Automating the Hartman-Schijve methodology for predicting interlaminar fatigue crack growth in fibre composites
File(s)
Accepted version
Author(s)
Chandwani, Ramesh
Timbrell, Chris
Blackman, BRK
Jones, Rhys
Kinloch, Anthony J
Type
Journal Article
Abstract
The Hartman-Schijve methodology offers a direct route to calculating various fatigue crack growth (FCG) rate curves that are associated with delaminations growing in fibre polymer-matrix composites. However, up to the present, only a ‘manual’ method has been described to deduce the values of the Hartman-Schijve constants that are needed for such calculations. Whilst this manual method may give reasonably acceptable results for calculating the Hartman-Schijve constants, it is a difficult and tedious implementation route. Thus, it may, if the operator is inexperienced, give relatively large errors in the values of the key constants that are needed to calculate the FCG rate curves. Furthermore, for very large data sets there is great difficulty incurred in manipulating such a large amount of data using the ‘manual method’.
Therefore, the main aim of the present paper has been to introduce a novel computer model and the associated software, ‘Zencrack: Material Curve Fitting Utility’ from Zentech International Limited, UK, to obtain automatically the Hartman-Schijve constants. The aim has been to deduce the ‘worst-case upper-bound’ FCG curve for small, naturally-occurring, delaminations in the composite material, or component. To achieve such an ‘automatic’ method, the current work (a) has taken previously-published algorithms that employ a ‘Total Least Squares’ method for the fitting process of the experimental input data to the Hartman-Schijve equation and (b) has investigated the effect of a normalising scaling factor. It is shown that an automatic calculation that includes all the input data gives the best representation of the Hartman-Schijve constants and is the recommended approach.
Therefore, the main aim of the present paper has been to introduce a novel computer model and the associated software, ‘Zencrack: Material Curve Fitting Utility’ from Zentech International Limited, UK, to obtain automatically the Hartman-Schijve constants. The aim has been to deduce the ‘worst-case upper-bound’ FCG curve for small, naturally-occurring, delaminations in the composite material, or component. To achieve such an ‘automatic’ method, the current work (a) has taken previously-published algorithms that employ a ‘Total Least Squares’ method for the fitting process of the experimental input data to the Hartman-Schijve equation and (b) has investigated the effect of a normalising scaling factor. It is shown that an automatic calculation that includes all the input data gives the best representation of the Hartman-Schijve constants and is the recommended approach.
Date Issued
2026-04-01
Date Acceptance
2026-01-28
Citation
Theoretical and Applied Fracture Mechanics, 2026, 143 (Part 1)
ISSN
0167-8442
Publisher
Elsevier BV
Journal / Book Title
Theoretical and Applied Fracture Mechanics
Volume
143
Issue
Part 1
Copyright Statement
Copyright © 2026 Published by Elsevier Ltd. This is the author’s accepted manuscript made available under a CC-BY licence in accordance with Imperial’s Research Publications Open Access policy (www.imperial.ac.uk/oa-policy)
License URL
Publication Status
Published
Article Number
105487
Date Publish Online
2026-01-29