Modelling the evolution of residual stresses during tensile testing of elastoplastic wires subjected to a previous bending operation

During coiling operations high residual stresses are frequently developed in steel wire. In this paper the stress distribution in wires during coiling, unwinding and subsequent tensile testing is modelled for numerous bending degrees, assuming perfect Voce plastic deformation and linear elastic behaviour. The influence of such residual stresses on the observed tensile test data can be deduced. It is shown that coiling with spool radii as used today industrially can lead to measurement of wire properties deviating significantly from the “true” properties of a properly coiled wire. Also, a method is proposed to deduce the original flow behaviour of coiled samples from tensile test curves, hence filtering the effect of the residual stresses.     

On analysis and measurement of residual stresses in the bending of sheet metals

A new method for evaluating distribution of residual stresses in bent sheet metals is presented. Due to the non-uniform distribution of strain and stress across thickness, springback on unloading induces residual stress in a bent specimen. The authors have formulated the problem and shown that the springback and residual stresses can be expressed as a function of geometric parameters and material properties of sheet metals, e.g. bending curvature, thickness, Young's modulus, work-hardening index, etc. The layer-removing method was used to determine the residual stresses in the study. By simulating the layer-removing process, analytical measurement of the residual stress was made. The analytical results were compared with the experimental data measured, and a good agreement was found.     

纳米陶瓷涂层磨削表面残余应力的研究进展

纳米陶瓷涂层材料具有高硬度和高耐磨性,采用超硬磨料的金刚石砂轮磨削是其最主要的加工方法,在磨削时容易出现表面残余应力而导致表面裂纹.目前,国外在纳米结构陶瓷涂层磨削表面残余应力的研究很少,我国正在对纳米陶瓷涂层材料超精密磨削后表面残余应力方面进行研究.介绍了纳米结构陶瓷涂层的研究背景,阐述了纳米结构陶瓷喷涂材料性能特点,分析了纳米结构陶瓷涂层的磨削研究动态和磨削表面残余应力的研究现状.分析研究表明,纳米结构陶瓷涂层的开发与研究将会受到越来越广泛的重视,其后续研究将是下一步的工作重点.     

Calculation of the bending stresses of involute teeth with longitudinal surface modification

The results of the simulation of the deformation mode in the root of the teeth of cylindrical involute gears under the action of a concentrated force are given. It is the first step in determining the bending strength of involute teeth in the case that at least some of them (those in a pinion or in a gear) have a longitudinal surface modification providing for a contact that is a point one from the theoretical point of view and local from the practical point of view. The investigations have been performed using the finite-element model developed in an ANSYS environment. Taking into account the effective (equivalent) stresses responsible for damaging the material of the teeth, the volume factor of the shape of the tooth has been reduced to a form that makes it possible to use the bending durability limits specified for ordinary (unmodified) teeth of involute gears with a theoretically linear contact, which enter the working stresses for estimating the bending resistance.     

The regularity of the formation of roughness and residual stresses during the vibroimpact hardening of components with a planar trajectory of vibration

The results are presented of the study of the computer spline simulation of the regularity of the formation of roughness and residual stresses over a finite set of bracket sections of an aircraft production unit with a 3D arrangement of surfaces by vibroimpact surface hardening with a planar trajectory of vibrations.     

Rheological modelling of residual stresses and deformations of plates during non-uniform cooling

The time–space distribution of eigen-stresses and residual deformations of a plane plate which reaches its final solid state through a given transition process of non-uniform cooling is described here by means of a simple visco-elastic rheological model.

The aging processes of the elastic and viscous properties are supposed to be temperature dependant in order to directly control the influence of the thermal history on the final stress and deformation conditions of the solid.

The model is able to reproduce qualitatively well the development of eigen-stresses in the spatially symmetrical cooling processes of tempering or toughening, as well as the formation of eigen-stresses and permanent bending in the spatially asymmetrical cooling processes of heat curving.     

