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The contour method is a new approach to measure the residual stress and use to provide a two-dimensional map of residual stresses. In this study, residual stresses were measured in the rods which produced by hot extrusion with high reduction cross section. The rods material was 6061 aluminum alloy and the effect of annealing heat treatment has been...
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Citations
... A first sample was shot blasted, the second sample was firstly heat treated and then shot blasted, the third sample was shot blasted and then heat treated and the last sample was just heat treated. After preparing the samples for modeling and evaluation of residual stress by using the contour method, a tensile-test was conducted on the samples and the mechanical properties determined [28]. ...
Corrosion is one of the most common complications in some industries. Two main factors causing corrosion are tensile stress and a corrosive environment, both of which require careful control. The purpose of this research is to achieve an optimal method of increasing corrosion resistance and also reducing tensile residual stress in API X60 gas pipelines. In the present study, residual stress has been examined in samples which have undergone either shot blast or heat treatment operations or both of them. In this research, 4 samples have been studied including: shot blasted, firstly heat treated then shot blasted, firstly shot blasted then heat treated and heat-treated using API-X60 steel pipe to indicate the best method of resistance to corrosion and stress. To investigate these properties, residual stress of these components has been examined by using the Contour Method and corrosion resistance has been studied through the Cyclic Polarization Resistance method. The results showed that the best corrosion resistance happen by the heat-treated sample (almost twice as much as the other methods) and also the most compressive residual stress observe in the firstly shot blasted and then heat-treated sample.
... Residual stresses, due to their effect on the strength, fatigue life, stress corrosion cracking, dimensional stability, and fracture of the material/ components, are one of the important issues in engineering. 27 According to the material and geometry of the workpiece, and the position of residual stress measurement, there are different methods for measuring residual stress. 28,29 Contour method is a relaxation-based method which can determine the two-dimensional map of residual stresses without limitation of the thickness and geometry. ...
... Olson et al. 46 classified the sources of errors of uncertainty to model error, and displacement error, and presented a model to calculate the uncertainty of the contour method. Honarpisheh and Nazari 27,47 investigated the effect of cross-section reduction on the residual stresses in hot-extruded aluminum specimens and presented the effect of the uncertainty sources on the results of the contour method. Olson et al. ...
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.
... In 2015, Olson et al. [49] classified random error sources for the contour method and presented a method to estimate its uncertainty. Honarpisheh and Nazari [50] and Aghaei et al. [51] investigated the accuracy and uncertainty of contour method results in different processes and proved that the contour method is a reliable and suitable method for constructing the 2D map of residual stresses. ...
In this study, residual stresses in hot-extruded Al-6061 rods with different cross-sectional reduction were investigated using the contour method. The contour method was used to provide a two-dimensional map of residual stresses. The residual stresses were evaluated along the radius of the rods with different cross-sectional reduction before and after annealing heat treatment, and the uncertainty of the contour method was estimated. The results indicate that in the extruded rods with high reduction of diameter, tensile residual stresses are generated in the rod core, which are balanced along the rod radius by compressive residual stresses at the surface. A decrease in the cross-sectional reduction or the rod diameter increase results in rise of residual stresses. The annealing heat treatment reduces residual stresses and creates a symmetrical balance between tensile and compressive residual stresses. The countour method application revealed that maximum and minimum uncertainties occurred at the rod center and perimeter, while the latter one had a greater effect on the residual stress estimation results. Introduction. Extrusion has numerous applications in continuous manufacturing in a wide variety of metals and alloys: numerous workpieces' cross sections are produced by the extrusion process. A specific characteristic of extrusion is high cross-sectional reduction that is achieved without the material fracture due to high triaxial compression conditions. Aluminum is one of the regular extruded materials [1], while Al-6061 aluminum alloy is one of the most widely used aluminum alloys because of its high strength. Besides, this alloy is heat-treatable and has good toughness and corrosion resistance characteristics [2]. The severe and non-homogeneous plastic deformation and cooling rate during the extrusion process lead to a change in microstructure and create distortion and residual stresses in products [3, 4]. Residual stresses have a direct and indirect influence on the performance of engineering structures. These stresses may have detrimental or beneficial effects on fatigue life, corrosion resistance, tensile strength, and dimensional stability. There are some destructive techniques to measure residual stresses in the industrial component, such as hole drilling [5, 6], slitting method [7-10], ring core method [11], deep hole drilling technique [12], and the contour method [13]. The evaluation of residual stress in the extrusion process was firstly performed in 1981 by McMeeking and Lee [14], who used the elastic-plastic analysis results and the finite element model. In another study, Pyzalla and Reimers [15] investigated the residual stress state of cold forward-extruded rods of C15 steel grade by X-ray, high energy synchrotron, and neutron diffraction methods. They found that, in case of the cold forward-extruded specimens, the compressive residual stresses occurred in the rod core, being balanced by tensile residual stresses in the outer part.
