The Investigation of Knitted Materials Bonded Seams Behaviour upon Cyclical Fatigue Loading

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1 ISSN MATERIALS SCIENCE (MEDŽIAGOTYRA). Vol. 23, No The Investigtion of Knitted Mterils Bonded Sems Behviour upon Cyclicl Ftigue Loding Git BUSILIENĖ 1, Eugenij STRAZDIENĖ 2, Virginijus URBELIS 3, Sigits KRAULEDAS 4 1 Fculty of Mechnicl Engineering nd Design of Kuns University of Tecchnology, Studentų str. 56, Kuns LT51424, Lithuni 2 Vilnius University of Applied Sciences, Didlukio str. 82, Vilnius LT-833, Lithuni 3 Product Development Deprtment, Grnerg AS, Bjovegen 1442, 5584 Bjo, Norwy 4 Textile Institute of Center for Physicl Sciences nd Technology, Demokrtų str. 53, Kuns LT-48485, Lithuni Received 18 August 216; ccepted 17 Octoer 216 In this reserch unixil tension ehviour of knitted mterils with onded sems is nlysed. The ojects of the investigtion were two types of knitted mterils, hving the sme fire composition (93 % PES, 7 % EL), ut different in knitting pttern, i. e. plin single jersey nd 1 1 ri. Bonded overlp sems were formed y chnging the orienttion of knitted mterils strips, i. e. prllel/prllel, prllel/is, prllel/perpendiculr, is/is nd is/perpendiculr. The strips of ech knitted mteril were joined y two types of thermoplstic polyurethne (PU) films different in thickness (75 m nd m). Mechnicl chrcteristics of onded sems were defined in longitudinl tension direction direction. During unixil tension such prmeters s mximl force Fmx (N) nd mximl elongtion ɛmx (%) were recorded from typicl tension digrms. The chnges of tested specimens strength nd deformtion were compred efore nd fter cyclicl ftigue tension the conditions of which were 5 cycles up to tension force F equl 24.5 N. The results hve shown tht chnges efore nd fter cyclicl ftigue tension re mostly determined y knitting pttern of mterils, the orienttion of knitted mterils strips in onded sem, ut not effected y thermoplstic polyurethne film. Keywords: knitted, onded sem, unixil tension, ftigue loding, thermoplstic film. 1. INTRODUCTION In recent sem onding is replcing trditionl sewing methods in silings, g filters, infltle ots, infltle toys, etc. The customers re looking for semless products mong outdoor, sportswer nd functionl grments, ir gs, utomotive nd household products. Sem onding nd welding re two sic methods for joining textiles mterils. In the first method thermoplstic film is pplied for onding two lyers of textile. It is ctivted y het nd pressure, i.e. film melts nd penetrtes into the mteril y creting joint etween two lyers. The second method involves welding of two frics y using hot ir, hot wedge, ultrsonic energy, lser, rdio frequency or impct [1 3]. Bonded sems re chrcterized y smooth surfce, semless ppernce nd enhnced werer comfort. They hve good permeility, improved strength nd recovery properties nd mke products lighter, stronger, more flexile nd stretchle compred to sewn grments [1, 3, 4]. Different thermoplstic films cn e used to ond the sme or different mterils [4 9]. On the other hnd, mterils or fric pieces cn e onded with ccessories comprising memrnes, linings, uttons, zippers, tpes nd wddings [1, 4, 1, 11]. Bemis compny is producing thermoplstic dhesive films which re used to replce stitched sems y onded Corresponding uthor. Tel.: E-mil ddress: git.usiliene@gmil.com (G. Busilienė) joints. They re mde from five polymer types such s polyurethne, nylon (polymide), polyester, polyolefin nd vinyl [4, 5]. Sewfree is soft, highly elstic, specilly formulted polyurethne dhesive film designed for frics nd hs een proven in the pplictions rnging from intimte pprel, life style grments, industril work wer, tents, wders, militry grments, ccessory items such s zips, pockets, cuffs, hems nd ptches [4, 5]. The investigtions of woven, knitted nd lminted textile mterils onded sems strength hve shown tht the qulity of onds depend upon proper selection of prmeters t two onding stges: film trnsfer nd lyer onding. The strength of onded sems ws investigted on se delmintion nd sher, the smples with onded sems were fixed in testing mchine grips y cross direction [12, 13]. Innovtive