Residual Stress Test Research Articles

Effect of Double Shot Peening on Room-Temperature Notched Fatigue Property of TC4 Titanium Alloy

Single shot peening (SSP) with cast-iron shot and double shot peening (DSP) with cast-iron shot and ceramic shot were applied to investigate the relationship between surface integrity status and the fatigue property of titanium alloy TC4 on the notched specimens (stress concentration coefficient Kt=1.7). Surface roughness, residual stress profile and fatigue curve of the notched specimens were tested using scanning profilometer, XRD residual stress tester and rotating-bending fatigue testing machine, respectively. The results showed that surface roughness decreased 18.3% from Ra 1.09 μm post SSP to Ra 0.89 μm after DSP. Moreover, the position of the maximum value of residual stress migrated out close to the surface and the value of surface residual stress raised 12.6% to-800MPa from SSP. Additionally, the fatigue limit of the notched specimens pose SSP increased 64.7% to 467MPa from 283 MPa of AM, furthermore, edged up by 8% from 432MPa on unpeened smooth samples. It may be concluded that the double shot peening on titanium alloy has, therefore, eliminated the weakness of fatigue property caused by stress concentration.

Residual Stress Analysis for Engine Block by the Grooving Method

The study of residual stress in engine block has the potential to provide the necessary infrastructure for a wide range of scientific and technological developments concerning the automobile industry. Such study can act as centre of excellence for scientific studies in the field of materials science and machinery as well as for industrial applications. The basic principle of measuring residual stress with grooving method and the main measuring steps were introduced in this paper. Groove cutting in the internal surface of engine block surrounds a given area in which the remaining stress is released, and then the strain results are recorded through strain gauge. The residual stress test data were compared at different positions of each engine block. It is found that engine blocks A and D on the sides of engine develop higher residual stresses than blocks B and C in the centre of engine. The stresses can be higher than 200MPa in tension in engine block A, depending on the geometry, size, microstructure, subsequent welding process, and cutting sequence. In addition, residual stress at the bottom of engine is higher than that at the top because of the structure of the engine. The residual stress is also calculated by numerical modeling method from which it shown that the condition is commendably fit the results which the distribution of stress.

Nondestructive Testing Residual Stress Using Ultrasonic Critical Refracted Longitudinal Wave

Residual stress has significant impacts on the performance of the mechanical components, especially on its strength, fatigue life and corrosion resistance and dimensional stability. Based on theory of acoustoelasticity, the testing principle of ultrasonic LCR wave method is analyzed. The testing system of residual stress is build. The method of calibration of stress coefficient is proposed in order to improve the detection precision. At last, through experiments and applications on residual stress testing of oil pipeline weld joint, vehicle's torsion shaft, glass and ceramics, gear tooth root, and so on, the result show that it deserved to be studied deeply on application and popularization of ultrasonic LCR wave method.

Fatigue life of the S960QL steel welded joints

Abstract. During fatigue tests connectivity, welded steel XaBo960 achieved a significant reduction in the durability of welded samples compared to samples taken from the parent material. for an explanation of the reasons for this phenomenon, residual stress and fatigue tests microfractography breakthroughs were studied. The study confirmed the occurrence of the weld area of substantial positive inclusions, residual stresses, and a high silicon content and sulphides which reduce the fatigue life of the welded joints [1, 2]. The explanation of these adverse events will be the subject of further research.

Effect of Shot Peening and Plasma Electrolytic Oxidation on the Intergranular Corrosion Behavior of 7A85 Aluminum Alloy

The effects of shot peening (SP) and plasma electrolytic oxidation (PEO) on the intergranular corrosion behavior of the novel high strength aluminum alloy 7A85 (AA 7A85) were investigated by electrochemical polarization and electrochemical impedance tests. The intergranular corrosion mechanism of SP, PEO and PEO combined with sealing-treated AA 7A85 was studied by the metallographic analysis, residual stress testing, X-ray diffractometer analysis and scanning electron microscopy. The results show that AA 7A85-T7452 is very sensitive to intergranular corrosion. SP would significantly improve its intergranular corrosion resistance. This is attributed to the combination action of residual compressive stress and grain refinement. PEO would reduce the largest corrosion depth by 41.6%. Moreover, PEO without sealing did not eliminate the intergranular corrosion due to the existence of the micropores and microcracks in the oxide coating. However, PEO combined with the SiO2 sol–gel sealing treatment could effectively protect the AA 7A85-T7452 from intergranular corrosion because of the good corrosion resistance and barrier function of the sealed coating.

