Crashworthiness Considerations for Van Structures

Transcription

1 Crashworthiness Consierations or Van Strutures Frank C. Günther DailerChrysler, Stuttgart, Gerany Suary: he rash behaior o an strutures nees to be analyze or a wie range o ehile weights. First, a iensional analysis o an rash probles is presente. hen a sipliie oel or assessing rash pulses or an strutures using DynaD is erie. Gien a DynaD reerene solution or the oplete struture, rash pulses or saller asses an/or initial eloities an be obtaine in ery little tie using a single egree o reeo oel. Keywors: rash, saety, DYNAD, autootie. -. Septeber Gra-Zeppelin-Haus, Frierihshaen

2 Introution: Oeriew o oputational atiities or oerial ehiles saety at DailerChrysler DynaD is use or any ierent probles relate to the saety o oerial ehiles. he tests onute or ans are soewhat siilar to those or passenger ars. For heay truks, other tests beoe releant.. Vans DynaD is use or siulations o: - Euro-NCAP ront an sie ipat (strutural/oupant), - Crash pulse or airbag ire/no ire onitions (strutural), - Various internal tests (strutural/oupant).. Heay truks DynaD is use or siulations o: - ECE R9 ab tests (strutural), - Sweish ab tests (strutural), - Crash pulse or airbag ire/no ire onitions (strutural), - Various internal tests (strutural/oupant). Crash pulse o an strutures A rash pulse gies the tie history o the rigi-boy eeleration o a an struture. It is signiiant or oupant saety an the esign o restraint systes. Large eelerations shoul be aoie sine they ake the esign o aequate atie an passie restraint systes ore iiult. Crash pulses are also use in the ire/no ire onitions o atie restraint systes. For a gien an struture an a gien type o rash, the rash pulse epens on the harateristi eloity o the rash an the harateristi ass. For stationary rash barriers, the harateristi eloity an harateristi ass are the eloity an ass o the an struture, respetiely. For oing barriers, the harateristi eloity is the eloity o the barrier. Assuing ieally inelasti ipat, onseration o oentu then gies a harateristi ass o b = + b, where b is the ass o the barrier, an is the ass o the ehile. For rash onigurations with a oing barrier, the harateristi ass is always saller than the ass o the ehile an the ass o the barrier. For ans, will ary wiely or any gien struture, sine payloa onstitutes a large perentage o the iu ehile ass. his otiates analyzing the eet o arying ehile ass on the rash pulse. Diensional analysis o an rash probles Diensional analysis is oonly use in the iel o lui ehanis. Howeer, it an be applie to other physial probles as well. Let us assue that the global aeleration o a gien an struture an be written as a untion o seeral iensional ariables, naely a t = t,,, F,,, () ( ) ; ag where t is the tie, is the total ass o the ehile, ehile, is the initial eloity, ag (onstan or a gien an struture), gien an struture), an is the harateristi requeny or iltering the rash pulse. is the ass o the eoring part o the F is the eletion-aerage resultant ore on the ehile is the harateristi length o the rush zone (onstant or a. -. Septeber Gra-Zeppelin-Haus, Frierihshaen

3 he iensional atrix takes on the ollowing or: F ag t a M L We nee to in = non-iensional ariables. Let us hoose the non-iensional ass o the rush zone ˆ =, ˆ, the ratio o energies Eˆ =, Eˆ F ag the non-iensional tie ˆ t t =, the non-iensional aeleration a a ˆ =, an the non-iensional iltering requeny ˆ =. his leas to the reorulate relation a () t = ˆ t ;,, Fag,. In other wors, the non-iensional rash pulse (non-iensional aeleration s. non-iensional tie) only epens on the perentage o ass in the rush zone, the ratio o energies, an the noniensional iltering requeny. Fig. shows two DynaD runs with the sae non-iensional ariables. Howeer, the initial eloity or the seon run was ouble an the total ass was iie by our. he plot was ae with the tie axis o the seon run sale by. an its aeleration axis sale by. hese atores were obtaine ro the expressions or iensionless tie an iensionless aeleration. As expete, the two sale rash pulses are irtually iential. In any ases, the eets o ariation o the non-iensional ass o the rush zone an o the noniensional iltering requeny an be neglete. his urther sipliies the aboe equation. Sipliie oel A sipliie oel an be obtaine by assuing that the an struture onsists o a assless, energyabsorbing rush zone an a peretly rigi rest o the struture, in whih the ass o the ehile is onentrate. he rush zone has a ore/eletion relation or loaing ( ) F = or > with the ore F an the isplaeent. his ore/eletion relation an be obtaine ro reerene rash pulse that is generate by a DynaD siulation o the oplete struture as ollows: Fro the DynaD siulation the global aeleration tie history a () t an the global isplaeent tie history () t an be extrate. hen the equation () t = a() t ( () t ) F =. -. Septeber Gra-Zeppelin-Haus, Frierihshaen

