Reduction Of Tensile Residual Stress Research Articles

Surface properties in turning of aluminum alloys applying different cooling strategies

The generation of heat during chip removal can affect the residual-stress state and thus the performance of machined parts. For this reason, the aim of this study is to determine and modify the process temperatures in turning of the aluminum alloy EN AW-2017. Therefore, the influence of dry machining, cold-air cooling (CAC), flood lubrication (FL), and minimum quantity lubrication (MQL) is investigated by measuring the temperature with a tool–workpiece thermocouple. In regard to the correlation between the cutting power and the temperature, the cutting speed is varied in the range of 50 m/min to 550 m/min while the depth of cut and the feed are kept constant. The results show that the contact area between the tool and the workpiece has to be considered for the evaluation of the measured temperature as it represents an average value over the tool–workpiece interface area. Since there is only a slight decrease of the process forces with increasing cutting speed, the modification of the surface properties has to be mainly influenced by the change of temperatures. Thus, process cooling entails a reduction of tensile residual stresses as a consequence of a decrease of the cutting temperature. Furthermore, the surface roughness values (Ra, Rz) are smaller when applying cooling lubricant. In contrast for low cutting speeds, the intensified built-up edge (BUE) formation leads to compressive residual stresses but deteriorates the surface quality. Hence, the combination of an effective cooling strategy and the temperature measurement allows for the generation and monitoring of advantageous surface properties during machining.

Effects of heat treatment on the microstructure, residual stress, and mechanical properties of Co–Cr alloy fabricated by selective laser melting

The mechanical properties and residual stress of dental Co–Cr–Mo (CCM) alloy depend on the manufacturing and post-processing methods, which affect the prognosis of dental prostheses. Two CCM alloys manufactured by casting and selective laser melting (SLM) were compared, and the effect of heat treatment temperature for CCM alloys manufactured by SLM method was evaluated. Specimens were fabricated by casting (Cast Co–Cr) and SLM (SLM Co–Cr). SLM Co–Cr specimens were heat treated at 750, 950, and 1150 °C to compare their properties. Microstructures were analyzed via scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and electron backscattered diffraction (EBSD), and the residual stress was measured via x-ray diffraction (XRD). Mechanical properties were evaluated by a Vickers hardness test and a tensile test; fractography was performed after this. The SLM Co–Cr group exhibited a decrease in porosity, grain size, increase in solid solution limit, and high residual stress compared to Cast Co–Cr; the ultimate tensile strength, yield strength, and hardness were also higher. The microstructures, residual stresses, and mechanical properties differed significantly depending on the heat treatment, and the strength and hardness showed a tendency inverse to that of the elongation. Type I residual stresses mostly decreased after 750 °C heat treatment, however type II and III residual stresses remained even after 1150 °C heat treatment. SLM presented superior mechanical properties to casting. Considering the reduction of tensile residual stress and increased ductility, CCM alloys should be heat treated at a temperature of 950 °C or higher.

THE INFLUENCE OF THE SHAPE OF WORKING SURFACE OF STRAIGHTENING ROLLERS OF VERTICAL AND HORIZONTAL STRAIGHTENING MACHINES ON THE STATE OF RESIDUAL STRESSES IN RAILWAY RAIL – SECOND STAGE OF RESEARCHES

The paper presents the results of the second stage of work on the influence of the shape of straightening rollers on the state of residual stresses in rails, conducted as part of a project co-financed by the National Centre for Research and Development. The tests included numerical simulations of the rail straightening process using a new roll pass design of vertical and horizontal straightener rollers, determination of stress distribution maps in the rail after straightening in successive rollers of both straightening machines, as well as measurement of residual stresses in the rails after straightening operation in industrial conditions. The tests were carried out on R260 grade 60E1 rails. The reduction of tensile residual stresses in the centre of symmetry axis of the rail foot was obtained up to an average level of 32 MPa, i.e. by more than four times less in relation to the level achieved using traditional technology.