Application of Magnetic Barkhausen Noise in the Evaluation of Heat Treatment Process

Magnetic Barkhausen noise (MBN) is a new technique on non-destructive testing of residual stress. The testing system based on virtual instrument was explored. It can achieve the MBN and deal with it in time. The technique is applied to analyze residual stress in the welding line of iron materials back and forth the heat treatment. Through comparing with the data of blind-hole method, the corresponding change between Barkhausen signals and residual stress is verified.

Effect study and application to improve high cycle fatigue resistance of TC11 titanium alloy by laser shock peening with multiple impacts

Laser shock peening (LSP) is an effective surface treatment for improving fatigue resistance of metallic materials, in which high-amplitude beneficial residual stresses and structure changes can be produced. In aero-engines, the compressor blade made of TC11 titanium alloy was prone to result in high cycle fatigue (HCF) failure. The aim of this paper was to utilize LSP with befitting parameters to improve the HCF performance of TC11 titanium alloy. Firstly, the microstructure and mechanical properties of TC11 titanium alloy with different LSP impacts were observed and measured via transmission electron microscope (TEM), residual stress tester and microhardness tester. High-density dislocations and nanostructure were observed in the surface layer. High-amplitude compressive residual stresses were induced and microhardness was remarkably improved. According to the effects, a set of LSP parameters with three LSP impacts was confirmed and applied on standard vibration specimens. Vibration fatigue tests were conducted to validate the strengthening effect on HCF strength. The fracture mechanism was analyzed by fracture analysis. The strengthening mechanism of LSP was indicated by establishing the relationship between fatigue characteristics and effects on residual stress and microstructural changes.

Residual stress distributions in welded stainless steel sections

Residual stress magnitudes and distributions in structural stainless steel built-up sections have been comprehensively investigated in this study. A total of 18 test specimens were fabricated from hot-rolled stainless steel plates by means of shielded metal arc welding (SMAW). Two grades of stainless steel were considered, namely the austenitic grade EN 1.4301 and the duplex grade EN 1.4462. Using the sectioning method, the test specimens were divided into strips. The residual stresses were then computed by multiplying the strains relieved during sectioning by the measured Young׳s moduli determined from tensile and compressive coupon tests. Residual stress distributions were obtained for 10 I-sections, four square hollow sections (SHS) and four rectangular hollow sections (RHS). Peak tensile residual stresses reached around 80% and 60% of the material 0.2% proof stress for grades EN 1.4301 and EN 1.4462, respectively. Based upon the test data, simplified predictive models for residual stress distributions in stainless steel built-up I-sections and box sections were developed. Following comparisons with other available residual stress test data, the applicability of the proposed models was also extended to other stainless steel alloys. The proposed residual stress patterns are suitable for inclusion in future analytical models and numerical simulations of stainless steel built-up sections.

Research on Making Constant Valve Block of Residual Compressive Stress Based on Ultrasonic Testing

We proposed a new method of measuring the residual stress for the component based on the acoustoelastic theory and focused on a new technology of making constant value block of residual stress by shot peening in order to solve problems of residual stress testing by ultrasound. Monitored the residual stress value of block by self-developed ultrasonic residual stress measurement system. The results indicate that the value of the test block changes not much, so it can provides a new way to improve the ultrasonic testing of residual stress.

Surface Roughness and Residual Stresses of High Speed Turning 300 M Ultrahigh Strength Steel

Firstly, a single factor test of the surface roughness about tuning 300 M steel is done. According to the test results, it is direct to find the sequence of various factors affecting the surface roughness. Secondly, the orthogonal cutting experiment is carried out from which the primary and secondary influence factors affecting surface roughness are obtained: feed rate and corner radius are the main factors affecting surface roughness. The more the feed rate, the greater the surface roughness. In a certain cutting speed rang, the surface roughness is smaller. The influence of depth of cut to the surface roughness is small. Thirdly, according to the results of the orthogonal experiment, the prediction model of surface roughness is established by using regressing analysis method. Using MatLab software, the prediction mode is optimized and the significance test of the optimized model is done. It showed that the prediction model matched the experiment results. Finally, the surface residual stress test of turning 300 M steel is done and the residual stress of the surface and along the depth direction is measured.

