Residual Stress Values Research Articles

The Application of Neutron Diffraction Techniques (NDT) in Measuring Residual Strain-Stresses of Engineering Materials

In order to quantitatively understand the residual strain distributions and benefits of engineering components following special technique treatment, such as Autofrettaging, Hot Isostatic Pressing (HIP) and Dissimilar Material Welding (DMW), the Neutron Diffraction Technique (NDT) has been employed recently to measure residual strain and stress distributions on following three cases of (a) Autofrettaged Aluminum 7075 high pressure vessels; (b) Hot Isostatic Pressed (HIPPED) heavy metals of tungsten clad in tantalum plate and (c) Dissimilar Material Welding (DMW) of 316L austenitic stainless steel and ferritic steel AS508 with Alloy 52 weld filler. This paper reports the recent research findings, including (a) NDT can identify optimal Autofrettage pressure level, by which load bearing capacity of the Autofrettaged pressure vessel increased by 215MPa; (b) NDT is able to reveal residual strains within heavy metals of Tungsten clad in Tantalum plate HIPPED and (c) NDT revealed a maximum residual tensile hoop stress value of about 494MPa in the interface between parent material SA508 and the weld seam. This is vital information for the post weld process and subsequent safe use of the dissimilar materials weld. Other researchers’ successful examples of working with NDT are also briefly reviewed. Future prospective of Engineering Materials Diffractometer (EMD) at CSNS is described too with a view to demonstrating the application and importance of NDT in revealing residual strain-stresses that are inevitable within engineering materials and engineering components following any manufacturing process.

Effect of Periodic Water Clusters on AISI 304 Welded Surfaces.

This study compared the effect of the interaction time of periodic water clusters on the surface integrity of AISI 304 tungsten inert gas (TIG) welded joints at different excitation frequencies, as the effect of the technological parameters of pulsating water jet (PWJ) on the mechanical properties of TIG welded joints are under-researched. The TIG welded joints were subjected to different frequencies (20 and 40 kHz) and traverse speeds (1–4 mm/s) at a water pressure of 40 MPa and a standoff distance of 70 mm. The effect of the interaction of the pulsating jet on the material and the enhancement in its mechanical properties were compared through residual stress measurements, surface roughness, and sub-surface microhardness. A maximum enhancement in the residual stress values of up to 480 MPa was observed in the heat-affected zone, along with a maximum roughness of 6.03 µm and a maximum hardness of 551 HV using a frequency of 40 kHz. The improvement in the surface characteristics of the welded joints shows the potential of utilizing pulsed water jet technology with an appropriate selection of process parameters in the treatment of welded structures.

The influence of the annealing mode on stress elimination in a foam glass structure

The purpose of this work was to establish the influence of features of the annealing mode on the value of residual stresses in the structure of porous inorganic materials using foam glass as an example. A single-stage uniform cooling mode at three different speeds was considered. The study was performed using a mathematical model. The algorithm for analyzing the stress?strain state of the foam glass sample consisted in solving a system of equations by the finite element method. The calculation results are presented in graphic form. The graphics show the changes in stress in the foam glass upon cooling at speeds of 100, 10 and 1?C min-1. The temperature difference and the viscosity values of the foam glass subsurface and central layers in dependency on different temperatures of the cooling onset are presented. It was concluded that it is necessary to carry out the annealing mode of foam glass in three stages: initial, glass transition step and stabilization step, meaning different cooling rates have to be applied in different stages.

Measurement of residual stress on H13 tool steel during machining for fabrication of FSW/FSP tool pins

The development of residual stresses in tools due to machining is a widely known fact and these residual stresses can often lead to unwanted modifications in tool life. Turning, tapering and threading are extensively used in various manufacturing processes and they are specially used for the machining of different types of Friction stir welding/ processing (FSW/FSP) tool pin profiles. FSP being a solid-state process undergoes high levels of plastic deformation and so tool pins having extreme values of residual stresses may pose a problem for longevity of tool life. In this research, turning, tapering, and threading operations were conducted to produce two types of FSW/FSP tool pin profiles namely taper cylindrical and taper threaded. H13 tool steel is extensively used to produce tools FSW/FSP and hence it was chosen. H13 tool steel workpiece with 110 mm length and 22 mm diameter was taken as the workpiece and machining operations were performed to produce FSW/FSP tool on CNC Lathe machine. The objective of the present study is to establish the values of residual stresses developed in both tool pin profiles by utilizing the PulsetecµX-360n portable stress analyzer setup. The results that are achieved are then compared for both the pin profiles – taper cylindrical and taper threaded. It was observed that sigma(x) and tau (xy) residual stresses, both are higher in the case of taper threaded pin, and tau (xy) value is significantly higher for taper threaded.

