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91.
92.
冻融循环作用下饱和砂岩损伤扩展模型研究 总被引:2,自引:1,他引:1
首先分析饱和砂岩所经历的冻融作用的特点,认为冻融作用是一种低周疲劳荷载,且砂岩冻融循环作用下的受力状态可简化为单向拉伸荷载的循环作用。基于以上分析,在疲劳损伤理论的基础上,建立砂岩在冻融循环作用下的损伤演化方程。同时,通过对饱和砂岩冻融循环过程中的物理性质的观测,及对砂岩自身结构特点的分析,选取砂岩的开孔隙率作为损伤变量。之后通过试验数据对所建立的损伤模型进行验证,并探讨损伤方程中各参数的确定方法。经过验证,该损伤模型能较好地反映饱和砂岩在冻融循环作用下的损伤扩展规律,可以为相关的研究提供参考。 相似文献
93.
致密砂岩油藏水驱渗流特征体现非线性渗流规律,存在启动压力梯度,且水驱过程中多孔介质会产生变形,岩石渗透率降低。通过电镜扫描试验研究致密砂岩纳米级微观孔隙特征,结合岩石颗粒分布特征,建立致密砂岩变形引起应力敏感理论模型,得到岩石介质变形系数,并与试验测试结果进行对比分析;建立考虑致密砂岩岩石变形影响的渗流数学模型,研究启动压力梯度及介质变形共同作用对油、水两相非线性渗流特征影响。算例结果表明,启动压力梯度与介质变形的耦合作用造成水驱渗流阻力增大,地层压降损失增大;介质变形系数越大,相同生产时间内原油采出程度越低,随着生产时间增加,地层压降损失幅度增大。 相似文献
94.
Oxidation of ZrB2–SiC‐Graphite Composites Under Low Oxygen Partial Pressures of 500 and 1500 Pa at 1800°C 下载免费PDF全文
Hua Jin Songhe Meng Zhang Xinghong Zeng Qingxuan Xie Weihua 《Journal of the American Ceramic Society》2016,99(7):2474-2480
The oxidation behavior of ZrB2–SiC‐graphite composites under low oxygen partial pressures of 500 and 1500 Pa at 1800°C was investigated. The phase composition and microstructure of the oxidized scale were characterized using TEM, SEM, XRD, XPS, EDS. The analytical results indicated that a low oxygen partial pressure had a remarkable effect on the oxidation mechanism of ZrB2–SiC‐graphite composites. When oxidized at 1500 Pa, the oxidation kinetics was controlled by the rate of oxygen diffusion into the composite. When the composite was oxidized at 500 Pa, control of the oxidation kinetics changed from the rate of oxygen diffusion to the rate of the oxidation reaction. The rate of oxidation decreased with decreasing oxygen partial pressure. Higher partial pressures of oxygen resulted in less oxidation resistance by the ZrB2–SiC‐graphite composites. 相似文献
95.
96.
Fracture behaviour and numerical study of resistance spot welded joints in high-strength steel sheet
Teruki Sadasue Satoshi Igi Koichi Taniguchi Rinsei Ikeda Kenji Oi 《Welding International》2016,30(8):602-613
Cross tension tests of resistance spot welded joints with varying nugget diameter were carried out using 980 MPa high strength steel sheet of 1.6 mm thickness. In proportion, as nugget diameter increased from 3√t to 5√t (where t is thickness), cross tension strength (CTS) increased while fracture morphology simultaneously transferred from interface fracture to full plug fracture. In cases of interface fracture, circumferential crack initiation due to separation of the corona bond arose at an early stage of loading. The crack opening process without propagation was recognized until just before fracture and then the crack propagated to the nugget immediately in a brittle manner around CTS. In full plug fracture, main ductile crack initiation from the notch-like part at the end of sheet separation occurred with the sub-crack initiated at an early stage. The ductile crack propagated toward the HAZ and base material to form full plug fracture. The mode I stress intensity factor was considered as a suitable fracture parameter because the circumferential crack behaved pre-crack for brittle fracture in the nugget region at the final stage. Based on the FE analysis, the mode I stress intensity factor was calculated as 116 MPa √m at CTS as fracture toughness for the nugget. With respect to full plug fracture, ductile crack initiation behaviour from the notch-like part was expressed by concentration of equivalent plastic strain. On the assumption that the ductile crack arose in critical value of equivalent plastic strain, the value was calculated as 0.34 by FE analysis. Reasonable interpretation for interface fracture and full plug fracture in the resistance spot welded joint was proposed due to first crack initiation by stress concentration, brittle fracture by using mode I stress intensity factor, and ductile crack initiation by using equivalent plastic strain. 相似文献
97.
