Failure Analysis on the Molecular Scale

Robert L. Stevenson, Ph.D.

Failures often start small. With care, they can be caught and remediated before they become catastrophic. A report from NIST demonstrates new technology that can image failures on the molecular scale. I recall that the Comet airplane had square windows that stress-cracked in the corners. As the planes aged and cycled from ground to flight level, the cracks grew, leading to explosive decompressions of the fuselage. Scientists at NIST have developed a sensitive technology to study stress deformation at the molecular level ^1,2

Figure 1 shows the orientation of fluorescent materials imbedded in a plastic and applied to a surface that was stressed with a punch.

Figure 1 – A punch was forced into a composite material laminated with a plastic containing fluorescent molecules, which were illuminated with a laser. After about 10,000 pulses, the size and direction of the arrows show the average local alignment of individual fluorescent molecules as a result of the strain produced by a square punch (dotted gray) driven into the target, and then pulled out at an angle toward the top of the image (yellow). (Credit: NIST)

Initially, the fluorescent materials were randomly oriented in 3-D. The piece was stressed with a square punch, which deformed the piece along the edge. The fluorescent molecules were carried along with the material displaced by the punch edge. The stress orientation was visualized by measuring the pattern of emitted light from the fluorescent probe molecules. The pattern required about 10,000 illumination cycles, but this is not much time with high repetition rate lasers. The magnitude of the deformation is given by the length of the vector and the orientation is the direction of vector movement.

This technology may show how structures begin to fail at the molecular level in composites and solid-state electronics, to list only two.

References

1. https://www.sciencedaily.com/releases/2019/02/190225145643.htm
2. Wang, M.; Marr, J.M. et al. Nanoscale deformation in polymers revealed by single-molecule super-resolution location–orientation microscopy. Materials Horizons; Online Jan 30, 2019; doi: 10.1039/c8mh01187g.

Robert L. Stevenson, Ph.D., is Editor Emeritus, American Laboratory/Labcompare; e-mail: [email protected]