PLASTIC HYBRID SOLUTIONS IN TRUCK BODY-IN-WHITE REINFORCEMENTS AND IN FRONT UNDERRUN PROTECTION

Transcription

1 PLASTIC HYBRID SOLUTIONS IN TRUCK BODY-IN-WHITE REINFORCEMENTS AND IN FRONT UNDERRUN PROTECTION Dhanendra Kumar Nagwanshi, Somasekhar Bobba and Ruud Winters SABIC s Innovative Plastic Business, Automotive, United States KEYWORDS Plastic hybrid Solutions, Crash & Energy management, Front underrun protection, BIW reinforcements (A-Pillar), Lightweight, ECE R29/3 and ECE R93. Abstract With new and evolving safety regulations and stringent emission standards, designing for vehicle safety as part of the total design process has been increasing since last decade. For heavy motor vehicles (trucks), this is driven by the new ECE R29/3 cabin safety regulations with emphasis on front impact and roll-over occupant safety. For the collision scenario that involves a truck and a passenger car, the ECE R93 regulation sets the requirements to be met in order to prevent the smaller vehicle from being pushed under the heavy truck in the event of a frontal collision. Steel countermeasures are typically used as structural reinforcing elements to fulfill these two regulations. This paper presents lightweight thermoplastic solutions, as an alternative to traditional metal based solutions. Two different design solutions as a reinforcement to body in white (BIW) are discussed in this paper: first a plastic/metal hybrid solution consisting a steel channel with thermoplastic reinforcing rib structure, and second a plastic/composite hybrid solution. Prototypes parts were developed for both metal plastic hybrid solutions and composite plastic hybrid solution and evaluated in a four point bending test and compared to the baseline metal solution. The plastic/metal hybrid reinforcement shows a 15% increase in energy absorption with 25% weight saving compared to metal solution. The plastic/composite hybrid solutions shows 30% increase in energy absorption with 45% weight saving compared to metal solution. 1

2 For ECE R93 regulation, a plastic/metal hybrids solution has been discussed as a front underrun protection device as an alternative to incumbent solutions. Proposed plastic-metal hybrid solution combine the advantages of inherent material properties of both metal and plastics and the manufacturing flexibilities of plastics. Conventional front underrun protection devices (FUPD) include an assembly of steel parts that are relatively heavy. A lightweight hybrid FUPD solution concept is presented in this paper. Finite Element methods using LS- DYNA are used to evaluate the performance of this FUPD. The study shows that the innovative modular concept has the potential to fulfill the safety requirements while enabling a weight saving of up to 40 percent compared to a full steel concept. Integration of additional functionalities into the hybrid structure can bring further cost advantages, ease of assembly and ease of replacement. This hybrid FUPD technology can also be developed for rear and side underrun protection. 1. Introduction. Vehicle body engineers use several methods to reinforce an automotive body structure in order to fulfil stringent regulations. A traditional approach is to add steel reinforcements inside the Body-In-White (BIW) structural members. They can also increase the grade (yield strength) or gage (thickness) of the steel used in the structural members. Steel reinforcements are commonly used in BIW-Pillars to improve the bending and buckling load capacity. In this paper, we will present two thermoplastic reinforcement designs used to improve the front impact performance. The first concept is a plastic/metal hybrid design, the second concept a composite/plastic hybrid design. A B-pillar replica is used to evaluate the performance of these thermoplastic-based solutions and comparative tests are carried out with traditional steel reinforcements. 2

3 Next to that, for the safety of car passengers, front underrun protection devices (FUPD s) are mounted on the front of a truck to help safeguard a car from diving under the truck in the event of a frontal collision. In 2001 the United Nations Economic Commission for Europe decided that all trucks manufactured as from that year need a front underrun protection system (FUPS). [1] Therefore, regulations have been established to govern the safety issues that come with large trucks traveling on the same roads with small trucks and cars [2]. In addition, due to stringent and rising fuel economy standards, the truck industry is looking for weight saving solutions. Plastic/metal hybrid concepts combine the advantages of inherent material properties of both metal and plastics and the manufacturing flexibilities of plastics. In order to meet the ECE R93 regulation, these plastic/metal hybrids can be used as an alternative to incumbent solutions. The conventional front underrun protection device (FUPD) is currently formed through the assembly of steel parts that are relatively heavy. An innovative lightweight hybrid FUPD solution concept is presented in this paper. 2. New safety regulations for heavy trucks. With new and evolving safety and weight reduction regulations and strategies, designing for vehicle safety as part of the total design process has been increasing over the last decade, with the effect of reducing the number of fatal and serious injury risks for car occupants and pedestrians. For the truck driver this is shown in the new ECE R29/3 cabin safety regulations [3] with emphasis on front impact and roll-over occupant safety, demanding a further reinforced cabin structure. Next to that, for the occupants of a passenger car, the ECE R93 regulation sets the requirements to be met in order to prevent the smaller vehicle from being pushed under the heavy truck in the event of a frontal collision. Steel countermeasures are typically used as structural reinforcing elements to fulfill these two regulations. Main considerations of both regulations will be described in the next paragraphs ECE R29/3 Cabin safety. In ECE regulation R29 Uniform Provisions Concerning the Approval of Vehicles with regard to the Protection of the Occupants of the Cab of a Commercial Vehicle 3 different test procedures are described [3] as shown in figure 1. 3

