Design of Vehicle Structures for Crash Energy Management

Transcription

1 Design of Vehicle Structures for Crash Energy Management

2 Slide 2 of 80 Introduction The final design was the product of a long evolution guided primarily by testing, supported by simple linear strength of material methods. Tools include simple spring-mass models, beam element models, hybrid models and finite element models. In recent years - demand from customers, regulators, and media to provide safer vehicles. 2

3 Slide 3 of 80 Introduction Current Design Practice - reviews the current modeling and design processes while identifying shortcomings for early design stages. Crash/Crush Design Techniques for Front Structures - examines techniques for analyzing the front-end system and to compute the performance design objectives of subsystems and components. Analytical Design Tools - introduces component design methods to create structural concepts for energy absorption and strength. Vehicle Front Structure Design for Different Impact Modes - discusses strategy for designing structures for different frontal impact modes, including vehicle-to vehicle crashes. 3

4 Slide 4 of 80 Current Design Practice Lumped Mass-Spring Models Limitations of LMS Models Comparison Between LMS and FE-Based crashworthiness Processes

5 Slide 5 of 80 Current Design Practice The Design process relies on calculating the crash pulse from either Lumped Mass-Spring (LMS) models or Finite Element (FE) models Two tasks: Vehicle body structure and major components packaged ahead of the front occupants, such as the power-train. Designing the occupant environment such as the dummy, restraints and vehicle interior surfaces.

6 Slide 6 of 80 LMS based crash pulse estimation Figures from Priya Prasad, 2005

7 Slide 7 of 80 FE Based Crash pulse Estimation Figures from Priya Prasad, 2005

8 Slide 8 of 80 The LMS Model Vehicle approximated by a one-dimensional lumped mass-spring system. acceptable for modeling the basic crash features. requires a user with extensive knowledge Crush characteristics from static crush setup. Figures from Priya Prasad, 2005

9 Slide 9 of 80 Test set up Crush Test setup Kamal s Lumped mass model Figures from Priya Prasad, 2005

10 Slide 10 of 80 Acceleration vs Time Simulated acceleration histories with those obtained from the test, and it shows a very good agreement can be achieved Figures from Priya Prasad, 2005

11 Slide 11 of 80 Side Impact LMS Model <#> of 78

12 Slide 12 of 80 LMS Models Pros: Quicker turnaround time parametric studies at earlier design stages Cons: One dimensional Requires prior knowledge of spring characteristics

13 Slide 13 of 79 3D models Initial Results compare well with full scale crash tests After 80 ms Figures from Priya Prasad, 2005

14 Slide 14 of 79 Frame Models and FE Models To overcome 1D, 3D simulation in MADYMO The model also includes the power train external surfaces to accurately capture contact with the barrier. 3D frame FE model Figures from Priya Prasad, 2005

15 Slide 15 of 80 Basic Principles of Designing for Crash Energy Management Match in 3D frame and FE model response for FOOTWELL intrusion Difficult to reproduce by 1D LMS models Figures from Priya Prasad, 2005

16 Crash/Crush Design Techniques for Front Structures Slide 16 of 80 Designing for crash is multidisciplinary - very close interaction of Biomechanics Structures Vehicle Dynamics Packaging Engineering analysis Manufacturing

17 Slide 17 of 80 Basic Principles of Designing for Crash Energy Management Frontal offset Crash 40 kmph Figures from Priya Prasad, 2005 Vehicle to vehicle crash 70 kmph

18 Slide 18 of 80 Basic Principles of Designing for Crash Energy Management Desired Dummy Performance Various occupant simulation models are used to study interactions between dummy, restraint system and the vehicle A family of crash pulses or signatures that successfully meet specific injury criteria are defined. These pulses, in turn, define objective criteria for vehicle design Desired crush sequence and mode will need to be selected and crush zones identified to assure the structural pulse Several models are developed in parallel to study

19 Slide 19 of 80 Basic Principles of Designing for Crash Energy Management Stiff cage Structural Concept Objective is to design a stiff passenger compartment structure Structure should have a peak load capacity to support the energy absorbing members in front of it, without exhibiting excessive deformation (intrusion)

20 Slide 20 of 80 Basic Principles of Designing for Crash Energy Management Figures from Priya Prasad, 2005

21 Slide 21 of 80 Basic Principles of Designing for Crash Energy Management Controlled Progressive Crush or Deformation With Limited Intrusion Rear, roof, and side impact energy-absorbing structures deform upon direct impact in a mixed axial and bending mode Bending dominant role low energy content In designs where light weight is desirable, axial mode will be a more appropriate candidate for energy absorption