Forming mechanisms-related residual stress development in single point incremental forming

The mechanical properties of a component are significantly influenced by the prevailing residual stress state. A deliberate induction of compressive residual stresses or a reduction of tensile residual stresses can improve the component properties, such as fatigue strength. Single point incremental forming is a flexible manufacturing process to produce complex shaped parts by the computerized numerically controlled movement of a hemispherical forming tool. Because the process parameters can be locally adjusted it is possible to influence the residual stress state of the component. The influence of the forming mechanisms bending, shearing and membrane stretching, as well as the role of the hydrostatic compression on the residual stress state is widely unknown. This work aims to fill this gap. Therefore, linear grooves are formed into AA5083 sheets in a single-stage incremental forming process. The residual stress state of the unclamped sheet is measured on both sides of the groove center by means of X-ray diffraction. The relative intensity of the dominant forming mechanism is adjusted by adapting the relevant process parameters step-down increment Δz and tool radius RTool. The forming mechanisms are analyzed numerically by splitting the total plastic energy into the three forming mechanisms bending, shearing and membrane stretching. The numerical results for bending and membrane stretching could be validated by crystallographic analysis. A shift in the energy ratio of the forming mechanism from bending to shearing with increasing relative step-down increment Δz/RTool could be observed numerically. The maximum residual stress amplitudes are found for Δz/RTool < 1. The results indicate that a deliberate residual stress state can be induced by adjusting the dominant forming mechanism of the process.

Influence of severe plastic deformation on fatigue life applied by ultrasonic peening in welded pipe 316 Stainless Steel joints in corrosive environment

Corrosive solutions have an enormous effect on fatigue life of components in refinery industry. Several post-processing solutions are proposed to improve the weld zone, which is affected by the corrosive solutions. Ultrasonic peening (UP) is developed to enhance the fatigue life, specifically in corrosive environments and corrosion resistance of the components. The enhancement mechanism of UP is based on severe plastic deformation and reduction of tensile residual stress in weld toe. In this research, the fatigue-corrosion life of welded 316 Stainless Steel (SS) pipe is enhanced through utilizing UP process with different diameters of strikers. Fatigue-corrosion life of the weld on 316 SS and 347 SS fillers, as experimental samples, is studied in corrosive environments. This study intends to shed more light on the influence of corrosion and strength in fatigue-corrosion life of the sample materials. Therefore, this article studies the microstructure and pitting corrosion of the samples at different zones. The experimental results showed enhancement of fatigue-corrosion life after applying UP. The results revealed that welding by using 316 SS filler and UP with striker diameter of 4 mm have the highest fatigue life in the simulated H2S corrosive environment.

The role of microstructure in the stress relaxation and tempering of laser clad Ti–6Al–4V

In this work a heat treatment procedure was performed on laser clad Ti–6Al–4V, which resulted in a reduction of tensile residual stresses in the clad samples as well and a decrease in the hardness of the clad layer with an increasing heat treatment time. The reduction in the residual stress was attributed to inter-phase stress relaxation brought about by the growth of the β phase. The reduction in hardness was attributed to an increase in the volume fraction of the soft β phase. Both the reduction in residual stress and hardness due to this heat treatment makes it an attractive method to heat treat both laser clad and additively manufactured Ti–6Al–4V components for improved mechanical properties.

OS0825 き裂を有する材料に対するウォータージェットピーニングの残留応力低減効果

Water jet peening is a method using cavitation jet peening to introduce compressive residual stress into target surface, which has already been applied in nuclear power plants as a measure against stress corrosion cracking. In this report, we confirmed the effects of the water jet peening on cracked surface. Visual inspection after water jet peening might not be available because crack is closed, in which case ultrasonic inspection will still work. Reduction of tensile residual stress around cracks is confirmed. In addition, we found that crack growth rate decreased after water jet peening in shallow stress corrosion cracking.

205202 超音波振動を用いた溶接残留応力の低減法 : 振動加速度の影響(一般01 材料科学・材料力学3)

Welding is widely used for construction of many structures. Residual stress is generated near the bead because of locally given heat. Tensile residual stress degrades fatigue strength. The authors propose a new method for reduction of tensile residual stress in which ultrasonic vibration is applied during welding. First, transmission of ultrasonic vibration is examined. Second, reduction of residual stress using ultrasonic vibration is examined. It is concluded that ultrasonic vibration is transmitted to specimen well and residual stress is reduced using ultrasonic vibration.

