Effect of Gas Flow Rates on Quality of Aerosol Jet Printed Traces With Nanoparticle Conducting Ink

This paper focuses on the influence of carrier gas flow rate (CGFR) and sheath gas flow rate (SGFR) on the quality of conductive traces printed with nanoparticle inks using aerosol jet printing (AJP). This investigation was motivated by previous results of two AJP specimens that were printed at different gas flow rates and yielded significantly different thermal cycling durability lifetimes. A parametric sensitivity study was executed by printing and examining serpentine trace structures at 15 different combinations of CGFRs and SGFRs. The analysis included quantifying the trace's macroscale geometry, electrical properties, and micromorphological features. Interesting macroscale results include an increase in effective conductivity with increasing CGFR. At the microscale, image processing of high magnification scanning electron microscope (SEM) images of the printed traces revealed that agglomerations of silver clusters on the surface of traces became coarser at higher CGFR and also that agglomerates in the bulk were finer than those on the surface. Crystalline silver deposits were observed at all flow rates. In addition, cross sectioning of the printed traces showed higher incidences of buried cohesive cracking at higher gas flow rates. These cohesive cracks reduce the robustness of the traces but may not always be visible from the surface. The degree of cohesive cracking was seen to be broadly correlated with the coarseness of the surface agglomerates, thus suggesting that the coarseness of surface agglomerates may provide a visible surrogate measure of the print quality. The results of this study suggest that print quality may degrade as gas flow rates increase.

FEM of Cracking during Nanoindentation and Scratch Testing in the Hard W-C Coating/Steel Substrate System

Finite element modelling (FEM) and eXtended FEM (XFEM) combined with the experimental nanoindentation and scratch tests have been used to simulate the process of cohesive cracking in W-C coating on softer and more ductile steel substrate during nanoindentation and scratch testing. The formation of single and multiple circular “frame” cohesive cracks in the sink-in zone during nanoindentation were explained by the development of high local tensile stresses in the coatings controlled by the plastic deformation of the substrate. Analogous mechanisms were successfully applied to the simulation of multiple Chevron type cracking during scratch testing. Thus, the ability of XFEM to predict the formation of different types of cohesive cracks was confirmed. It was also demonstrated that both nanoindentation and scratch tests in combination with XFEM can be used as the methods to determine the strength and fracture toughness of thin coatings.

Cohesive Cracking Simulation of Asphalt Mixture with Reflective Crack through XFEM

Firstly, the parameters of cohesive zone model in ABAQUS software are calibrated through the cohesive constitutive model determined by cohesive potential energy, which is provided by Oriz and Pandofi（1999）. Then, the validity and liability are verified by the single element example which compares extended finite element simulation with experimental results. Lastly, it puts forward the model of FEM based on the highway pre-sawed cracks. The curve of CMOD with changing temperature is obtained, and the curve can be divided into three stage segments. The middle stage segment changes dramatically for the local cracking in the crack tip field between asphalt surface and base. The research results illustrate the cracking mechanisms of asphalt pavement under changing temperature.

Cohesive Cracking Simulation of Concrete Using Effective Modulus

The research methods of Cohesive Zone Model (CZM) are introduced and the parameters of cohesive zone model in ABAQUS software are calibrated based on the cohesive constitutive model determined by the fracture energy. Besides adopting exponential cohesive zone model, this paper applies a bilinear one to simulate the crack propagation of a simply supported single-edge notched concrete beams SE(B) (Mode I) and make comparisons with experimental result. Finally, the results represent effectiveness of the effective modulus and the special advantage in term of failure of fracture based on the cohesive zone model, which is of directly guiding significance for achieving a deep going understanding of crack propagation.