SEDL / STP / STP1416-EB / STP10632S

Qualification Using a Nested Experimental Design

Ruffner, D
Materials Engineer and Project Manager, The Boeing Company, Mesa, AZ

Jouin, P
Materials Engineer and Project Manager, The Boeing Company, Mesa, AZ

Pages: 14    Published: Jan 2002

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Abstract

The general aviation approach was taken in these material qualifications, where it is assumed that a large portion of composite material property batch-to-batch variability can be reproduced in the laboratory through independent layup and cure of panels, termed a process lot. A nested experimental design was used to quantify the actual sources of variability for hot/wet tension and compression strengths, and dry and wet glass transition temperatures. Two large crossplied panels, each representing a process lot, were independently made from each of three qualification batches. Two subpanels, each representing a machine lot, were cut from each process lot panel, then independently machined into coupons, moisture conditioned, and tested. With these three nested experimental levels the batch-to-batch variability can be partitioned into true batch variability, laminate fabrication, coupon test, and within sample variability. Results indicate that true batch variability was a relatively minor contributor to material property variability as a whole.