Axial Residual Stress Research Articles

A Methodology of Appropriate Weld Procedures for Axial Compressive Residual Stress on Inner Surface in Multi-Pass Girth Welded Pipe Joint

A Methodology of Appropriate Weld Procedures for Axial Compressive Residual Stress on Inner Surface in Multi-Pass Girth Welded Pipe Joint

Preparation of graded multilayer materials and evaluation of residual stresses

It is generally difficult to join ceramics to alloys by conventional welding technologies to fabricate graded multilayer materials with various excellent engineering properties. In this study, MoSi 2 and 316L stainless steel are chosen a typical example and are joined together using the spark plasma sintering technique. To evaluate the joint quality, the interlayer system of the graded material is characterized using analysis of the residual stress by the finite element ANSYS code. The results show that dense uniformed joints can be achieved with such graded inter-layers because the coefficient of thermal expansion (CTE) of each interlayer closely matched over a wide temperature range. Such a compatibility between the graded inter-layers prevents MoSi 2 with low toughness from the occurrence of microcracks resulted from the residual stresses formed during cooling of the joint. Further theoretical analysis indicates that with the increase in the compositional distribution exponent ( P), maximum radial and axial residual tensile stress first increases and then decreases. In addition, with the increase in the number ( n) of graded layer, maximum radial and axial residual tensile stress decreases gradually.

Laser-assisted machining of hardened steel parts with surface integrity analysis

Machining of hardened steel components has traditionally been the domain of grinding. A laser-assisted machining (LAM) process with a larger material removal rate is developed to replace the currently used hard turning and grinding operations for machining hardened steel shafts. A three-dimensional transient thermal model is developed to predict the temperature field in the hollow shaft of varying thickness undergoing laser-assisted turning. The laser-assist effect on surface quality and subsurface integrity is investigated in terms of surface finish, size control, microhardness, microstructures and residual stresses. LAM produces the parts of a good surface finish of R a less than 0.3 μm, a more uniform surface hardness distribution and no microstructure change. The thermal expansion effect on the actual depth of cut is experimentally studied to achieve accurate size control in LAM. It is shown that LAM produces about 150 MPa more compressive surface axial residual stresses than hard turning and reduces the variation in hoop stress than those produced by hard turning.

Effect of the weld groove shape and pass number on residual stresses in butt-welded pipes

This study used finite element techniques to analyze the thermo-mechanical behaviour and residual stresses in butt-welded pipes. The residual stresses were also measured in some welds by using the Hole-Drilling method. The results of the finite element analysis were compared with experimentally measured data to evaluate the accuracy of the finite element modelling. Based on this study, a finite element modelling procedure with reasonable accuracy was developed. The developed FE modelling was used to study the effects of weld groove shape and weld pass number on welding residual stresses in butt-welded pipes. The hoop and axial residual stresses in pipe joints of 6 and 10 mm thickness of different groove shapes and pass number were studied. It is shown that these two parameters may have significant effects on magnitude and distribution of residual stresses in welded pipes.

Effect of the welding heat input on residual stresses in butt-welds of dissimilar pipe joints

This study used finite element techniques to analyse the thermo-mechanical behaviour and residual stresses in dissimilar butt-welded pipes. The residual stresses at the surface of some weld specimens were measured experimentally by using the hole-drilling method. The results of the finite element analysis were compared with experimentally measured data to evaluate the accuracy of the finite element modelling. Based on this study, a modelling procedure with reasonable accuracy was developed. The developed finite element modelling was used to study the effects of welding heat input on magnitude and distribution of welding residual stresses in butt-welded pipes made of ferritic and austenitic steels. The hoop and axial residual stresses in dissimilar pipe joints of 8 mm thick for V-groove shape were studied. It is shown that the welding heat input has a significant effect on magnitude and distribution of residual stresses in the stainless steel side of the studied joints.

Spherical motion burnishing implemented on lathes

This paper presents a new method of mechanical surface treatment of external cylindrical surfaces and it is called “Spherical motion burnishing” (SMB). The axes of the workpiece and ring-shaped tool having toroidal acting surface intersect at angle θ=2°. The tool motion is superposition from a spherical motion and rectilinear translation with respect to the workpiece. The contact between the surface treated and its enveloped-tool acting surface is one of sliding friction in the presence of a lubricant. The method can be implemented on conventional machine tools, in particular on lathes by means of a relatively simple device and tool. To evaluate the manufacturing potentials of the SMB method a designed experiment has been carried out. The quality of the treated surfaces of workpieces made of low- and medium-carbon steel has been investigated experimentally. Mathematical models of the roughness and the residual axial normal stresses have been obtained on the basis of a planned experiment. The authenticity of the models has been proved on the basis of four extra tests. The method can be classified as mixed burnishing because it combines the advantages of hardening, dimensional burnishing and smoothing burnishing.

