Nanoparticle Enabled Metal 3D Printing
Metal additive manufacturing (AM) enables the production of complex, geometrically optimized parts ranging from heat exchangers to turbine blades that would be inefficient to produce using casting or subtractive manufacturing methods . Selective laser melting (SLM) is a metal AM technique that employs a scanning laser (typically near infrared, near-IR) to heat and melt a bed of metal powders, allowing layer-by-layer manufacturing of metal parts. My interest lies in using nano/microscale powder functionalization to fundamentally 1)overcome barriers that inherently make some metals difficult to 3D print via SLM and, expanding the suite of materials for metal AM and 2) control the microstructural evolution of printed parts to reach create hierarchical structures with desired properties. A direct example is the printing of biocompatible titanium alloy hip implants that are mechanically compatible with the surrounding bone and promote osteointegration, i.e., "mechanobio-compatible" implants .
Hierarchical Fracture Resistance of Bone
Human bone is a hierarchically arranged composite that has intrigued scientists for decades. Part of the reason why it has been challenging to fully understand the structure and properties of bone is because of its multi-scale nature: components range in size from some nanometers to microns to millimeters and centimeters. Understanding how the multi-scale components work in concert to provide bone with exceptional mechanical properties has been very challenging. Here we showed in situ microscale fracture experiments reveal nanofibril toughening in human bone leads to unique hierarchical toughening. submitted
Fracture and Fatigue of Micro/Nano materials
In contrast to the now-ubiquitous experiments on measuring compressive strengths of nano- and micro-sized materials, small scale fracture experiments have been far less pursued for because of linear elastic and elastic-plastic fracture mechanics (LEFM, EPFM) minimum specimen size restrictions and 2) the standards for fracture experiments that provide valid measurements of toughness at the macroscale pose significant fabrication and experimental difficulties when adapting to microscale. We developed an experimental methodology that enables conducting in-situ three-point bending fracture and fatigue experiments on free-standing micron-sized beams, similar to the ASTM standardized single edged notched bend experiments. We validated this methodology using various materials including single crystalline silicon, fused silica, and acrylates. submitted
Nanoscale Disorder and Size-effect in Human Bone
In human bone, an amorphous mineral serves as a precursor to the formation of a highly substituted nanocrystalline apatite. However, the precise role of this amorphous mineral remains unknown. Here, we show by using transmission electron microscopy that 100–300nm amorphous calcium phosphate regions are present in the disordered phase of trabecular bone. Nanomechanical experiments on cylindrical samples, with diameters between 250nm and 3,000nm, of the bone’s ordered and disordered phases revealed a transition from plastic deformation to brittle failure and at least a factor-of-2 higher strength in the smaller samples.
Microgravity Dependent Fracture Properties of Bone
We currently have an on going project with Ruth Globos at NASA AMES studying the change in microstructure and micro- and nanomechanical properties of bone that have been subjected to both real and simulated microgravity. MicroCT courtesey of Nathan O' Neil.