Degree Of Material Degradation Research Articles

Analysis of Platen Superheater Tube Degradation in Thermal Power Plants via Destructive/Non-Destructive Characteristic Evaluation

Coal-fired power plants operating under Korea’s standard supercritical pressure operate in a high-temperature environment, with steam temperatures reaching 540 °C. A standard coal-fired power plant has a 30-year design life, and lifespan diagnosis is performed on facilities that have operated for more than 100,000 h or 20 years. Visual inspection, thickness measurements, and hardness measurements in the field are used to assess the degree of material degradation at the time of diagnosis. In this study, aging degradation was assessed using an electromagnetic acoustic transducer to measure the change in transverse ultrasonic propagation speed, and the results were compared to microstructural analysis and tensile test results. Based on the experimental results, it was found that the boiler tube exposed to a high-temperature environment during long-term boiler operation was degraded and damaged, the ultrasonic wave velocity was reduced, and the microstructural grains were coarsened. It was also confirmed through tensile testing that the tensile and yield strengths increased with degradation. Our findings prove that the degree of change in mechanical properties as a function of the material’s degradation state is proportional to the change in ultrasonic wave velocity.

Evaluation of the Impact of Organic Fillers on Selected Properties of Organosilicon Polymer.

Eco-friendly composites are proposed to substitute commonly available polymers. Currently, wood–plastic composites and natural fiber-reinforced composites are gaining growing recognition in the industry, being mostly on the thermoplastic matrix. However, little data are available about the possibility of producing biocomposites on a silicone matrix. This study focused on assessing selected organic fillers’ impact (ground coffee waste (GCW), walnut shell (WS), brewers’ spent grains (BSG), pistachio shell (PS), and chestnut (CH)) on the physicochemical and mechanical properties of silicone-based materials. Density, hardness, rebound resilience, and static tensile strength of the obtained composites were tested, as well as the effect of accelerated aging under artificial seawater conditions. The results revealed changes in the material’s properties (minimal density changes, hardness variation, overall decreasing resilience, and decreased tensile strength properties). The aging test revealed certain bioactivities of the obtained composites. The degree of material degradation was assessed on the basis of the strength characteristics and visual observation. The investigation carried out indicated the impact of the filler’s type, chemical composition, and grain size on the obtained materials’ properties and shed light on the possibility of acquiring ecological silicone-based materials.

Ageing properties of a polyoxymethylene copolymer exposed to (bio) diesel and hydrogenated vegetable oil (HVO) in demanding high temperature conditions

The increasing use of renewable biofuels in the transportation sector has driven attention on the incompatibility issues between biofuels and the polymeric materials used in the vehicle fuel system. Here, the ageing effects on a polyoxymethylene copolymer exposed to four types of fuels; petroleum diesel, biodiesel, a commercial mixture of these, and hydrogenated vegetable oil (HVO) at demanding high-temperature conditions, were investigated and compared with its performance in air. The degree of material degradation during ageing was highest in the presence of the non-polar fuels (HVO/petroleum diesel). The samples aged in different fuels underwent the same increase in crystallinity due to annealing. Surface powdering was observed on the sample aged in the fuel mixture. The negative effects from a combination of plasticization and swelling, induced by the sorbed fuel, oxidation and surface cracks dominated the changes in mechanical properties, leading to reduced stiffness, strength and extensibility. The results indicate that care should be taken when choosing this polymer in contact with, especially, non-polar fuels at severe conditions.

Bio-Based Packaging Materials Containing Substances Derived from Coffee and Tea Plants.

The aim of the research was to obtain intelligent and eco-friendly packaging materials by incorporating innovative additives of plant origin. For this purpose, natural substances, including green tea extract (polyphenon 60) and caffeic acid, were added to two types of biodegradable thermoplastics (Ingeo™ Biopolymer PLA 4043D and Bioplast GS 2189). The main techniques used to assess the impact of phytocompounds on materials’ thermal properties were differential scanning calorimetry (DSC) and thermogravimetry (TGA), which confirmed the improved resistance to thermo-oxidation. Moreover, in order to assess the activity of applied antioxidants, the samples were aged using a UV aging chamber and a weathering device, then retested in terms of dynamic mechanical properties (DMA), colour changing, Vicat softening temperature, and chemical structure, as studied using FT-IR spectra analysis. The results revealed that different types of aging did not cause significant differences in thermo-mechanical properties and chemical structure of the samples with natural antioxidants but induced colour changing. The obtained results indicate that polylactide (PLA) and Bioplast GS 2189, the plasticizer free thermoplastic biomaterial containing polylactide and starch (referred to as sPLA in the present article), both with added caffeic acid and green tea extract, can be applied as smart and eco-friendly packaging materials. The composites reveal better thermo-oxidative stability with reference to pure materials and are able to change colour as a result of the oxidation process, especially after UV exposure, providing information about the degree of material degradation.