Nonlinear electrostatic behavior for two elastic parallel fixed–fixed and cantilever microbeams

In this paper, the electrostatic pull-in behavior of two elastic parallel fixed–fixed and cantilever microbeams in microelectromechanical systems (MEMS) are investigated. The nonlinear electrostatic equations are considered due to some important effects including: residual stresses, fringing field and axial stresses. Various residual stresses in two elastic parallel fixed–fixed models are considered. Step by step linearization method is used to solve the equations. The numerical results reveal that the step by step linearization method is highly efficient, and it is the easiest one to calculate the pull-in voltage. In the proposed models, the pull-in voltages are considerably decreased when compared to the pull-in voltages of simple fixed–fixed and cantilever models.

Relationship Between Fiber Gratings Reflectivity and Laser Fabrication Parameters

This study concentrates to investigate the relationship between laser fabrication parameters and reflectivity of fiber gratings. The fiber Bragg grating system, comprising Excimer Laser, Mask Aligner, Optical Spectrum Analyzer and Tunable Laser Source was utilized to fabricate the fiber gratings. A series of experiments were carried out for the fabrication of fiber gratings and to observe the effect of laser fabrication parameters on the reflectivity of fiber gratings. These samples were fabricated with different reflectivitys ranging from 27 to 93% at constant pulse rate i.e. 1Hz. The amount of reflectivity is the extent to which the index modulation in the fiber core changes. The higher the reflectivity of a fiber grating, the more microstructural changes occur within the lattice of the photosensitive core and the more the residual axial stress builds up within the cross section of the fiber. Here, we discussed only two laser fabrications parameters i.e. effect of pulse energy on reflectivity of fiber grating and effect of exposure time on reflectivity of fiber grating/Bragg wavelength. Based on the results of this study, it is inferred that reflectivity is exponentially increased, as the pulse energy increase at constant UV exposure time and attained saturation at pulse energy i.e. 165mJ. The low pulse energy produces a low reflectivity fiber Bragg grating even after a longer UV exposure time. It is also concluded that both reflectivity and Bragg wavelength are increased rapidly in the beginning with the increase of UV exposure time and then become saturated at UV exposure time i.e. 110min, even though pulse energy is constant. It means that the induced index of modulation was increased with the increasing of UV exposure time.

Welding of ASTM A106 Gr. B steel pipes for high-temperature service – part 1 – residual stress analysis

Welding is the principal process of manufacture used in the fitting and repair of tube sections. However, there is a lack of information about the alterations mechanically/metallurgically caused by the welding heat cycle, especially about the behaviour of the residual stresses. The objective of the first part of this work was to evaluate the welding residual stress in small diameter pipes used in oil refineries. Two-inch diameter pipes were welded using the manual GTAW process. AWS ER 70 S3 filler rods with diameters of 2.5 and 3.25 mm were employed. An electronic power supply was used, together with data acquisition systems to control the welding parameters. Stress measurements were carried out with an X-ray mini diffractometer. The axial residual stress profiles determined in the outer surface of the pipes were formed by compressive stresses in the weld region (the fusion zone and heat affected zone) and for tension stresses in the areas more distant from the weld bead. The evidence suggested that on the inner surface of the pipes, the stress profile is the opposite from that observed for the outer surface, with tension stress in the welding zone and compressive stress in the region further from the weld bead.

Comparison of the mechanical and resonance properties of thin film silicon MEMS fabricated at 110 and 250 °C

Microbridges with a thin film hydrogenated amorphous silicon structural layer deposited at 100 °C and 250 °C were fabricated by surface micromachining on glass substrates using aluminum as the sacrificial layer. These microbridges were electrostatically actuated and their frequency response was measured optically. The resonance frequency and quality factors of the microbridges were measured and used to characterize their mechanical properties. A comparison is made to microbridges with the structural layer deposited at 100 °C using a photoresist as a sacrificial layer. Microbridges fabricated using an Al sacrificial layer process show the presence of measurable axial residual stresses and have higher quality factors.

Origin of axial prestretch and residual stress in arteries.

