IMPACT BEHAVIOR OF COMPOSITE MATERIALS USED FOR AUTOMOTIVE INTERIOR PARTS

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1 0 th HSTAM International Congress on Mechanics Chania, Crete, Greece, 5 7 May, 03 IMPACT BEHAVIOR OF COMPOSITE MATERIALS USED FOR AUTOMOTIVE INTERIOR PARTS Mariana D. Stanciu, Ioan Curtu and Ovidiu M. Terciu Department o Mechanical Engineering Transilvania University o Brasov Brasov, Romania mariana.stanciu@unitbv.ro Keywords: Composite, Impact, Automotive, Vibration, Displacement Abstract. This paper presents experimental research on dynamic behavior o door panel made o composite (polypropylene and lignocellulose). The structure o vehicle door with complex geometry (spatial and plan) is stressed by dynamic orces which depend on intensity o acceleration during the impact rom closing and opening. To establish velocities and accelerations developed during the impact, the structure was analyzed, both experimentally and using inite element method (FEM). Four cases were analyzed aiming to establish the inluence o gasket and pawl o vehicle door on the acceleration size recorded during the impact. For each case two values o push orce were applied by means o spring and trigger system. Knowing accelerations o points located on the door panel, were determined displacements. Experimental results were compared with those obtained by FEM in terms o using two types o composite materials. It was ound that at low speeds, the acceleration o the impact is aected by sealing and door stopper. The elastic and mechanical properties o the composites inluence the size o displacement: in case o lignocelluloses composites the displacements are with 0-30% lower than polypropylene panel. INTRODUCTION Studies have shown that modern man spends on average two and a hal away in the vehicle and or this reason, lately, to put great importance on comort, saety and quality o lie []. Besides the technical perormance o a vehicle, aesthetics, comort and saety o the car interior is another important criterion in purchasing a particular model. Thus, the door panel is an important component o the vehicle or which panel design must take into account the wear resistance and other mechanical stresses variables over time and with dierent intensities, capacity o thermal and acoustic insulation, the interchangeability o components and inally a low cost manuacturing. During closing the car door, the door panel is stressed dynamic by inertia orces due to its mass []. In the literature these researches are generally investigated with inite element method and are perormed to predict the lie o components. Su Hong studied the behavior o door panels, rom the point o view o lie, or a number o load cycles [3]. Their research has been done both by numerical methods and experimental studying the atigue stresses o plastic material rom door panel composition. R. Iyengar in collaboration with Ford and Rouge Steel, presents a study regarding the phenomena that occur when car door slamming, both theoretically and experimentally [4]. Experimental research study involved measuring the accelerations o eight points in the metal structure o the door and six points in the interior door panel surace, comparing the results obtained rom the two structures with those obtained by numerical methods. Hörnlund studied dynamic response in time domain and requency, damping actor determining orced vibration and resonance requencies measured at dierent points o the door panel [5]. Lee studied the vibration arising in door panels [6]. Experimental tests were perormed using a stand equipped with a robotic arm which recorded the level o noise and vibration o door panel. Y. Chen (0) researched the sustainability o car door use, looking through experimental methods, damping capacity o car body. It was also revealed that the shock caused by slamming the door is the main application which inluence the lie o the door panels [7]. In this paper, the behavior o door panels made o composite (polypropylene and lignocellulose) to the shock is analyzed. Door structure characterized by a complex geometry (spatial and in plan) is stressed by variable dynamic orces directly dependent o acceleration during the impact rom closing - opening. To establish velocities and accelerations developed during impact, the car door was experimentally analyzed. THEORETICAL BACKGROUND To determine velocities and accelerations developed during impact, the phenomena that develop during closing door were analyzed in terms o mechanical, kinematic and dynamic. Thus, the door located in the "0"

2 position, makes an angle θ to the inal position "" (closed position - Figure, a). On door - the segment 0-, with corresponding angle θ, acting outside orce (F ext ) with application point at a certain distance (d) rom the axis o rotation. Ater removing the external orce door keeps rotation on segment -, with corresponding angle θ until the inal impact position "". Known as input the ollowing parameters: F ext - value external orce, m - mass o vehicle door; m comp - door panel weight; θ - maximum opening angle o the door (segment 0-); θ - opening angle door that apply external orce (segment 0-); θ - angle opening door that no longer apply external orce (segment - ); d - distance rom the hinge to the point where outer orce is applied; d - distance rom the hinge to the center o gravity o the door; l - length door; h - height o the door. To simpliy calculations, it was considered that the panel is rectangular. Forces and reactions during rotary motion and their positions are shown in Figure.a. and air resistance orce with a parabolic distribution on the surace o the door has a value o /3 o the maximum orce (Figure. b). a) b) Figure. a) Position o orce related to the axis o rotation and reactions occurring during rotation; b) Distribution o air resistance orce The air resistance orce varies rom hinge to end o the door and can be calculated with the ormula: ρ v Fr = S c x, () 3 where: ρ v is dynamic pressure o air (ρ relative air density, v velocity); S door surace; c x drag coeicient. Since the air resistance orce has a parabolic distribution, the distance d rom the hinge to the resultant orce F r o air resistance has a value ¾ o the length o the door, resulting: Friction moment o hinge M, is calculated as: 3 d = l. () 4 M = µ N r m, (3) where: µ is riction coeicient, which takes into account the material and surace quality; N orce due to door mass orce; r m - pivot radius o the two hinges [8,9]. For 0- segment expression o kinetic energy is: i0 = F d θ F d θ M θ, ext r (4) where: J is the inertia moment o the door; ω - angular velocity due to the outer orce at point ""; ω - i0 angular velocity in position "0"; F r the air resistance orce; d distance rom hinged to the resultant orce; M - riction momento o hinge. As the angular velocity in position "0" is zero, it ollows that equation (4) reduces to: = F d θ F d θ M θ. ext r (5) For - segment, where no external orce acts on the door, applying the same theorem o variation o

