Search

It is of great significance to study the damage and fracture mechanism of trigonometrically symmetric eutectic multiphase ceramics with excellent mechanical properties at room temperature and high temperature. According to the microstructure characteristics of inner triangular symmetric eutectic in multiphase ceramics, a two-scale cell model containing triangular symmetric eutectic was established. The fracture stress of cohesive bond in eutectic was calculated by considering the conditions of cohesive bond fracture at interface phase and fiber junction. The damage variable was introduced and combined with cohesive bond fracture stress to establish the microcosmic damage fracture stress model of eutectic Based on the Dugdale Barenblatt model, the damage localization band model is established by introducing the micro damage fracture stress as the residual strength. It is found that with the increase of fiber volume fraction, the strong confinement of interface phase is destroyed, the residual strength decreases and the length of damage localization band increases with the increase of fiber volume fraction. Reducing the damage degree and selecting the appropriate fiber volume content can increase the fracture stress of eutectic, and then reduce the length of damage localization band, increase the threshold value of crack instability propagation, and enhance the material strength.

Aimed to evaluate the coexistence of bacterial and fungal diversity and their correlation with enzymatic activity in response to biochar. This study performed aerobic composting based on typical agricultural wastes of sheep manure with additive apple tree branch biochar at distinct concentration (0, 2.5, 5, 7.5, 10 and 12.5% corresponding from T1 to T6). The result demonstrated that appropriate amendment of biochar enriched bacterial diversity (1646-1686 OTUs) but interestingly decreased fungal diversity (542-630 OTUs) compared to control (1444 and 682 OTUs). Biochar addition enhanced all enzymatic activities and its correlation with bacterial was more complex than fungal community (786 and 359 connect edges). The dominant microbes comprised of Firmicutes (45.2-35.2%), Proteobacteria (14.0-17.5%), Basidiomycota (32.4-49.5%) and Ascomycota (11.3-37.5%) among all the treatments. Overall, biochar regulates the composting microenvironment by influencing the microbial diversity and associated enzymatic activities.

Blueberry (Vaccinium spp.) is one of the five major healthy foods for humans and is recognized as the "king of the world fruit", which has attracted great interest in the phytogenic prebiotics market. Blueberry fruit is favored for its delicious taste and its various functional ingredients (organic acids, phenolics, minerals and vitamins) with multitherapeutic value (antioxidant, anti-inflammatory, anticancer, neuroprotective and vision improvement properties). However, fresh blueberries are highly perishable since they are vulnerable to mechanical damage and microbial decay, resulting in a short shelf life and inevitable subsequent economic losses. Due to the strong seasonal availability and limited storage period of blueberries, their derived bioactive products have emerged as functional foods. Novel food developments that are currently available include blueberry fruit juice, wine, vinegar, jam, dried fruit, pulp powder, colorant and flavoring additives used in cake, biscuit, bread, yogurt, and jelly. This review systematically describes the current status of blueberry fruit as bioactive ingredients and valuable food products with greater nutraceutical health potential of blueberries.

The grass-waste management model affects soil organic carbon (SOC) and the microorganism community structure; however, studies on the relationship between the fungal community structure and the SOC chemical component at the aggregate level are poor. Solid-state 13C NMR and 18 S rDNA methods were used to evaluate the relationship between the SOC chemical composition and fungal community abundance at the aggregate level. Grass mulching significantly increased the percentage of labile carbon O-alkyl C (5.19%–11.79%) and decreased the instability of SOC (1.38–0.69). Microaggregates contained higher alkyl C (33.77%) and lower aromatic C (18.31%), and the A/O-A ratio (1.03) was higher than that of macroaggregates (0.89–0.96). Ascomycota, Basidiomycota and Mortierellomycota dominated the fungal community at the phylum level, and their abundance increased after grass mulching. Microaggregates supported more microbial diversity and richness and were rich in the Ascomycota (36.69%–67.49%) phylum, while LM aggregates were rich in Basidiomycota (5.62%–39.84%). We proved that changes in the O-alkyl C, carbonyl C, aromatic C and alkyl C of SOC chemical components were closely connected to fungal community composition, which together explained the change in fungal composition by 63.81%–71.99% among aggregates. We concluded that alterations in the chemical form of organic carbon were closely related to a change in the soil fungal community. This connection has a positive impact on soil nutrient utilization and SOC conversion in fruit-grass composite ecosystems and promotes the understanding of the relationship between the soil microbial community and nutrient cycling during long-term grass waste utilization.

