MAIN TOPICS,ABSTRACTS ＆ KEY WORDS-Mfect of surface roughness on the results of residual stress measurement

Spherical indentation strain-gauge method is one of methods to m easure the surfaced residual stress with m easurem ent depth of 0. 1mm. The im pact of surface roughness on residual stress results was discussed. The results have shown th at, in tests ① and ② , Rx is droppedby 14 MPa approximately with the surface roughness being decreased from 0. 75 μm to 0. 55 μm . While in 44 MPa with the surface roughness being decreased from 0 . 75 μm to 0. 55 μm . Compared to tests ① and ② , the effect of the surface roughnesson residual stress results is more significant in tests ③ and ④ , and the reduction effect of surface roughness on residual stress measurement is enhanced. In engineering application, most components are already in different stress states. Therefore, the influence on residual stress m easurem ent can not be ignored. Residual stress of a 2219-T87 A1 alloy plate was m easured. With the confidence level of 0. 95 , the confidence interval is [-122.515,-113.8849] MPa.

MODIFIED LAYER REMOVAL METHOD FOR MEASUREMENT OF RESIDUAL STRESS DISTRIBUTION IN THICK PRE-STRETCHED ALUMINUM PLATE

The integrated structure parts are widely used in aircraft. The distortion caused by residual stresses in thick pre-stretched aluminum plates during machining integrated parts is a common and serious problem. To predict and control the machining distortion, the residual stress distribution in the thick plate must be measured firstly. The modified removal method for measuring residual stress in thick pre-stretched aluminum plates is proposed and the stress-strain relation matrix is deduced by elasticity theory. The residual stress distribution in specimen of 7050T7451 plate is measured by using the method, and measurement results are analyzed and compared with data obtained by other methods. The method is effective to measure the residual stress.

Measurement and Analysis on Hardness and Residual Stress of Heavy Forging after Heat Treatment

The hardness and residual stress in the forging for cold roller during low temperature tempering,and the relationship of residual stress and cooling temperature of high temperature tempering for heavy forgings were studied.The stress relaxation constant at low temperature tempering and the elasto-plastisity inversion temperature at high temperature tempering were found.The results are of great importance to determine rational tempering cooling process of heavy forgings.

INFLUENCE OF RESIDUAL STRESS AND SURFACE MORPHOLOGY ON FATIGUE PROPERTIES OF STEEL 60Mn

Influence of residual stress and surface morphology induced by shot-peening on fatigue behav- ior of a medium temperature tempered spring steel 60 Mn has been studied.The compressive residual stress induced in the near-surface region may improve fatigue limit from 930 to 1010 MPa,and the very high tensile residual stress in the interior may reduce it from 1010 to 940 MPa,whereas the severe surface damage may cause a drop-off of it from 1010 down to 800 MPa.Fatigue cracks initiated in such position where the equivalent Mises stress,including residual stress,exceeded the local strength of the material.The compressive residual stress, induced by shot-peening,may intensify the effect of crack closure,so as to decrease the crack growth rate.

Experimental Research on Residual Stress in Surface of Silicon Nitride Ceramic Balls

The influence of the residual stress in surface of ceramic balls on the fatigue life is large, because the life of silicon nitride ball bearings is more sensitive to the load acted on the bearings than the life of all-steel ball bearings. In this paper, the influence of thermal stress produced in sintering and mechanical stress formed in lapping process on residual stress in surface of silicon nitride ceramic balls was discussed. The residual compress stress will be formed in the surface of silicon nitride ceramic balls after sintering. The residual tensile stress will be formed in surface of silicon nitride ceramic balls in lapping process, and the size of abrasive particle is smaller, such trend is stronger. In this paper the residual stress was measured by the xylometric measurement in which the material in surface was peeled with lapping. The distribution of residual stress in surface can be calculated with the variation in specific volume. The technological parameter with which the material was peeled by lapping was given, for minimizing the extra influence of the residual stress forming in peeling on the original residual stress in surface, the abrasive particle size would not be too small and the load impressed would not be too large. Some experimental researches on residual stress in surface of silicon nitride ceramic balls were made. The surface of silicon nitride ceramic balls presented residual compressive stress after sintering and the influence of the ball size on the residual stress is feeble. It is expected that the size of ball blank is same for achieving the same residual compressive stress in surface on balls after final machining. In lapping process, the surface of silicon nitride ceramic balls presented residual tensile stress, the larger the load which is impressed on single ball, the larger the amplitude of residual tensile stress is; the smaller the abrasive particle, the stronger the trend of plastic deformation is and the larger the amplitude of residual tensile stress is.

