Two-photon absorption (TPA) is confined at the focus under tight-focusing conditions, which provides a novel concept for micro-fabrication using two-photon photo-polymerization in resin. The development of three-dimensional micro-fabrication by femtosecond laser was introduced at first, then the merits of femtosecond two-photon photo-polymerization was expatiated. Femtosecond laser direct scanning three-dimensional (3D) micro-fabrication system was set up and corresponding controlling software was developed. We demonstrated a fabrication of three-dimensional microstructures using photo-polymerization of resin by two-photon absorption. The precision of micro-machining and the spatial resolution reached 1um because of TPA. The dependence of fabricated line width to the micro-fabrication speed was investigated. Benzene ring, CHINA and layer-by-layer of log structures were fabricated in this 3D- micro-fabrication system as examples.
Sheet metal forming is a widely applied industrial process that can be found in the fields of aerospace and automobile panel’s production, the conventional forming of sheet metal is realized by the Die and Mold, this method usually give rise to high cost, long production periods and little flexibility. In this paper, a flexible forming technique of sheet metal based on laser shock peening is presented and some preliminary experiments were carried out with Nd:Glass laser of a pulse of 20 nanoseconds long and 1.064μm wavelength, an energy per pulse of 10 to 30 joules. The mathematical modeling of sheet metal bulging based on laser shock peening was established, and a finite-element analysis method based on the ABAQUS software is applied to simulate the sheet bulging process. The numerical simulation indicates that the results agree well with the experiments under one laser shock peening. The investigation revealed that the combination of numerical simulation and experiments is a useful method to obtain the optimized laser parameters, and to better understand the sheet deformation characteristics under laser shock loading.
A new technique about evaluation of the adhesion strength of the film on the metallic substrate is presented in this article and the mechanism ofdynamic decohesion induced by the directed pulsed laser irradition forming is investigated elementarily from the theory. The procedure of laser-induced decohesion of TiN layers on SUS3O4 stainless steel has been investigated by means of in-situ laser interference ultrasonic measurements. The experiments were carried out by using a ?=532nm, ?=8ns (FWHM ) laser pulses irradiating the TiN film on the metallic substrate with a series of energy densities. The damage degree and dynamical procedure have been studied as a function of the energy density of laser pulses. The results demonstrate that interferometer measurements are a suitable non- invasive in-situ diagnostics tool for the assessment of the damage of the films that additionally provide valuable information conceming the process dynamics. Such results indicate that the dynamic decohesion procedure of the films is the most likely mechanism responsible for the laser-induced spallation process. At last the adhesion of the films on the metallic substrate are evaluated quantitatively.
Finite element simulation of measuring the film-matrix interface strength was the most concern of this paper. Instead of in previously reported measurements the experimentally measured free surface velocity, enegry and pessure of laser pulse in the present article allowed definition of the loading conditions in the numerical model. On the basis of theory for laser hypervelocity impact dynamics, experiment was predigested into two relative but non-coupling processes, transient thermal analysis and transient dynamics analysis. In the former, the procedure employed for the solution of thermal equation was the generalized trapezoidal rule. In the latter, the Crank-Nicholson difference time integration method was employed for the solution of wave equation. Based on the experiments, a model for laser-induced film spallation was proposed to study the propagation of stress wave and to evaluate the spall resistance of sputtered films. The analyzed result showed the dynamic adhesive strength of the TiN coating on the 304 stainless steel substrates is 183.64Mpa. It is theoretically proved that the interface stress triggering the film pry-offs was not single superimposition of pressure pulse and reflected tensile pulse, but multi-superimposition of pressure and tensile pulses.
A new technique about high-strain-rate fast and fine forming of metal sheet is presented in this article and the mechanism of laser shock forming is investigated elementarily from the theory. The studies indicate that when the high energy density laser impacts on the energy absorbing layer, which is coated on the surface of metal, the surface layer absorbs laser energy and forms high temperature and density plasma layer. During the duration of the pulsed laser radiation, the plasma layer expands acutely under the constraining layer, its density increases and the temperature elevates. In the end the plasma layer ejects and explodes and then as a result, the high-breadth shocking wave forms. The metal sheet obtains forming impulse in the ejection and explosion of plasma and subsequently, the said energy scatters in the form of plastic work. Using laser shock forming, metal sheet forming is realized without mould and the dimensions of the obtained shape are determined by the boundary condition. This technique can achieve fine forming at or beyond micrometer-level.
With the aim of quantitative measuring the dynamic adhesive strength of Al2O3film/Fe, we use a modified laser spallation setup, and let high-power laser pulse shock the energy absorbing thin coating, then cause a pressure pulse propagating to matrix. At the free surface, a laser probe is used to record the epicentral surface displacement history caused by elastic wave which propagating to the free surface. Though the analysis of elastic wave, data processing and a computer simulation, we propose a novel model of the attenuation and the dispersion of the elastic wave. After characterizing, we obtain a new spallation criteria corresponding to progressive damages at the film- matrix interface, i.e. interface delamination, film spallation and film expulsion, respectively. At the same time, according to the arrival time and attenuation pattern of the elastic wave, we also propose a new computer algorithm for estimating the source fracture dimension.
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