... A 2D map of residual stresses was measured using the contour method at the first, second, and third passes of CGP. In the contour method, cutting the samples and releasing residual stress cause to deform the cutting surface, so by measuring the displacements on the cutting planes and processing them, and then simulating processed displacements using a finite element model, the residual stresses are calculated (Honarpisheh and Nazari, 2017;Alinaghian et al., 2018a;Jafari et al., 2019;Moazam and Honarpisheh, 2019;Alinaghian et al., 2018b). With considering the aging effect can be expressed that duration time between CGP process and residual stress measurement (about 12 h) is not important, because with forming at the room temperature and using commercial pure copper alloy with high purity of Cu (99.93 %) and lack of alloying components (< 0.07 %) such as Mg, Al, Ni, etc., the aging ability of the sheet is not significant. ...
In this research, the influence of microstructure parameters on the residual stresses of ultrafine-grained sheets was investigated. For this purpose, the constrained groove pressing (CGP) process was carried out on the copper sheets with 3 mm thickness, and residual stresses of the CGPed sheets was measured using the contour method. Microstructure of the CGPed specimens was evaluated by the optical microscopy, micro x-ray diffraction (micro-XRD), and transmission electron microscopy (TEM) experiments. Microstructure parameters including crystallites size, dislocations density, and lattice strain were calculated using Williamson-Hall and Williamson-Smallman equations, and the calculated results were validated by the TEM images. The influence of these parameters on the residual stresses was investigated by analysis of variance (ANOVA) method, and two approaches were considered in this way. According to the results, the CGP process can create nanostructures in the CGPed sheets, and with increasing number of CGP passes, grains size, crystallites size, lattice strain, and residual stresses decrease, and density of dislocations increases. Microstructure parameters have a significant effect on the macro-residual stresses, and strain is the most effective parameter. Also, in the ultrafine-grained sheets, micro-parameters have an undeniable contribution, which is the same as that of macro-parameters on the macro-residual stresses.
... Because of non-uniform plastic deformation and grain refinement, the CGP process creates residual stress in the CGPed sheets. Residual stress is one of the factors that affects the mechanical behaviors of materials and can cause either an improvement or a decline in the properties [30][31][32][33]. The stress relief heat treatment is a recovery step of the annealing during which residual stress is alleviated without decreasing the mechanical properties of materials [34]. ...
In this research, the effect of stress relief annealing heat treatment on mechanical properties, microstructure, and residual stresses of a severe plastic deformation technique, known as constrained groove pressing (CGP), was investigated. For this purpose, the CGP process was performed on the commercial pure copper sheet with 3-mm thickness. The hardness, strength, homogeneity, microstructure, and residual stresses before and after stress relief annealing heat treatment were evaluated. Hardness and homogeneity on the surface and thickness were investigated and strength in both of groove direction and transverse groove direction were determined. Also, microstructure was studied along the thickness of CGPed samples, and the contour method was used for 2D residual stress measurement. The results indicate, with increasing number of CGP passes, hardness, strength, and homogeneity increase, while the mean grain size and residual stress decrease. Stress relief annealing reduces the mean grain size in the first pass but increases the mean grain size in the subsequent passes, causing a decrease of mechanical properties. Also, stress relief annealing increases residual stresses due to increasing microstructure heterogeneity.
Measurement of residual stress in rail foot, according to manufacturing standards is mandatory. In this study, the ring-core method and the sectioning technique are used to measure the residual stresses. A calibration technique for the ring-core method has been explained and simulated by the finite element analysis. The calibration coefficient for certain parameters and various depths of the annular groove has been determined. The ring-core method has been simulated for the uniaxial residual stress field and it is observed that the maximum error in maximum principal residual stress was about 13% which is about 5% of material yield stress. The residual stresses have been measured at the UIC 60 rail foot by the ring-core method and the sectioning technique, and the results are in good agreement with earlier investigations in this field. Also, it has been indicated that maximum residual stresses on the rail foot are not in the longitudinal direction and in the subsurface of the rail foot the maximum principal direction about coincides with the longitudinal direction. Both methods indicated tensile residual stresses on the rail foot, but the ring-core method predicted 27% higher longitudinal residual stress on the rail foot in comparing with the sectioning technique.
