Papers by Keyword: e-Modulus

Abstract: Concretes with frame structure produced by using the technology of separate concreting by immersing a coarse aggregate in a low-viscosity mortar matrix due to an increased concentration of coarse aggregate have an increased E-modulus, reduced creep coefficient and cement volume in concrete compared to traditional vibrational compaction concretes. Production concrete using separate concreting technology by immersing a coarse aggregate in a mortar matrix with low-viscosity allows to obtain a frame structure of concrete with a concentration of coarse aggregate up to 0.7 when a voidness of coarse aggregate is equal 0.28. The real concentration of coarse aggregate in a concrete structure depends on the particle size of the coarse aggregate, the cross-section dimensions of the structure, and the reinforcement coefficient. The influence of geometric dimensions and the coefficient of reinforcement on the concentration of coarse aggregate in the concrete with frame structure is studied. The concentration of coarse aggregate decreases with the growth of the S/V modulus (S – area, m², V – volume, m³) and the reinforcement coefficient, but the decrease in the E-modulus does not exceed 5%. Conclusion: regardless of the type of construction and reinforcement, the concrete of the frame structure must have a sufficiently high uniformity of deformation properties.

Abstract: The stress-strain diagrams of concrete with frame structure made with content of coarse aggregate from 0.56 till 0.64 m³/m³, with crushed granite (E-modulus = 71 GPa) and crushed silica sandstone (E-modulus = 42 GPa) are shown. It is shown that the stress-strain diagram of the concrete with frame structure made with coarse aggregate with E-modulus 42 GPa is almost linear over the entire loading range. Stress-strain diagram of concrete made with coarse aggregate with E-modulus 71 GPa has three zones. It is concluded that the concentration of intrastructural stresses under loading in the concrete with frame structure with a decrease in the ratio of E-modulus of the coarse aggregate/E-modulus of the mortar matrix is decrease that is why bad decision is to use coarse aggregate with high level of E-modulus, such as crushed granite, in concrete with frame structure.

Abstract: Conditional quantitative criteria characterizing the shrinkage crack resistance of various concretes and a model describing the change in the proposed criteria depending on the magnitude of shrinkage deformation, creep coefficient, tensile strength kinetics and shrinkage strain kinetics for ordinary concrete and self-compacting concrete are proposed. The proposed criteria for the class C40/50 concrete have been calculated and it was shown that self-compacting concrete can potentially have higher crack resistance during shrinkage. To ensure high cracking resistance during shrinkage when choosing superplasticizers and mineral additives, attention should be paid to their effect on shrinkage, creep and E-modulus of the cement stone. It should exclude additives that increase the shrinkage and E-modulus and reduce creep of cement stone.

Abstract: The applicability of a proposed model similar to a well-known Hirsch's model for predicting the E-modulus of concrete and the creep coefficient of concrete depending on the composition of the concrete, the properties of the components of concrete mix and the possible effect of the superplasticizer on the deformation properties of cement stone both under short-term and long-term loading is proved. Value ​​of the E-modulus of self-compacting concrete can be reduced to 20% with respect to the ordinary concrete of equal compressive strength, which is confirmed by the model calculation data and some experimental data. For concretes with mineral additives, the influence of mineral additives on the E-modulus was not established. Both an increase and decrease in the E-modulus is possible. The effect depends on the type of additive. The creep coefficient of self-compacting concrete, obtained by calculation according to the model, due to the increased content of cement stone and the possible influence of superplasticizer on the creep of cement stone, can be from 1.3 to 1.8 of the coefficient of creep of ordinary concrete. This result agrees well with some experimental data. The creep coefficient of concrete with mineral additives (silica fume, white ash and metakaolin), obtained by calculation according to the model, can be from 0.5 to 0.6 of the coefficient of creep of ordinary concrete. This result agrees well with some experimental data.

Abstract: Y₂O₃ has a great application potential at reaction barrier coating of high-temperature composites due to its high thermodynamic stability and high melting point, and the phase structure stability at high temperature and structure dependent mechanical property are key parameters for this application. Y₂O₃ thin films were deposited on silicon (100) wafers by DC magnetron sputtering with various oxygen partial pressure and substrate bias, and then vacuum annealing at 1000°C was performed to investigate the phase structure stability. The microstructure, stress and hardness of as-deposited and annealed Y₂O₃ thin films were explored by X-ray diffraction, transmission electron microscope, and nanoindenter. The result showed that as-60 bias voltage was applied to substrate, cubic-c phase formed regardless of variation of oxygen partial pressure, and the cubic-c phase remains stability and crystallinity became better after annealing at 1000 °C.In addition, the hardness and modulus also just had minor changes as a function of oxygen partial pressure. As oxygen partial pressure was kept at 0.043 Pa, phase transition from cubic-c to monoclinic-b phase took place with increasing substrate bias, accompanying by the increment of hardness and modulus, and 1000 °Chigh-temperature annealing resulted in that as-deposited monoclinic-b phase transforms to cubic-c phase.

Abstract: Radiation processing of polymers is a well-established and economical commercial method of precisely modifying the properties of polymers. The industrial applications of the radiation processing of plastics and composites include polymerization, cross-linking, degradation and grafting. Radiation processing mainly involves the use of either electron beams from electron accelerators or gamma radiation from Cobalt-60 sources. The PBT Polybutylene terephthalate was used in this research and the tensile behaviour was investigated at the ambient temperature. Results demonstrate that PBT has higher values of tensile strength and E-modulus with the increased irradiation dose and it has decreased elongation at break. This behaviour leads to the expansion of these materials in the automotive and electrical industry.

Abstract: The Impulse Excitation Technique (IET) is a non-destructive technique for evaluation of the elastic and damping properties of materials. This technique is based on the mechanical excitation of a solid body by means of a light impact. For isotropic, homogeneous materials of simple geometry (prismatic or cylindrical bars), the resonant frequency of the free vibration provides information about the elastic properties of the materials. Moreover, the amplitude decay of the free vibration is related to the damping or internal friction of the material. At present, IET is a well-established non-destructive technique for the calculation of elastic moduli and internal friction in monolithic, isotropic materials. Standard procedures are described in ASTM E 1876-99 and DIN ENV 843-2. IET can also be performed at high temperature (HT-IET) using a dedicated experimental setup in a furnace and constitutes a valuable tool in the field of mechanical spectroscopy. In the present work, the most recent advances in high temperature characterization using IET at K.U. Leuven are presented: the deformation behaviour of WC-Co hard metals, softening phenomena in TiB2, relaxation mechanisms in ZrO2 composites and “in-situ” monitoring of the damage evolution in uniaxially pressed metallic green compacts during delubrication.