Axial Residual Stress Research Articles

Effect of Diet and Age on Arterial Stiffening Due to Atherosclerosis in ApoE(-/-) Mice.

This work analyzes the progressive stiffening of the aorta due to atherosclerosis development of both ApoE(-/-) and C57BL/6J mice fed on a Western (n=5) and a normal (n=5) chow diet for the ApoE(-/-) group and on a normal chow diet (n=5) for the C57BL/6J group. Sets of 5 animals from the three groups were killed after 10, 20, 30 and 40 weeks on their respective diets (corresponding to 17, 27, 37 and 47 weeks of age). Mechanical properties (inflation test and axial residual stress measurements) and histological properties were compared for both strains, ApoE(-/-) on the hyper-lipidic diet and both ApoE(-/-) and C57BL/6J on the normal diet, after the same period and after different periods of diet. The results indicated that the aorta stiffness in the ApoE(-/-) and C57BL/6J mice under normal diet remained approximately constant irrespective of their age. However, the arterial stiffness in the ApoE(-/-) on the hyper-lipidic diet increased over time. Statistical differences were found between the group after 10 weeks and the groups after 30 and 40 weeks of a hyper-lipidic diet. Comparing the hyper-lipidic and normal diet mice, statistical differences were also found between both diets in all cases after 40 weeks of diet, frequently after 30 weeks, and in some cases after 20 weeks. The early stages of lesion corresponded to the first 2 weeks of diet. Advanced lesions were found at 30 weeks and, finally, the aorta was completely damaged after 40 weeks of diet. In conclusion, we found substantial changes in the mechanical properties of the aorta walls of the ApoE(-/-) mice fed with the hyper-lipidic diet compared to the normal chow diet groups for both the ApoE(-/-) and C57BL/6J groups. These findings could serve as a reference for the study of changes in the arterial wall properties in cases of atherosclerosis.

Behavior of a girth-welded duplex stainless steel pipe under external pressure

This study attempts to investigate the effects that external pressure has on the residual stress behavior in a girth-welded duplex stainless steel pipe. At first, FE simulation of the pipe girth welding is performed to identify the weld-induced residual stresses and depressions using sequentially coupled three-dimensional (3-D) thermo-mechanical FE formulation. Then, 3-D elastic–plastic FE analysis is carried out to evaluate the residual stress redistributions in the girth-welded pipe under external pressure. The residual stresses and plastic strains obtained from the thermo-mechanical FE simulation are employed as the initial condition for the analysis. The FE analysis results show that the hoop compressive stresses induced by the external pressure significantly alter the hoop residual stresses in the course of the mechanical loading, i.e. the hoop residual stress distributions on both surfaces of the pipe weld shift downward considerably, whilst the axial residual stresses are little affected by the superimposed external pressure.

Biaxial Residual Stress Mapping for a Dissimilar Metal Welded Nozzle

This paper describes a sequence of residual stress measurements made to determine a two-dimensional map of biaxial residual stress in a nozzle mockup having two welds, one a dissimilar metal (DM) weld and the other a stainless steel (SS) weld. The mockup is cylindrical, designed to represent a pressurizer surge nozzle of a nuclear pressurized water reactor (PWR), and was fabricated as part of a weld residual stress measurement and finite-element (FE) modeling round-robin exercise. The mockup has a nickel alloy DM weld joining an SS safe end to a low-alloy steel cylinder and stiffening ring, as well as an SS weld joining the safe end to a section of SS pipe. The biaxial mapping experiments follow an approach described earlier, in PVP2012-78885 and PVP2013-97246, and comprise a series of experimental steps and a computation to determine a two dimensional map of biaxial (axial and hoop) residual stress near the SS and DM welds. Specifically, the biaxial stresses are a combination of a contour measurement of hoop stress in the cylinder, slitting measurements of axial stress in thin slices removed from the cylinder wall, and a computation that determines the axial stress induced by measured hoop stress. At the DM weld, hoop stress is tensile near the OD (240 MPa) and compressive at the ID (−320 MPa), and axial stress is tensile near the OD (370 MPa) and compressive near the midthickness (−230 MPa) and ID (−250 MPa). At the SS weld, hoop stress is tensile near the OD (330 MPa) and compressive near the ID (−210 MPa), and axial stress is tensile at the OD (220 MPa) and compressive near midthickness (−225 MPa) and ID (−30 MPa). The measured stresses are found to be consistent with earlier work in similar configurations.

