Virtual evaluation of energy exchange between two deformable body during low-energy impact. Application to the case of “Head on bonnet” impact according to WG17 and ACEA protocol

All over the world, and mainly in United States, since 1977 to 1991 the research centers of the main automotive companies had processed several statistical data on real accidents between vehicles and pedestrians taking care, obviously, to pedestrians' injury[7]. In latest years a research group of EEVC (European Enhanced Vehicle Safety Committee) had examined the statistic works of past twenty years and subsequent several scientific papers, and had realized some documents about "pedestrian test" procedures[2,6,7]. In reference papers of period 1977 - 1997 and in EEVC documents, the scientists describe a proposed homologative test for child-head impact; it is represented by an impact simulation of a standardized impactor on car bonnet, in order to evaluate the child-head injury as deceleration of its center of gravity. Injury evaluation criteria is an energy criterion and is quantified by the HPC index (Head Performance Criteria also called, without distinction, HIC - Head Injury Criteria) defined as follows: [GRAPHICS] in which t(1) and t(2) are respectively initial and final impact's instants (t(2)-t(1) is the integration range) and a is acceleration resultant vector, measured by an accelerometer mounted in the head-impactor. Impact duration generally doesn't exceed the 20 ms (milliseconds); in this range we can recognize two different phases: the first phase, dependent mainly on the local bonnet stiffness, with a length of time never greater than 4 ms and a second phase until the end of the phenomenon, dependent on boundary conditions and impacting bodywork parts, impacting engine parts and so on. In the first phase we can find the maximum acceleration's value, that heavily affects the final value of HPC [3]. In 1998, WG 17 has published a new testing protocol that was approved by EuroNCAP and European Community and fixed it as homologative criteria since 2010[10. For the period until 2010 the automotive companies had unanimously accepted a testing protocol less restrictive than the EuroNCAP one: the ACEA Protocol [11, 14] that will became a homologative criteria since 2005; this fact involves new compatibility problem for new car designer, because since 2005 all the vehicle will be homologated For determining the entity of damage on pedestrians we refer to the measurement scale called Abbreviated Injury only if they will respect the biomechanical values' range imposed by new testing protocol. Our paper pays attention on Child Head impact phenomena (the high priority impact both for WG17 and for ACEA protocol) and on the factors that affect the increase of HIC values. Other studies had demonstrated that in the middle area of the bonnet the acceleration peak, that heavily affects the value of HIC, strictly depends on "structural" parameters [3] of the bonnet; our paper is based on this studies and wants to reproduce, using numeric simulation, the Child impact dynamic (a very low-energy impact.... only 150 Joule) in order to demonstrate the importance of kinetic phenomena despite of the deformation's one. We can justify the validity of this hypothesis by the comparison of impact simulation of ACEA and WG17 test; these protocols are different for mass of impactor and speed of impact (for ACEA we have an impactor of 3.5 Kg that hits the bonnet with a 35 Km/h speed while for WG17 we have an impactor of 2.5 Kg that hits with a 40 Km/h speed). Child Head impact simulation in accordance with WG17 protocol was made and correlated on physical tests made on a FIAT Punto 60 by TNO (with an average correlation index of +/-10%)[5]. The test simulated, for the evaluation aim of our study, was made on a sub-system composed by the complete bonnet with its catch and hinges and was simulated in the explicit FEM code PamCrash

State of the art on Pedestrian Safety Simulation

Purpose: The aim of this work is to explain the work of Design Methods’ research group of Department of Mechanical Engineering of Salerno University, in the field of research regarding vehicles pedestrian safety problem, taking care to finite element methods and models used and developed for vehicle design and optimization. Design/methodology/approach: Our developed models show a very good Numeric/Experimental correlation, and we’ve numerically certified our virtual impactors, designed following EEVC-WG17 specification. These impactors have been tested also at higher speed and we have obtained a good correlation with some problems because of the critical behavior of the foam solved following different model-design optimization methods. Findings: Best results obtained and explained in this paper are concerning impactors modeling and certification, and Experimental/Numerical correlation of full impact tests. Research limitations/implications: The achievement of the maximum possible pedestrian safety performance, compatibly with the others, sometimes conflicting, performances, is one of the main objectives to reach, for the automotive industry by now and, above all, for the future. Practical implications: According to a surveying by European Community research committee, the risk of die for pedestrians and cyclists because of street incidents is eight/nine times higher than one of the occupants of motor vehicles. From statistics we’ve found that the greatest part of these accidents is due to the collision of the pedestrian on the front part of motor vehicles, and that fact affects the considerations on the passive safety. Originality/value: The most Important Automotive industries had understood the impact of new regulations about homologation and began to study the problem and particularly how to introduce new Homologation parameters in their Product development cycles, today based on Virtual Prototyping of the Whole Vehicle and final Physical testing of few physical prototypes

Methodology development of human task simulation as PLM solution related to OCRA ergonomic analysis

In the current demanding global marketplace, ensuring that human fit, form and function are comprehensively addressed, is becoming an increasingly important aspect of design and, in particular, obliges the most important automotive industries to develop more flexible assembly lines and better methods for PLM solution. In the meantime, designers attempt to elaborate product development methodologies that conform health and safety standards while still maximizing the productivity. The aim of this work consists in developing a methodology based on preventive ergonomics and feasibility analyses of assembly tasks, simulating a work-cell, in which acts a digital human model (manikin), in order to maximize human safety and performance and analyze manikin interaction in the virtual environment. In ergonomic analyses the OCRA protocol will be used, evaluating different involvement degrees of upper limb segments. The methodology is carried out by ergonomic tool of DELMIA software, using Digital Human Models technology