4 (a) (b) (c) Figure 1: Load cases for ECE regulation 29: Test A front impact (a), test B front pillar impact (b) and test C roof strength test (c) [3]. In test A a square rigid pendulum is swung against the front of the cab with an energy of 29.4 kj for vehicles with a gross vehicle mass < 7.5 tons and an energy of 55kJ in case of a gross vehicle mass > 7.5 tons. The impact position is such that the center of gravity of the impactor is located 50 mm below the R-point of the driver seat (figure1a). In test B a round rigid pendulum, overlapping the A-pillars, is swung against the front A-pillar/window area with an energy of 29.4 kj. Its center of gravity is midway between the lower and the upper windscreen frame (figure 1b). This test is not applicable to vehicles with a gross mass <7.5 tons. Test C comprises out of 2 parts. First part is a dynamic load of 17.6 kj under an angle of 20 (P1 in figure 1) and is only applicable to vehicles with gross mass >7.5 tons. The roof strength test (load P2 in figure 1c) where a load equal to the maximum authorized front axle(s) mass is applied to the roof of the cab is applicable to all vehicle masses (subject to a maximum of 98kN). After performing these test the vehicle should exhibit enough survival space to accommodate a specified manikin (or a fiftieth percentile hybrid 2/3 male dummy). The cab should also remain attached to the frame and no opening of doors is allowed. In chapter 3 the possible use of plastics in BIW reinforcements is shown, helping to meet these requirements while minimizing the weight. 4

5 2.2. ECE R93 Front Underrun Protection Devices (FUPD s). To prevent cars from underrunning trucks in the event of a frontal crash, regulation ECE R93 [2] was set up. For an FUPD it is required that it offers adequate resistance against forces applied and it should also satisfy certain dimensional requirements as described below ( test conditions and procedures part of ECE R93) Figure 2: Dimensional requirements: a. dimensional requirements and loading positions, b. maximum allowed deformation after applied load, c: upper deformation limit definition of cross member outside P1 position. Dimensional requirements, as shown in figure 2, are: - Section height cross member >100 mm for N2 and >120mm for N3 vehicles. - Outermost surfaces must be smooth or horizontally corrugated bolts or rivets may not protrude beyond the surface more than 10 mm - Width of FUPD: Not exceed mudguard covering wheels, not more than 100 mm shorter than outermost pint of the tyres of the front axle or 200 mm from the outermost points of the access steps to the drivers cabin (figure 2a). - Points of application of force should not be higher then 445 mm, positions shown in figure 2a. - Deformation after the load application: the distance of the front of the FUPD to the foremost part of the truck should not exceed 400 mm (figure 2b). - Ground clearance should not be more than 400 mm between the 2 points P1. Outboard of these points the clearance might be greater providing the underside is not above a plane passing through the underside of the FUPD directly below point P1 and forming a slope at 15 above the horizontal (figure 2c). 5

