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Research on Smart Materials: Application of ER and MR fluid in an Automotive Crash Energy Absorber

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Research on Smart Materials: Application of ER and MR fluid in an Automotive Crash Energy Absorber Research on Smart Materials: Application of ER and MR fluid in an Automotive Crash Energy Absorber R.P. Delivorias Reportno. MT04.18 Supervisors: Prof. Dr. Ir. M.G.D. Geers Prof. Dr. Ir. J.S.H.M. Wismans Coach: Dr. Ir. W.J. Witteman Eindhoven University of Technology Department of Mechanical Engineering Automotive Engineering - Vehicle Safety Eindhoven, March 16, 2004 ii Summary The number of serious and fatal accidents in daily traffic is weakening the last ten years. Airbags, modern belt systems and developments in interior and bodywork have mainly pro- vided this positive tendency. However, one thinks that this tendency will not go on in the near future with the present safety applications. Car safety has become an important concept in automotive industry. The safety of a vehicle in relation to the occupants is one of the research areas of institutes like TNO and the TU/e. These developments are of crucial importance to continue this positive tendency. Research is performed on e.g. more intelligent systems like airbags and belt pre-tensioners with variable ignition time. Also, constructive aspect are of importance in this research. The concept ’compatibility’ plays an essential role. It is mainly related to constructive differences between vehicles which can results in a increased risk of injury of the occupants. Differences in weight of the vehicles and the stiffness of the frontstructure are here the most important. This internship is related to the use of ’Smart Materials’ in crushable zones. The possi- bilities with so-called electrorheological and magnetorheological fluids are discussed. These fluids are able to change very fast from a liquid state to a nearly solid state when subjected to an electric or magnetic field. The application of these fluids in an crushable zone would be a move in the right direction of compatible behavior. From earlier research follows that at certain velocities (32, 52 and 64 [km/u]) optimal deceleration curves exist in which the level of injury is minimal. A crushable zone determines the deceleration of the vehicle to a large extend. Through application of ER and MR fluids stiffness variations are possible which can be optimized before or during the collision. In this report there will be a extensive description of ER and MR fluids. Also, the properties of these fluids are discussed and with that the non-Newtonian behavior. A few theoretical models such as the Bingham model and the Herschel-Bulkley model are considered. In here, the possibilities of an advanced crushable zone are discussed. The achievable force level, the dynamic range and the geometry are important aspects which are determined by use of a list of demands. In the final chapter the designs are tested against a list of demands. The con- clusions and discussions which follows from this research determines in considerable measure the feasibility of the systems. iii iv Samenvatting Het aantal ernstige en dodelijke ongelukken in het dagelijkse verkeer is in de laatste tien jaren drastisch afgenomen. Airbags, vernieuwde gordelsystemen en ontwikkelingen in interieur en carrosserie hebben grotendeels voor deze positieve trend gezorgd. Echter, men verwacht dat deze trend zich in de toekomst niet zal doorzetten met de huidige veiligheidsvoorzieningen. Voertuigveiligheid is een belangrijk begrip geworden in de automotive industrie. De veiligheid van een voertuig t.b.v. de inzittenden behoort tot een van de onderzoeksgebieden in onder- zoeksinstituten zoals TNO en de TU/e. Deze ontwikkelingen zijn van cruciaal belang om deze positieve trend door te zetten. Onderzoek wordt gedaan naar o.a. intelligentere sys- temen zoals airbags en gordelspanners met variabel ontstekingstijdstip. Ook constructieve aspecten komen in het onderzoek naar voren. Het begrip compatibiliteit speelt hierin een es- senti¨ele rol. Het heeft met name betrekking op de constructieve verschillen tussen voertuigen wat kan resulteren in een verhoogd risico op letsel voor de inzittenden. Verschillen in het gewicht van de voertuigen en in de stijfheid van de voorstructuur zijn hierin de belangrijkste. Deze stage heeft betrekking op het gebruik van ’intelligente materialen’ in kreukelzones. De mogelijkheden met zogenaamde electrorheologische en magnetorheologische vloeistoffen wor- den besproken. Deze vloeistoffen zijn in staat om, onder invloed van een magnetisch/electrisch veld, razendsnel van een olieachtige vloeistof in een vaste substantie te veranderen. De toepassing van dergelijke vloeistoffen in een kreukelzone zou een goede stap kunnen zijn in de richting van compatibel gedrag. Uit onderzoek is naar voren gekomen dat bij bepaalde snelheden (32, 52 en 64 [km/u]) optimale deceleratiecurves bestaan waarbij het letselniveau minimaal is. Een kreukelzone