Ai Xin Feng

Simulation, analysis and validation of residual stresses on LY2 aluminium alloy by laser shock processing with elliptical spot

Abstract The effects of laser shock processing on the residual stresses of the LY2 aluminium alloy samples with elliptical spot (long axis length, 12 mm; short axis length, 3 mm) were experimentally investigated, and the effects of the overlapping rate on the residual stresses were simulated using the Abaqus software. The simulated residual stresses were basically in agreement with the measured data, and the relationship between the magnitude and uniformity of residual stress and the overlapping rate was also addressed. Results show that the largest stress magnitudes are located on the top surface of the sample, and the greatest uniformity is achieved by the overlapping of elliptical laser spots. The overlapping rate is critical for the uniformity of the residual stress across the surface. Within a certain impact number range of one to four times, increasing the shocked number can increase the magnitude of residual stress near the surface but not effectively increase the plastically affected depth.

Study of the Effect of Coatings on Mechanical Properties of TC4 Titanium Alloy during Laser Shock Processing

During the process of laser shock processing (LSP), we use high power Nd:Glass laser systems which result in significantly improve fatigue properties and stress corrosion cracking in titanium components. An ablative coating such as black painting and aluminum foil are used to protect the titanium component from surface melting by laser pulse, which adversely affects sample fatigue life. Three different shock-processing configurations are considered: non-ablative exposure, aluminum foil and confined ablation with black painting. We analyzed effect of the coatings on the shock wave propagation into the titanium specimen and the resulting change in mechanical properties versus depth. Near the surface, yield strength and hardness are found to be increased by laser shock, the titanium surface for all coatings increased in yield strength by 16% to 37%. The result have demonstrated that surface hardness can be improved by 31 percent over a machine worked surface with black paintings and be improved by 25 percent with aluminum foil .The experiment aim is to report the effect of the ablative, sacrificial coatings on the laser pulse generation of shock waves and their propagation into the titanium alloys and the resulting change in mechanical properties below the surface versus depth.

A Study on the New Method of Laser Scratch Testing Technique to Characterize Interfacial Adhesion Between Thin Film and Substrate

The interfacial adhesion between thin film and substrate are often the predominant factor in determining the performance and reliability of thin film-substrate system. A new method of laser scratch testing technique is presented to characterize the interfacial adhesion between film and substrate, which synthesizes the advantages of traditional scratching technique and laser measuring technique. The laser scratching mechanism is analyzed----thermal-stress spallation caused by the quasi-static heating of long pulse infrared laser and cold denudation of short pulse far-ultraviolet radiation laser, and the laser scratch equipment is introduced as well. Long pulse infrared laser scratch testing technique can be applied to detect thermal barrier film, such as hard tool film, decoration film, DLC film, function film and so on, while far-ultraviolet radiation laser scratch testing technique can be applied to detect macromolecule film and semiconductor material. Introduction The film mentioned is the general designation of surface plate film, surface coating or surface modifying layer. Thin film is one of the important means applied to improve surface performance of material, which gives the parts the property such as high wear-resistance, high corrosion-resistance, high heat-resistance, high fatigue-resistance and so on. As the result, resource and energy can be saved, the performance of substrate and film can be fully performed respectively, and the production cost can be reduced. Thin film has been used for a variety of purposes in myriad applications such as aeronautics and astronautics, mechanical engineering, electronic technology, optical engineering and computer science, etc. Regardless of its different applications, an adequate adhesion to the underlying substrate is one of the most importances. Concomitantly, the necessarity to develop advanced techniques for quantitative and correct assessment of adhesion of thin film and substrate is apparent [1]. Various kinds of advanced films appear with each passing day such as hard film, photoelectricity film, magnetic film and LB film, etc., and great achievements have been constantly made in the fields of various kinds of advanced film manufacturing technology. On the other hand, the technology of film performance measurement and control seems no much progress, especially the experimental technology of quantitative analysis of interfacial adhesion between thin film and substrate. This has affected the further development of thin film science, and the contradiction becomes bigger day by day. The quantitative measurement of interfacial adhesion between thin film and substrate has already become a headache to which scientists of various countries devote themselves [1-3]. There are nearly 355 techniques for measuring interfacial adhesion, such as scratch test, indentation, laser acoustic, laser ablation, laser spallation, etc. [2-3]. Each technology and mechanism of measurement has some limitation and some problem need to be improved, such as the instability, disagreement between different methods, etc. The difficulty is that the interfacial adhesion to be measured is the synthetic result of the elastic and plastic behaviors of film and substrate, friction and other related parameters. The relationship between critical value of film rupture and interfacial adhesion has not yet been clarified so far, and there is no one single technique which can be applied Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 615-619 doi:10.4028/www.scientific.net/KEM.259-260.615

Design of Grate Bed Heat Recovery Unit and Simulation Analysis

For the current problem that grate bed can not recover its own waste heat in the course of cycle working, combined with the structure of the chain grate and hot air flow process, a three-section heat recovery unit of grate bed and waste heat recovery hot air flow process are designed. According to the principle of repeated convective heat transfer, the amount of recovering waste heat of heat recovery unit is estimated, and simulation analysis is conducted by using fluent software. The results show: after three heat exchange between the hot exhaust gas at around 100°C and the grate bed, the hot gas at a temperature of around 427 °C can be obtained, and the waste heat recovery rate is above 60%; simulation results are compared with the estimated value so that it can be obtained that the differences between the two values in the temperature of three-section outlet gas are basically consistent, about 8°C, 4°C, 7°C respectively, which verifies the effectiveness of the heat recovery unit design and the accuracy of Fluent simulation.

