The effect of the cement-sand matrix structure on the strength of protective structures under the influence of conventional weapons

Objective of the article is to determine the dependence of stresses on the surface of the coating plate of a special structure under the influence of an explosion, the parameters of the protective structure modified with a cement-sand matrix. Important aspects of this work are the geometric characteristics of the auxetic structure, as well as the strength properties of the concrete composite, which is represented by strength classes B30, B45 and B60. The study used the following methods: numerical modeling, statistical analysis and experimental planning in the ANSYS Explicit Dynamics software package, where the cement-sand matrix was described by the Drucker-Prager strength criterion. The study found that protective structures with round and square voids are not able to protect the coating plate of a special structure when exposed to an explosion. On the contrary, plates with auxetic construction have demonstrated their effectiveness, significantly absorbing energy during explosive impacts. When calculating for 27 different combinations of factors, ANSYS Explicit Dynamics obtained stresses in the coating plate ranging from 22 to 81 MPa. Based on these data, regression analysis was performed, which made it possible to construct a mathematical model in the form of a polynomial equation of the second degree. This model combines the stress level (Y) with three key factors: the ratio of the cell area to the system (x₁), the ratio of the void area to the material (x₂) and the strength of the concrete (x₃). The adequacy of the obtained model was confirmed by the Fisher criterion, where the calculated value of F $$(F_c = 19.0811)$$ is higher than the tabular value $$(F_t = 1.9881)$$. This indicates the ability of the model to adequately describe the process under study. The created regression model makes it possible to more accurately select the parameters of energy-absorbing structures at the design stage. The establishment of optimal geometric parameters of an auxetic structure provides an opportunity to develop protective structures that significantly increase the resistance of a special structure to explosive impacts, which helps to increase the survivability of significant objects and reduce damage from dynamic loads.