Influence of cyclic stress intensity threshold on the scatter seen in cyclic Mode I fatigue delamination growth in DCB tests. (1st June 2017)

• Record Type: Journal Article
• Authors: Mujtaba, A.; Stelzer, S.; Brunner, A.J.; Jones, R.
• Is Part Of: Composite structures. Volume 169(2017)
• Page Start: 138
• Page End: 143
• Publication Date: 2017-06-01
• Subjects: FAA AC20-107B -- Fatigue -- Delamination growth -- Scatter -- NASGRO; Composite construction -- Periodicals; Composites -- Périodiques; 624.18
• DOI: 10.1016/j.compstruct.2016.07.080
• Languages: English
• ISSNs: 0263-8223

Abstract

Abstract: Whilst composite materials are now widely used in aircraft structural components for certification purposes current designs are such that any delamination/disbond will not grow. Despite this limit fleet data and data obtained from full scale fatigue tests reveal that small sub mm initial delaminations/disbonds can grow when subjected to operational flight loads. To account for this the US Federal Aviation Authority advisory circular AC20-107B outlines a slow growth approach for certifying composite/bonded aircraft structures. A key point in AC20-107B is that growth must be both slow and predictable. Since the life of an airframe is determined by the growth of the fastest (lead) crack/delamination/disbond any analysis tool developed for a composite/bonded airframe requires the ability to predict the both the scatter in delamination/disbond growth and thereby the growth of the lead delamination/disbond in the airframe. To this end the present paper reveals that the Hartman-Schijve variant of the NASGRO equation would appear to show promise for capturing the scatter seen in Mode I delamination tests associated with specimens fabricated from nominally identical material supplied by two different suppliers. It is shown that the values of the constants in the Hartman-Schijve equation associated with these two sources are consistent and the scatter in growth can captured by allowing for small variations in the fatigue threshold term.