mterils joining methods enter fshion industry. They llow to construct grments of exceptionl design nd performnce properties. The re of onded sems is not sufficiently studded yet, especilly when seprte pieces of knitted mterils re onded in different directions course, wle or is. The qulity of such sems is dependent upon the structure of jointed mterils, their mechnicl properties, orienttion nd the type of onding mterils. On the other hnd, the qulity of sems defines esthetic view of grments, their physiologicl comfort nd durility, e.g. of close fitted sports clothing. Our previous investigtion hs shown tht the ehviour of knitted mterils onded sems under ixil 18

2 punching efore nd fter cyclicl ftigue punching re mostly determined y the thickness of thermoplstic film, ut not effected y the orienttion of knitted mterils strips in onded sems [14]. The im of this investigtion ws to determine the effect of thermoplstic film nd the orienttion of knitted mterils strips in onded sems upon deformtionl ehviour of knitted mterils onded sems under unixil tension efore nd fter cyclicl ftigue loding. 2. EXPERIMENTAL DETAILS Two types of knitted mterils of the sme fire content (93 % PES, 7 % EL), which were produced t Lithuni Stte Reserch Institute Centre for Physicl Sciences nd Technology were investigted. The first mteril P of plin jersey knitting pttern ws knitted on single jersey circulr knitting mchine JEPY 18E. The second mteril R of 1 1 ri pttern ws knitted on doule jersey circulr knitting mchine CMO4A 15E. Both smples were produced using the sme polyester fire spun yrn the density of which ws 2 tex nd the sme elstne yrn the density of which ws 4.4 tex (Tle 1). The stitch density S ws determined y clculting the numer of courses nd wles per unit length ccording to EN ISO 14971:26 stndrd. The re density m ws determined ccording to EN ISO 12127:1999 nd the thickness t ws determined ccording to EN ISO 584:2 stndrd. Two thermoplstic polyurethne (PU) films hving different nominl thickness t n nd modulus m d, were used for the investigtions (Tle 2). The types of films were Tle 1. Chrcteristics of investigted knitted mterils selected tking into ccount the recommendtions of Bemis compny, which stted tht oth Sewfree rnd thermoplstic films cn dhere to wide rnge of textile mterils. Soft elstomeric dhesives re designed to e used in the pplictions where het sensitive frics, low ctivtion tempertures nd high elsticity is required. Product (3415) is descried s good nd product (326D) is descried s excellent in the pplictions with polyester frics [4, 5]. The specimens (2 5 mm) were prepred with onded overlp sems the width of which ws 1 mm nd which were oriented in longitudinl tension direction of the specimen (Fig. 1). Five types of onded smples for ech knitted mteril nd thermoplstic film were constructed y chnging the orienttion of knitted mteril strips (2 3 mm) in respect to specimen s longitudinl direction (Fig. 1): WW oth mteril strips were tensioned in wle direction; WC one mteril strip ws tensioned in wle, the other in course direction; W45 one mteril strip ws tensioned in wle, the other in is (45 ) direction; CC oth mteril strips were tensioned in course direction; C45 one mteril strip ws tensioned in course, the other in is (45 ) direction. The specimens onding ws performed with GTK DEA 25R press t two stges using the sme.3 N/mm 2 (3 Br) pressure: 1 st thermoplstic film of 1 mm width ws trnsferred onto the right side of lower strip y pplying 11 C temperture for 5 s; silicon pper ws peeled off in 5 minutes; 2 nd the left side of upper strip ws lid on the thermoplstic film nd ws onded y pplying 14 C temperture for 3 s. Fric symol Fric content Knitting pttern Stitch density S, cm -1 Are density m, courses, Sv wles, Sh g/m 2 Thickness t, mm P plin jersey % PES, 7 % EL R 1 1 ri * PES polyester, EL elstne Tle 2. Chrcteristics of investigted thermoplstic polyurethne (PU) films [4] Symol Code* Glue line temperture rnge Softening point Nominl thickness tn, m Weight m, g/m 2 Modulus** md, N C C 14 C 326D 83 C * Industril codes of Sewfree rnd thermoplstic films ** Modulus: force required to pull 25.4 mm wide smple t the specified guge to 1 %. 1. WW 2. WC 3. W45 4. CC 5. C45 Fig. 1. The schemes of knitted mteril strips orienttion in onded overlp sems 181

