Deriving exponential and power law slow crack growth parameters from dynamic fatigue of indented or as-polished window material coupons

Ryan Colin M.; Johnson Kevin R.; Harris Daniel C.

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Deriving exponential and power law slow crack growth parameters from dynamic fatigue of indented or as-polished window material coupons

机译：Deriving exponential and power law slow crack growth parameters from dynamic fatigue of indented or as-polished window material coupons

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Knowledge of slow crack growth rate in a window material is required to determine the design life of a window in which cracks grow under the influence of applied service stress. Parameters that characterize crack growth rate can be measured by dynamic fatigue in which coupons are taken to failure at several constant stress rates. The slower the stress rate, the more time is available for cracks to grow during the strength measurement, and the lower the stress at which the coupon fails. That is, coupons tested at a slower stress rate are weaker than coupons tested at a faster stress rate. The rate of slow crack growth is commonly fit to either a power law or an exponential law. The exponential law provides the more conservative estimate of design life and is prescribed for use by the U.S. National Aeronautics and Space Administration to design windows for manned vehicles. Well-established analytical equations are used to derive the power law crack growth parameters from dynamic fatigue measurements of as-polished (unindented) coupons. There are no exact analytical equations to derive power law parameters from indented coupons or to derive exponential law parameters from unindented or indented coupons. Approximate procedures have been used to derive crack growth parameters when there are no exact equations. We now describe a numerical method that gives the power and exponential laws for both unindented and indented coupons by least-squares fitting of dynamic fatigue measurements. A MATLAB code is provided to carry out the calculations. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License.

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《Optical Engineering》 |2022年第6期|067104-1-067104-16|共16页
作者
Ryan Colin M.; Johnson Kevin R.; Harris Daniel C.;
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作者单位

Naval Air Warfare Ctr;

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收录信息美国《科学引文索引》(SCI);美国《工程索引》(EI);
原文格式 PDF
正文语种英语
中图分类光学仪器;
关键词
slow crack growth; optical window design; indentation dynamic fatigue; exponential law crack growth; BK7 glass; INDENTATION FLAWS; GLASS; ALGORITHM; CERAMICS;

Deriving exponential and power law slow crack growth parameters from dynamic fatigue of indented or as-polished window material coupons

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