Papers by Keyword: Thermomechanical Properties

Abstract: In this paper, the possibility of characterizing the thermomechanical behavior of metals using the virtual fields method (VFM) and suitable specimens with heterogeneous strain and temperature fields was demonstrated using simulated experiments. The used geometry is a double-notched tensile test with a Gaussian distribution of temperature over the surface. The chosen constitutive model is the Johnson-Cook hardening law coupled with the Hill48 anisotropic yield criterion. First the VFM strategy and the simulated experiments are described. Then the results are presented showing three case studies, (i) only the effect of the temperature is identified, (ii) the whole set of constitutive parameters is identified at the same time, (iii) a two-step identification is performed. The potentiality of the method as well as the main problems are discussed extensively.

Abstract: A study of the influence of refractories’ structure on the thermomechanical properties of the lining of the equipment of tunnel kilns has been carried out. The lining of kiln trolleys is subjected to a mechanical stress distributed evenly over the entire area and the most dangerous to brittle materials, as well as to tensile thermal stresses. The magnitude of the tensile thermal stress depends on the material and the structure of the lining. The mechanisms of destruction of products made of fireclay and liquid concrete have been studied. Mineralogical and petrographic analysis of fireclay refractories have been used, as trolley lining has established metasomatic interaction of the lining with the vapor-gas component of the kiln, as well as with the metal of the trolleys. Monolithic products, made of low-cement concrete with corundum filler, are characterized by high strength and resistance to abrasion. The total value of compression and thermal expansion stresses for them is 3.08 MPa, which is half the value of those of fireclay. When conducting the research to optimize the composition of trolley lining, a technology for manufacturing two-layer concrete blocks, combining the advantages of compositions, based on corundum and fireclay, has been developed. The chemical and granulometric composition of fireclay-based concrete in the lower thermal insulation layer and electrocorundum-based concrete in the upper reinforcing layer were selected in such a way, as to ensure similar values of linear thermal expansion coefficients and prevent possible destruction along the boundary between the layers during the operation.

Abstract: Polyarylate (PA, polyoxybenzoyl) is a heat-resistant linear aromatic polyester with a high degree of crystallinity, high physicomechanical and tribotechnical properties that is limited in the possibilities of processing into products. The polymer has low deformability and fluidity in the range of softening temperatures, as well as narrow temperature processing intervals, limited by the destruction temperatures. A promising way to obtain compacts from PA is explosive processing, which ensures the simultaneous realization of high pressure (up to 10 GPa) and temperature (up to 1000 °C). Comparative results of morphology, crystalline and chemical structure and thermomechanical properties of polyarylate after static pressing (SP) and explosive processing (EP) are presented. It was found that EP at the pressure of 2.8 GP, which excludes the destruction and decomposition of polymer compacts, does not cause significant changes to its phase composition, crystalline and chemical structure. The monolithic compacts obtained by EP have higher thermostability and heat deflection temperature than statically compressed ones.

Abstract: The effect of Hydrogen on thermo-mechanical properties and performance of metals and alloys are of critical importance. In recent years, the relevance of H-metal interactions has been broadened into functional metallic compounds and alloys as they find use in energy and medical applications. Here, we aim to assess the influence of H-content on thermal, physical, chemical, and mechanical properties on Nickel-Aluminum alloys using Molecular Dynamics (MD) and Density Functional Theory (DFT) methods. We report studies on Ni₃Al, Al₃Ni, AlNi with H-content ranging from 1% to 10% at elevated temperatures for different structures such as B1, B2, L10, A4 and random and ordered in L12 to establish enthalpy-temperature-concentration, volume-temperature concentration, volume-pressure-concentration relationships. From these relationships we derive thermodynamic and mechanical properties such as thermal expansion, bulk modulus and Young modulus.

