Effect Of Mechanical Degradation Research Articles

Understanding the Effect of Mechanical Degradation on the Performance of Solid-State Batteries through Particle Simulations

All-solid-state batteries (ASSBs) have garnered significant interest as a promising alternative to conventional lithium-ion batteries, offering improved safety, higher energy density, longer lifespan, faster charging and wider operating temperature range. A key advantage of ASSBs is the use of solid electrolytes (SE), which eliminate the risks associated with flammable liquid electrolytes. However, the complex electrochemical behavior and multi-scale nature of ASSBs pose challenges in designing and optimizing their performance. This study employs Discrete Element Method (DEM) particle-based models to better understand degradation behavior of ASSBs by considering electrochemical reaction, mass and charge transfer, intercalation expansion and material deformationOur simulations were developed in MATLAB and were performed on a half-cell configuration comprising a SE-layer and an anode electrode. The anode electrode was composed of a particle mixture containing active material (AM) and SE. In our simulations, Si was employed as AM, which experiences substantial intercalation expansion during charge cycling 1. Our previously developed DEM model2,3 resolved elastic and plastic deformation of both AM and SE particles which become compressed due to the intercalation expansion. The simulation of intercalation was achieved by integrating the Newman electrochemical model,4 into the DEM mechanical model. Building on our earlier study5, where the Li concentration was resolved within each AM particle, this study is also accounting for the Li-ion potential within each SE particle. Interparticle conduction and diffusion were computed by determining the contact area of AM-AM and SE-SE contacts, which were affected by the compression of the electrode. The electrochemical reaction was calculated at the AM-SE interface using the Butler-Volmer equation, and in addition the influence of compressive stress on the reaction6 was included.Figure 1(a) depicts the Li concentration and Li-ion potential distribution within the half-cell during charging at different states of charge (SOC), while Figure 1(b) provides a 3D view of the distributions at a SOC of 50%. A considerable expansion of the Si anode is evident. The gradients of Li concentration and Li-ion potential signify significant mass and charge transfer resistance during the charging process. Comparing the distribution of the particles, the anode becomes more porous after the first cycle for the same value of SOC. This effect is attributed to the extensive expansion of the Si anode, leading to plastic compression of the SE layer, which becomes more compact after each cycle. The growing porosity diminishes the contact area between particles, ultimately resulting in the degradation of the half-cell's capacity. In addition to SE-layer compaction, this study aims to investigate several degradation mechanisms and their impact on the performance of ASSBs, including the development of shell voids resulting from AM-SE delamination, crack propagation through SE, and fragmentation of AM.The results of this study provide valuable insights into understanding the effect of mechanical degradation on the performance of ASSBs. By improving our understanding of these mechanisms, we can work towards enhancing the durability and lifespan of ASSBs, ultimately contributing to the development of next-generation energy storage systems. Acknowledgment This work was supported by JSPS KAKENHI Grant-in-Aid for Scientific Research on Innovative Areas, “Science on Interfacial Ion Dynamics for Solid State Ionics Devices, Computational & Data Science” (Gp-A03, grant number 19H05815); and MEXT “Program for Promoting Researches on the Supercomputer Fugaku” (Fugaku battery & Fuel Cell Project), grant number JPMXP1020200301. References M. N. Obrovac and L. Christensen, Electrochem. Solid-State Lett., 7, A93 (2004).M. So, G. Inoue, R. Hirate, K. Nunoshita, S. Ishikawa, and Y. Tsuge, J. Electrochem. Soc., 168, 030538 (2021).M. So, G. Inoue, R. Hirate, K. Nunoshita, S. Ishikawa, and Y. Tsuge, Journal of Power Sources, 508, 230344 (2021).J. Newman and K. E. Thomas-Alyea, Electrochemical Systems, 3rd edition., p. 672, Wiley-Interscience, Hoboken, N.J, (2004).M. So, S. Yano, A. Permatasari, T. D. Pham, K. Park, and G. Inoue, Journal of Power Sources, 546, 231956 (2022).G. Bucci, T. Swamy, S. Bishop, B. W. Sheldon, Y.-M. Chiang, and W. C. Carter, J. Electrochem. Soc., 164, A645 (2017). Figure 1

