Papers by Keyword: Material Degradation

Abstract: Chimneys are high-rise buildings indispensable for the operation of important plants in industry and in energy. The paper deals with the description and evaluation of defects found on reinforced concrete structures in the chimney interspace. The object of the inspection was a chimney with a reinforced concrete monolithic stem and an offset protective casing. The space between the housing and the stem is ventilated. During the operation of the chimney, aggressive condensate penetrates into the interspace, as a result of which unprotected reinforced concrete structures can degrade.

Abstract: In this paper, a numerical/experimental study is introduced on a carbon fibre reinforced polymer composite panel experiencing the tail-pipe fire phenomenon. This phenomenon, being of main concern for an Airplane during the engine-starting phase, can be qualitatively described as the ignition of a flame outside the nozzle impacting the adjacent aircraft structural components, such as the wing or the tail. The tail-pipe fire phenomenon is characterized by a variable duration and may cause the overheating or even the damage of the aircraft components. A numerical model, able to simulate the thermomechanical behaviour of composite structures under fire, is proposed. The presented approach, considering a strong coupling between the thermal and the structural fields and taking into account thermal and mechanical properties degradation, has been implemented in the commercial FEM software ABAQUS and applied to a stiffened composite panel. The numerical model has been validated by comparing the ABAQUS numerical results to the experimental data obtained by an ad-hoc campaign including mechanical tests under variable thermal conditions. The comparisons, performed in terms of Temperature-Time and Load-Strain evolution histories, showed a good agreement between numerical and experimental data, confirming the robustness of the proposed numerical tool and its effectiveness in predicting damage onset and propagation due to the presence of high thermal gradients.

Abstract: Interaction of high energy electrons with spacecraft materials, such as polyimide (PI, Kapton-H®), is known to cause their physical degradation. However, understanding of the chemical nature of this damage and the effect on the electrical and optical properties of PI is still limited. This lack of understanding limits predictive spacecraft models (charging, thermal, etc) as only pristine material properties are used for calculation. This is a major source of error in spacecraft construction and anomaly resolution, since PI properties change after exposure to the space environment. In the presented study, we analyze the chemical, electrical, and optical changes to polyimide after exposure to 90 keV electrons.

Abstract: In chemical processing plants and petroleum refineries, the pressure vessels and pipelines suffered often from fire accidents and thus resulted in the metal materials were in overheating state. Elevated temperature could cause the changes in metallographic structure and have unfavorable effects on material mechanical properties. In order to understand better the influence laws of overheating on metallographic structures and material mechanical properties, the methods of theoretical analysis and experimental research were used and the effects of thermal exposure temperature, duration time and cooling rate on microstructure of low-alloy steel 12MnNiVR, were studied systematically. The study can provide basis data for the material properties database of metal material suffered from fire accident, and afford technical supports in the key technologies on fire damage FFS (Fitness-For-Service) integrity assessment.

Abstract: In chemical processing plants and petroleum refineries, the pressure vessels and pipelines suffered often from fire accidents and thus resulted in the metal materials were in overheating state. Elevated temperature could cause the changes in metallographic structure and have unfavorable effects on material mechanical properties. In order to understand better the influence laws of overheating on metallographic structures and material mechanical properties, the methods of theoretical analysis and experimental research were used and the effects of thermal exposure temperature, duration time and cooling rate on microstructure and mechanical properties of low-alloy steel 12MnNiVR, were studied systematically. In the paper, mechanical testing (hardness test) are carried out to understand changes in the mechanical properties that would be observed in the metal exposed to elevated temperatures during a fire accident. The study can provide basis data for the material properties database of metal material suffered from fire accident, and afford technical supports in the key technologies on fire damage FFS (Fitness-For-Service) integrity assessment.

Abstract: The purpose of this paper is to present the results of observation of material degradation process in steel samples under combined conditions of static and cyclic dynamic loading, using selected electromagnetic NDT methods. To evaluate damages a Barkhausen noise observation, an AC magnetization, a magnetic flux leakage and eddy current method were used.

Abstract: In order to evaluate the degradation of the epoxy coating in nuclear power plants, acoustic wave velocities of epoxy films are measured using defocused scanning acoustic microscopy system(SAM). Unlike metals, the surface of the epoxy coating on the concrete liner is so thin and wavy that the conventional ultrasonic techniques for acoustic velocity of epoxy coating are hard to apply. Acoustic velocities of bulk waves are determined from V(z,t) curves of mode-converted waves generated in the film by SAM. Epoxy films are fabricated and degraded under various accelerated aging conditions, and both of longitudinal and shear wave velocities of the epoxy film are measured. Approximately 10% of reduction in acoustic wave velocity is observed from experimental results when the aging is developed fully in epoxy films. It is also found that longitudinal wave is more sensitive to deterioration of epoxy coating than transverse wave.

Abstract: In spite of frequent defect in industrial boilers, life assessment or diagnostic method for them has not been studied. In this research, SB410 carbon steel used in industrial boilers is simulated with artificial aging heat treatment. To do qualitative life assessment, differences in micro-structures and hardness of SB410 by the degradation time are studied. In addition, variation in material properties by aging was observed with the tensile test at room temperature and 179 °C and changes in ductile to brittle transition temperature was observed with the charpy impact test performed at several test temperature.

Abstract: The nondestructive evaluation technique for the material degradation is necessary because of the limitation of conventional destructive methods. In this study, an ultrasonic velocity measurement method was attempted for the estimation of the creep damage of degraded modified 9Cr-1Mo steel. The specimens with seven different kinds of aging periods were prepared by an isothermal heat treatment at 690
. The ultrasonic velocity was measured by an immersion method. The correlation between the measured ultrasonic velocity and tensile properties were studied. The ultrasonic velocity has an declining tendency with the increase of heat treatment time. A correlation between the ultrasonic velocity and aging parameter were established, which allows one to estimate the material degradation of modified 9Cr-1Mo steel.

Abstract: Evolution of microstructure due to service exposure to high temperature has a strong effect performance of heat resistant steels. In case of modified 9Cr-1Mo steels, precipitation of Fe2Mo-type laves phases and coarsening of M23C6-type carbides are the primary cause of degradation of mechanical properties such as creep resistance, tensile strength and toughness. Therefore creep tests have been carried out on modified 9Cr-1Mo steels to examine the effect of aging and stress on the creep strength. Additionally vibrating sample magnetometer is used to measure hysteresis loop.