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1.
In multi-seam mining, the interlayer rock strata between the upper coal seam(UCS) and the lower coal seam(LCS) appear damage and strength weakening after mining the UCS. Ground stability control of the gob-side entry retaining(GER) under the gob with close distance coal seams(CDCS) is faced with difficulties due to little attention to GER under this condition. This paper focuses on surrounding rock stability control and technical parameters design for GER under the gob with CDCS. The floor rock strata damage characteristics after mining the UCS is first evaluated and the damage factor of the interlayer rock strata below the UCS is also determined. Then, a structural mechanics model of GER surrounding rock is set up to obtain the main design parameters of the side-roadway backfill body(SBB) including the maximum and minimum SBB width calculation formula. The optimal SBB width and the water-to-cement ratio of high water quick-setting material(HWQM) to construct the SBB are determined as 1.2 m and 1.5:1.0,respectively. Finally, engineering trial tests of GER are successfully carried out at #5210 track transportation roadway of Xingwu Colliery. Research results can guide GER design under similar mining and geological conditions.  相似文献   
2.
In present paper, a new model is proposed and embedded into the finite element software ABAQUS to estimate the time dependent failure probability of the solid oxide fuel cell stack. The results show that sealant is the potential failure region of the solid oxide fuel cell stack, while the failure probability of the anode, electrolyte and cathode are very small within the operation time of 50,000 h. The creep and damage distribution of the components reflect that the proposed model can reasonably predict the time dependent failure probability of the solid oxide fuel cell stack. Increasing either the characteristic strain, Weibull modulus or decreasing the operating temperature can decrease the failure probability of the SOFC stack. For the sealant, to ensure the high temperature integrity of the SOFC stack, the characteristic strain should be larger than 0.01 or Weibull modulus should be higher than 8.0 under the operating temperature of 600 °C.  相似文献   
3.
本文针对准东矿区巨厚煤层典型赋存特征,以大井矿区为研究对象,通过识别覆岩关键层及含水层,采用UDEC数值模拟方法,建立大井矿区巨厚煤层开采覆岩力学模型,对不同开采方法覆岩含水层破坏进行了模拟研究。结果表明:研究区覆岩关键层分为4层、覆岩含水层共2层;开采厚度相同时,大采高开采覆岩下沉量、裂隙带发育高度及开采对含水层的扰动影响均大于放顶煤开采;采高24m,推进长度为300m时,导水裂隙已发育至含水层Ⅱ;主关键层对覆岩位移、裂隙分布及开采对含水层的扰动影响起关键作用。  相似文献   
4.
The toughening mechanism in continuous fiber toughened ZrB2-SiC ceramic matrix (Cf/ZrB2-SiC) composites was studied upon introduction of pyrolytic carbon coating at the fiber/matrix interface. The real-time deformation behavior, surface crack initiation and evolution of Cf/ZrB2-SiC composites under tensile load were studied using in-situ scanning electron microscopy (SEM) to determine the typical damage modes and toughening mechanisms. A refined microscopic representative volume element (RVE) inserting the cohesive zone elements was established to study the PyC interface layer damage by using finite element method. It was found that PyC interface layer damage induced by thermal residual stress (TRS) was one of critical factors affecting the mechanical performance of the Cf/ZrB2-SiC composites. The critical thickness of the interface layer was also further determined by analyzing the effect of interface layer thickness on the distribution of TRS, which can guide the design of PyC interface layer for manufacturing the Cf/ZrB2-SiC composites.  相似文献   
5.
In the aim of providing a reliable technique to monitor the development of damage in 0°/90° melt-infiltrated SiC-fiber reinforced prepreg laminate ceramic-matrix composites, it was hypothesized that the electrical resistivities of different layers of this material were significantly different due to their free Si content and morphology. Three distinct layers: a 0° fiber ply, a 90° fiber ply and a matrix only ply, were distinguished in the composite architecture. Free silicon is the most conductive phase in this composite system; however, the Si content and morphology were different in each of the three types of plies. Unidirectional and [0°/90°]2s specimens enabled quantification of ply-level resistivities. An electric circuit model was constructed; it consists of parallel resistors where each resistor represents a ply in the composite system. This ply-level electrical model was validated using composites of different vintages which contained different silicon contents. A room temperature stepped fatigue test was conducted and the ply level circuit model was used to discern crack morphology with the support of acoustic emission and digital image correlation.  相似文献   
6.
The fuel cell gas diffusion media (GDM) is a highly porous carbon-fiber-reinforced thin composite layer. The experimental response of these materials is observed to be highly nonlinear at low-stress levels. The cyclic mechanical response of GDM is investigated in terms of stiffness and damage parameters. The prediction of the state of deformation in GDM is vital in relating GDM's properties to ohmic and transport losses. To this end, a compressible form of the phenomenological model is proposed to capture the experimental cyclic response accurately. The model is constituent dependent; that is, the cumulative cyclic stress-strain response of GDM is a function of individual constituent phases present in the material. These individual constituents are porous matrix and reinforced fibers. The model hence derived for a typical GDM material, can predict residual strain, hysteresis, and damage quotient associated with the stress softening. This advanced model is implemented in the numerical domain to evaluate the response of the polymer electrolyte fuel cell (PEFC) unit cell. The stress-strain distribution fields are analyzed and compared with those of conventional GDM models. The results point to a remarkable deviation from the conventional notion of structural analysis.  相似文献   
7.
