Available at: https://digitalcommons.calpoly.edu/theses/3078
Date of Award
6-2025
Degree Name
MS in Mechanical Engineering
Department/Program
Mechanical Engineering
College
College of Engineering
Advisor
Eltahry Elghandour
Advisor Department
Mechanical Engineering
Advisor College
College of Engineering
Abstract
Material testing is essential across industries such as aerospace, automotive, and construction, playing a critical role in verifying material selection, diagnosing failures, and understanding the development of flaws in structures. These insights are key to designing successful, reliable systems. Conventional metal foil strain gauges are low cost and reliable but provide limited sensitivity with a typical gauge factor around 2. Extensometers provide highly sensitive strain measurements with the disadvantage of a bulky form factor. With advanced materials such as carbon nanotubes, it is possible to manufacture a sensor with the sensitivity closer to that of an extensometer with the small form factor of a metal foil strain gauge. This thesis developed a strain sensor utilizing the piezoresistive properties of carbon nanotubes, and compared it with conventional metal foil strain gauge, extensometer, and finite element analysis data for uniaxial tensile and cantilever beam tests. The CNT sensor was found to be 82% more sensitive to strain resulting in a 5.65% higher Young’s modulus than extensometer and FEA data during tensile testing of a fiberglass specimen. Additionally, an optimized CNT sensor was found to be 160% more sensitive than a metal foil strain gauge and 48% more sensitive than this study’s initial CNT sensor for aluminum cantilever beam tests. Double cantilever beam (DCB) tests were performed with metal foil strain gauges resulting in strain within 8.09% of FEA and hand calculations, with many of the samples within 2.09%. The optimized CNT sensor is expected to be within 4% of this data when applied to the DCBs, similar to results of this study’s aluminum cantilever beam test.