Analysis and assessment of the stress-strain state of large-sized metal structures

The stress-strain state of large-sized metal structures is investigated. The causes and consequences of the formation of residual stresses and strains are shown. Methods for predicting residual stresses and strains by the calculation method are presented. Destructive and non-destructive methods for determining the stress-strain state of large-sized metal structures are presented. The influence of local deformations and clearances during assembly on the value of residual stresses and deformations is shown on the example of a typical curved large-sized metal structure, characteristic for the design of antenna devices of radar stations and air traffic control systems. Conclusions are made about the importance of analyzing and evaluating the stress-strain state of large-sized metal structures. Radar stations and air traffic control systems during operation experience extreme multi-parameter loads and thermal effects. To ensure the high reliability of their work, a thorough and accurate analysis is required, followed by an assessment of the stress-strain state of the bearing large-sized component parts of metal structures already manufactured and only being designed at the stage of experimental design work, in order to be able to choose the correct technological, constructive and organizational sequence for their manufacture. In modern production, metalworking methods are used, based on a sharp increase in the energy concentration on the treated surfaces of the elements, which contributes to the uneven distribution of thermodynamic potentials over their volume. The critical state is stress concentration in the metal structure, which can lead to its destruction. In zones of stress concentration, a complex stress state always arises, volumetric or flat. The type of local stress state significantly affects the level of loads that the metal structure can withstand without destruction. The most dangerous is a comprehensive uneven stretching. The conditional characteristics of the mechanical properties of a material such as tensile strength or elongation, determined in accordance with current standards, are not enough to calculate the loads that the structure can withstand without breaking. Also, the stress-strain state of the metal structure affects the dimensional stability in the metal structure, which leads to the need to use special technological solutions to relieve and relax existing residual stresses and strains. A sufficiently accurate assessment of predicting the stress-strain state of large-sized metal structures can be a model model, which analyzes and evaluates residual stresses and strains in-situ, and the level of breaking load when testing a model model under appropriate temperature conditions is taken as a criterion for assessing the health of a material. However, this method for large-sized metal structures is not always technically feasible and often unprofitable due to the large size of structures, the duration and cost of testing, the difficulty of creating full-scale operating conditions, etc. The problem of determining the calculated stress-strain state of a metal structure can be solved by separate solution of thermomechanical and deformation subtasks according to empirical formulas using the finite element method or the extended finite element method. Moreover, for the reliability of determining the calculated stress-strain state, it is necessary in the mathematical model to take into account many factors affecting the magnitude of the residual stresses and strains. The indicated assumptions, as well as the complexity of the proposed calculations, do not allow accurate prediction of the subsequent stress-strain state of large-sized metal structures having complex geometric and spatially oriented shapes. It is possible to use non-destructive and destructive methods to determine the actual stress-strain state of metal structures. For a more accurate assessment of the stress-strain state of metal structures, we must cut the object and subject the interior to the measurement of residual stresses. For this, it is possible to use two main methods: the stress relaxation method and the method of intrinsic deformation. As practice shows, it is necessary to predict residual stresses during welding of various types of joints without performing complex calculations of thermal elastoplastic analysis. In these cases, the following two simpler methods can be used: the use of experimental databases and the use of effective internal deformation, which is a source of residual stress. As an example, deformations of welded large-sized metal structures, typical for antenna systems of radar stations and made of sheet metal, are predicted. Thus, we can conclude that a preliminary and actual assessment of the stress-strain state of welded metal structures, especially large ones, is a difficult task, but its importance can hardly be underestimated. In this regard, new methods and techniques are constantly appearing that allow this to be done with the greatest accuracy and less computational complexity.

Nondestructive testing magnetic methods adaptation to the metal products accumulated strain and residual stresses determine

The first kind residual stresses (RS) is one of the key metal characteristics, that significantly affect the critical machine parts durability. To date, most of the RS experimental determination methods is based on layer-by-layer surface layer (SL) metal removal and has a number of disadvantages, the main of which are high labor intensity, the quickly RS determine inability without destroying the workpiece. In this regard, it is important to develop the RS and accumulated strain determining experimental Express on the basis of non-destructive testing (NDT) methods. The paper presents the experimental results and describes the relationship between the samples relative strain and RS values after 3-point bending and uniaxial tension with the parameters measured by magnetic NDT methods.

