Won-Shik Chu

Locomotion of inchworm-inspired robot made of smart soft composite (SSC)

A soft-bodied robot made of smart soft composite with inchworm-inspired locomotion capable of both two-way linear and turning movement has been proposed, developed, and tested. The robot was divided into three functional parts based on the different functions of the inchworm: the body, the back foot, and the front foot. Shape memory alloy wires were embedded longitudinally in a soft polymer to imitate the longitudinal muscle fibers that control the abdominal contractions of the inchworm during locomotion. Each foot of the robot has three segments with different friction coefficients to implement the anchor and sliding movement. Then, utilizing actuation patterns between the body and feet based on the looping gait, the robot achieves a biomimetic inchworm gait. Experiments were conducted to evaluate the robots locomotive performance for both linear locomotion and turning movement. Results show that the proposed robots stride length was nearly one third of its body length, with a maximum linear speed of 3.6 mm s(-1), a linear locomotion efficiency of 96.4%, a maximum turning capability of 4.3 degrees per stride, and a turning locomotion efficiency of 39.7%.

Measurement and Compensation of Spring-back of a Hybrid Composite Beam

Fiber-reinforced composite materials have been advanced in various applications for their excellent mechanical and electromagnetic properties. On their manufacturing processes, however, thermo-curing inherently produces the undesired thermal deformation, so-called spring-back, mainly caused by temperature drop from the process temperature to room temperature. In order to fabricate designed part geometry, the spring-back must be understood especially in hybrid composites consisting of distinct groups of different materials. In this research, the spring-back of a hybrid composite beam is measured by a series of experiments, and is predicted by the classical lamination theory (CLT) and finite element analysis (ANSYS). To confirm the predicted spring-back, {glass fiber/epoxy} + {carbon fiber/epoxy} asymmetric hybrid composites are fabricated under various conditions such as cure cycle, laminate thickness, stacking sequence, and curing sequence. The results from CLT and FEA agree well with the experimental data, but the spring-back cannot be removed completely. To fabricate flat hybrid composite beams, a web-based spring-back compensation service is developed. The CLT-based code allows the user to predict spring-back and to fabricate a mold that compensates spring-back.

Fabrication of micro parts using nano composite deposition system

Purpose – The purpose of this research, is to develop a nano composite deposition system (NCDS) to fabricate three dimensional functional nano composite parts.Design/methodology/approach – The NCDS is a hybrid system in which material removal process by mechanical micro machining and/or the deposition process is combined.Findings – Hybrid RP technology showed higher precision than those made by casting or deposition process. Tensile strength of the hydroxyapatite‐acrylic composite was about four times higher than that of resin‐only specimen while MWCNT composite did not show much improvement.Originality/value – The paper illustrates new approaches for rapid prototyping techniques with various materials and high precision.

Evaluation of morphological architecture of cellulose chains in grass during conversion from macro to nano dimensions

Abstract The cellulose nanowhiskers (CNW) are of imminent importance in the development of ecofriendly green material for environment. Morphological study of their structure was carried out after extraction from grass. The controlled alkali and acid hydrolysis after soxhlet extraction of bleached fiber in ethanol and water provided a mixture of micro/nano fiber which can be further converted into CNW by mechanical treatment. Width of obtained CNW were found to be ~10-65 nm with length of several nanometers as evidenced by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The changes in dimensions during alkali treatment, bleaching and acid hydrolysis of grass exhibited an interesting architecture and clarify the phenomenon of separation of nano level fibrils from the matrix of hemicellulose and lignin which starts after swelling of fibers and opening from middle followed by splitting from each other. The nanofibers were embedded in the matrix surrounded by amorphous layers. The size of fibers was directly associated with the extent of treatments. The crystalline part of fiber was intact during hydrolysis which must be attributed to easy removal of amorphous region by penetration of hydronum ions from acid. The results of SEM and TEM were correlated with the Scanning Ion Microscopy (SIM) which showed a direct evidence of breaking of thick fiber strands resulting in the formation of sharp edged crystalline entities composed of cellulose crystals.

Internet-based Composite Repair

As composite materials are gaining wide acceptance in aircraft structures, the repair of damaged composites is becoming an important issue. Composite repair, however, has been performed more or less in a manual fashion, an integrated repair system is desirable. In this paper, an Internet-based advisory service (Repair Advisory Service, RAS) for composite repair is proposed to increase the efficiency of the repair process. Based on the client-server architecture, RAS offers time-effective sharing of engineering knowledge between remote locations, easy maintenance and update of the application software, and ubiquitous access to the services. The web browser is used as the user interface, which provides an easy access to the service and software friendly environment. The RAS system provides integrated design and repair tools for repair technicians and engineers as follows: (1) A design software for scarf repair and lap repair estimates the tensile failure and shear failure of repaired structures. (2) A structural repair manual is provided in the PDF document for viewing, and a web search engine can search the document. (3) A fabrication module of RAS generates a CNC toolpath to cut repair patches. (4) A CNC-based prepreg cutting machine has been developed to implement an automated composite repair. A scenario for the web-based remote repair was proposed, and a test repair was performed on an aircraft wing. The RAS service is open to public and available at http://fab.snu.ac.kr/ras.