6 - Maximum ground clearance of underside of FUPD between points P1 should not exceed 450 mm during the test. Forces that need to be applied to the FUPD are shown in table 1. The forces can be applied through a square surface, maximum 250 mm in height and max 400 mm in width. Table 1: Forces to be applied at different load locations shown in figure 2a. Test Load (kn) outer edge (P1) center (P3) off center (P2) ECE R93 80 kn/ 50% of vehicle weight whichever is less 80 kn/ 50% of vehicle weight whichever is less 160 kn/ 50% of vehicle weight whichever is less When tested the forces should be applied as quickly as possible and the FUPD or the vehicle should withstand this for at least 0.2 seconds. 3. A-Pillar reinforcements to meet EC-R29/3 regulation. A traditional approach to reinforce an automotive body structure is to add steel reinforcements inside the Body-In-White (BIW) structural members or to increase the grade (yield strength) or gage (thickness) of the steel used in the structural members. Steel reinforcements are commonly used in Pillars to improve the bending and buckling load capacity. In the next paragraphs, 2 lightweight thermoplastic hybrid reinforcement solutions, a plastic/metal hybrid and a composite/plastic hybrid reinforcement, and their performance are compared to an incumbent high strength steel reinforcement. This is done by testing the bending behavior of a Pillar replica. 6

7 3.2. Plastic metal hybrid reinforcements. Plastic-Metal hybrid (PMH) technology has the potential to produce a structure with a mechanically interlocked connection between both materials. The design synergy studied in this project between plastic and metal inserts can conceptually deliver mechanical performance properties of importance to end users, like excellent resistance to bending, compression, and torsional load. The hybrid solution concepts presented in this article allow metal to be located only in areas with higher stiffness requirements and thus offer the potential for truck makers to realize increased design and weight efficiency. The overmolding injection process combines metal stamping with plastic structures, which can increase design freedom for feature integration and reduce the number of steps required for assembly [4]. The use of PMH in a passenger s car B-pillar was demonstrated in the past by SABIC [5]. This study, based on simulation results, showed that a potential weight saving of 25 % is possible at same performance as a high strength steel reinforcement. In the current paper the effect of reinforcements on a pillar replica is discussed. Different reinforcements were then added to check the effect on 4-point bending performance. Using a conventional reinforcement made out of a high strength steel (350Mpa yield stress) U-profile weighing approximately 850 grams was compared to the performance of a plastic metal hybrid made out of Noryl GTX (PPO/PA blend) weighing approximately 650 grams. (Figure 3) In this case Noryl GTX is used as its high temperature resistance makes it possible to use it in the E-coat process. (a) (b) Figure 3: High strength steel reinforcement (a) and Noryl GTX plastic-metal hybrid (b) reinforcements used in the test. 7

8 As shown in figure 4 the approximately 25% lighter plastic-metal reinforcement can take up a similar peak load and, due to its honeycomb design, retains this peak load longer during the further deformation of the beam. This results in a ca. 20% better energy absorption by the plastic/metal-hybrid (see figure 5). Figure 4: Effect of reinforcements on 4-point bending performance of a replica pillar: comparison unreinforced, high strength steel reinforcement, plastic metal hybrid reinforcement. 3.3 Composite hybrid reinforcements. If further weight reduction is needed, composite hybrid structures can be used as reinforcement. A thermoplastic composite shell can be formed using glass- or carbon fiber tapes or laminates (see figure 5), and then over molded with an unfilled or filled thermoplastic material. Resin compatibility is crucial here. Resin combinations that can withstand the E- coat cycle, such as Noryl GTX were tested and showed an increased performance in the 4- point bending test as described in par

9 Figure 5: Using composite laminates/tapes back-molded with thermoplastic resins to produce a plastic composite hybrid beam. Compared to the 850 grams high strength steel reinforcement, the tested composit hybrid had a weight of 450 grams. This means a ~45% weight reduction compared to the high strength steel reinforcement and a further ~30% weight reduction compared to a Metal plastic hybrid. Wrt the energy absorption, that is represented by the area below the force/deflection curves shown in figure 6, the performance improvement is ~30% against the high strength steel insert. Figure 6: Effect of reinforcements on 4-point bending performance of a replica pillar: an unreinforced, b high strength steel reinforcement, c plastic metal hybrid reinforcement, d plastic composite hybrid reinforcement. 9

10 4. Front underrun protection devices. Next to BIW reinforcements it might also be possible to use plastic-metal or plasticcomposites hybrids in Front underrun protection devices. In this chapter an innovative FUPD design concept, including its potential manufacturing and assembly processes, is presented. A method that could be considered for making the conceptual modular light-weight support structure is discussed as well. Predictive engineering tools are used to evaluate performance of the concept modules against current regulatory requirements in the United States and Europe. 4.1 Incumbent metallic solution. An example of a generic underrun protection device attached to rails/chassis, which consists of more than four individual steel components, is shown in Figure 8. Conventional all steel FUPDs are typically fitted on to the truck like this. These steel solutions are heavy due to exhaustive use of rolled steel channels and members. Manufacturing of conventional FUPDs typically involves multiple operations like stamping of steel structures and joining processes. In the first step, two components (2, 3) are welded to form an individual section. In the second step, the support brackets (4) are welded to a transversal front beam (5). In the final stage, the two substructures (2, 3) and (4, 5) are bolted and welded to the rails and chassis, as shown in Figure 7. In this example, for a 12 tons truck, the components 2-5 of figure 8 have a total weight of approximately 44 kilograms. Figure 7: Generic/ conventional full metallic FUPD (a) assembly and (b) split-up with detail of sub-structural components. 10

