Thermal Design and Testing of a Passive Helmet Heat Exchanger With Additively Manufactured Components

Additive manufacturing (AM) processes allow for complex geometries to be developed in a cost- and time-efficient manner in small-scale productions. The unique functionality of AM offers an ideal collaboration between specific applications of human variability and thermal management. This research investigates the intersection of AM, human variability and thermal management in the development of a military helmet heat exchanger. A primary aim of this research was to establish the effectiveness of AM components in thermal applications based on material composition. Using additively manufactured heat pipe holders, the thermal properties of a passive evaporative cooler are tested for performance capability with various heat pipes over two environmental conditions. This study conducted a proof-of-concept design for a passive helmet heat exchanger, incorporating AM components as both the heat pipe holders and the cushioning material targeting internal head temperatures of ≤ 35°C. Copper heat pipes from 3 manufactures with three lengths were analytically simulated and experimentally tested for their effectiveness in the helmet design. A total of 12 heat pipes were tested with 2 heat pipes per holder in a lateral configuration inside a thermal environmental chamber. Two 25-hour tests in an environmental chamber were conducted evaluating temperature (25°C, 45°C) and relative humidity (25%, 50%) for the six types of heat pipes and compared against the analytical models of the helmet heat exchangers. Many of the heat pipes tested were good conduits for moving the heat from the head to the evaporative wicking material. All heat pipes had Coefficients of Performance under 3.5 when tested with the lateral system. Comparisons of the analytical and experimental models show the need for the design to incorporate a re-wetting reservoir. This work on a 2-dimensional system establishes the basis for design improvements and integration of the heat pipes and additively manufactured parts with a 3-dimensional helmet.

Knowledge Sharing and Evolution of Industrial Cloud Robotics

Industrial Cloud Robotics (ICR), with the characteristics of resource sharing, lower cost and convenient access, etc., can realize the knowledge interaction and coordination among cloud Robotics (CR) through the knowledge sharing mechanism. However, the current researches mainly focus on the knowledge sharing of service-oriented robots and the knowledge updating of a single robot. The interaction and collaboration among robots in a cloud environment still have challenges, such as the improper updating of knowledge, the inconvenience of online data processing and the inflexibility of sharing mechanism. In addition, the industrial robot (IR) also lacks a well-developed knowledge management framework in order to facilitate the knowledge evolution of industrial robots. In this paper, a knowledge evolution mechanism of ICR based on the approach of knowledge acquisition - interactive sharing - iterative updating is established, and a novel architecture of ICR knowledge sharing is also developed. Moreover, the semantic knowledge in the robot system can encapsulate knowledge of manufacturing tasks, robot model and scheme decision into the cloud manufacturing process. As new manufacturing tasks arrived, the robot platform downloads task-oriented knowledge models from the cloud service platform, and then selects the optimal service composition and updates the cloud knowledge by simulation iterations. Finally, the feasibility and effectiveness of the proposed architecture and approaches are demonstrated through the case studies.

Fabrication of Knee Prostheses by Means of SLM: Process and Functional Characterization

This article presents manufacturing of exemplary knee prostheses using selective laser melting (SLM) technology. All phases of design and production are considered, from acquisition of the STL build file to optimization of process parameters, printing and post-build heat treatments. Geometric differences are acquired and compared with a 3D scanner.

Printing of Microscale Nanotwinned Copper Interconnections Using Localized Pulsed Electrodeposition (L-PED)

Nanotwinned (nt) metals exhibit superior electrical and mechanical properties compared to their coarse-grained and nano-grained counterparts. They have a unique microstructure with grains that contain layered nanoscale twins divided by coherent twin boundaries (TBs). Since nanotwinned metals have low electrical resistivity and high resistance to electromigration, they are ideal materials for making nanowires, interconnections and switches. In this paper we show the possibility of making nanotwinned copper interconnections on a non-conductive substrate using a novel additive manufacturing technique called L-PED. Through this approach, microscale interconnections can be directly printed on the substrate in environmental conditions and without post processing.

Repeatability Assessment and Sensitivity Analysis of Needle Insertion Physical Experiment

Needle insertion physical experiments are used as the ground truth for model validation and parameter estimation by measuring the needle defection and tissue deformation during the needle-tissue interactions. Hence parameter uncertainties can contribute experiment errors. To improve the repeatability and accuracy of such experiments, one-at-a-time (OAT) sensitivity analysis is used to study the impacts of the factors, such as stirring temperature, frozen time, thawing time during the process of making hydrogels as well as repeated path insertion and different puncture plane in the planer needle insertion experiments. The results show that the puncture plane has the greatest effect on the repeatability of needle insertion physic experiments, followed by repeated path insertion, while other factors have the least effect. The results serve to guide future experiment design for greater repeatability and accuracy.

