Department: Mechanical & Aerospace Engineering
Research Institute Affiliation: Graduate Program in Materials Science and Engineering
Faculty Advisor(s): Vitali Nesterenko

Primary Student
Name: Chien-Wei Lee
Email: chl099@ucsd.edu
Phone: 858-361-9470
Grad Year: 2015

Using impact testing to analysis non-linear stress and strain relation of O-rings under dynamic loading is the main subject of this research paper. Using the same technique this testing method can be applied to study any strain-rate dependent deformation compound materials. O-rings are widely used in hydraulic and pneumatic equipments in sealing of drive shafts, pistons and lids thus its static elastic properties are well studied by industry. O-rings are also broadly used in industry as shock absorber. The static highly non-linear elastic property from its circular shape and the elastomer natural of rubber brings up spectacular non-linear strain rate dependent hysteresis dynamic characteristic. This property makes it one of the preferred elements to assemble strongly nonlinear double power law and dissipative low dimensional metamaterials. In papers the mechanical properties of metamaterials were investigated numerically and experimentally, while quasistaic stress-strain data was used to approximate dynamic strongly nonlinear double power law stress-strain curve of O-rings under dynamic interaction of rigid masses. It's noticeable that the strongly non-linear dynamic behavior of large strain deformation of toroidal O-rings in compression was not studied. Due to viscoelastic behavior of material of O-rings, stress conditions are obviously strain rate sensitive in mediate to high strain rate deformation which will affect their dependence of force on displacement and also dissipative properties. By studying stress-strain curve derived from force history during impact, this paper also study energy dissipative properties during compressive deformation of O-rings using moderate impact velocity and comparing the data with verified experimental static compressive properties. Two instruments independently recorded both force acting on the top and bottom of samples: one is the accelerometer mounted on the drop mass and another one was the load cell mounted in the supporting anvil beneath samples. The similarity between the two data corroborates the assumption of force equilibrium under moderate strain rate. Decent noise to signal ratio augment the validness of impact testing which overcome a common difficulty in traditional dynamic impact testing. The deformation of O-rings was monitored using a high speed camera in the same time to record engineering strain independently. It was shown that dynamic and static responses of O-rings are significantly different. The experimental data force-time history and impact and recoil velocity of impacter allowed us to evaluate energy dissipative properties of O-rings which we plan to use in the design of low dimensional, energy absorbing and dispersive metamaterials.

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