Plane Residual Stress Research Articles

Determination of the macroscopic residual stress: Modeling and experimental evaluation of texture and local grain-interaction

When the texture is present in the sheet, it is extremely difficult to test the residual stress based on the X-ray diffraction method. Based on the two extreme traditional Voigt and Reuss models, this paper proposes two specific corresponding local models (local Voigt and local Reuss) for the measurement of the plane residual stress of cold rolled sheet texture materials. The residual stress test results of CuNiSi specimen using these two local models show that the proposed local models are credible and can accurately characterize the residual stress in the specimen. In addition, based on the X-ray diffraction sin2ψ method of the classic residual stress test, a weighted average residual stress calculation method is proposed for cold-rolled texture materials. The dψ-sin2ψ method was used to analyze the effect of texture on residual stress. The results show that the copper texture C{211}〈111〉 in CuNiSi specimen has the effect of concentrating the residual compressive stress in the region. The stress increased by about 50 MPa. However, the effect of brass texture B{011} 〈211〉 and R texture R{011} 〈211〉 on residual stress was not obvious.

Analytical modeling of residual stress in direct metal deposition considering scan strategy

Existence of high tensile residual stress in the additively manufactured parts result in part failure due to crack initiation and propagation. Herein, a physics-based analytical model is proposed to predict the stress distribution much faster than experimentation and numerical methods. A moving point heat source approach is used to predict the in-process temperature field within the build part. Thermal stresses induced by steep temperature gradient is determined using the Green’s functions of stresses due to the point body load in a homogeneous semi-infinite medium. Then, both the in-plane and out of plane residual stress distributions are found from incremental plasticity and kinematic hardening behavior of the metal, in coupling with the equilibrium and compatibility conditions. Due to the steep temperature gradient in this process, material properties vary significantly. Hence, material properties are considered temperature dependent. Moreover, the specific heat is modified to include the latent heat of fusion required for the phase change. Furthermore, the multi-layer and multi-scan aspects of the direct metal deposition process are considered by incorporating the temperature history from the layers and scans. Results from the analytical residual stress model showed good agreement with X-ray diffraction measurements, which is used to determine the residual stresses in the IN718 specimens.

Plane residual stress measurement using ultrasonic considering weak anisotropy of metallic material

Ultrasonic velocity variation (UVV) along different directions induced by material weak anisotropy will lead to residual stress measurement error using ultrasonic inevitably. In this research, the influence of weak anisotropy on residual stress measurement is analyzed theoretically and experimentally. Firstly, the in-plane acoustoelastic wave equation is modified by considering material anisotropy, which can be characterized by two in-plane anisotropic parameters. Further, an analysis model is also established to express the linear superposition of weak anisotropy and acoustoelastic effect on UVV. Based on this, a plane residual stress measurement method has been developed, which was verified using the rolling aluminum alloy plate after friction stir welding. From the comparison with hole-drilling method, it was adequate and capable to measure the plane residual stress by the relative UVV along three particular directions.

Study of Residual Stress Relaxation Mechanics Using a Micro-indent Method

The aim of this study is to show the feasibility and accuracy of a micro-indent method to comprehensively evaluate the relaxation mechanics of residual stress in specimens of rolled aluminium alloy. This micro-indent method was adapted to implement four annealing treatments. The residual displacements were measured using a high-accuracy measuring machine, which enables to decrease the absolute error down to ±300 nm. This study presents an innovative data analysis using Mohr's circles, which allowed to study all directions of the in- plane residual stress for different relaxation times. The results revealed that the relaxation process finishes when the residual stress relief is completed in some preferential directions and then, a brief stress recovery phase begins.

Effect of Coating Surface Finishing on Fatigue Behavior of C450 Steel CAPVD Coated with (Ti,Cr)N

The present study evaluated the effect of the surface quality of a custom 450 stainless steel substrate coated with a (Ti,Cr)N nanolayer by cathodic arc physical vapor deposition on fatigue performance in air and in a 3.5% NaCl solution. Scanning electron microscopy was used to locate crack origin sites and characterize the coating. X-ray diffraction was used to analyze the phase formation and measurement of residual stress in the coating. The results showed that the determined in plane residual stress is compressive, with amount of \(- 2.8 \pm 0.4\) GPa. Chemical mechanical polishing was used to decrease the coating surface roughness (Ra from 0.35 to 0.07 µm). This significantly decreased the area having a high stress concentration and delayed the appearance of micro-cracks in the coating during fatigue testing. The results showed that when the material is tested under axial loading at a maximum alternating stress of 555 to 930 MPa, the fatigue strength of coated specimens with polished surfaces increased 10.6% in air and 26.7% in NaCl solution over the coated specimens with normal surfaces. Post-treatment of the coating increased the fatigue strength 3.5% in air and 10.1% in NaCl solution over the uncoated specimens and the weakness of CAPVD coating was eliminated in the field of fatigue.

