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91.
Liu Rongmei 《力学与实践》1979,42(4):442
建立了扁担挑物的动力学模型和动力学方程,并进行了数值求解。扁担挑物时存在三种频率,即重物类似于单摆的振动频率、挑运者的步行频率和扁担-重物系统铅垂方向的振动频率。计算结果表明,为了获得较好的挑担体验,三种频率应该相互协调。当人挑担行走的频率为扁担-重物系统铅垂方向振动频率的70%,$\sim$,80%时,肩部铅垂附加动反力为重物重力的30%左右且与肩部铅垂运动同相,当重物类似于单摆的振动频率为人步行频率的25%,$\sim$,30%时,重物的摆角和肩部受到的水平附加动反力均较小,从而有利于人挑担行走。 相似文献
92.
High-speed holographic microscopy is applied to take three successive photographs of fast propagating cracks in Homalite 100 or in Araldite B at the moment of bifurcation. Crack speed at bifurcation is about 540 m/s on Homalite 100, and about 450 m/s on Araldite B. From the photographs, crack speeds immediately before and after bifurcation are obtained, and it is found that discontinuous change of crack speed does not exist at the moment of bifurcation in the case of Homalite 100, but exists in the case of Araldite B. From the photographs, crack opening displacement (COD) is also measured along the cracks as a function of distance r from the crack tips. The measurement results show that the CODs are proportional to √r before bifurcation. After bifurcation, the CODs of mother cracks are proportional to √r, though the CODs of branch cracks are not always proportional to √r. The energy release rate is obtained from the measured CODs, and it is found that energy release rate is continuous at bifurcation point in both cases of Homalite 100 and Araldite B. Energy flux that shows the energy flow toward a crack tip is also obtained. 相似文献
93.
ASYMPTOTIC DYNAMIC SOLUTION TO THE MODE Ⅰ PROPAGATING CRACK-TIP FIELD IN ELASTIC-VISCOPLASTIC MATERIAL 总被引:1,自引:0,他引:1
Li Fan-chun 《应用数学和力学(英文版)》2003,24(2):208-215
A new elastic-viscoplastic mode was proposed to analyze the stress and strain fields surrounding the tip of a propagating mode Ⅰ cracks. A proper displacement pattern was suggested and asymptotic equations were derived, and numerical solutions were illustrated. The analysis and calculation show that the crack-tip field is of logarithmic singularity for smaller viscosity, however no solution exists for large viscosity. By a careful analysis and comparison, it is found that the present results retain all merits of those given by Gao Yu-chen, while removing existing problems. 相似文献
94.
The paper deals with the three-dimensional dynamic problem for an elliptic crack interacting with a normally incident harmonic compression–expansion wave, considering the contact interaction of the crack faces. An asymmetric solution is obtained using an iteration algorithm developed earlier. Numerical results are presented 相似文献
95.
V. A. Storozhenko 《International Applied Mechanics》2003,39(12):1464-1472
A technique is proposed to identify the principal central axis of inertia in a joint-suspended inhomogeneous rigid body from its vertical revolution. The problem is reduced to synchronizing the revolution of the body with the revolution of a fictitious mathematical pendulum 相似文献
96.
微孔洞型的分形断裂理论初探 总被引:1,自引:0,他引:1
初步研究并提出微孔洞型的分形断裂理论,建立了主裂纹与微孔洞汇合的分形模型,并以此为基础确定了分维D与连接区厚度Δ和孔洞平均半径r之间的关系,推导了微孔洞与主裂纹连接的能量准则,讨论了分维与断裂韧性之间的关系。 相似文献
97.
在沙丁机基础上,实现了反射式动态云纹测量法。该法可用于不透明模型的动态位移,应变及应力场的研究。 相似文献
98.
倒立摆的摆起过程是复杂的非线性力学与控制的综合问题,当力学模型和参数确定时,寻求有效方法计算控制律函数是实现摆起的关键。本文以倒立双摆模型为研究对象,将动态设计变量优化方法引入对摆起开环控制律的分析,编制计算机程序进行数值仿真,确定了控制律函数与状态量随时间变化的状态,为复杂强非线性系统的控制提出了一种有效方法。 相似文献
99.
本文主要通过汽车稳定杆在疲劳试验中应力、刚度拟动态试验,采用电测法^[1],在分析杆件中实际应变和位移的基础上进行逆解分析,从而确定稳定杆的实际刚度,支座摩阻反力矩和应力集中系数,为建立稳定杆的简化力学分析及其疲劳寿命预测提供试验依据. 相似文献
100.
Based on the theory of elastic dynamics, multiple scattering of elastic waves and dynamic stress concentrations in fiber-reinforced
composite are studied. The analytical expressions of elastic waves in different regions are presented. The mode coefficients
of elastic waves are determined in accordance with the continuous conditions of displacement and stress on the boundary of
the multi-interfaces. By using the addition theorem of Hankel functions, the formula of scattered wave fields in different
local coordinates are transformed into those in one local coordinate to determine the unknown coefficients and dynamic stress
concentration factors (DSCFs). The influences of the distance between two inclusions, material properties and structural size
on the DSCFs near the interfaces are analyzed. As examples, the numerical results of DSCFs near the interfaces for two kinds
of fiber-reinforced composites are presented and discussed.
The project supported by the National Natural Science Foundation of China (19972018) 相似文献