Aerospace Science and Technology 29 (2013) 413–425 Contents lists available at SciVerse ScienceDirect Aerospace Science and Technology www.elsevier.com/locate/aescte Modiﬁcation of the critical projectile diameter of honeycomb sandwich panel considering the channeling effect in hypervelocity impact Pilseong Kang a,1 , Sung-Kie Youn b,∗ , Jae Hyuk Lim c a Dept. of Mechanical Engineering, KAIST, Republic of Korea b Dept. of Mechanical Engineering, KAIST, 373-1 Guseong-dong, Yuseong-gu, Daejeon, 305-701, Republic of Korea c Satellite Structure Department, Korea Aerospace Research Institute (KARI), 169-84 Gwahak-ro, Yuseong-gu, Daejeon 305-806, Republic of Korea article info abstract Article history: Received 8 November 2012 Received in revised form 15 April 2013 Accepted 28 April 2013 Available online 15 May 2013 Keywords: Hypervelocity impact Honeycomb sandwich panel (HC/SP) Channeling effect Honeycomb (HC) core Smoothed particle hydrodynamics (SPH) Ballistic limit equation (BLE) In this paper, a variation of the critical projectile diameter of honeycomb sandwich panel (HC/SP), due to the channeling effect, is investigated by using smoothed particle hydrodynamics (SPH). Before performing numerical study on the channeling effect, the results of 2-D hypervelocity impact simulation were compared with the experimental results in order to validate the simulation along with searching proper simulation parameters such as equation of state, strength model, and failure model. And then, analysis of the channeling effect is performed with different cell sizes, wall thicknesses and depths of HC core in accordance with the speciﬁcations of commercial HC cores. As a result of the study, it is revealed that the HC core cell size is the most inﬂuential parameter on the channeling at normal incidence impact. Also the critical projectile diameter appears to be varying with the HC core cell size due to the channeling effect. Finally, the modiﬁed critical projectile diameters of HC/SP are presented by introducing the decrement of critical projectile diameter.  2013 Elsevier Masson SAS. All rights reserved. 1. Introduction Honeycomb sandwich panels (HC/SP) are frequently employed in spacecraft structures. They serve dual purposes; one is to pro- vide structural stiffness to the spacecraft, and the other is to pro- tect the spacecraft from the hypervelocity impact of orbital debris and micrometeoroid. Since the Whipple shield was developed to protect spacecrafts from the impact of orbital debris and microm- eteoroid in 1947 [24], many researches about hypervelocity impact on HC/SP have been conducted. Both HC/SP and the Whipple shield have two separated layers of sheet. However, unlike the Whipple shield, the HC/SP has HC core between the sheets. Due to the pres- ence of HC core, the hypervelocity impact phenomenon of HC/SP is more complex than that of the Whipple shield. It is known that the debris cloud produced at the impact is channeled by the walls of honeycomb (HC) core cells, and the channeling affects the dam- age of the rear facesheet of HC/SP. In short, the debris cloud in HC/SP cannot be spread widely, but it is restricted by cell walls of HC core. Thus the debris cloud ﬂows along the cell wall direction of HC core in a ﬁnite number of HC core cells. This phenomenon is called the channeling effect. * Corresponding author. Tel.: +82 42 350 3034; fax: +82 42 350 3210. E-mail addresses: newnoen@kaist.ac.kr (P. Kang), skyoun@kaist.ac.kr (S.-K. Youn), ljh@kari.re.kr (J.H. Lim). 1 Tel.: +82 42 350 5034; fax: +82 42 350 3210. The channeling effect caused by HC core was mentioned for the ﬁrst time in the research of Anon [1] in 1964. Sennet and Lathrop [19] found the channeling effect from impact tests on HC/SP. They stated about the relationship between facesheet spacing and cell diameter of HC core. Jex et al. [13] concluded that HC/SP shows higher protective performance than the Whipple shield because the absorption of impact energy by HC core is dominant over the channeling, when comparing HC/SP with the Whipple shield at the oblique impact of orbital debris. Shephard and Scheer [20] pointed out that HC/SP could be used as a shield for a space station, but it was worse than the Whip- ple shield. Frost and Rodriquez [8] conducted hypervelocity impact experiments for composite HC/SP and developed a ballistic limit equation (BLE) which gives the critical projectile diameter caus- ing perforation on the target. However, the ballistic limit equation was not expressed by variables of cell size, thickness and mate- rial of HC core. Lambert et al. [15] explained the effects of size and depth of HC core on the channeling qualitatively with the comparison of the Whipple shield BLE. After that, various types of HC/SP BLEs have been developed by many researchers [21–23], but channeling effect of HC/SP is roughly mentioned and its inﬂuence on the damage is evaluated differently in each research. Taylor et al. [23] performed hypervelocity impact simulations and experi- ments for single HC/SP and double HC/SP. They developed a BLE for HC/SP by modifying the Whipple shield BLE based on the sim- ulation and experimental results. However, this BLE was valid only for speciﬁc HC/SPs and the effect of HC core was represented by 1270-9638/$ – see front matter  2013 Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.ast.2013.04.011