Fabrication of Efficient Electrodes for Dye-Sensitized Solar Cells Using Additive Manufacturing

Dye-Sensitized Solar Cells (DSSC) are third generation solar cells used as an alternative to c-Si solar cells. DSSC are mostly flexible, easier to handle and are less susceptible to damage compared to c-Si solar cells. Additionally, DSSC is an excellent choice for indoor application as they perform better under diverse light condition. Most DSSCs are made of liquid medium sandwiched between two conductive polymer layers. However, DSSCs have significantly lower efficiencies compared to silicon solar cells. Also, use of liquid medium resulting in leaking of liquid, and occasional freezing during cold weather, and thermal expansion during hot weather conditions. DSSC can be manufactured in small quantities using relatively inexpensive solution-phase techniques such as roll-to-roll processing and screen printing technology. However, scaling-up the DSSC manufacturing from small-scale laboratory tests to sizeable industrial production requires better and efficient manufacturing processes. This research studies the feasibility of using additive manufacturing technique to fabricate electrodes of DSSC. The study aims to overcome the limitations of DSSCs including preventing leakage and providing more customized design. Experimental studies are performed to evaluate the effects of critical process parameters affecting the quality of electrodes for DSSC. Volume resistivity test is performed to evaluate the efficiency of the electrodes. In this study, the electrodes of DSSC are successfully fabricated using Fused Disposition Modeling (FDM) 3D printing technique. The results of this study would enable additive manufacturing technology towards rapid commercialization of DSSC technology.

Additive Manufacturing for Civil Infrastructure Design and Construction: Current State and Gaps

Additive manufacturing (AM) has applications in several fields ranging from aerospace and consumer goods to the medical industry. However, applications of AM in civil infrastructure design and construction are very limited. Based on information shared at the NSF workshop on Additive Manufacturing (3D Printing) for Civil Infrastructure Design and Construction in July 2017, this paper summarizes the current state of the field, gaps, and recommendations.

Cooling Process for Directional Solidification in Directed Energy Deposition

Additive manufacturing (AM) for metals has attracted attention from industry because of its great potential to enhance production efficiency and reduce production costs. Directed energy deposition (DED) is a metal AM process suitable to produce large-scale freeform metal products. DED entails irradiating the baseplate with a laser beam and launching the metal powder onto the molten spot to produce a metal part on the baseplate. Because the process enables powder from different materials to be used, DED is widely applicable to valuable production work such as for a dissimilar material joint, a graded material, or a part with a special structure. With regard to parts with a special structure, directional solidification can prospectively be used in the power plant and aerospace industries because it can enhance the stiffness in a specific direction via only a simple process. However, conventional approaches for directional solidification require a special mold in order to realize a long-lasting thermal gradient in the part. On the other hand, from the viewpoint of thermal distribution in a produced part, DED is able to control the gradient by controlling the position of the molten pool, i.e., the position of the laser spot. Moreover, unlike casting, the thermal gradient can be precisely oriented in the expected direction, because the laser supplies heat energy on the regulated spot. In this study, the applicability of DED to directional solidification in Inconel® 625 is theoretically and experimentally evaluated through metal structure observation and Vickers hardness measurements. Furthermore, the effect of two different cooling processes on directional solidification is also considered with the aim of improving the mechanical stiffness of a part produced by DED. The observations and experimental results show that both the cooling methods (baseplate cooling and intermittent treatment with coolant) are able to enhance the hardness while retaining the anisotropy.

Active Control of Fabricating Nanofibrous Wavy/Helical Arrays Using Near-Field Electrospinning

A novel and simple near-field electrospinning (NFES) method has been developed to fabricate wavy or helical nanofibrous arrays. By alternating the electrostatic signals applied on auxiliary-electrodes (AE), the structural parameters of deposited patterns can be actively controlled. Compared with the traditional electrospinning methods based on the bending and buckling effects or collector movement, the proposed method shows advantages in the controllability, accuracy, and minimal feature size. Forces operating on the electrospinning jet and the time-varying electric field distribution were analyzed to explain the kinematics of the jet. Nanoscale wavy and helical patterns with various structural parameters were fabricated. The effects of experimental process parameters on structural parameters of deposited patterns were analyzed to demonstrate the controllability of our method in fabricating wavy or helical nanofibrous structures. It is envisioned that this method will benefit the applications in the field of photovoltaic devices, sensors, transducers, resonators, and stretchable electronics.

A Flexible Tactile Sensor Based on Porous Graphene Sponge for Tiny Force Measurement

Flexible tactile sensors have been utilized for epidermal pressure sensing, motion detecting, and healthcare monitoring in robotic and biomedical applications. This paper develops a novel piezoresistive flexible tactile sensor based on porous graphene sponges. The structural design, working principle, and fabrication method of the tactile sensor are presented. The developed tactile sensor has 3 × 3 sensing units and has a spatial resolution of 3.5 mm. Then, experimental setup and characterization of this tactile sensor are conducted. Results indicated that the developed flexible tactile sensor has good linearity and features two sensitivities of 2.08 V/N and 0.68 V/N. The high sensitivity can be used for tiny force detection. Human body wearing experiments demonstrated that this sensor can be used for distributed force sensing when the hand stretches and clenches. Thus the developed tactile sensor may have great potential in the applications of intelligent robotics and healthcare monitoring.