A non-linear model predictive control strategy to minimise mechanical degradation effects of lithium-ion battery

Mechanical stresses are not only developed inside the active material of the composite electrode, but also in the solid electrolyte interface layer (SEI) due to the graphite expansion. Due to diffusion induced stress (DIS) phenomena, stresses in the negative electrode are generated during charging and discharging cycles. This article presents the proposed optimal charging profile explicitly incorporating the effects of mechanical degradation. Non-linear model predictive control approach along with Gauss pseudo-spectral method is used to optimise charging trajectories. It is assumed that active material is not the weakest material but system is modelled based on SEI break and repair effect. The dynamics of battery is represented by a single particle model. The simulated results are compared with benchmark constant current constant voltage (CCCV) strategy. Furthermore, proposed methodology is compared with optimal CCCV using cycle life ageing experimental scenario. It is estimated that stress amplitude decreased by 7% and nominal capacity increased by 11% using the proposed optimal charging profile.

Effect of UV Exposure on the Mechanical Properties of Polyurethane-Coated Fabrics

Polyurethane materials can be used industrially in different ways, some of which can be used as textile materials or as auxiliary materials applied to textile materials. Polyurethane stands out as a widely used polymer for coating textile products used in outdoor applications, because of high stability at low temperature, flexibility, no or very little volatile organic component content, high water resistance, pH stability, excellent solvent resistance, weather resistance, and many other chemical and mechanical properties. In the study, cotton, polyester, and viscose fabrics were coated with polyurethane and aged under UV light to investigate the causes and behaviors of the mechanical degradation effects of UV on the coating material and fiber. The results indicate that the PU coating process improves the mechanical properties of textile materials while being exposed to UV rays deteriorates the fabric structure. The deterioration in the structure of raw and coated fabrics with the effect of UV increased the air permeability. According to the results of DSC analysis, the increase in the time of UV exposure did not create significant differences in terms of thermal degradation temperatures in both cotton and viscose fabrics. The glass transition temperatures (Tg) increase with more exposure to UV rays, and the UV exposure time had a negative effect on the melting temperature (Tm) and enthalpy (ΔH) of coated polyester fabrics.

The effects of mechanical degradation on the quasi static and dynamic stiffness of polyester yarns

Polyester fibers are the most used in the manufacture of ropes for mooring systems and offshore operation, thus being constantly subjected to different situations. Such requests are implicated in a variety of load conditions, and their effects must be studied. This work presents data referring to an experimental study on the behavior of the quasi-static and dynamic stiffness of polyester yarns considering different mechanical levels of degradation and use. The study is performed with five different types of multifilament samples, these were extracted from a virgin spool and sub-ropes tested for tension and fatigue. The experimental procedure is carried out through an initial characterization where the linear density, the Yarn Break Load - YBL and the linear tenacity of the samples are determined. Continuing with the experimental tests, a procedure standardized by ISO 18962-2 is then carried out, consisting of three quasi-static stages and three dynamic stages, where the data acquired in the tests allow the determination of a dimensionless stiffness value. The results showed an increase in the quasi-static stiffness, tending to a plateau, and a linear increase in the dynamic stiffness, but with somewhat similar behavior between the samples. The results related to the total quasi-static stiffness also show that the specimens extracted from sub-ropes that underwent fatigue present greater total non-dimensionalized stiffness, this is indicative of the mechanical fatigue procedure as an improvement of the specimens, giving them greater stiffness, and consequently greater stresses rupture, a behavior that should be explored in future studies.