4 is a paraetrize representation o the ore/eletion relation. he sipliie oel an be written as = ( ) with () = an the initial eloity () =. his seon-orer, non-linear initial alue proble an be sole with a saller ass or a saller initial eloity, or both. O ourse, as shown by the iensional analysis o the preious setion, there is no unaental ierene between arying initial eloity an arying total ass. Note that a larger ass or a larger initial eloity annot be use, sine they woul lea to eletions that are larger than those o the reerene solution. We use DynaD with a non-linear spring an a point ass to integrate the aboe equation. he sript language Perl is use to extrat a loa ure ro the noout ile o the ull struture DynaD reerene oel an to generate the input ek or the sipliie oel. CPU tie or the sipliie oel is on the orer o agnitue o a ew seons. Both iltere an uniltere aeleration ata an be use to obtain the ore/eletion ures. Currently, we aor the use o uniltere aeleration ata, sine the global isplaeent an eloity history o the reerene oel an then be reproue exatly by the sipliie oel i the original ass an initial eloity are use. Exaple struture o test the quality o the sipliie oel, an iealize struture shown in Fig. is use. It onsists o a eorable part (let) representing the rush zone an ipating a stonewall, an a rigi part (right) with point asses representing the rest o the ehile. he rush zone onsists o % o the total ass o the struture. otal ass an initial eloity are arie. Fig. shows the inluene o the initial eloity on the rash pulse o the iealize struture, iltere with a Hz low pass ilter. Note that the length o the rash pulse epens on the initial eloity, whereas the agnitue o the aeleration reains about the sae. he tie axis is ilate. Fig. shows the inluene o the total ass on the rash pulse o the iealize struture. he rash pulse hanges in agnitue. his is the behaior that woul be expete by inspetion o the ierential equation o the sipliie oel. Consier now Fig., whih shows the eet o ierent initial eloities on the sipliie oel. he rash pulse o a kg, /s struture is use as reerene solution or the ore/eletion ure. he two other rash pulses are obtaine using the sipliie oel. Coparing Fig. an Fig., we in that the general shape o the rash pulse is reproue well by the sipliie oel. here are, howeer, notieable ierenes espeially where the /s rash pulse was use as the reerene solution or a /s initial eloity run. Fig. shows the eet o total ass on the sipliie oel. he rash pulse o a kg, /s struture is use as reerene solution or the ore/eletion ure. he kg rash pulse ro Fig. is athe quite well. he kg rash pulse is o quite a bit, espeially the loation o the onset o the plateau. Conlusions A sipliie oel or assessing rash pulses or an strutures was presente. Gien a DynaD reerene solution or the oplete struture, rash pulses or saller asses an/or initial eloities an be obtaine in ery little tie using a single egree o reeo oel. his etho sees ery proising where eiations o ass an initial eloity ro the reerene oel are sall.. -. Septeber Gra-Zeppelin-Haus, Frierihshaen

5 run run Diensional Analysis ie [s], run Aeleration [/s^], run.. Aeleration [/s^], run. 9 Fig. : Deonstration o iensional analysis. ie [s], run Fig. : Iealize struture with eorable (let) an rigi (right) part.. -. Septeber Gra-Zeppelin-Haus, Frierihshaen

6 Coparison o Dierent Initial Veloities 9 kg, /s, % e. kg, /s, % e. kg, /s, % e. Aeleration [/s^] 9 Fig. : Inluene o initial eloity on rash pulse ie [s] Coparison o Dierent Masses kg, /s, % e. kg, /s, % e. kg, /s, % e. Aeleration [/s^] 9 Fig. : Inluene o total ass on rash pulse. ie [s]. -. Septeber Gra-Zeppelin-Haus, Frierihshaen

7 Coparison o Dierent Initial Veloity Salings 9 kg, /s, % e. kg, /s, % e. kg, /s, % e. Aeleration [/s^] 9 ie [s] Fig. : Eet o initial eloities on the sipliie oel. Coparison o Dierent Mass Salings kg, /s, % e. kg, /s, % e. kg, /s, % e. Aeleration [/s^] 9 Fig. : Eet o total ass on the sipliie oel. ie [s]. -. Septeber Gra-Zeppelin-Haus, Frierihshaen