Test and mesoscopic finite element analysis on mechanical properties degradation of aged coated fabrics

Tes and mesoscopic ini e elemen analysis on mechanical p ope ies deg ada ion o aged coa ed ab ics VIII In e na ional Con e ence on Tex ile Composi es and In la able S uc u es STRUCTURAL MEMBRANES 2017 Qilin Zhang, Yun ing Li TEST AND MESOSCOPIC FINITE ELEMENT ANALYSIS ON MECHANICAL PROPERTIES DEGRADATION OF AGED COATED FABRICS STRUCTURAL MEMBRANES 2017 QILIN ZHANG*, YUNTING LI† *College o Ci il Enginee ing Tongji Uni e si y 200092 Shanghai, China. E-mail: zhangqilin@ ongji.edu.cn † College o Ci il Enginee ing Tongji Uni e si y 200092 Shanghai, China. E-mail: liyun ing[email p o ec ed]m Key wo ds: PVDF-coa ed Fab ics, Ageing Beha io , Mechanical P ope y, Mesoscopic Fini e Elemen Analysis. Summa y. In his pape he mechanical p ope ies deg ada ion o aged coa ed ab ics is in es iga ed. Tes s on he ension s eng h and he ea ing s eng h o he aged ab ics a e ca ied ou , which is om he memb ane oo o Qingdao S adium used o mo e han 13 yea s. The s eng h deg ada ion deg ees o he aged ab ics a e ob ained. Due o he con igu a ion o ab ics he nume ical simula ion on i s s ess s a e as well as i s ac u e p ocess and mechanism is e y di icul . In his pape , a mesoscopic ini e elemen model o plain wo en ab ics s ess analysis is es ablished based on wo en con igu a ion ab ic cells. The nume ical analysis shows ha a i m ya n-ya n connec ion a in e lacing poin would make ab ics has high shea s i ness and concen a es ensile s ess on he edge o he ab ics in which applied load. I coincides wi h he bi-axial ensile es , in which c uci o m specimen ac u e always a he a ms ins ead o co e a ea. Finally he ac u e c i e ion is buil up o new and aged ab ics on he basis o he es and analysis esul s o his pape . 1 INTRODUCTION Memb ane s uc u e, wi h many ad an ages including a ligh weigh , good ligh ansmission, lexible s e ch, s ong sense o shape and g ea a chi ec u al pe o mance, is well ecei ed and has been widely used in public shel e s uc u es. Buil on a bend in he Ri e Thames in G eenwich, London, he Millennium Dome is one o he mos amous B i ain's landma ks. The wo ld's mos luxu ious Uni ed A ab Emi a es Bu jAl-A ab ho el in Dubai is a double-laye memb ane s uc u e o he building. I is buil on a man-made island wi h a ligh g ace ul sailboa s yling shape and in eg a ed in o he su ounding landscape. Besides, he memb ane s uc u es a e p e e ed in he many public buildings, such as S adium and Ai po . Howe e , he memb ane s uc u e also has essen ial sho coming, ha is, compa ed wi h he s eel, conc e e, glass and o he building ma e ial, memb ane ma e ial is mo e easily aging and could cause he des uc ion o he s uc u e. To ensu e sa e y, aging o 125 Qilin Zhang, Yun ing Li 2 memb ane ma e ials is an impo an subjec . Many esea ch on he e ec s o di e en ac o s on he aging o memb ane ma e ials ha e been ca ied ou wi h a i icial accele a ed ageing me hod [1-8] o ou doo ageing me hod[9-12]. These s udies a e he basis o he s udy o aging p ope ies o memb ane ma e ials. Fo u he unde s anding o ma e ial aging, he aging coa ed ab ics emo ed om a s adium been selec ed as esea ch objec s, a lis o mechanical es s a e ca ied ou . To igu e ou i s aging mechanism, nume ical simula ions a e also pe o med. This pape consis s o wo main pa s, expe imen s udy and nume ical analysis. 2 AGING PROPERTIES OF PVDF To e alua e he du abili y o coa ed ab ics a e aging in a s uc u e ou doo , a se ies o con as expe imen s was ca ies ou be ween he na u al ageing coa ed ab ics emo ed om a s adium buil in 2007 and he new specimens o he same ype o coa ed ab ics. Mechanical p ope ies o coa ed ab ics, including ensile, ea ing and bonding s eng h, a e es ed acco ding o DG/T J082019-2007 (2007)[13]. The main es esul s and analysis a e as ollows [14]. 