3 kinetic energy, the ollow equation is obtain: Mariana D. Stanciu, Ioan Curtu and Ovidiu M. Terciu = F d θ + M θ, where ω is the angular velocity o the outer orce due to point "". Knowing that even at the speed o 0-30 km/h, the orce o air resistance can be neglected, the two equations (5) and (6) become: r (6) = F d θ M θ (7) ext respectively, = M θ. O the two relations (7) and (8) we can determine the angular velocities respectively, knowing the angular velocities can be determined velocities v and v, corresponding to positions "" and "". Door speed during rotation has a linear distribution along its length and can be calculated with the expression: where ω is the angular velocity, R - radius equal to the length o the door (l). v = ω R, r (0 R), (9) Knowing the speed o the rotating door in dierent positions we can calculate the time course o the initial position until closing. The acceleration can calculated by measuring the traveled distance since the door contacts the irst item o depreciation respectively door lock by pressing the point that the door gasket. During impact o the car door and body, the accumulated kinetic energy becomes strain energy (mechanical work inside) [0]. Thus, we can write the ollowing expression: E = E c de = U, (0) where E is strain energy (denoted with U). Strain energy is taken on by one hand by deormation o rubber de gasket located on the perimeter o the door, and on the other hand by steel structure deormation. Considering that the metal structure o the door has small deormations (negligible), rubber gasket and door lock are designed to cushion the impact o the car door. The main stress o door panel which is stressed by inertial orces due to own weight is bending. Thus the relation (0) can be written as: E M EI ( x) l = dx c + 0 z where k is the stiness o the door seal vehicle, M - bending moments, E - longitudinal elasticity modules, Iz - axial moments o inertia. 3 MATERIALS AND METHOD 3.. Experimental set-up Experimental tests ocused on determining accelerations recorded during closing car door. Such accelerations were measured in the point o the metal structure (reerence point) and the door panel made o polyvinyl acetate. Based on measured accelerations, the displacements o door panel points were determined. Experimental stand, shown in Figure is composed o a subassembly o the Logan model 005 vehicle manuactured in Romania, integrating all elements o the structure o the door and the body. Accelerometers were placed symmetrically on the surace o the door both inside and outside, A corresponds with A and A3 with A4, at the same distance rom the axis o rotation o the hinge and A5 accelerometer was placed on the metal structure in the peripheral area o the panel the door. The selected items or measurements correspond to those where the maximum displacements through numerical analysis were recorded. For processing and analysis o recorded signals was used Pulse program o the Department o Mechanical Engineering and Automotive o "Transilvania" University o Brasov, Romania. kx, (8) ()

4 Figure. Experimental stand or simulating the action o a closing car door stressed by outside orces - body structure o Logan vehicle, - metal structure o the door; 3 - door panel, 4 - spring device and trigger system or the application orce. a) b) Figure 3. The ixing points o acceleration on the door panel: a) interior, b) exterior Four cases were analyzed aiming the inluence o seal and stop on the accelerations recorded during the impact and lock time. For each case, dierent values o push orces were applied (F and F) by means o spring and trigger system. The compression o device spring was perormed in two stages, resulting two values o spring 5 and 50 mm. Thus, or each case 8 tests were perormed, 4 or each value o applying orce. In Table are presented the tested cases. Case I Case II Case III Case IV 3.. Results and discussion With gasket (), Without pawl With gasket () With pawl () Without gasket With pawl () Without gasket Without pawl F=436 N F=436 N F=436 N F=436 N F=87 N F=87 N F=87 N F=87 N Table : Cases o testing The main eatures resulting rom experimental tests reer to: variation o acceleration to impact measured by the accelerometer in point 5 (Figure 3, b), the time closing o door, the displacement o point in relation to point, the displacement o point 3 in relation to point 4. In Figures 5 and 6 are presented the variation charts o recorded experimental data. Similarly graphs were obtained or variation o acceleration and displacement in related with time or each test. Displacements o door panel points were calculated by the dierence between displacement o inside point w int and displacement o outer point w ext, ater the impact, considering that the metal structure o the door is more rigid and deorms very little. Figure 5. The variation o point 5 acceleration (case II, F spring =436 N, test )