Numerical and experimental characterization of gas permeation through membranes with consideration of mechanical degradation in proton exchange membrane fuel cells

Exposed to severe loading condition in fuel cells, the perfluorinated sulfonic-acid (PFSA) membrane degrades over time, which becomes the primary cause of the increasing transmembrane gas permeation during the service. As a result, the hydrogen crossover rate increases with the damage propagation, leading to loss in power and life. However, the effect of mechanical degradation on gas permeability of membrane cannot be quantitatively estimated due to difficulties in damage observation and modeling. This paper first establishes a numerical technique to predict the gas permeation through membrane with consideration of mechanical degradation. Blister test as well as gas permeation test are conducted for the verification of the numerical model. The model shows great prediction accuracy, based on which the uneven distributed damage and its effect on gas permeability are analyzed. Result shows that the gas permeation rate grows with pressure and mechanical degradation has a remarkable contribution, accounting for about 7.3% of total permeation rate at testing pressure of 130 kPa. Finally, the varied membrane shape and gas permeability, which all accelerate the gas permeation, are further analyzed based on the numerical model.

Characterization of Nonlinear Viscoelastic Properties of Enhanced Oil Recovery Polymer Systems Using Steady-Shear Rheometry

SummaryEnhanced oil recovery (EOR) polymer systems such as hydrolyzed polyacrylamide (HPAM) solutions flowing in porous media at high fluxes were reported to cause shear-thickening, a nonlinear viscoelastic (NLVE) phenomenon. Bulk rheological studies are usually performed to characterize the viscous and viscoelastic behaviors of polymer solutions in porous media. To characterize the viscoelastic properties, oscillatory shear rheology based on linear viscoelastic (LVE) data and extensional rheology based on NLVE data have been used. Although both extensional flow and high-speed shear flow can stretch and thicken polymer solutions in a nonlinear fashion, steady-shear rheometry has been used to measure only the viscous and thinning behavior of HPAM systems. In this paper, (a) the thickening ability of HPAM polymer systems formulated with contrasting salinity and molecular weight (MW) concentration is characterized in bulk shear rheometry to analyze if the thickening in the pure shear field correlates with the thickening behavior reported in porous media and other rheometry and (b) the thickening intensity of the polymer solutions of varying salinity concentration in the bulk shear field is compared with the reported mechanical degradation effects in the literature.The shear-thickening index obtained by fitting a power-law model to thickening data in steady-shear rheograms is higher for the high-saline, high-MW low-concentration HPAM systems that have inherently higher nonlinear viscoelasticity. Furthermore, the thickening behavior observed due to salinity variation in bulk steady shear contrasts with linear oscillatory shear behavior but conforms to the thickening behavior observed in porous media and in the extensional field. This signifies that polymer-EOR researchers performing comparative studies on low-salinity and high-salinity polymer floods, and having a shear rheometer at their disposal, must look beyond linear oscillatory rheology and make use of nonlinear steady-shear rheology. There is a direct relation between the shear-thickening index of saline HPAM solutions and their mechanical degradation intensity. This paper shows that the high-speed data in steady-shear rheometry that are usually ignored in EOR literature have useful information and the notion that HPAM solutions are purely thinning in the bulk shear field needs to be reconsidered.

Analysis of performance degradation on the components in polymer electrolyte membrane fuel cell by dissecting the oxygen diffusion region

Performance degradation due to mechanical effect is an important durability issue for polymer electrolyte membrane fuel cells (PEMFCs). Mechanical degradation mainly occurs during the startup/shutdown mode at subzero temperature. However, studies about the contribution of mechanical degradation to the main PEMFC components of the gas diffusion layer (GDL) and catalyst-coated membrane (CCM) have not been analyzed quantitatively under various operating conditions. In this study, the freeze-thaw accelerated stress test (AST) is newly developed and performed to identify the exclusive effect of mechanical degradation on the GDL and CCM under normal and subzero conditions. Under normal conditions, the PEMFC performance result indicates that CCM has a larger degradation than the GDL owing to an increase in oxygen transport resistance and low water saturation point. Under subzero conditions, a cold start is experimentally investigated using the constant voltage method, revealing that the oxygen transfer coefficient dominantly affects the heat generation term in the 0-D model. Therefore, this study provides design guidelines for high-durability PEMFC components (GDL and CCM) and new insights into the interactive effects between heat and oxygen transport under normal and subzero conditions.

