Applied Mechanics and Materials Vols. 217-219

Abstract: Interactions of femtosecond–laser with various transparent media are great focused recently because of some interesting phenomena produced. This experiment is aimed to investigate super-comtinuum generation of femtosecond lasers (800nm, 1 kHz) with PM567-doped PMMA polymers. And we, to our knowledge, first founded: variable white light filaments in which spectrum changed from super continuum to pumped light spectrum. The circle structures of the variable spectrum are recorded and are analyzed in theory and experiment; moreover, the effect of interaction time on the filaments; last, founding PM567-doped PMMA has the properties of the Photorefractive crystal in the field of super-comtinuum generation.

Abstract: In this paper, the finite element simulation of laser drilling process has been carried out for the nickel alloy DD6. Both the transient temperature field and thermal stress field were computed via the commercial software package ANSYS. Based on the method of dimensional analysis, the dependence of various non-dimensional parameters on both fields was specified and demonstrated in graphical forms.

Abstract: A novel diode-pumped solid-state continuous-wave (CW) laser technology has been demonstrated for high-performance low-temperature polycrystalline silicon thin-film transistors (TFTs) fabrication. The CW laser-crystallized (CWC) poly-Si thin films indicated the excellent crystallinity with the flat surface morphology at grain boundary. Besides, the CW laser activation is a low-thermal budget process and can achieve the lower sheet resistance of 50 Ω/□ and uniformly redistributed dopant profiles. The n-channel CWC TFTs revealed the superior field-effect mobility reaching 505 cm²/V-s and the lower subthreshold swing as compared with the conventional excimer laser-crystallized ones.

Abstract: Based on finite element method, the FEA model used for analyzing fatigue properties of sample treated by laser shot peening (LSP) was established. In order to research the influence of material intensity on LSP effect, two kinds of wrought magnesium alloys AZ31B and ZK60 with different intensity were chosen as object, the compressive residual stress and fatigue life after LSP were analyzed. After spring back analysis the elastic strain is released in material inner, the value of compressive residual stress was reduced; after LSP with 3 times, the fatigue life gains of AZ31B and ZK60 were 105% and 163%, respectively. The results show that strengthening effect of high intensity material treated by LSP is better than that of low intensity material.

Abstract: The principle and features of laser cladding technology was described, and the fiber laser equipment was introduced. Coat an alloy wear-resistant layer on the failure surface of mine hydraulic prop, motor rotor, shovel drum and other shaft-parts by using fiber laser cladding technology, and take mine hydraulic prop as an example to introduce the steps of the fiber laser cladding. The results show that the fiber laser cladding repair technology can significantly improve the quality, hardness, wear resistance, service life of shaft-parts surface.

Abstract: This thesis introduces the concept of laser blanking and analysis the hardness differences, the ripple, the dross through experiments. Through this we get know the factors and data changes which are affecting the quality of laser blanking cutting. The results show that the cutting quality, such as the laser power, material thickness, cutting speed, focus position, air pressure and the shape parameter fluctuations, is very sensitive to the process conditions. Any factor changes will have an effect on the cutting quality.

Abstract: Micro dimples have been generally considered as a valuable texture which can improve lubrication and reduce wear of the sliding surfaces by acting as reservoirs of lubricants and grinding debris. Laser shock processing (LSP) is an innovative surface treatment technology which can modify metals and shape metallic parts accurately. In this study, a new process for micro dimple fabrication which could be called laser peen texturing (LPT) was proposed based on LSP. LPT experiments were performed on Oxygen-Free High Conductivity (OFHC) copper. Influences of experimental parameters on geometrical characteristics of micro dimples were investigated. It was found that after LPT, the pile up was generated around the dimple .The diameter, depth and aspect ratio of the micro dimples increase with the laser power density and repeated shock number, but all of them saturated gradually. From matellographic analysis, grain refinement was observed obviously beneath the dimple.

Abstract: Based on the functions of good surface bearing, lubricating and wear-resisting properties, this paper designs several microstructures including tangent ring, separated annular slot, positive direction reticular slot, etc. Microstructure is shaped by laser carving method, and contrastively analyzed compared with 3-D bearing curve and related parameters of ideal functional surface. The results demonstrate that functions of surface can be met by certain designed and processed shapes. Laser carving is a fast and convenient surface microstructure shaping method, in which as texture surface of separated annular slot, the shape of 3-D bearing curve stands to reason, and relevant parameter values and surface performances are good and obvious respectively.

Abstract: The time-resolved optical emission spectroscopy of Ti-Al alloy plasma produced by the Nd:YAG high-power laser pulses with wavelength of 1064nm was investigated both in air and vacuum conditions. The comparative studies gave detailed insights that the plasmas produced in air were much hotter and denser. The quantitative descriptions indeed suggested that a cascade avalanche process would be happen followed by air plasma firstly, before the laser impacting the target surface. On the other hand, the laser energy may be considerably attenuated via hotter and denser plasma, the amount of laser energy on the target surface remarkably decreased in air condition. In addition, at high-power laser irradiance levels, there was an auto regulatory area near the target surface and the plasma parameters tend to be saturated

Abstract: As the technology which is commonly used on the cutting large irregular curved sheets has many disadvantages, such as incorrect cutting path, poor cutting accuracy. By analyzing the sheet cutting process, a three-dimensional and five-axis laser scribing robot is developed, which is based on surface matching. This robot can acquire the data of the workpiece surface automatically through the non-contact measurement. The date model can be generated by computer. The matching method is based on curvature and arc length of feature points. By matching data model and ideal model, robot can choose the optimal trajectory for laser cutting. From experimental results, the robot is designed rationally. It can make the scribing path closest to the ideal track and has extensive utility value.