Thermally Driven Mechanical Behavior Of Thermally Responsive Liquid Crystal Elastomer Fiber

Self-excited oscillation is a phenomenon that can obtain energy directly from a constant external environment to maintain periodic motion.The application of such phenomenon to a motion system can achieve self-sustained motion of the system,and the motion process does not require portable batteries and periodic external stimuli,and the frequency and amplitude of periodic self-sustained vibration only depend on the inherent parameters of the system,which has a strong robustness and therefore has great potential application value.In recent years,thermally responsive fiber-mass systems based on the principle of selfexcited oscillation have received much attention because of their ability to harvest energy from the environment.The fiber-mass system composed of thermally responsive liquid crystal elastomers is able to maintain its own continuous vibration in a non-uniform temperature field,and during the vibration process,it can convert low-grade thermal energy from the external environment into mechanical energy for the purpose of energy harvesting.However,in the theoretical modeling of the thermally responsive fiber-mass system,the complex problem of coupling thermodynamics and nonlinear dynamics needs to be considered,and the theoretical derivation process is still challenging.The current theoretical analysis is generally still based on the most primitive thermodynamic equations and is very lengthy,which limits its practical application.If an intrinsic model of the thermally responsive fiber-mass system can be developed,it will become very convenient to analyze the thermally driven mechanics of this type of system.In this paper,a fiber-engine module is abstracted from the thermally responsive fibermass system,and its intrinsic structure model is first established by theoretical analysis,and then the asymptotic relations of the fiber-engine module are further derived when the heat conduction characteristic time is short.The asymptotic relationship of the fiber engine module is similar to the Kelvin-Voigt viscoelastic model consisting of a damper and an elastic spring,whose thermally driven mechanical behavior is jointly determined by the equivalent damper and the elastic spring.The modulus of elasticity of the equivalent spring is determined by the parameters of temperature gradient,elasticity and thermal contraction coefficient in the asymptotic relation,and the damping coefficient of the equivalent damper is determined by the temperature gradient,elasticity and thermal contraction coefficients and the characteristic time of heat conduction in the asymptotic relation.The convenience of the application process of the fiber engine module intrinsic model and asymptotic relations is then demonstrated in different cases.When the characteristic time of the heat conduction process is zero,the damping effect of the fiber engine module disappears,and the fiber-mass system at this time is equivalent to an elastic spring,and the elastic modulus is mainly determined by the temperature gradient,the thermal contraction coefficient and the elasticity coefficient.In the investigation of the influence of the system parameters on the vibration process,it is known that the elasticity coefficient and the thermal contraction coefficient affect the vibration frequency,while the damping effect in the environment only increases the energy consumption of the system and reduces the vibration amplitude.In the case of small characteristic time,it is known from the self-excited oscillation of the single/dual fiber-mass system that the thermally responsive fiber-like engine can maintain its own periodic vibration by absorbing heat from the environment.Subsequently,the influence of system parameters on the self-excited oscillations is analyzed,and it is concluded that the fiber elasticity coefficient and thermal contraction coefficient affect the vibration frequency,amplitude and equilibrium position of the self-excited oscillations of the fiber engine,while the damping effect in the environment only affects the amplitude.In addition,it is concluded from further theoretical analysis that the thermally driven selfexcited oscillation of the fiber engine has the potential to drive the frame to jump on the hot surface,and adjusting different system parameters affects the self-excited oscillation of the fiber engine while affecting the possibility of the frame jump.The fiber engine self-excited oscillation is not only capable of converting thermal energy into mechanical energy,but also of driving machinery through it.The main difference between engines is the level of performance,and it is of great importance to study the factors influencing the performance of fiber engines.By using the example of a fiber engine driving a stirrer,it is possible to investigate the factors influencing the power density of the fiber engine.It is found that there is an optimal heat transfer characteristic time that allows the fiber engine to reach the maximum power density,and then the influence of these parameters on the power density of the fiber engine is inferred by investigating the influence of other system parameters on the self-excited oscillation of the fiber engine at the optimal characteristic time.In this way,it not only deepens the understanding of the thermally responsive fiber thermal drive mechanics behavior,but also provides a theoretical basis for increasing the power density of fiber engines in applications,which promotes their applications in soft robotics,micro/nano devices,and biomedical instrumentation.Figure[50] reference[104]...