Reduction of tensile residual stresses during the drawing process of tungsten wires

Tungsten wires are commonly used in the lighting industry as filaments for lamps. During the drawing process, the inhomogeneous deformation imparted by the drawing die causes tensile residual stresses at the wire surface in circumferential direction. These stresses have a detrimental effect for the wire because they are responsible for driving longitudinal cracks, known as splits. This work proposes two methods for reducing the residual stresses during wire drawing, namely applying an advanced die geometry and performing an inexpensive post-drawing treatment based on targeted bending operations. These two methods are analyzed with finite element simulations using material parameters obtained by mechanical tests on tungsten wires at different temperatures as input data. The computed results predict a substantial reduction of the circumferential residual stresses, thus reducing the risk of splitting.

20617 超音波振動を用いたブロック材の溶接残留応力の低減法(振動音響利用,一般講演)

Welding is widely used for construction of many structures. Residual stress is generated near the bead because of locally given heat. Tensile residual stress degrades fatigue strength. The authors propose a new method for reduction of tensile residual stress in which ultrasonic vibration is applied during welding. First, transmission of ultrasonic vibration is examined. Second, reduction of residual stress using ultrasonic vibration is examined. It is concluded that ultrasonic vibration is transmitted to specimen well and residual stress is reduced using ultrasonic vibration.

21721 超音波振動を利用した溶接残留応力の低減 : 加熱装置による検討(振動の積極的利用,一般講演,学術講演)

Welding is widely used for construction of many structures. Residual stress is generated near the bead because of locally given heat. Tensile residual stress degrades fatigue strength. The authors propose a new method for reduction of tensile residual stress in which ultrasonic vibration is applied during welding. First, transmission of ultrasonic vibration is examined. Second, reduction of residual stress using ultrasonic vibration is examined using heater instead of welding. It is concluded that ultrasonic vibration is transmitted to specimen uniformly and residual stress is reduced using ultrasonic vibration.

21720 超音波振動を利用した溶接残留応力の低減に関する研究 : 溶接による検討(振動の積極的利用,一般講演,学術講演)

Welding is widely used for construction of many structures. Residual stress is generated near the bead because of locally given heat. Tensile residual stress degrades fatigue strength. The authors propose a new method for reduction of tensile residual stress in which ultrasonic vibration is applied during welding. First, transmission of ultrasonic vibration is examined. Second, reduction of residual stress using ultrasonic vibration is examined. It is concluded that ultrasonic vibration is transmitted to specimen well and residual stress id reduced using ultrasonic vibration.

Reduction of Residual Stress of Welded Joint Using Local Plasticity Caused by Ultrasonic Vibration

Welding is widely used for construction of many structures. It is well known that residual stress is measured on welded joint. In this paper, a new method for reduction of residual stress using ultrasonic vibration during welding is proposed. Two thin plates are butt-welded. When ultrasonic vibration is used on one plate, tensile residual stress is reduced at center of the bead. Second, ultrasonic vibrations with different frequencies are applied on both plates. In this case, reduction rate of residual stress increases. Next, reduction of tensile residual stress is demonstrated by simulation method using an analytical model with dynamic characteristics of welded joint.

Development for automatic welding system with reduction of residual stress. Effect of vibrations with different frequencies

Development of automatic welding system is an important problem for automatic manufacturing system. It is well known that residual stress is measured near the bead because base metal is heated near the bead. Tensile residual stress on the surface degrades fatigue strength. In this paper, the effect of vibrations with different frequencies on reduction of residual stress is examined. Firstly, two thin plates are butt-welded using ultrasonic vibrations with different frequencies on each plate. When thin plates are welded using ultrasonic vibrations with different frequencies, tensile residual stresses are reduced and reduction rate is largest compared with other conditions. Secondly, two thin plates are butt-welded using ultrasonic vibration and vibration with low frequency. In this case, tensile residual stresses are reduced and reduction rate is largest compared with other conditions. Thirdly, a welding of automobile wheel for automatic welding system is performed using ultrasonic vibration. As a result, it is confirmed that the reduction of residual stress is reduced. Lastly, reduction of tensile residual stress is demonstrated using an analytical model based on elasto-plastic characteristic. Ill. 6, bibl. 2 (in English; summaries in English, Russian and Lithuanian).

