Journal of Bionic Engineering (2023) 20:2786–2796https://doi.org/10.1007/s42235-023-00403-4

A Stifness?Tunable Composite with Wide Versatility and Applicability Based on Low?Melting?Point Alloys 

Jiawei Xiong1  · Bo Sun1  · Chunbao Liu1,2 · Konghua Yang1  · Yuchao Luo1  · Yunhong Liang2,3 · Zhiwu Han2  · Lei Ren4  · Zhaohua Lin1

Chunbao Liu liuchunbao@jlu.edu.cn Zhaohua Lin linzhaohua@jlu.edu.cn 

1 School of Mechanical and Aerospace Engineering, Jilin University, Changchun 130022, China 

2 Key Laboratory of Bionic Engineering, Ministry of Education, Jilin University, Changchun 130022, China 

3 Liaoning Academy of Materials, Shenyang 110167, China 

4 Department of Mechanical, Aerospace and Civil Engineering, University of Manchester, Manchester M139PL, UK

Abstract: Flexible materials are essential in bionic felds such as soft robots. However, the lack of stifness limits the mechanical performance of soft robots and makes them difcult to develop in many extreme working conditions, such as lifting and excavation operations. To address this issue, we prepared a stifness-tunable composite by dispersing low-melting-point alloy into thermosetting epoxy resin. A dramatic and rapid change in stifness was achieved by changing the state of matter at lower temperatures, and accurate control of the composite modulus was achieved by controlling the temperature. When the alloy content is at 30vol%, the tensile modulus changes 41.6 times, while the compressive modulus changes 58.9 times. By applying the composite to a fexible actuator, the initial stifness of the actuator was improved by 124 times, reaching 332 mN/mm. In addition, the use of stifness-tunable materials in the wheel allowed for timely changes in the grounding area to improve friction. These fexible materials with manageable mechanical properties have wide applicability in felds including bionics, robotics, and sensing. Our fndings provide a new approach to designing and developing fexible materials with improved stifness and controllability. 

Keywords: Stifness-tunable composite · Manageable mechanical properties · Flexible actuator