Residual Stresses Comparison Determined by Short-Wavelength X-Ray Diffraction and Neutron Diffraction for 7075 Aluminum Alloy

High strength Al alloy 7075 is widely used in aeronautic and space domains. However, when the thick plate of 7075 alloy is quenched improperly, large residual stress (RS) will be produced which leads to the loss of performance in resistance corrosion, fatigue and fracture. It is necessary to get the detailed information about residual stress distribution in the quenched plate. Conventional X-ray diffraction, a viable residual stress test method, can only reveal the RS state near surface layer due to limited penetrated depth. RS in the bulk components now can usually be analyzed by neutron diffraction or hard X-ray diffraction of high energy synchrotron in non-destructive way. Here a novel non-destructive method using short-wavelength characteristic X-ray diffraction meter (SWXRD) with the X-ray tube of tungsten anode target to determine the RS within the materials is developed in China. This paper revealed the RS distribution in a 20 mm thick plate of 7075 Al alloy determined by SWXRD and typical neutron diffraction (in LLB laboratory of France). The RS distribution through the thickness of Al plate shows a good agreement with the result determined by SWXRD compared with neutron diffraction.

Weld Failure Analysis of Air Radiator

The air radiator had been in service for more than 30 years until a notch failure occurred. In this paper, a rare notch failure is completely investigated by means of macroscopic and microscopic observations, microstructural inspection, chemical analysis, and residual stress test. The results show that the notch failure mode of the air radiator is attributed to high-cycle fatigue fracture, due to the welded lapping surfaces near the notch on both sides of the corrugated plate trough not being put onto one plane during the welding process. Therefore, in order to prevent or reduce possible tensile stress, it is recommended that the welded lapping surfaces be put onto one plane before welding.

Experiment investigation of laser shock peening on TC6 titanium alloy to improve high cycle fatigue performance

Laser shock peening (LSP) is an innovative surface treatment technique, and can significantly improve the fatigue performance of metallic components. In this paper, the objective of this work was to improve the fatigue resistance of TC6 titanium alloy by laser shock peening. Firstly, the effects on the microstructure and mechanical properties with different LSP impacts were investigated, which were observed and measured by X-ray diffraction (XRD), transmission electron microscope (TEM), residual stress tester and microhardness tester. Specially, nanostructure was detected in the laser-peened surface layer with multiple LSP impacts. Whereafter, a better parameter was chosen to be applied on the standard vibration fatigue specimens. Via the high-cycle vibration fatigue tests, the high cycle fatigue limits of the specimens without and with LSP were obtained and compared. The fatigue results demonstrate that LSP can effectively improve the fatigue limit of TC6 titanium alloy. The strengthening mechanism was indicated by analyzing the effects on the microstructure and mechanical properties comprehensively.

Experimental Research on the Relationship between Surface Polishing and Fracture Strength for Ground Ceramics

Fracture strength is one of the key mechanics performances for engineering ceramics products, greatly influenced by the microscopic topography and residual stress field of ground surface. In this work, several testing equipments, such as the metallurgical microscope, surface profiler and X ray residual stress tester were introduced to investigate the relationships between microscopic topography, surface roughness, residual stress and fracture strength of ground ceramics, after the surface grinding and mechanical polishing. The experimental results show that a smoother machined surface with low roughness and residual stress is obtained through polishing with absolute alcohol for 20 minutes; the fracture strength of Si3N4SiC and Al2O3 are increased by 6.64%8.18% and 6.58% respectively, comparing to the ceramics without polishing; the surface stress concentration and residual tensile stress of polished ceramics are both reduced after an appropriate time of polishing process, which causes a certain improvement of ground fracture strength.