ИССЛЕДОВАНИЕ ФОРМИРОВАНИЯ ОСТАТОЧНЫХ НАПРЯЖЕНИЙ ПОСЛЕ УПРУГОПЛАСТИЧЕСКОЙ ДЕФОРМАЦИИ СТЕНОК ТРУБЫ ИЗ ДИСПЕРСНО-УПРОЧНЕННОГО АЛЮМИНИЕВОГО СПЛАВА В РЕЗУЛЬТАТЕ ВОЗДЕЙСТВИЯ ВНЕШНЕГО ДАВЛЕНИЯ

The formation of residual stresses after elastic-plastic deformation of pipe walls as a result of external pressure is studied using the approach based on a combination of methods of the physical theory of plasticity and mechanics of a deformable solid. As a result of the research, it is found that at the same value of the applied pressure, the thickness of the area subjected to plastic deformation is less for the alloys reinforced with large particles than for those reinforced with small particles. The values of the circumferential and axial residual stresses exceed the value of the radial residual stresses by more than an order of magnitude. Therefore, in the first approximation, the radial residual stresses can be neglected.

Experimental and numerical study to minimize the residual stresses in welding of 6082-T6 aluminum alloy

One of the most important negative consequence in the fusion welding processes is the generation of tensile residual stresses in welded joints. The main goals of this work are to determine the optimal combination of welding parameters to minimize the residual stress level and the influence of each welding parameter in that feature to weld 6082-T6 aluminum alloy plates using the GMAW welding process. To achieve these goals was implemented the Taguchi orthogonal array (L27) to define the design of numerical and experimental tests. All combinations were simulated in the Simufactwelding 6.0 software, from which it was possible to obtain the values of maximum residual stresses. The data treatment was carried out, reaching the combination of levels for each parameter. With ANOVA analysis was found that the parameter with the greatest influence in the residual stress generation was the welding speed, while the parameter with the least influence was the torch angle. Also, to minimize the residual stresses it was observed that the optimal combination of welding parameters is welding current intensity of 202 A, welding speed of 10 mm/s, and 30° of inclination of the angular torch. The two simulations that resulted in the highest and lowest residual stresses were validated experimentally by the hole drilling method to measure the residual stresses.

Investigation of process parameters and plate local thickening on residual stresses in hot stamping process

In this paper, local-thickened plates are adopted for aluminum alloy square cups stamping with relatively low values of residual stresses and small radius at the bottom corner. By utilizing numerical and experimental methods, the effects of process parameters and plate local thickening on the residual stress distribution of hot stamped aluminum alloy square cups are studied. Furthermore, the influence of plate local thickening on the radius of bottom corner of square cups is also investigated. The results showed that with an increase in the forming temperature, blank holder force and die corner radius, residual stresses in hot stamped square cups can be reduced. The same effect can be achieved by decreasing the die entrance radius. As opposed to the flat plates, using local-thickened plates can not only reduce the residual stresses values in hot stamped square cups, but also decrease the radius at the bottom corner of square cups. When the optimized thickening scheme of plate is used, the smaller radius at the bottom corner, the lower residual stresses in the square cups are obtained.

Релаксация механических напряжений в эпитаксиальных пленках кубического карбида кремния на кремниевых подложках с буферным пористым слоем

The results of the work quantitatively and qualitatively illuminate the processes of relaxation of misfit stresses arising during the epitaxy of cubic silicon carbide on silicon. Analysis of stress distributions of mechanical stress in 3C-SiC / Si and 3C-SiC / por-Si heterostructures is carried out. The essential role of the porous buffer layer in reducing the magnitude of misfit stresses is shown. The theoretical study data are confirmed by the experimental values of residual stresses in 3C-SiC / Si and 3C-SiC / por-Si samples.

Relaxation patterns of technological residual voltage in the surface layer of high-strength steel when cyclically loaded

Experimentally investigated patterns of changes in technological residual stresses under the influence of variable pressure in the surface layer became 30XNS2A. A mathematical model of relaxation of residual compressive stresses created by surface plastic deformation techniques with symmetrical cyclical bending of samples has been proposed. An empirical expression is proposed for assessing the final value of residual stresses as a result of cyclic loading, depending on the stress amplitude of a symmetric cycle. An expression is given for estimating the coefficient of relaxation rate of residual compressive stresses from their initial value, amplitude of alternating stresses and material properties. The constants of these expressions are determined for various construction materials. The theoretical dependences describe well the obtained experimental data. To predict the level of residual stress realization under operational loading, a formula was obtained to calculate their change as a result of the action of a step loading block with different amplitudes and duration of their action at each of the stages.

