IGF Research Project N Safer High Heels

Transcription

1 IGF Reserch Project N Sfer High Heels Survivl of compnies in the fshion nd sesonlly dependent sectors such s the footwer industry depends upon their ility to implement the ltest trends. Shoe ottoms nd heels re prticulrly importnt design elements. And yet fshionle ldies shoes, ove ll those with high heels, clerly lso hve to ssure the sfety of their werers. In fct, some of the designs considered re rejected s unrelisle during the cretion of prcticlly every collection. Gol of the Project The gol of the PFI reserch project presented here, which ws funded through the orgnistion for promotion of Industril Community Reserch nd Development IGF nd undertken together with nother reserch estlishment, the Reserch Institute for Lether nd Plstic Sheeting (Forschungsinstitut für Leder und Kunststoffhnen ggmh, FILK), ws to improve the technicl relisility of fshionle heel designs in ldies shoes. Insoles, heels, nd methods of heel ttchment were therefore nlysed. Discussions with ldies shoe mnufcturers reveled tht in prticulr very high nd slender heels, such s tht depicted in Fig. 1, cuse prolems. It cn e ssumed tht prcticle solution for the ttchment of such heels could e pplied in principle to the ttchment of ll other heels. Fig. 1: Prolem heel The forces nd moments cting on different types of heels were determined with the id of vrious mesuring systems (Fig. 2). A sensor sole in shoe ws used to mesure the plntr pressure distriution. Strin guges were ttched to the exterior of the heel, to the heel line, nd to the exposed shnk piece of the insole. The test persons lso wlked over forcemesuring pltform. Fig. 2: Mesuring systems used Prüf- und Forschungsinstitut Pirmsens e. V. Sitz der Gesellschft: Pirmsens Geschäftsführerin: Dr. Kerstin Schulte Pge 1 of 5

2 The tests were undertken with experienced werers of high heels. The test shoes used re shown in Fig mm 55 mm 65 mm 70 mm Fig. 3: Side views of the test shoes is n e e een the mid-tred point of the heel tip nd the heel height mesuring point projected onto the wlking surfce is n e e een the mid-tred point of the heel tip nd the ll tred point The shoes re designted s follows: S55 Shoe with 55 mm heel lift S65 Shoe with 65 mm heel lift S70 Shoe with 70 mm heel lift S100 Shoe with 100 mm heel lift Results Forces cting on the heels perpendiculr to the wlking surfce cn exceed the ody weight force y up to 15 %. The mgnitude of the mximum forces depends upon the design of the heel. Higher heels give rise to higher mximum forces (Fig. 4); however, this dependence is lso suject to the influence of other fctors such s heel shpe nd positioning. Fig. 4: Comprison of the mgnitudes of the resultnt force F xyzmx for the four heel vrints Pge 2 of 5

3 As seen in Fig. 5, the times t which the mximum tensile nd compressive stresses re recorded y the strin guges on the heel nd on the shnk spring do not coincide with the times of occurrence of the mximum force F zmx on the force-mesuring pltform. It therefore follows tht the forces responsile for extreme stresses on the heel nd the shnk re smller thn F zmx. Fig. 5: Chrcteristic fetures of the stress curves The stress profiles determined with the id of the strin guges ttched to the ck of the heel nd to the shnk revel oth similrities nd differences etween the heel vrints. In prticulr, S70 showed numer of distinctive fetures ttriutle to the prticulr shpe nd positioning of the heel. The pronounced individul influence of the test person in serching for temporry equilirium on the smll re of contct of the heel is evident from the stress profiles recorded y the strin guges plced on the side of the heel. Development of Insole Mterils As prt of the project, Freierg-sed FILK hd the tsk of improving the properties of the insoles to permit more relile ttchment of heels y inside niling. Thermoplstic elstomers were initilly tested s insole mterils. However, these mterils proved unsuitle for the cold forming process used in insole production. A second pproch ws to develop insole lmintes s three-lyer composites: Bse lyer, textile reinforcement, nd top lyer. Cellulose-sed insole mterils were used for the se nd top lyers. Nrrow frics woven from mono- nd multifilment yrns spun from glss nd Pge 3 of 5

4 polyester fires s well s idirectionl frics of vrious structures mde up of the sme kinds of fires served s reinforcing textiles. The tested composite mterils showed vlues indictive of significntly improved pin holding strength compred to reference mterils without textile reinforcement (even without shnk piece). The heel pin holding strength could lso e incresed 2.5-fold on use of lower priced polyester fire sed nrrow frics. The orienttion of the textile with the wrp direction trnsverse to the cutting direction is dvntgeous ecuse it gives n 18 to 26 % greter pin holding strength thn tht with the wrp direction prllel to the cutting direction. Two insole lmintes re shown in Fig. 6. Susequent werer trils were conducted with insole lmintes which were reinforced only in the heel region. The desired improvement of heel ttchment could thus e chieved in highly cost effective mnner. ) ) Fig. 6: Exmples of insole lmintes ) Durlite, Gerster fric , Texon 480 ) Durlite, Cprol reinforcement textile, single lyer, Texon 480 Development of New Method of Heel Attchment PFI ws serching ove ll for new method of ttching the most prolemtic type of heel shown in Fig. 1. Tests were conducted with screw-on metl rod which ws ttched to the insole, or more precisely to the shnk piece, y mens of threded union (Fig. 7). The strength of ttchment vi this threded union ws tested y the method of dynmic heel ttchment testing developed y PFI (Fig. 8). Fig. 7: Heel ttchment vrint 1 Heel rod, 2 Attchment of heel to insole Fig. 8: Procedure for dynmic testing of heel ttchment Pge 4 of 5

5 Werer Trils Two options were selected for werer trils. One pir of ldies shoes ws produced with insoles mde of the lminted mteril which gve the est results in the pin holding test. For this pir inside heel niling ws used to ttch clssicl lock heel (shoe with the white lock heel in Fig. 9). The newly developed heel rod ws used to produce the other pir (shoe in the foreground of Fig. 9). Fig. 9: Test shoe with the newly developed heel ttchment vrint Both vrints were worn y test person nd rted s good with regrd to comfort while wlking nd stility while stnding. This is prticulrly importnt for the test shoe with the heel rod ecuse the test person is stnding on very smll re. This version offers solution for prticulrly difficult types of heels. IGF Project N of the Test nd Reserch Institute Pirmsens e.v. PFI, Mrie-Curie-Str. 19, Pirmsens strted in Jnury, 2014, nd ws concluded in Decemer, It ws funded y the Federl Germn Ministry of Economics nd Energy through the Germn Federtion of Industril Reserch Associtions («Areitsgemeinschft industrieller Forschungsvereinigungen» AiF) within the IGF progrmme for promoting industril coopertive reserch in ccordnce with resolution dopted y the Germn Prliment. We wish to tke this opportunity to express our grtitude for this funding. The results re presented in detil in the concluding report of this project. A copy cn e ordered from the contct elow. For further questions plese contct: Dr. Monik Richter Deprtment Mnger Shoe Technicl Reserch nd Development Phone: , Emil: monik.richter@pfi-germny.de Pge 5 of 5