Equivalent method of different grades of steel target plates under blast loads in the cabin based on plate thickness compensation

Experimental investigation of internal explosion effects on ship structures still faces fundamental challenges. The prohibitively high costs of specialized naval steel plates impose disproportionate financial burdens on experimental budgets. Additionally, the restricted availability of standardized thickness variants has dimensional scaling conflicts during reduced-scale internal explosion experiments. This research proposes an equivalent substitution method for scaled model testing. The methodology enables a strategic replacement of naval steel with conventional steel while maintaining response similitude during the internal explosion of ship structures. The primary research objective focuses on validating the equivalent substitution method for conventional steel as a replacement for specialized naval steel without degrading the accuracy of the recorded data. According to the principle of central deformation similarity, the equivalence relationship among target plates of different grades was established under the assumption of structural integrity during the explosion. Based on the theory of large deflection of thin plates, the relationship between plate thickness and deformation was clarified thoroughly. An equivalence substitution method for different plate grades was explained, and an equivalence substitution method for different plates was proposed. It provides a theoretical foundation for substituting specialized naval steel with conventional steel. Comprehensive numerical simulations were conducted using the finite element analysis software AUTODYN to validate the proposed method. The simulations modeled the dynamic response of four different grades of steel target plates (921A steel, 907A steel, Q235 steel, and Q355 steel) under internal blast loading. The maximum deviation between the simulation results and experimental data is only 5.6%, thereby fully confirming the accuracy and reliability of the numerical model. The equivalence relationships among grades under internal blast loading with different charge volume ratios (0.1, 0.2, 0.4, 0.8, and 1.0) were further explored through extensive numerical simulations involving four plates grades (Q235, Q355, 907A, and 921A) with various thicknesses. A fitting analysis of equivalent plate thickness was conducted. By integrating empirical formulas correlating equivalent plate thickness with dynamic yield strength, the substituted target plate showed less than 10% deviation in central deformation compared to the original plate. The proposed equivalence method for steel target plates of different grades under internal explosion loads has been demonstrated to be both rational and practically applicable. This provides a theoretical foundation and empirical reference for substituting specialized naval steel with ordinary steel in internal explosion experiments.