Кинетика поврежденности предварительно циклированной малоуглеродистой стали с крупнозернистой и субмикрокристаллической структурой

The kinetics of accumulation of microcracks and fracture at various stages of tension of grade 20 steel specimens with coarse-grained and ultrafine-grained (UFG) structure obtained by the equal-channel angular pressing (ECAP) has been studied. To study the effect of mechanical degradation, a part of the samples was subjected to preliminary cycling to a relative lifetime of 50 %, followed by tensile tests, during which the parameters of acoustic emission, deformation fields obtained by digital image correlation were evaluated, and the intensity of the residual magnetic field was measured. The length and density of surface microcracks were measured by optical microscopy using computer image analysis. It is established that pre-cycling causes hardening of the material and a decrease in its plasticity. The fracture stages were revealed, and fatigue crack origins were found on the internal delaminations of specimens with a UFG structure after preliminary cyclic loading. It is shown that the formation of the UFG structure after the ECAP of specimens made of grade 20 steel leads to hardening, reduction of the fracture work, the area of the plastic zone, maximum major deformations and damage, as well as to an increase in the number of AE signals and the intesity of the residual magnetic field.

Corrosion degradation of aluminium alloys using a computational framework

The paper describes the corrosion based degradation of aluminium alloys using an analytical and numerical framework. The corrosion rate was calculated using analytical equations for aluminium sheets subjected to a corrodent. Parametric analysis for the pit morphology, diameter, depth and distribution on the plate was conducted using finite element analysis. A comparison between elliptical and circular pits of the same area was also made for stress magnification using numerical analysis. It was observed that the stress generated at constant load when a specimen corrodes due to pitting is directly proportional to the pit diameter and pit depth. Zigzag pit morphologies due to the combined effect of mechanical degradation and corrosion have the highest stress at the corners of the pattern, while circular pits have the highest stress at the centre of the pit. The zigzag pit morphology has more detrimental effects than circular pits. For multiple distributed pits, the pits closer to the specimen edges exhibit higher stress values than those near the centre of the specimen. The effect of multiple or quantitatively increased number of pits having smaller geometric properties has a more detrimental effect than a single pit with larger geometric attributes.

Effects of mechanical degradation on the stiffness of polyester yarns

Effects of mechanical degradation on the stiffness of polyester yarns

Biological cells and coupled electro-mechanical effects: The role of organelles, microtubules, and nonlocal contributions

Biological cells are exposed to a variety of mechanical loads throughout their life cycles that eventually play an important role in a wide range of cellular processes. The understanding of cell mechanics under the application of external stimuli is important for capturing the nuances of physiological and pathological events. Such critical knowledge will play an increasingly vital role in modern medical therapies such as tissue engineering and regenerative medicine, as well as in the development of new remedial treatments. At present, it is well known that the biological molecules exhibit piezoelectric properties that are of great interest for medical applications ranging from sensing to surgery. In the current study, a coupled electro-mechanical model of a biological cell has been developed to better understand the complex behaviour of biological cells subjected to piezoelectric and flexoelectric properties of their constituent organelles under the application of external forces. Importantly, a more accurate modelling paradigm has been presented to capture the nonlocal flexoelectric effect in addition to the linear piezoelectric effect based on the finite element method. Major cellular organelles considered in the developed computational model of the biological cell are the nucleus, mitochondria, microtubules, cell membrane and cytoplasm. The effects of variations in the applied forces on the intrinsic piezoelectric and flexoelectric contributions to the electro-elastic response have been systematically investigated along with accounting for the variation in the coupling coefficients. In addition, the effect of mechanical degradation of the cytoskeleton on the electro-elastic response has also been quantified. The present studies suggest that flexoelectricity could be a dominant electro-elastic coupling phenomenon, exhibiting electric fields that are four orders of magnitude higher than those generated by piezoelectric effects alone. Further, the output of the coupled electro-mechanical model is significantly dependent on the variation of flexoelectric coefficients. We have found that the mechanical degradation of the cytoskeleton results in the enhancement of both the piezo and flexoelectric responses associated with electro-mechanical coupling. In general, our study provides a framework for more accurate quantification of the mechanical/electrical transduction within the biological cells that can be critical for capturing the complex mechanisms at cellular length scales.