Fabrication of a biodegradable drug delivery system with controlled release made of PLGA/5‐FU/hydroxyapatite

Purpose – Rapid prototyping (RP) technology has been widely applied in biomedical research. The purpose of this paper is to describe how a scaffold composite drug delivery system (DDS) was fabricated using a nano composite deposition system (NCDS).Design/methodology/approach – A biocompatible and biodegradable thermoplastic polymer (poly(DL‐lactide‐co‐glycolide acid)) was used as the matrix, and a mixture of anti‐cancer drug (5‐fluorouracil) and bio‐ceramic (hydroxyapatite – HA) was added to the polymer to form a bio‐composite material for the DDS. An in vitro drug release test showed that the release rate of the drug composite could be controlled by the amount of HA for 50 days.Findings – Faster release was observed for the DDS with higher weight percent of HA. The relationship between release rate and the amount of HA showed a bi‐linear manner, and bi‐linear drug release models were developed based on the experimental results.Originality/value – Cylindrical scaffolds were fabricated with polymer/drug/ad...

Rapid prototyping and testing of 3d micro rockets using mechanical micro machining

The trend of miniaturization has been applied to the research of rockets to develop prototypes of micro rockets. In this paper, the development of a web-integrated prototyping system for three-dimensional micro rockets, and the results of combustion tests are discussed. The body of rocket was made of 6061 aluminum cylinder by lathe process. The three-dimensional micro nozzles were fabricated on the same aluminum by using micro endmills with φ100μm~φ500 μm diameter. Two types of micro nozzle were fabricated and compared for performance. The total mass of the rockets was 7.32 g and that of propellant (gun powder) was 0.65 g. The thrust-to-weight ratio was between 1.58 and 1.74, and the flight test with 45 degree launch angle from the ground resulted in 46 m~53 m of horizontal flight distance. In addition, ABS housing for the micro machined rocket was fabricated using Fused Deposition Modeling (FDM). A web-based design, fabrication, and test system for micro nozzles was proposed to integrate the distributed hardware resources. Test data was sent to the designer via the same web server for the faster feedback to the rocket designer.

MIMS : Web-based Micro Machining Service

Presented in this paper is a Micro Machining Service (MIMS) based on the World Wide Web (WWW) technologies. Taking advantage of the bi-directional communications of the WWW, the fabrication process of micro machining can be expedited and becomes more viable for students or researchers. In order to ensure an easy access to the service, web browsers are used as the user interface of MIMS. A three dimensional geometry generated from a commercial CAD system is uploaded as an STL (Stereo Lithography) file, and the process parameters for three-axis CNC micro milling are to be selected via the user interface. The communication architecture is based on the three-tier client-server model. Depending on the users knowledge on micro machining, novice or expert, controllable input parameters are differentiated, but at any case an STL-based process planner automatically provides NC codes. To achieve high precision, scanning toolpath and pencil-cut toolpath are created by a curve-based polyhedral machining method. The hardware system for micro machining was established, and a couple of sample parts were fabricated by micro endmills. The parts fabricated by scanning toolpath followed by pencil-cut toolpath resulted in less form error (within 1.5%) than the parts fabricated only by scanning toolpath. This service is available at http://fab.snu.ac.kr/cam.

Preparation and structural evaluation of nano reinforced composites from cellulose whiskers of grass and biodegradable polymer matrix

Biocomposites of polylactic acid with cellulose whiskers from grass were prepared and reinforced with nanolayer-filled ionomer (Surlyn®). Three types of polymer composites were fabricated by filling the whiskers in polylactic acid at 5, 10, and 15% concentration. The analysis of resulting products was conducted by monitoring the functional group variation, crystallinity, and thermal behavior. The addition of clay-filled ionomer appeared to enhance the interfacial adhesion between filler and matrix by chemical and physical bonding. The migration tendency of different components inside silicate layers was also studied where the confinement of host polymer chains occurred between clay platelets, after modification through ionomer.

Design and Performance Evaluation of Soft Morphing Car-Spoiler

Automotive wings are considered to be aerodynamic devices which have a significant effect on the driving, braking and cornering performances by influencing the flow of fluids around the vehicle without changing the weight of the vehicle. The wings have developed from having a fixed shape to multi-sectional wings in order to amplify the advantages of their aerodynamic effect in specific situations such as cornering and braking. However, the multi-sectional wings based on flaps, ailerons, and slats have to modify their surface or camber using hinged parts. These discrete sections create aerodynamic losses during shape changes. In this paper, a morphing car-spoiler based on a reinforced elastomer capable of continuous self-actuation throughout its surface was applied to a small-scale vehicle without slotted parts or mechanical elements. The designed morphing car-spoiler consists of a woven type Smart Soft Composite (SSC) which was made by weaving Shape Memory Alloy (SMA) wires and glass fibers embedded in a polydimethylsiloxane (PDMS) polymeric soft matrix. The phase transformation from martensite to austenite of the SMA wires creates an axial load in the longitudinal direction resulting in symmetric bending of the spoiler. Using an open-blowing type wind tunnel, tests were conducted on the stand-alone spoiler to verify its aerodynamic effects. Furthermore, to evaluate its performance in practice, the morphing car-spoiler was mounted on a small-scale vehicle and tested in a closed-type wind tunnel. Results show that the morphing car-spoiler generates a downforce which increases the normal tire adhesion and that it is possible to adapt its shape for various situations such as cornering and braking.Copyright