Research on Residual Stress of Engineering Ceramic Grinding Surface

As a kind of special hard and brittle engineering materials, in the grinding process, ceramic parts are prone to product cracks which affect seriously on the strength of the parts, and the residual stress is the main reason for cracks producting. Grinding parameters, grinding force and grinding temperature have a certain impact on the residual stress, and the residual stress effects on the fracture strength and fatigue strength of parts. ceramic grinding surface residual stress are caused by the combined effect, like plastic deformation, phase change, the microscopic plastic deformation of the material and the cold burnishing. The residual stress test several methods have X-ray diffraction method, perturbation degree method, indentation fracture. thermal elastic-plastic finite element method can be used to calculate grinding surface residual stress on ceramic and other hard and brittle materials.

Effect of step biasing on diamond-like carbon films deposited by pulsed unbalanced magnetron sputtering

Diamond-like carbon (DLC) films were deposited on Si substrates by pulsed unbalanced magnetron sputtering with different bias configurations: constant bias and step biasing. The structure, surface morphology, and mechanical properties of the DLC films were investigated by Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy (AFM) and nanoindentation etc. It has been found that the sp3 content in the DLC films deposited with step biasing is less than that deposited under constant bias. AFM measurements show that the root-mean-square (RMS) surface roughness of the films deposited with step biasing is less than that deposited under constant bias; and the smaller step increase of bias, the lower the RMS roughness. Nanoindentation and residual stress tests indicate that step biasing with 20 min of time intervals and with 20 V of bias reduces the stress of DLC films from 5.8 to 3.5 GPa with little sacrifice of hardness from 13.3 to 12.5 GPa. The results above are useful for the practical application of DLC films.

The Effect of Aging on the Relaxation of Residual Stress in Cast Aluminum

Most cast aluminum-engineered components are water quenched after the solution-treatment cycle of the casting process. This rapid water quenching has the potential to induce high residual stresses in regions of the castings. Reducing the amount of residual stress can have a promising effect on the life of the component. This study was conducted to quantify how aging affects the amount of residual stress in an aluminum casting. An engineered high residual stress test sample and quenching technique has been developed, and a relaxation study has been completed. The study focused on four different temperatures: 463 K, 493 K, 513 K, and 533 K (190 °C, 220 °C, 240 °C, and 260 °C) and a range of aging times (0.3 to 336 hours). The aging data were used to verify a stress relaxation model. The results indicated that as the aging temperature increased, the amount of relaxation of the residual stress increased.

Experiment investigation on microstructure and mechanical properties of TC17 titanium alloy treated by laser shock peening with different laser fluence

In this paper, microstructure, microhardness, and residual stress of TC17 titanium alloy treated by laser shock peening (LSP) with different laser fluence were examined and compared by x-ray diffraction, scanning electron microscope, transmission electron microscope, microhardness test, and residual stress test. The results of microstructure point out that microstrains and grain-refinement are generated in the material surface layer which is a severe plastic deformation layer. In relation to the microhardness and residual stress, the results indicate that LSP can obviously improve the hardness and introduce a great compressive residual stress which also has a good thermal stability.

Cracking analysis of bolster cover plate in C70 freight wagons

After two year service, cracks are frequently found at the under surface of the bolster cover plate which seriously affect the reliability of the freight wagon. The stress state of bolster cover plate should be analyzed on the basis of preliminary analysis, residual stress test, static stress test and dynamic stress test. The scope of this paper is to study the causes and characteristics of the cracks, which performed by fracture mechanics analysis and FEM analysis as well as stress tests. The research results have then been used for predicting the crack initiation life and propagation life.

The Study on Residual Stress Testing of Humidity Effect and Distribution Law for PMMA

Polymethyl methacrylate (PMMA) has shown some excellent performances. However the humidity environment affects mechanical properties of PMMA seriously. In this work, the digital phase-shifting photoelasticity is used to test the humidity stress of the boundary according to which we concluded that the boundary stress decreases gradually from the boundary to the inner. The mathematical model of the boundary stress distribution is established based on the distribution law of the boundary stress. This mathematical model can be used to predict the effect of the humidity environment to the boundary stress, and guide PMMA to use safely.