Comparative characterization of NiTi filaments and NiTi knit-induced air-gap effects on heat transfer in a smart textile system

Šalej Lah, Alenka (author)

This article presents a comparison of the different diameters and characterization of nickel–titanium (NiTi) alloy and the effect of an NiTi knit-induced air gap on heat transfer in a smart textile system. Weft-knitted fabric was produced using commercially available cold-worked NiTi wires (filaments), enabling active thermal insulation in protective garments by adjusting the air gap between two fabric layers in response to changes in environmental temperature. For this study, NiTi alloy filaments containing 54.8 wt. % nickel and 45.2 wt. % titanium with a diameter of 100 μm was used. The transition temperatures of the NiTi filaments were tailored for the intended application, with the austenite start temperature set at approximately 70 °C and the martensite start temperature set at around 20 °C. Various methods for determining transition temperatures were compared, including differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and electrical resistance measurements (ERM), all of which yielded consistent results. Mechanical properties were evaluated through tensile tests conducted with an Instron dynamometer at room temperature (20 °C) and in a heated chamber at 100 °C. The stress-strain response of the annealed NiTi alloy exhibited the characteristic four-stage behaviour typical of shape memory materials. All obtained results were also compared with previously reported data for NiTi alloy filaments with a diameter of 200 μm, showing good agreement. In addition, the impact of the NiTi knit-induced air gap on heat transfer behaviour in thermal protective composites was investigated. This study confirms that 100 μm NiTi filaments can be effectively optimized for smart textile applications through controlled annealing, with heat treatment at 500 °C producing suitable transformation temperatures consistently validated using DSC, DMA and ERM methods. Additionally, integrating an annealed NiTi knit into a textile composite increases the air gap at elevated temperatures, thereby reducing heat transfer and significantly enhancing the thermal insulation and adaptive performance of the smart textile system.

• Language: English
• Keywords: NiTi alloy, Nitinol, shape memory materials, air gap, heat transfer
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: Str. 60–75
• Numbering: Vol. 69, no. 1
• PID: 20.500.12556/RUL-181358
• UDC: 677
• ISSN on article: 0351-3386
• DOI: 10.14502/tekstilec.68.2026017
• COBISS.SI-ID: 274011395
• Publication date in RUL: 03.04.2026

Record is a part of a journal

• Title: Tekstilec : glasilo slovenskih tekstilcev
• Shortened title: Tekstilec
• Publisher: Zveza inženirjev in tehnikov tekstilcev, Splošno združenje tekstilne industrije, Zveza inženirjev in tehnikov tekstilcev, Splošno združenje tekstilne industrije, Društvo inženirjev in tehnikov tekstilcev, Univerza v Ljubljani, Naravoslovnotehniška fakulteta, Oddelek za tekstilstvo, Založba Univerze v Ljubljani
• ISSN: 0351-3386
• COBISS.SI-ID: 763396

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Title: Primerjalna karakterizacija filamentov NiTi in vpliv zračne reže, inducirane s pletivom NiTi, na prenos toplote v pametnem tekstilnem sistemu

Abstract

V članku je predstavljena primerjava različnih premerov in karakterizacija zlitine nikelj-titan (NiTi) ter vpliv zračnega sloja, induciranega s pletivom NiTi, na prenos toplote v pametnem tekstilnem sistemu. Votkovno pletivo je bilo izdelano iz komercialno dostopnih hladno deformiranih žic NiTi (filamentov). Takšno pletivo omogoča aktivno toplotno izolacijo v zaščitnih oblačilih z uravnavanjem zračnega sloja med dvema plastema tkanine, ki se odziva na spremembe temperature okolja. V raziskavi so bili uporabljeni filamenti zlitine NiTi s premerom 100 μm, ki so vsebovali 54,8 mas. % niklja in 45,2 mas. % titana. Temperature prehoda filamentov NiTi so bile prilagojene predvideni uporabi, pri čemer je bila začetna temperatura avstenita približno 70 °C, temperatura začetka martenzita pa približno 20 °C. Primerjane so bile različne metode določanja temperatur prehoda, vključno z diferencialno vrstično kalorimetrijo (DSC), dinamično mehansko analizo (DMA) in meritvami električne upornosti (ERM), pri čemer so vse metode dale skladne rezultate. Mehanske lastnosti so bile določene z nateznimi preskusi, izvedenimi na dinamometru Instron pri sobni temperaturi (20 °C) in v ogrevani komori pri 100 °C. Napetostno-deformacijski odziv žarjene zlitine NiTi je pokazal značilno štiristopenjsko obnašanje, značilno za materiale z oblikovnim spominom. Vsi dobljeni rezultati so bili primerjani s predhodno objavljenimi podatki za NiTi filamente s premerom 200 μm, pri čemer je bilo ugotovljeno dobro ujemanje. Dodatno je bil raziskan vpliv zračnega sloja na obnašanje prenosa toplote v toplotno zaščitnih kompozitih, induciranega s pletivom NiTi. Raziskava potrjuje, da je mogoče 100-μm filamente NiTi učinkovito optimizirati za uporabo v pametnih tekstilijah z nadzorovanim žarjenjem pri temperaturi 500 °C, kar zagotavlja ustrezne transformacijske temperature, potrjene z metodami DSC, DMA in ERM. Vključitev žarjenega pletiva NiTi v tekstilni kompozit pri povišanih temperaturah uspešno poveča zračni sloj, zmanjša prenos toplote ter s prilagodljivim delovanjem pametnega tekstilnega sistema bistveno izboljša toplotno izolativnost.

• Keywords: zlitina NiTi, Nitinol, materiali z oblikovnim spominom, zračni sloj, prenos toplote