On the Foundations of the Ultrasonic Non-Destructive Determination of Stresses in Near-the-Surface Layers of Materials： Review

The foundation of the ultrasonic non-destructive determination of stresses in near-the-surface layers of solids is presented. The method is based on the regularities of Rayleigh wave propagation in solids with initial （residual） stresses. A description of the above mentioned method and examples of stress determination are presented. Examples are considered as applied to the residual stresses arising at electric welding and the operating stresses arising at loading.

Representation of residual stress symbol in the technical product documentation

A representation of residual stress graphic symbols in technical product documents is studied.The residual stress state of the product can be annotated in the technical product documents such as design drawings,process documents,test reports,papers and monographs.The composition of residual stress and the design of basic symbols,measurement method symbols,relief method symbols and state symbols of residual stress,and the representation of annotation for residual stress in documents are introduced.Residual stress symbol can be used in the design,manufacturing,inspection and service for the residual stress state requirements of the products in the mechanical manufacturing industry,as well as in light industry,daily necessities and other related industries.

Numerical Calculation and Experimental Research on Residual Stresses in Precipitation-hardening Layer of NAK80 Steel for Shot Peening

Shot peening can improve fatigue strength of materials by creating compressive residual stress field in their surface layers,and offers a protection against crack initiation and propagation,corrosion,etc.And fatigue fracture and stress corrosion cracking of NAK80 steel parts are improved effectively.Currently there lacks in-depth research in which the beneficial effect of the residual stress may be offset by the surface damage associated with shot peening,especially in terms of the research on the effective control of shot peening intensity.In order to obtain the surface residual stress field of NAK80 steel after shot peening,the samples are shot peened by pneumatic shot peening machine with different rules.The residual stress in the precipitation-hardening layer of NAK80 steel is measured before and after a shot peening treatment by X-ray diffraction method.In order to obtain true residual stress field,integral compensation method is used to correct results.By setting up analytical model of the residual stress in the process of shot peening,the surface residual stress is calculated after shot peening,and mentioning the reason of errors occurred between calculated and experimental residual stresses,which is mainly caused by the measurement error of the shoot arc height.At the same time,micro hardness,microstructure and roughness in the precipitation-hardening layer of NAK80 steel before and after shot peening were measured and surveyed in order to obtain the relation between shot peening strength and surface quality in the precipitation-hardening layer.The results show that the surface quality of NAK80 steel is significantly improved by shot peening process.The over peening effect is produced when the shot peening intensity is too high,it is disadvantageous to improve sample＇s surface integrity,and leading to reduce the fatigue life.When arc high value of optimal shot peening is 0.40 mm,the surface quality is the best,and the depth of residual stress in the precipitation-hardening layer reaches to about 450 μm.Numerical calculation is very useful to define the process parameters when a specific residual stress profile is intended,either to quantify the benefits on a specific property like fatigue life or to help on modeling a forming process like shot peen forming.In particular,the proposed parameter optimization in the progress of shot peening and effective control of the surface texture provide new rules for the quantitative evaluations of shot peening surface modification of NAK80 steel.

Effect of surface stress and surface-induced stress on behavior of piezoelectric nanobeam

A new continuum model is developed to study the influence of surface stress on the behaviors of piezoelectric nanobeams. Different from existing piezoelectric surface models which only consider the surface properties, the proposed model takes surfaceinduced initial fields into consideration. Due to the fact that the surface-induced initial fields are totally different under various boundary conditions, two kinds of beams, the doubly-clamped beam and the cantilever beam, are analyzed. Furthermore, boundary conditions can affect not only the initial state of the piezoelectric nanobeam but also the forms of the governing equations. Based on the Euler-Bernoulli beam theory, the nonlin- ear Green-Lagrangian strain-displacement relationship is applied. In addition, the surface area change is also considered in the proposed model. The governing equations of the doubly-clamped and cantilever beams are derived by the energy variation principle. Com- pared with existing Young-Laplace models, the proposed model for the doubly-clamped beam is similar to the Young-Laplace models. However~ the governing equation of the cantilever beam derived by the proposed model is very different from that derived by the Young-Laplace models. The behaviors of piezoelectric nanobeams predicted by these two models Mso have significant discrepancies, which is owing to the surface-induced initial fields in the bulk beam.

