Processability of high-strength aluminum 6182 series alloy via laser powder bed fusion (LPBF)

The growing demand for more materials available for the LPBF-process, in particular high-strength aluminum alloys, is evident in the market. In the present work, a systematic investigation of the processability of aluminum 6182 series alloys, using LPBF, was carried out. For this purpose, the influence of process parameters, especially of enhanced preheating by heating the substrate plate during the LPBF process, on the microstructure of EN AW 6182 specimens was studied.Experiments were conducted at different preheating temperatures always using the same d-optimal design-of-experiments, the laser power, scanning speed, hatch distance, and laser focus position being varied over a wide range.It was found that the preheating temperature has the strongest impact on hot cracking. Higher temperatures result in a significantly reduced number of hot cracks in the microstructure. Moreover, an equiaxed microstructure of the specimens manufactured can be observed at preheating temperatures of 500 °C. In addition to the preheating temperature, the achievable part density is most strongly affected by the laser focus position and the laser power, whereas the hatch distance shows no discernible impact on the part density. Furthermore, neither the hatch distance nor the laser focus position shows any significant effect on hot cracking.In combination with the optimal scanning parameters, crack-free parts with a fully equiaxed grain structure and densities > 99.0% can be manufactured via LPBF at a preheating temperature of 500 °C.

Systems-of-Systems MS&A for Complex Systems, Gaming and Decision for Space Systems

This chapter discusses advanced modeling, simulation and analysis (MS&A) approaches for supporting complex space system, gaming and decision support system (DSS) using systems-of-systems perspective. The systems-of-systems MS&A approaches presented here also address capability-based approach for supporting US defense acquisition life cycle with a laser focus on the pre-award acquisition phase and combined game theory and wargaming for acquiring complex defense space systems. The chapter also provides an overview of existing models and tools for the design, analysis and development of the government reference system architecture solution and corresponding acquisition strategy in a complex defense systems-of-systems environment. Although, the proposed MS&A approaches presented here are focused on defense space systems, but the approaches are flexible and robust that can be extended to any civilian and commercial applications.

Characterization of Energetic Protons Generated in the ShenGuang-II UP Petawatt Laser Interactions with Foil Targets

The characterization of energetic protons generated in the ShenGuang-II UP petawatt laser interactions with foil targets has been systematically studied. The proton energy spectra and angular distributions are measured with a radiochromic film stack. It shows that the proton energy spectra have a Boltzmann distribution with temperature of about 2.8 MeV and cutoff energy of about 20 MeV. The divergence angles of protons vary from 10° to 60°, dependent on the proton energy. The proton source size and location are investigated via the proton point-projection mesh imaging. The proton virtual sources are found to locate tens to hundreds of microns in front of the foil target, depending on the proton energies. A Monte Carlo simulation estimates the diameter of the virtual proton source to be about 12 μm for the protons with energy of 16.8 MeV, which is much smaller than the laser focus size of about 50 μm. The spatial resolution of the 16.8 MeV proton imaging is quantified with the point spread function to be about 15 μm, which is consistent with the proton virtual source size. These results will be important for the users conducting experiments with the protons as a backlighting source on the ShenGuang-II UP petawatt laser.

Diffusivity Measurement by Single-Molecule Recycling in a Capillary Microchannel

Microfluidic devices have been extensively investigated in recent years in fields including ligand-binding analysis, chromatographic separation, molecular dynamics, and DNA sequencing. To prolong the observation of a single molecule in aqueous buffer, the solution in a sub-micron scale channel is driven by a electric field and reversed after a fixed delay following each passage, so that the molecule passes back and forth through the laser focus and the time before irreversible photobleaching is extended. However, this practice requires complex chemical treatment to the inner surface of the channel to prevent unexpected sticking to the surface and the confined space renders features, such as a higher viscosity and lower dielectric constant, which slow the Brownian motion of the molecule compared to the bulk solution. Additionally, electron beam lithography used for the fabrication of the nanochannel substantially increases the cost, and the sub-micron dimensions make the molecule difficult to locate. In this paper, we propose a method of single-molecule recycling in a capillary microchannel. A commercial fused-silica capillary with an inner diameter of 2 microns is chopped into a 1-inch piece and is fixed onto a cover slip. Two o-rings on the sides used as reservoirs and an o-ring in the middle used as observation window are glued over the capillary. The inner surface of the capillary is chemically processed to reduce the non-specific sticking and to improve capillary effect. The device does not require high-precision fabrication and thus is less costly and easier to prepare than the nanochannel. 40 nm Fluospheres® in 50% methanol are used as working solution. The capillary is translated by a piezo stage to recycle the molecule, which diffuses freely through the capillary, and a confocal microscope is used for fluorescence collection. The passing times of the molecule through the laser focus are calculated by a real-time control system based on an FPGA, and the commands of translation are given to the piezo stage through a feedback algorithm. The larger dimensions of the capillary overcomes the strong sticking, the reduced diffusivity, and the difficulty of localizing the molecule. We have achieved a maximum number of recycles of more than 200 and developed a maximum-likelihood estimation of the diffusivity of the molecule, which attains results of the same magnitude as the previous report. This technique simplifies the overall procedure of the single-molecule recycling and could be useful for the ligand-binding studies in high-throughput screening.

Listening with Curiosity – Tracking the Acoustic Response of Portable Laser Ablation

Nowadays, one of the methods of choice for minimal invasive sampling of solid matter is laser ablation (LA). Routine LA sampling is performed commonly in the laboratory and the amount of ablated mass can directly be monitored and analysed. By contrast laser-based sampling in the field, using a portable laser ablation system (pLA), still remains challenging concerning low-absorbing or NIR-transparent samples. The current hardware is limited in regards to photon energy and density resulting in unsteady ablation. But as the actual amount of collected mass is the major crux of on-site sampling, with this performance it is often unknown and estimates can only be made based on the experience from prior method development and the experience of the user. In the following work an easy-to-use method to monitor the amount of ablated material collected during laser-based sampling by measuring the acoustic response is presented. The pLA-system was coupled to inductively coupled plasma mass spectrometry (ICPMS) via a diffusion driven gas exchange device (GED) which allowed to monitor mass removal and acoustic response quasi-simultaneously. For the current instrumentation only actual mass removal leads to the formation of shockwaves (SW) and, thus, acoustic signals. These events can be used as indicator for executed LA events and counted on an individual basis. The intensity of acoustic signals has been shown to correlate with the LA mass, i.e., the amount of ablated material. This allows to perform re-adjustment of the laser focus during sampling for optimal ablation based on the intensity of the acoustic signal. Likewise, acoustic intensity together with counting allows the operator to make estimates about total mass sampled. Therefore, unsuccessful laser aerosol collection in the field shall become a thing of the past.

Accommodate and adapt- coaching in COVID-19 environment

Tennis play worldwide has been heavily impacted by COVID-19, with many of our landmark events not being played or postponed to non-traditional times. Many tennis facilities have had to close due to governmental restrictions to stem the growth of the coronavirus pandemic. As we start to come out of this lockdown, there is an opportunity to leverage the health benefits and natural physical distancing aspects of tennis to come out stronger and increase our global awareness of our sport, where one can play while having fun at any age. A major stakeholder in this realization is the coach. It is hoped that this article can provide some practical insight into how with a laser focus on learning methodology, skill acquisition, and a player-centered approach, we can accommodate, adapt and grow our sport.