11 4.2 Plastic-Metal hybrid solution concept. As described in paragraph 3.2. plastic/metal hybrid concepts combine the advantages of inherent material properties of both metal and plastics and the manufacturing flexibilities of plastics. These features of the hybrid concept can lead to part solutions that are more cost effective. In this study, a modular hybrid concept was conceived to form a FUPD. In the concept presented here, the conventional brackets (components 2, 3 and 4 in Figure 7) which connect the front bar and rails, are replaced with a metal-plastic hybrid structure. The module-based structure is made by over-molding the steel insert with a long glass fiber reinforced polypropylene (STAMAX TM resin) as shown in Figure 8. Figure 8: Plastic-Metal hybrid FUPD structure (steel = light grey, plastic = dark grey). This concept can minimize assembly efforts as only two substructures must be joined to form a full scale FUPD The total weight of the 2 hybrid support structures and the horizontal beam is 25 kilograms, so compared to the existing full metal FUPD, a weight reduction of ~40 percent is possible in this case. For a 12 tons truck, predictive-based FE (finite element) analyses were performed on the concept to optimize the designs and evaluate mechanical performance. As observed in figure 9, the hybrid FUPD meets the safety requirements when applying the loads as described in regulation ECE R-93 (see paragraph 2.2, figure 2). The simulated X - displacement (loading direction) of hybrid structures is 260 mm for load P1 and 270 mm for load P2, much lower than the maximum allowable value of 400 mm. 11

12 Figure 9: Deformation contours for Plastic-Metal hybrid FUPD loading at P1 (left) and P2 (right) locations. 5. Conclusions and perspectives. BIW Reinforcements: The focus of this study was to develop alternative countermeasure concepts designed to meet the new ECE R29 Cabin safety regulations. A plastic/metal hybrid and a plastic/composite hybrid thermoplastic reinforcement concept were therefore compared to a traditional steel reinforcement baseline in a 4 point bending test. These plastic metal hybrid reinforcement showed an increase in energy absorption of ~ 15 percent at a reduced weight of ~ 25 percent compared to a high strength steel reinforcement. For the plastic/composite hybrid energy absorption increase was ~ 30 percent at a weight reduction of ~ 45 percent compared to the high strength steel design. The tests show that these thermoplastic designs could be viable alternatives to locally strengthen the load bearing sections of the Body-In-White. These thermoplastic hybrid countermeasure designs can meet strength and stiffness requirements and further give the benefit of a high strength to weight ratio. Front underrun protection devices: Based on results from quasi-static simulations, the innovative modular concept described in this paper has the potential to help truck makers fulfill safety requirements of the ECE-R93 standard while enabling a weight saving of up to 40 percent compared to a full steel concept that meets the same requirements for the same vehicle (12-tons truck). 12

13 The modular hybrid structure concept has the potential to deliver reduced weight (~40% in this case study) and easier assembly and replacement compared to the baseline solution. The cost advantages of these concepts can be further enhanced by integration of additional functionalities into the hybrid structures and ease of assembly and replacement. This hybrid FUPD technology can also be developed for rear and side underrun protection. REFERENCES 1. DIRECTIVE 2000/40/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 26 June 2000 on the approximation of the laws of the Member States relating to the front underrun protection of motor vehicles and amending Council Directive 70/156/EEC 2. E/ECE/TRANS/505 Regulation No E/ECE/324/Rev.1/Add.28/Rev.2 + E/ECE/324/Rev.1/Add.28/Rev.1/Amend.3 Regulation No Plastics Application Technology for Safe and Lightweight Automobiles, SAE International Book, ISBN: ISBN: Kulkarni, S. and Marks, M., "Thermoplastic Roof Crush Countermeasure Design for Improved Roof Crush Resistant to Meet FMVSS-216," SAE Technical Paper , 2011, doi: /