Effect of microscopic aggregation behavior on polymer shear resistance

ABSTRACTThe study of polymer aggregation behavior effect on shear resistance shed light on the synthesis of antishear polymer for oil displacement and enhances the application effect of polymer flooding. The effects of mechanical degradation on the properties of polymer solutions were studied by using partially hydrolyzed polyacrylamide (HPAM), hydrophobically modified HPAM (HMPAM), and dendritic hydrophobic associative polymers (DHAP), which are characterized by “granular,” “chain,” and “cluster” aggregation behavior, respectively. The results show that mechanical shearing can dramatically reduce the performance of polymer solution. The shearing resistance can be effectively enhanced by improving the polymer aggregation behavior. After being strongly sheared, hydrophobically associating polymers can still partially restore its network through hydrophobic association, therefore rebuild the solution viscosity. For DHAP, the broken molecular chains distribute more evenly in solution after shearing. In addition, the strength of reconstructed network structure of DHAP is better than that of HMAPM, which implies a better shear resistance. Furthermore, the hydrophobic association of linear polymers will increase their static adsorption on quartz sand. Meanwhile, DHAP with stronger spatial structure has less static adsorption, which is beneficial to maintain a higher polymer concentration in solution. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48670.

Quantification of the Viscoelastic Effects During Polymer Flooding: A Critical Review

Summary Since the late 1960s, several enhanced–oil–recovery (EOR) researchers have developed various continuum and pore–scale viscoelastic models for quantifying the altered injectivity and incremental oil recovery because of the polymer's viscoelastic effects. In this paper, limitations in each of the continuum and pore–scale models are discussed. The critiques are made on the basis of the contradicting literature. Most of the earlier models rely on the exclusive use of the Deborah number to quantify the viscoelastic effects. The Deborah number overlooks mechanical–degradation effects. There exists a large difference in the magnitudes of the reported Deborah number in the literature because of the inconsistency in using different relaxation time and residential time. Oscillatory relaxation time used by most of the EOR researchers to calculate the Deborah number failed to distinguish the different porous–media behavior of the viscous and viscoelastic polymer. Therefore, the accuracy of relaxation time obtained from the weak oscillatory field for EOR applications in porous media is questionable. The main limitation with all the existing continuum viscoelastic models is the empirical reliance on coreflood data to predict the shear–thickening effects in porous media. The strain hardening index, needed for quantifying the thickening regime, cannot be obtained by the conventional shear rheological techniques. The conventional capillary number (Nc) failed to explain the reduction in residual oil saturation (Sor) during viscoelastic polymer flooding. Pore–scale viscoelastic models use the conventional oscillatory Deborah number for quantifying the polymer's viscoelastic effects on Sor reduction. However, this approach has many drawbacks. Discussions on the shortcomings of the existing viscoelastic models caution the current chemical EOR (cEOR) researchers about their applications and potential consequences. Also, this research provides a path forward for future research to address the limitations associated with the quantification of viscoelastic flow through porous media.

Transverse fatigue behaviour of steel-UHPC composite deck with large-size U-ribs

With increasing traffic volumes, fatigue of orthotropic steel decks (OSDs) has become a critical issue in recent years. In this study, an innovative composite deck composed of large-size U-ribs, a thin ultra-high-performance concrete (UHPC) layer and headed studs is proposed to enhance the fatigue properties of OSDs. Experimental and numerical approaches were combined to investigate the transverse fatigue behaviour of the proposed composite deck. A large-scale composite deck specimen was fabricated and tested under cyclic loading. The experimental results revealed the progressive failure process of the composite deck. The effects of damage accumulation in UHPC layer and headed studs on the mechanical behaviour of steel-UHPC composite deck were evaluated. The results indicated that the mechanical degradation in the composite deck system accelerated the damage accumulation in the fatigue-prone details of OSDs. It is necessary to consider the effects of mechanical degradation in fatigue resistance evaluation.