Eutectic composite ceramics has a wide range of applications in the aerospace industry due to its excellent mechanical properties. The rupture stress of the materials is a subject of considerable importance. Eutectic composite ceramics primarily consist of rod-shaped crystals, with a small amount of particles and preexisting defects dispersed throughout. Aligned nano-micron fibers are embedded within the rod-shaped crystals. Rupture stress of a eutectic composite ceramic depends on its fracture surface energy and preexisting defects. In this study, the equivalent fracture surface energy of a eutectic ceramic composite was calculated based on its additional fracture work. Next, the effects of the preexisting defects were considered. Then, a micromechanical model of the eutectic composite ceramic was established based on its microstructural characteristics. The defects were assumed to be lamellar, and the surrounding matrix was assumed to be transversely isotropic. Using this information, the rupture stress of the eutectic ceramic composite was predicted. A comparison of the theoretical and experimental results indicated that the predicted rupture stresses corresponded with the tested data.

Based on the microscopic characteristics of fiber reinforced composite ceramics, the slippage stress at the interface of composite ceramics under external loading is analyzed. The relation between the applied strain of the triangular symmetrical eutectic and the load of composite ceramics is confirmed. And the maximum shear stress that the triangular symmetrical eutectic can endure is computed. The yield shear stress was calculated by the hardness and fracture toughness of composite ceramics. When the maximum shear stress which the triangular symmetrical eutectic can bear is equal to the yield shear stress, the slipping stress of micro-mechanical interface in composite ceramics is obtained. The results showed that fiber inclusions in the eutectic having smaller dimension and larger volume content would provide larger partial plastic deformation of composite ceramics.

Study of damage and fracture models to analyze the fracture mechanism of eutectic composite ceramics is of considerable importance because no accurate fracture models are available for these materials. Eutectic composite ceramics are composed of microcells with random direction. We present herein a model that predicts the damage and fracture of eutectic composite ceramics based on analysis of defect stability and the damage localization band. Firstly, given the microstructure of eutectic composite ceramics, a mesodomain and a microcell model are constructed. The local stress field in the mesodomain is then analyzed based on the interaction direct derivative estimate. Secondly, the stability of a defect around particles in a microcell is analyzed, and the stress intensity factor of an annular defect under the applied stress field and the residual stress field in the particle are calculated. The stress intensity factor of a defect is controlled by the residual stress when the defect extension is small. However, it is controlled by the applied stress when the defect extension is large. Finally, a model for the damage localization band at the crack tip is constructed based on the Dugdale–Barenblatt model. The residual intensity is the important factor affecting the length of the damage localization band. When the damage variables reach their largest value, the residual intensity and the length of the damage localization band attain their minimum value. This work provides the theoretical basis for further study of the damage mechanics of eutectic composite ceramics and guides the engineering applications of these materials.

A mechanical model for the strength prediction of composite ceramics (CC) with nano-interface and micro-interface is presented based on nano-interface damage mechanism and micro-interface damage me...

Analysis of the effective properties and elastic stress field in two-scale composite ceramics as mechanical properties analyzer can be a daunting task to handle. Here, we address the most prominent hurdles, namely, the complex structure characteristics of dual-scale multiphase ceramics. We propose two-scale matrix-inclusion model and conducts the mechanical properties analysis of two types of scale interfaces to improve calculation accuracy. Our model estimates the different field at the nano-interface under different applied loadings, along with the considering on continuous condition of stress and displacement at nano-interface and the condition of far-field stress-strain. We show how to solve the problem of solving the elastic field of a thin interface layer into a problem of solving the incompletely combined interface elastic field under different conditions, analyzing the slip stress field of the meso-contact interface under longitudinal and transverse shear.