Intelligent optimization system for powder bed fusion of processable thermoplastics

Powder bed fusion (PBF) represents a class of additive manufacturing processes with the unique advantage of being able to fabricate functional products with complex three-dimensional geometries. PBF has been broadly applied in highly value-added industries, including the biomedical device and aerospace industries. However, it is challenging to construct a comprehensive knowledgebase to guide material selection and process optimization decisions to satisfy the product standards of various industries based on a poor understanding of process-structure-property/performance relationships for each type of thermoplastic. In this paper, an intelligent optimization system is proposed to establish quantitative relationships between process parameters and multiple optimization objectives, including mechanical properties, productivity, energy efficiency, and degree of material degradation. Polyurethane is considered as a representative thermoplastic because it is sensitive to thermal-induced degradation and has a relatively narrow process window. Material and powder properties as functions of temperature are investigated using systematic material screening. Numerical models are created to analyze the interactions between laser beams and polymeric powders by considering the effects of chamber thermal conditions, laser parameters, temperature-dependent properties, and phase transitions of polymers, as well as laser beam characteristics. The theoretically predicted features of melting pools are validated experimentally and then utilized to develop quantitative relationships between process parameters and multiple optimization objectives. The established relationships can guide process parameter optimization and material selection decisions for polymer PBF.

Tuning Crystal Structures of Iron-Based Metal-Organic Frameworks for Drug Delivery Applications.

Iron-based metal–organic frameworks (Fe-MOFs) have emerged as promising candidates for drug delivery applications due to their low toxicity, structural flexibility, and safe biodegradation in a physiological environment. Here, we studied two types of Fe-MOFs: MIL-53 and MIL-88B, for in vitro drug loading and releasing of ibuprofen as a model drug. Both Fe-MOFs are based on the same iron clusters and organic ligands but form different crystal structures as a result of two different nucleation pathways. The MIL-53 structure demonstrates one-dimensional channels, while MIL-88B exhibits a three-dimensional cage structure. Our studies show that MIL-53 adsorbs more ibuprofen (37.0 wt %) compared to MIL-88B (19.5 wt %). A controlled drug release was observed in both materials with a slower elution pattern in the case of the ibuprofen-encapsulated MIL-88B. This indicates that a complex cage structure of MIL-88 is beneficial to control the rate of drug release. A linear correlation was found between cumulative drug release and the degree of material degradation, suggesting the biodegradation of Fe-MILs as the main drug elution mechanism. The cytotoxicity of MIL-88B was evaluated in vitro with NIH-3T3 Swiss mouse fibroblasts, and it shows that MIL-88B has no adverse effects on cell viability up to 0.1 mg/mL. This low toxicity was attributed to the morphology of MIL-88B nanocrystals. The very low toxicity and controlled drug release behavior of Fe-MIL-88B suggest that better materials for drug-delivery applications can be created by controlling not only the composition but also the crystal structure and nanoparticle morphology of the material.

Dielectric response characterization of in-service aged sheds of (U) HVDC silicone rubber composite insulators

Investigations of bulk dielectric properties of specimens extracted from in-service aged and aged UHVDC composite insulator sheds are reported in this paper. The program of the study included measurements of DC conductivity and complex permittivity at frequency range 10−4–103 Hz at various temperatures in dry and wet (water immersion) conditions. The obtained results are analyzed by considering a combination of relations describing various dielectric relaxation modes in dielectrics, included three Cole-Cole types of responses and a hopping process. The hopping has the strongest impact on the responses in the whole frequency range. Two of the Cole-Cole responses appearing in the low frequency range are attributed to Maxwell-Wagner-Sillars relaxations at macroscopic and mesoscopic levels; first one representing interfacial polarization at the border between specimen and air gap in the electrode arrangement, while the second one is attributed to the charge relaxation at filler boundaries and internal cavities in the polymeric materials. The third Cole-Cole process, active at higher frequencies, is considered as a sign of polymer degradation, as it shifts with the ageing to higher frequencies. Based on the results of this study, it is claimed that dielectric response measurements on specimens of in-service aged composite insulator sheds can provide useful information on the degree of material degradation. In addition, a water immersion test in combination with such measurements may be a good way to enhancing the observed changes.

Development of the Acoustic Method for Assessing the Degree of Degradation of 08Kh18N10T Steel at Early Stages of Fatigue Fracture*

The algorithm is created to assess the degree of material degradation at the stage of structural damge accumulation using the acoustic method. The results of the acoustic investigations of 08Kh18N10T steel at fatigue fracture are presented.