Study of mechanical degradation of sulfonated poly (ether ether ketone) membrane using ex-situ hygrothermal cycles for polymer electrolyte fuel cell application

In this study, an ex-situ method is used to investigate the mechanical degradation of sulfonated poly (ether ether ketone) membranes. The mechanical degradation is carried out by hygrothermal cycles test in different cycles as 1 s t to 10 t h cycles as a function of temperature and relative humidity for 700 min. The water uptake, dimensional stability, mechanical properties, and hydrogen crossover through specimens of degraded membranes are investigated after different cycle numbers. Additionally, morphological and structural characterizations included field emission scanning electron microscopy, atomic force microscopy, and X-ray diffraction are employed for understanding of mechanical degradation effects on SPEEK membranes properties. Results suggest that SPEEK membrane due to simultaneous creep and exposure to elevated temperatures and various humidity levels encounters microstructural rearrangement. The mechanical results show the ultimate tensile strengths and Young modules of SPEEK membranes increase and SPEEKs' toughness drops by approximately 80% at the end of the experiment and they act more brittle in the tensile test. Moreover, the AFM results show preexistent dead-end hydrophilic domains join each other to form more hydrophilic morphology within SPEEK and accordingly, water uptake increases. Furthermore, hydrogen crossover rate increases due to thinning and micro-flaws formation in the thickness direction and morphology evolution.

Effect of mechanical degradation of laminated elastomeric bearings and shear keys upon seismic behaviors of small-to-medium-span highway bridges in transverse direction

Laminated elastomeric bearings have been widely used for small-to-medium-span highway bridges in China, in which concrete shear keys are set transversely to prohibit large girder displacement. To evaluate bridge seismic responses more accurately, proper analytical models of bearings and shear keys should be developed. Based on a series of cyclic loading experiments and analyses, rational analytical models of laminated elastomeric bearings and shear keys, which can consider mechanical degradation, were developed. The effect of the mechanical degradation was investigated by examining the seismic response of a small-to-medium-span bridge in the transverse direction under a wide range of peak ground accelerations (PGA). The damage mechanism for small-to-medium-span highway bridges was determined, which can explain the seismic damage investigation during earthquakes in recent years. The experimental results show that the mechanical properties of laminated elastomeric bearings will degrade due to friction sliding, but the degree of decrease is dependent upon the influencing parameters. It can be concluded that the mechanical degradation of laminated elastomeric bearings and shear keys play an important role in the seismic response of bridges. The degradation of mechanical properties of laminated elastomeric bearings and shear keys should be included to evaluate more precise bridge seismic performance.

Effects of isolated chemical and mechanical degradation stressors on the ionomer morphology in fuel cell membranes

The present work aims to understand the specific effects of isolated chemical and mechanical degradation stressors on the morphology and physico-chemical properties of fuel cell membranes. Chemical and mechanical degradation stressors are isolated in two specific, carefully designed accelerated stress tests of fuel cells. Degraded membranes are then extracted and systematically analyzed through contrast enhanced transmission electron microscopy, thermogravimetric analysis, and water sorption measurements. Statistical analysis of the ionomer morphology shows that chemical degradation dilates hydrophilic pores and disintegrate ionomer bundles, while the water uptake per unit area decreases. However, significant ionomer mass loss is found to reverse the water sorption trend, leading to an increased water uptake per ionomer mass unit, in agreement with the dilation effect. In contrast, mechanical degradation merely causes a slight ordering of the morphology and a marginal increase in water uptake due to bulk water residing in membrane cracks formed by fatigue-fracture. Compounded chemical and mechanical degradation effects are therefore considered particularly harmful, given the ability to bridge mesoscale morphological alterations induced by chemical degradation to macroscale damage propagation under mechanical stress cycles, leading to ultimate membrane failure.

