Theoretical Analysis On Penetration Of Rigid Projectiles And Numerical Simulations Of SHPB Test

This thesis consists of two parts, Part 1 focuses on the theoretical analysis on penetration of rigid projectiles and includes Chapter 2 and Chapter3; Part 2 is numerical simulations of SHPB test using 921A steel pure shear hat-shaped specimens and consists of Chapter 4 andChapter 5.Firstly, Chapter 1 introduces the developments of theoretical researches on penetration of rigid projectiles which cover theoretical models of penetration of plain concrete target, metallic target and soil target, and then summarizes the dimensionless numbers dominated in pentetration; also the applications of numerical simulation in SHPB technology and researches on adiabatic shear deformation is reviewed briefly in this chapter.According to the dimensionless formula of DOP (depth of penetration) of different targets penetrated by a rigid projectile, Chapter 2 theoretically analyses the resistive force which the target exerts on the projectile during the penetration of a rigid projectile. In particular, the threshold V_c of impact velocity applicable for the assumption of constant resistive force is formulated by impulse analysis. The various values of V_c of different pairs of projectile-target are calculated out and consistence with corresponding numerical results is observed.Chapter 3 discusses the ratios of DOP of different targets under the same penetration condition. It is declared that various targets may be equivalent to each other. Finally the applicable range of the equivalence and the feasibility of targets substitution is discussed by integrating the available test data.A series of numerical simulations of SHPB test using 921A steel pure shear hat-shaped specimens are conducted with ANSYS/LS-DYNA and validated by the SHPB tests in Chapter 4. Integrated with the theory of stress wave in a SHPB system, the wave propagation in the bars and the dynamic deformations of the specimen under different loading rates V₀ (or stress pulsesσ₁(t) are analyzed, and typical wave shapes are identified for different loading rates. Numerical tests of SHPB under ultrahigh strain rate are specially conducted, which are unable to be done realistically. The different deformation and failure of the hat-shaped specimens under different loading rates are distinguished, and the applicability of strain waves in the bars under ultrahigh loading rates is also discussed.Integrated with the simulation results in Chapter 4, the adiabatic shear deformations of specimen are observed in Chapter 5. The initiation and the propagation of an adiabatic shear band (ASB) and the corresponding distribution of temperature field in the specimen are analyzed. The fields of stress, strain and temperature in the tip of an ASB, and the spread speed, the width as well as the type of the ASB are all studied.Finally, Chapter 6 summarizes the research work and gives some recommendations for future work.