3 Fig. 2. The scheme of knitted mterils strips onding with thermoplstic polyurethne (PU) films Bonding conditions were chosen not only tking into ccount the recommendtions of Bemis compny, ut lso in respect to the results of erlier investigtions [4, 5, 12, 13]. All specimens efore testing were kept in stndrd tmosphere conditions (φ = 65 ± 2 %, T = 2 ± 2 o C) for 24 hours ccording to stndrd EN ISO 139:25. Strength prmeters, deformtion ehviour nd nisotropy level of onded systems were defined nd evluted y unixil tensile testing (Fig. 3). Unixil tension efore nd fter smples ftigue loding y 5 cycles ws performed with stndrd tensile testing mchine Tinius Olsen H1K ccording to the requirements to EN ISO stndrd. Testing conditions were: specimen length etween testing mchine grips 1 mm, specimen width 5 mm, pre-tension 1 N/5 cm, tension rte 1 mm/min. Mximl force F mx (N) nd mximl elongtion ɛ mx (%) were recorded from typicl tension curves. The numer of specimens for one smple ws 5, vrition coefficient did not exceed 8 %. The conditions of cyclicl tensile ftigue loding were 5 cycles up to tension force F = 24.5 N, which correspond to grments wering lod [15]. The velocity of cyclicl tensile ftigue loding ws 5 mm/min. The numer of specimens for one smple ws 5, the vrition coefficient did not exceed 7.5 %. 3. RESULTS AND DISCUSSION Two knitted mterils which re different in knitting pttern, stitch density S, re density m nd thickness t were chosen for the investigtion of onded sems ehviour in unixil tension. Stitch density of plin jersey knitted mteril P is higher y 21.7 % in wle direction nd lower y 56.3 % in course direction s compred to 1 1 ri knitted mteril R. Mentime R mteril cn e chrcterised y 19.7 % higher re density m nd y 13.8 % higher thickness t when compred to plin single jersey knitted mteril P. Typicl unixil tension curves of non-onded knitted mterils P nd R re presented in Figure 3. It is evident Tle 3. Unixil tension chrcteristics of knitted mterils tht there is no significnt difference in tensile ehviour of plin jersey knitted mteril P in wle nd course directions (Fig. 3, ). The ehviour of 1 1 ri knitted mteril R in wle nd course directions differs significntly (Fig. 3, ). Also, P smple cn e chrcterised s less nisotropic ecuse its mximl force F mx nd mximl elongtion ɛ mx in wle nd course directions differ y 15.8 % nd 1.1 %, respectively (Tle 3). Higher nisotropy is chrcteristic for knitted mteril R, ecuse mximl force in wle direction is higher lmost twice (95 %) nd elongtion in this direction is less more thn twice (112.8 %) when compred to course direction (Tle 3) [16]. Five types of onded sems were prepred with oth investigted mterils P nd R nd oth thermoplstic films nd ccording to the schemes, which re presented in Figure 1. Unixil tension curves of two min sem types: WW (oth onded strips were tensioned in wle direction) nd CC (oth onded strips were tensioned in course direction) re presented in Figure 3. The results show tht no significnt difference exists if sems were onded with or polyurethne films, ecuse F mx nd ɛ mx vlues did not exceed error limits. It ws oserved tht the strength F mx of onded sems PWW, PWW, PCC, PCC of less nisotropic mteril P decresed y 18 % nd y 25 % in respect to non-onded mteril strengths in wle nd course directions. Mximl elongtion ɛ mx of the sme sems decresed y 66 % nd 77 %, respectively (Fig. 3, ). Different results were otined for more nisotropic R mterils onded sems RWW, RWW, RCC nd RCC, which were stronger y 12 % nd y 52 % in respect to non-onded mteril strengths in wle nd course directions (Fig. 3, ), though extensiility ecme less y 117 % nd 86 %, respectively. The ssumption cn e mde tht onded systems WW nd CC from less nisotropic mteril ecme weker nd less extensile, ut lmost twice stronger, especilly when tensioned in wle direction, nd less extensile for more nisotropic mteril in comprison to non-onded smples. There is no evident difference etween the mximl elongtion ɛ mx of ll ten types of onded sems of knitted mteril P the sme s there is no significnt difference etween the elongtions ɛ mx in wle P w nd course P c directions of non-onded smples (Fig. 4, ). It should e noted tht onded sems re less extensile y 59.6 % 82.1 % nd y 75.7 % 1.5 % when compred to elongtions in wle P w nd course P c directions. Deformtionl ehviour of ten types of nisotropic R mterils onded sems is different. Mteril symol Wle direction Course direction Anisotropy coefficient t mximl Fmxw, N ɛmxw, % Fmxc, N ɛmxc, % force, KF = Fmxc/Fmxw elongtion, K ɛmxw/ɛmxc P R