Random Walk Analysis of the Effect of Mechanical Degradation on All-Solid-State Battery Power

Mechanical and electrochemical phenomena are coupled in defining the battery reliability, particularly for solid-state batteries. Micro-cracks act as barriers to Li-ion diffusion in the electrolyte, increasing the average electrode’s tortuosity. In our previous work, we showed that solid electrolytes are likely to suffer from mechanical degradation if their fracture energy is lower than 4 J m− 2 [G. Bucci, T. Swamy, Y.-M. Chiang, and W. C. Carter, J. Mater. Chem. A (2017)]. Here we study the effect of electrolyte micro-cracking on the effective conductivity of composite electrodes. Via random analyzes, we predict the average diffusivity of lithium in a solid-state electrode to decrease linearly with the extension of mechanical degradation. Furthermore, the statistical distribution of first passage times indicates that the microstructure becomes more and more heterogeneous as damage progresses. In addition to power and capacity loss, a non-uniform increase of the electrode tortuosity can lead to heterogeneous lithiation and further stress localization. The understanding of these phenomena at the mesoscale is essential to the implementation of safe high-energy solid-state batteries.

Diode laser heat treatment of lithium manganese oxide films

The crystallization of lithium manganese oxide thin films prepared by radio frequency magnetron sputtering on stainless steel substrates under 10Pa argon pressure is demonstrated by a laser annealing technique. Laser annealing processes were developed as a function of annealing time and temperature with the objective to form an electrochemically active lithium manganese oxide cathode. It is demonstrated, that laser annealing with 940nm diode laser radiation and an annealing time of 2000s at 600°C delivers appropriate parameters for formation of a crystalline spinel-like phase. Characteristic features of this phase could be detected via Raman spectroscopy, showing the characteristic main Raman band at 627cm−1. Within cyclic voltammetric measurements, the two characteristic redox pairs for spinel lithium manganese oxide in the 4V region could be detected, indicating that the film was well-crystallized and de-/intercalation processes were reversible. Raman post-analysis of a cycled cathode showed that the spinel-like structure was preserved within the cycling process but mechanical degradation effects such as film cracking were observed via scanning electron microscopy. Typical features for the formation of an additional surface reaction layer could be detected using X-ray photoelectron spectroscopy.

クリープ予ひずみおよび繰り返し予ひずみを与えられたＣｒＭｏＶ鋼におけるクリープ，疲労き裂進展速度

The effect of mechanical degradation in a long-term-operated component on the creep- and fatigue-crack growth rates was studied. Creep-crack-growth tests and fatigue-crack growth tests were performed on creep-pre-strained and cyclic-strained CrMoV rotor-steel specimens.It was found that under constant load, creep-crack growth rates, da/dt, of the creep-pre-damaged specimens were higher than those of virgin specimens. It was also found that under the same stress intensity factor K, da/dt in the case of about 10%-crept and creep-void-induced specimens was increased 5 times, while in the case of 0.8%- and 2.8%-crept specimens, it only increased a little. However, all the data fall in a narrow scatter band in the relationship between creep J integral C* and da/dt.Another result showed that fatigue-crack growth rates, da/dN, of creep- and fatigue-pre-damaged specimens were higher than those of virgin specimens. Under the same stress intensity factor range ΔK, da/dN in an about 10%-crept specimen was increased 20 times. And da/dN in fatigue-pre-damaged specimens were accelerated 10 times. However, the results of the strain-controlled crack growth test fall in a narrow scatter band in the relationship between J integral range ΔJ and da/dN.These results suggest that the creep remaining lives and fatigue remaining lives of the mechanically damaged CrMoV rotor steel can be estimated by using C* & ΔJ of the damaged material and the da/dt and da/dN values of the virgin material.