Fabrication of simulated plate fuel elements: Defining role of stress relief annealing

This study involved fabrication of simulated plate fuel elements. Uranium silicide of actual fuel elements was replaced with yttria. The fabrication stages were otherwise identical. The final cold rolled and/or straightened plates, without stress relief, showed an inverse relationship between bond strength and out of plane residual shear stress (τ13). Stress relief of τ13 was conducted over a range of temperatures/times (200–500°C and 15–240min) and led to corresponding improvements in bond strength. Fastest τ13 relief was obtained through 300°C annealing. Elimination of microscopic shear bands, through recovery and partial recrystallization, was clearly the most effective mechanism of relieving τ13.

Through-Thickness Stresses in Automotive Sheet Metal after Plane Strain Channel Draw

A series of samples from four automotive materials - AKDQ, HSLA50, DP600, and AA6022-T43 - were deformed in a channel draw processes with different levels of draw bead penetration. As a result, varying magnitudes of deformations in plane strain mode and residual stresses were obtained. Through-thickness stress profiles were obtained non-destructively using a novel, high resolution X-ray diffraction technique.

Laser ultrasonic diagnostics of residual stress

Ultrasonic NDE is one of the most promising methods for non-destructive diagnostics of residual stresses. However the relative change of sound velocity, which is directly proportional to applied stress, is extremely small. An initial stress of 100 MPa produces the result of δV/V∼10 −4. Therefore measurements must be performed with high precision. The required accuracy can be achieved with laser-exited ultrasonic transients. Radiation from a Nd-YAG laser (pulse duration 7 ns, pulse energy 100 μJ) was absorbed by the surface of the sample. The exited ultrasonic transients resembled the form of laser pulses. A specially designed optoacoustic transducer was used both for the excitation and detecting of the ultrasonic pulses. The wide frequency band of the piezodetector made it possible to achieve the time-of-flight measurements with an accuracy of about 0.5 ns. This technique was used for measuring of plane residual stress in welds and for in-depth testing of subsurface residual stresses in metals. Plane stress distribution for welded metallic plates of different thicknesses (2–8 mm) and the subsurface stress distribution for titanium and nickel alloys were obtained. The results of conventional testing are in good agreement with the laser ultrasonic method.

Distortion control in welding by mechanical tensioning

This paper investigates the potential of mechanical tensioning (MT) to reduce the magnitude of residual stresses in welds and to eliminate buckling distortion. Both friction stir (FSW) and arc welds have been produced from the aluminium alloy AA2024, with different levels of tensile stress applied along the weld line either during or after welding. The resulting welds have been characterised in terms of out of plane distortion, residual stresses and microstructure. Buckling distortion was eliminated by stretching plates to between 35 and 70% of the yield stress of the material during welding. For each set of welding parameters investigated, an optimum tensioning stress has been identified, which eliminates the tensile residual stress peak across the weld zone, along with distortion. This optimum tensioning stress increases in line with the heat input of the welding process. When MT stresses are increased beyond this optimum value, then distortion arises once more and a band of compressive stress is formed across the weld zone.

Duality in Metal Cutting: Impact to the Surface Layer Residual Stress

This paper concerns the residual stress formation during the processes of rigid kinematics mechanical surface treatment. Taking conventional turning as example, we examine the features of the deformation zone, which cause the principal residual stress deviation from speed and feed directions and their in-depth rotation governing in-plane shear residual stress formation. Three stress components of the plane residual stress state are presented as functionally combined. The existence of materials providing residual stress distribution by principally different ways is theoretically predicted. The formation of the residual stress states of different types is confirmed by experimental results. A hypothesis based on the simple shear cutting deformation approach is advanced to explain the revealed relationships.

Twist Resulting in High Strength Steel Sheet Hat Channel Product Consisting of Straight Portion Combined with Curved Portion

This paper deals with a complex shaped hat channel product, which combines a straight part with a curved part in the longitadinal direction. Twist in the longitudinal direction is the most typical and serions of all dimensional inaccuracies in the product. Influencing factors in twisting can be classified into in-plane residual stress and residual moment. At first, by varying forming conditions such as the blank holding force and the cushion force, the inthence of the in plane residual stress on twist of the shrink and the stretch flange are investigated. Contrary to expectation, the in-plane residual stress had almost no relation to twist. Subsequently, by slitting the flanges and the side wall to release the residual moment, the influence of the residual moment on twist was investigated. It was observed that the residual moment plays an important role on twist. Based on the above, certain regions of the die radius are varied to control residual moment. As a result. the twist was decreased experimentally.