4 RWW RWW PWW PWW PCC PCC P w P c R w RCC RCC R c Elongtion e mx, % Elongtion e mx, % Fig. 3. Typicl unixil tension curves of investigted mterils P () nd R () nd their onded systems WW nd CC, where c course direction; w wle direction (coefficient of vrition vried in the limits of 2.16 % 5.78 %) The lowest elongtions were otined for: WW sem where oth mteril strips were tensioned in wle direction; WC sem, where one mteril strip ws tensioned in wle, the other in course direction; W45 sem, where one mteril strip ws tensioned in wle, the other in is (45 ) direction (Fig. 4, ). The highest elongtion (higher y % in respect to WW sem) ws chrcteristic for CC sem, where oth mteril strips were tensioned in course direction. Medium elongtion (higher y 59 % in respect to WW sem) ws chrcteristic for C45 sem, where one mteril strip ws tensioned in course, the other in is (45 ) direction. It is evident tht onded sems one strip of which is tensioned in wle direction, e.g. WW, WC, W45, will e chrcterised y the lowest elongtion vlues, even lower thn those of non-onded R mterils: from 82.5 % to % in respect to wle R w nd from % to % in respect to course R c direction. It should e noted tht extensiility of CC 7 onded sem re similr to the extensiility of non-onded mteril in wle R w direction. Mentime the most significnt effect upon onded sems strength nd extensiility ws otined tking into ccount the type of knitting pttern nd the orienttion of mterils strips in onded sems, especilly in the cse of 1 1 ri knitted R mteril. The results of cyclicl tensile ftigue loding y 5 cycles up to tension force F = 24.5 N show tht it hs no significnt effect upon tensile elongtion of onded systems with oth nd thermoplstic films (Fig. 5, ). The elongtion ɛ mx5 of onded sems from plin jersey knitted mteril P decresed y 8.8 %, the elongtion ɛ mx5 of onded sems from 1 1 ri knitted mteril R incresed y 12.7 %, except onded sems RWC nd RW45, they incresed y 9.8 % (Fig. 5, ). 7 Tensile elongtion mx, % Tensile elongtion mx, % P w P c R w R c Fig. 4. Unixil elongtion of plin jersey knitted mteril in wle Pw nd course Pc directions (), nd of 1 1 ri knitted mteril in wle Rw nd course Rc directions (), nd ten types of onded sems (coefficient of vrition vried in the limits of.61 % 5.81 %) 183

5 PWW mx, % 35 PWW RWW mx, % 35 RWW PWC 25 PWC RWC 25 RWC PW45 5 PW45 RW45 5 RW45 PCC PCC RCC RCC PC45 PC45 RC45 RC45 ɛmx, % ɛmx5, % ɛmx, % ɛmx5, % Fig. 5. Unixil elongtion of plin jersey knitted P mterils () nd 1 1 ri knitted R mterils () onded sems efore ɛmx nd fter unixil ftigue loding ɛmx5 (coefficient of vrition vried in the limits of.61 % 7.99 %) P w P c R w R c Fig. 6. Unixil tensile force of plin jersey knitted nd mteril in wle Pw nd course Pc directions () nd of 1 1 ri knitted in wle Rw nd course Rc directions (), nd ten types of onded sems (coefficient of vrition vried in the limits of 1.48 % 5.78 % Bonded sems WW nd CC of plin jersey knitted mteril P re the strongest, while onded sem C45 is the wekest (Fig. 6, ). The difference of F mx etween them reches 64.7 % in the cse of thermoplstic film. Mximl strength of the sems onded with thermoplstic film re more stle, ecuse the difference etween them is only 32.2 %. It cn e seen tht the strength of sems where oth strips re orientted in wle WW direction is similr to the strength of non-onded mteril in wle P w nd course P c directions (Fig. 6, ). In the cse of 1 1 ri knitted mteril R the strongest re the sems where oth onded strips re orientted in wle WW direction, the wekest CC nd C45 sems. In Figure 6, it cn e seen tht the strength of WC nd W45 sems is close to the strength of non-onded mteril in wle R w direction. The difference etween them comprises 4.4 % 26.7 %. The strength of C45 sem is close to the strength of non-onded mteril in course R c direction. PWC PW45 PWW F mx, N PWW PWC PW45 RWC RW45 RWW F mx, N RWW RWC RW45 PCC PCC RCC RCC PC45 PC45 RC45 RC45 Fmx Fmx5 Fmx Fmx5 Fig. 7. Unixil tensile forces of plin jersey knitted mteril P () nd 1 1 ri knitted mterils R () onded sems efore Fmx nd fter unixil ftigue loding Fmx5 (coefficient of vrition vried in the limits of.4 % 7.5 %) 184

