Fundamental Research On Electro-mechanical Behavior Of Dielectric Elastomer Actuators

Dielectric elastomer is a new type of intelligent polymer viscoelastic material.It has been fabricated into actuators,generators,artificial tendons and so on with the advantages of light weight,high viscoelasticity and high energy density.Especially,it indirectly converts electrical energy into mechanical energy with the characteristics of fast response and large strain.It has been widely used in the fields of optics,mechanics,biomedicine and so on.In the application of dielectric elastomer actuators,there are some problems that need to be solved urgently.Firstly,most of the studies only choose one material for viscoelastic analysis in the selection of dielectric elastomer actuators,and neglect the influence of the material's tensile and fatigue properties on the actuators.Secondly,as an important factor affecting the dynamic electrical properties of dielectric elastomers,the voltage loading method is not systematic enough.Finally,in the design of many actuator structures,because of the single and asymmetric displacement direction,the applicability in application is low,which needs further study.In this paper,three kinds of dielectric elastomers(acrylic,neoprene and urethane)were made into national standard dumbbell-shaped test sheets for tensile test.It is concluded that the stress-strain curve of dielectric elastomers increases in a "S" shape at the same speed,and the faster the tensile speed is,the greater the stress is.At the same strain rate of 500 mm/min,the maximum response stress of dielectric elastomers is neoprene(3.9 MPa)> urethane(1.8 MPa)> acrylic(1 MPa).The tensile properties of three dielectric elastomers are strengthened by adding fibers.It is found that Young's modulus is proportional to the number of fibers in the tensile elastic stage,and the fitting curve is in agreement with the actual situation.Tensile frequency influences fatigue properties of materials.The stress range of acrylic dielectric elastomer is less than 1 Hz in the same strain range of 100%-200% and 0.5 Hz.At the same time of 1000 cycles,the strain curve at 0.5 Hz is 0.25 s ahead of time,and the strain curve at 1 Hz is 0.1 s ahead of time.The stress ranges of three dielectric elastomers under the same strain at 1Hz and 10000 cycles are neoprene > urethane > acrylic.In viscoelasticity test,the relative loss energy of acrylic dielectric elastomer increases slowly with the increase of frequency.At the same frequency,the energy loss properties of three dielectric elastomers are acrylic > urethane > chloroprene.Finally,the dielectric elastomer of acrylic is selected as the material of actuator,which needs large strain,small stress and stable energy loss.The electric field of acrylic dielectric elastomer under different strains was studied by selfmade pre-stretching instrument.The results are as follows: the effect of electric field on acrylic dielectric elastomer is more significant with the increase of pre-stretching.When pre-strain is 300%,the area change ratio is 1.91,but when pre-strain is more than 300%,the material is easily destroyed by machinery.The faster the loading voltage is,the larger the area change ratio is.When applied 0.4 kV/s triangular wave electric field,breakdown damage is easier with the increase of wave number.Under the condition of linear voltage speed of 0.0125 kV/s and pre-strain of 300%,by comparing the two newly developed actuators(double-cone and diaphragm type)from three aspects of generation force,rotation angle and response time,it is found that the bi-cone type actuator produces less force(0.2 N)than the concave-drum type(0.5 N),but the maximum rotation angle(16 °)of the bi-cone type actuator is larger than the concave-drum type(9 °),and simultaneously produces rotation.The response time of dynamic angle was 74.2 s.Mooney-Rivlin three-parameter constitutive equation fitted the tensile curve of acrylic dielectric elastomer with 0.04 error.The tensile curve was validated by MSC.MARC software.The simulation predicted that the maximum stress produced by the biconical actuator under 500% pre-tension was 3.005 MPa and could reach 36.7 °.