Papers by Keyword: Stress Wave

Abstract: The zonal disintegration mechanism in rock masses around deep tunnels is totally controversial. Because this phenomenon basically depends on the stress-wave amplitude, fluctuating and declining in rock masses particularly around deep tunnels. This paper intends to theoretically solve the problem of stress-wave propagation. For this purpose, a physical model of stress-wave propagation is established in rock masses around the deep tunnels. Further, the wave equation is solved for rock masses of deep tunnels. Taking Dingji Tunnel in southern of China as a case-study, the central radius of partition is calculated theoretically and compared with the measured results in rock masses around deep tunnels. The research results of this paper gives a certain promotes to the theory of zonal disintegration in rock masses and have certain guiding significance for deep rock engineering.

Abstract: How to examine and describe the defects in timber is vital for assessing the performance of an ancient timber structural building. This paper mainly elaborates the methodology of detecting the defects in ancient timber structures. The detection method includes preliminary condition survey, stress-wave tomography test, and correction with resistographic drilling. By means of above detection, the defects inside a timber structural building could be described more accurately.

Abstract: The attenuation of stress wave induced by impact load in multi-layered thin cylindrical rods has been investigated and analyzed. Firstly, based on stress wave propagation theory, the one dimension solution of the response of stress wave in three-layered media has been given. Secondly, a three-layered thin cylindrical rod has been established through FEM, and the propagation and attenuation of stress wave in it has been analyzed. The analytical and numerical results showed that the stress wave attenuation could be achieved by using multi-layered media.

Abstract: The dynamic process of cracks initiation in brittle materials during high speed cutting is primary for the analysis of material fracture mode and finished surface. Cast iron was considered in this paper and discrete element method (DEM) was employed to create a density packed bonded-particle model for studying its machining cracks. The numerical tests of split Hopkinson pressure bar (SHPB) and oblique plane impact were conducted to calibrate the dynamic behaviour of the model. The cutting simulations were carried out for a range of rake angles and cutting speeds. The results showed that both the processes of cracks initiation and the cracks distribution were different greatly under different cutting conditions and the cracks number increased with the cutting speed. In addition, within the detection zone in the model, the duration of crack initiation decreased dramatically with the increase of cutting speed in the lower range. But for the high speed cutting, the duration tended to be stable and was not affected by cutting speed and it was very close to the time of stress wave produced by cutting arriving at the zone. Furthermore, the stress state of particles’ connectors under the action of stress wave was analysed, which suggests that the stress wave is the key factor causing cracks initiation of brittle materials during high speed cutting.

Abstract: Taking stress wave propagation into account, the governing equations of composite bar with the clamped-fixed boundary conditions considering FSDT (first order shear deformation theory) are derived on the basis of Reddy’ theory and solved by the variable-separated method. The analytic expression of the critical buckling load is obtained basing on the characteristics of homogeneous linear equations having nonzero-solution. The results of the theoretical study and the numerical calculation indicate that FSDT has influence on dynamic buckling of composite bar, and the critical buckling load is small when FSDT is considered. They also show that the magnitude of effect taken by FSDT is small when the layer angle is big.

Abstract: Taking into account the effects of stress wave and the moment of inertia, the governing equations of composite laminated plate under the axial step load are derived by using Hamilton principle. Based on Variable Separation Method, the analytical expression of the critical dynamic buckling load for symmetry composite laminated plates with one edge fixed and three edges simply-supported can be deduced by considering the characteristics of the buckling solution, and the buckling mode is also acquired. Using MATLAB software, the relationship between the critical load and length can be obtained. The influences of different layer parameters and the order of the mode on the dynamic buckling are discussed.

Abstract: Considering the effect of stress wave, the dynamic buckling of circular cylindrical shells under an axial step load is discussed using the classical shell theories and the state-space technique in the paper. Based on the Hamilton’s principle, the dynamic buckling governing equations of shells are derived and solved with the Rayleigh-Ritz method. If the linear homogeneous equations have a non-trivial solution, the determinant of the coefficient matrix must be equal to zero, so the expression of the critical load on the dynamic buckling is got. The relationship between the critical load and length is obtained by using MATLAB software. The influences of boundary conditions, thickness, the number of circumferential waves and the number of axial waves on the dynamic buckling loads are discussed based on numerical computation.

Abstract: How to truncate stress wave is an important problem that must be considered in design of engineering structure. As an effective detection method of stress distribution, the dynamic photoelasticity has been wide used in stress analysis, such as detection of mechanical structure, civil engineering and water conservancy etc. In this paper, the stress wave isochromatic fringe at different interface structure has been obtained through vertical shooting experiment. The structural stress wave propagation rule of three kinds of case is studied by comparison fringe pattern. The experimental research results show that the stress wave propagation can be effectively guided to a fixed direction through installed connecting parts in structural connection position and the method can avoid integrity damage of structure caused by local large stress changes. Finally, the dynamic photoelasticity is an intuitive and effective way to study stress wave truncation problem.

Abstract: After analyzing the propagation of stress wave at different angles of inclination, strength parameters and the group number of structural plane. The results of research are summarized as follows: Due to the change of propagation direction in structural planes with different angles of inclination, the original propagation rule of stress wave changes too, the peak velocity of the monitory point gets relatively flat as the strength parameters of structural plane turn greater. Stress wave repeatedly refracts and reflects in many groups of structural plane, then the appropriate dynamic characteristics of the wave no longer maintains as the number of group increases or decreases. By analyzing and verifying the slope instance, the test result provides a reference for studying dynamic response rules.

Abstract: The dynamic response of the square tube subjected to the impact of a mass was investigated by using experimental and numerical methods. The square tube was impacted by a mass at the velocity ranging from 5.09 m/s to 12.78 m/s, and different progressive buckling modes were obtained. The numerical simulation was also carried out to analyze the buckling mechanism of the square tube. The results show that there is obvious stress wave propagation and strain localization in the tube, which has a significant influence on the buckling mechanism of the tube. The stress wave and inertia of the mass play different roles at various impact velocities. And buckling mechanism at low velocity is mainly caused by stress wave, whereas the buckling mechanism at high velocity is resulted from the inertial of the mass.