Search

• A new damage model is proposed to simulate very low cycle fatigue crack growth. • The proposed model considers failure cycle and load ratio terms for cyclic loading. • Failure cycle term is derived from plastic strain energy under low cycle fatigue. • Load ratio term is derived from the mean stress correction factor for low cycle fatigue. • Prediction results show good agreement with crack growth and fracture surface data. An energy-based damage model for simulating very low cycle fatigue (VLCF) crack growth is proposed to improve the prediction accuracy of our previous model. Modifications are made to explicitly include the terms related to failure cycle and load ratio. The parameters related to these terms are determined from mean fatigue life model of the material. The proposed damage model is validated by comparing with through-wall cracked pipe test data for Type 316 stainless steel. Predicted failure cycles are very close to experimental data, improving the prediction accuracy of our previous model. Comparison of fracture surfaces also shows good agreement. Conclusion: Proposed energy-based damage model improves the prediction accuracy for low load amplitude and different load ratios under very low cycle fatigue crack growth [Display omitted]. [ABSTRACT FROM AUTHOR]

Amorphous Zn–Sn–O (zinc–tin–oxide, ZTO) thin films were deposited with a mixed ZnO/SnO2 target through RF sputtering. The deposited Zn–Sn–O thin films were characterized using physical/chemical probing tools, such as optical characterization based on spectroscopic ellipsometry, surface morphology via atomic force microscopy, chemical information determined through X-ray photoelectron spectroscopy, and structural monitoring of crystallinity using X-ray diffraction. The ZTO thin-film transistors were constructed with a bottom-gate structure using thermally grown SiO2 as the gate dielectric. The Zn–Sn–O TFTs were characterized in terms of the channel thickness, dielectric thickness, and annealing temperatures, and degradation tests were performed at higher temperatures than under ambient conditions. The Zn–Sn–O thin film transistors were optimized at a ZTO thickness of 40nm, a SiO2 gate dielectric thickness of 100nm after annealing at 500°C, and had an on/off ratio of 8.22×10+7, a field-effect mobility of 12.90cm2/Vs, a threshold voltage of 4.32V, and an S-slope of 0.69V/decade. [ABSTRACT FROM AUTHOR]

The oxygen nonstoichiometry of La2Ni0.95Al0.05O4.025 + δ ( LNAO) is measured as a function of oxygen partial pressure ( pO2) and temperature by coulometric titration method and thermogravimetric analysis ( TGA) in 800°C-1000°C temperature range and 10−16-1 atm pO2 range. The partial molar quantities for mixing of oxygen were calculated and results were compared with the literature results on La2NiO4 + δ ( LNO). The variation in activity coefficient of holes versus oxygen nonstoichiometry illustrated an early positive deviation of the activity coefficient of holes from unity, leading to [ABSTRACT FROM AUTHOR]

Modern structural concrete members have become longer and slender, and the prestressed concrete method is an efficient way for sufficiently satisfying the strength and serviceability requirements of such members. Particularly, pretensioned concrete members are typically produced as a precast system that can reduce the construction time and waste significantly by minimizing on-site work. Thus, the pretensioned precast concrete structure is an effective method that can meet both environmental and economic demands in international society. Productivity of the pretensioned members, however, is significantly influenced by the timing of releasing prestress, because prestressing forces can be transferred when the target compressive strength of early age concrete is attained. Unfortunately, the allowable compressive stress at transfer specified in current design code provisions may not be reliable in some practical situations, and those stress limits were determined by empirical methods without a theoretical basis. To overcome such problems, a reasonable estimation equation for allowable compressive stress at transfer was proposed in this paper using extensive analyses based on the Strength Design Method (SDM), in which the eccentricity ratio of the tendon, the sectional size and shape, the level of prestress, and the self-weight moment were considered. The allowable releasing compressive stresses specified in international design codes and based on the proposed equation were compared to test results collected from literature. These comparisons indicated that the allowable stresses specified in current design codes provided unconservative evaluation results for pretensioned members with low eccentricity ratios and conservative results for those with high eccentricity ratios, while the proposed equation reasonably evaluated the allowable compressive stresses of pretensioned members with rectangular, tee, and inverted tee sections. [ABSTRACT FROM AUTHOR]