高張力鋼の低温割れを防止する新低変態温度溶接材料の開発

There has been growing interest in high strength steel with a tensile strength higher than 800 MPa, which would be ideal for weight reduction and better performance of steel structures. However, there are two major problems in the application of high strength steel to structures. One is that the fatigue strength of welded joints is far lower than that of the base metal, and the other is that the weld metal and the heat-affected zone (HAZ) are likely to have cold cracking. These problems must be solved before high strength steel can be widely used in steel structures. As a solution to the problem of cold cracking, a reduced preheating type of high strength steel has recently been developed in which cold cracking in the HAZ is reduced by reduction of alloy components (lower Ceq, Pcm) without loss of strength. However, since the resistance to cold cracking of the weld metal has not been improved, preheating of the weld metal is still necessary, and the problem remains toward its wider use. Recently, Ohta et al. developed a low transformation-temperature welding consumable, in which compressive residual stress is induced by transformation expansion of martensitic transformation of weld metal at a low temperature near room temperature, and demonstrated that this consumable improves the fatigue strength of welded joints. We considered that the reduction of tensile residual stress in the low transformation-temperature welding consumable might also be effective in decreasing the cold cracking and that this consumable would be useful in manufacturing high performance welded joints with improved fatigue strength and cold-cracking resistance. In the present study, we examined the effects of low temperature-transformation weld materials on the prevention of cold cracking in high strength steel. Firstly, the y-shaped weld cracking tests demonstrated that reduction of residual tensile stress induced by martensitic transformation expansion of weld metal was effective in reducing cold cracking. Secondly, the effects of the degree of joint constraint on cold cracking in low transformation-temperature weld materials were examined by the y-shaped and H-shaped weld cracking tests. The cracking ratio was high at low degrees of joint constraint and low at high degrees of joint constraint. Two causes were considered: one was that the reduction of tensile residual stress by transformation expansion is higher at a higher degree of joint constraint, and the other was that the weld metal of martensitic structure alone is sensitive to cold cracking. According to the above investigation, we attempted to develop a weld material with high resistance to cold cracking at different degrees of constraint. To maintain the effects of reduction of tensile residual stress by transformation expansion to reduce the amount of diffusible hydrogen and the sensitivity of cracking, which are other causes of cracking, we designed and developed a 2-microstructure phase weld metal (martensite + retained austenite) by modifying the low temperature-transformation weld material to obtain a lower Ms point. We examined the effects of the degree of joint constraint on cold cracking, and confirmed that the cracking rate of the modified rod was almost 0% at all degrees of constraint, and its resistance to cold cracking was high.

Effects of Thermal Residual Stress on Mechanical Properties of SiC Whisker Reinforced Al&amp;ndash;Mg and Al&amp;ndash;Li Alloys Composites

Effects of residual stresses measured by X-ray diffraction on mechanical properties in the extruded pure Al, age-hardenable Al-Li, Al-Li-Cu alloys and solution-hardening Al-Mg alloy matrices composites reinforced with SiC whiskers have been investigated as a function of whisker volume fraction and heat treatment process. The tensile residual stress in the matrix decreased remarkably by liquid nitrogen (L.N.) treatment, and dislocation density in the L.N.- treated composite is higher than that in the water-quenched composite. The tensile residual stress in the matrix decreases the tensile yield strength and increases the compressive one, and many dislocations increase also both at the yield strengths. Consequently, the tensile yield strength of the L.N.-treated composites is considerably increased by double positive effects, which one is due to the reduction of tensile residual stress and the other is the increase of the average dislocation density in the matrix. Finally, an application of the positive effects of L.N. treatment for the age hardenable Al-Li-Cu alloy composites leads further increase of the tensile strength compared to the conventionally aged composites.