Mingyuan Lu

Characterisation of Interfacial Adhesion of Thin Film/Substrate Systems Using Indentation-Induced Delamination: A Focused Review

This review summarized the research works on the characterisation of interfacial adhesion in thin film/substrate bilayer structure by use of indentation testing. It focused on the delamination mechanics between a thin film and a substrate induced by indentation and the quantitative characterisation of interfacial strength in such bilayer systems. Three major techniques were introduced, namely conventional indentation, cross-sectional indentation and acoustic emission assisted indentation. A number of theoretical models and finite element simulation studies were discussed, in association with the experimental investigations. Key words: Thin film, bilayer, delamination, adhesion, indentation, acoustic emission

Synthesis, microstructure, and mechanical behaviour of a unique porous PHBV scaffold manufactured using selective laser sintering

Selective Laser Sintering (SLS) is a promising technique for manufacturing bio-polymer scaffolds used in bone tissue engineering applications. Conventional scaffolds made using SLS have complex engineered architectures to introduce adequate porosity and pore interconnectivity. This study presents an alternative approach to manufacture scaffolds via SLS without using pre-designed architectures. In this work, a SLS process was developed for fabricating interconnected porous biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) scaffolds with large surface areas and relative porosities of up to 80%. These characteristics provide great potential to enhance cell attachment inside the scaffolds. The scaffold microstructure was dependent on the laser energy density (LED) during the SLS process. An increase in LED led to scaffolds with higher relative densities, stronger inter-layer connections, and a reduced quantity of residual powder trapped inside the pores. An increase in relative density from 20.3% to 41.1% resulted in a higher maximum compressive modulus and strength of 36.4 MPa and 6.7 MPa, respectively.

Strain rate dependence in the nanoindentation-induced deformation of Mg-Al intermetallic compounds produced by packed powder diffusion coating

Nanoindentation was performed on τ-Mg32(Al, Zn)49 and β-Mg17Al12 intermetallic coatings and on a AZ91E Mg alloy substrate using loading rates of 0.03 to 30 mNs-1. Pop-in phenomenon was observed during loading in the two intermetallic coatings and in the substrate. Both the magnitude of the pop-ins and the time interval between two consecutive pop-ins increased with increasing loads. The phenomenon was attributed to plastic instability, which is known as the Portevin-Le Châtelier effect. The morphologies of the indent impressions at different strain rates on the t phase, the β phase and the substrate were also investigated using atomic force microscopy. Pile-up occurred in the τ and β phases and was found independent of the strain rate; no obvious pile-up occurred on the AZ91E substrate. The AZ91E substrate exhibited creep rates greater than those of the intermetallic phases, and all of the creep rates increased with the loading rate.

In vitro degradation of a unique porous PHBV scaffold manufactured using selective laser sintering: IN VITRO DEGRADATION OF A UNIQUE POROUS PHBV SCAFFOLD

Biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) scaffolds have shown great promise for bone tissue engineering applications. The investigation of their hydrolytic degradation is thus essential to understand the effect of hydrolysis on the complex biodegradation behavior of PHBV scaffolds. In this study, we investigated the degradation behavior of high molecular weight PHBV scaffolds manufactured using selective laser sintering (SLS) without using predesigned porous architectures. The manufactured scaffolds have high specific surface areas with great water-uptake abilities. After an incubation of 6 weeks in phosphate-buffered saline solution, the structural integrity of the scaffolds was unaffected. However, a significant decrease in molecular weight ranging from 39% to 46% was found. The measured weight loss was negligible, but their compressive modulus and strength both decreased, likely due to water plasticization. These findings suggest that hydrolytic degradation of PHBV by means of bulk degradation was the predominant mechanism, attributed to their excellent water absorptivity. Overall, the PHBV scaffolds manufactured using SLS exhibited adequate mechanical properties and satisfactory structural integrity after incubation. As a result, the scaffolds have great potential as candidates for bone repair in clinical practice.

Molecular dynamics simulation of the deformation of single crystal gallium arsenide

Three-dimensional molecular dynamics (3D MD) simulation was carried out to investigate the deformation of single crystal gallium arsenide (GaAs) during nanoindentation. Tersoff potential was used to simulate the atomistic interaction under an extremely low load of indentation. The coordination number and atomic displacement were studied and the cross-sectional profiles of the simulated indent were examined. The simulation results revealed that the lattice deformation of GaAs was influenced by polarity, showing distinct patterns on different crystalline planes. Slip band and dislocation were found to be the dominant deformation phenomena.