Beschleunigte Prüfmethoden zur Charakterisierung des langfristigen Materialverhaltens kontinuierlich glasfaserverstärkter Verbundwerkstoffe unter statischer Last

Translated title of the contribution: Accelerated test methods for the characterisation of long term material properties of continuous glass fibre reinforced composites under static load

Stefan Gloggnitzer

Research output: ThesisDoctoral Thesis

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Abstract

Fibre reinforced composite materials offer a high potential for the usage in structural applications due their specific and adjustable material properties. Corresponding examples are composite gas cylinders or weight loaded composite components as structural reinforcing elements of concrete structures. In all these applications, the material system is affected by long-term static loads. Viscoelastic material properties, damage accumulations and material degradation effects based on the continuous static loadings lead to changings in the material properties, which have to be detected and considered over the whole application time range. The experimental characterization of these material changings in conventional test procedures, such as creep test, requires comparable test and application times, which is for application times of several decades impossible to reach by economic test methods. Therefor special test and characterization methods are necessary to determine long-term material properties within limited testing times. Such testing methods are available in principle, which allow determining long-term material properties in accelerated test approaches by the intensification of material demanding factors, normally temperature or mechanical loads, in combination with principles of temperature- or stress-time superposition. However, these methods are developed for materials with pronounced viscoelastic properties, so the applicability on continuous reinforced composites is not ensured and requires the examination. In addition, the development of generally novel test procedures and methods was a basic aim of this thesis, which was achieved by the development of the novel stress rate accelerated creep rupture test method SRCR. To verify the applicability of the SRCR and other already known accelerated test methods, corresponding experimental tests were performed and the results are compared to conventionally determined test results. Therefore, angle ply composites fibre orientations of 0 °, ± 45 ° and 90 ° were manufactured. The performed conventional creep test shows, that loads along the fibre orientation lead to low time and stress dependent creep elongations. On the other hand, for ± 45° and 90° type laminates, where the material properties a clearly dominated by the matrix component, a significant increase of creep elongation at continuous loading was shown. Generally, for all investigated laminates an obvious decrease in material strength over loading time under static loading conditions was shown. Additional long-term material characterisation based on various accelerated test procedures, shows that the novel developed test method SRCR delivers the best comparable test results to conventional creep rupture tests. On the other hand, the other novel accelerated characterisation method for these materials, fatigue tests with increasing R-ratio, could not provide reliable long-term material properties. The also known accelerated test method, stepped isostress method SSM, showed especially for the ± 45° type laminate no sufficient match compared to the corresponding long-term results out of conventional creep rupture tests, whereby all investigated accelerated test methods lead to an overestimation of real long-term creep behavior. Nevertheless, some of the investigated accelerated test methods, especially the SRCR allow for time efficient material characterisation to provide reliable long term data. However, further investigation is required to clarify the underlying damage mechanisms in order to establish corresponding structure-property correlations.
Translated title of the contributionAccelerated test methods for the characterisation of long term material properties of continuous glass fibre reinforced composites under static load
Original languageGerman
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Pinter, Gerald, Assessor A (internal)
  • Schledjewski, Ralf, Assessor B (internal)
Publication statusPublished - 2019

Bibliographical note

no embargo

Keywords

  • Angle ply composites
  • creep
  • creep rupture
  • fatigue
  • time-stress-superposition
  • SRCR
  • SSM

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