22 Controlled Progressive Crush or Slide 22 of 80 Deformation With Limited Intrusion (contd) Primary crush zone - relatively uniform, progressive structural collapse Main energy absorbing structure- fore section of the power train compartment Secondary crush zone -structural interface between the energy absorbing and occupant compartment structures Avoid excessive load concentrations Design strategy soft front zone- to reduce the vehicle s aggressivity in pedestrian-tovehicle and vehicle-to-vehicle collisions Two stiffer zones - primary and secondary. Primary main EA structure in the fore section Secondary structural interface between absorber and compartment Extends to the dash panel and toe board areas

23 Slide 23 of 79 Design of structural topology / Based on ability to design in the crush mode for primary crush zones Based on simplified 3D models Once a skeleton is ready design loads can be estimated Using Quasi Analytical studies Sizing of thin shell components using computer codes. (ex. SECOLLAPSE) Crush criteria will dictate the structural design. NVH criteria and durability can be easily met if designed for crash. Figures from Priya Prasad, 2005 architecture Model by Mahmood and Paluszny

24 3-D hybrid modelling of front end 3D hybrids and collapsible beam elements used Possible to analyze asymmetric impacts The model grows progressively The designed structures / sub-structures are readily analyzed in a system environment system Lumped Mass Slide 26 of 80 Figures from Priya Prasad, 2005 Finite Element

25 Slide 27 of 80 Evolving front-end system modelling LMS model LMS + FE model LMS + FE model ( increased FE) Complete FE with minimal LMS Figures from Priya Prasad, 2005

26 Slide 28 of 80 Analytical Design Tools Component Design Column - axial load in compression Beam - bending or combined bending and axial compression Types of Deformations: Buckling/collapse of a structural component is called local when the deformations (buckle/fold) are of local character and the collapse is confined to an isolated area of the component It is global (an example is an Euler-type column buckling) when the whole component becomes deformed and subsequently collapses

27 Slide 29 of 80 Analytical Design Tools Two Issues Collapse Modes for Absorption of the kinetic energy of the vehicle Axial Bending Crash resistance or strength to sustain the crush process and/or maintain passenger compartment integrity

28 Slide 30 of 80 Axial / Bending Mode Axial Most Effective Difficult to achieve Bending Local hinges are formed Structures designed for axial mode can also fail in this mode <#> of 78

29 Axial Collapse Mathematical Modelling Slide 31 of 80 purely analytical / strictly experimental approaches Analytical Modeling mechanics and kinematics of folding Assumptions were limiting Average or mean crush load estimated from the energy balance by equating the external work done by the crush load with energies dissipated in different types of deformation mechanisms in a folding process Figures from Priya Prasad, 2005

30 Slide 32 of 80 Axial Collapse P m = M o C 1/3 t -1/3 where P m is the mean/average crush force M o = σ o t 2 / 4,the fully plastic moment, σ o, is the average flow stress (σ o = (0.9 to 0.95) σ u ), σ u is the ultimate tensile strength of the material, C = 1/2 (b+d) with b and d being the sides of a rectangular box column, t its wall thickness

31 Slide 33 of 79 Variation of structural effectiveness Experimental results = specific energy (SE) / specific ultimate strength (SUS) SE = maximum energy / weight SUS = US / density = material volume / total volume Plot for square and rectangular thin wall columns Figures from Priya Prasad, 2005

32 Slide 34 of 80 Axial Collapse Experimental: The expression for mean crush load is obtained from the expression for specific energy (E s =P m /ρφa o ) and is of the form: P m = η σ u φ A o ρ being the density and A o the overall area of the section as defined by its outer circumference

33 Slide 35 of 80 Mahmud and Paluszny Local buckling at critical loads Leads to collapse and subsequent folding For low t/b ratios Large irregular folds Crumpling Global Buckling or Bending type instability <#> of 78 Folding pattern of thin-walled box with very small thickness/width ratio

34 Slide 36 of 79 Experimental Results For high t/b ratios Buckling loads more than material strength Stable even with geomtrical / loading imperfections Limit for compactness Folding pattern of thin-walled box with large thickness/width ratios ( t b) 0.48[ (1 ) / E] * y Similar formulations for rectangular sections Figures from Priya Prasad, 2005

