Understanding Microdroplet Formations for Biomedical Applications

This paper focuses on understanding microdroplet formation of sodium alginate biopolymer at various concentrations utilizing drop-on-demand inkjet technology. We investigate the effect of sodium chloride on the rheology of sodium alginate and derive a correlation between the size of the droplet versus the size of the microcapsules formed. Varying sizes of microcapsules are formed based on different concentrations of calcium chloride solvent. This understanding will give insight for fabricating drug delivery capsules and tissue scaffolds that are subject to extreme ambient conditions when interfaced with in-vivo environments.

Biodegradable Mg for Bone Implants: Corrosion and Osteoblast Culture Studies

Corrosion and cell culture experiments were performed to evaluate magnesium (Mg) as a possible biodegradable implant material. The corrosion current and potential of a Mg disk were measured in different physiological solutions. The corrosion currents in cell culture media were found to be higher than in deionized water, which verifies that corrosion of Mg occurs faster in chloride solution. Weight loss, open-circuit potential, and electrochemical impedance spectroscopy measurements were also performed. The Mg specimens were also characterized using an environmental scanning electron microscope and energy-dispersive x-ray analysis (EDAX). The x-ray analysis showed that in the cell culture media a passive interfacial layer containing oxygen, chloride, phosphate, and potassium formed on the samples. U2OS cells were then co-cultured with a Mg specimen for up to one week. Based on visual observation, cell growth and function were not significantly altered by the presence of the corroding Mg sample. These initial results indicate that Mg may be suitable as a biodegradable implant material. Future work will develop small sensors to investigate interfacial biocompatibility of Mg implants.

Thermal and Electrical Transport in Carbon Nanofiber Interconnects

We study reliability of carbon nanofibers (CNFs) under high-current stress by examining CNF breakdown on four different configurations, suspended or supported, with/without tungsten deposition. The suspended results are consistently explained with a heat transport model taking into account Joule heating and heat dissipation along the CNF, while supported cases show a consistently larger current density just before breakdown, reflecting effective heat dissipation to the substrate.

Behavior and Mechanisms of Bolt Self-Loosening Under Transverse Load Due to Vibrations of a Washer Along an Arc

Self-loosening mechanisms of a bolt were investigated by Finite Element Method, under the assumption of a twist at the center of a circular joined structure in which the bolt was set along a certain pitch circle. In this structure, the bolt is loosened by combining the translational and rotational external loads. In the case of a large pitch circle structures in which self-loosening occurs, the directions of friction shear forces on the threads were along concentric circles; however, the instantaneous center of rotation was located one-side near the thread surface, and the center was eccentric with the axis of the bolt. If the radius of the pitch circle is set smaller, the instantaneous center of rotation moves closer to the center of the bolt, and finally reaches to the same position at the center of the bolt. On the other hand, the directions of friction shear forces on pitch diameter of one thread were calculated theoretically using the inclination and friction on a pressure flank. The results were in good agreement with FE analysis. By considering these mechanisms, it was estimated that the number of occurrence of self-loosening in one vibration cycle changes at the border when the diameter value of the pitch circle equals that of the screw threads. If the diameter of the pitch circle becomes smaller than that of the screw threads, the number changes from two to one. With the exception of torsional center-fastened structures, since the pitch circle is very small, self-loosening of general joined structures will occur twice in one vibration cycle.

Effects of Process Parameters on Shrinkage Uniformity and Birefringence of Injection-Compression Molded Parts

Injection-compression molding (ICM) with greater flexibility than conventional injection molding (CIM) can produce parts with better quality. In this work, polystyrene (PS) parts were molded by ICM technology. The effects of seven dominating process parameters, including mold temperature, melt temperature, compression force, compression distance, compression speed, compression time, and delay time, on both shrinkage uniformity and birefringence of PS parts were investigated. The results showed that compression force is the most important parameter for part shrinkage uniformity. The position with a lowest shrinkage moved towards the gate with increased compression distance. There is a remarkable increase in birefringence with larger compression forces. There is certain relationship between shrinkage uniformity and birefringence results.

Formation of Carbon Nanotube-Polymer Composites With Different Concentrations of Polystyrene Solution

In this study, polystyrene was mixed with toluene by ratios of 1 wt%, 2 wt%, and 3 wt% to create polystyrene solutions. CNTs-polymer composites have been fabricated by introducing polymeric material into the CNT film grown by plasma enhanced chemical vapour deposition (PECVD). The nanotubes act as conductive filler to the composite and resulting in increases in surface conductivities. Depending on the concentration of the polystyrene solution, the increases in conductivity varied. It is shown that the surface conductance is lower for CNT-polymer composite with higher concentrated polystyrene solution.

