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The investigation of residual welding stresses is extremely essential for the choice of efficient structural forms of designed welded structures and for the correct choice of technological welding methods for manufacturing welded structures. In spite of the substantial data amount obtained as a result of the investigations carried out earlier the distributions of residual stresses and their impact upon working capacity of welded joints carried out during welding under conditions of low climatic temperatures is studied insufficiently. Actually there are no works on experimental investigations of residual stresses of welding under cold climatic conditions. The purpose of the work consists in the investigation of the character of residual stress distribution in end welded joints of structural steel St3sp after welding under low climatic temperature conditions by power sources with pulse and constant parameter measurements. To investigate residual stresses there was carried out plate welding at room and negative air temperatures. There were chosen and carried out two welding modes: pulse-arc welding with modulated current with the frequency of 1.67Hz and direct current welding. The definition of residual stresses was carried out with the use of X-ray method based on the measurement of material lattice micro-deformations caused by their effect. On the basis of the investigation results it was revealed that a welding temperature affects a value and a character of weld stresses. At air temperature decrease up to -45ºC irrespective of the welding mode chosen the increase of a tensile residual welding stress level in welded joints by 40…50% is observed. In comparison with dc welding during welding with modulated current there are formed residual stresses with a lower level of mean values both at room (+20ºC) temperature, and at negative one (-45ºC). The increase of a tensile residual stress level during welding under cold air conditions is connected with the necessity to increase the rate of energy input at welding, and also with the increase of steel strength properties at temperature decrease.

In modern space devices, a significant number of parts and assemblies of various shapes are in contact interaction. Moreover, the materials from which they are made often differ in thermophysical and mechanical properties. When designing such connections, it becomes necessary to be able to reliably carry out thermal and strength calculations, both for the entire structure as a whole, and for individual contact nodes, with the possibility of adjusting their characteristics. As a tool for regulating the conductivity of contacts, the use of coatings of contacting surfaces can be used. Modeling a metal-coating-metal contact pair allows you to optimally select the coating material and its required thickness.

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The presented work describes a modified technique for numerical modeling the characteristics of contact pairs in technical systems, based on the use of microgeometry parameters of contacting surfaces. The microgeometry parameters of the contacting surfaces are determined according to the measurements of their roughness profile. The described technique allows one to reduce significantly the sample size of the values of local extrema of microprotrusions and microdepressions that have a real impact on the value of contact thermal resistance. The described technique can significantly reduce time and hardware costs and simplify the calculation procedure itself. In addition, the proposed methodology by introducing a specified sampling interval allows you to set the required level of accuracy at the initial stage.