Dynamics And Piezoelectric Vibrational Energy Harvesting Research Of Bi-stable Hybrid Laminate

Energy harvesting from mechanical vibrations has become increasingly important in recent years,mainly due to the low power requirement of small electronic components,such as the wireless sensor networks used in monitoring applications.Powering of small electronics using the vibrational energy available in their environment could eliminate their dependence on external power sources,like batteries,thus realizing self-powered capabilities and making them operate in an uninterrupted fashion over prolonged periods.Compared with electromagnetic and electrostatic mechanisms,piezoelectric vibrational energy harvesting technique has received the greatest amount of attention due to its major advantages,such as large power density,easy application,simple structure,without electromagnetic interference,easy integration and so on.Conventional vibration linear energy harvesters are effective only when the vibration frequency is at or very close to its resonant frequency.However,the frequency of ambient vibrations generally is random or at a certain range,so rendering typical linear harvesters unsuitable for the most practical application,and the broadband energy harvesting is particularly significant.Using nonlinearity is one way to obtain broadband energy harvesting,so the bi-stable structure is a promising alternative for broadband energy harvesting owing to its nonlinear dynamic response.Bi-stable composite laminate is one typical bi-stable structure,which can realize large deformation during its snap-through behavior.This bi-stability property leads to rich dynamic responses occurring over a wide frequenc y range.The bi-stable laminate becomes one potential solution to realize the broadband vibrational harvesting.In this thesis,based on the background of piezoelectric vibrational energy harvesting,a new type of bi-stable broadband energy harvester is designed and investigated by combining the bi-stable hybrid symmetric laminate(BHSL).The main works are listed below.The configuration prediction of BHSL is investigated to obtain the characteristics of its stable configuration.The curvature and mid-plane strain distribution of BHSL with free boundary are analyzed by finite element(FE) model,and a theoretical model for configuration prediction of BHSL is established according to those distribution laws,and the influence of lay-up and geometry on the stable configuration is analyzed.It is found that the double-curvature and uniform distribution are the key features of BHSL.Considering the actual condition,the theoretical configuration prediction model is presented for BHSL with cantilevered boundary,and the influence of lay-up and geometry of BHSL on the stable configuration is investigated by this theoretical model,FE model,and experiments.To understand the large-deformation and nonlinear characteristics of BHSL,the snap-through behavior of BHSL with four-points supporting boundary and the cantilevered boundary is simulated by FE model and verified experimentally,and the influence of lay-up and geometry on the snap-through response of the cantilever BHSL is analyzed.It is found that the bifurcation phenomenon occurs at the displacement-force curves of the snap-through behavior.According to the previous results of configuration,three types of BHSL with different lay-up and distinct stable configuration are selected.The strain variations in two directions of BHSL during the snap-through process is investigated by FE model and experiments,which act as the basis to estimate the dynamic response of BHSL and verify the uniformity of strain distribution.For these cantilevered BHSLs,the first order linear natural frequencies and corresponding modes are analyzed by FE model to obtain the inherence properties,and the dynamic FE model is established to simulate the vibration response of BHSL.The nonlinear dynamic responses of the cantilever BHSL are investigated under the different excitation levels experimentally by monitoring the strain variations in two directions at three positions of the laminate.The experimental strain variations at three monitoring positions are employed to estimate whether the snap-through behavior has occurred during the vibration,and the single-well or cross-well vibration mode can be decided.Moreover,the cross-well vibration mode is verified according to the strain variation law.The above research about the statics and dynamics of BHSL can provide the basis for the design of bi-stable piezoelectric energy harvester.Base on the characteristics of BHSL’s stable configuration,four types of bi-stable piezoelectric energy harvester(BPEH)are designed with different lay-ups and PZT shape,and FE model of BPEH is employed to analyze its stable configurations and the stress status of PZT.These BPEHs are manufactured experimentally,and the charging performance is used to obtain the initial voltage induced by the stable configuration which is compared with the results predicted by FE model.When BPEH transits between two configurations periodically,the output power is measured and compared with the linear piezoelectric energy harvester(LPEH) with the same setting.FE model is employed to study the influence law of three parameters on the longitudinal curvature and initial voltage of BPEH,which are lay-up,the hybrid wide and side length of PZT,respectively.Additionally,the relation between the strain and the initial voltage are analyzed to reveal the basic characteristic of BPEH.Five types of BPEH are manufactured to verify the influence law of three parameters,and the stable configurations and initial voltages are measured respectively.Moreover,the dynamic responses of BPEH are explored under a certain excitation level by experiments,and the output power corresponding to periodic snap-through and different dynamic response is obtained.In the last part,BPEH with smaller size and lower longitudinal curvature is designed and manufactured,which is more suitable for energy harvesting.Simultaneously,three types of LPEH with the same geometry are designed to illustrate the characteristics and advantages of BPEH.The output voltage and power of BPEH and the LPEHs are investigated systematically under the different excitation levels by experiments.Through the performance comparison between BPEH and LPEH,it is found that BPEH has a higher output voltage and power,and the wider effective bandwidth benefiting from its nonlinearity response.The influence law of acceleration,frequency,and the amounts and position of PZT on the output power is analyzed,and BPEH’s characteristics of broadband and taking full advantage of PZT are illustrated further.Aiming to the drawbacks of BPEH,such as low natural frequency and high requirement of excitation level,a new entire-aluminum hybrid lay-up is designed for BPEH.The stable configurations,natural frequency and dynamic response of this new BPEH are verified by experiments and FE model.In order to lower the requirement of excitation,the tip mass is employed for BPEH.According to the restoring force feature,a lumped-parameter numerical model based on the Duffing equation is proposed for BPEH with a tip mass to predict the dynamics of BPEH.