Investigating the residual stress in additive manufacturing of combined process in powder bed fusion and directed energy deposition

Residual stress is the secondary stress that still exists even after removing all loads. Parts manufactured by directed energy deposition on powder bed fusion contain residual stress, which can be compressive or tensile. When performing directed energy deposition processing on a powder bed fusion substrate, if these residual stresses are not considered, it may cause stress fatigue cracks, deformation, corrosion cracks, design examples, and premature component failure. Residual stress calculation is very important for deformation analysis, life prediction, and evaluation of failure causes. The purpose of this study is to understand the residual stress evaluation of powder bed fusion substrate additives made of stainless steel 316L powder in directed energy deposition treatment. In order to evaluate the residual stress value in additive manufacturing, the value can be obtained by X-ray diffraction technique.

Stress-strain state during recovery objects with corrosion defects by welding

The urgency of the problems connected with periodical diagnostics and repair of the linear section of main pipelines and the expediency of the use of repair technologies for restoration of the required wall thickness are proved. The experimental part of the work was the welding of a corrosion defect on the outer surface of the pipe by successive surfacing of the “filament” rollers in the environment of CO2 (MAG) – metal active gas and manual arc (MMA) – manual metal arc method in three layers, with a contour seam. The results of the residual stress-strain state obtained experimentally by brewing the defect of corrosive origin are presented, as well as the modeling of the stress-strain state (NDS) by the finite element method (ITU), which is formed at the same time on the section of a tube of 17G1C steel with a diameter of 1420 × 16 mm. As a defect model, a hollow oval shape with dimensions of 100 × 60 mm and a depth of 6 mm in the central part was made. The analysis and comparison of stress distribution, plastic deformations and displacements for these methods were made. The main factors influencing the VAT are established. It is shown that the VAT for different welding methods has the same distribution pattern, but differs in size. An assumption is made about the interconnection of displacements of the sample in the formation of residual stresses in the free state and, in the presence of rigid ligaments. The appropriateness of using the MAG method of repairing the thinned section of the main pipeline in terms of the formation of residual VAT rates has been confirmed. The effect is related to the formation of an area with increased values of residual tensile stress after the overlap of the last seam of each layer due to the effect of transverse and longitudinal shrinkage of the metal through the interaction of the last roller in the layer with the side wall of the defect.

Experimental and Numerical Investigation into Residual Stress During Turning Operation for Stainless Steel AISI 316

RS (residual stresses) represent the main role in the performance of structures and machined parts. The main objective of this paper is to investigate the effect of feed rate with constant cutting speed and depth of cut on residual stresses in orthogonal cutting, using Tungsten carbide cutting tools when machining AISI 316 in turning operation. AISI 316 stainless steel was selected in experiments since it is used in many important industries such as chemical, petrochemical industries, power generation, electrical engineering, food and beverage industry. Four feed rates were selected (0.228, 0.16, 0.08 and 0.065) mm/rev when cutting speed is constant 71 mm/min and depth of cutting 2 mm. The experimental results of residual stresses were (-15.75, 12.84, 64.9, 37.74) MPa and the numerical results of residual stresses were (-15, 12, 59, and 37) MPa. The best value of residual stresses is (-15.75 and -15) MPa when it is in a compressive way. The results showed that the percentage error between numerical by using (ABAQUS/ CAE ver. 2017) and experimental work measured by X-ray diffraction is range (2-15) %.

On the interplay of microstructure and residual stress in LPBF IN718

The relationship between residual stresses and microstructure associated with a laser powder bed fusion (LPBF) IN718 alloy has been investigated on specimens produced with three different scanning strategies (unidirectional Y-scan, 90° XY-scan, and 67° Rot-scan). Synchrotron X-ray energy-dispersive diffraction (EDXRD) combined with optical profilometry was used to study residual stress (RS) distribution and distortion upon removal of the specimens from the baseplate. The microstructural characterization of both the bulk and the near-surface regions was conducted using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). On the top surfaces of the specimens, the highest RS values are observed in the Y-scan specimen and the lowest in the Rot-scan specimen, while the tendency is inversed on the side lateral surfaces. A considerable amount of RS remains in the specimens after their removal from the baseplate, especially in the Y- and Z-direction (short specimen dimension and building direction (BD), respectively). The distortion measured on the top surface following baseplate thinning and subsequent removal is mainly attributed to the amount of RS released in the build direction. Importantly, it is observed that the additive manufacturing microstructures challenge the use of classic theoretical models for the calculation of diffraction elastic constants (DEC) required for diffraction-based RS analysis. It is found that when the Reuß model is used for the calculation of RS for different crystal planes, as opposed to the conventionally used Kröner model, the results exhibit lower scatter. This is discussed in context of experimental measurements of DEC available in the literature for conventional and additively manufactured Ni-base alloys.

