Overall aim: understand and exploit surface properties & structures to control sliding interfaces for improvements in health and energy
1. Lubricity Driven by Soft Material Parameters
Traditional lubrication theory is based on hard impermeable materials that undergo dramatic transitions from boundary to hydrodynamic lubrication as a function of the surface profiles, load and sliding speed conditions, and viscosity of the lubricant. The mechanisms for this theory do not capture the lubrication behavior of hydrogel materials, which rely on polymeric mesh structure and its interactions with water to support applied loads and provide low friction. As such, material parameters such as water content and hydrophilicity must contribute to theories of hydrogel lubrication. These investigations will seek to unveil the contributions of these material parameters to hydrogel lubrication and use them to predict and engineer hydrogels specifically for lubricity.
Funded project: NSF CAREER 1751945 
Paper: “Challenges and opportunities in soft tribology,” Tribology-Materials, Surfaces & Interfaces
Paper: “Poroelasticity-driven lubrication” in Soft Matter
Paper: “Soft hydrated sliding interfaces as complex fluids” in Soft Matter
2. Wear of Soft Materials
Wear is the gradual removal of material at a sliding interface. In hard materials this is related to the hardness, and the volume of material removed can be measured using mass or topography. However, in soft materials like elastomers and hydrogels, it is less clear what the properties are that control the wear, as well as how the worn particles behave. These investigations seek to map the parameters which control wear, with a focus on transitions between modes of wear.
Funded project: NSF CAREER 1563087
Paper: “Wear Mode Control of Polydimethylsiloxane (PDMS) by Load and Composition,” Wear
Paper: “Self-regenerating compliance and lubrication of polyacrylamide hydrogels,” Soft Matter
Paper: “Hydraulic Fracture Geometry in Ultrasoft Polymer Network,” International Journal of Fracture
3. Snap maneuver of the click beetle
Click beetles, or skipjacks, are a family of beetles which can snap their bodies in an explosive maneuver that takes place in milliseconds, not unlike the maneuvers of the trapjaw ant or mantis shrimp. The body parts and tissues can be modeled as mechanical contacts. This exciting collaborative work with Aimy Wissa’s Bio-inspired Adaptive Morphology Lab and Marianne Alleyne’s Bioinspiration Col-LAB-orative (ABC lab) is continuing to evolve.
Paper: “Latching of the click beetle (Coleoptera: Elateridae) thoracic hinge enabled by the morphology and mechanics of conformal structures,” Journal of Experimental Biology
4. Wear of Rail Steels
The steel used in bogie wheelsets (traincar wheels) has to be tough enough to resist fatigue cracking, but softer than the rails they ride on. Fatigue cracks can nucleate on the surface or in the subsurface, and the evolution of the near-surface also controls the surface wear. These investigations seek to discover the interplay between fatigue and wear in hardened steels.
5. Collaborative Efforts
Our group collaborates across the campus, the USA, and the world.
Paper: “An indentation-based approach to determine the elastic constants of soft anisotropic tissues,” Journal of the Mechanical Behavior of Biomedical Materials
Paper: “Mechanically-Guided Deterministic Assembly of 3D Mesostructures Assisted by Residual Stresses” small