为了了解砂岩多阶段性应力分布特征,进行了多步压剪实验,加载速率分别为0.02 kN/s、0.1 kN/s、0.5 kN/s,并同步采集全过程声发射信号。利用最大似然估计法分析了声发射能量统计分布特征,结果表明:(1)多步压剪试验的能量概率密度函数符合幂定律分布,并满足能量上的幂律无尺度分布;(2)加载阶段与恒压阶段声发射信号量相差较大,跨越能量数量级有所不同,但加载、恒压阶段的概率密度函数与整体概率密度函数具有统一性,并可以用同一个幂值来表征;(3)加载阶段与恒压阶段幂值分布具有相似性,与概率密度函数形成良好对应;(4)恒压状态下的岩石具有流变特征,声发射能量信号在小能量区间服从线性分布;(5)加载后期,由于裂纹的扩展以及成核过程岩石会发生相变,此阶段能量概率密度函数与全过程保持一致,不受之前能量信号影响。 相似文献
98.
99.
Amartya Bhattacharjee Ryan C. Hurley Lori Graham-Brady 《Journal of the American Ceramic Society》2022,105(5):3062-3080
The paper presents a numerical model to study the transition of brittle materials from a cracked solid to a granular medium under impact loading. The model addresses competitive crack coalescence in the transition regime and provides insight into the onset of comminution and the initial conditions for subsequent granular flow. Crack statistics obtained from initial flaws using a wing crack growth-based damage model have been used to discretely model elliptical cracks in three dimensions. These discrete cracks are either generated randomly in space or with a constraint that minimizes the intersection between neighboring cracks. These cracks are then allowed to coalesce with nearby cracks along with favorable directions and the output fragment statistics are predicted. A simple statistical model is proposed that suggests a transition criterion resembling the one obtained from the numerical model. Initial fragments are power-law distributed similarly to experimental observations and particle-based models. A generalized form of a microstructure-dependent granular transition criterion based on a threshold measure of crack lengths has been proposed. This model can be implemented in numerical codes to activate granular physics and calibrate the initial conditions of granular flow, such as fragment size and morphology. 相似文献
100.
Jun Chen Zhiyu Huang Dongfang Liu Ying Zhang Hanmin Li Hongsheng Lu 《Journal of surfactants and detergents》2022,25(4):527-536
In the process of the tertiary recovery of oil and gas resources, it is necessary to use external fluids to displace the crude oil in the reservoir. Whether the crude oil on the surface of the rock can be effectively displaced and the wettability of the rock can be changed to avoid re-adsorption by the crude oil is directly related to the level of oil recovery. Therefore, it is critical to study the cleaning and wettability reversal of reservoir rock surface. Because microemulsions have outstanding performance in changing the wettability of rocks and solubilizing crude oil, this paper uses cetyl trimethyl ammonium bromide (CTAB) as a surfactant and n-butanol as a co-surfactant to prepare microemulsions. The performance of microemulsions with different microstructures on the cleaning and wettability changes of crude oil on the rock surface were studied. The results show that the water-in-oil (W/O) microemulsion has good cleaning efficiency, and the oil removal rate on the sandstone core surface can reach 79.65%. In terms of changing the wettability of the rock surface, W/O, bi-continuous phase (B.C.) and oil-in-water (O/W) microemulsions can change the core surface from lipophilic to hydrophilic. And the effects of the B.C. and O/W microemulsions are more obvious. The microemulsion system that was prepared based on cationic surfactants has a good application prospect in changing the wettability of the reservoir and cleaning the adsorbed crude oil. 相似文献