5 Figure 6. Variation o displacements o point and (case I, F spring = 436 N, test ) In Table are presented the experimental results in terms o: impact acceleration a imp, m/s ; closing time o door t inc, s; displacement o point related to point w -, mm; displacement o point 3 related to point 4 w 3-4, mm. Cases o testing I II III IV Force o spring, F arc N Average values o accelaration during the impact, a imp [m/s ] Average values o closing time [s] Average values o displacement w - [mm] Average values o displacement w 3-4 [mm] Table : Experimental results Closing time o door varies depending on the intensity o push orce. Thus, at high speed, the values o closing time are similarly regardless o the presence or damping elements (seal and pawl). Reduction o orce intensity leads to large variations o door closing time being inluenced by the existence o damping elements. In Figure 0 is shown variation o closing time o door depending on the analyzed cases and orce intensity. Experimental tests have shown that at low speeds, the acceleration o the impact is aected by sealing and door stopper. Thus, in Figure 7 it can be seen that in case II, the acceleration is decreased by both action o gasket and pawl compare to cases III and IV were the absence o gasket or both components produce a high values o acceleration. At high levels o speed during the closing door, the presence o pawl does not aect the acceleration o the impact, so it is greatest where the seal is missing. Figure 7. Comparison o acceleration values or all tested cases Figure 8. Variation o closing time In Figure 9 are shown the values obtained by numerical and experimental methods or two dierent materials o door panel namely polypropylene panel and lignocellulosic composite laminates, or an average acceleration o 350 m/s upon impact.

6 Figure 9. Displacements values obtained through numerical and experimental method It can be seen that the values o displacements in case o lignocellulosic composite are with about % lower than the polypropylene panel commonly used in manuacturing. These low values are due to the high rigidity and low weight o the new material. 4 CONCLUSIONS Experimental investigations reveal phenomena that occur during shock due to closing the door in dierent condition o loading and damping. Thus, door rotation is not inluenced by the air resistance orce because the resulted velocity have values ranging rom 0.83 to. m / s. Kinetic energy gained by the moving door turns in strain energy at the close, being taken over by the gasket, door lock and metal structure o the body and door. The mass o door panel inluence the intensity o loading due to inertial orces which are developed. Ater experimental tests it was noticed that there is a delay rom the time o impact until the displacements reach a positive peak, this delay being caused by the dierent velocity o shock waves propagation inside the material. I the door is pushed with a small orce, the presence o pawl leads to increase o impact accelerations. When the door is pushed with great orce, the pawl does not aect the values o the impact accelerations and closing times, these values being inluenced only by the quality seal. Dierences between displacement values obtained by numerical methods and those obtained experimentally on door panel, are 7.35% or measured point "" and 6.06% or measured point "3". REFERENCES [] Terciu, O.M., Curtu, I., Stan, G., Cerbu, C. (00), "Lignocellulosic composites or automotive industry", in The th International Congress on Automotive and Transport Engineering CONAT00, Brasov, Romania, -3 October 00, pp. 7-4, ISSN [] Lorenzo, M., Lorenzo, R. R., Giuseppe, P., Andrea, T. (0) The Automotive Body, vol. II: System Design, Springer Dordrecht Heidelberg London New York, ISBN [3] Su, H., Dunn, C,. Krajcirovic, A. (009), CAE Virtual Door Slam Test or Plastic Trim Components. SAE Technical paper series (09), 9, 003, (date o acces: ), available: ISSN [4] Iyengar, R., Chang, T., Laxman, S., Thirupathi, S. (004), A Comprehensive Study o Door Slam (06), (date o acces:.0.00), available: ISSN [5] Hörnlund, M., Papazoglu, A., (005) "Analysis and measurements o vehicle door structural dynamic response", Master s dissertation, Lund University, Lund, Sweden, ISSN [6] Lee, H., Park, H., Na, H., Kim, J. (009), Simple Test Method or Squeak & Rattle Evaluation o Door Trim by Using Statically Repeated Loading Robot Arm. SAE 009 Noise and Vibration Conerence and Exhibition (), 8, 009, (date o acces:.03.00), available: ISSN [7] Chen, Y., Lepley, D., Cutting, C., Araki, T. (0), French Door Open/Close Durability Evaluation by Multibody Dynamics Method. SAE 0 World Congress & Exhibition (0758),, 0, (date o acces: ), available: DOI: 0.47/ [8] Vlase, S., (005) Mecanica. Dinamica (in Romanian), Ed. Inomarket, Brasov, ISBN [9] Vlase, S., (004) Mecanica. Statica (in Romanian), Ed. Inomarket, Brasov, ISBN [0] Curtu, I., Biţ, C., (000) Rezistenţa Materialelor şi Teoria Elasticităţii, Partea a III-a, (in Romanian) Braşov, Editura Universităţii Transilvania.