A review of welding residual stress test methods

Due to local uneven heating during the welding process,the residual stress of the structure after welding affects the reliability of it.In order to ensure the reliability,it is of great significance to test the residual stress distribution of the welded joint.It has always been the focus to find a simple and feasible method for residual stress testing to quickly and accurately obtain the residual stress distribution of welded joints.The mechanical measurement method has high measurement accuracy,convenient and easy operation,but it will cause certain damage to the components.Physical measurement method can avoid damage to components,but its test cost is usually high,and its measurement accuracy can also be affected by the material microstructure characteristics of welded components.Based on the advantages and disadvantages of these two residual stress test methods,a modal test method is proposed.This method is a non-destructive measurement method.Based on the mathematical relationship between the residual stress of the welded structure and the natural frequency(mathematical model),the natural frequency is measured through the modal test to calculate the residual stress quickly.However,it is difficult to establish a mathematical model with this method,and it is not suitable for realization.

Research progress of residual stress determination in magnesium alloys

With the research development of the magnesium alloys,the deformation or stress corrosion induced by residual stress(RS)attracted extensive interests in industry and research efforts extensive.However,there are relatively few studies on the RS of magnesium alloys in the world.The generation cause of RS in magnesium alloys was analyzed at first.Several methods of determinate the RS,including destructive methods(drilling hole,crack compliance,layer exfoliation etc.)and non-destructive methods(X-ray Diffraction,Neutron Diffraction,Short Wavelength X-ray Diffraction)were summarized.The factors that influence the measuring accuracy of XRD method were emphasized.The research trends of RS in magnesium alloys were put forward.

Prediction model of residual stress field in aluminum alloy plate

Residual stress distributions in 7075 aluminum alloy thick plates with different thicknesses and different quenching speeds were measured. A shape function of stress distribution was proposed based on the internal stress distribution characteristics of aluminum alloy. Using nonlinear regression technology,the function between stress value of key points on internal stress curve and surface stress of the plate was obtained. Based on the measured surface stress,stress value of key points and stress distribution shape,the internal stress distribution can be reconstructed. The experiments show that the model is of good engineering practicality.

Influences of Tool Wear on Residual Stress and Fatigue Life of Workpiece in Hard Cutting Process

Tool wear has an important influence on the residual stress distribution on the machined surface.Also,it will influence the fatigue life of finished workpiece. In this research,the hard turning process of hardened die steel Cr12 MoV was studied by using PCBN tool with considering tool wear. Based on the numerical treatment of residual stress,the dispersion and distribution curves of different tool wear were fitted,and the influence mechanism of tool wear on the residual stress distribution of machined surface was analyzed.Based on the theory of fatigue mechanics and mathematical statistics,the mathematical model for difference of stress dispersion and fatigue life was established. The rotating and bending tests were carried out on the standard parts after cutting process for the workpiece. The influence of tool wear on fatigue life was revealed by fracture surface morphology and fatigue life study. The results provide theoretical support for control of residual stress and the fatigue property of the machined surface under the actual working conditions.

Nondestructive test of weld residual stresses by acoustoelastic technique

The fundamentals of acoustoelastic theory and the principle of acoustoelastic nondestructive stress analysis related ultrasonic test Instrument for weld residual stresses are described. The weld residual stress distribution in butt-welded joints was measured by the acoustoelastic stress analysis, which uses the pulse echo overlap method to measure the speed difference in ultrasonic shear waves polarized in principal directions, and a new method of evaluating the material anisotropy is proposed. The results indicate that the anisotropic coefficient of the welded metal is much greater than that of the parent metal. the longitudinal residual stress distributions measured by the acoustoelastic technique are coincident with those obtained by the theoretical analysis, and the measuring accuracy is much greater than that obtained by the resistance strain gauge.