Influence of thick-walled cylinders length on the residual stresses generated during the single-cycle mandrelling

The paper presents methodology and results of experimental study by Sachs method the effect of length of mandrelled thick-walled cylinders made of steel grade 50 (0.5% C) with 5 mm diameter hole, outer diameter of 15 and 25 mm on residual stresses. Based on the review of studies, it was noted that this effect may be both due to uneven process of mandrelling along the cylinder length and due to zero axial residual stresses on its faces. It was found that the length of cylinders has the strongest influence on axial residual stresses. With allowances between 0.9 and 7.1% and length reduction from 40 to 10 mm, the largest absolute value of axial residual stresses decreases from 210 to 50 MPa. It was noted that when the outer diameter of cylinders is 15 mm their length significantly influence on both hoop and radial residual stresses. With the above-mentioned decrease in cylinders length, absolute values of hoop and radial residual stresses in the region adjacent to the hole, depending on the mandrelling allowance, increase (from -135 to -205 MPa and from -45 to 55 MPa respectively, when allowance is 7.1%), decrease (from -315 to -235 MPa and from -135 to -95 MPa respectively, when allowance is 0.9%) and remain almost unchanged (when allowance is 3.4%). Impact of length on these stresses is weak when the outer diameter of cylinders is 25 mm.

Residual Stress in the Welding Joint of Layered Cylindrical Vessels Including the Weld Clad Effect

Layered cylindrical vessels are widely used in process industries. The weld clad is applied before the girth welding of layered-to-layered sections. In this paper, a numerical method was used to predict residual stresses in a layered-to-layered joint with weld clad. The results showed that high residual stresses were generated in the weld and heat affect zone (HAZ), and a discontinuous stress distribution was generated. The through-wall axial residual stress at the weld centerline (WCL) was predominately tensile. The axial residual stress in each layer at the HAZ demonstrated a bending type distribution. The through-wall hoop residual stress at the WCL was predominately compressive in the V-groove zone, and it was tensile in the U-groove zone. The weld clad can decrease the peak residual stress in the tip of the interlayer gaps.

A study on the effect of weld induced residual stresses and the influence of weld sequencing of centrifugal extractor rotating bowl using numerical simulation and experimental validation

Centrifugal Extractors (CE) are the most preferred extraction equipment for the separation of fissile material from radioactive fission products in fast reactor spent fuel reprocessing in order to reduce damage to the solvent by minimizing the residence time. During fabrication of thin section high speed CE rotating bowls, several important factors such as heat input, weld speed, groove geometry, number of passes and weld sequencing are to be considered to control weld induced residual stresses and distortions. The thermal cycles due to concentrated heat input applied during the welding process, generates inhomogeneous plastic deformation and in turn the residual stresses in the weld metal. The presence of tensile residual stresses increase the susceptibility of a weld to fatigue damage, stress corrosion cracking (SCC) and fracture. A 3-D finite element analysis using SYSWELD software, for a three plane GTAW circumferential butt joint is carried out to predict weld induced residual stresses and distortions during fabrication of CE rotating bowls. The GTAW process was simulated using a nonlinear heat transfer analysis with the moving double ellipsoidal heat source model and a sequentially coupled thermo-metallo-mechanical analysis. This study includes temperature dependent thermo-physical, thermo-mechanical properties and isotropic hardening model. The axial and hoop residual stresses on the inner and outer surfaces are computed. Tensile residual stress on the inner surface and compressive residual stress on the outer surface are observed and their impacts on the CE rotating bowl are discussed. The importance of weld sequencing and its inference is investigated and validated against the experimental results.

Simulation of interface damage in metal matrix composites under off-axis loading using cohesive zone model

A finite element, micromechanical model is developed to predict the inelastic behavior of SiC/Ti composites subjected to off-axis loading using a three-dimensional representative volume element (RVE). The model includes the effects of manufacturing process thermal residual stresses together with interface damage and fiber coating. The cohesive zone model is used to consider the imperfect interface between the fiber and matrix. Introducing a unique failure criterion for various off-axis angles is the main novelty of this study. Apart from interface damage, plastic deformation of the matrix is also considered as another source of nonlinearity. Appropriate boundary conditions are imposed on the RVE to allow simultaneous application of a combined normal axial and transverse and axial shear loading plus thermal residual stresses. Results of the presented finite element model are compared with experimental data for stress–strain response, initiation of nonlinearity, and ultimate strength in various off-axis angles which show good agreement. Moreover, parametric studies are conducted to examine the effects of thermal residual stress and fiber volume fraction (FVF) on the mechanical response of the material.

