The article discusses the strength of concrete and other brittle materials in the case of non-uniform biaxial type of compression (σ1 > σ2 > 0) and triaxial compression of σ1 > σ2 = σ3 > 0 type (it was assumed that σ> 0 corresponds to compression). It is noted that, when considering the biaxial loading in the accepted model, probabilistic nature of distribution of stresses along the contour of pores and inclusions, i.e. stress causing formation and propagation of cracks in the material, plays an important role. Moreover, the stress across the circuit pores was regarded as a three-dimensional random field of S(α,β,γ,ω),where ω - is a random argument. Considering the average number of overshoots NR we believed that the random field of S is not homogeneous (not stationary): its expectation is not constant, but is a function of nonrandom arguments Мs = Мs(α;β;γ). External load, corresponding to NR = const (and at the same time constant of level exceedance probability), first increases and then decreases a little. Heating up to 300оС (573K) and 400оС (673K) leads to violations, and long-term load leads to significant changes in the macro- and microstructure of concrete.
The article is devoted to some aspects of research of hostile environment influence on the concrete durability. The mechanism of formation of chaotically diversified difficult structure is described. Chemical interactions of cement with active components of diffusion in steam space are examined. Measures for receiving conditions under which the volume of products of reaction will be equal to the volume of the reacted alkaline components of a cement stone are offered. High-quality and quantitative changes in a pore space, which are irrespective of density and the relative molecular mass of reaction products are described. Besides, movement and distribution of gaseous products of reaction in volumes of a cement stone are simulated. Reasonable integrated dependences of influence of aggressive environment on various types of concrete surfaces are given. The methods of corrosion control offered in article allow substantially to lower or absolutely to exclude adverse effect of hostile environment on concrete and reinforced concrete structures already at a stage of selection of composition of concrete mix. In this case service life of concrete and reinforced concrete structures will increase.
The article is concerned with the research of the processes of formation of the structure and properties of systemically alloyed low carbon steel 10H3G3MF in initially hardened and initially cold-deformed condition at high speed thermal-cycle processing (TCP). Metallographic, dilatometric and fractographic analysis, transmission electronic microscopy and uniaxial tensile test and impact test (salt spray chamber) are used as the research methods. It is shown that the maximum fine crushing of grain structure of austenite to 1 micron with high speed TCP of the researched steel in initially cold-deformed condition occurs at the first cycle of heating to 900 ° C, at the same time nanostructural condition of martensite is realized with an average size of stick in the plane of the foil of 60 ± 10 nm, which results in a substantial increase of complex of mechanical properties. It was found that in all studied modes of high speed TCP the ? ? ?-conversion with heating in the inter-critical temperature range consists of three stages.
This work is devoted to the experimental study of a glass/polyester composite laminate under impact shock. Based on a thermodynamic approach, the objective is the evaluation of specific interlaminar delamination energy in a multi-layer composite material under impact loading causing damage to it by cracking. For modeling impact loading, it is used an experimental device based on the principle of Charpy test which is to measure residual energy of a mass movement following a shock at speeds generally between 1 and 4 m/s, on a test piece cut of standardized dimensions requested in bending. Some of available energy is consumed by the rupture of the test piece. The results of this work showed that for impact test, mode I fracture energy is function of impact speed and the load fall energy. These results could be useful in the design of multilayer structures in composite materials subjected to impact loads.