Congrès International d'Architecture Moderne

About: Congrès International d'Architecture Moderne is a based out in . It is known for research contribution in the topics: Boundary value problem & Jet (fluid). The organization has 393 authors who have published 403 publications receiving 4104 citations.

Comparative Study of the Structural-Phase State and Mechanical Properties of Ni–Cr(X) and Fe–Cr(X) Heat-Resistant Alloys Fabricated by Additive Technologies

Abstract: Comparative studies of peculiarities of the formation, thermal stability of the structure, and mechanical properties of heat-resistant alloys based on iron and nickel and fabricated using additive technologies (ATs) by laser metal deposition and selective laser melting are performed. It is established that a cellular structure is formed in alloys fabricated by the laser metal deposition and small pores up to 200 nm in size are present. The structure of alloys fabricated by selective laser melting contains elements with a globular and lamellar morphology and incompletely melted regions, as well as large pores on the order of 5 μm in size. The possibility of manifestation of the nanophase hardening effect due to the presence of nanodimensional particles of chromium silicides is shown. A comparative analysis of mechanical properties of materials under study is performed. It is shown that iron-based alloys possess higher strength and lower ductility when compared with nickel alloys. All studied samples fabricated by selective laser melting have higher strength characteristics when compared with alloys fabricated by laser metal deposition. Short-term annealing at 900–1000°C for 1 h noticeably decreases both strength and plasticity in tensile and compression tests at room and elevated temperatures. Alloys based on iron and nickel fabricated by laser metal deposition and subjected to compression tests at t = 900°C have similar strength characteristics. In contrast with iron-based alloys, additional annealing of the nickel-based AT alloy almost does not decrease its strength characteristics.

Thermal Plasticity: Unidirectional Proportional Loading

Abstract: This chapter deals with the problems of the theory of thermal plasticity in which, under proportional change of stress tensor components, the plastic deformation increases at a loading and heating, and does not vary at unloading and cooling. The temperature range in which creep can be neglected is considered. Analysis of results of material tests under uni- and multi-axis stress at various temperatures shows that, with reference to the specified brand of the problems, non-isothermal variants of the theory of plastic flow and the deformation theory correctly enough present evolution of plastic deformations. The beginning of the plastic flow or its renewal after the intermediate unloading happens when the stress intensity reaches a generalized non-isothermal surface of yielding. Unlike an isothermal loading, the conditions and rate of plastic strain evolution depend on a relationship of rates of the temperature and stress intensity; in particular, plastic strains can increase under reduce of stresses, but increase of temperature. Rational methods of step-by-step calculation of elastoplastic deformations are stated in application to the non-isothermal loading. As the initial approach, the elastic solution is used at small plastic strains, and the solution for ideally plastic body—at major strains. Instances of such solutions are demonstrated. It is shown that the growth of temperatures at combined stress leads to diminish of a short-term carrying capacity of a structure because of the change of a material strength characteristics, while a role of temperature stresses induced by a non-uniform heating distinctly weakens when plastic strains considerably exceed the thermal expansion.

Special Problems of Thermal Integrity

Abstract: The chapter contains information on the special problems of thermal integrity, which can be of interest for the readers aimed to gain deepened understanding about some peculiarities of materials’ and constructions’ behavior at elevated temperatures. For problems of non-isothermal dynamics (Sect. 12.1), it is shown that influence of the material thermal extension on detail natural oscillation frequencies with temperature increase can be different. Alteration of contact conditions between machine parts (for example, change negative clearances on tightness or on the contrary) and occurrence of the temperature stresses, especially in thin-walled structures, can change their rigidity and the frequency spectrum. A possibility of directional change of a body shape by serial variable heating of its separate body sections having various elastoplastic temperature-dependent mechanical properties is demonstrated in Sect. 12.2. This effect, used in a number of technological processes, is illustrated on simple examples. Though in the majority of practical thermal strength problems, the temperature state of a body is supposed known and not dependent on its stress–strain state, and for an explanation of some effects, it is necessary to address to the “coupled” theory of the thermoelasticity considering thermodynamic link of mechanical and thermal processes. The bases of this theory in rather simple treatment are stated in Sect. 12.3. The coupling effect is illustrated by calculations of energy dispersion during elastic vibrations and influence of convective heat exchange on material deformation at tensile trials. In Sect. 12.4, the fundamentals of the wave theory of thermal conductivity considering (unlike the classical theory) a finite speed of thermal stream and temperature propagation over a solid are briefly stated, and the influence of this factor on unsteady temperatures and stresses propagation at a heat shock on a semi-infinite body is shown.

On-farm assessment of the sustainability of small-scale dairy systems with three methods based on indicators

Abstract: Small-scale dairy systems are important contributors to national milk supplies in many areas of the world, and an option to ameliorate rural poverty in developing countries. In Mexico, they comprise over 78% of dairy farms. These systems must be sustainable in order to persist in the future. By applying several methods to assess the sustainability of farms, valuable information is collected on the practical, operational, and systemic requirements, as well as an insight into the difficulties in the use of each tool in practice. The objective was to assess the sustainability of small-scale dairy systems during the rainy season. Three methods were compared (IDEA, RISE, and SAFA) to evaluate their ability to deal with such systems in the Mexican context. Ten small-scale dairy farms were assessed from June to November 2018. Monthly semi-structured interviews were applied to collect economic, social, and environmental information. The three methods met criteria for on-farm assessments, with no large differences among them. The IDEA method was more applicable in the context of small-scale dairy systems because its indicators may be collected on-farm and were easy to measure. RISE requires more specialized technical information not always available at the small-scale farm level, and SAFA covered the largest number of indicators but is better suited for large-scale systems. The IDEA and RISE methods are adequate tools to assess the sustainability of small-scale dairy systems. The mean overall sustainability score over the three methods for the 10 assessed farms was 55.3±5.7 over 100. This medium level of sustainability indicates areas of opportunity to enhance the sustainability of small-scale dairy systems.

Interaction between periodic disturbances and a turbulent jet

Abstract: The results of a numerical and experimental investigation of the interaction between harmonic disturbances and a turbulent jet are presented. On the basis of large eddy simulation it is established that the narrow-band noise of a supersonic jet considerably increases, when the forcing amplitude amounts to thousandths and more of the total pressure of the flow within the nozzle. An analysis of the results of a laboratory experiment on the measurement of the longitudinal velocity spectra in the core of a low-velocity jet shows that the acoustic disturbances generated by a fan inside the nozzle lead to the generation of intense tonal hydrodynamic disturbances in the low-velocity jet.