Influence of Laser Remelting Process Parameters on Residual Stresses in Nodular Cast Iron 500 - 7

The measurement of residual stresses is very important in dynamically loaded precision machine parts which have been subjected to different kinds of heat treatment. Designers very frequently demand the presence of compressive residual stresses after heat treatment and finish grinding of the surface, since this increases the fatigue strength of the material and reduces the danger of fracture. In this investigation of the residual stresses after laser surface remelting, the size and variation of residual stresses were measured as a function of the modified layer depth on flat samples of nodular cast iron. Optimal laser remelting conditions were chosen, while the way of guiding the laser beam over the surface of flat samples was varied. To measure residual stresses, the relaxation method was used, including gradual electrochemical removal of the modified layer in which the deformation of the specimen was measured by resistance strain gauges.     

Evaluation and Correlation of Residual Stress Measurement in Steel

The stress patterns relevant for the assessment of the post production service behaviour of plain carbon hot strip mill plates were evaluated on the surface and at various depths. The hole drilling strain gage (HDSG) is a standard, well proven, semi-destructive technique and is employed for the purpose. However, this technique requires skill and is slow in operation. The magnetic Barkhausen technique (MBE) is non destructive and is still in an experimental stage, but has tremendous potential and has been tried here in steel plant environment. The objective is to establish whether MBE technique could be used as an alternative to HDSG technique. The calibration for MBE results was done under controlled compressive and tensile loading. The stress profiles were determined at six locations along rolling and transverse directions using these two techniques. The rolling stresses using HDSG method were found to be tensile near the surface, increase with depth and saturate at 0.5 to 1 mm depths. The transverse stresses were low tensile or compressive near the surface and saturate to low tensile values at similar depths. The stresses (averaged over a certain depth) by MBE are tensile in rolling direction and compressive in transverse direction. Correlation plots between residual stresses by HDSG method up to different depths and average stress by MBE show that that a good correlation exists at 0.35 mm depth. Beyond this depth, correlation is not good. It is true that for the material of the sheet and the frequency employed, the MBE results are not relevant beyond this depth. Also, the equivalent uniform stress as measured by HDSG method would deviate more and more from the actual stress as we go deeper.     

Influence of process parameters for induction hardening on residual stresses

Fatigue behaviour of induction hardened parts is largely dependent on the correct combination of hardening depth and the magnitude and distribution of residual compressive stresses in the surface layer. The objective of this work was to study experimentally the residual stresses at the surface layer of induction hardened cylindrical specimens. Two microstructures, quenched-tempered and normalised were investigated. The process parameters of induction hardening were varied to give a constant hardness penetration depth. The residual stresses were measured using the X-ray diffraction method. The investigated induction hardened samples showed a constant biaxial residual stress-state at the surface. The directions of the principal stresses deviated slightly from the defined circumferential and longitudinal directions. However, the shear stresses at the surface were of a small magnitude. This experimental investigation showed that the process parameters of induction hardening influence the residual stress-state of hardened parts to a great extent.     

Effect of cutting speed and tool rake angle on residual stress distribution in machining 2024-T351 aluminium alloy — unlubricated conditions

The residual stress distribution in the machining of 2024-T351 aluminium alloy was measured using an electrolytic etching technique. Ring-shape specimens were machined under unlubricated orthogonal conditions with high-speed steel tools having rake angles of 10, 15, 20 and 25° at cutting speeds ranging between 0.5 and 1.25 m sec^–1. The results of the investigation show that the residual stresses are compressive at the machined surface and decrease with depth beneath the machined surface. The maximum (near-surface) residual stress and the depth of the severely stressed region increase with an increase in the cutting speed. There seems to be little change in the residual stress distribution due to a change in the rake angle. The results are interpreted in terms of the variations in the amount of surface-region deformation produced by changes in cutting conditions.     

On the relationship between the length of Palmqvist cracks and residual surface stresses in WC-Co

WC-Co cylinders were subjected to cyclic compressive stresses for varying numbers of cycles and maximum compressive stresses. The fractional changes in the length of Palmqvist cracks and in the residual surface stresses were measured after precompression. It is found that the relationship between Palmqvist crack length and residual surface stresses depends on the conditions of precompression, and thus Palmqvist crack lengths cannot provide quantitative information on residual surface stresses.     