The damage evolution of microcracks that dispersed in eutectic composite ceramics is an important factor leading to fracture failure. We propose a meso damage model (CMMC), which uses our proposed two-scale cellular model with microcracks, and fully considers the characteristics of the microstructure on the eutectic composite ceramics, thus providing a more objective structural modeling. In addition, there are two significant features existing in CMMC: One is to use the interaction direct derivative (IDD) estimate method to calculate the additional flexibility increment caused by a single open elliptical microcrack, which considers the spatial orientation of the microcrack. The other is that the additional flexibility tensor from the microcrack system is obtained by introducing probability density function and selecting appropriate microcrack growth criteria. Experiments on the related datasets show that CMMC achieves the consistent results compared with the experimental data. Furthermore, the effects of microcrack aspect ratio and microstructure parameters on the effective properties of multiphase ceramics were analyzed by using numerical method.

Purpose According to the microstructural characteristics of composite ceramic, the strain field distribution regularity of triangular symmetrical composite eutectic is obtained from the stress field distribution regularity of three-phase element in composite ceramic. In allusion to the damage of composite eutectic, it is introduced as a variable in this paper with the aim to determine the strain field distribution regularity of triangular symmetrical composite eutectic with damage behavior. Design/methodology/approach On the basis of the relationship between strain field and fiber inclusions volume fraction, the strain field of composite eutectic is analyzed. Findings The strain field of composite ceramic is distinctly dependent on the fiber inclusions volume fraction, fiber diameter and damage behavior of composite eutectic by quantitative analysis. The strain in matrix parallel to eutectic is the maximum linear strain and the main factor for the damage and fracture of eutectics. Originality/value The foundation of the strength research of composite eutectic is laid.

Purpose This paper aims to promote a strength model for TiC-TiB2 composite ceramic with non-ellipsoidal particles bridging. Based on the microstructure of TiC-TiB2 composite ceramic, equivalent average residual stress under particles interaction is calculated with the interact direct derivative estimate. Supposing the crack opening displacement keeps ellipsoidal under the TiB2 particles bridging, crack growth resistance curve is obtained. Design/methodology/approach Composite strength under R-cure with crack unstable propagation is calculated. Based on this model, influences of particles volume fraction, shape, size and other parameters on strength are analyzed. Findings Results indicated that calculated values are consistent to the tested data. Crack growth resistance increases with crack propagation and TiB2 volume fraction. The TiB2 particle does not pull-out entirely even ceramic fracture. Ceramic strength increases with the TiB2 particle volume fraction, the ratio of platelet diameter and thickness, and it reduces with particle thickness. Originality/value Supposing the crack open displacement keeps ellipsoidal under the TiB2 particles bridging, crack growth resistance curve is obtained.

Composite ceramic has the excellent properties at normal and high temperatures, especially when the structure of the composite eutectic is triangular symmetrical. Obviously, mechanical behavior and fracture properties of composite ceramic closely relates to the micro-structure of symmetrical triangular eutectic. In order to reveal the mechanical properties of eutectic composite ceramic, it is necessary to determine the intrinsic strength of triangular composite eutectic. Since the fiber and matrix of triangular symmetrical composite eutectic sharing a same covalent bond, the theoretical cohesion strength of symmetrical triangular eutectic was obtained by the combination-separation displacement of intrinsic bond. Basing on micro-structure plastic deformation before fracture of composite eutectic matrix, the dislocation pile-up model of eutectic composite ceramics was established. And then intrinsic bond fracture shear stress of triangular symmetrical composite eutectic was given by using the theory of dislocation pile-up. According to the macroscopic structure properties of triangular symmetrical composite eutectic and the distribution of stress field of composite eutectic, intrinsic strength of eutectic was obtained. The results shows that intrinsic strength of triangular symmetrical composite eutectic possessed clear size-dependence and the stress decreases with the increases of the diameter of fiber inclusions.