Kinetic model study of moisture sorption–desorption–resorption in triangular-shaped vinyl ester filler/epoxy composites

A phenomenological diffusion model was used to study and describe moisture sorption–desorption–resorption kinetics in triangular-shaped vinyl ester filler/epoxy composites at 80 °C. The model was derived to predict the experimental anomalous weight gain behaviors of epoxy composites during moisture sorption and resorption, and estimate the degree of material degradation and loss observed as negative weight change during desorption. To verify the applicability of the model, acid anhydride–cured epoxy composites were prepared at varied alignment (parallel or staggered), spacing (1 or 5 mm), and orientation (pointed or flat) of triangular-shaped vinyl ester fillers. Moisture sorption–desorption–resorption experiment was performed by immersion of specimens in deionized water for 1200 h, followed by vacuum drying for 300 h, and water reimmersion for 300 h. The parameters of the model were calculated from nonlinear regression of percent weight change versus time experimental data. The model was found to be in good agreement with the weight change kinetic curves of all specimens. Results of three-way analysis of variance of model parameters showed the degree of material degradation and moisture diffusion coefficients during sorption, desorption, and resorption to be significantly affected by triangular-shaped filler alignment, spacing, and orientation. Using staggered over parallel alignment and 5-mm over 1-mm spacing decreased material degradation and moisture transport rate during desorption in composites. Increasing the spacing from 1 to 5 mm decreased moisture diffusion during sorption. Orienting the fillers from pointed to flat decreased moisture diffusion during resorption. Effect of interaction of filler spacing and orientation was also found to be statistically significant on the diffusion rate during sorption.

Experimental methods to determine in-plane material properties of polyurethane-coated nylon fabric

Experimental procedures have been developed to obtain the mechanical stiffness and strength properties of an orthotropic polyurethane-coated nylon fabric for use in a finite element analysis of an inflatable, deployable structure. A method that utilizes a specialized material test fixture and photogrammetry to collect the linear and angular displacement data has been employed. Different material holding methods were compared with the objective of producing strength values not influenced by gripping and that allow for use of machine displacement to estimate longitudinal strains during cyclic testing. A series of tension and bias tension tests provided material properties such as Young’s modulus in both warp and fill directions, Poisson’s ratios in plane and through the thickness, and shear modulus. Results obtained from the photogrammetry method show good correlation to machine readings using a pinched gripping method. Additionally, cyclic tests gave the continuous load–unload response and the hysteresis characteristics of the stress–strain in plane and indicated the degree of material degradation. The shear stress–shear strain behavior and shear modulus values are acquired using bias tension tests on 45° skewed specimens.

Characterization of fatigue damage of Al6061-T6 with ultrasound

Ultrasonic methods are widely used for the degradation assessment of metals due to their high sensitivity. The remaining life cycle of metal can be estimated by ultrasonic parameters, because ultrasonic attenuation is significantly affected by changes in material properties from accumulated fatigue in aluminum. However, it is difficult to evaluate the overall degradation of aluminum with a single test. So, previous research has been limited to evaluate local areas of fatigued aluminum. Also, even though voids are present in fatigued fracture surfaces of Al6061-T6, many researchers have considered changes in ultrasonic properties in the fatigued aluminum as dislocation damping. Characterizing the effects of voids on the remaining life of fatigued Al6061-T6 with ultrasound has not yet been systematically investigated. So, in this study, we examined the relationship between fatigue properties and ultrasonic attenuation of fatigued Al6061-T6, and estimated the overall change of material properties from 2D C-scan images and SEM observations. Fatigued Al6061-T6 samples at 0 to 85% of fatigue life were prepared for evaluating fatigue life cycle. Finally, degradation indexes of attenuation, which can describe the state of fatigued samples better than ultrasonic attenuation, are proposed to estimate the degree of material degradation for evaluating degraded areas of fatigued samples based on C-scan images and SEM observations.

Mesoscopic Thermal-Mechanical Fire Damage Modeling of High Performance Concrete

High performance concrete will undergo thermal-mechanical degradation or even spalling under high temperature conditions, such as fire, and the safety of concrete structures will be endangered. To prevent concrete from fire damage, the damage mechanism should be thoroughly understood. In this paper, an anisotropic damage model is presented to analyze the thermal-mechanical degradation of concrete. The vapor pressure and the moisture transport are taken into account. The damage evolution history can be traced with the temperature propagation and the degree of material degradation can be predicted through the model.

A study on fracture surface of aged turbine rotor steel by fractal dimension

Since fracture surface presents clear evidence to describe the circumstances of material failure event, analysis of fracture surface should provide plenty of useful information for failure prevention. Thus if we extract proper information from the fracture surface, the safety evaluation for plant component could be more accurate. In general, the chaotic morphology of fracture surface is determined by the degree of material degradation as well as by other factors such as type of load, geometry of specimen, notch condition, microstructure of material and environment. In this research, we developed a fractal analysis technology for the fracture surface of aged turbine rotor steel based on the slit-island technique using an image analyzer. Moreover the correlation between the fractal dimension and the aging time was studied.

