One of the most active and well-researched topics in our understanding of material sciences has been the bending, twisting and breaking of materials. For an extremely important reason too! The safety of modern human societies depends on the reliability and performance of objects under loads and environmental conditions.
Despite being thought to be well understood, an interesting gap in our understanding has been brought to light by researchers at Drexel University. The Material Science and Engineering researchers suggested in a report that all manner of layered materials, ranging from sedimentary rocks to thin slices of graphite, form a series of ripples and internal buckles as they undergo deformation.
Our existing understanding through the popular Dislocation Theory (in which the operative deformation micromechanism is a defect known as a dislocation) has been successful in explaining metal deformation. However, dislocation does not accurately account for the rippling and kink band formation observed in many layered solids.
The research team at Drexel University, led by professor Michel Barsoum, head of the MAX/MXene Research Group, realized the implications of the idea of ‘ripplocation’ when they came across a paper published by MIT. The paper suggested the new deformation micromechanism of ‘ripplocation’ (described as an atomic-scale ripple), and showed that the physics of dislocation and ‘ripplocations’ are fundamentally different.
Dislocation theory explains the observed cases when planes of layered solid materials bounce back and return to their original form (such as in elastic materials) or remain permanently indented ( such as in inelastic materials) upon being loaded and unloaded at their edge. Ripplocation behaviour helps explain another third observed case, where the material returns to its original form while dissipating large amounts of energy. This effect was labelled as “kinking non-linear elasticity” by Barsoum about a decade ago.
The researchers also noted that the effect of kinking non-linear elasticity is a strong function of confinement of the material, or constraining of its edges. This type of confinement is nearly always present in nature when materials are being stressed.
Barsoum’s team gathered evidence for ripplocation throughout the internal layers of bulk layered materials by carefully examining computer models where graphitic atomic layers were compressed edge on. The team observed that the deformation was consistent with the atomic-level rippling effect. The researchers also tested samples of a layered ceramic known as MAX phase in the lab, and through high resolution transmission electron microscope images of the defects that formed, noted that the deformations were not dislocations, but rather were consistent with what ripplocations would look like.
Ripplocation is an important scientific finding as it applies to most layered materials, including geological formations, and is subsequently important for understanding the behavior of materials in multiple fields including geology, nuclear engineering and microelectronics.
For more information on ripplocation visit the report by the researchers at Drexel University here, and view videos on ripplocation models and simulations on Youtube.