Characterization of the Electrically-Actuated Micro Circular Plate

In this study presents a hybrid numerical scheme comprising the differential transformation method and the finite difference approximation technique to analyze the nonlinear dynamic response of the micro circular plate. The analysis takes account of the axial residual stress and hydrostatic pressure acting on micro circular plate upper surface. The effects of the residual stress, initial gap height, and thickness on the pull-in voltage of the micro circular plate are systematically explored. Overall, the proposed method provides an accurate and versatile means of analyzing the complex nonlinear behavior of the electrostatically-actuated microstructures.

Исследование влияния анизотропии поверхностного пластического упрочнения на распределение остаточных напряжений в полых и сплошных цилиндрических образцах

surface plastic hardening, roller burnishing process, hydraulic shot blasting procedure, deformation anisotropy, solid and hollow cylindrical samples, residual stresses, mathematical model, experimental data For the calculation of residual stresses and plastic strains in hollow and solid surface-hardened cylindrical specimens we suggest the mathematical models, which take into account both the cases of hardening leading to the isotropy (hydraulic shot blasting procedure) and to the anisotropy (roller burnishing process) of plastic strains in the surface layer. The introduced mathematical model has a hardening anisotropy parameter which ties the axial and circumferential components of the residual plastic strains tensor. We use the determined axial and/or circumferential components of the residual stresses tensor as the input information. Also we use the following assumptions: smallness of the off-diagonal elements of the residual plastic strains tensor and residual stresses tensor, plastic incompressibility of material, absence of the secondary plastic strains of the material in the compression area of the surface layer. The boundary value problems of the hardened layer stress-strain state estimation after the hardening for the hollow and solid cylindrical specimens are solved and the solution is given in the paper. We give the method for the mathematical model parameter identification under the condition of selfequilibrated residual stresses and the method for the experimental determination of residual stresses by the circles and strips approach. Also, the cycle of the hardening experiments for the hollow and solid specimens from the 40Kh steel (having different proportions of internal and outer diameters) in the roller burnishing process and hydraulic shot blasting modes was performed with the determination of the residual stresses. The mathematical model adequacy is verified through the comparisons with experimental data; good agreement of the calculated and experimental data is demonstrated. The calculated numerical values of the hardening anisotropy parameter are given. The fact that the procedure of surface anisotropic hardening (roller burnishing process) leads to the strong layering of the epures of axial and circumferential residual stresses in depth of the hardened layer is established. Contrastingly, the case of the isotropic hardening (hydraulic shot blasting) leads to almost coinciding epures. Using the experimental and calculated data we have shown that the hardening of tool roller type leads to the larger absolute values of the compressing stresses, which by more than 30% exceeds the stresses after the hardening of hydraulic shot blasting type for the specimens of the same geometry. For the main results of the research we have given the necessary data in the table and also we have presented the epures for the residual stresses distribution. © PNRPU

Pull-in voltage analysis of electrostatically actuated MEMS with piezoelectric layers: A size-dependent model

A size-dependent model for electrostatically actuated microbeam-based MEMS (micro-electro-mechanical systems) with piezoelectric layers attached is developed based on a modified couple stress theory. By using Hamilton's principle, the nonlinear differential governing equation and boundary conditions of the MEM structure are derived. In the newly developed model, the residual stresses, fringing-field and axial stress effects are considered for the fixed–fixed microbeam with piezoelectric layers. The results of the present model are compared with those from the classical model. The results show the size effect becomes prominent if the beam dimension is comparable to the material length scale parameter (MLSP). The effects of MLSP, the residual stresses and axial stress on the pull-in voltage are also studied. The study may be helpful to characterize the mechanical and electrostatic properties of small size MEMS, or guide the design of microbeam-based devices for a wide range of potential applications.

Experimental and theoretical studies of the influence of a tensile load on the relaxation of residual stresses in a hardened cylindrical specimen under creep conditions

This paper presents an experimental and theoretical study of the influence of a tensile load on the relaxation of residual stresses in a hardened cylindrical specimen of ZhS6KP alloy under creep conditions at 800°C. An experimental study was conducted to investigate the distribution of the axial residual stress tensor component across the thickness of the hardened layer after hardening by air shot blasting using microbeads and after creep loading for 50 and 200 h under a tensile load of 150 and 250 MPa. A detailed theoretical analysis of the problem was performed. In all loading regimes, the calculated and experimental values of the residual stresses were found to be in good agreement. It was shown that at low tensile load, the relaxation rate decreased in comparison with the case of thermal exposure in the absence of a tensile load and, with increasing load intensity, it increased.

