Semester

Spring

Date of Graduation

2014

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Edward M. Sabolsky

Committee Co-Chair

Darran Cairns

Committee Member

Thomas Evans

Committee Member

Dave Graham

Committee Member

Kostas Sierros

Abstract

The need for force feedback and spatial awareness of contact in harsh environment applications, such as space servicing, has been unsatisfied due to the inability of current sensor technology to resist environmental effects. In this work, capacitive sensors based on a porous polymer-ceramic composite structure were evaluated for potential use in future operations within robotic end-effectors, withstanding temperatures ranging from -80 °C to 120 °C and forces up to 350 kPa. A thin-film design is utilized to allow for ease of embedding, allowing sensors to be implemented into exciting robotic hardware with minimal intrusion, and protecting sensors from electron bombardment, radiation, and point concentrations from metal-on-metal contact. Furthermore, said embedding is proposed to protect against environmental effects including electron bombardment, radiation, atomic oxygen, and damage caused by point concentrations during metal-on-metal contact.;The novel sensor design optimizes constituent properties to maximize the response and reduce background noise, hysteresis, and thermal and mechanical drift. Selection of continuants and design parameters is presented explicitly, including synthesis and preparation of necessary materials and execution of processing methods. Qualification of the design is achieved through thorough dynamic, quasi-static, and long term static thermomechancial loading schedules ranging from -80 to 120 ºC and 20 to 360 kPa with in-situ electrical acquisition. The final composition is also shown to meet necessary outgassing standards for in-orbit operations. Additional parameters are presented for selection of necessary substrate and electrode materials, further optimizing the applied technology.;An analytical model for pressure sensors is also constructed, predicting the capacitive response of a porous, polymer-ceramic composite under an applied pressure. Consisting of mechanical and dielectric counterparts, the iterative model is constructed in detail. The elastic modulus of the three-phase material is approximated by first considering only the polymer-ceramic composite mixture, and then incorporating porosity into the solid composite model. A new model has been developed for approximating the changing elastic modulus of porous polymers undergoing quasi-static compression, which induces the collapsing pores. Necessary material constants were obtained from experimental data published in literature. The permittivity of the paraelectric polymer matrix is modeled, accounting for piezodielectric effects imposed by external pressure and thermally induced stresses caused by substrate pinning. Similarly, the ferroelectric ceramic filler is modeled, considering changes in polarization caused by thermally induced phase transformations in the crystal structure. The final model is evaluated against experimental data, providing insight into composition and microstructure effects on the sensor response.

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