Some comments on residual stresses induced during quenching

The quenching process is known, to induce large residual stresses. These stresses cause difficulty in maintaining close tolerances on the components during manufacture. In the present investigation a simple technique has been developed to measure the residual stresses caused due to quenching of plain carbon steel. The results indicate that largo magnitudes of compressive residual stresses are induced beneath the surface due to the quenching process.     

Characterisation of residual stresses in heat treated,high strength aluminium alloy extrusions

Residual stresses were measured in rectilinear aluminium bars quenched using an aqueous polyoxyethylene glycol (PAG) solution or cold-water. Residual stresses were measured with neutron diffraction and a superposition-based method using mechanical strain release measurements. Three orthogonal stress components were measured along two transverse lines using neutron diffraction. The longitudinal residual stresses were mapped over a transverse cross-section using the contour technique. A primary slice removal technique mapped three orthogonal residual stresses over a transverse cross-section in the PAG extrusion. Residual stresses were found to vary from biaxial compressive in the part boundaries to triaxial tensile in the interiors. There was close correlation between the neutron diffraction and mechanical strain release techniques. PAG quenching demonstrated lower residual stresses.

This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.     

The effect of residual stresses arising from laser shock peening on fatigue crack growth

Residual stresses have in the past been introduced to manipulate growth rates and shapes of cracks under cyclic loads. Previously, the effectiveness of shot peening in retarding the rate of fatigue crack growth was experimentally studied. It was shown that the compressive residual stresses arising from the shot peening process can affect the rate of crack growth. Laser shock peening can produce a deeper compressive stress field near the surface than shot peening. This advantage makes this technique desirable for the manipulation of crack growth rates. This paper describes an experimental program that was carried out to establish this effect in which steel specimens were partially laser peened and subsequently subjected to cyclic loading to grow fatigue cracks. The residual stress fields generated by the laser shock peening process were measured using the neutron diffraction technique. A state of compressive stress was found near the surface and tensile stresses were measured in the mid-thickness of the specimens. Growth rates of the cracks were observed to be more affected by the tensile core than by the compressive surface stresses.     

Stresses in a nonlinearly hardening pipe after expansion to large deformations,inelastic unloading,and removal of its inner layers

The problem of the numerical determination of residual stresses in an elastoplastic nonlinearly hardening pipe of V95ochT2 material in plane strain is examined.It is shown that due to secondary plastic deformations that develop during unloading, the greatest residual circumferential stresses reside at a certain distance from the inner surface of a thick-wall pipe.Removal of the internal layer of the pipe gives rise to a small change in the circumferential compressive stresses on its inner surface. In this case, the zone where the maximum residual circumferential compressive stresses reside is shifted deeper into the pipe with a simultaneous decrease in the distance from this zone to the new inner surface of the piper, which is formed after removal of a layer of metal.Translated from Problemy Prochnosti, No. 11, pp. 111–114, November, 1989.     

面齿轮磨削齿面力热耦合及残余应力研究

根据面齿轮磨削残余应力的产生机理和Prandtl-Reuss方法,建立磨削表层热弹塑性力学本构关系;基于面齿轮磨削方法和Gleason接触原理,得出碟形砂轮磨削点接触椭圆方程参数、磨削力和磨削热流量的数学模型。构建面齿轮磨削单齿3D有限元模型,采用小步距移动法模拟磨削载荷的移动,仿真磨削温度场,得到磨削瞬态最高温度位于...     

Experimental evaluation of the effect of residual stress field on crack growth behaviour in C(T) specimen

The effects of the residual stress field resulting from shot peening and the indentation technique were investigated in relation to fatigue crack closure and crack growth behaviour. Compact Specimens of 20NiCrMo2 were used in this investigation. The regions of residual stress field were located behind the fatigue crack tip. Crack closure behaviour was measured with back face strain and crack mouth opening displacement gauges. Crack length was monitored by the compliance and microscopic methods. Residual stress was measured by the incremental hole-drilling method. Subsequently the closure level, propagation rate and resulting crack growth retardation were studied. Crack closure and attendant growth retardation were shown to be dependent on the residual stress field. Residual stresses produced by shot peening and indentation were both compressive. The maximum value of residual stress for both operations were on the surface and at the same intensity. However, the residual stress induced by the indentation technique was deeper. The results showed that the closure effect was stronger in the case of indentation technique.     

