The Methods And Applications Of Intermediate-high Strain Rate Mechanical Tests Based On Structural Vibration

The intermediate-high strain rate mechanical properties of materials are of great importance to no matter academic research or industrial manufacturing.The experimental data of material at intermediate-high strain rate is the foundation of the mechanical study of material.However,due to the signal ringing effect,the strain based load sensor can only provides effective material tests data at the strain rate lower than100/s.To surmount the limitation of the present technologies,this thesis analyzed the dynamic response of the load sensor at intermediate-high strain rate testing condition.A signal processing algorithm based on structural dynamics and perturbation method is introduced.A algorithm matched sensor-specimen system is designed.The tests frame introduced in this these is proved effective and portable thorough experiments.To recall the loading signal from observed signal under intermediate-high strain rate condition,a basic signal processing algorithm,which considers the vibration of the load sensor,is established by postulating the sensor follows the single spring-mass vibration model.The observed signal after the fracture of the specimen(tail wave)is used for dynamic parameters calibration by nonlinear fitting.The basic algorithm is polished by applying the perturbation method.The properties of the polished algorithm is investigated based on two order spring-mass system.A robust and easy-to-use modified algorithm,which is called semi-period perturbation method(SPPM)in this thesis,is established based on mathematical experiments.To satisfy the available condition of the SPPM,there should be only single vibration mode observed during the dynamic response of the sensor.Correspondingly,the suitable sensor is called single-mode-vibration sensor(SMVS).The design guiding of SMVS is provided based on the dynamic analysis of the existing sensor in this thesis.A SMVS for typical metal specimen is designed and verified by experiments.Based on high order spring-mass system,it is pointed out that the damping characters of the base material of sensor may disturb the reliability of the single-mode-vibration hypothesis.A TEST-TO-PASS is designed and the SMVS in this thesis is proved stable to any damping characters of base material.This thesis conducted the intermediate-high strain rate tensile tests(200/s-1 000/s)for both Q235 steel and 6061 Al based on high speed hydraulic drawing machine.The test method introduced in this thesis is proved effective by results analyzing.The engineering difficulties and the application potential of this test method based on drop tower is discussed based on experiments.The test method introduced in this thesis is called single-mode-vibration method(SMVM).As application extension,the intermediate-high strain rate tests for Al-plastic film from smart phone battery is designed and conducted.The defects of the original design of SMVS for membrane material is studied and modified.The portability of the SMVM is further verified.