Numerical Evaluation of an Add-On Vehicle Protection System

Transcription

1 Numerical Evaluaion of an Add-On Vehicle Proecion Sysem Geneviève Toussain, Amal Bouamoul, Rober Durocher, Jacob Bélanger*, Benoî S-Jean Defence Research and Developmen Canada Valcarier 2459 Bravoure Road, Quebec (Qc), G3J 1X5, Canada *Numerica Technologies Inc. 1 Inroducion Defence Research and Developmen Canada (DRDC) has been involved in programs o reduce he vulnerabiliy of vehicles o mines and improvised explosive devices for many years. In his work, DRDC was mandaed o design and opimize an add-on vehicle proecion sysem. Tesing an enire vehicle agains improvised explosive devices or blas landmines is boh ime-consuming and expensive; herefore, o reduce coss, numerical simulaions using he LS-DYNA hydrocode [1] were performed o suppor he developmen phase of he proecion sysem. A finie elemen model of a simplified full-scale model of he vehicle called a mock-up was developed for his purpose. This model included he criical secions ha were likely o be affeced by a hrea. Finie elemen sudies were hen performed o compare he performance of several proecion designs and o orien on he choice of he final one. This paper presens he loading model ha was used o simulae he effec of a landmine on he srucure, he finie elemen (FE) models of he baseline and of hree conceps and finally, a comparison of he relaive performance of he differen proecion sysem designs. 2 Loading model Several approaches have been used o simulae he loading profile generaed by landmines [2]. Sudies such as in [3 o 6], presened he mine impulse loading model developed a DRDC, which ransforms he specific impulses given by Wesine s empirical equaion [7] ino iniial velociies ha can be applied as iniial condiions o nodes of shell elemens locaed in he direc line of sigh from he mine o he srucure. The empirical equaion of Wesine e al. [7] ha predics he specific impulse impared o a fla plae placed over a buried landmine is provided below [3]: i v 7 anh d x, y z d 3.25 E z (1) z 5 4 A 3 8 anh 2.2 z 3 2 (2) where z is he sand-off disance of plae P (parallel o he ground) o he cener of he mine, E is he energy release by he explosive charge, is he densiy of soil, is he burial deph o he cener of he mine and A is he cross-secional area of he mine, d=(x 2 +y 2 ) is he radial disance from he cener of he mine. Four crieria, depending on, z, E, A, d, and he seismic P-wave velociy in he soil, mus be me when using equaion 1 [3].

2 One limiaion of his impulse model is is inabiliy o load a FE srucure made of solid elemens. Therefore, a pressure-based mine loading model was developed by DRDC o address his limiaion. This model, mainly based on he Wesine impulse model [3, 7], uses a pressure ime-space disribuion o apply he loading condiions on he srucure. To validae his model, a series of numerical simulaions were conduced wih various pressure ime-space disribuion funcions and differen coefficiens and he resuls were compared wih experimenal daa. The general form of he pressure P() calculaed on a solid elemen is shown in Figure 1: Fig. 1: Pressure as a funcion of ime P( ) P0 f ( ) (3) where P 0 is he maximum pressure applied on a solid elemen and i is deermined using he specific impulse (I s ) prediced by Wesine. P Is f ( ) (4) 0 where f() is a user inpu funcion and is defined as: f a ) 1 e sin( ) (5) 0 ( 0 where is he curren ime, 0 is a user inpu consan and corresponds o he ime for which he pressure is applied (afer 0, he loading is equal o 0), =*/ 0 and a is a consan. This model has he flexibiliy o apply iniial condiions on solid elemens ha are mainly in he direc line of sigh from he mine. Parameers such as mine characerisics (i.e. diameer, mass, explosive naure), he locaion and deph of burial are considered and can be modified depending on he condiions o be simulaed. 3 Numerical simulaions 3.1 Finie elemen models The FEMAP sofware [8] was used o generae and mesh he simplified full-scale model of he baseline mock-up, as shown in Figure 2. Each par of he CAD model was meshed wih Lagrangian solid elemens using a consan sress solid elemen formulaion and for shell elemens wih Belyschko-Tsay formulaion and 2 inegraion poins in he hickness. The FE model conained approximaely elemens. The ma_plasic_kinemaic model implemened in LS-DYNA [1] was used o model he maerial response for each par of he mock-up. The plae was 5083-H321 Aluminium [9] while brackes were defined by ASTM A572 Seel, grade 50 properies [9]. Addiional lumped masses were disribued over several sraegic locaions on he model o represen he addiional mass of he vehicle. Graviy loading was applied o all pars of he model.

3 Fig. 2: General view of he mock-up A conac_auomaic_single_surface and conac_auomaic_surface_o_surface keywords were used o define he conacs beween all pars. The pressure based mine loading model was used o apply he iniial loading genereed by a landmine deonaion under he srucure. Table 1: Maerial properies [9] 5083-H321 ASTM A572 G50 ASTM A514 Densiy, kg/m Young s modulus, E GPa Poisson s raio, Yield sress, y MPa Tangen modulus MPa To mee a higher level of proecion, modificaions o he baseline add-on proecion sysem had o be invesigaed. Numerical simulaions were hus performed during he developmen phase on several conceps o help design and opimize a new mine-proecion sysem ha can be used o proec a specific vehicle. Figure 3 shows close-up and exploded views of he baseline proecion sysem as well as for hree conceps. In general, all proecion sysems were composed of a plae (in blue), welds (in green) and brackes (in yellow). a) Baseline (lef) b) Concep 1 (righ) c) Concep 2 (lef) d) Concep 3 (righ) Fig. 3: Proecion sysems