bepaalt in grote mate de deceleratie van een voertuig. Door toepassing van ER/MR vloeistoffen zijn stijfheidsvariaties mogelijk die voor of tijdens een botsing geoptimaliseerd kunnen worden naar een bepaalde snelheid. In dit verslag wordt uitgebreid ingegaan op ER en MR vloeistoffen. Er wordt ingegaan op de eigenschappen van deze vloeistoffen waarbij met name het niet-Newtonse gedrag naar voren komt. Enkele theoretische modellen zoals het Bingham model en het Herschel-Bulkley model worden behandeld. Vervolgens worden drie ontwerpen met toepassing van MR vloeistof uitgebreid besproken. Hierin komen de mogelijkheden van een geavanceerde kreukelzone aan de orde. Het haalbare krachtenniveau, het dynamische bereik en de geometrie zijn hierin belangrijke aspecten. Deze aspecten zijn vanuit een eisenpakket vormgegeven. In het laatste hoofdstuk worden de ontwerpen getoetst aan een eisenpakket. De conclusies en discussies die hieruit voortkomen bepalen in grote mate de haalbaarheid van de systemen. v vi Contents Summary iii Samenvatting v 1 General Introduction 1 1.1 Description of the research issue . 6 1.2 Project Boundaries . 7 1.3 Internship Outline . 8 2 Introduction to ER and MR fluids 9 2.1 ER fluids . 10 2.1.1 Working principle . 11 2.1.2 Modes of use . 12 2.1.3 Material Composition . 13 2.1.4 Applications . 16 2.1.5 Design Constraints, Advantages and Disadvantages . 18 2.2 MR fluids . 19 2.2.1 Working principle . 19 2.2.2 Modes of use . 21 2.2.3 Material Composition . 22 2.2.4 Applications . 24 2.2.5 Design Constraints, Advantages and Disadvantages . 26 2.3 Requirements for Safety Systems in Automobiles . 29 2.3.1 In general . 29 2.3.2 Crash Situation Requirements . 30 vii viii Contents 2.3.3 Cost Requirements . 32 2.3.4 General Applicability Requirements . 33 2.3.5 Testing the requirements against ER and MR fluids . 35 2.3.6 ER or MR fluid? . 41 3 Theory Modelling 45 3.1 Fluid Models . 46 3.1.1 Bingham Model . 46 3.1.2 Other Viscoplastic Models . 48 3.2 Pressure Control Valve Using MR Fluid . 52 3.2.1 Pressure-Flow Characteristics of MR Fluid Relief Valve . 53 3.3 Quasi-Static Modelling of MR Dampers . 56 3.3.1 Basic Geometry Design Considerations . 56 3.4 Damper Based on a Disk Shape MR Valve . 61 4 Practical Modeling 65 4.1 The Necessity of An Advanced Crushable Zone . 66 4.1.1 Cable-supported frontal car structure . 68 4.1.2 Optimal decelerations curves . 68 4.1.3 Energy absorption by friction . 71 4.1.4 Design of a hydraulically controlled frontal car structure . 73 4.2 Design of an Advanced Crushable Zone . 75 4.2.1 Advanced Crushable Zone Using Pressure Control Valves . 75 4.2.2 Advanced Crushable Zone Using Smart Dampers . 82 4.2.3 Advanced Crushable Zone Using Parallel Disk Shaped Valves . 90 5 Feasibility Study 97 5.1 Testing the designs against the list of demands . 98 6 Conclusions and Recommendations 103 6.1 Conclusion . 103 6.2 Discussion and recommendations for further research . 104 A Properties MR fluids 107 Contents ix B Derivation of NCE 121 C MR Fluid Flow in Annular Duct 125 C.1 MR Fluid Flow in an Annular Duct . 126 C.2 Modeling based on the Herschel-Bulkley model . 127 C.3 Modeling based on the Bingham model . 134 D MR Fluid Flow in Parallel Duct 137 D.1 Modeling based on the Herschel-Bulkley model . 140 D.2 Modeling based on the Bingham model . 142 E MR Fluid Flow in an Parallel Disk Shaped Valve 145 Bibliography 149 x Contents Chapter 1 General Introduction During the last years much research is performed in traffic safety. One must not only think of vehicles, also motorbikes, bicycles and pedestrians are under discussion. Still the amount of people having an accident, or in the worst case having a fatal accident, is shocking (see fig. 1.1). Figure 1.1: Tendency of fatal traffic accidents in five categories [CBS 2003] 1 2 Chapter 1. General Introduction The last years there is a positive tendency, which is mostly attributed to electronic applica- tions such as airbag systems en belt pre-tensioners (fig.1.2) Also constructive applications for example folding steering column, SIPS (Side Impact Protection System) by Volvo (fig.1.2) and applications of ’Smart Materials’ will entry. The government has realize compulsory crash tests by way of legislation. It is an absolute necessity for manufacturers to satisfy these regulations. Nevertheless there are various opinions about this topic. The regulations have to extend with tests like side-impact crashes and rear crash tests. A big problem in designing crash safety devices is the restricted flexibility in the constructed safety cage and the crushable crash zones. Since the vehicle is only tested on two crash tests, one has only paid attention to constructive applications which satisfy these tests. Figure 1.2: Constructive and electronic safety applications: SIPS by Volvo [www.ciragan.com] and airbag technology [www.cookecorp.com] 3 About 60 percent of the car collisions are frontal, of which two-third is between two vehicles. The circumstances, in which collisions take place, differ a lot.
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