According to isotropy of parallel fiber eutectic, the no- damage strain field in parallel fiber eutectic is obtained from the flexibility tensor of parallel fiber eutectic. Considering the damage behavior of parallel fiber eutectic, damage variables are introduced to determine the strain field of parallel fiber eutectic. The damage strains in the matrix, interphase, and fiber of parallel fiber eutectic are quantitatively analyzed. Results show that damage strains are not only associated with the fiber volume fraction of parallel fiber eutectic, but also with the damage degree., {"references":["C. Baudin, and M. H. Sayir, \"Failure Mechanisms in Directionally Solidified Alumina-titania Composite\", Key Engineering Materials, vol. 290, 2005, pp. 199–233.","A. Sayir, M. H. Berger, and C. Baudin, \"Microstructural and Mechanical Properties of Directionally Solidified Ceramic in Al2O3-Al2TiO3 Sysitems\", Ceramic Enigineering & Science Proceeding, vol. 2, 2005, pp.225–233.","J. Echigoya, \"Structure of Interface in Directionally Solidified Oxide Eutectic Sysitems\", Jouenal of the European Ceramics Society, vol. 8, 2005, pp. 1381–1387.","A. Sayir, S. C. Farmer, \"The Effect of the Microstructure on Mechanical Properties of Directionally Solidified Al2O3/ZrO2(Y2O3) Eutectic\", Acta mater., vol. 48, 2000, pp. 4691–4697.","Z. M. Zhao, L. Zhang, Y. G. Song, \"Microstructures and properties of rapidly solidified Y2O3 doped Al2O3/ZrO2 composites prepared by combustion synthesis\", Scripta Materialia, vol. 55, 2006, pp. 819–822.","J. Q. Zhang, J. Wu, S. L. Liu, \"Cyelically thermo-mechanical plasticity analysis for a broken fiber in ductile matrix composites using shear lag model\", Composites Science and Technology, vol. 62, 2002, pp. 641–654.","X. D. Zhi, J. M. Wu, F. FAN, \"Failure of single-layer reticulated cylindrical shells subjected to earthquakes\", Chinese Journal of Computational Mechanics, vol. 25, 2008, pp. 770–773.","R. Talreja, \"A conceptual framework for interpretation of MMC fatigue\", Materials Science and Engineering, vol. A200, 1995, pp. 21–28.","J. Liu, Y. M. Li, F. P. Zhang, \"Effect of strain softening on delamination tip-field in composite laminate\", Chinese Journal of Computational Mechanics, vol. 23, 2006, pp. 387–362.\n[10]\tB. F. Li, J. Zheng, X. H. Ni, \"Mechanical Properties of Composite Ceramic with Triangular Symmetrical Eutectic Colony\", Chinese Journal of Applied Mechanics, vol. 29, 2012, pp. 127–132.\n[11]\t\tX. C. Jiang, H. P. Xie, H. W. Zhou, \"Analysis of Relationship between Macroscopic Damage Variable and Mesoscopic Damage Variable of quasi-brittle Materials under Compression\", Rock and Soil Mechanics, vol. 9, 2008, pp. 2531–2536.\n[12]\tP. Maimi, and J. A. Mayugo, \"A Three-dimensional Damage Model for Transversely Isotropic Composite Laminates\", Journal of Composite Materials, vol. 42, 2008, pp. 2717–2745.\n[13]\tX.H. Ni, J. Zheng, X. Q. Liu, \"Strength Model of Eutectic Ceramic Composite\", Chinese Journal of Solid Mechanics, vol. 30, 2009, pp. 116–121.\n[14]\tT. Sun, X. H. Ni, B. H. Han, \"Analysis of damage strain field for ceramic composite with eutectic interphases\", Chinese Journal of Computational Mechanics, vol. 29, 2012, pp. 527–531.\n[15]\tX. Q. Liu, X.H. Ni, Y.T. Liu, \"Mesomechanical Strength Model of Nano-Fibers Composite Ceramics\", Solid State Phenomena, Vols. 121-123, 2007, pp. 1157–1160."]}

Strengthening and toughening mechanisms in composite ceramics is complex. A change in a single parameter induces multiple property variations. The multiple changes in properties are often incompletely represented in theoretical models. This incompleteness in the parameter chosen fails to explain the mechanism of failure in composite ceramics. The exponential toughness function is used to represent the pull-out toughening mechanism, which dominates the crack growth resistance curve(R-curve). The strengthening-toughening model is established based on the Mori-Tanaka method(M-T method). The influence of inherent defects on toughness function and strength is analyzed by using this model. The theoretical result is compared with the experiment data. This model exactly reflects the change in strength. The theoretical result indicates that defects change the toughness function. Moreover, micro-cracks increase toughness size a c, and the strength of crack instable extensions acutely decreases as defect content increases. This presented model establishes the relationship among the important mechanical parameters of defect, strength, elastic modulus, and the R-curve.