Impedance spectroscopy was applied to MnO x-based thin films prepared in symmetric and asymmetric electrode configurations, i.e., Pt/ MnO x/ Pt and Ta/ MnO x/ Pt, respectively. Equivalent circuit analysis suggests the presence of higher resistance surface layers adjacent the electrodes, in addition to a higher conductivity component at central portions of the MnO x thin films. The asymmetric configuration enables the Ta/ MnO x interfacial layer to facilitate the redox transport of oxygen ions, where significant changes in resistance with the electric field are responsible for the higher on/off resistance ratio in Ta/ MnO x/ Pt. The higher dielectric constant and bias-dependent capacitance and resistance support the coexistence of both oxidized surfaces and interfacial layers. [ABSTRACT FROM AUTHOR]

Numerous experimental and analytical investigations have been conducted on the shear strength of steel fibre reinforced concrete (SFRC) members. However, most existing strength evaluation models are empirical equations based on limited experimental results lacking in theoretical basis, and these models may lead to overly conservative, uneconomical designs owing to the assumption of 45° crack inclination. They also cannot be expanded to estimate load-deformation responses of SFRC members. In order to overcome these limitations in existing models, this study proposes a theoretical model in which the contribution of steel fibres to shear resistance mechanisms of SFRC members, considering the random distribution characteristics and directionality of fibres at the crack interfaces, is reflected in a smeared-truss model. In particular, the pull-out failure of fibres caused by bond failure between fibres and the surrounding concrete is considered. Shear tests on SFRC beams were also conducted in this study with the primary parameters of fibre volume fraction and compressive strength, and experimental results from the literature were used for validation purpose. The proposed model shows a high level of accuracy in strength evaluation for a total of 103 experimental results. The crack inclination angles estimated by the proposed model range from 22° to 30° and agree well with the experimental results of this work. This demonstrates that the 45° crack angle assumed in the existing shear strength evaluation models is unnecessarily conservative. [ABSTRACT FROM AUTHOR]

A 532nm Nd:YAG laser was applied to crystallize amorphous Si thin films in order to evaluate the applicability of Nd:YAG laser to low-temperature polycrystalline Si technology. In this study, we aim at enhancing uniformity as well as crystallinity. In order to achieve the goal, a new optical system called as a diffusing system was used to enhance the uniformity of irradiating beam profile, consequently improving the quality of crystallized microstructures. Optimal processing parameters for high crystallinity and uniformity were developed by design of experiments (DOE). To investigate crystallinity and uniformity, Raman spectroscopy and optical microscopy were utilized. Therefore, the effectiveness of Nd:YAG laser is suggested as a feasible alternative that is capable of crystallizing the amorphous Si thin films. [ABSTRACT FROM AUTHOR]

Abstract: Our understanding on the shear behavior of SFRC members is still quite limited due to the complex inter-combinatorial mechanisms of shear transfer. Some efforts have been made to extend the application of modified compression field theory and the soften truss model to SFRC members. It is difficult, however, for such models to reflect some of the key behavioral characteristics of SFRC, such as the fiber directionality at the crack interfaces, the differences of bond strengths by fiber types, and the pull-out failure of fibers at crack. Thus, in this study, a nonlinear finite element analysis procedure has been developed that sufficiently reflects the material properties and behavioral characteristics of SFRC, and can be applied to obtain the shear behavior. The accuracy and rationality of the proposed model were also verified in this study by comparing to the recent experimental results on the SFRC shear panels. [Copyright &y& Elsevier]

[Display omitted] • A model is proposed to predict initiation of crack growth in a cracked component under very low cycle fatigue loading. • Mechanism of crack initiation in a cracked component under monotonic and very low cycle fatigue is assumed to be the same. • The cyclic C(T) tests are performed under displacement and load control conditions. • Predicted fatigue cycles for initiation of crack growth agree well with the experimental data. In this paper, a model is proposed to predict the initiation cycle of a cracked component under very low cycle fatigue. The prediction model is based on the simple assumption that mechanism of crack initiation in a cracked component under very low cycle fatigue loading is the same as that under monotonic loading, and is given in terms of the plastic component of monotonic J and cyclic ΔJ. For validation, predicted cycles are compared with displacement-controlled cyclic C(T) test data with two load ratios and load-controlled C(T) test data with two amplitudes. The predicted cycles based on 0.2 mm crack growth are similar in all cases. [ABSTRACT FROM AUTHOR]

