove pressing on the microstructure, mechanical properties and hardening behaviour of Ti6Al4V alloy

Abstract Due to its high strength-to-weight ratio and remarkable resistance to corrosion, Ti6Al4V alloy finds its use in a wide range of fields such as defence, aerospace and biomedical applications. To further enhance its properties and widen its applications, this paper focuses upon the novel application of constrained groove pressing (CGP) on Ti6Al4V alloy at elevated temperatures as it is hard-to-deform at room temperature due to its HCP structure. Till date, CGP is reported mainly on FCC and BCC alloys which are relatively easier to deform as compared to HCP alloys and metals, especially at room temperature. In this work, CGP process has been successfully performed on Ti6Al4V at 750 °C and 550 °C. Mechanical and microstructural evolution in CGP processed (CGPed) material is characterized by tensile testing, microhardness testing, optical microscopy, SEM Fractography and XRD. Enhancement in mechanical properties at room temperature such as yield strength, ultimate tensile strength and microhardness is observed more for CGP at 550 °C as compared to CGP at 750 °C and as-received material. Further analysis of tensile test results revealed that CGPed specimens at 750 °C and 550 °C follow different hardening behaviour although hardening mechanism for both is governed by Voce hardening model. Optical microscopy revealed fine distribution of β-phase along the grain boundaries in CGPed specimens. Microstructural analysis showed evolution of grain structure due to dynamic recrystallization in CGPed specimen at 750 °C whereas work hardening and grain fragmentation was observed for CGP at 550 °C. As-received (AR) and CGPed Ti6Al4V were observed to follow the Hall Petch relationship. SEM Fractography was performed on broken tensile test specimens, revealing the change in mode of failure from ductile mode for AR to mixed ductile-brittle mode for CGPed specimen at 550 °C. No precipitates were observed in SEM images which confirmed strain hardening effect of CGP and inherent voids as the main reason of failure. XRD analysis confirmed bulk strain hardening in CGPed Ti6Al4V. Thus, CGP at elevated temperatures may effectively be used for tailoring the microstructure and mechanical properties of Ti6Al4V alloys for extending its application domain.

Influences of the constrained groove pressing on microstructural, mechanical, and fracture properties of brass sheets

Constrained groove pressing (CGP) was used for the production of fine-grained brass sheets in different conditions. The process was conducted up to two cycles on brass sheets at room temperature and then half cycle at the temperature of 200 °C. Optical microscopy (OM), scanning electron microscopy (SEM), microhardness measurement, and plane stress fracture toughness was used to investigate the microstructure, mechanical properties, and fracture behavior. Microhardness measurement showed the capability of the CGP process in increasing the hardness of the refined sheets. It also showed the inhomogeneity of the hardness along the thickness of the sample after the process. The Digital Image Correlation (DIC) technique was used to investigate the elastic and plastic factors of the sheets along with the major mechanical properties of samples. The results showed a slight increase and reduction in the Young modulus and Poisson’s ratios after the process, respectively. Moreover, after two CGP cycles applying half cycle at the temperature of 200 °C did not show any significant effect on these values. The strength coefficient was as like as yield and ultimate strengths increased by increasing the number of the passes. However, processing at a higher temperature of 200 °C showed lower values for the parameters, as mentioned earlier, compared to the specimens processed at room temperature. The strain hardening index experienced a major reduction after the CGP process due to the effects of strain hardening. The anisotropy coefficient, which plays a critical factor in the severe deformation of sheets, was increased after the CGP process. However, this ratio decreased in higher passes or elevated temperatures. The highest anisotropy coefficient was obtained after the first cycle of the process. Moreover, SEM observation of the fracture surface showed shearing ductile rupture mode in the processed samples rather than ductile mode due to appearing of small and elongated dimples.

Development of new fiber textures for enhancing mechanical properties of 2024 Al alloy using elevated-temperature constrained groove pressing

Constrained groove pressing (CGP) is a type of severe plastic deformation (SPD) employed for sheet metal strengthening. In this investigation, the annealed 2024 Al alloy sheets were employed to conduct the CGP operation at 300 °C temperature and up to three cycles. Afterward, complementary experiments, namely metallography, texture, hardness, and tensile tests were conducted with various deformed and undeformed sheets. As an important observation, a new fiber texture was developed during the third cycle of the CGP operation, affecting the ductility enhancement of this sample besides certain improvement in its ultimate strength. Moreover, in the deformed sheets, existence of hardest orientation, i.e. [111] ‖ RD, in the 1-passed sample with high intensity and creation of some new and soft orientations, i.e. [104] ‖ TD and [326] ‖ ND in the 2-passed specimen and [718] ‖ ND in the 3-passed workpiece, during the CGP process resulted in production of worksheets having specific mechanical properties. It was found that the 1st pass of the CGP process increased the yield strength (YS), ultimate tensile strength (UTS), and hardness of the alloy by 45%, 21%, and 71%, respectively. The worksheets produced via the 2nd and 3rd CGP cycles had higher YS, UTS, and hardness in comparison with the annealed worksheets. The material elongation was improved in the 3rd pass significantly, namely 41%. The precipitations evolutions and the γ-fiber overall intensity are the two most important factors for increasing elongation in the 3-passed specimens. Fractography of the fracture surfaces, also, confirmed these mechanical properties changes in different CGPed samples.