Upper Leg impactor modelling for Pedestrian Test simulation using F.E.M. explicit codes

Between 1977 and 1980, mainly in the United States and in Australia, independent research centres began to process several statistical data on accidents between vehicles and pedestrians, taking cam, obviously, to pedestrians' injury. That problem in the early 80' became also interesting for European research centres. In 1990 a research group of EEVC (European Enhanced Vehicle Safety Committee) had examined statistical data of past twenty years and scientific research published about this topic, and had presented several documents about "pedestrian test" procedures. In reference papers of this twenty years period (1977-97) and in documents of EEVC, the scientists describe a proposed test for upper-leg impact; it is represented by the impact of a standardised impactor (that simulate the human leg/pelvis) on car front-part; those documents have been updated in 1994, 1998 and finally in 2002 while Euro-NCAP, since 1998 had used them to realize, in specialized laboratories, tests for giving a rate for car-safety judgement EEVC wants to introduce those tests for the new homologation program since 2010. For that test there's not a "lighter" version provided by ACEA Protocol, so it will works not before 2010 but EuroNCAP rating on pedestrian safety is still working and takes into account the Upper-Leg test too. The most Important Automotive industries had understood the impact of those new regulations about homologation and began to study the problem and particularly how to introduce those new Homologation parameters in their Product development cycles, today based on Virtual Prototyping of the Whole Vehicle and final Physical testing of few physical prototypes. The impactor was created in order to evaluate the in several parts of the Upper-leg using two parameters: - Sum of Forces coming from two transducers positioned in the upper and lower part of the impactor, in order to evaluate the injury on the upper (neck) and lower parts of femur bone; - Maximum. bending moment applied on the central part of the element that simulates the femur bone. Those two parameters are useful to evaluate what happens when a pedestrian, that cross a road orthogonally to the vehicle way, is rammed by a car, and hits the Bonnet leading edge with the Upper part of the Leg injuring femur and pelvis zone. Impactor used to evaluate the damage in pedestrian test is made by TRL and is quite similar to the structure of the Human femur: it has a very complicated system to simulate the whole bone-flesh-skin apparatus and, in particular, has two layers of special ConforTM Foam CF-45 Blue that has the same mechanical behaviour of human flesh, in an other scientific paper we have published the results on the dynamic characterization of that Foam at medium and high impact velocity; in this paper we have simulated the whole Upper-leg Impactor, in PamCrash environment, using the ESI formulation of the Skin and using the results of characterization of all other elements with experimental tests. After this work of modelling we have tested the Impactor by the simulation of the Certification Tests, as described in the EEVC and EuroNCAP norms, in order to obtain the same results of the experimental test. The Numenc/Experimental correlation is very good and we've numerically certified our impactor. We've also made several tests, whose Experimental results are published, at higher speed and we have obtained some correlation problems because of the critical behaviour of the flesh at high speed simulation but the results on different cases show the same output behaviour, giving us an instrument to resolve that problem

Lower Leg impactor modelling for Pedestrian Test simulation using F.E.M. explicit codes

In late 70', mainly in the United States and in Australia, independent research centres had processed several statistical data on accidents between vehicles and pedestrians, taking care, obviously, to pedestrians' injury. That problem in the early 80' became also interesting for European research centres. In 1990 a research group of EEVC (European Enhanced Vehicle-Safety Committee) had examined statistical data of past twenty years and scientific research published about this topic, and had presented several documents about "pedestrian test" procedures. In reference papers of period of twenty years (1977-97) and in documents of EEVC, the scientists describe a proposed test for lower-leg impact; it is represented by the impact of a standardised impactor (that simulate the human leg) on car front-part; those documents have been updated in 1994, 1998 and finally in 2002 while Euro-NCAP, since 1998 had used them to realize, in specialized laboratories, tests for giving a rate for car-safety judgement. EEVC wants to introduce those tests for the new homologation program since 2010. A "lighter" version of those tests will be performed on new-cars, also for homologation, using ACEA Protocol, which is easier to per form, since 2005. The most Important Automotive industries had understood the impact of those new regulations about homologation and began to study the problem and particularly how to introduce these new Homologation parameters in their Product development cycles, today based on Virtual Prototyping of the Whole Vehicle and final Physical testing of few physical prototypes. EEVC lower-leg impactor was thought in order to evaluate the injury in several parts of the leg using three parameters: - Deceleration of the higher part of the tibia in order to evaluate the injury on Tibia bone; - Shear displacement in the knee joint in order to evaluate the damage that occurs at the human knee for the displacement of the patella towards the higher part of the Tibia - Maximum bending angle in non-natural way of deformation of the knee (in left or right side) that causes the injury for knee ligaments. Those three parameters are useful to evaluate what happens when a pedestrian, that cross a road orthogonally to the vehicle direction, is rammed by a car, and hits the Bonnet and the bumper by Leg (femur/tibia). Impactor used to evaluate the damage in pedestrian test is made by TRL and is quite similar to the structure of the Human leg: it has a very complicated joint system. In this study we have simulated the Legform Impactor, using FEM processor PamCrash (TM), using the ESI (TM) Kinematic joint formulation. After that work of modelling we have tested the Impactor by the simulation of the Certification Tests, as described in the EEVC and EuroNCAP norms, in order to obtain the same results of the experimental test. The Numeric/Experimental correlation is very good and we've numerically certified our FEM impactor