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.

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.

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.

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.

Migration of Nanoclay in PP/PS Blend and Effect of Its Localization on Cell Structure

In this work, the migration of clay in polypropylene/polystyrene (PP/PS) blend and the effect of its final localization on cell structure of microcellular foamed blend nanocomposites were studied. To observe the clay migration, a multilayered blend, alternatively superposed PS and PP/clay films with a thickness of 0.2 mm, was subjected to low shear flow. Batch foaming was performed on obtained blend nanocomposites to study the influence of the nanoclay localization on cell structure by using CO2 as the foaming agent. When subjected to flow, most clay dispersed in PP phase migrated into PS gradually. The migration of nanoclay caused smaller mean cell diameter and higher cell density to foamed PS. With the reduction of nanoclay content in PP phase, the cell density of PP foam decreased due to the reduction of heterogeneous nucleation sites and the mean cell diameter became smaller.

A Study on Evaluation of Impact Strength of Adhesive Joints Subjected to Impact Shear Loadings

Adhesive joints in mechanical structures are subjected to static loading as well as impact loading. It is desired for the adhesive joints to have sufficient strength under both static and impact loadings. A lot of studies on the adhesive joints and the joint strength subjected to static loading have been carried out and examined. A few research works on the adhesive joint subjected to dynamic loading have been done, however, it has not fully elucidated for applying the joints to important sections in mechanical structures. In this study, the impact strength of adhesive joints subjected to impact shear loading is investigated using modified split Hopkinson pressure bar (SHPB) apparatus. The shear strength of adhesive joint, in which a solid cylinder is bonded to a hollow cylinder by an adhesive, is determined from maximum applied shear stress. A commercial thermosetting epoxy adhesive is used in the experiments. At the same time, the stress distributions in the joints subjected to impact shear loading are simulated by the finite-element analyses (FEA). The effect of adhesive thickness is investigated experimentally and computationally. It is shown that the strength is greatly affected by the adhesive thickness and the effect on the stress distributions in the joint is discussed.

Machinability Studies and Artificial Neural Network Modeling of Turning Al-SiC (10p) Metal Matrix Composites

The paper presents the results of an experimental investigation on the machinability of fabricated Aluminum metal matrix composite (A356/SiC/10p) during continuous turning of composite rods using medium grade Polycrystalline Diamond (PCD 1500) inserts. MMC’s are very difficult to machine and PCD tools are considered by far, the best choice for the machining of these materials. Experiments were conducted at LMW-CNC-LAL-2 production lathe using PCD 1500 grade insert at various cutting conditions and parameters such as surface roughness, specific power consumed, and tool wear were measured. Machining was continued till the flank wears land on the tool crossed 0.4 mm. The influences of cutting speed on the insert wear and built-up edges (BUEs) formation were studied. The present results reaffirm the suitability of PCD for machining MMCs. Though BUE formation was observed at low cutting speeds, at high cutting speeds very good surface finish and low specific power consumption could be achieved. An Artificial Neural Network (ANN) model has been developed for prediction of machinability parameters of MMC using feed forward back propagation algorithm. The various stages in the development of ANN models VIZ. selection of network type, input and output of the network, arriving at a suitable network configuration, training of the network, validation of the resulting network has been taken up. A 2-9-3 feed forward neural network has been successfully trained and validated to act as a model for predicting the machining parameters of Al-SiC (10p) -MMC. The ANN models after successful training are able to predict the surface quality; specific power consumption and tool wear for a given set of input values of cutting speed and machining time.

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.

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.