Abs ract : Visualization studies were performed both experimentally and theoretically to observe stress wave propagation in a material and its interaction with the free surface of the material in a blasting process. PMMA (polymethyl-methacrylate) plates were used as a transparent material. The stress wave was generated by initiation of an electric detonator. The stress waves in the PMMA specimen with the right-angled corner were observed by means of the shadowgraph system using a Q switched ruby laser as a light source. In addition to the experiment, a numerical analysis using smoothed particle hydrodynamics (SPH) was also carried out to clarify the dynamic behavior of stress waves in the blasting process. Transmittance and reflection of the stress wave at the free surface could be visualized by both the experiment and the numerical analysis.t
We analyze the dynamics of stress waves interacting with the right-angled and/or the semicircular free surface in the PMMA (polymethyl-methacrylate) specimen using the smoothed particle hydrodynamics (SPH) method. The stress waves emanate from the charge hole and interact with the free surface. The results obtained from the numerical calculation are compared with experimental results of the model blasting using the electric detonator as a charge. The stress waves in PMMA and shock waves in air are observed by means of the laser-shadowgraph method. Propagation of stress waves, reflection and transmittance at the interface between PMMA and air are visualized both experimentally and numerically.
Mechanical breakage systems are generally employed to demolish a portion of a concrete building, however it is time consuming and costly. And the mechanical demolition work involves various risks such as those associated with occupational safety and presents a noise hazard to the general public living in the vicinity. Therefore, alternative methods for such work have been sought. For this purpose, a dynamic breakage system utilizing diamond-shaped charge holders was proposed to rapidly remove the desired portion of the concrete foundation. The charge holders which initiate crack growth were placed inside a concrete mass along the desired fracture plane. In this study, full-scale blast experiments utilizing the charge holders were introduced and the roughness of fracture planes was observed using a 3-dimensional photography system. In order to verify the effect of the charge holders on fracture controlling in full-scale blast experiments, the fracture processes of the concrete blocks were analyzed using the dynamic fracture process analysis (DFPA) code. The mechanism required to achieve controlled breakage was discussed after taking into account the influence of various loading conditions and crack tip velocity. It was found that the DFPA tool is a useful instrument in the analysis of full scale blast experiments.
Fracture control in blasting is very important in underground excavation and demolition of concrete structures. It is valuable to obtain an understanding of the dynamic behavior of stress waves in the blasting process for the development of fracture control method. Experimental visualizations and numerical simulations were performed to observe the propagation and interaction of stress waves between two charge holes in blasting. These are related with control of fracture planes along the line connecting the charge holes in smooth blasting. In model experiments using PMMA plates, the stress waves were generated by initiation of electric detonators at the charge holes and were observed by means of the visualization system. The dynamic behavior of stress waves in the blasting process was also visualized by numerical simulation using the smoothed particle hydrodynamics (SPH) method. The dynamic behavior of stress waves is discussed by means of the experimental results and the simulation results.
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