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Self-healing ceramic composites are promising smart materials for high-temperature applications. Experimental and numerical studies have been performed to more fully understand their behaviors, and kinetic parameters such as the activation energy and frequency factor have been reported to be indispensable for investigating healing phenomena. This article proposes a method of determining the kinetic parameters of self-healing ceramic composites using the oxidation kinetics model of strength recovery. These parameters are determined by an optimization method using experimental strength recovery data under various healing temperatures, times, and microstructural features on the fractured surfaces. Alumina and mullite matrix-based self-healing ceramic composites such as Al2O3/SiC, Al2O3/TiC, Al2O3/Ti2AlC (MAX phase), and mullite/SiC, were selected as the target materials. The theoretical strength recovery behaviors of the cracked specimens obtained from the kinetic parameters were compared with the experimental results. The parameters were within the previously reported ranges, and the predicted strength recovery behaviors reasonably agreed with the experimental values. The proposed method can also be applied to other self-healing ceramics with matrices reinforced with different healing agents to evaluate oxidation rate, crack healing rate, and theoretical strength recovery behaviors to design self-healing materials used in high-temperature applications. Furthermore, the healing ability of composites can be discussed regardless of the type of strength recovery test.

Bones of humans and animals combine two unique features, namely: they are brittle yet have a very high fracture toughness linked to the tortuosity of the crack path and they have the ability to repeatedly heal local fissures such that full recovery of overall mechanical properties is obtained even if the local bone structure is irreversibly changed by the healing process. Here it is demonstrated that Ti 2 AlC MAX phase metallo-ceramics also having a bone-like hierarchical microstructure and also failing along zig-zag fracture surfaces similarly demonstrate repeated full strength and toughness recovery at room temperature, even though the (high temperature) healing reaction involves the local formation of dense and brittle alumina within the crack. Full recovery of the fracture toughness depends on the healed zone thickness and process zone size formed in the alumina reaction product. A 3-dimensional finite element method (FEM) analysis of the data obtained from a newly designed wedge splitting test allowed full extraction of the local fracture properties of the healed cracks.

Self-healing materials have been recognized as a promising type of next-generation materials. Among them, self-healing ceramics play a particularly important role, and understanding them better is necessary. Therefore, in this study, we applied the oxidation kinetics-based constitutive model to finite element analysis of a series of damage-healing processes in self-healing ceramics (alumina/SiC composites). In the finite element analysis, the data on the microstructure distribution, such as relative density, size and aspect ratio of pores, and grain size, were taken as input values and reflected onto the parameters of a continuum damage model using a fracture mechanical model. We then performed a 3-point bending analysis, to consider both the self-healing effect under certain temperature and oxygen partial pressure conditions and scatter of the strength of the ceramics. Our results confirmed that the proposed methodology can reasonably reproduce both strength recovery and damage propagation behavior in self-healing ceramics.

The most prominent effect of the weakest link theory, which is used to derive the Weibull statistics of ceramic strength, is the size effect. In this study, we analyze the size effect on ceramic strength using the finite element analysis (FEA) methodology previously proposed by the authors. In the FEA methodology, the data of the microstructure distribution (i.e., relative density, size, and aspect ratio of the pore and the grain size) are considered as input parameters of a continuum damage model via a fracture mechanical model. Specifically, we examine five sizes of rectangular specimens under three types of loading conditions. Then, we simulate the fracture stresses of sets of 30 specimens under each size and loading condition and obtain the relationship between the scale parameter and effective volume using the Weibull distribution. The results suggest that the proposed FEA methodology can be applied to the analysis of the fracture probability of ceramics, including the size effect.

Adhesion is one of essences with respect to rubber friction because the magnitude of the friction force is closely related to the magnitude of adhesion on a real contact area. However, the real contact area during sliding depends on the state and history of the contact surface. Therefore, the friction force occasionally exhibits rate-, state-, and pressure dependency. In this study, to rationally describe friction and simulate boundary value problems, a rate-, state-, and pressure-dependent friction model based on the elastoplastic theory was formulated. First, the evolution law for the friction coefficient was prescribed. Next, a nonlinear sliding surface (frictional criterion) was adopted, and several other evolution laws for internal state variables were prescribed. Subsequently, the typical response characteristics of the proposed friction model were demonstrated, and its validity was verified by comparing the obtained results with those of experiments conducted considering the contact surface between a rough rubber hemisphere and smooth acrylic plate.

We propose a new theoretical kinetic model of strength recovery by oxidation-induced self-healing of surface cracks in composites containing a healing agent (HA). The kinetics is a key parameter in the design of structural components that can self-heal the damage done in service. Based on three-dimensional (3D) observations of crack-gap filling, two crack-gap filling models, i.e., a bridging model and a tip-to-mouth filling model, are incorporated in the proposed kinetic model. These crack-gap filling models account for the microstructural features of the fracture surfaces, crack geometry, and oxidation kinetics of the healing-agent. Hence, the minimum and maximum remaining flaw sizes in the healed crack gaps are estimated for various healing temperatures, times, and oxygen partial pressure conditions. Further, the nonlinear elastic fracture mechanics suitable for small-sized remaining flaws, together with a statistical analysis of the original Weibull-type strength distribution, enables the prediction of upper and lower strength limits of the healed composites. Three sintered alumina matrix composites containing silicon carbide (SiC)-type HAs with various volume fractions and shapes, together with monolithic SiC ceramics, are considered. The strength of the healed-composite predicted by our model agrees well with the experimental values. This theoretical approach can be applied to HAs other than SiC and enables the design of self-healing ceramic components for various applications.