A full-field residual stress estimation scheme for fitness-for-service assessment of pipe girth welds: Part II – A shell theory based implementation

With the two key controlling parameters identified and their effectiveness demonstrated in Part I of this study series for constructing a continuous residual stress profile at weld region, a classical shell theory based model is proposed in this paper (Part II) for describing through-thickness residual stress distributions of both axial and hoop components at any axial location beyond weld region. The shell theory based model is analytically constructed through an assembly of two parts: One represents weld region and the other represents the remaining component section away from weld. The final assembly of the two parts leads to a closed form solution to both axial and hoop residual stress components as a function of axial distance from weld toe position. The effectiveness of the full-field residual stress estimation scheme is demonstrated by comparing with a series of finite element modeling results over a broad range of pipe weld geometries and welding conditions. The present development should provide a consistent and effective means for estimating through-thickness residual stress profile as a continuous function of pipe geometry, welding heat input, as well as material characteristics.

Fatigue life of laser clad hardfacing alloys on AISI 4130 steel under rotary bending fatigue test

Fatigue life study of structures constructed by laser cladding using two types of hardfacing alloy, Stellite 6 (Co base) and Deloro 40G (Ni base) on AISI 4130 steel substrate was conducted using rotary bending fatigue test at ambient temperature 20°C. The laser clad specimens showed a reduced fatigue life compared to the specimen without cladding but of the same size due to the presence of residual stresses in substrate and coating regions. The presence of higher compressive residual stresses in substrate region and lower tensile residual stress in coating region of specimen laser clad with Stellite 6 generated longer fatigue life compared to the specimens laser clad with Deloro 40G, at a similar coating thickness level. With the same final structure size, coating thickness produced an inversely proportional effect on fatigue life where thinner coatings result in less reduction of fatigue life compared to thicker coating. The analytical model employed in this study demonstrated that thinner coatings alters axial residual stress by generating lower tensile residual stress in coating region which enhance fatigue life, compared to thicker coatings. This work has demonstrated the influence of coating type, coating thickness and load level on the fatigue life of the laser clad structures.

The Effect of Specimen Size on the Determination of Residual Stress in Polymer Pipe Wall

As a result of the production process, there are axial and tangential residual stresses present in pressure pipes made of polymer materials such as polyethylene or polypropylene. The residual stress magnitude and distribution have a significant influence on the pipe lifetime. In this contribution the results from experiments focused on determining the tangential residual stress distribution in the walls of polypropylene pipes of different dimensions are compared. The experimental method used involves measuring the deformation of ring shaped specimens that were slit in the axial direction. Measured deformation of the ring specimen is a result of the tangential and axial stress superposition. However, the effect of the axial residual stress depends on the specimen axial dimension and tangential residual stress estimated basing on experimental data should be corrected according to axial dimension of the specimen used. The correction suggested in this article is determined based on three-dimensional FEM simulations of the experiment.

An Experimental Investigation into Additive Manufacturing-Induced Residual Stresses in 316L Stainless Steel

Additive manufacturing (AM) technology provides unique opportunities for producing net-shape geometries at the macroscale through microscale processing. This level of control presents inherent trade-offs necessitating the establishment of quality controls aimed at minimizing undesirable properties, such as porosity and residual stresses. Here, we perform a parametric study into the effects of laser scanning pattern, power, speed, and build direction in powder bed fusion AM on residual stress. In an effort to better understand the factors influencing macroscale residual stresses, a destructive surface residual stress measurement technique (digital image correlation in conjunction with build plate removal and sectioning) has been coupled with a nondestructive volumetric evaluation method (i.e., neutron diffraction). Good agreement between the two measurement techniques is observed. Furthermore, a reduction in residual stress is obtained by decreasing scan island size, increasing island to wall rotation to 45 deg, and increasing applied energy per unit length (laser power/speed). Neutron diffraction measurements reveal that, while in-plane residual stresses are affected by scan island rotation, axial residual stresses are unchanged. We attribute this in-plane behavior to misalignment between the greatest thermal stresses (scan direction) and largest part dimension.

