Design of Contact-aided Compliant Cellular Mechanisms for use as an Energy Absorbing Structure

Open Access
Author:
Hyland, Jennifer Elizabeth
Graduate Program:
Mechanical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 19, 2012
Committee Members:
  • Mary I Frecker, Thesis Advisor
Keywords:
  • contact-aided compliant mechanism
  • cellular structure
  • microfabrication
  • laser micro-machining
  • energy absorption
Abstract:
Contact-Aided Compliant Cellular Mechanisms (C3M) are compliant cellular structures with integrated contact mechanisms. While extensive work has been reported in the literature on traditional honeycombs of varying geometries under dynamic and static loading, contact-aided compliant cellular mechanisms under quasi-static crushing or impact have not been previously considered. This thesis addresses this void through the optimization of a hexagonal honeycomb unit cell containing a contact mechanism. The focus of the thesis is on the design, fabrication, and testing of C3M structures for energy absorbing applications. The addition of contact mechanisms increases cell performance via changing the loading path. The honeycomb unit cell, defined by a set of variables, is analyzed using finite element analysis. Each unit cell is subjected to an input velocity over some time. Two optimization problems were formulated using MATLAB and finite element analysis to find the best cells for different input velocities. The optimization problem that is formulated maximizes the strain energy per area of a contact-aided compliant cellular mechanism. Two- and three-variable optimization problems are considered, using variables that define the cell geometry and the initial contact gap. It is found that with the addition of a contact mechanism, more strain energy can be absorbed when compared to the same cell without a contact mechanism. The lost mold rapid infiltration forming (LM-RIF) microfabrication process is used to fabricate C3M structures from metallic (mesoscale 316L Stainless Steel) materials. The parts are also fabricated through laser micro-machining. Both processes directly fabricate the structures from the use of CAD models. After the parts are fabricated, they are tested experimentally and the results are compared.