The evaluation of the R‐curve behavior of ceramics, which is characterized by an increase in crack resistance with crack propagation, is crucial for advancing their implementation in engineering applications that require high reliability. In this study, we investigated the applicability of a finite element analysis (FEA) approach that implements a continuum damage model embedded with a cohesive‐zone relationship to predict crack occurrence and the subsequent increase in crack resistance (toughness) of ceramics. Specifically, by employing a compliance‐based method, the R‐curve behavior was systematically examined under a bending load to assess the impacts of fracture stress and toughness on diverse chevron‐notched specimens. The output critical stress intensity factors were found to increase with the crack length, eventually converging nearly to the input fracture toughness. Subsequently, the stable crack growth behavior obtained from the FEA and experiment under a three‐point bending test of high‐purity alumina was compared. A consistent result was confirmed in the force–displacement relationships. Furthermore, the R‐curve behavior of the target material could be indirectly evaluated using the present approach. The results support the effectiveness of the present approach, highlighting the quantitative assessment of not only crack initiation but also R‐curve behavior under arbitrary boundary conditions.

Albuminuria is an important risk factor for end-stage kidney disease and cardiovascular mortality. This 1-year observational study aimed to assess the effect modification of alcohol drinking on the association between salt intake and albuminuria. Overall, 448 employees at a pharmaceutical company in Japan who underwent annual health checkups in both 2017 and 2018 were evaluated. The main exposure of interest was drinking frequency at their first checkups categorized as rarely, occasionally, and daily. To assess the association between the changes in salt intake and albuminuria, the differences in salt intake estimated from single-spot urine specimens and the urinary albumin-to-creatinine ratio (UACR) between 2017 and 2018 were calculated for each subject. A multivariable-adjusted linear regression model showed a significant association between ∆salt intake and ∆Log UACR (per 1 g/day of ∆salt intake, adjusted ß 0.16 [95% confidence interval 0.14, 0.19]) and an effect modification between drinking frequency and ∆salt intake (P for interaction = 0.088). The association between ∆salt intake and ∆Log UACR was enhanced by drinking frequency in a dose-dependent manner (per 1 g/day of ∆salt intake, adjusted ß 0.13 [0.06, 0.19], 0.16 [0.12, 0.20], and 0.20 [0.13, 0.27] in rare, occasional, and daily drinkers, respectively). In conclusion, the results of the present study indicated that salt-induced albuminuria was enhanced in subjects with higher drinking frequency, suggesting that salt restriction may have a stronger renoprotective effect in subjects with higher drinking frequency.

In futuristic vehicle traveling simulation on a rough terrain, it is desirable to perform terramechanics analysis that reflected appropriate road surface information. This paper presents a multi-stage analysis method that seamlessly performs the terrain formation process and trafficability evaluation. Simulation of wind-blown ripple formation based on cellular automaton was adopted as an example, and fields were created for terramechanics analysis. Then, trafficability characterization was performed with a single rigid wheel on virtually created terrain fields based on resistive force theory. The analysis results showed that the traveling performance of a single wheel could be evaluated for various terrain fields and under various traveling conditions. The multi-stage analysis method presented in this paper can be employed for simulations in extreme environments such as planetary surfaces, deserts, and disaster sites, where sensing is difficult.

Alcohol consumption is one of the major modifiable risk factors of hypertension. The aim of the present retrospective study was to assess the clinical impact of obesity on the association between alcohol consumption and the incidence of hypertension. The present study included 5116 male and 6077 female university employees with a median age of 32 (interquartile range 27–39) who underwent annual health checkups between January 2005 and March 2013. Self-reported drinking frequency was recorded at their first checkup and categorized into rarely and 1–3, 4–6, and 7 days/week. During the median observational period of 4.9 years (interquartile range 2.1–8.3), hypertension, defined as systolic/diastolic blood pressure of ≥140/90 mmHg and/or self-reported treatment for hypertension, was observed in 1067 (20.9%) men and 384 (6.3%) women. Poisson regression models adjusted for clinically relevant factors revealed a dose-dependent association between drinking frequency and the incidence of hypertension in men (adjusted incidence rate ratio [95% confidence interval] of men who drank rarely, 1–3, 4–6, and 7 days/week was 1.00 [reference], 1.12 [0.97–1.30], 1.42 [1.19–1.70], and 1.35 [1.14–1.59], respectively; Ptrend < 0.001). However, this association was not observed in women. The dose-dependent association was significant in nonobese men (body mass index (BMI) < 25 kg/m2), but not in obese men (BMI ≥25 kg/m2) (P for interaction between drinking frequency and BMI = 0.072). The present study provides clinically useful evidence to identify the drinkers who may reap the health benefits of abstinence from alcohol consumption.