In this study, the cyclic behavior and the microstructure under cyclic loading of a semi-crystalline thermoplastic polyether ether ketone (PEEK) are investigated. Macroscopic strain life experiments under uniaxial loading condition were conducted at strain amplitudes ranging from 0.02 mm/mm to 0.04 mm/mm and at ambient temperature. Scanning electron microscopy (SEM) analysis was performed on fatigue specimens to examine crack incubation sites and microstructural inclusions responsible for incubating fatigue cracks. Other microstructural inclusion properties including inclusion type (pore or particle), inclusion size, and nearest neighbor distance of inclusions were also obtained. Based on the experimental results, the strain-based fatigue model was employed to obtain strain-life fatigue properties and e-N fatigue curves of PEEK.
This paper describes the details of an experimental investigation focusing on vibration characteristics of a carbon composite ultralight unmanned aerial vehicle (UAV). Modal characteristics of the UAV wings are obtained and compared for two separate configurations: 1) wings mounted on the suspended aircraft to simulate a free-free arrangement and 2) a single wing mounted vertically in a fixture to test in a shaker-table approach. The aircraft structure has a total empty weight of 155-lb with an overall length of approximately 20.6-ft. and consists of four primary components: the fuselage body with an integrated vertical stabilizer, a horizontal stabilizer, and the right and left wings. All structural components are fabricated from oven-cured laminated carbon composite materials using uniaxial and biaxial prepreg fabric. Multiple dual-axis accelerometers on the wing structure are used to obtain in-plane and out-of-plane excitations which are used to determine the dynamic properties which include the natural frequencies and the associated mode shapes and damping coefficients.
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