Time-dependence of rock deformation and fracturing is often ignored.However,the consideration of the time-dependence is essential to the study of the deformation and fracturing processes of materials,especially for th...Time-dependence of rock deformation and fracturing is often ignored.However,the consideration of the time-dependence is essential to the study of the deformation and fracturing processes of materials,especially for those subject to strong dynamic loadings.In this paper,we investigate the deformation and fracturing of rocks,its physical origin at the microscopic scale,as well as the mechanisms of the time-dependence of rock strength.Using the thermo-activated and macro-viscous mechanisms,we explained the sensitivity of rock strength to strain rate.These mechanisms dominate the rock strength in different ranges of strain rates.It is also shown that a strain-rate dependent Mohr-Coulomb-type constitutive relationship can be used to describe the influence of strain rate on dynamic rock fragmentation.A relationship between the particle sizes of fractured rocks and the strain rate is also proposed.Several time-dependent fracture criteria are discussed,and their intrinsic relations are discussed.Finally,the application of dynamic strength theories is discussed.展开更多
Time-dependent contact angles were measured by depositing sessile drops of wa-ter on the polymer surfaces and monitoring the drop shape as a function of time. It was found that contact angles decreased sharply with co...Time-dependent contact angles were measured by depositing sessile drops of wa-ter on the polymer surfaces and monitoring the drop shape as a function of time. It was found that contact angles decreased sharply with contact time and the equilibrium contact angle was finally attained after a certain time. Values of starting (θ s) and equilibrium contact angles (θ e) obtained by the sessile drop method depend on polymer properties. The Wilhelmy plate technique was used to measure advancing and receding contact angles. The variations of starting (θ s) and equilibrium contact angles (θ e), advancing (θ a) and receding contact angles (θ r) have been studied on the oxidized surface of polymers containing polybutadiene block to explore the cause of time-dependence in contact angle measurement and the meaning of θ s and θ e. The results showed the linear relationships between starting (θ s) and advancing contact angles (θ a), the equilibrium (θ e) and receding contact angles (θ r). The similar relationship was also established between the contact angle hysteresis (θ a?θ r) and differences (θ s ?θ e) in starting contact angles and equilibrium contact angles. Therefore, time-dependence in contact angle measurement was mainly attributed to the surface reconstruction when water drops were deposited on polymer surfaces. The starting contact angle was contributed by the hydrophobic component on polymer surface and the equilibrium contact angle mainly by the hydrophilic component of polymer. These results not only demonstrated the interdependency between two contact angle measurements, the sessile drop method and the Wilhelmy plate technique, but also provided the experimental evidence to explain the cause of time-dependent contact angle. This may also provide a new method to study dynamic behavior of polymer surface.展开更多
基金Supported by the National Science Foundation of China (50825403)the Beijing Natural Science Foundation of China (KZ200810016007)
文摘Time-dependence of rock deformation and fracturing is often ignored.However,the consideration of the time-dependence is essential to the study of the deformation and fracturing processes of materials,especially for those subject to strong dynamic loadings.In this paper,we investigate the deformation and fracturing of rocks,its physical origin at the microscopic scale,as well as the mechanisms of the time-dependence of rock strength.Using the thermo-activated and macro-viscous mechanisms,we explained the sensitivity of rock strength to strain rate.These mechanisms dominate the rock strength in different ranges of strain rates.It is also shown that a strain-rate dependent Mohr-Coulomb-type constitutive relationship can be used to describe the influence of strain rate on dynamic rock fragmentation.A relationship between the particle sizes of fractured rocks and the strain rate is also proposed.Several time-dependent fracture criteria are discussed,and their intrinsic relations are discussed.Finally,the application of dynamic strength theories is discussed.
文摘增塑剂(plasticizers,PLAs)是工业生产中广泛使用的高分子材料助剂,伴随着主产品的使用而进入环境中,很可能会对环境中的生物甚至人类的健康产生危害。因此,以3种常见的PLAs:双酚A(bisphenol A,BPA)、双酚S(bisphenol S,BPS)和三丁氧基乙基磷酸酯(tris(2-butoxyethyl)phosphate,TBEP)为研究对象,运用直接均分和均匀设计射线法分别设计二元和三元混合物体系,应用时间微板毒性分析方法系统测定3种污染物及其混合物体系对淡水发光菌青海弧菌(Vibrio qinghaiensis sp.-Q67,Q67)的毒性,应用浓度加和(concentration addition,CA)分析混合物的毒性相互作用,采用绝对残差(deviation from CA model,dCA)定量评估毒性相互作用强度,并结合热图法分析相互作用强度变化规律。采用电镜扫描分析Q67细胞形态,二苯胺显色法和考马斯亮蓝法测定Q67细胞的DNA和可溶性蛋白质大分子的泄露情况来探究3种PLAs及其混合物可能的毒性作用机理。结果表明,BPA、BPS、TBEP对Q67均具有明显的急性毒性,且急性毒性均大于长期毒性;以半数效应浓度负对数值为毒性指标,3种PLAs在同一暴露时间的毒性顺序:BPA>BPS>TBEP;混合物体系BPA-BPS呈现协同作用,而BPS-TBEP、BPA-TBEP、BPA-BPS-TBEP呈现拮抗作用,且相互作用强度均受暴露时间和混合物浓度的影响;BPA-BPS-R4射线的协同作用强度最强,dCA绝对值为0.411,BPA-BPS-TBEP-R1射线的拮抗作用最明显,dCA绝对值为0.670;3种PLAs及其混合物对Q67的作用主要通过破坏细胞的结构和形态,使其DNA和可溶性蛋白质大量流失,造成细胞大量死亡。
基金supported by the Natural Science Foundation of Zhejiang Province(Grant No.Z503201)Education Committee of Zhejiang Province(Grant No.20031164)
文摘Time-dependent contact angles were measured by depositing sessile drops of wa-ter on the polymer surfaces and monitoring the drop shape as a function of time. It was found that contact angles decreased sharply with contact time and the equilibrium contact angle was finally attained after a certain time. Values of starting (θ s) and equilibrium contact angles (θ e) obtained by the sessile drop method depend on polymer properties. The Wilhelmy plate technique was used to measure advancing and receding contact angles. The variations of starting (θ s) and equilibrium contact angles (θ e), advancing (θ a) and receding contact angles (θ r) have been studied on the oxidized surface of polymers containing polybutadiene block to explore the cause of time-dependence in contact angle measurement and the meaning of θ s and θ e. The results showed the linear relationships between starting (θ s) and advancing contact angles (θ a), the equilibrium (θ e) and receding contact angles (θ r). The similar relationship was also established between the contact angle hysteresis (θ a?θ r) and differences (θ s ?θ e) in starting contact angles and equilibrium contact angles. Therefore, time-dependence in contact angle measurement was mainly attributed to the surface reconstruction when water drops were deposited on polymer surfaces. The starting contact angle was contributed by the hydrophobic component on polymer surface and the equilibrium contact angle mainly by the hydrophilic component of polymer. These results not only demonstrated the interdependency between two contact angle measurements, the sessile drop method and the Wilhelmy plate technique, but also provided the experimental evidence to explain the cause of time-dependent contact angle. This may also provide a new method to study dynamic behavior of polymer surface.