Reliability Analysis on Errors of Measuring Residual Stress in 7050 Aluminum Alloy with X-Ray Diffraction

The error distribution of residual stress tested by X-ray diffraction on 7050 aluminum alloy was studied. In this paper, residual stress was measured, independently and repeatedly, many times on 7050 aluminum alloy with X-ray diffraction, then the errors about 50 stress values within the range of 30MPa were analyzed by the hypothesis testing. The results indicate that the errors of the residual stress measurement on 7050 aluminum alloy were followed the law of normal distribution about and the errors can be estimated by the least square calculator. The research lays the foundation to subsequent researches on the inherent law of the residual stress measurement with X-ray diffraction and the residual stress distribution and accuracy of stress of material surface.

Experiment study on CO2 laser cleaning rubber sulfuring mould

Parameters and mechanisms of cleaning rubber layer from a rubber sulfuring mould with CO2 laser are analyzed. Laser cleaning is a non-abrasion way, and it can improve mould service life. There are cleaning threshold and damage threshold in laser cleaning, and cleaning percentage of the surface increases with laser power density. The effects of laser parameters on cleaning and performance of the cleaned surfaces are studied. The results show that pulse laser can remove rubber layer completely under proper parameters when the value of laser cleaning threshold is 5~35J/cm2, and no damages are found on substrate surface, mould abrasion that is cleaned by laser decreased.

The Fracture Microphology of the Ceramics by Strong Laser Shock Processing

The laser shocking to the Al2O3 ceramics was proceeded, and the fracture microphology that formed from the strong laser shock processing (LSP) was analyzed by the Scanning electron microscopy (SEM). It was discovered that the feature of ceramics responds differently when the laser energy was changed. The brittle fracture that consists of intergranular fracture and cleavage fracture was the main mode under high energy laser shocking (laser pulse enegry: 42J); the macroscopical fracture characteristic was the radial crack. When the laser energy reduced to a fit level (25J), the brittle fracture of ceramics appears to the characteristic of plastic deformation, its fracture microphology appears lots of slippage lines, and the macroscopical feature of radial crack under 42J become subulate crack. While the energy reduced to 15J, the Al2O3 ceramics did not fracture, its micro-hardness ascended, a feature of micro-plastic deformation was existed under the low energy. The reason of the brittle materials appears to the feature of plastic deformation was analyzed.

Study on Deformation Behaviors of LD31 (6063) Aluminum Alloy Sheet by Oblique Angle Laser Shock

Laser shock forming of metal sheet usually effects on the surface of work-piece in normal direction by laser beam, and produces shock wave force which is vertical to the surface of work-piece. But it is difficult to shock in normal direction during processing on the surface of forming camber, so it needs to study on oblique angle laser shock processing. LD31 forging aluminum alloy sheet is shocked by Nd-glass laser in the paper, model and mode of oblique angle laser shock processing is found, and transmitting characteristics of plasma stress wave is discussed. The experiment results show that the angle between input beam and sample normal is bigger, component of forces that parallel with sample surface is bigger, the deformation eccentricity is bigger and bigger. When the angle is bigger, the area of laser beam spot becomes bigger too, energy density becomes smaller, deformation becomes shallower.

Nondestructive measurement of the residual stress TiN thin film coated on AISI 304 substrate by x-ray stress analyzer

Titanium nitride films are deposited on AISI 304 steel with a hollow-cathode-discharge (HCD) ion-plating technique. The status of residual stresses in TiN thin film coated on AISI304 substrate by HCD is studied by x-ray diffraction stress analyzer. By analyzing morphology of the residual stress of TiN thin film at interface between TiN film and AISI 304 substrate, the adhering mechanism of TiN thin film is understood as follows: the mechanical interlocking had important contribution to the adhesion strength, the thermal stress is the major factor which resulting TiN thin film peeling off spontaneously. The results show that the value of thin film is -210MPa~-650Mpa, and the thermal stress is compressive, the intrinsic stress is tensile, origins of the residual stress are primarily discussed.

Analysis the Dynamic Strain of AM60 Magnesium Alloy by Means of a Single Laser Shock Processing

In order to study the dynamic response of metal of laser shock processing, dynamic strain curves of AM60 Magnesium alloy during laser shock processing were measured by resistance strain gauges. Dynamic strain curves of three equiangular rosette near the shock spot and three strain gauges of different distances from the spot center were studied. The results indicated that the strain rate of AM60 Magnesium alloy decreased and plastic deformation increased with increasing impact times. And one dimensional strain hypothesis of laser shock processing was reasonable.