Subcritical crack growth parameters in glass as a function of environmental conditions
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RESEARCH PAPER
Subcritical crack growth parameters in glass as a function of environmental conditions Christopher Brokmann · Stefan Kolling · Jens Schneider
Received: 6 February 2020 / Accepted: 21 August 2020 © The Author(s) 2020
Abstract In the present work, subcritical crack growth in soda–lime silicate glass is investigated under different environmental conditions. Crack growth parameters as a function of temperature and humidity were determined by dynamic fatigue tests, which has been verified by using the in-situ method of filming crack growth during experiments. The specimens were predamaged for constant initial crack lengths in all specimens using the Vickers indentation test. The determined parameters were compared with those from literature in order to discuss existing deviations of subcritical crack growth parameters in literature. These deviations may be caused by environmental conditions and different chemical compositions of the glass. Arrest lines were used to determine the ratio of crack width to crack depth in Vickers indented specimens. For the initial crack depth, images of fracture surfaces were taken using an scanning electron microscope. Furthermore, the influence of humidity and temperature on the C. Brokmann (B)· S. Kolling Institute of Mechanics and Materials, Technische Hochschule Mittelhessen, Wiesenstrasse 14, 35390 Giessen, Germany e-mail: [email protected] S. Kolling e-mail: [email protected] J. Schneider Institute for Structural Mechanics and Design, Technical University of Darmstadt, Franziska-Braun-Straße 3, 64287 Darmstadt, Germany e-mail: [email protected]
failure stress of unindented specimens with a constant initial crack length was simulated. Keywords Glass · Subcritical crack growth · Environmental influence · Failure strength · Vickers indentation 1 Introduction The strength of glasses has been studied and discussed in a number of publications and books, e.g. Haldimann et al. (2008), Wachtman et al. (2009), Quinn (2007) and Meyland et al. (2019). Test methods for strength are defined in national and international standards. The strength behavior of glass as a function of temperature and humidity is often considered only as a coarse approximation. For example, the European standard for determining the strength of glass by means of a coaxial ring-on-ring test specifies a relative humidity of 40– 70% during experiments c.f. EN DIN 1288 (2000). Thereby it could already be shown that the environmental conditions have an enormous influence on the failure strength of glass, (Wiederhorn and Bolz 1970; Ronchetti et al. 2013). The failure strength of glasses and other almost ideally brittle materials is dominated by micro flaws. These micro flaws are distributed randomly over the entire surface of the glass and grow sub-critically when an external stress is applied. Depending on the growth time and growth rate, sub-critical crack growth has a significant influence on the failure stress. Due to their
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different depth, these
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