Research On Several Scientific Rules In Protective Engineering And The Mechanism Analysis

Layered structure is a common layout of protective engineering in the cut-and-cover works. With the increasingly stronger penetration ability and the more and more powerful explosion strength of the new earth penetrators, to develop an advanced protective engineering which has the better abilities in anti-penetration and anti-explosion becomes more and more important. Focused on this key issue, the penetration mechanism of long-rod penetrator vertically penetrating semi-infinite targets, especially concrete targets, and the protective performance of the multi-layered structure,cavities-contained structure,shells-contained structure were mainly researched. Based on the research conclusions, an advanced modular composite shielding cover structure and an advanced modular composite distribution layer structure were put forward. The main contents are as fellows:1) Study on the penetration mechanism of long-rod penetratorAimed at long-rod penetrator vertically penetrating semi-infinite target, the influence rules and the influence mechanism of some main factors (cross-section shape,nose shape,aspect ratio,density ratio between penetratior and target,incident velocity,strength of penetrator and target) on normalized penetration depth were systematically investigated, and several instructive conclusions were developed. Such as: penetration depth of the penetrator with triangle section is obviously deeper than that of the penetrator with circular section because of the Self-sharpening effect; the influence rules of the nose shape on the normalized penetration depth under the conditions of different strength of targets were researched, and some new conclusions were provided; the relations between penetrator velocity and incident velocity,penetrator velocity and penetration velocity,normalized penetration depth and incident velocity in the quasi-steady stage of penetrating were presented; for constant kinetic energy long-rod penetrator, the optimal values of aspect ratio,incident velocity,rotation velocity is presented when the maximum depth is obtained. All those can be referenced for the design of advanced penetrator and target.2) Research on anti-penetration performance of concrete target and the structure design of the advanced modular shielding coverAn improved engineering model and algorithm which improves the calculation accuracy and effenciency on concrete anti-penetration was built, and the geometrical similarity of concrete anti-penetration model was analyzed and the correction function for the big scale test was developed. Experimental technique of SHPB for porous hard and brittle materials was analyzed and summarized, and experimental research on static/dynamic mechanical properties of steel fiber reforced concrete (SFRC) with different steel fiber contents was conducted, and the relation between the strength of the concrete and the steel fibre content was presented. Test investigation on anti-penetration performance of these SFRC targets and the bistratal composite SFRC targets were carried on, and the relation between the incident velocity and the residual velocity was presented. Finally, based on the conclusions above, an advanced modular composite shielding cover structure was developed.3) Protective performance of multi-layered structure and cavities-contained structure and its applicationThe propagation of elastic waves in multi-layered structure was analyzed theoretically and the optimized layouts were provided. To investigate the protective performance of the multi-layered structures and the cavities-contained structures, a series of large-scale similarity tests and numerical simulations were conducted. The results indicate: the multi-layered structures have better protective performance for the transmission and reflection in the structures of the stress waves, and the periodically layered structure is the more efficient structure; the cavities-contained structures have better protective performance for the reflection/diffraction/screening effect of stress waves nearby the cavities.4) Protective performance of shells-contained structure and the structure design of the advanced modular distribution layerThe defense properties of the cylindrical cavities-contained structures and the cylindrical shells-contained structures were compared by the LS-DYNA software. The investigation results indicate that the clipping effect of them was close but the latter had the better"anti-collapse"performance, so defense properties of the latter are better than that of the former. Aimed at the structures that contained the shells of different geometrical parameters and allocation, a series of numerical calculations were conducted and some instructive conclusions were developed, such as: when the horizontal space between the shells was decreased, the more effective protection of the structure was obtained, but if the deformation and crushing resistance were taken into account, one half of the radius of the shell is the optimal space between the shells; In the structure with two-layer cylindrical shells, when the interlayer spacing is bigger than a certain threshold, the smaller the interlayer spacing is, the better the protection performance is; and the protection performance of the stagger structure is better than that of the aligned structure. Finally, based on the conclusions above, an advanced modular composite distribution layer structure was developed.