The structural protein elastin endows large arteries with unique biological functionality and mechanical integrity, hence its disorganization, fragmentation, or degradation can have important consequences on the progression and treatment of vascular diseases. There is, therefore, a need in arterial mechanics to move from materially uniform, phenomenological, constitutive relations for the wall to those that account for separate contributions of the primary structural constituents: elastin, fibrillar collagens, smooth muscle, and amorphous matrix. In this paper, we employ a recently proposed constrained mixture model of the arterial wall and show that prestretched elastin contributes significantly to both the retraction of arteries that is observed upon transection and the opening angle that follows the introduction of a radial cut in an unloaded segment. We also show that the transmural distributions of elastin and collagen, compressive stiffness of collagen, and smooth muscle tone play complementary roles. Axial prestresses and residual stresses in arteries contribute to the homeostatic state of stress in vivo as well as adaptations to perturbed loads, disease, or injury. Understanding better the development of and changes in wall stress due to individual extracellular matrix constituents thus promises to provide considerable clinically important insight into arterial health and disease.

원전 노즐 용접부 잔류응력 예측을 위한 Round Robin 해석 결과 분석

This paper provides simulational round robin test results for welding residual stress prediction of safety/relief nozzle. To quantify the welding variables and define the recommendation for prediction and determination of welding residual stress, 6 partners in 5 institutes participated in round robin test. It is concluded that compressive axial and hoop residual stress occurs in dissimilar metal weld and pre-existing residual stress distribution in dissimilar metal weld was affected by similar metal weld due to short length of safe end. Although the reason for the deviation among the results was not pursued further, the effect of several key elements of FE analyses on welding residual stress was investigated in this paper.

ねじ谷底の残留応力とボルトの疲労強度の関係 : 第1報,転造丸溝試験片の残留応力について(機械要素,潤滑,工作,生産管理など)

A hypothesis was presented concerning the effect of the axial residual stress at the first thread root of a bolt on its fatigue strength. However, this has not yet been verified since the residual stress which may exist locally around the thread root cannot be measured or estimated with sufficient accuracy. This study aims to clarify the effect of the axial residual stress on the fatigue strength quantitatively by using newly developed technologies. As the first step, the residual stress at the root of groove-rolled specimen was measured by X-ray method with CCD positioning system, and two-dimensional FEM simulation for groove rolling process was performed by using DEFORM with simple plane strain model. The experimental results show that the compressive residual stress of 700MPa level exists at the root surface, and the maximum residual stress of 1200MPa level is generated at the inner layer of about 0.5mm from the surface. Such a residual stress distribution can be simulated by FEM although it is affected by the coefficient of shear friction and the restraint conditions which may affect the circumferential material flow in groove rolling process.

Finite-element analysis of residual stresses in Al2O3–TiC/W18Cr4V diffusion bonded joints

Abstract The residual stress distribution in Al 2 O 3 –TiC/W18Cr4V diffusion bonded joints was calculated using finite element method (FEM). The effects of pressure and interlayer on the axial stress and shear stress were also studied. The results show that the gradients of the axial stress and shear stress are great near the joint edge and are flat near the center of the joint. The maximal tensile axial residual stress is reached on the ceramic side at the ceramic/interlayer interface. The maximal shear residual stress is at the two interfaces of ceramic/Ti interlayer. With the increase of bonding pressure, the maximal tensile axial stress decreases and the compressive axial stress increases. But there is small effect of pressure on the shear stress. With Ti–Cu–Ti interlayer instead of Ti interlayer, the maximal axial residual stress has little decrease and the maximal shear residual stress decreases greatly. Near the edge of the joint, Ti–Cu–Ti interlayer reduces the residual stresses. The site of shear fracture in Al 2 O 3 –TiC/W18Cr4V diffusion bonded joints agrees with the simulated residual stress distribution.

Simulation and Analysis of Residual Stress in the Graded Interlayer of MoSi2 Composite/316L Stainless Steel Joint

We reported the simulation and the analysis of the residual stress within the graded interlayered joints of MoSi2 to 316L stainless steel fabricated by spark plasma-sintering (SPS) technique. The residual stress in the joints was analyzed by the finite element ANSYS code. The results show that the maximum radial and axial residual tension stresses first decrease and then increase with the increase of the compositional distribution exponent (P), and consistently decrease with the increase of the number (n) and the thickness (d) of graded layer, respectively. The optimal values of compositional distribution exponent, the thickness, and the number of graded interlayered joints of the MoSi2 composite/316L are P = 0.8, d = 1.0 mm, and n = 9, respectively. The residual tension stresses in the samples treated by nine graded interlayers are reduced to 24% and 25% of those in the joints without the interlayer, respectively.