Evolution of microstructure and mechanical properties of Ti6Al4V alloy by multiple passes of constrained groove pressing at elevated temperature

Constrained groove pressing (CGP) is one of the best available sheet material processing technique for grain refinement and improving material properties without changing the original dimensions of the specimen. In this work, CGP is successfully performed on 10 mm thick mill-annealed Ti6Al4V plates at a temperature of 550 °C up to three passes. Microstructure studies reveal that grain size decreased from 18.81 μm in as received (AR) sample to 9.24 μm after third pass. XRD studies confirm the lattice strain and grain refinement phenomenon by peak shifting and broadening. Work hardening and grain refinement lead to increase in microhardness from 346 HV in AR to 392.1 HV, 365.9 HV and 371.4 HV in one pass, two pass and three pass CGP processed (CGPed) Ti6Al4V respectively. CGP leads to improvement of YS from 964.75 MPa in AR to 1085.01 MPa, 1068.11 MPa and 1078.63 MPa in one, two and three pass CGPed Ti6Al4V respectively. Similarly, UTS is observed to improve from 1014.12 MPa in AR to 1118.26 MPa, 1015.21 MPa, 1098.05 MPa in one, two and three pass CGPed Ti6Al4V respectively. SEM fractography reveals change in the mode of fracture of Ti6Al4V from ductile to ductile-brittle mode before and after the CGP process. Work hardening behavior of CGPed Ti6Al4V changes from stage III and IV to purely stage III along with initial instantaneous hardening rate increases after the first pass and decreases for the subsequent passes. CGP on Ti6Al4V alloy at 550 °C is found to have a significant effect on the stabilization of its microstructure and mechanical properties which can be useful for extending CGP for HCP alloys and their applications in aerospace and defense sector.

Effect of severe plastic deformation on evolution of intermetallic layer and mechanical properties of cold roll bonded Al-Steel bilayer sheets

In this study, evolution of intermetallic layer of the cold roll bonded bilayer of Aluminum-Steel sheets, during severe plastic deformation (SPD) followed by annealing has been investigated. The effect of such evolution on mechanical properties has been discussed. For this purpose, Constrained Groove Pressing (CGP) was used as a SPD process. Field emission scanning electron microscope equipped with energy dispersive spectroscopy and optical microscopy were used for examination of intermetallic compounds morphology and composition. Meanwhile, tensile properties of the bilayer sheets were evaluated. According to microstructural observations, continuous intermetallic layer was formed during rolling and annealing processes. This intermetallic layer was completely cracked into very fine particles after the first pass of CGP. Some of these intermetallic compounds were pushed into the base layers by the shear stress and some of them remained at the interface. Moreover, it was observed that during the CGP process, at the interface and between remaining intermetallic compounds and fresh surfaces of both Al and steel, new bonds were formed. After formation of such new bonds and during the second step of the CGP process, flattening process, mechanical interlocks were created. However, after the second CGP pass, no intermetallic compound was observed at the interface yet delamination was seen. Due to formation of intermetallic compounds at the bonding area and the vicinity of it, reinforced area, mechanical interlocks and higher dislocation density in that region, the ultimate tensile strength (UTS) increased after the first pass of CGP, but due to delamination, it decreased in second pass. The effect of evolution of bond structure on the tensile strength was measured by using bonding portion (BP) criterion defined as the difference in the UTS of the bonded versus non-bonded samples undergone similar deformation and annealing treatment. The BP values show similar trend to the UTS data, increased at the first pass and decreased at the second pass. In the following study, the CGPed samples have been annealed in order to recover the intermetallic layer. The CGPed samples were annealed at 350 °C, 400 °C and 450 °C for 30, 60 and 90 min. The optimum thickness of 2.6 μm was observed at the 450 °C in 30 min annealing treatment. The UTS, BP and elongation to break increased 7%, 32% and 60%, respectively, in comparison to those of the as-CGPed sample.

Effect of the uncertainty of multi-cut contour method and friction coefficient on residual stresses of constrained groove pressing process

Constrained groove pressing (CGP) process is a severe plastic deformation (SPD) method that can create ultrafine-grained microstructure in the sheet metals. In this study, residual stresses of the CGP process and the effect of the friction coefficient on the residual stresses were investigated. The residual stresses were measured in two directions using a multi-cut contour method and a mathematical-finite element model was developed to estimate the uncertainty of results of the multi-cut contour method. In order to study the effect of the friction coefficient on the residual stresses, a 3D finite element model was employed and the results of it were validated with the experimental results of the CGP process. According to the results, residual stresses in the first pass of CGP are compressive on the surface and gradually change to tension at the center of the thickness. Investigation of the effect of the first cut on the residual stresses and uncertainty of the second cutting plane showed that the effect of the first cut is only confined to regions near the intersection of the two cuts. Distancing from the intersection of two cuts causes the effect of the first cut to be ineffective on the second cut. Also, evaluation of the effect of friction coefficient on the residual stress illustrated that friction has a direct relationship with the residual stresses.