• Load interaction effect on fatigue crack growth under large scale yielding conditions. • Crack growth measurement in through-wall cracked pipe tests under variable large amplitude fatigue loading. • No crack acceleration or retardation observed due to the load change in experiment. • Numerical FE debond analysis to simulate through-wall cracked pipe test for further understanding. • No crack closure observed from FE simulation under variable large amplitude fatigue loading. Conclusion: Load interaction under large scale yielding did not affect the fatigue crack growth for through-wall cracked pipe owing to no crack closure In this paper, the load interaction effect on fatigue crack growth under large scale yielding conditions is investigated, via combined experimental and finite element (FE) analyzes of a through-wall cracked pipe. For the fatigue load amplitude, two amplitudes were applied to the through-wall pipe, 75% and 85% of the experimental maximum load under monotonic loading. For the loading type, periodic overload, high-low and low-high loading sequences were applied. It is experimentally found that the change of crack growth rate due to load interaction does not occur under large scale yielding, in contrast to the behavior under small scale yielding. Numerical analysis using FE debond analysis further shows that crack closure does not occur in the through-wall cracked pipe under large scale yielding fatigue loading, which can explain no load interaction effect on fatigue crack growth, observed in the present experiment. [Display omitted] [ABSTRACT FROM AUTHOR]

The statistical design of experiments was successfully carried out in order to synthesize monodisperse silica spheres using a fractional factorial design with a resolution of V. In this design, the input variables were the temperature, the concentration of NH3, the concentration of TEOS, the methanol/n-prophyl alcohol ratio, and the distilled water. The output variables were the particle size, standard deviations, and the degree of agglomeration. Simultaneous consideration of the particle characteristics allowed for an optimum regime in the experimental conditions in addition to an understanding of the experimental variables. The concentrations of TEOS and distilled water are determined to be statistically significant variables for the controlling of the particle sizes. The size of the monodisperse silica spheres was found to be approximately 400 nm. [ABSTRACT FROM AUTHOR]

[Display omitted] • A hardening model is proposed to simulate deformation of cracked structure under large amplitude cyclic loading. • Cyclic C(T) tests for TP304 stainless steel is performed with two load amplitudes. • FE debonding analysis is applied to develop the proposed hardening model. • The model calculates isotropic hardening in the first loading cycle. • From the unloading of the first cycle, a Chaboche combined hardening model is used. A new cyclic hardening model is proposed based on combined experimental and numerical analyses to simulate the deformation of a cracked structure under large amplitude cyclic loading. In the experiment conducted herein, compact tension specimen tests made of TP304 stainless steel were subjected to large-amplitude cyclic loading. Then, finite element (FE) analysis was performed using the ABAQUS debond option to develop a cyclic hardening model. In the proposed cyclic hardening law, isotropic hardening was calculated in the first loading cycle. To assess the unloading of the first cycle, a Chaboche combined hardening model was used. The model results agreed well with the experimental displacement data. The effects of hardening in the first loading cycle on the yield surface and equivalent plastic strains in the subsequent cycles are presented as well. [ABSTRACT FROM AUTHOR]

La-doped BaTiO 3 ceramics are essential materials in electronic devices, finding applications in multilayer ceramic capacitors and positive temperature coefficient thermistors. While the electrical properties of La-doped BaTiO 3 have been investigated, the impact of its room-temperature resistivity anomaly on dielectric properties remains unclear. We synthesized pristine and La-doped BaTiO 3 (0.1 – 0.5 mol%) powders via hydrothermal methods, and then sintered bulk samples. Their resistivities (DC and AC), Curie temperature, room-temperature dielectric constant, and lattice volume with varying La doping concentrations were characterized. Beyond 0.3 mol%, the shift from electronic to ionic charge compensation mechanisms resulted in abrupt changes in resistivities, Curie temperature, and dielectric constant near 0.3 mol%. Given minimal changes in average grain size and relative density near 0.3 mol% La, the dominant factor influencing the dielectric constant peaking near this concentration was the shift in charge compensation mechanism. [ABSTRACT FROM AUTHOR]