Abstract: In the present study, epoxy based composite filled with meso and non-porous silica microspheres with similar size were prepared respectively and their rheological and thermo-mechanical properties were studied systematically. The results showed that the mesoporous silica/epoxy composites showed much higher viscosity, storage modulus and glass transition temperature (Tg) while lower coefficient of thermal expansion (CTE) than did epoxy composites with nonporous silica particles, which could be attributed to the stronger interface interaction between the mesoporous silica filler with larger specific surface area (BET) and the epoxy matrix.

Abstract: Processing of copper substrates by Ti ions was carried out using «KVANT-03MI» equipment by means of a vacuum-arc ionic source with the titanium cathode. By X-ray and SEM methods it was established that after ionization in the surface layer of substrate the intermetallides of Cu-Ti system form. There is the CuTi₃ preferred phase in surface layer of substrate depending on time of processing by Ti ions. The mechanism of formation of observable net structure of surface layer by sputtering of copper atoms by Ti ions the subsequent deposition and their crystallization in the form of microislets of CuTi₃ intermetallide on surface of a copper substrate have been suggested.

Abstract: In this paper, addition of Fe-Ni, MnZn-ferrite, and CNF (carbon nanofiber) absorbers in the Kevlar fiber fabric-reinforced epoxy resin composites resulted in excellent absorbing properties as well as other required properties such as light-weight (as low as 2.2 g/cm³), small thickness (~2 mm), high mechanical strength (up to 380 MPa) and thermal stability (up to 120 °C). Reflection loss testing of the laminates FM-3 showed that the peak reflection loss was-45 dB at the frequency of 10.4 GHz, and the absorbing waveband at-10dB was 12 GHz (from 6 to 18GHz). The study also indicated that the content of the added absorbers was limited by the viscosity (or flowability) of the resin-absorber mixed suspensions.

Abstract: The industrial application (under a confidential clause) concerns a ceramic/steel assembly. This PhD research is concerned with providing a reliable industrial bonding between ceramic and steel using structural adhesive. This industrial joint shall withstand a wide range of temperatures with brutal thermal changes. This paper focuses on the adhesive formulation. Indeed, we needed to compromise the adhesive flexibility: soft enough to resist the thermal stresses and compensate the coefficient of thermal expansion mismatch between the two substrates. We find this good compromise with DGEBA and Novolac epoxy based adhesive separated or blended. The influence of the different formulation parameters on the initial properties was studied by chemical, rheological and thermal tests on adhesive samples. Depending on those formulations, we observed different behaviours in term of glass transition temperature, cross-linking time and flexibility.

Abstract: The problems of thermomechanical phenomena, which occur in low stability – porous ceramic material (LS-PCM) submitted to thermal shock, are discussed. The authors tried to answer the question concerning the usefulness of Hot Distortion tests (HD) for estimation of parameters necessary in data base of simulation codes, which permit to simulate the phenomena in casting-mould system. These parameters should be accessible as temperature function, especially in high temperature range of LS-PCM used as mold heating using poured casting. The new methodology and equipment, based on British Cast Iron Association (BCIRA) method, allowed to study LS-PCM specimen feature called Hot Distortion method. In this paper the modified HD methodology, are shown. The modified apparatus DMA includes two thermal sources (electric and gaseous) used to 114 x 25 x 6 mm and 120 x 22 x 22 mm sample heating were tested and analyzed. The measurement and recording of chosen parameters, i.e. deformation (distortion) during heating and variability of surface temperature fields in heated sample, by use of pyrometer and thermal camera are presented. The virtual volume temperature field in heating sample was simulated. The comparative analysis of both, experimental and virtual results are realized. This permitted also to estimate the substitute thermo-physical coefficients using inverse solution by try & error method for predefined boundary conditions on bottom and upper specimen surfaces.

Abstract: The deformation and recrystallization behaviour of a range of Nb microalloyed steels has been studied using hot torsion. This work focuses on the change from strain dependent to strain independent recrystallization behaviour as a function of the alloy content, initial microstructure and deformation conditions. It is found that there is a complex interaction between deformation, recrystallization and strain induced precipitation, which has significant implications for controlled rolling in hot strip and plate mills. The data also revealed that the pre-existing precipitates did not influence the behaviour of post deformation softening.