Specific features of the deformation of steels in hydrogen

We have studied the effect of hydrogen on the mechanical properties of foils made of 08Kh18N12T steel under uniaxial tension. The initial stages of deformation in hydrogen require forces smaller by a factor of 3–5. In the case of biaxial tension of membranes made of this steel, their deformation ability also increases. The effect of hydrogen on the axial residual stresses of the first kind in 08Kh18N12T, 40Kh, and ShKh15 steels manifests itself in the activation of tensile deformation (inducing of compressive stresses). We have recorded a 30% increase in the fatigue limit of an austenitic alloy in hydrogen with a pressure of 30 MPa (the reference medium is air).

Finite element simulation of welding and residual stresses in a P91 steel pipe incorporating solid-state phase transformation and post-weld heat treatment

The finite element (FE) method has been applied to simulate residual axial and hoop stresses generated in the weld region and heat-affected zone of an axisymmetric 50-bead circumferentially butt-welded P91 steel pipe, with an outer diameter of 145 mm and wall thickness of 50 mm. The FE simulation consists of a thermal analysis and a sequentially coupled structural analysis. Solid-state phase transformation (SSPT), which is characteristic of P91 steel during welding thermal cycles, has been modelled in the FE analysis by allowing for volumetric changes in steel and associated changes in yield stress due to austenitic and martensitic transformations. Phase transformation plasticity has also been taken into account. The effects of post-weld heat treatment (PWHT) have been investigated, including those of heat treatment holding time. Residual axial and hoop stresses have been depicted through the pipe wall thickness as well as along the outer surface of the pipe. The results indicate the importance of including SSPT in the simulation of residual stresses during the welding of P91 steel as well as the significance of PWHT on stress relaxation.

An analysis of thermal residual stresses in SiC f/Cu composites when TiC or Ni as binder

The interfacial bonding strength of SiC fiber reinforced copper matrix composites is extremely weak. Using Ti or other metallic elements such as Fe, Ni, Mo can improve the fiber/matrix bonding strength because these elements can form carbides or an interdiffusion zone between the fiber and the matrix though a heat treatment. In this paper, a TiC reaction layer or Ni interlayer is introduced as a binder, and thermal residual stresses (TRS) in the SiC fiber, TiC or Ni interlayers, and matrix are simulated by means of finite element method. The results indicate that the matrix undergoes significant plastic deformation when the composite is cooled to room temperature from the bonding temperature, and the residual plastic strains are highest around the interlayers and decrease as distance from the interlayer increases; the values and distributions of hoop stresses and Von Mises stresses in the matrix are nearly identical when different interlayers are used , while the magnitudes of these stresses are significantly different in different kinds of interlayers. The distribution characteristics of axial residual stresses in the matrix change when different interlayers are used, and Ni is superior to TiC as the axial stresses greatly decrease near the axial end of the composite.

Numerical Simulation of Welding Residual Stress and Post-Weld Heat Treatment for Dissimilar Steel Welded Joint

By the finite element analysis software ABAQUS and the function of coupling process between heat and stress, the welding residual stress of Cr5Mo and 20 steel joint was analyzed. In addition the heat treatment of dissimilar steel welded joint was simulated. The residual stress distributions of dissimilar steel welding and heat treatment after welding were obtained. The comparison of welding residual stress between the homogenous steel and dissimilar steel was carried out. The results indicate that the welding residual stress of the same steel is lower than that of dissimilar steel welded joint obviously. Because of the difference of thermal expansion coefficient for base metal and welding microstructure, the relatively higher residual stress is produced due to the bigger thermal expansion coefficient of base metal. The highest annular residual stress is in welding line root of internal wall, while the highest axial residual stress is in welding line surface of outer wall. The welding residual stress of dissimilar welded joint is reduced obviously after heat treatment. The research results provide the possibility for optimizing the welding procedure and improving the reliability of dissimilar steel welding joint.

Effect of the interpass temperature on the predicted residual stress distributions in a multipass welded piping branch junction

A sequentially coupled three‐dimensional thermomechanical finite element model has been developed to predict residual stress distributions in a multipass welded piping branch junction. The residual stresses at the branch and run pipe cross‐sections, as well as along the circumferential weldlines on the outer surfaces of both the run and the branch pipes and on the inner surface of the branch pipe, are predicted. Three levels of interpass temperature have been selected to investigate their effect on the peak residual stresses. It is revealed that the interpass temperature has a significant effect on the residual stresses. As the interpass temperature is increased, both the peak hoop and the axial residual stresses at the run and branch cross‐sections decrease. The peak normal stresses along the circumferential weldline on the outer surface of the run pipes are also reduced. However, increasing the interpass temperature had a negligible effect on the peak tangential residual stresses along the circumferential weld line on the inner surface of the branch pipe. The results presented and the modelling technique described in the current study can be used towards formulating a recommendation to optimize residual stress profiles in multipass welded complex geometries through better interpass temperature control.