PSI - Issue 52

Huadong Xu et al. / Procedia Structural Integrity 52 (2024) 52–62 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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2.4. An evaluation methodology for energy absorption

Energy absorption capability is an important index to evaluate the shielding performance of materials. An evaluation methodology for energy absorption was proposed in this work, based on initial velocity of projectile, penetrated layers in fabric targets, the depth and volume of the impact crater on witness plate. In fact, the impact results of the targets were divided into two categories: penetrated and non-penetrated. To reasonably, the specific absorbed energy S , which is the absorbed energy divided by the areal density of the penetrated fabric layers, was selected to describing the energy absorption capability of various targets. For the case of non-penetrated, the residual kinetic energy of the projectiles can be regard as zero due to the targets are not penetration. The specific absorbed energy S is described as Eq. (1): s = 1 2 p ( I 2 – R 2 ) (1) where the I and R represent the velocity of projectile before and after impact, respectively. p is the projectile mass. The is the total areal density of the penetrated fabric layers in target, which is defined as the mass of the total penetrated fabric layers tp divided by the area of the impact plane t . Thus, the unit of s is J/(kg/m 2 ). For the case of penetrated, the residual kinetic energy of projectiles cannot be accurately calculated due to the broken and fragmentation of materials. However, the remaining kinetic energy of the projectile and its fragments could be estimated by the relationship between the kinetic energy and the volume of crater Tanaka et al. (2008) . = 713( ) 1.09 (2) where the is the total volume of impact craters, and is remaining kinetic energy of the fragments from broken projectile. The specific absorbed energy S could be expressed as: = 1 2 2 − (3) It may be noticed that Eq. (2) is an empirical formula for Al 2017 projectiles and Al 5056 targets. The chemical composition and material properties of Al 5056 and 5A06 Al plates are similar. Young’s modulus of both materials is 71 GPa, and the tensile strengths are 290 MPa and 339 MPa, respectively. Therefore, it is assumed that Eq. (2) is suitable for the current situation. The depth and volume of the impact crater on witness plate was measured by 3D measuring laser microscope. Taking the witness plate of ceramic fabric (Nextel) target as an example, the measurement process of impact crater volume and depth is shown in Fig. 3.

Fig. 3. Microscopic morphology and size measurement of impact crater in witness plate at ceramic fabric (Nextel) experiment. (a) Impact crater. (b) Microscopic appearance. (c) 3D shape. (d) Volume measurement. (e) Depth measurement.