Residual stress measurements of computer aided design/computer aided manufacturing (CAD/CAM) machined dental ceramics

Residual stress analysis is becoming more important in terms of understanding the strength and fatigue behaviour of ceramic materials. The residual stresses after computer aided design/computer aided manufacturing (CAD/CAM) machining according to dental practice were analysed for two different kinds of dental ceramics, a feldspathic porcelain and a glass-ceramic. A mechanical strain gauge element was used to measure the deformation of dental test inlays during material removal by etching the surface of the sample. From these data the residual stress depth profile could be calculated for crystalline as well as amorphous materials. The strain gauge results were compared to X-ray diffraction data. The depth profile of the residual stress for both ceramics showed compressive stress at the surface of the machined ceramics, changing towards tensile stress at a depth of 10 to 15 μm from the surface. Ceramics with pronounced plastic deformation behaviour in CAD/CAM machining revealed higher residual stresses as well as a more distinct stress anisotropy in terms of grinding direction. This revised version was published online in November 2006 with corrections to the Cover Date.     

Residual stresses on flat specimens of different kinds of grey and nodular irons after laser surface remelting

Abstract

Laser surface remelting is one of the best procedures for surface modification of ferrite–pearlite nodular irons. Using this procedure on cast irons it is possible to achieve a very high wear resistance, which can be compared with the wear resistance of surface hardened heat treatable steels. The properties of the modified layer depend on the microstructure before heat treatment and on the amount of energy input transferred into the surface layer of the specimen. The research work has focused on the study of residual stresses after laser surface remelting of different kinds of grey and nodular irons. The identification of residual stresses was performed using the relaxation method, which involved measuring specimen strain. The results of the measured residual stresses confirm that the stresses strongly depend on laser surface remelting conditions. The measurement of residual stresses is very important in exacting dynamically loaded machine parts, which have been subjected to different kinds of heat treatment. In designing parts designers very frequently demand the presence of compressive residual stresses after heat treatment and finish grinding of the surface, since this increases the fatigue strength of the material and reduces the danger of fracture.     

Comparison of Electronic Speckle Laser Interferometry Hole-Drilling and X-ray Diffraction Techniques for Determination of Residual Stresses in the Heat Treated Steels

Carburizing is widely used to improve wear resistance and fatigue life of high duty machine parts. Fatigue performance of the carburized components is greatly dependent on the residual stress state in the surface layer. The aim of this paper is to measure the depth profiles of residual stresses in the carburized steels by electronic speckle laser interferometry (ESPI) assisted hole-drilling, and to compare the results with those measured by X-ray diffraction technique. To comprehend the differences in the residual stress state, the low-C steel components were carburized, and then, tempered in the range of 180–600 \(^{\circ }\)C. Microstructural investigations and hardness measurements were also conducted. The results obtained from both techniques gave identical results, and showed that the beneficial compressive residual stresses exist at the surface after carburizing, and their magnitudes decrease with increasing tempering temperature. It was concluded that ESPI assisted hole-drilling, with optimized drilling and stress calculation parameters, is suitable for determining the residual stress state of the carburized and tempered steels.     

Zur Ermittlung verformungsbedingter Makro- und Mikroeigenspannungen durch mechanische und röntgenographische Eigenspannungsanalysen

Analysis of deformation induced residual macro-and microstresses by mechanical and X-ray methods Residual stress distributions in plastically deformed tensile and bending specimens of perlitic steel were analysed using X-ray diffraction technique and incremental holedrilling method. After tensile loading compressive residual stresses are measured by X-ray analysis in the ferrite phase. Consequently X-ray analysis detects compressive microstresses. In the case of bending specimens residual macrostresses are superposed with residual microstresses after unloading. In no case identical residual stress values were measured by X-ray and hole drilling methods. Microstresses can be separated combining both measurement methods. Microstresses after tensile loading were found to be greater than in surface layers of respective bending samples subjected to the same amount of plastic strain.     

