We studied the dynamic fracture mechanical behavior of rock under different impact rates. The fracture experiment was a three-point bending beam subjected to different impact loads monitored using the reflected causti...We studied the dynamic fracture mechanical behavior of rock under different impact rates. The fracture experiment was a three-point bending beam subjected to different impact loads monitored using the reflected caustics method. The mechanical parameters for fracture of the three-poim bending beam specimen under impact load are analyzed. The mechanism of crack propagation is discussed. Experimental results show that the dynamic stress intensity factor increases before crack initiation. When the dynamic stress intensity factor reaches its maximum value the crack starts to develop. After crack initiation the dynamic stress intensity factor decreases rapidly and oscillates. As the impact rate increases the cracks initiate earlier, the maximum value of crack growth velocity becomes smaller and the values of dynamic stress intensity factor also vary less during crack propagation. The results provide a theoretical basis for the study of rock dynamic fracture.展开更多
点云的几何精度、反射强度信息对于多线激光雷达(light detection and ranging,LiDAR)的实际应用有着重要的意义。针对扫描几何条件对点云质量的影响,本文构建了扫描距离、入射角度与多线激光雷达信号衰减的模型关系,从理论上分析了扫...点云的几何精度、反射强度信息对于多线激光雷达(light detection and ranging,LiDAR)的实际应用有着重要的意义。针对扫描几何条件对点云质量的影响,本文构建了扫描距离、入射角度与多线激光雷达信号衰减的模型关系,从理论上分析了扫描距离、入射角度对点云几何精度、反射强度的影响,提出了一种基于平面拟合的点云质量评估方法。在5~50 m的扫描距离、0°~60°的扫描入射角情况下,对3种多线激光雷达进行了测试。实验结果表明,随着扫描距离和入射角度的增加,多线激光雷达的测距中误差逐渐增加,点云反射强度准确性逐渐降低。展开更多
The reflected optical caustics method is applied to study dynamic fracture problems in hardened cement paste. First both the unreinforced cement paste and the glass fibres reinforced cement paste specimens were fabric...The reflected optical caustics method is applied to study dynamic fracture problems in hardened cement paste. First both the unreinforced cement paste and the glass fibres reinforced cement paste specimens were fabricated and the reflective coating on the surface of the specimen was prepared. Secondly the crack path and the shadow spot patterns during the crack propagation process for the two specimens were recorded by using a multi-spark high speed camera.Thirdly some dynamic parameters of two cement paste specimens including crack onset time the dynamic stress intensity factor and crack growth velocity were determined and analyzed comparatively.This indicates that the glass fibres can improve the fracture resistance and delay fracture time.These results will play an important role in evaluating the dynamic fracture properties of cement paste.展开更多
We study the smooth-pasting property for a class of conditional expectations with reflected Levy process as underlying state process. A relationship between local times and regulators for the doubly reflected Levy pro...We study the smooth-pasting property for a class of conditional expectations with reflected Levy process as underlying state process. A relationship between local times and regulators for the doubly reflected Levy process is established. As applications, we derive the analytic pricing formula for a zero-coupon defaultable bond when the default intensity （resp. the stochastic loss rate） is modeled as one-sided （resp. double-sided） reflected Levy processes. Finally, some numerical illustrations are provided.展开更多
基金the support of the National Natural Science Foundation of China (Grant No.50774086 and 50874109)
文摘We studied the dynamic fracture mechanical behavior of rock under different impact rates. The fracture experiment was a three-point bending beam subjected to different impact loads monitored using the reflected caustics method. The mechanical parameters for fracture of the three-poim bending beam specimen under impact load are analyzed. The mechanism of crack propagation is discussed. Experimental results show that the dynamic stress intensity factor increases before crack initiation. When the dynamic stress intensity factor reaches its maximum value the crack starts to develop. After crack initiation the dynamic stress intensity factor decreases rapidly and oscillates. As the impact rate increases the cracks initiate earlier, the maximum value of crack growth velocity becomes smaller and the values of dynamic stress intensity factor also vary less during crack propagation. The results provide a theoretical basis for the study of rock dynamic fracture.
文摘点云的几何精度、反射强度信息对于多线激光雷达(light detection and ranging,LiDAR)的实际应用有着重要的意义。针对扫描几何条件对点云质量的影响,本文构建了扫描距离、入射角度与多线激光雷达信号衰减的模型关系,从理论上分析了扫描距离、入射角度对点云几何精度、反射强度的影响,提出了一种基于平面拟合的点云质量评估方法。在5~50 m的扫描距离、0°~60°的扫描入射角情况下,对3种多线激光雷达进行了测试。实验结果表明,随着扫描距离和入射角度的增加,多线激光雷达的测距中误差逐渐增加,点云反射强度准确性逐渐降低。
基金The Ph.D.Programs Foundation of Ministry of Education of China(No.20120023120020)the National Natural Science Foundation of China(No.51404273)
文摘The reflected optical caustics method is applied to study dynamic fracture problems in hardened cement paste. First both the unreinforced cement paste and the glass fibres reinforced cement paste specimens were fabricated and the reflective coating on the surface of the specimen was prepared. Secondly the crack path and the shadow spot patterns during the crack propagation process for the two specimens were recorded by using a multi-spark high speed camera.Thirdly some dynamic parameters of two cement paste specimens including crack onset time the dynamic stress intensity factor and crack growth velocity were determined and analyzed comparatively.This indicates that the glass fibres can improve the fracture resistance and delay fracture time.These results will play an important role in evaluating the dynamic fracture properties of cement paste.
基金supported by National Natural Science Foundation of China(GrantNos.11001213,71201074 and 70932003)NCET-12-0914the Fundamental Research Funds for the Central Universities(Grant No.K5051370001)
文摘We study the smooth-pasting property for a class of conditional expectations with reflected Levy process as underlying state process. A relationship between local times and regulators for the doubly reflected Levy process is established. As applications, we derive the analytic pricing formula for a zero-coupon defaultable bond when the default intensity （resp. the stochastic loss rate） is modeled as one-sided （resp. double-sided） reflected Levy processes. Finally, some numerical illustrations are provided.