35 Slide 37 of 79 Axial Collapse Practical Curve Theoretical curve P max can be attenuated by appropriate imperfections To minimize load transferred to other structures Load Vs. Deflection plots for design in axial collapse

36 Slide 38 of 80 Methods of folding Depends on the local geometry No of flat plates / flanges at corners Designed so as to initiate appropriate folding Angle / T / Y folds Angle folds

37 Slide 39 of 80 Stability of the Axial Collapse (Folding) Process All compressively loaded elements can loose stability Leading to premature buckling Loss of energy absorption Presumably after critical collapse length has been reached Experimental correlations have been developed Figures from Priya Prasad, 2005

38 Slide 40 of 80 Bending Collapse In most collision scenarios except, for side impact, mixed modes involving axial compression and bending or sometimes even torsion. Component failure triggered at the location where compressive stress reaches critical value, the side or flange of the section to buckle locally, which initiates formation of a plastic hinge-type mechanism. The bending moment at the newly-created plastic hinge cannot increase any more, the moment distribution changes and a further increase of the external load creates additional hinges, until eventually, the number and the distribution of hinges is such that they turn the structure into a kinematically movable, linkage-type collapse mechanism The overall collapse mechanism is controlled by hinge location and is dependent on the instantaneous strength (load capacity) distribution, which is a function of the loading state

39 Slide 41 of 79 Bending modes Local buckling initiates a plastic hinge When compressive stress reaches a critical value Further increase of load causes more hinges Overall collapse mechanism is controlled by hinge locations

40 Slide 42 of 79 Different Collapse modes Compressively loaded flange of a compact section Flange collapse of noncompact sections Web collapse of stiffened or narrow flange beams <#>

41 Slide 43 of 80 Load-deflection characteristics of a plastic hinge Taken from Kecman s thesis Classic plastic hinge Thin walled beams Hinge collapse with material separation Figures from Priya Prasad, 2005

42 Slide 44 of 79 Stiffness of the hinge Studies have been done to estimate bending behaviour of hinges Curve A: Plastic Hinge Solid sections of very thick walled beams of ductile materials B: Thin walled beams that buckle locally Drop off in stiffness depends on Section compactness Stability of axial collapse Smaller t/d, smaller σ cr /σ y steeper drop off <#>

43 Slide 45 of 79 Moment-rotation characteristics of thin-walled beam Very little energy absorbed in that initial deformation Most of the collision energy is converted into the plastic deformation energy of the hinge, which corresponds to the area under the tail segment of the M-θ curve Figures from Priya Prasad, 2005

44 Slide 46 of 79 Bending Collapse The shape and geometry of the collapsed mechanism plays a significant role in determining the amount of energy absorbed on closer examination, distinct deformation mechanisms such as bending about stationary hinge/yield lines and rolling along specific yield lines can still be identified. Figures from Priya Prasad, 2005 Uniaxial bending collapse section and a combined bending (bending about non-principal axis) of a rectangular section

45 Slide 47 of 80 Combined Loading SECOLLAPSE ( software) The strength of each sub-element of a component section is related to the total applied stress When one of the sub-elements reaches its maximum (crippling) strength, the geometry of the section is distorted in such a way that the collapse of the subelement induces the collapse of the whole component. Thus, SECOLLAPSE automatically generates a failure surface appropriate to the component and the loading case investigated Verification of analytical models is normally done in well-controlled laboratory tests.

46 Slide 48 of 80 Structural Joints Structural joints define the end conditions and constraints for structural load carrying elements such as beams and columns. control, to a considerable degree, the stiffness of the vehicle structural systems Till recently, joints designed for NVH and manufacturability Crash energy requirements are more demanding The tools most likely to be used in their design and development rely on non-linear FE plate and shell analysis, supported with appropriate tests

47 Slide 49 of 79 Design of Substructures After designing components it is necessary to check the complete structure / sub structure Structure collapses in stages Figures from Priya Prasad, 2005 Collapse sequence in a convoluted design

48 Analytical Design Tools for Crash Hybrid Models Energy Management Combination of LMS and FE like methods Slide 50 of 80 Complete front end of a vehicle is modeled using multiple types of elements such as shells, beams, springs and masses. Uses Explicit FE crash codes for simulation KRASH (explicit dynamic code developed for aircraft crash simulation) - Structure is deformable beam element with collapse characteristic from actual testing. Quick analysis of different design alternatives Poor co-relation with experimental tests The crush characteristics generally non-isotropic Internal effects alter mode of collapse extensive exp. & understanding of crash needed by user