Consideration of residual stress and geometry during heat treatment to decrease shaft bending

In automotive industry, heat treatment of components is implicitly related to distortion. This phenomenon is particularly obvious in the case of gearbox parts because of their typical geometry and precise requirements. Even if distortion can be anticipated to an extent by experience, it remains complex to comprehend. Scientific literature and industrial experience show that the whole manufacturing process chain has an influence on final heat treatment distortions. This paper presents an approach to estimate the influence of some factors on the distortion, based on the idea of a distortion potential taking into account not only geometry but also the manufacturing process history. Then the idea is developed through experiments on an industrial manufacturing process to understand the impact of residual stress due to machining on shaft bending and teeth distortion during heat treatment. Instead of being measured, residual stress is being neutralized. By comparing lots between each other, connections between gear teeth geometry and manufacturing steps before heat treatment are obtained. As a consequence, geometrical nonconformities roots can be determined more easily thanks to this diagnosis tool, and corrective actions can be applied. Secondly, the influence of product geometry on bending is experimentally considered. Moreover, metallurgical observations enable to explain the influence of workpieces geometry on shaft bending. Thanks to the obtained results, process and product recommendations to decrease shafts bending are proposed.     

Influence of laser spot overlap effect on residual stresses during laser-shock-wave processing of materials

Laser-shock-wave processing (LSWP) of materials is an innovative material processing technology in which considerable compressive residual stresses are generated in the surface region and contribute to improved strength and performance parameters. We analyze performance capabilities of lasers operating at higher frequencies and lower energy levels compared to lasers used with traditional LSWP technologies. Finite element modeling of compressive residual stresses at different stages of laser spot overlap for BT-6 titanium alloys is carried out. The results are compared with the known experimental data. It is shown that they are correlate well with each other.     

Predicting residual stresses and distortion during multisequence welding of large size structures using FEM

A three-dimensional thermomechanical finite element (FE) analysis is carried out to model and predict the influence of welding sequence on the generation of distortions and residual stresses in large size T-joints. To simulate industrial welding conditions, the influence of nine welding sequences on the magnitude of distortion in both the plate and the stiffener was investigated. The addition of new material during welding was simulated using an element “birth and death” technique, while the moving welding arc was considered as a volumetric heat source with a double ellipsoidal distribution. The investigated material is a structural steel used for fabrication of large size structures in the hydroelectric industry. To calibrate the model and validate the simulation results, welding-induced distortion for one sequence was initially modeled and the results were compared with experimental measurements. The optimum welding sequences for the base plate and the reinforcement plate were determined. The results indicated also that the predicted distortions obtained from three-dimensional FE analysis are in reasonable agreement with experimental measurements.     

Ultrasonic testing of the stressed state of pipelines with consideration of the temperature factor

The effect of temperature changes on the estimation of biaxial stresses in pipelines by the acoustic method is considered. A method of using the acoustoelastic effect for the estimation of the uniaxial and biaxial stressed states using the changes in the propagation times of longitudinal and shear elastic waves along the normal to the surface of a pipe before and after changes in stress is described. Uniaxial stresses or the difference between biaxial stresses may be estimated by measuring mutually perpendicularly polarized shear wave delays, whose relative difference proportional to the stress value is temperature-independent. The algorithms for estimating the biaxial stresses incorporate parameters that are sensitive to the difference between the temperature dependences of the velocities of longitudinal and shear waves. Some experimental data on the estimation of the error of the method that were obtained at variable temperatures and the results of taking the temperature factor into account in the algorithms for estimating the stresses by the ultrasonic method are given.     

Stress-strain state of tight joints under a bending moment

The stress strain state of tight joints under the action of a flexural torque is simulated by the finite-element method. The stress intensity at the contact zone in determined in characteristic cross sections of the shaft and the joint. The conditions of possible joint opening are established.     