Various damage detection methods have been proposed by several researchers in the past few decades. Amongst them, the efficiency of mode shapes in detecting damage has been demonstrated by many researchers when further processed. In most cases, the processing involves expansion or reduction of the mode shape data. However, vital information that are damage-prints are often lost during processing of the mode shape data. In addition, most of these processes involve long and complex computation, thus, leading to inaccurate damage identification. In this study, a simple and fast damage identification technique is proposed to identify damage in beam structures. Interval analysis is applied to the mode shapes of a beam structure in the damaged and undamaged states. The interval situations of each of the beam's segment via mode shape are derived to obtain the upper and lower bounds and the derived bounds are compared. To establish a relationship for identify the damaged point, a possibility of damage existence is defined for each segment of the beam structure. The mode shape increment is defined as the increase in the mode shape value. Furthermore, a damage measure index that provide enhance damage information is obtained as the product of the possibility of damage existence and mode shape increment. A numerical model of a simply supported steel beam is applied to demonstrate this method by imposing damage through thickness reduction of elements in segments. In addition, a parametric analysis is carried out to evaluate noise effect by considering varying damage severities and different noise levels. The results showed that this method is simple and provides considerable accurate results.  相似文献   
8.
为得到不同配比下某铜矿尾砂胶结充填体的动力学特性及损伤度,对灰砂比分别为1∶4、1∶6、1∶8和1∶10,质量浓度为72%的充填体试件开展了相似加载应变率下的常规单轴冲击试验。结果表明:1)加载应变率为30s-1,灰砂比为1∶4和1∶6的试件内部胶结力较强,受到冲击荷载后残余强度较高,仅在边缘处出现少量层状剥落,相同条件下灰砂比为1∶8、1∶10的试件破坏后多以粉质与劈裂柱状体的形式存在,基本丧失原有强度。2)灰砂比为1∶4、1∶6、1∶8和1∶10所对应的损伤值d分别为0.238、0.258、0.443和0.476,当灰砂比由1∶6变化为1∶8时,损伤变量值增幅达171.71%,此阶段充填体整体力学性质大幅度降低,动态抗压强度降低,动弹模量减小,但破坏应变增加,充填体变形性能趋向于脆性。  相似文献   
9.
The use of hydrogen as a fuel is increasing exponentially, and the most economical way to store and transport hydrogen for fuel use is as a high-pressure gas. Polymers are widely used for hydrogen distribution and storage systems because they are chemically inert towards hydrogen. However, when exposed to high-pressure hydrogen, some hydrogen diffuses through polymers and occupies the preexisting cavities inside the material. Upon depressurization, the hydrogen trapped inside polymer cavities can cause blistering or cracking by expanding these cavities. A continuum mechanics–based deformation model was deployed to predict the stress distribution and damage propagation while the polymer undergoes depressurization after high-pressure hydrogen exposure. The effects of cavity size, cavity location, and pressure inside the cavity on damage initiation and evolution inside the polymer were studied. The stress and damage evolution in the presence of multiple cavities was also studied, because interaction among cavities alters the damage and stress field. It was found that all these factors significantly change the stress state in the polymer, resulting in different paths for damage propagation. The effect of adding carbon black filler particles and plasticizer on the damage was also studied. It was found that damage tolerance of the polymer increases drastically with the addition of carbon black fillers, but decreases with the addition of the plasticizer.  相似文献   
10.
SiCf/PyC/SiC and SiCf/BN/SiC mini-composites comprising single tow SiC fibre-reinforced SiC with chemical vapor deposited PyC or BN interface layers are fabricated. The microstructure evolutions of the mini-composite samples as the oxidation temperature increases (oxidation at 1000, 1200, 1400, and 1600?°C in air for 2?h) are observed by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction characterization methods. The damage evolution for each component of the as-fabricated SiCf/SiC composites (SiC fibre, PyC/BN interface, SiC matrix, and mesophase) is mapped as a three-dimensional (3D) image and quantified with X-ray computed tomography. The mechanical performance of the composites is investigated via tensile tests.The results reveal that tensile failure occurs after the delamination and fibre pull-out in the SiCf/PyC/SiC composites due to the volatilization of the PyC interface at high temperatures in the air environment. Meanwhile, the gaps between the fibres and matrix lead to rapid oxidation and crack propagation from the SiC matrix to SiC fibre, resulting in the failure of the SiCf/PyC/SiC composites as the oxidation temperature increases to 1600?°C. On the other hand, the oxidation products of B2O3 molten compounds (reacted from the BN interface) fill up the fracture, cracks, and voids in the SiC matrix, providing excellent strength retention at elevated oxidation temperatures. Moreover, under the protection of B2O3, the SiCf/BN/SiC mini-composites show a nearly intact microstructure of the SiC fibre, a low void growth rate from the matrix to fibre, and inhibition of new void formation and the SiO2 grain growth from room to high temperatures. This work provides guidance for predicting the service life of SiCf/PyC/SiC and SiCf/BN/SiC composite materials, and is fundamental for establishing multiscale damage models on a local scale.  相似文献   
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