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Understanding effectiveness of stitching in suppression of impact damage: An empirical delamination reduction trend for stitched composites
Composites Part A: Applied Science and Manufacturing 43 #6 (2012)
Tan et al of Purdue University, Indiana, Tokyo Metropolitan University and Japan Aerospace Exploration Agency, Japan, studied delamination reduction in stitched composites subjected to impact loading.  This empirical-based Delamination Reduction Trend (DRT) is developed based on an extensive series of low-velocity impact tests using specimens of different laminate thicknesses, stitch densities and stitch thread linear (mass) densities, subjected over a range of impact energy levels.  The DRT simply relates two parameters: normalized delamination area (DelamNorm) and stitch fiber volume fraction (Vft), to characterize the effectiveness of stitching in impact damage suppression.  DRT evidently shows a bi-linear behavior: first, an initial linearly decreasing relationship of DelamNorm with Vft; and second, a plateau which indicates maximum delamination area reduction limit of 40% by stitching.  Experimentally observed mechanisms are presented and discussed with the aim to justify and explain the bi-linear behavior of DRT. The DRT is further validated with numerous published literature results and has demonstrated excellent agreement. (RDC 5/9/2012)

Damage control using discrete thermoplastic film inserts
Composites Part A: Applied Science and Manufacturing 43 #6 (2012)
Yasaee et al of University of Bristol and Imperial College, United Kingdom, controlled delamination growth in a GFRP panel subjected to a low velocity impact by inserting discrete thermoplastic film rings at selective interfaces centred around the impact.  This has been shown to arrest delamination thus allowing damage control.  Using six different layup configurations the thermoplastic film rings have been shown to suppress delamination crack growth at the desired interfaces. This resulted in manipulation of the damage footprint areas. Configurations that reduced delamination area by up to 38% demonstrated an improved CAI strength of up to 18% relative to a baseline panel. However, two configurations which saw an increase in delamination area by up to 30% showed similar CAI strengths to the baseline panel. This finding would confirm that it is the delamination interface location that influences the CAI strength not the damage footprint area.  (RDC 5/5/2012)


Roger D. Corneliussen

Maro Polymer Links
Tel: 610 363 9920
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Copyright 2012 by Roger D. Corneliussen.
No part of this transmission is to be duplicated in any manner or forwarded by electronic mail without the express written permission of Roger D. Corneliussen

* Date of latest addition; date of first entry is 5/5/2012.