4 Fig. 4: Comparison of he relaive hicknesses of he proecion plae a) Baseline (waffle cross-secion) b) Concep 1 (waffle cross-secion) c) Concep 2 (full plae) d) Concep 3 Figure 4 presens a comparison of a cross-secion of view of he proecion plae for each concep. The maximum hickness of each concep had he same value and was scaled o one. The main difference beween he baseline and Concep 1 was an increase in he waffle plae hickness by 17% (see Figures 4a and b respecively). In addiion, welds and brackes were boh sricly modified o increase he aachmens rigidiy. The second and hird conceps are shown in Figures 3c and 3d, respecively. The design of he welds and brackes of Concep 2 were he same as in Concep 1 excep ha he brackes maerial was replaced for ASTM A514 seel [9] and he maerial used o define he welds was changed. Concep 2 was also modeled wih a full plae. For Concep 3, he only difference wih Concep 2 is ha some maerial was removed from he enire middle secion of he plae o increase he disance beween he plae and he floor and herefore, allow for more deflecion of he plae below he floor while reducing slighly he mass of he proecion sysem. Figure 5 shows a comparison of he mass of he proecion sysems relaive o he baseline proecion sysem. The mass of he proecion sysem over he enire mass of he vehicle corresponds o 0.88%, 1.11%, 1.45% and 1.35% for he baseline, Conceps 1, 2 and and 3 respecively. Fig. 5: Comparison of he relaive mass of he proecion sysems 3.2 Comparison The following secion presens a comparison of he displacemen and deformaion of he four configuraions. Figure 6 shows a higher displacemen of he plae for he baseline and Concep 1 as compared o Conceps 2 and 3. Figure 7 demonsraes clearly ha he deformaion of he baseline and Concep 1 is much larger han in he case of Conceps 2 and 3. Figures 8 and 9 presen he normalized Von-Mises sresses in he proecion plae for he baseline and Concep 3.

5 Fig. 6: Normalized displacemen Fig. 7: Deformaion of he plae. Fig. 8: Normalized Von-Mises sresses (Baseline)

6 Fig. 9: Normalized Von-Mises sresses (Concep 3) Figure 10 shows a comparison of he srains in he brackes and in he welds beween he baseline and Concep 3. The baseline showed high srains in almos all he aachmen poins while in Concep 3 here was fewer srains localised in only few aachmen poins. a) Baseline (lef) b) Concep 3 (righ) Fig. 10: Effecive Plasic Srain Based on he finie elemen analyses, he modificaions incorporaed ino Conceps 2 and 3 showed an improvemen in he performance compared o he baseline performance in erms of deformaion of he plae and he rigidiy of he aachmens o he frame. Conceps 2 and 3 are he conceps ha absorb mos of he energy from he mine and deforme less compared o he oher configuraions. Conceps 2 and 3 show beer energy absorpion capaciy han he oher configuraions Copyrigh by Arup

7 4 Summary In his sudy, finie elemen simulaions were performed during he developmen phase of a modified proecion sysem of a vehicle, o compare he performance of several conceps. Conceps 2 and 3 showed an increase performance when compared o he oher designs from an energy absorpion sandpoin. The combinaion of numerical simulaions and a progressive experimenal es program proved o be an efficien approach o evaluae conceps, o perform opion analyses and o design a successful mine-proecion sysem. The approach of using a combinaion of a progressive experimenal program in conjuncion wih numerical analysis mehods help o refine he numerical models o provide improved accuracy and increase he confidence of he predicive capabiliy of he numerical analyses. Finie elemen simulaions conribued considerably o reduce he coss and ime in developing and choosing he bes concep. The modeling of welds was no fully invesigaed and is he subjec of fuure work. 5 Acknowledgmens The auhors would like o hank Dr. Claude Forier, Mr. Séphane Dumas and Mr. Jean-Luc Bédard for heir inpu o his work. 6 References [1] Livermore Sofware Technology Corporaion, [2] Toussain G. and Bouamoul A. Comparison of ALE and SPH mehods for simulaing mine blas effecs on srucures. DRDC Valcarier. TR Unclassified. Unlimied disribuion. (2010). [3] Tremblay J. Impulse on Blas Deflecors from a Landmine Explosion. DRDC Valcarier. DREV- TM Unclassified. Unlimied disribuion. (1998). [4] Williams K. and Poon K. A Numerical Analysis of he Effec of Surrogae Ani-Tank Mine Blass on he M113. DRDC Valcarier. DREV TM Unclassified. Unlimied disribuion. (2000). [5] Williams K., McClennan S., Durocher R., S-Jean B. and Tremblay J. Validaion of a Loading Model for Simulaing Blas Mine Effecs on Armoured Vehicles, 7 h Inernaional LS-DYNA Users Conference. (2002). [6] Williams K. and Fillion-Gourdeau F. Numerical Simulaion of Ligh armoured Vehicle Occupan Vulnerabiliy o Ani-Vehicle Mine Blas, 7 h Inernaional LS-DYNA Users Conference. (2002). [7] Wesine P. S., Morris B. L., Cox P.A. and Polch E.Z. Developmen of Compuer Program For Floor Plae Response From Land Mine Explosions, Souhwes Research Insiue. (1985). [8] [9]