Reflection hologram interferometry combined with hole drilling technique as an effective tool for residual stresses fields investigation in thin-walled structures

A detailed description of unconventional two-step technique of residual stresses determination is presented. This technique has the highest possible sensitivity with respect to plane residual stress components compared with all other destructive mechanical methods. The first step is a high-precision measurement of in-plane displacement components describing a distortion of drilled hole in principal strain directions due to residual stresses redistribution. The second stage is a choice of the most reliable transition model that is capable of deriving accurate residual stresses values from holographic interferometry data. A full metrological justification of both steps is established. Specific approach to a quantitative interpretation of fringe patterns arising near probe hole in terms of absolute fringe order difference is proposed and effectively implemented. Basic relations that allow us a quantitative determination of residual stress components are derived. A wide series of high-quality actual fringe patterns inherent in the procedure involved is obtained. Sophisticated technique for reference fringe patterns constructing is developed and implemented in order to carefully estimate and verify an accuracy of results obtained. A capability of the developed technique is demonstrated in the course of residual stress fields determination at the proximity of welded joints of thin aluminium specimens. Residual stress distributions corresponding to four different welding technologies are presented. An excellent correlation between most of the actual and numerically simulated fringe patterns is demonstrated for different types of residual stress state. It is shown how residual stresses of high level up to 200 MPa in aluminium alloy can be measured by means of the technique developed.

Influence of heat transfer on the development of residual stresses in quenched steel cylinders

In this paper results of systematic FE-calculations about the influence of characteristic points of the temperature dependent heat transfer coefficient, especially the Leidenfrost point and the point of maximum heat transfer coefficient on the development of residual stresses are discussed. The numerical investigations were carried out for SAE 1045 and 4140 steel cylinders with 10 and 20 mm O quenched in water and oil, respectively. In this work experimentally determined h, T-curves are linearly approximated in the successive stages of heat transfer. Changes of the Leidenfrost-temperature do not influence the middle plane residual stresses of the cylinders investigated

The relationship between microstructure and residual stress in YBa 2Cu 3O 7− x

Sol-gel films of YBa 2Cu 3O x (YBCO) were deposited by spray pyrolysis on 10 cm diameter by 0.05 cm thick polycrystalline MgO wafers. The films were deposited in 1 microm increments up to 5 microm and characterized by electrical measurements, optical and electron microscopy, and X-ray diffraction. In plane residual stresses of the films were obtained by a shadow moire interferometry technique. The YBCOMgO interface was characterized by bevel polishing and fluorescence analysis. The films contain substantial in-plane residual stresses as a result of chemical reaction of the YBCO and MgO. Cu diffuses into the MgO so that a substantial amount of Y 2BaCuO 5 phase forms near the interface. The largest tensile stress was 0.96 GPa in a 4 microm thick film. The stresses were highest at the center of the wafer and decreased toward the edge, and the in-plane stresses caused cracks to form. Formation of the 211 phase influenced T c (onset) and T c (zero resistance). The T c onset was 78 to 92 K, and T c (zero resistance) was 15–65 K depending on film thickness.

Residual stress modelling by experimental measurements and finite element analysis

The paper describes an experimental-numerical technique for modelling plane residual stress fields with application to steel slabs containing laser welds of different geometry. This technique is based on the analysis of the strain measured by several small-size strain gauges as a function of the depth of a narrow slot which was cut in the slab itself in small increments. This information was combined with sensitivity coefficients obtained via finite element models in order to derive initial strain distributions for the welded plates. These distributions allowed a prediction to be made of the residual stresses acting in generic bodies extracted from the original plates. The stress fields predicted for square specimens cut from the slabs were then compared with the measured values, showing a fairly good agreement.

Acoustoelastic evaluation of arbitrary plane residual stress states in non-homogeneous, anisotropic plates

In this paper it is shown that relative ultrasonic velocity measurements can be used to determine the difference of normal stress components ( T 22 − T 11) in non-homogeneous, anisotropic plates containing arbitrary residual stress states. It has previously been demonstrated that measurements with horizontally polarized shear waves (SH-waves) can be used to determine ( T 22 − T 11) unambiguously in plates with unknown material property variations. However, previously the theory relating the velocity of SH-waves to stress and material anisotropy was limited to the case where the principal directions of stress are parallel to the axes of material symmetry. In this paper, we remove this restriction by extending the theory. We also suggest possible experimental procedures for validating the new theory.

Detection and measurement of strain in glass

Introductory the basic theoretical principles for the assessment of the stress-strain relationship are alluded to, with special respect to the plane state of stress. Then it is shown, in what way permanent residual stresses originate in glass and how they can be detected qualitatively. After that the usual measuring methods for the quantitative determination of stresses are discussed. Beginning with purely manual photo-elastic methods, which use so-called compensators for the determination of the magnitude of stresses, the development of automatical measuring systems, provided that the directions of the principal stresses are known, is described. Finally, a new fully automatic measuring system for stresses is presented. This system is able to determine the maximum stresses, including their sign, without any precondition. In the second part the special properties of residual stresses in the case of drawn and floated glass are discussed. Based on pattern of isoclinics, which have been experimentally determined fundamental statements concerning the state of plane residual stress of flat glass are made. Finally, some typical results of measurement are presented and discussed.

Photoelectric polarimeter for measuring plane residual stresses in shaped glass

Photoelectric polarimeter for measuring plane residual stresses in shaped glass