Strength improvement of welded joints of aluminum alloys by laser processing
Investigation is made into the influence of preliminary treatment of aluminium alloys surface for diffusion welding with the aid of laser impulses. It is proved that preliminary laser treatment of the aluminium alloys surface of 1201 and 1151 types for diffusion welding increases welds strength by 30% as compared to the widely used treatment inflow discharge plasma. Besides, laser treatment substantially reduces working hours of the process. Metallographic analysis of the structure of specimens treated in the regime of ″ laser irradiation with subsequent diffusion welding ″ has proved that the weld lacks the narrow sharp boundary zone which is a usual place of initiation and propagation of cracks.
A proсеss for fabriсating 5.mm-thiсk shеets from alloy l565сh with rеcrystallized grains lеss than l0 µm in sizе is dеvеlopеd, whiсh involvеs supеrplastiс forming and providеs еlеvatеd mесhaniсal propеrtiеs at room tеmpеratuге.Тhе paramеtеrs of supеrplastiсitу and thе mесhaniсal propеrtiеs of alloy l565сh arе dеtегminеd. Tеst forming оf a domе-shapе modеl part is pеrformеd.
The process of ablation of a gold target by femto- and picosecond laser radiation pulses has been studied by numerical simulations using an atomistic model with allowance for the electron subsystem and the dependence of the ion–ion interaction potential on the electron temperature. Using this potential, it is possible to take into account the change in the physical properties of the ion subsystem as a result of heating of the electron subsystem. The results of simulations reveal a significant difference between the characteristics of metal ablation by laser pulses of various durations. For ablation with subpicosecond pulses, two mechanisms of metal fracture related to the evolution of electronic pressure in the system are established.
The paper is oriented toward the problem of determination of rheological characteristics of a material by free bulging testing. This information about the material behavior is used for design of gas forming technologies for production of complex shell parts used in aerospace industry. Realization of such technologies requires pressure forming regimes which can be calculated using computer simulation. The material model describing its behavior during hot forming is one of the most important inputs of the simulation. Tensile testing is the most popular way of investigation of the material behavior. A significant disadvantage of this method is that the material formed in conditions of uniaxial tension which is not similar to the one realized in gas forming technologies. Free bulging technique considered in the paper allows one to study the behavior of a material during hat forming in condition of biaxial tension. Inverse analysis utilizing a special semianalytical model for the direct task is used for interpretation of the results. The model is based on the differential equation describing the evolution of dome height using special relation for the calculation of specimen thickness at the dome pole. This approach was applied for the processing of experimental results obtained by forming of industrial aluminum alloys. The obtained material constants were also used in finite element simulation of bulging process by MSC.Nastran software in order to verify the efficiency of proposed technique. The results of the simulations were found to be in good agreement with the experimental data.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.
This volume presents new results in the study and optimization of information transmission models in telecommunication networks using different approaches, mainly based on theiries of queueing systems and queueing networks .
The paper provides a number of proposed draft operational guidelines for technology measurement and includes a number of tentative technology definitions to be used for statistical purposes, principles for identification and classification of potentially growing technology areas, suggestions on the survey strategies and indicators. These are the key components of an internationally harmonized framework for collecting and interpreting technology data that would need to be further developed through a broader consultation process. A summary of definitions of technology already available in OECD manuals and the stocktaking results are provided in the Annex section.