Self-healing materials could make aircraft and automobile parts last over 100 years

Good news!

"Researchers ... have achieved sustained self-healing of a composite material. The findings promise to extend the lifetime of aircraft and automotive parts by a century ..."

From the significance and abstract:

"Significance

Delamination damage has long hindered the safety and lifetime of fiber-reinforced polymer composites. This failure mode not only undermines their lightweight mechanical advantage but also amplifies the cost and environmental impact of these modern structural materials, which are inherently challenging to repair/recycle.

Here, we innovate self-healing by automating in situ thermal remending to achieve 1,000 delamination heal cycles, an order-of-magnitude greater than prior studies. The life extension unlocks new science where diminishing interfacial chemical reactions and fiber debris accumulation contribute to a gradual, asymptotic decline in fracture recovery that follows a Weibull distribution. Our findings show this self-healing strategy for interlaminar fracture is repeatable on a scale far exceeding typical composite design lifetimes, thus shedding delamination from structural concern.

Abstract

... Synthetic fiber-reinforced polymer (FRP) composites also leverage material hierarchy via fibrous reinforcement encapsulated within a polymer matrix, maximizing stiffness and strength. However, the layered architecture of laminated FRP composites makes them vulnerable to interlaminar delamination—debonding of fibers from the matrix—which significantly compromises structural integrity. Recently, we introduced a self-healing strategy via in situ heating, where soft yet tough thermoplastic inclusions achieve interlaminar fracture recovery via polymer chain re-entanglement, i.e., thermal remending. Here, in our latest embodiment, by automating in situ thermo-mechanical experiments, we achieve an order-of-magnitude enhancement in self-healing repeatability—reaching an unprecedented 1,000 cycles. Healing begins at 175% and slowly declines to 60% of the mode-I fracture resistance of a plain (nonhealing) composite, revealing unique chemo-physical mechanisms that govern this behavior. Both fiber-debris accumulation in the molten poly(ethylene-co-methacrylic acid) (EMAA) healing agent, and waning interfacial chemical reactions between the EMAA and epoxy matrix, contribute. A Weibull distribution capturing this complex fracture recovery predicts an asymptotic healing limit above 40%, suggesting sustained repair is possible. Translating these newfound thermal remending results into real-world context, a modest quarterly self-healing schedule could maintain interlaminar fracture repair of FRP composites for over 125 y—well beyond the typical design life of many modern structures including aircraft and wind turbines. Thus, this latest self-healing paradigm effectively eliminates delamination as a failure mode."

Self-healing materials could make automobile parts last over 100 years – Physics World

Self-healing for the long haul: In situ automation delivers century-scale fracture recovery in structural composites

Self-healing process A composite material, suffering from a delamination fracture, uses an embedded healing agent (blue) to fill and fix the crack. Scale bars: 0.5 mm. 

'Stunning' discovery: Fatigue in metals can heal itself

Amazing stuff! This could be a game changer!

"Scientists for the first time have witnessed pieces of metal crack, then fuse back together without any human intervention, overturning fundamental scientific theories in the process. If the newly discovered phenomenon can be harnessed, it could usher in an engineering revolution—one in which self-healing engines, bridges and airplanes could reverse damage caused by wear and tear, making them safer and longer-lasting. ...
"What we have confirmed is that metals have their own intrinsic, natural ability to heal themselves, at least in the case of fatigue damage at the nanoscale," ...
Although scientists have created some self-healing materials, mostly plastics, the notion of a self-healing metal has largely been the domain of science fiction. ...
In 2013, Michael Demkowicz ... began chipping away at conventional materials theory. He published a new theory, based on findings in computer simulations, that under certain conditions metal should be able to weld shut cracks formed by wear and tear. ..."

From the abstract:

"Fatigue in metals involves gradual failure through incremental propagation of cracks under repetitive mechanical load. In structural applications, fatigue accounts for up to 90% of in-service failure. Prevention of fatigue relies on implementation of large safety factors and inefficient overdesign. In traditional metallurgical design for fatigue resistance, microstructures are developed to either arrest or slow the progression of cracks. Crack growth is assumed to be irreversible. By contrast, in other material classes, there is a compelling alternative based on latent healing mechanisms and damage reversal. Here, we report that fatigue cracks in pure metals can undergo intrinsic self-healing. We directly observe the early progression of nanoscale fatigue cracks, and as expected, the cracks advance, deflect and arrest at local microstructural barriers. However, unexpectedly, cracks were also observed to heal by a process that can be described as crack flank cold welding induced by a combination of local stress state and grain boundary migration. The premise that fatigue cracks can autonomously heal in metals through local interaction with microstructural features challenges the most fundamental theories on how engineers design and evaluate fatigue life in structural materials. We discuss the implications for fatigue in a variety of service environments."

'Stunning' discovery: Metals can heal themselves (sorry, but this only a copy of the primary news source)

Stunning discovery: Metals can heal themselves (primary news source) Microscopic cracks vanish in experiments, revealing possibility of self-healing machines

Autonomous healing of fatigue cracks via cold welding (no public access)

Green marks the spot where a fissure formed, then fused back together in this artistic rendering of nanoscale self-healing in metal, discovered at Sandia National Laboratories. Red arrows indicate the direction of the pulling force that unexpectedly triggered the phenomenon.

Self-Healing of Crystal Voids in Perovskite Nanocrystals

Good news!

"... The field of self-repairing materials is rapidly expanding, and what used to be science fiction might soon become reality ... scientists who developed eco-friendly nanocrystal semiconductors capable of self-healing. Their findings, recently published in Advanced Functional Materials, describe the process in which a group of materials called double perovskites display self-healing properties after being damaged by the radiation of an electron beam. ...

Nanocrystals are the smallest material particles that remain naturally stable. Their size makes certain properties more pronounced and enables research approaches that would be impossible on larger crystals, such as imaging using electron microscopy to see how atoms in the materials move. This was, in fact, the method that enabled the discovery of self-repair in the lead-free perovskites.

The perovskite nanoparticles [researchers] examined the particles using a transmission electron microscope, they discovered the exciting phenomenon. The high-voltage electron beam used by this type of microscope caused faults and holes in the nanocrystals. The researchers were then able to explore how these holes interact with the material surrounding them and how they move and transform within it.

They saw that the holes moved freely within the nanocrystal but avoided its edges. The researchers developed a code that analyzed dozens of videos made using the electron microscope to understand the movement dynamics within the crystal. They found that holes formed on the surface of the nanoparticles, and then moved to energetically stable areas inside. The reason for the holes’ movement inwards was hypothesized to be organic molecules coating the nanocrystals’ surface. Once these organic molecules were removed, the group discovered the crystal spontaneously ejected the holes to the surface and out, returning to its original pristine structure – in other words, the crustal repaired itself."

From the abstract:

"... Void trajectories and velocities are calculated for TEM [transmission electron microscopy] videos. An inaccessible, protected volume for migration near the nanocrystal outer surface is discovered, confining the migration of voids to inner crystal parts. Once surface passivation in the form of organic ligands is removed, void dynamics changes, to enable annealing of the voids and self-healing of the crystal. It is determined that surface ligand protection against void migration is extending several atomic layers below the crystal surface. Modeling based on these results predict equilibrium positions for the voids, which are discovered in the data. The study suggests that tuning of organic ligand density influences structural stability and crystal defect tolerance in double perovskites. ..."

Self-Repairing Electronics Are on the Way

Self-Healing of Crystal Voids in Double Perovskite Nanocrystals Is Related to Surface Passivation (no public access)