On the possibility of evaluating the stressed state of pipelines using a magnetic method

It is shown that the monitoring of the stressed state of pipelines with the use of a method based on the evaluation of magnetic properties of a pipe metal allows one to solve completely the problems of improving the reliability of a pipeline system of compressor shops, namely, evaluate the stressed state of pipelines, to detect stress concentration zones, monitor the change of stresses in a construction just during the repair of a pipeline and adjustment of pipeline supports, and optimize the character of the reduction in the stress level.     

管线钢管JCO精确弯曲成形技术

为了减小管线钢管JCO成形工艺中成形管坯的椭圆度,基于塑性弯曲工程理论和机器视觉测量技术提出了管线钢管JCO精确弯曲成形工艺。在管坯首道次成形过程中,采用两次预弯法,识别出板材的弹复规律,结合管坯目标成形角,预测出精确的压制行程;在后续成形道次中,利用误差补偿技术循环补偿上一道次的成形误差,实现管坯每道次精确弯曲成形。确定了适合管坯端面的图像处理算法、图像处理流程和直线检测算法,提出了采用正三角形作为标定模板求解摄像机外部参数的标定方法,由单幅图片快速、高精度地标定出摄像机的外部参数,建立了将图像角转换为管坯真实成形角的数学模型。实验结果表明,管坯成形角监测误差在0.2°以内,可控制成形管坯的椭圆度在1.5%以内,减小了成形管坯的椭圆度,改变了成形管坯的椭圆度控制依赖于操作者经验的现状。     

Determination of anisotropy of strengthening and residual stresses in a steel sample cylinder treated with a roller

A mathematical model for determining residual stress fields and plastic deformations in a hardened layer of a sample cylinder after anisotropic strengthening is described. A procedure is set forth and the model is identified on the example of sample cylinders made of 40XH steel after running with a roller. Experimental and calculation results are analyzed.     

Kinetics of edge crack in the field of residual stresses

A methodical approach and program for calculating the kinetics of flat crack extension with an arbitrary front configuration in the spatial elements of constructions have been developed. The technique creates possibilities to estimate cyclical growth and changes in the front configuration at an arbitrary distribution of stresses. The experimentally calculated method of estimating the crack dimensions has been stated. The example of calculating a crack in the pipeline in the presence of residual stresses and taking into account T stresses is presented.     

A nondestructive acoustic method for estimating the residual stresses in a hardened layer

A theoretical model for estimating the residual stresses in a hardened layer of axially symmetric articles by a nondestructive acoustic method is considered. A technique of experimental investigations and an algorithm for estimating the residual stresses are presented. The envelope of a signal scattered by a structure and arising during propagation of ultrasonic waves in a hardened layer is qualitatively identified.     

Evaluating the level of residual stresses in anisotropic electric steel

The level of residual stresses (RS) in anisotropic electric steel (AES) is its most important functional characteristic that is responsible for losses of electric power in magnetic circuits of transformers during their service life. Reasons are given for the emergence of RS in AES and the known estimation methods are provided, the main shortcoming of the latter being the lack of quantitative estimates of RS. A simple and practically feasible method is suggested for estimating RS based on measurement of the anisotropy of magnetic properties of AES.     

Measurement method and pipe wall misalignment adjustment algorithm of the pipe butting machine

This paper presents a runout measurement method and a novel finite grouping method to predict and optimize the rotational angle and translational displacement of butting pipes to minimize pipe wall misalignment (PWM). This study develops a method to minimize the PWM of the pipes excluding the positions of welding seams. In this method, the measurement data are divided into finite groups and the criteria are created to identify the positions of welding seams and eliminate the effect of the welding seams. Finally, the rotational angle and translational displacement of the butting pipes are optimized to minimize the PWM. A butting machine is designed to implement this method. The machine is benchmarked by a standard smooth pipe to minimize system errors. Three butting experiments have been performed with welded pipes of diameter 406 mm. The comparison shows that the computation results agree with the experimental results very well. The maximum PWMs in three experiments are less than 1.87 mm, which satisfies the butting requirements, that is, a PWM of less than 2.0 mm. Then, the uncertainties of the measurement results are discussed.