Design and Manufacture of Spiral Bevel Gears With Reduced Transmission Errors

A method for the determination of the optimal polynomial functions for the conduction of machine-tool setting variations in pinion teeth finishing in order to reduce the transmission errors in spiral bevel gears is presented. Polynomial functions of order up to five are applied to conduct the variation of the cradle radial setting and of the cutting ratio in the process for pinion teeth generation. Two cases were investigated: in the first case the coefficients of the polynomial functions are constant throughout the whole generation process of one pinion tooth-surface, in the second case the coefficients are different for the generation of the pinion tooth-surface on the two sides of the initial contact point. The obtained results have shown that by the use of two different fifth-order polynomial functions for the variation of the cradle radial setting for the generation of the pinion tooth-surface on the two sides of the initial contact point, the maximum transmission error can be reduced by 81%. By the use of the optimal modified roll, this reduction is 61%. The obtained results have also shown that by the optimal variation of the cradle radial setting, the influence of misalignments inherent in the spiral bevel gear pair and of the transmitted torque on the increase of transmission errors can be considerably reduced.

Design and Validation of an In-Mold Shrinkage Sensor

Dimensional consistency is a critical attribute of molded products, yet part dimensions are frequently only estimated from cavity pressure or part weight measurements. An in-mold shrinkage sensor is designed and validated. The design includes a deflectable diaphragm instrumented with strain gages connected in a full bridge circuit. In operation, the diaphragm is deflected due to the pressure of the melt in the mold cavity. Molded part shrinkage is then measured as the polymer melt solidifies, shrinks, and retracts from the mold wall. A design of experiments is conducted to validate the performance of the sensor as a function of packing pressures, cooling time, melt temperature, and coolant temperature. The results indicate the sensor outperforms both cavity pressure transducers and regression models, and is able to measure the shrinkage to an absolute accuracy of 0.01 mm for a 2.5 mm thick part.

Development of a Novel Method for Dry Grinding of Soft Steel

Compared to other machining processes, grinding involves high specific energy. This energy mainly transforms to heat which makes detrimental effects on surface integrity as well as tool wear. In dry grinding, as there is no cutting fluid to transmit generated heat in the contact zone, reducing grinding energy and grinding forces are crucial. Presented in this paper are some of the promising results of the systematic research work carried out by the authors in order to come closer to the goal of pure dry grinding. A new method to reduce the heat by superimposing ultrasonic vibrations on workpiece movement is presented. The obtained results show that the application of ultrasonic vibration can eliminate the thermal damage on the workpiece and decrease the grinding forces considerably. A decrease of up to 60% of normal grinding forces and up to 40% of tangential grinding forces has been achieved.

A New Design of Tooth Profiles Increases Synchronous Belt’s Fatigue Life

Synchronous belt and its driving pulley have non-conjugate tooth profiles. Because of non-conjugate motion and polygon effect, interference occurs during incomplete meshing, resulting in excessive wear and tear at tooth-root, which are the main forms of failure of synchronous belts. Tooth cracking also results from uneven stress distribution and/or increased maximal stress. In addition to discovering better materials to increase the strength of the belt’s teeth, optimization of the geometry of tooth profiles of belt and pulley to decrease the maximum tooth-root stress and to reduce interference during meshing is critical in improving the carrying capacity and increasing the belt’s life span. In the present study we proposed a new design of synchronous belt’s and pulley’s tooth profiles, modifying several key geometric parameters commonly used in synchronous belts’ designs. Applying the conformal mapping function and the theory of plane elasticity we systemically investigated the distribution of stress and distortion at the belt’s and pulley’s teeth of varying geometric parameters and analyzed the interference during meshing using an approach to investigating tooth profiles of non-constant pitch diameter. Finite Element Analysis showed that with the same load the maximum principal stress values of belt teeth in complete meshing in our design (STSB) were 54.4% and 67.8% of that of HTD (by Uniroyal) and STPD (by Good Year) belts with an 8 mm pitch commonly used in automobiles, respectively. The uneven distribution of stress along the edge of tooth profile was reduced, and the interference during meshing minimized with our design. We then experimentally tested belts made of the same materials with the three designs manufactured by the same factory. The belts were tested in the enclosed type of testing machine for synchronous belt’s fatigue-life, power = 6.5 kW and speed = 1500 r/min with test belt tension at 400 N. The fatigue lives of the belts (n = 5 each group) were 988 ± 36, 439 ± 21 and 665 ± 22 hours (mean ± SD) for STSB, HTD and STPD belts (p<0.0001), respectively, demonstrating the superiority of our design. We anticipate that the new design will have wide applications not limited to the automobile industry.