Jet Engine Fan Blade Containment

Dry aramid fabrics such as Kevlar 49 are wrapped around jet engine cases to contain a released fan blade, and certifying that design requires the fabric response at the strain rates of a blade-out event rather than those of a standard tension test.

This programme, run with Subramaniam D. Rajan of ASU under Federal Aviation Administration funding, characterised those fabrics and built the material models that go into explicit finite element simulations of containment. The work covered uniaxial and biaxial tension of Kevlar 49, in-plane shear, single yarn pullout, the effect of yarn crimp and weave architecture, and the transition in behaviour from quasi-static loading up to high rate. Zylon and nylon fabrics were tested alongside Kevlar, the latter with NASA.

The measurements fed LS-DYNA material models for multi-layer fabric, which were then validated against ballistic impact tests. The modelling work is summarised in the chapter Damage modeling of ballistic impact in woven fabrics, by Rajan and Mobasher.

Testing at these rates needed a servo-hydraulic high speed machine, and the machine itself became a research subject. With Marc Mignolet of ASU the group carried out a modal analysis of the load frame, because at high rate the measured signal carries the dynamic response of the machine as well as that of the specimen. Separating the two is what makes the resulting stress-strain data trustworthy, and the same approach was checked against aluminium alloy 6061-T6 at intermediate strain rates.

From the test programme