The proton‐conducting oxides, widely employed as electrolytes in ceramic electrochemical cells, exhibit remarkable proton conductivity that facilitates efficient energy conversion processes. However, their inherent refractory nature poses a challenge in producing chemically stoichiometric and physically dense electrolytes within devices. Here a novel approach is presented, dual‐phase reaction sintering, which can overcome the inherent low sintering ability of the representative BaCeO3‐δ‒BaZrO3‐δ proton conducting oxides. This approach involves the simultaneous transformation of a two‐phase mixture (comprising fast‐sintering and slow‐sintering phases) into a complete single‐phase solid solution compound, along with the densification of the electrolyte, all accomplished within a single‐step heating cycle. During the dual‐phase reaction sintering process, the grains of the fast‐sintering phase experience rapid growth owing to their intrinsic superior sintering ability. Additionally, this growth is augmented by the Ostwald ripening behavior manifested by the smaller slow‐sintering phase. This synergistic strategy is validated using BaCe0.4Zr0.4Y0.1Yb0.1O3‐δ, and its applicability in electrochemical cells is demonstrated, resulting in a significant enhancement in performance. These findings offer insights into streamlining the preparation of refractory ion‐conducting ceramic electrolytes while maintaining their intrinsic properties for practical applications. [ABSTRACT FROM AUTHOR]

Background: Brugada syndrome (BrS) and arrhythmogenic cardiomyopathy (ACM) are inherited cardiac diseases that may predispose to ventricular arrhythmia. Although overlapping features between BrS and ACM have been demonstrated previously, it remains to be determined whether genetic testing for ACM-related genes is needed in BrS probands. Method: Based on a single-center, retrospective registry of BrS, we aimed to verify genetic profiles of BrS using a next-generation sequencing panel, and further analyzed genetic testing of ACM-related variants in Brugada phenotypes. Results: Among a total of 119 Brugada phenotypes, 114 patients (95.8%) were male and the mean age of onset was 43.6 years. Genetic variants were identified in 25 of the 42 patients who underwent genetic testing. Fifteen patients had BrS-related genotypes, including SCN5A in 6 patients, and non-SCN5A genes in 9 patients (SCN10A, HCN4, SCN3B, and KCNE3). Nineteen patients underwent additional genetic testing with cardiomyopathy panel, which revealed ACM-related genotypes (2 PKP2, 1 DSG2, 1 TMEM43, 1 JUP, and 1 DSP) present in 6 patients (31.5%). None of the patients had structural or electrocardiographic features that fulfilled the diagnostic criteria for ACM. Conclusions: In clinical setting, ACM-related genes were identified in a significant proportion of Brugada phenotypes, supporting the argument that genetic testing of ACM overlapping is needed. Follow-up imaging studies should be considered to monitor if the disease progresses to ACM. [ABSTRACT FROM AUTHOR]

This paper proposes a numerical method to simulate ductile fracture of a cracked pipe using small punch test data. The method is using FE damage analysis method based on the multi-axial fracture strain energy density model. The parameters in the damage model can be extracted solely from small punch test data, using which compact tension and circumferential through-wall cracked pipe tests are simulated. To validate the proposed method, simulation results are compared with TP316L experimental data. For the compact tension test, faster crack growth is predicted but for the pipe test, good agreement is obtained. The effect of the stress triaxiality on the prediction accuracy is discussed. • A numerical method to simulate ductile fracture of cracked pipe using small punch test data. • FE damage analysis based on the multi-axial fracture strain energy density model. • Damage model determined from small punch test data. • Comparison of simulation results with C(T) and circumferential through-wall cracked test data. [ABSTRACT FROM AUTHOR]

A novel approach combining conventional contact- and projection-lithography techniques has been devised to implement microelectrodes, down to submicron size, across isolated site-specific features as small as 2–3 micron. For both ex-situ and in-situ electrical characterization, such features of interest are isolated interfaces and grain boundaries in electroceramics and multilayer devices, including those in as-prepared TEM specimen. The procedure has been discussed for implementing 4-probe microelectrodes across several individual isolated grain boundaries of a commercial ZnO varistor containing 2–10 micron size grains. In addition, we discuss the results from dc 4-probe I-V and ac 2-probe impedance measurements across individual grain boundaries, and dc 2-probe I-V and ac 2-probe impedance measurements from grain interiors isolating these grain boundaries. Over and above the generally observed properties of isolated grain boundaries, the measurements reveal (1) inhomogeneity and applied-bias-polarity dependent asymmetry in the nonlinear I-V characteristics of grain boundaries, (2) possible presence of non-ohmic electrode-ceramic contact resistance in 2-probe measurements, and (3) a gradual process of irreversible degradation of the nonlinear I-V behavior with respect to thermal runaways upon application of a dc bias across isolated grain boundaries. [ABSTRACT FROM AUTHOR]