6 The difference etween them is 21.9% 26.1 %. The results of cyclicl tensile ftigue loding reveled tht it hd insignificnt effect upon tensile strength F mx5 of knitted mterils R onded sems (Fig. 7, ), ut it effected the strength F mx5 of plin jersey knitted mteril P onded sems, especilly when onded with thermoplstic film (Fig. 7, ) the modulus of which is more thn twice lower thn tht of film (Tle 2). The highest decrese ws oserved for onded sems WW (49.3 %), WC (35.6 %) nd CC (48.8 %), which were onded with film nd for onded sem WW (34.1 %), which ws onded with film. A little it lower decrese ws oserved for C45 (15.5 %) nd C45 (18.3 %) onded sems with oth thermoplstic films nd. In the cse of 1 1 ri knitted mteril R medium decrese in the limits of 8.9 % 25.8 % ws oserved for WW nd WC sems onded with oth nd thermoplstic films. 3. CONCLUSIONS The effect of thermoplstic film thickness nd the orienttion of knitted mterils strips upon unixil tensile ehviour of onded overlp sems efore nd fter cyclicl ftigue loding ws determined. The strength nd extensiility of onded sems strongly depend upon the structure of knitted mteril nt its orienttion in the sem. Investigtion results hve reveled tht more stle sems re otined for less nisotropic mterils. The performnce of such sems is close to tht of non-onded mterils deformtionl ehvior. The results of the investigtions hve shown tht the orienttion of strips of low nisotropy mteril P does not hve significnt effect upon deformtionl ehviour of onded sems. The sems WW, where oth strips re orientted in wle direction, re stronger y 64.7 % when compred to the other sems, ut weker y 18 % when compred to the strength of non-onded mteril strength in wle P w nd course P c directions. It must e noted tht the extensiility of ll the sems mde of P mteril re similr, ut less extensile y 59.6 % 1.5 % when compred to non-onded knitted mteril P tensioned in oth directions. Different results were otined in the cse of high nisotropy mteril R, ecuse the orienttion of mteril strips hd evident effect upon deformtionl ehviour of onded sems. The sems WW, oth strips in which re orientted in wle direction, ecme stronger y % when compred to the other sems nd stronger y % when compred to non-onded knitted mteril strength tensioned in wle P w nd course P c directions. The wekest re C45 sems the strength of which re close to non-onded knitted mteril in course direction R c, ut weker y 26 % in respect to non-onded knitted mterils strength in wle direction R w. The strength of WC nd W45 sems re close to non-onded knitted mterils strength in wle direction R w. The most extensile re CC onded sems the extensiility of which re close to non-onded knitted mterils extensiility in wle direction R w, ut lower y 87.1 % in respect to non-onded knitted mterils extensiility in course direction R c. The lowest extensiility is chrcteristic for WW, WC nd W45 sems nd it is less y % % when compred to the extensiility of CC sems nd y 82.5 % 112 %, nd y % % in respect to non-onded knitted mterils extensiility in wle R w nd course R c directions, respectively. REFERENCES 1. Jn, P. Assemling technologies for functionl grments An overview. Indin Journl of Fire nd Textile Reserch : pp Gierenz, G., Krmnn, W. Adhesive nd Adhesive Tpes, Wiley-VCH Verlg gmh, 21: 138 p. 3. Jones, I.-A., Wise, R.-J. Novel joining methods pplicle to textiles nd smrt grments. Pper presented t Werle Futures Conference, University of Wles, Newport, Wles, Septemer 25. (ccessed 18 July 214). 4. Bemis Associte Inc. 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