Stress analysis of welded joints in internal stiffener rings in an aluminum cylinder

Structural weight is one of the key criteria for vessels used in marine industries. The use of stiffeners and stringers strengthens the structure with the addition of a minimum weight. In cylindrical pressure vessels under hydrostatic pressure, mostly ring-type stiffeners are used. In order to join a stiffener ring to the vessel, welding is a conventional method. However, this process generates welding residual stresses and distortions, which can be added to external loads and cause structural failure. This study aims to develop a comprehensive simulation tool to predict distortions and residual stresses generated due to fillet-welded stiffener ring on an aluminum cylinder. Therefore, a hybrid numerical simulation approach has been employed. The simulation strategy has been implemented by using finite element software ANSYS enhanced with a number of subroutines. Results showed that the stiffener ring changes distortion trend in all orientation, especially in the radial direction with a reduction up to 15% in stiffener ring position. On the other hand, the radial residual stress was negligible and the hoop residual stress was tensile in the fillet weld region, with half of the base metal tensile strength magnitude, except in the start and the end of weld. Moreover, the axial residual stresses in the weld region on inner and outer surface of vessel in stiffener ring position were tensile and compressive, respectively.

Ultrasonic stress evaluation through thickness of a stainless steel pressure vessel

This paper investigates ultrasonic method in stress measurement through thickness of a pressure vessel. Longitudinal critically refracted (LCR) waves are employed to measure the welding residual stresses in a vessel constructed from austenitic stainless steel 304L. The acoustoelastic constant is measured through a hydro test to keep the pressure vessel intact. Hoop and axial residual stresses are evaluated by using different frequency range of ultrasonic transducers. The welding processes of vessel shell and caps are simulated by a 3D finite element (FE) model which is validated by hole-drilling method. The residual stresses calculated by FE simulation are then compared with those obtained from the ultrasonic measurement while a good agreement is observed. It is demonstrated that the residual stresses through thickness of the stainless steel pressure vessel can be evaluated by combining FE and LCR method (known as FELCR method).

Residual stress distribution in extruded polypropylene pipes

This paper deals with the experimental determination of residual stress and other inherent properties, density, yield stress, specific enthalpy of fusion and melting point temperature, of a polypropylene grade for pipe applications. The most important of these characteristics is the residual hoop (circumferential) stress, because it has a considerable effect on pipe lifetime. The experimental procedure for obtaining the residual hoop stress distribution by measuring the deflection of axially slit ring specimens is described and the data are evaluated by two approaches – a method based on theory of a curved beam and an older method based on theory of a thick-walled cylinder. Numerical modelling by FEM is employed to simulate the behavior of the ring specimens. The experiment was carried out on a set of 8 polypropylene pipes of different dimensions. The results for these pipes are compared, and a general equation describing the residual hoop stress distribution independently of pipe dimensions is proposed. Also, the influence of axial residual stress on the hoop residual stress is studied and, with the help of FEM, a correction of the results for long pipes is derived.

Measurement of the Distribution of Residual Stresses in Layered Thick-Walled GFRP Pipes

The objective of this study is to measure the axial, circumferential, shear and radial residual stress distributions in three thick-walled glass fibre reinforced plastic (GFRP) filament-wound pipes, two of which are layered. The measurement of residual stresses was carried out using a recently published layer removal method which overcomes the limitations of previous techniques and can be applied to layered anisotropic pipes of any wall thickness. Layers of approximately 0.3 mm thickness were incrementally ground from the outer surface of the pipes. The resulting strains were measured on the inner surfaces. A least-squares polynomial was fitted to each measured data set, and used to calculate the corresponding stress distributions. All of the resulting axial, hoop and shear stress distributions adhere to the requirement of self-equilibrium and the radial stress distributions all vanish to zero at the inner and outer surfaces. The radial stresses of the layered pipes showed a tendency to have two peaks, one for each layer, a consequence of the two-stage manufacturing process of these pipes. The measured axial and hoop stresses of all three pipes were similar at the inner surfaces despite significant differences in the stiffnesses in the principal directions arising from different wind angles.

Study on the Residual Stress and Fatigue Performance of Cold Expansion Hole on 7050-T7451

Cold expansion was employed on 7050-T7451 aluminum. Residual stresses were measured, fatigue tests were carried out for joints with different expansion, and the fracture surfaces of specimens were observed by scanning electron microscope (SEM). The results show that residual compressive stresses generate by cold expansion process. The maximum values of radial residual compressive stresses locate the middle of the inner wall of the hole and residual compressive stresses extend radially up to one diameter from the edge of the hole. Axial residual compressive stresses distribute near the exit. The fatigue lives N50 and N95,95 for specimen with strengthened hole with 5% expansion are respectively 3.54 and 3.68 times compared with non-strengthened hole. Fatigue fracture morphology shows the characteristics of mixed transgranular fracture and the propagation speed of the crack along horizontal direction is larger than vertical direction.