The frequency-dependent impedance/dielectric behavior of the brick-layer model (BLM) was investigated vs. grain size and local parameters (resistivity, dielectric constant, and grain boundary width). The simulation shows a maximum in capacitance vs. grain size, governed by the grain boundary-to-grain interior resistivity ratio. The BLM was employed to analyze the 500 °C impedance behavior of polycrystalline cerium dioxide from the nano- (∼15 nm grain size) to the micro- (∼4 μm grain size) regime. The grain boundary resistivity is orders of magnitude larger than that of the grain interiors in the microcystalline specimen. This contrast is significantly smaller in the nanocrystalline specimens, suggesting enhanced conduction at grain boundaries. The limitations of the BLM for simulating the behavior of complex electroceramic microstructures are discussed. [ABSTRACT FROM AUTHOR]

Zirconium oxides were deposited using plasma-enhanced atomic layer deposition (PEALD) involving (2-(N-methylamino)1-MethylEthyleneCyclopentadienyl)Bis(DiMethylAmino)Zr (abbreviated as CMEN-Zr) and oxygen plasma as zirconium and oxygen sources. The zirconium oxide thin films demonstrate temperature-independent growth rates per cycle of 0.94 A/cycle at 150–215 °C. The deposited ZrO2 thin films were characterized using numerous analytical tools, i.e., X-ray photoelectron spectroscopy for chemical bonding state and composition, X-ray diffraction for crystallinity, atomic force microscopy for surface morphology, field-emission scanning electron microscopy for cross-sectional analysis, spectroscopic ellipsometry and UV–visible spectrophotometry for optical characterization, capacitance–voltage measurements for dielectric constants and atomic defects, and current–voltage characteristics for electrical information. The insulating features of the crystalline and stoichiometric ZrO2 films were implemented in the anode composites to evaluate the influence of ALD-based nano-features on the electrochemical performance of solid oxide fuel cells, with the main emphasis on anode performance. The presence of nanomaterials on Ni/YSZ anode composites is analyzed to determine the negative effects on electrochemical performance and the degradation of cell performance of solid oxide fuel cells (SOFCs). The artificial design was proven to be effective in controlling the cell performance as long as proper material design was adopted in SOFC electrodes. [ABSTRACT FROM AUTHOR]

In this work, loess-based materials were designed based on a multicomponent composite materials system for ecofriendly natural three-dimensional (3D) printing involving quick lime, gypsum, and water. The 3D printing process was monitored as a function of gypsum content; in terms of mechanical strength and electrical resistance, in the cube-shaped bulk form. After initial optimization, the 3D printing composition was refined to provide improved printability in a 3D printing system. The optimal 3D fabrication allowed for reproducible printing of rectangular columns and cubes. The development of 3D printing materials was scrutinized using a multitude of physicochemical probing tools, including X-ray diffraction for phase identification, impedance spectroscopy to monitor setting behaviors, and mercury intrusion porosimetry to extract the pore structure of loess-based composite materials. Additionally, the setting behavior in the loess-based composite materials was analyzed by investigating the formation of gypsum hydrates induced by chemical reaction between quick lime and water. This setting reaction provides reasonable mechanical strength that is sufficient to print loess-based pastes via 3D printing. Such mechanical strength allows utilization of robotic 3D printing applications that can be used to fabricate ecofriendly structures. [ABSTRACT FROM AUTHOR]

• Fracture tests under monotonic and cyclic loading are performed using compact tension specimens. • Two materials, SA508 Gr. 1a and TP316, are considered. • Crack growth is simulated via the ABAQUS debonding option simulate. • Suitable hardening models under monotonic and cyclic loading are found. • The effect of the loading mode on crack tip deformation and stress fields are discussed. In this paper, experiment and FE analyses are performed to investigate crack tip deformation and stress fields under monotonic and large amplitude cyclic loading. Fracture tests using C(T) specimens made of SA508 Gr.1a and TP316 are performed under monotonic and cyclic loading. Using the debonding analysis, it is found that the isotropic hardening model is relevant for monotonic loading, the kinematic hardening for SA508 Gr.1a under cyclic loading, and the Chaboche combined hardening for TP316 under cyclic loading. Using the relevant hardening model, crack tip deformation and stress fields at crack initiation and growth are presented. [ABSTRACT FROM AUTHOR]