A numerical simulation method of natural fragment formation and injury to human thorax

Abstract

Objective: Fragment injury is a type of blast injury that is becoming more and more common in military campaigns and terrorist attacks. Numerical simulation methods investigating the formation of natural fragments and injuries to biological targets are expected to be developed.

Methods: A cylindrical warhead model was established and the formation process of natural fragments was simulated using the approach of tied nodes with failure through the explicit finite element (FE) software of LS-DYNA. The interaction between the detonation product and the warhead shell was simulated using the fluid-structure interaction algorithm. A method to simulate the injury of natural fragments to a biological target was presented by transforming Lagrange elements into smooth particle hydrodynamics (SPH) particles after the natural fragments were successfully formed. A computational model of the human thorax was established to simulate the injury induced by natural fragments by the node-to-surface contact algorithm with erosion.

Results: The discontinuous velocities of the warhead shell at different locations resulted in the formation of natural fragments with different sizes. The velocities of natural fragments increased rapidly at the initial stage and slowly after the warhead shell fractured. The initial velocities of natural fragments at the central part of the warhead shell were the largest, whereas those at both ends of the warhead shell were the smallest. The natural fragments resulted in bullet holes that were of the same shape as that of the fragments but slightly larger in size than the fragments in the human thorax after they penetrated through. Stress waves propagated in the ribs and enhanced the injury to soft tissues; additionally, ballistic pressure waves ahead of the natural fragments were also an injury factor to the soft tissues.

Conclusion: The proposed method is effective in simulating the formation of natural fragments and their injury to biological targets. Moreover, this method will be beneficial for simulating the combined injuries of natural fragments and shock waves to biological targets.

Keywords: Finite element analysis; Fluid–structure interaction; Fragment injury; Human thorax; Smooth particle hydrodynamics.

Fig. 1

Computational model. (A) Natural fragment warhead displayed without trinitrotoluene charge; (B) Natural fragment warhead and air domain; (C) Human thorax.

Fig. 2

Interaction between detonation product and warhead shell. (A) t = 2.5 μs; (B) t = 10 μs; (C) t = 15 μs; (D) t = 22.5 μs; (E) t = 25 μs; (F) t = 35 μs; (G) t = 60 μs; (H) t = 90 μs.

Fig. 3

Formation of natural fragments. (A) t = 20 μs; (B) t = 25 μs; (C) t = 35 μs; (D) t = 50 μs; (E) t = 60 μs; (F) t = 70 μs, (G) t = 80 μs; (H) t = 90 μs.

Fig. 4

Velocity histories of natural fragments at typical positions of warhead shell.

Fig. 5

Characteristic parameters of natural fragments along the axial direction of warhead shell. (A) Initial velocity; (B) Radial displacement.

Fig. 6

Velocity distribution of natural fragments in different forms. (A) Lagrange elements; (B) Smooth particle hydrodynamics particles.

Fig. 7

Relative locations of natural fragments and human thorax.

Fig. 8

Penetration process of natural fragments into the human thorax. (A) t = 12.5 μs; (B) t = 20 μs; (C) t = 40 μs; (D) t = 60 μs; (E) t = 80 μs; (F) t = 100 μs; (G) t = 150 μs; (H) t = 200 μs.

Fig. 9

Strain distribution of human thorax during penetration process of natural fragments. (A) t = 12.5 μs; (B) t = 20 μs; (C) t = 40 μs; (D) t = 60 μs; (E) t = 80 μs; (F) t = 100 μs; (G) t = 150 μs; (H) t = 200 μs.

Fig. 10

Velocity histories of nodes located at typical fragments.