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Automated, optically assisted fatigue crack growth method for plastics using cracked round bar specimens / submitted by Paul J. Freudenthaler
AutorInnenFreudenthaler, Paul Johann
Beurteiler / BeurteilerinLang, Reinhold Walter
ErschienenLinz, 2018
UmfangIV, 46 Blätter : Illustrationen
HochschulschriftUniversität Linz, Masterarbeit, 2018
Schlagwörter (GND)Plastik / Ermüdungsriss / Charakterisierung / Automation / Optisches Verfahren
URNurn:nbn:at:at-ubl:1-21252 Persistent Identifier (URN)
 Das Werk ist gemäß den "Hinweisen für BenützerInnen" verfügbar
Automated, optically assisted fatigue crack growth method for plastics using cracked round bar specimens [10.1 mb]
Zusammenfassung (Englisch)

The aim of this thesis was the development of a new method for automated fatigue crack growth characterization in plastics utilizing cracked round bar (CRB) specimens. Existing methods for automated and direct crack growth characterization either are limited to the compact tension (CT) specimen geometry (Schöffl, 2014; Bradler, 2014; Schläger, 2015; Leitner, 2016) or do not allow for the use of temperature housings (Saberi Fathi, 2014). Therefore, a solution with only a single angle of view for image capture via the front window of the temperature housing was pursued. To gain information about the whole crack circumference with only one angle of view, an electrodynamic tension-torsion test system of the type Instron ElectroPuls E10000 together with a newly developed specimen fixation were used to rotate the specimen around its own axis while also applying the axial fatigue loading. Since the exact moment of image capture is essential during fatigue testing, a real-time image acquisition system based on a National Instruments compactRIO system was developed. The system measures the force and rotation angle values coming from the Instron testing machine and decides, in due consideration of delay times, when to trigger the lighting and camera sensor. The used optical components enable the capture of the whole specimen perimeter with a resolution of up to 5.5 m. A computer program, controlled via graphical user interface (GUI), automatically grabs, archives and analyzes the images. The program measures the crack lengths within the captured image and allocates the results, together with the prevailing number of loading cycle and rotational angle in a data file, to enable further evaluation. The developed method allows for highly sensitive crack length measurement, giving thorough information about the full circumferential crack lengths, at a very high sample rate. Eccentricities and stepwise crack growth can be visualized for the first time at this high level of detail, enabling further investigations of these phenomena. However, to gain results comparable to conventional fatigue crack growth kinetics curves, well adjusted data reduction must be applied. As an application example, three CRB specimens received out of the same extruded polyethylene (PE) rod were tested at 80C with equal mechanical loading conditions. Despite the differences between the tests in total testing time, eccentricity and stepwise crack growth, the resulting crack growth kinetics data hardly differed. Therefore, this method enables acquisition of highly reproducible crack growth kinetics data at elevated temperatures within standard temperature chambers. Furthermore, the single point of view offers high flexibility for future testing environment housing designs including the use of transparent, harsh media for application specific testing.

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