49 Slide 51 of 80 Analytical Design Tools. Collapsible Beam Finite Element Elastic-Plastic Beam With Plastic-Hinge Model extensively to model the bending collapse of beams, large rotation angles (deep collapse) Severe limitations when designing for energy absorption by axial folding Earlier S frame in Crush: limited to a planar frame. also modeled with rigid beams and rotational springs elastic-plastic beam with a plastic-hinge at the end is a more accurate method of modelling

50 Slide 52 of 80 Collapsible Beam FE EP Beam with Plastic Hinge Simulation of elastic-plastic hinge in beams using rotational springs Figures from Priya Prasad, 2005

51 Slide 53 of 80 Super-Collapsible Beam Element capable of handling combined axial loads in the presence of multi-plane bending useful in analyzing the crush behavior of front and rear vehicle structures rails first fold axially, then deform in bending VCRUSH - a specialized computer program with this element formulation

52 Slide 54 of 80 Design of Substructures Super-Collapsible Beam Automotive components are generally made of thin-walled sheet metal that can be divided into many sub-elements A sub-element is a four-node plate or shell supported by the adjacent sub-element In the crippling and folding stages, the plane section-remain-plane assumption is no longer valid because of the large distortion. For moderate thin-walled sub-elements, σ cr > σ y where σ y is the yield stress. In this case, yielding occurs earlier than buckling and the second stage should be yielding stage

53 Slide 55 of 80 Design of Substructures buckled: σ cr σ < σ max elastic: σ < σ cr folding: σ cor σ σ min crippling: σ max σ σ min Figures from Priya Prasad, 2005 σ min σ max σ cor are the maximum, minimum and corner crushing stresses

54 Slide 56 of 80 Design of Substructures Thin-Walled Finite Beam Element Failure mode of the beam element is complicated Caused due to the crippling of the thin plates The element stiffness formulation after sub-element buckling is important Extensive test observations, however, give indications that failure modes follow certain rules, making the failure mode predictable The first crippled sub-element buckles inboard and the adjacent ones buckle outboard. The fold length of the first crippled sub-element controls the length of the hinge Deformation pattern is approximately proportional to the stress pattern at crippling

55 Slide 57 of 79 Thin-Walled Finite Beam Element Possible to predict the shown failure mode For each fold, the axial deformation at section C.G. and the rotation can be calculated as: ε = dl/d2ε n θ = artg(ε n /d 2 ) where ε n is the fold length at first crushed node, dl, is the distance from the C.G. to the neutral axis and d 2 is the distance from the first crushed node to the neutral axis. Failure happens in 4 stages Figures from Priya Prasad, 2005

56 Slide 58 of 79 Failure in stages Bending Crash Mode Each cycle represents a fold process Points 1,2,3,4 can be pre-determined Energy better predicted than P or M Axial Crash Mode Figures from Priya Prasad, 2005

57 Slide 59 of 80 Incorporating Dynamic Effects In LMS models through a single dynamic factor Usually related to a crash rate Vary with the construction of the vehicle b cause the collapse modes and inertial effects vary with vehicle In FE models through effect of strain rate on tensile (compressive) properties of materials <#> of 78

58 Slide 60 of 80 Effect of strain rate on steels Change in strength given by. V k 2 r log( ) V1 where k r is experimental determined and V 1, V 2 are the strain rates. Also, strain rate sensitivity exponent is given by m ln( 2 ) / ln( 2 ) 1 1 <#> of 78

59 Slide 61 of 80 Dynamic Effects Two sources: The effects of strain-rate on the yield and flow strengths of the material. The inertia effects on the internal load distribution that may affect both the overall and local collapse modes. How to incorporate Dynamic Effects in the models

60 Slide 62 of 80 Structural Programming The buckling-crippling-folding process involves severely large deformation and the element stiffness formulation should consider this effect. The resultant stiffness can be derived as: where [K] = [K e ] + [K a ] + [K b ] + [K g ] [K e ] is the small deformation stiffness [K a ] and [K b ] are the axial and bending stiffness due to large deformation and [K g ] is the bending stiffness due to axial force, usually called geometric stiffness *Ka+ and *Kb+ are the functions of displacement y [Kg] is function of axial force.