2.1 Coa ing The educ ion o b igh ness a he sunny side is 56.42%, while ha a he shaded side is 30%. Acco ding o he mic oscopic mo phology o he ab ic coa ings (Fig. 1), he ageing coa ing a he shaded side has some bulges, bu he e is no c ack and pul e iza ion. Howe e , he ageing coa ing a he sunny side is ull o c acks, wi h bulges and pul e iza ion. The colo change and c acks caused by ageing a he sunny side is mo e se e e han ha a he shaded side. Acco ding o he aging p inciple o polyme s，i is mainly due o he ageing mechanism o high polyme ma e ial, namely up u e o molecula chain (deg ada ion) and c osslinking o mac omolecula chain [15]. 126 Qilin Zhang, Yun ing Li 3 Figu e 1: Pho og aphs o he coa ing by SEM: (a) new coa ing×500 (b) ageing coa ing a he shaded side×500 (c) ageing coa ing a he sunny side ×500 (d) new coa ing×10000 (e) ageing coa ing a he shaded side×10000 ( ) ageing coa ing a he sunny side ×10000 2.2 Fo ce a ailu e & ea ing s eng h The esul s o o ce a ailu e and ea ing s eng h es s a e p esen ed in Table 1. In wa p di ec ion, o ce a ailu e o he new ab ics is 8132 N/5 cm, while ha o he ageing is 7329 N/5 cm. In we di ec ion, o ce a ailu e o he new ab ics is 7051 N/5 cm and ha o he ageing one is 6792 N/5 cm. Tes esul s show he o ce a ailu e o ab ics dec eases by 9.9% in wa p di ec ion and dec eases by 3.7%in we di ec ion. In wa p di ec ion, ea ing s eng h o he new coa ed ab ics is 1217 N, while ha o he ageing is 937 N. In we di ec ion, ea ing s eng h o he new coa ed ab ics is 1163 N and ha o he ageing is 818 N. Expe imen al esul s show ha ea ing s eng h o aging coa ed ab ics dec eases by 23% in wa p di ec ion and 29.6% in we di ec ion. Possibili y P o signi ican di e ence a e 1.5E-18 and 2.8E-29 in wa p and we espec i ely, which a e lowe han 0.05. T- es p o es ha ea ing s eng h o he new and aging ma e ial has no able di e ence in wa p and we di ec ions. In addi ion, i can be ound ha he deg ada ion o ea ing s eng h is mo e ob ious han ha o o ce a ailu e, which is consis en wi h o he esea ches [4, 8, 24]. Table 1: Fo ce a ailu e es ing esul s Ma e ial Tensile o ce (N/5cm) Tea ing s eng h (N) Wa p We Wa p We New 8132 7051 1217 1163 Ageing 7329 6792 937 818 Reduc ion 9.9% 3.7% 23.0% 29.6% 3 NUMERICAL ANALYSIS In o de o analyse s ess o aging memb ane ma e ial. The nume ical model o coa ed ab ics is buil . The e a e h ee pa s in his sec ion. S ess cha ac e is ics o he coa ed ya n we e analysed and angen ial ac ion a he in e laced poin o ab ics was discussed. Besides, he e ec o coa ing ha dening on ab ic was s udied. 127 Qilin Zhang, Yun ing Li 4 3.1 Me hod Coa ed ab ics memb ane can be analyzed on h ee scales: mac oscopic, mesoscopic and mic oscopic. In his pape , modelling and analysis a e on he mesoscopic. A ya n is he basic cons i uen ma e ial. Modelling ool is Texgen which [16, 17] is de eloped by he Polyme Composi es G oup a he Uni e si y o No ingham as a modelling p e-p ocesso o a a ie y o applica ions including solid mechanics. I p o ide a g aphical use in e ace o de ine pa h, sec ion shapes and dimensions o a ya n and disc e ize ya ns by a buil -in mesh gene a o . In his pape , wo we ya ns and wo wa p ya ns a e in e laced e ically o o m a uni cell as ig. 2 shown. In Texgen, ya n pa h is ep esen ed by a spline S(u). As ig. 3 shown, 9 con ol poin s a e de ined and Na u al cubic spline is selec ed. Sec ion shape o ya ns a e len icula acco ding o SEM abo e. Wid h and heigh is 1.8 and 0.4 espec i ely. O he pa ame e s a e shown in he Table 2. Geome ic in o ma ion is acco ding o SEM o he ya n. Figu e 2: Uni cell Figu e 3: Ya n pa h and con ol poin s Figu e 4: The c oss sec ion o ageing coa ed ab ic 128 Qilin Zhang, Yun ing Li 5 Table 2: Pa ame e s o ya ns Pa ame e s Wa p We Ya n linea densi y 0.0002002 kg/m 0.00011 kg/m Fibe densi y 1.37g/cm 3 1.37g/cm 3 To al ibe a ea 