Planning, Designing, and Implementing Heat-Straightening Repair of Bridges

The use of heat straightening to repair damaged steel bridges requires careful planning and design of the repair. This planning begins with the engineer, who provides guidelines for both supervision and implementation of the repair through the supervisor and contractor. The process begins with damage assessment and includes checking for fractures, measuring the degree of damage, evaluating the degree of material degradation, and checking geometric distortion. The second step is to plan the repair by analyzing the degree of damage, determining maximum strains, selecting heating patterns, and developing a constraint plan. A methodology is provided for this planning and design. In addition, the responsibilities of the supervisor and the contractor are given. Practitioners are primarily targeted and guidelines are provided for implementing heat-straightening repairs.

Fatigue crack growth behavior of Ti-6AI-4V at elevated temperature in high vacuum: Petit, J., Berrata, W. and Boucher, B. Scr Metall Mater26 12 (June 1992) pp 1889–1894

Powder bed fusion (PBF) represents a class of additive manufacturing processes with the unique advantage of being able to fabricate functional products with complex three-dimensional geometries. PBF has been broadly applied in highly value-added industries, including the biomedical device and aerospace industries. However, it is challenging to construct a comprehensive knowledgebase to guide material selection and process optimization decisions to satisfy the product standards of various industries based on a poor understanding of process-structure-property/performance relationships for each type of thermoplastic. In this paper, an intelligent optimization system is proposed to establish quantitative relationships between process parameters and multiple optimization objectives, including mechanical properties, productivity, energy efficiency, and degree of material degradation. Polyurethane is considered as a representative thermoplastic because it is sensitive to thermal-induced degradation and has a relatively narrow process window. Material and powder properties as functions of temperature are investigated using systematic material screening. Numerical models are created to analyze the interactions between laser beams and polymeric powders by considering the effects of chamber thermal conditions, laser parameters, temperature-dependent properties, and phase transitions of polymers, as well as laser beam characteristics. The theoretically predicted features of melting pools are validated experimentally and then utilized to develop quantitative relationships between process parameters and multiple optimization objectives. The established relationships can guide process parameter optimization and material selection decisions for polymer PBF.

電気化学的手法を用いた２．２５Ｃｒ‐１Ｍｏ鋼の経年劣化の非破壊評価

2.25Cr-1Mo steel is one of heat resistant materials used most widely in fossil power plants as a header and a boiler tube. The most important phenomenon in material deterioration of 2.25Cr-1Mo steel during a long term operation is carbide coarsening. Carbide coarsening causes such changes in mechanical properties as softening or reduction both of creep strength and of toughness.In this paper, a new nondestructive method for detection and evaluation of these material degardations in 2.25Cr-1Mo steel by means of an electrochemical technique is described. The main results obtained are as follows.(1) A degree of material degradation can be evaluation by the peak value of current density (ΔIp) obtained by the anodic polarization measurement. Since ΔIp corresponds to the rate of selective dissolution of coarse carbides M6C, the amount of M6C carbides can be evaluated quantitatively by ΔIp.(2) ΔIp shows a good correlation with ΔFATT. Hence, the toughness reduction can be nondestructively estimated by ΔIp measurement.(3) ΔIp can be regarded as a representative parameter showing the decrease in Mo concentration in grains caused by M6C (Mo-rich) carbide coarsening. ΔIp shows a good correlation with hardness change ΔHv. Based on this interrelation, the degree of softening can be nondestructively estimated.(4) The L.M.P. value of materials used in actual plants can be estimated by ΔIp measurement. Hence, the actual operational temperature can be estimated from the operation period with high accuracy.

Nondestructive Evaluation of Hygrothermal Effects on Fiber-Reinforced Plastic Laminates

Abstract Ultrasonic tests were performed on glass-, carbon-, and Kevlar®-fiber-reinforced plastic laminates that had been exposed to varying hygrothermal ambient conditions. Results reveal similar trends between ultrasonic attenuation measurements and the degree of material degradation as reflected by laminate strength characteristics. A slow decrease in attenuation with almost no degradation was found to be common in all laminates exposed to cold water immersion. Hot water immersion seems to affect significantly glass-fiber-reinforced and Kevlar-fiber-reinforced plastic laminates, which exhibited an increase in attenuation with exposure time. Such a trend is attributable to the degradation process found to be significant in glass-fiber-reinforced plastics and almost nonexistent in the carbon-fiber-reinforced plastic systems.