61 Vehicle Front Structure Design for Different Impact Modes Slide 63 of 80 Vehicle Front Structure Design for Different Impact Modes Vehicle Front Structure Design for Current Standards FMVSS 208 NCAP Test IIHS Test Vehicle-to-Vehicle Frontal Collisions Preliminary Relationships in Head-on Frontal Collision Strategies for Designing Front Structures for Head-on Impact Assessment of Analytical Tools

62 Vehicle Front Structure Design for Different Impact Modes Slide 64 of 80 The vehicle structure, along with its restraint system, is designed to provide optimum protection to its occupants with no regard to occupant s safety of the colliding vehicle Research published in the recent years point out that severe injuries occur in incompatible vehicle-to vehicle crashes Ultimate goal of research in both the U.S. and in Europe is to develop a test procedure that ensures occupants safety real-world collisions involving single vehicles striking objects such as trees, bridge abutments, roadside structures and buildings

63 Vehicle Front Structure Design for Current Standards Slide 65 of 80 FMVSS 208 The standard sets performance requirements for occupant protection in frontal crash, which are measured using anthropomorphic test devices (dummies) located in the front seat Either a passive restraint (air bag) or a combination of air bag and lap/shoulder belt system may restrain the dummies Vehicle is launched to impact a rigid barrier from 30 mph at 90 degrees to the barrier surface

64 Vehicle Front Structure Design for Current Standards Slide 66 of 80 NCAP It is identical to FMVSS 208, except for increasing the impact speed to 35 mph and restraining the front dummies by lap/shoulder belts in addition to the passive air bag Regardless of the vehicle mass, the decelerations of these vehicles during crash are approximately the same Designing vehicles for NCAP testing promotes the stiffness of the structure to be proportional to the mass of the vehicle

65 Slide 67 of 80 Contents Deceleration of light and heavy vehicles: NCAP testing Figures from Priya Prasad, 2005

66 Vehicle Front Structure Design for Current Standards Slide 68 of 80 IIHS Test When designing vehicle front structure for offset impact with deformable barrier, both the light and heavy vehicles cause bottoming of the barrier material Test promotes a stiffer front structure for heavy vehicles Figures from Priya Prasad, 2005

67 Slide 69 of 79 Vehicle-to-Vehicle Frontal Collisions Only frontal collision are considered, and only the case of head-on impact between two vehicles It is still complex because of different masses, geometries, and stiffness. Figures from Priya Prasad, 2005

68 Slide 70 of 80 Preliminary Relationships in Head-on Frontal Collision Conservation of Momentum if v 1 and m 1 are the velocity and mass of the heavier vehicle and v 2 & m 2 are the velocity and mass of the lighter vehicle, and the velocity after the crash is assumed to be the same for both vehicles V f, then: V f = (m 1 v 1 + m 2 v 2 ) / (m 1 +m 2 ) = m 2 V c / (m 1 +m 2 ) = m 1 V c / (m 1 +m 2 )

69 Slide 71 of 79 Conservation of Momentum Knowing (V f ) helps to calculate the change of vehicle velocity during impact, which is a good indicator of the severity of impact on each vehicle, from the following: Δ v 1 = V f - v 1 and, Δ v 2 = V f - v 2 An expression of the Δ v s ratio in terms of μ = ( m 1 / m 2 ) > 1, the mass ratio of the two vehicles: ( Δ v 2 / Δ v 1 ) = (m 1 /(m 2 ) = μ For the special case where v 2 = - v 1 = v 0, the expression for the velocity after impact,

70 Slide 72 of 80 Conservation of Momentum V f = [(m 1 - m 2 )/(m 1 +m 2 )] v 0 When m 1 = m 2, V f = 0. But, when m 1 m 2, i.e. μ = ( m 1 / m 2 ) > 1, and defining V c as pre-impact closing velocity between the two vehicles, that is, V c = v 1 - v 2, The above equations may be written as follows: V f = * (μ - 1 )/( μ + 1)+ v 0 Δ v 1 = V c /( μ + 1) Δ v 2 = * (μ )/( μ + 1)+ V c

71 Slide 73 of 80 Delta V2 for mass ratios and closing velocities The figure shows that for vehicles designed for NCAP testing, Vc=70 mph is too severe of a case to handle, regardless of the mass ratios of the vehicles involved. However, in theory, a Vc=50mph is manageable for up to approximately μ = 2.1. But a Vc= 60 mph, the critical mass ratio at which Δ v2 is 35 mph is 1.4 Figures from Priya Prasad, 2005