Effect on microstructural and mechanical properties of Inconel 718 superalloy fabricated by selective laser melting with rescanning by low energy density

In this study, the residual stress reduction through low energy density reheating method in selective laser melting (SLM) process and the correlation between microstructure and mechanical properties were investigated. Inconel 718 superalloy specimens were manufactured via SLM and subjected to reheating (RH) strategies with different energy density, which was based on laser rescanning method. The microstructures were characterized by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The microstructure was observed in the vertical section, parallel to the building direction. With a scanning speed decrease in the RH conditions, the low angle grain boundary (LAGB) and average misoriented region fraction progressively increased. RH conditions exhibited higher Vickers hardness, tensile strength, and yield strength than those of the as-built condition, which increased slightly when the scanning speed was increased. Thermal residual stress was generally higher at z-axis than that at the x-axis. The lowest residual stress value was observed in the highest scanning speed RH condition, and as the scanning speed decreased, it became similar to that of the as-built condition.

Experimental Analysis of Repair Welding Alternatives for Shipbuilding DH36 Plates

Repair by welding is widely used in the shipbuilding industry during ship construction. The effect of the residual stress distribution induced by the welding process on the ship structure is important for the repair effectiveness. This article presents an experimental study of the residual stress distribution induced by repair welding in the plates that are typically used in ships and offshore structures. Different repair techniques are evaluated to identify the best practice associated with residual stress values. Recommendations for repair welding are discussed, and modifications to the present practice are proposed.

Biodegradation evaluation of poly (lactic acid) for stent application: Role of mechanical tension and temperature

AbstractIn this study, an experimental investigation is conducted on mechanical characteristics of poly(lactic acid) (PLA), before, and during degradation for stent application. A bioreactor is designed and fabricated to mimic in‐vivo environment of the body for studying degradation behavior of PLA fibers manufactured by melt spinning method. Beside PLA fibers, the degradation of PLA braided stents is investigated as control samples. To measure stress–strain and stress relaxation properties of PLA fibers, tensile, and relaxation tests are conducted. The decreasing trend of Young's modulus, variations in residual stress value after relaxation and pattern of stress relaxation are found during degradation. The influence of effective parameters, that is, temperature and stress, on PLA degradation is also studied. Moreover, the PLA degradation is analyzed by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA) and microscopic images. GPC results indicate the molecular weight decreases from 196,000 to 80,000 due to degradation while DSC analysis confirmed that the degradation promote an increase in PLA degree of crystallinity (from 43.3% to 59.8%). In addition, TGA results show that the PLA thermal stability decreases during degradation. This study provides useful information on PLA properties during degradation to assess the material in context of degradable stents.

Assessment of the Impact of Shot-Peening on the Fatigue Life of a Compressor Blade Subjected to Resonance Vibrations.

This publication presents an assessment of the influence of a surface treatment such as shot-peening on the fatigue life of a compressor blade exposed to resonant vibrations. As part of the work, a geometric model of the blade was developed, and a numerical modal and fatigue analysis were performed. The fatigue analysis was based on the Manson–Coffin–Basquin and Ramberg–Osgood models. Additionally, the location of the highest equivalent stresses was established. Based on the results of the strength analysis, two points were identified where a fatigue crack may potentially occur. As part of the work, the influence of different values of residual stresses on the results of the fatigue life was determined. The obtained results were compared to the literature values of fatigue life for this blade. A secondary objective of the study was to determine the size of the grains at various points of the blade, as well as the thickness of the layer plasticized as a result of peening. The relationship between the location of the highest values of the equivalent stresses and the thickness of the plasticized layer was determined. An explanation of the effect of shot-peening on the increase in the fatigue life of the blade was proposed.

Experimental-numerical study of laser-shock-peening-induced retardation of fatigue crack propagation in Ti-17 titanium alloy

Residual stresses induced by laser shock peening in Ti-17 titanium specimens were experimentally and numerically investigated to identify the mechanisms and generation conditions of the retardation of fatigue crack propagation (FCP). The retardation was experimentally observed with fatigue life prolonged by 150%. A multi-step simulation strategy for fatigue life prediction is applied, which successfully predicts the experimentally observed FCP behavior. The fractographic observations and numerical simulation indicate that crack closure, as opposed to other microstructural influences, is the dominant effect on retardation. The studies of multi-FCP aspects show that significant retardation occurs in specimens at high values of residual stresses, small peening gap distances, and lower externally applied loads.