Three-Dimensional Thermo-Elastic-Plastic Finite Element Method Modeling for Predicting Weld-Induced Residual Stresses and Distortions in Steel Stiffened-Plate Structures

The objective of the present paper is to develop nonlinear finite element method models for predicting the weld-induced initial deflection and residual stress of plating in steel stiffened-plate structures. For this purpose, three-dimensional thermo-elastic-plastic finite element method computations are performed with varying plate thickness and weld bead length (leg length) in welded plate panels, the latter being associated with weld heat input. The finite element models are verified by a comparison with experimental database which was obtained by the authors in separate studies with full scale measurements. It is concluded that the nonlinear finite element method models developed in the present paper are very accurate in terms of predicting the weld-induced initial imperfections of steel stiffened plate structures. Details of the numerical computations together with test database are documented.

SURFACE CHARACTERISTICS OF 10Ni3MnCuAl STEEL BY SHOT PEENING

The surface of grinding 10Ni3MnCuAl steel is processed by the shot peening with different intensities. After shot peening, the metallographic structure of 10Ni3MnCuAl steel and the micro-structure on the surface layer are analyzed. The micro-hardness in the shot peening affected layer and the residual pressure stress are surveyed. The changes of surface quality, such as micro-hardness, metallographic structure and residual stress caused by shot peening are investigated. The result shows that shot peening can significantly improve surface quality and fatigue life of 10Ni3MnCuAl steel. The over peening effect is produced when the shot peening intensity is high, and it leads to the decrease of the fatigue life. When the optimal arc high value of shot peening is 0. 40 mm in experiments, the best surface quality is obtained and the depth of the residual stress in the precipitation-hardening layer reaches 450μm.

Experimental Study on Surface Integrity of Ti-6Al-4V in High Speed Side Milling

Aiming at the surface integrity of titanium alloy Ti-6Al-4V in high speed side milling, a series of side mill- ing tests were carried out with uncoated carbide milling cutter at various milling speeds. Surface roughness, residual stress, subsurface microstructure and microhardness variations were investigated. The surface roughness measurement results present that the milling speed from 80 to 120 m/min fails to produce better and more stable roughness values compared with the result obtained from 320 to 380 m/min. The residual stresses in the feed direction and axial depth of cut direction are in similar trends for the two milling speed levels mentioned above. Moreover, the residual stress pro- duced at 320 to 380 m/min is lower and more stable than that at 80 to 120 m/min. The microstructure analysis shows that the volume of β phase in the near surface becomes smaller and the deformation of β phase in the near surface be- comes obvious with the increase of the milling speed. Subsurface microhardness variation was observed down to 200 μm below the machined surface at 80 to 120 m/min and down to 160 μm at 320 to 380 m/min. It is concluded that better surface integrity and higher material removal rate can be obtained at 320 to 380 m/min than at 80 to 120 m/min.

Mechanical Properties and Microstructure of Bionic Non-Smooth Stainless Steel Surface by Laser Multiple Processing

Laser multiple processing, i.e. laser surface texturing and then Laser Shock Processing (LSP), is a new surface processing technology for the preparation of bionic non-smooth surfaces. Based on engineering bionics, samples of bionic non-smooth surfaces of stainless steel 0Crl 8Ni9 were manufactured in the form of reseau structure by laser multiple processing. The mechanical properties (including microhardness, residual stress, surface roughness) and microstructure of the samples treated by laser multiple processing were compared with those of the samples without LSP The results show that the mechanical properties of these samples by laser multiple processing were clearly improved in comparison with those of the samples without LSP The mechanisms underlying the improved surface microhardness and surface residual stress were analyzed, and the relations between hardness, comnressive residual stress and roughness were also presented.

Effect of Microstructure of Cementite on Interphase Stress State in Carbon Steel

The experiments related to stress states of ferrite and cementite in carbon steels were carried out including in situ four-point bending and tensile test by X-ray diffraction technique. Stresses in the cementite phase can be measured by conventional X-ray diffraction instrument after a specific treatment on the specimen surface. In order to estimate the stress states in two phases, the X-ray elastic constants of two phases in single-phase state （PXEC） are determined by the experimental X-ray elastic constants of them in composite state （CXEC）. The effects of volume fraction and particle size of spheroidal cementite on the interphase stress state are estimated. The experimental results are in good agreement with the theoretical relationships reported in the previous studies.