72 Slide 74 of 80 Conservation of energy By applying conservation of energy theorem, the total energy absorbed by both vehicles (through deformation) during crash can be computed from the following equation : E def. = ½ [(m 1 m 2 )/(m 1 +m 2 )] (Vc 2 ) The deformation energy depends on the two masses and the closing velocity V c of the two colliding vehicles. In terms of (μ) and (m2) E def. = ½ [(m 2 ) (μ) / (1+(μ)] (Vc 2 )

73 Slide 75 of 80 Conservation of energy When two vehicles are individually designed to absorb the energy during frontal rigid barrier impact, they are capable of absorbing the energy of that crash. The analysis is valid regardless of the mass ratio of the two vehicles. This finding shows that the design of compatible structures is possible, and over-crush of the light vehicle can be avoided Figures from Priya Prasad, 2005

74 Distribution of Energy and Deformation Slide 76 of 80 Formulae give energy absorbed by the two vehicles, and they do not help in determining the way that total energy is shared by the individual vehicle Many researchers used a linearization technique to approximate the dynamic crushing characteristics of the vehicle during rigid barrier crashes The linear approach has been found to be very crude.

75 Slide 77 of 79 Linear approximation of vehicle deceleration vs. crush Figures from Priya Prasad, 2005

76 Slide 78 of 79 Strategies for Designing Front Structures for Head-on Impact Comparison: head-on collision and rigid wall impact Linear approximation of crash pulse unsuitable for simplified analysis Figures from Priya Prasad, 2005

77 Slide 79 of 79 Strategies for Designing Front Structures for Head-on Impact The Mass Ratio (μ) & Closing Speed (vc) Vehicles are designed for ratio of 1.36 to 1.6 Closing speed is taken from 60 to 70 mph Figures from Priya Prasad, 2005

78 Slide 80 of 80 Contents Strategies for Designing Front Structures for Head-on Impact Energy and crush distribution targets Many researchers express the opinion that during head-on collision, each of the vehicles involved should absorb an amount of energy that is proportional to its mass For the heavy vehicle of mass m 1, E 1 should be E 1 = m 1 E def / (m 1 +m 2 ) For the light vehicle of mass m2, the energy would be E2 E 2 = m 2 E def / (m 1 +m 2 )

79 Slide 81 of 79 Assessment of Analytical Tools The most simplistic model was the use of two rigid masses and two linear springs to model the complete system impact Others modeled the power-train of both vehicles to capture their interface and how it might influence the behaviour Mass-spring model of two colliding cars Schematic model of crush system Figures from Priya Prasad, 2005

80 Slide 82 of 79 Assessment of Analytical Tools Simulation of head-on impact of two cars had been conducted with 1-D lumped spring mass approach as early as the 1970s. It proved to be very useful in understanding fundamental mechanics of collision and the factors which influence the behavior such as closing speed, mass ratio and structural stiffness of each vehicle Application of 1-D LMS models for head-on impact simulation Figures from Priya Prasad, 2005

81 Slide 83 of 79 Assessment of Analytical Tools To manage the vehicleto-vehicle offset impact and possibly the mismatch in geometry of the colliding vehicles, the three-dimensional lumped masses and springs with MADYMO have been used Car-to-car full frontal impact Figures from Priya Prasad, 2005

82 Slide 84 of 79 Assessment of Analytical Tools Another 3D simplified modeling technique, implemented advanced beam elements, has been used for studying the factors influencing compatibility between vehicles Beam elements combined with shell elements and other rigid body masses, hybrid modeling Beam element model of body structure Figures from Priya Prasad, 2005

83 Slide 85 of 80 Conclusions A test to check occupants safety in vehicle-tovehicle collision will inevitably emerge. In fact, some vehicle manufacturers have already provided plans to check their designs for this impact mode in their product development process. Current design standards (the rigid barrier and offset deformable barrier tests) promote not readily crushable in a head-on collision

84 Slide 86 of 80 Conclusions Several simplified models are used, but the hybrid technique may be the most promising, since it combines features that are suitable and easy to apply by engineers. It also overcomes the oversimplification in 1-D modeling that may not be correct for vehicle-to-vehicle simulation. Designing the back-up and compartment structures of a small light vehicle for approximately 30 g s average force in a two-level crash pulse would significantly improve its safety in head-on collision with a heavier full-size vehicle with closing velocity of 60 mph and mass ratio of 1.33.

85 Slide 87 of 80 Reference VEHICLE CRASHWORTHINESS AND OCCUPANT PROTECTION edited by Priya Prasad et al., 2004, American Iron and Steel Institute 2000, Town Centre, Southfield, Michigan 48075