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2026 Vol.39, Issue 2 Preview Page

Research Paper

Constitutive and Structural Modeling of SMA-Driven Knitted Soft Actuator Unit Cell Under Large Deformation

대변형 하에서 SMA 구동 니트형 연성 액추에이터 유닛 셀의 구성 및 구조 모델링

Muhammad Umar Elahi1
,
Heung Soo Kim2*
무함마드 우마르 일라히1
,
김 흥수2*
1Ph.D. Student, Department of Mechanical, Robotics and Energy Engineering, Dongguk University, Seoul, 04620, Korea
2Professor, Department of Mechanical, Robotics and Energy Engineering, Dongguk University, Seoul, 04620, Korea
1동국대학교 기계로봇에너지공학과 박사과정
2동국대학교 기계로봇에너지공학과 교수
*Corresponding Author
30 April 2026. pp. 105-109
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Abstract

Shape memory alloy (SMA)-integrated knitted actuators can generate large, compliant deformation through temperature-induced phase transformation; however, their response is strongly nonlinear owing to loop kinematics and large rotations. This study develops a constitutive-structural modeling methodology for an SMA-driven knitted soft actuator unit cell under large deformation, with emphasis on the plain-pattern P-loop as a baseline architecture. In experimentally reported knitted SMA actuators, a NiTi (55wt% Ni-45wt% Ti) core wire wrapped with polyester fibers is heated by electrical current, thus resulting in martensite-to-austenite transformation. In the present numerical study, electrical heating is not modeled explicitly; instead, thermally driven actuation is represented by a prescribed thermal load. A 3 × 3 P-loop unit cell is constructed using a weft-knit geometry pipeline and imported into ANSYS for nonlinear analysis. The SMA response is captured using the built-in SMA material capability in ANSYS under a temperature increase from 25°C to 90°C, and the structural problem is solved with large-deformation kinematics to capture out-of-plane loop deformation. Contact and self-contact between yarn segments are disregarded in the current model to isolate the primary thermally driven deformation coupling. The simulations reproduce the expected loop-level tightening and geometry-driven amplification of deformation in the out-of-plane direction, thus demonstrating that the unit-cell model can quantify actuation-induced shape changes in knitted architectures. The proposed methodology provides a practical approach for evaluating and comparing knitted patterns at the unit-cell level. Additionally, it serves as a basis for future extensions, including contact, electro-thermal coupling, and experimental validation.

Keywords
shape memory alloy
knitted actuator
P-loop
unit -cell model
large deformation
thermomechanical analysis
ANSYS

본 연구는 대변형 조건에서 형상기억합금(SMA) 기반 편성(knitted) 소프트 액추에이터의 거동을 해석하기 위한 구성-구조 연성 수치모델링 방법론을 제시한다. 기준 구조로 평직(plain) 패턴의 P-루프를 채택하고, 실제 액추에이터 기하 치수에 기반한 위사 편성 기하 생성 절차를 통해 3 × 3 P-루프 유닛셀을 구성하였다. 실험 기반 SMA 편사에서는 폴리에스터로 피복된 NiTi 코어 와이어에 전류 가열이 적용되어 마르텐사이트-오스테나이트 상변태와 이에 따른 회복 수축이 발생한다. 본 연구에서는 전기-열 연성을 직접 모델링하지 않고, SMA 구성요소에 온도 증가(25°C → 90°C)를 부여하는 방식으로 구동 효과를 구현하였다. 수치해석은 ANSYS의 SMA 재료 모델과 기하학적 비선형 대변형 해석을 결합하여 수행되었으며, 루프 재구성과 면외 변형을 정확히 포착하였다. 또한 주요 열구동 변형 메커니즘에 집중하기 위해 실 간 접촉 및 자기접촉은 제외하였다. 해석 결과, SMA 회복 변형에 의해 루프 조임(loop tightening)이 유도되고, 편성 구조의 기하학적 특성으로 인해 면외 변형이 증폭됨을 확인하였다. 제안된 유닛셀 기반 모델링 방법은 다양한 편성 패턴의 구동 성능을 효율적으로 비교･평가할 수 있는 실용적 도구를 제공하며, 향후 접촉 효과, 전기-열 연성, 그리고 실험 검증을 포함하는 고정밀 모델로 확장될 수 있다.

키워드
형상기억합금
편성 액추에이터
P-루프
유닛셀 모델
대변형
열-기계 연성 해석
ANSYS
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Information
  • Publisher :Computational Structural Engineering Institute of Korea
  • Publisher(Ko) :한국전산구조공학회
  • Journal Title :Journal of the Computational Structural Engineering Institute of Korea
  • Journal Title(Ko) :한국전산구조공학회 논문집
  • Volume : 39
  • No :2
  • Pages :105-109
  • Received Date : 2026-02-26
  • Revised Date : 2026-03-03
  • Accepted Date : 2026-03-04
  • DOI :https://doi.org/10.7734/COSEIK.2026.39.2.105
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