0.146554mm 2 0.08052 mm 2 Fibe diame e 25μm 25μm Fibe pe ya n 300 165 Mechanical model o ya ns a e de ined in Abaqus [18]. Tensile p ope ies a e de ined using expe imen al da a as iso opic hype elas ic ma e ials. The s ess-s ain cu es a e shown in Figu e 5. The Poisson's a io is 0.4. The coa ing is de ined as elas ic ma e ial. Figu e 5: S ess-s ain cu es o ya ns 3.2 Resul s and analysis In he coa ing p ocess o he ab ic, he e may be wo modes o ac ion in he in e sec ion o wa p and we ya ns. The i s si ua ion is ha wa p and we ya ns is bonded a he in e lace poin s. The second is he coa ing ma e ial is no pene a ed inside and he e is only angen ial ic ion a he in e lace poin s. In his pape , he s ess s a e o he ya n unde ension in abo e wo cases is compa ed and analysed. F om ig. 6-a, in he bonding mode, s ess o he whole ya ns a e mo e concen a ed a some loca ion, while i is uni o m in he ic ion-mode. In he bonding mode, he maximum and minimum alues di e by 1/3, howe e , s ess a e kep a he same le el in he ic ion mode. Acco ding abo e, when he ya ns a e independen a he in e lace poin , he ab ics would show a g ea e s eng h due o a easonable s ess dis ibu ion. A e applied coa ing, i ya ns o he ab ics bonding oge he , he s ess o ya ns concen a ed in he ee a ea be ween he in e lace poin s and i eaches o he maximum a bo h ends o he len icula sec ion. 129 Qilin Zhang, Yun ing Li 6 (a) Bonding oge he a in e lace poin (b) F ic ion model a in e lace poin Figu e 6: S ess nephog am o wo models Conside ing he modulus o elas ici y changes when he coa ing is aged, he ollowing sec ions compa e he e ec o he coa ing ha dening on he in e nal s ess o he ab ic. Wi h wo di e en elas ic modulus o coa ing, s ess o ya ns in a uni cell a e shown in Figu e 7. In Figu e 7-a, when elas ic modulus o coa ing E is 15 MPa, he s ess concen a e on he edge o a ya n. F om Figu e 7-b, when elas ic modulus o coa ing E is 150 MPa, he e is a e age dis ibu ion s ess in a ya n. In addi ion, s ess a e con as ed a h ee ypical posi ions o a ya n, as Figu e 8 shown. Unde he same load, s ess-s ain cu es o h ee poin s on a ya n was show in Figu e 9. F om Figu e 9-a, i is easy o ind ha he e is a g ea di e ence a h ee poin s. Howe e , in Figu e 9-a, s ess in he h ee posi ions is much close . Ha dening o he coa ing end o a mo e equal dis ibu ions o s ess. The imp o emen o s ess concen a ion can make he ya n o ce mo e uni o m and he ab ic s eng h highe I should be emphasized ha he elas ic modulus o he coa ing discussed abo e is much smalle han ha o he ya n. I he modulus o coa ing and ya n on he same le el, i will cause s ess concen a ion in he coa ing and he bonding posi ion, and he o ce condi ion needs a u he s udies. (a) Elas ic modulus o coa ing E=15 MPa (b) Elas ic modulus o coa ing E=150 MPa Figu e 7: S ess o wo models 130 Qilin Zhang, Yun ing Li 7 (a) Poin 1 (b) Poin 2 & a. Poin 3 Figu e 8: Typical posi ion (a) Elas ic modulus o coa ing E=15MPa (b) Elas ic modulus o coa ing E=150 MPa Figu e 9: S ess-s ain cu e 4 CONCLUSIONS Based on he abo e esea ch, he ollowing conclusions a e ob ained: - Aging coa ing has c acks, powde and o he aging cha ac e is ics. - Tensile s eng h o coa ed ab ics dec ease by less han 10% and ea ing s eng h dec eased o 20%~30% - Nume ical analysis shows ha angen ial ac ion a he in e laced poin o ab ics g ea ly a ec he dis ibu ion o s ess. When he wa p and we a e bonded a he in e lace poin s, s ess is concen a ed on he edge o a ya n. I he e is only ic ion in angen ial a he in e lace poin s, s ess dis ibu ion o a ya n is mo e e en. - A e aging, he ha dening o he coa ing will lead o a mo e uni o m s ess dis ibu ion o he ya n. This may be one o he easons why he ensile s eng h o he ab ic does no dec ease signi ican ly a e aging REFERENCES [1] Zhang YY. 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