Procedure to Perform a Validated Incremental Hole Drilling Measurement: Application to Shot Peening Residual Stresses

Abstract: The paper describes a test rig designed to check and assess the accuracy of the incremental hole drilling (IHD) method. An external load produces a controlled linearly through thickness variable uniaxial stress field (reference bending stress), known with good accuracy, that can be applied and removed at each hole increment. After the separation between the bending relaxed strain from the residual stress relaxed strain, it is possible to reproduce the bending stress distribution in order to have complete confidence of the residual stress measurement. The bending verification of the IHD method was already proposed by other investigators before, but residual stress measurements were then performed on independent configurations. The proposed testing procedure gives a ‘real time’ verification of the residual stress measurement. Any experimental malfunctioning due to the operator inexperience, or any error during the stress calculation from the relaxed strain would produce an evident difference between the expected reference bending stress and the IHD bending stress output. Moreover, the reference bending stress helped for understanding that the not perfect hole cylindrical shape causes an underestimate of the predicted stress near the surface. A zero depth offset correction was proposed. This correction was tested on the reference bending stress, and then applied to the residual stress prediction. Three shot peening residual stresses IHD measurements were successfully validated by means of the bending stress; moreover, they were in good agreement with independent X‐ray diffraction measures also proposed in the paper.     

考虑应变率影响的厚壁筒残余应力场分析

本文针对弹塑性拉压循环加卸载条件下，不同的应变率（１０－４－１０－２ｓ－１）变化，对高强钢（ＰＣｒＮｉ３ＭｏＶ）材料的屈服应力、应变硬化参数和反向屈服应力等参量的影响进行了实验研究，提出了便于理论计算的简化弹塑性本构模型，并假设拉屈服应力与压屈服应力的差值不随应变率的不同而发生变化，这一假定与实验结果相符合，且便于工程计算。针对厚壁筒自紧加工工艺的残余应力场分析问题，用本文提出的模型对厚壁筒在四种不同的应变率条件下进行自紧加工时残余应力场的变化及不同的自紧效果进行了详细的分析和比较，并提出了改进工艺过程和提高自紧效果的建设性意见。     

Experimental Investigation Into the Fatigue of Welded Stiffened 350WT Steel Plates Using Neutron Diffraction Method

Abstract: The propagation of fatigue cracks under constant amplitude cyclic loading was studied in welded stiffened steel plates. The residual stresses in the stiffened plates were measured using the neutron diffraction strain‐scanning technique. The neutron diffraction measurements indicated that, in general, the residual stresses were tensile near the welded stiffeners and compressive between the stiffeners and ahead of the starter notch tips. Fatigue testing indicated that the fatigue crack growth rates of the stiffened plates were, in general, lower than that of a corresponding unstiffened plate, especially near the notch tips, where compressive residual stresses existed. An analytical method, using Green's function, was developed to predict the fatigue crack growth rates. Reasonable accuracy was obtained.     

Stability of shot peening induced residual stresses and their influence on fatigue lifetime

Mechanical surface treatment methods such as shot peening may improve the fatigue strength of materials. In this study, the effect of shot peening on strain controlled constant amplitude fatigue loading of a near pearlitic microalloyed steel was investigated. The stress amplitudes throughout the whole lifetime were followed, in addition to detailed recording of stress-strain hysteresis loops, particularly at small cycle numbers. The detailed relaxation of residual stresses and the changes in full width of half maximum (FWHM) of the X-ray peak at the surface and in depth as function of the number of cycles and plastic strain were recorded. By these techniques, the onset as well as the rate of relaxation of residual stresses could be followed at different strain amplitudes. Pronounced increase in lifetime of the shot peened specimens tested at total strain amplitude smaller than 0.3% (corresponding to 0.034% plastic strain amplitude) was achieved. This coincides with reasonably stable residual stresses at the surface and in depth.     

Effects of the machining conditions on the strain hardening and the residual stresses at the roots of screw threads

The strain hardening and the formation of the residual stresses at the roots of threaded joints produced by machining according to American Petroleum Institute (API) standards was investigated. Initially the problem is defined and then an experimental technique was developed for measuring the residual stresses at the roots of fine screw threads. The screw thread was cut on a tubular bar from chromium–nickel based alloyed steel. Residual stresses were measured by the electro-chemical layer removal technique. Experimental work showed that, sever strain hardening and the concentration of residual stresses at the roots of the screw threads took place depending on the machining conditions. Strain hardening in the range of 320–430 HV were found on the screw thread surfaces as compared to the base hardness of 260 HV. Residual stress ranging from 600 to 1450 MPa was developed as compared to the material tensile strength of 850 MPa. The depth for maximum residual stress is around 20 μm.