This study successfully deals with the inhomogeneous dimension problem of load separation assumption, which is the theoretical basis of the normalization method. According to the dimensionless load separation principl...This study successfully deals with the inhomogeneous dimension problem of load separation assumption, which is the theoretical basis of the normalization method. According to the dimensionless load separation principle, the normalization method has been improved by intro- ducing a forcible blunting correction. With the improved normalization method, the J-resistance curves of five different metallic materials of CT and SEB specimens are estimated. The forcible blunting correction of initial crack size plays an important role in the J-resistance curve estima- tion, which is closely related to the strain hardening level of material. The higher level of strain hardening leads to a greater difference in JQ determined by different slopes of the blunting line. If the blunting line coefficient recommended by ASTM E1820-11 is used in the improved nor- realization method, it will lead to greater fracture resistance than that processed by the blunting line coefficient recommended by ISO 12135-2002. Therefore, the influence of the blunting line on the determination of JQ must be taken into full account in the fracture toughness assessment of metallic materials.展开更多
当前基于车桥耦合系统的桥梁频率间接识别方法普遍对行驶车辆参数和速度有较大约束,难以应用于正常行驶的普通车辆。为了解决这一问题,该文提出了一种考虑车辆无量纲响应的桥梁频率间接识别方法。首先,以无量纲化的车-桥耦合运动学方程...当前基于车桥耦合系统的桥梁频率间接识别方法普遍对行驶车辆参数和速度有较大约束,难以应用于正常行驶的普通车辆。为了解决这一问题,该文提出了一种考虑车辆无量纲响应的桥梁频率间接识别方法。首先,以无量纲化的车-桥耦合运动学方程为基础,构建基于改进子空间识别法的系统状态方程与输出信号方程,建立了考虑时间差的车辆双轴无量纲响应差值信号方程,从理论上有效地消除了状态方程与输出信号中的路面平整度信息,突破了传统子空间识别法对车辆参数的限制,使该方法适用于任何普通车辆,同时验证了基于单次行驶双轴车辆响应的桥梁频率间接识别方法对简支梁桥频率识别的可行性。然后,通过数值计算探讨了车辆行驶速度、路面平整度等级和随机车辆荷载对桥梁频率间接识别的影响。计算结果表明,充分的荷载激励对桥梁频率的稳定识别非常重要,并且能够激发桥梁高阶模态的振动,更有利于桥梁高阶频率的识别。最后,针对一座实际服役的高墩简支梁桥开展现场行车试验,基于车桥动态接触力作为信号输入,验证子空间识别法获得桥梁频率的可行性和准确性。试验结果表明,短时随机子空间识别方法可以提取测试桥梁前2阶频率,在高阶频率的识别中有着更优于MOESP(multivariable output error state space,MOESP)子空间识别法的效果。展开更多
基金supported by the National Natural Science Foundation of China(Nos.11472228 and 11202174)the Sichuan Provincial Youth Science and Technology Innovation Team(No.2013TD0004)
文摘This study successfully deals with the inhomogeneous dimension problem of load separation assumption, which is the theoretical basis of the normalization method. According to the dimensionless load separation principle, the normalization method has been improved by intro- ducing a forcible blunting correction. With the improved normalization method, the J-resistance curves of five different metallic materials of CT and SEB specimens are estimated. The forcible blunting correction of initial crack size plays an important role in the J-resistance curve estima- tion, which is closely related to the strain hardening level of material. The higher level of strain hardening leads to a greater difference in JQ determined by different slopes of the blunting line. If the blunting line coefficient recommended by ASTM E1820-11 is used in the improved nor- realization method, it will lead to greater fracture resistance than that processed by the blunting line coefficient recommended by ISO 12135-2002. Therefore, the influence of the blunting line on the determination of JQ must be taken into full account in the fracture toughness assessment of metallic materials.
文摘当前基于车桥耦合系统的桥梁频率间接识别方法普遍对行驶车辆参数和速度有较大约束,难以应用于正常行驶的普通车辆。为了解决这一问题,该文提出了一种考虑车辆无量纲响应的桥梁频率间接识别方法。首先,以无量纲化的车-桥耦合运动学方程为基础,构建基于改进子空间识别法的系统状态方程与输出信号方程,建立了考虑时间差的车辆双轴无量纲响应差值信号方程,从理论上有效地消除了状态方程与输出信号中的路面平整度信息,突破了传统子空间识别法对车辆参数的限制,使该方法适用于任何普通车辆,同时验证了基于单次行驶双轴车辆响应的桥梁频率间接识别方法对简支梁桥频率识别的可行性。然后,通过数值计算探讨了车辆行驶速度、路面平整度等级和随机车辆荷载对桥梁频率间接识别的影响。计算结果表明,充分的荷载激励对桥梁频率的稳定识别非常重要,并且能够激发桥梁高阶模态的振动,更有利于桥梁高阶频率的识别。最后,针对一座实际服役的高墩简支梁桥开展现场行车试验,基于车桥动态接触力作为信号输入,验证子空间识别法获得桥梁频率的可行性和准确性。试验结果表明,短时随机子空间识别方法可以提取测试桥梁前2阶频率,在高阶频率的识别中有着更优于MOESP(multivariable output error state space,MOESP)子空间识别法的效果。
