Papers by Keyword: Thermal Ageing

Abstract: During a long-term operation of nuclear power plants (NPP), the changes of structural material properties occur. To ensure the safe and reliable operation, it is necessary to monitor and evaluate these changes mainly on components from primary circuit of NPPs. One of the dominant ageing mechanisms of NPP components besides the radiation embrittlement and the fatigue loads is the thermal ageing. The thermal ageing is the temperature, material and time dependent degradation mechanisms due to long-term exposure at the operating temperature of 570 K.This paper describes the project for thermal ageing monitoring at primary piping in NPP Bohunice Unit 3. There are summarized the results obtained from evaluation of original primary piping material.

Abstract: The effect of thermal ageing on the properties and microstructure of Al-Mg-Si alloy was investigated. In this work, an extruded Al-6063 alloy samples were used as the main materials. In order to study the effect of thermal ageing, the alloy samples were solution treated at 530 °C and then quenched into water before artificially aged at elevated temperatures between 120 and 250 °C. The ageing response and mechanical properties was monitored by Vickers hardness and tensile tests, respectively. The analysis of surface fracture and microstructure of peak aged alloy were carried out by means of scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. Result shows that the highest hardness value and tensile properties is gained by the alloy that aged at 120 °C. It is found that increasing in hardness and strength values of the alloy are due to precipitates formation during thermal ageing. Fracture analysis on peak-aged condition indicates that the alloy having more ductility after thermal ageing. The result shows that the higher ageing temperature will lead to the higher ductility of the Al-6063 alloy, as a results the alloy’s strength is reduced.

Abstract: The exposure of wool fabrics to light, humidity and heat are inevitable, which will accelerate their ageing, as time goes on. The exact influences of these factors were not being parallel compared and studied previously, but are very important for preparing suitable storage or display environment for wool fabrics, especially for those excavated old wools in history. Hereby, wool fabrics were treated by heat ageing, hydrothermal ageing, UV ageing and UV & ozone ageing to figure out the effects of light, humidity and heat on their physical and chemical changes resulted in the degradation of wool. The performances of the wool fabrics with different treatments were investigated by thermogravimetric analysis (TGA), angle contact test, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray diffraction (XRD), etc. It has been found that thermal ageing resulted in the maximum yellowness of the wool fabrics. Hydrothermal ageing was most functional in decreasing the breaking strength and crystallinity of the wool fabrics. UV lighting induced significant hydrophilicity increase on the surfaces of the wools. The addition of ozone on UV lighting did not facilitate the further ageing of wool fabrics much.

Abstract: A number of studies have been carried out previously to investigate the suitability of palm oil as dielectric insulation fluid in transformers. Among the important studies is the ageing performance of palm oil. In this paper, a study was carried out to investigate the dielectric properties of Refined Bleached and Deodorized (RBDPO) Olein after subjected to thermal ageing. A low temperature ageing was carried out at 85°C for 5 days. The AC breakdown voltage, dielectric dissipation factor, relative permittivity and resistivity of RBDPO were examined throughout the ageing duration. It was found that the RBDPO performs reasonably well under low temperature ageing.

Abstract: Mechanical testing is foremost a means to measure material performance, however it provides a probe into the complex elastic, viscoelastic and viscoplastic behavior of polymer morphologies. The techniques in this work utilize variables of time/frequency, temperature, stress and strain with emphasis on dynamic and modulated implementation. Several instruments were used since a particular instrument does not provide all of the capabilities. The material response is complex and it has been resolved into typically instantaneous and time-dependent components. Some of the techniques are widely used and these have been extended, while other techniques introduce control over alternate variables. Polycarbonate was chosen as the main example with support from similar polymers, though the techniques are applied to many polymer types.

Abstract: The weight loss rate, FTIR characteristic, static mechanical properties and dynamic mechanical properties of neat epoxy resin and glass fiber/ epoxy resin laminates (GF/EP) after thermal-cold cycling were studied in this paper. The rule of static tensile and flexural strength of neat epoxy resin and GF/EP after ageing was investigated through the static mechanical properties analysis. The ageing mechanism of GF/EP was studied by analyzing the storage modulus (E′), loss modulus (E"), loss factor of GF/EP and FITR of epoxy resin. The results show that the weight loss rate increases with the ageing time，which is up to 9% after 400 times ageing cycle. The strength and flexural strength of GF/EP decreased by 6% and 21% after ageing, while the tensile strength of neat epoxy resin increases by 8% and its flexural strength increases slightly after ageing. The mechanism analysis reveals that internal defects of GF/EP would be induced by thermal-cold cycling stress, which results in the interface bonding strength dropping and the performance reducing.

Abstract: Reversible and irreversible events can be resolved) using modulated temperature DSC and TMA. Each technique has advantages, those for TMA include longer times and slower scan rates that allow greater approach to material equilibrium. The thermal expansion coefficient and glass transition temperature can be isolated from relaxations and structural changes. Modulated temperature thermomechanometry (mT-TM) is used to characterize amorphous thermoplastics including PS, PMMA, PC and PPO, and the results including annealing, heating and cooling.

Abstract: Degradation of reactor pressure vessel (RPV) steels due to neutron irradiation embrittlement is directly related to safety and life of the nuclear power plant (NPP). In order to ensure structural integrity and safe operation of NPP, surveillance programs are conducted to monitor and predict the changes in RPV materials. Availability of irradiated specimen from RPV or irradiation of specimens under simulated conditions of RPV for conducting fracture toughness tests remains a major problem in surveillance programs. In order to resolve this problem, various methods are adopted to experimentally simulate the effect of neutron irradiation on mechanical behavior of RPV steels using electron irradiation, thermal aging, strain hardening, combined quenching and hardening and pre-straining combined with heat treatment. This paper presents a review of the existing research on experimental simulation of neutron irradiation damage through various methodologies and discusses the future scope of their application in plant safety and life assessment of RPV’s.

Abstract: This work presents the results of an experimental investigation on the effects of thermal ageing over the residual fatigue strength of AA2618-T6511 aluminium alloy. Among others, this kind of light alloy finds practical applications in highly stressed engine components, such as pistons, that are typically subjected to both thermal and fatigue loads. Thermal cycles are responsible for ageing phenomena, that involve the precipitation of silicates, with a corresponding progressive damage of the microstructure and weakening of the mechanical characteristics of the material. Artificial ageing has been reproduced in laboratory by means of thermal cycles controlled in time and temperature. These variables have been correlated to the hardness values measured on the surface of specimens. Bending fatigue tests have been performed on a rotating machine in a temperature controlled environment. The experimental S-N diagram is finally presented, as a function of the tested temperature, in order to provide a design tool for the fatigue life estimation of AA2618 components.