Showing papers by "Ehsan Toyserkani published in 2016"

A comprehensive analytical model for laser powder-fed additive manufacturing

Abstract: This paper addresses a comprehensive analytical model for the laser powder-fed additive manufacturing (LPF-AM) process, also known as directed energy deposition AM. The model analytically couples the moving laser beam with Gaussian energy distribution, the powder stream and the semi-infinite substrate together, while considering the attenuated laser power intensity distribution, the heated powder spatial distribution and the melt pool 3D shape with its boundary variation. The particles concentration on transverse plane is modeled with Gaussian distribution based on optical measurement. The model can effectively be used for process development/optimization and controller design, while predicting adequate clad geometry as well as the catchment efficiency rapidly. Experimental validation through the deposition of Inconel 625 proves the model can accurately predict the clad geometry and catchment efficiency in the range of specific energy that is corresponding to high clad quality (maximum percentage difference is 6.2% for clad width, 7.8% for clad height and 6.8% for catchment efficiency).

Single-step synthesis of graphene quantum dots by femtosecond laser ablation of graphene oxide dispersions

Abstract: In the last few years, graphene quantum dots (GQDs) have attracted the attention of many research groups for their outstanding properties, which include low toxicity, chemical stability and photoluminescence. One of the challenges of GQD synthesis is finding a single-step, cheap and sustainable approach for synthesizing these promising nanomaterials. In this study, we demonstrate that femtosecond laser ablation of graphene oxide (GO) dispersions could be employed as a facile and environmentally friendly synthesis method for GQDs. With the proper control of laser ablation parameters, such as ablation time and laser power, it is possible to produce GQDs with average sizes of 2–5 nm, emitting a blue luminescence at 410 nm. We tested the feasibility of the synthesized GQDs as materials for electronic devices by aerosol-jet printing of an ink that is a mixture of water dispersion of laser synthesized GQDs and silver nanoparticle dispersion, which resulted in lower resistivity of the final printed patterns. Preliminary results showed that femtosecond laser synthesized GQDs can be mixed with silver nanoparticle dispersion to fabricate a hybrid material, which can be employed in printing electronic devices by either printing patterns that are more conductive and/or reducing costs of the ink by decreasing the concentration of silver nanoparticles (AgNPs) in the ink.

Method and apparatus for aerosol-based three-dimensional (3D) printing of flexible graphene electronic devices

Abstract: The disclosure is directed at a method and system for three-dimensional (3D) printing of flexible graphene electronic devices and deposition of graphene on non-planar surfaces. By using a printer ink that includes a stabilized graphene powder and a pair of solvents, the printer ink provides for a material that overcomes disadvantages of current systems. In one embodiment, the pair of solvents are cyclohexanone and terpineol. The stabilized graphene powder preferably includes a polymer such as, but not limited to ethyl cellulose.

On the sensitivity and repeatability of fiber Bragg grating sensors used in strain and material degradation measurement of magnesium alloys under cyclic loads

Abstract: In the present study, for the first time, Fiber Bragg Grating (FBG) sensors are employed to measure the cyclic-strain induced on AZ31B extrusion samples during rotational bending tests (RBTs). The importance of this observation will be highlighted by considering the risk of failures under this circumstance in the modern technologies such as aerospace, while any in situ cyclic strain measurement has not been reported under RBTs. For this purpose, first, the accuracy of strain measurements captured by the FBG sensor in the elastic and plastic regimes is investigated by comparing the FBG measured strain with the data obtained simultaneously by a standard extensometer during uniaxial pull-push tests. The results confirm that the FBG sensor is able to measure the strain up to 1.3 % (plastic region) accurately. Next, the strains of the specimens are measured under different bending moments during RBTs in both the elastic and plastic regimes, hence monitoring the degradation of material during the test. The experiments uncover that the strain amplitude of the samples is decreased as the number of cycles increases in the plastic regime until the sample is stabilized. However, the strain response of the material under a bending moment of 2.5 Nm (in the elastic regime) remains constant during the test. This paper concludes that the measurement of strain amplitude evolution, with respect to the number of cycles, in a rotating bending cyclic test with FBG sensors is feasible with high level of accuracy and repeatability in the cyclic testing in the elastic region.

Mechanical properties of additive-manufactured porous titanium bio-structures with oriented macro-scale channels

Abstract: This article addresses the influence of macro-scale channels with a diameter of 1 mm on the physical and mechanical properties of additive-manufactured porous titanium (Ti) structures, which can be used as bone implants. Different orientations and numbers of channels within the additive-manufactured structures were used in this study. The produced samples were characterized through porosity, shrinkage measurements, as well as mechanical compression tests. The results demonstrate that the channel orientation in the structure influences the shrinkage rate in the parts made with horizontally or vertically orientated channels, in which a relatively isotropic shrinkage is achieved after sintering. In addition, mechanical ultimate strength of the structure can be tailored to the desired properties (such as the surrounding bone) via the channel orientation in the structure, where the overall porosity is affected by the number of channels existing in the structure.