Research Fields of System design with advanced composites laboratory
(SDAC lab)
We investigate the behavior of anisotropic materials such as fiber reinforced composites (carbon/epoxy composites, glass/polypropylene composites) including bio-tissues (bones, muscles and tendons) by using analytical and experimental methods. We also design various machine components and medical devices such as bone plates using fiber reinforced composites. The major research fields are as follows:
Smart sensor comprising of Nanohybrid of ZnO nanoparticles and Carbon Nanotube in PDMS
The flexible devices made of stretchable electronic materials can be incorporated into clothing or directly attached with the human body to monitor various vital signs of human. Instead of developing new materials, engineering of new structural constructs from established materials is the current mainstream strategy. ZnO nanoparticle possess the piezoelectric property and when combined with CNT we can build a smart sensor to be applicable in variety of filed including body motion detection, health monitoring, and robotics.
Sensor made of Highly Aligned Carbon Nanotube
The carbon nanotube has wide application in wearble devices due to its marvelous electromechnical properties. Sensors made of carbon nanotube and elastomer has ability to detect the strain but lack the property of anisotropic. The anisotropic property of the carbon nanotube based sensor can be used if it is aligned in a particular direction. Sensors made of aligned carbon nanotube using electric filed enjoys the benefits of anisotropic hence the dirctional sensing is possible. These aligned nanotubes then can be sealed in elastomenr to avoid the environmental effect and abrasion.
Simulation technique of long bones fractures healing using biphasic mechano-regulation algorithm when fixed with composites implants
Radial fractures in tibia bones are commonly occurring fractures treated with internal fixation prostheses such as intramedullary nails and bone plates, depending on the type of fracture. Metallic implants have high Young’s modulus which may cause complications like stress shielding, bone resorption, slow healing, implant failure and sometimes non-union. An ideal implant should maintain the loading balance allowing appropriate micro-movement and gradual transfer of body weight from implant to the callus which finally strengthens the bone.
A biphasic mechano-regulation algorithm (deviatoric strain and fluid flow) was implemented to verify healing status and calluses generation. The algorithm was implemented for 112 iterations and executed utilizing the Python programming language and ABAQUS 6.12 software package. The initial loading, fracture geometry, implant type and fastening conditions influences the healing performance which is sensitive to biomechanical environment.
Structural design of composite structures by
using long fiber prepreg sheets (LFPS) for mass production
The mechanical performance and productivity of composite structures generally depend on the dimensions of the fiber, mainly continuous and chopped fibers. Complex-shaped composite structures made of continuous fibers exhibit excellent mechanical properties but low productivity using mainly the vacuum bag degassing method in an autoclave. In contrast, composite structures made of chopped fibers show high productivity using conventional automated forming processes such as extrusion but exhibit poor mechanical properties. Using long fibers whose lengths are between those of continuous and chopped fibers results in moderate mechanical properties and improved productivity. LFPS(Long Fiber Prepreg Sheet) consists of chopped carbon fibers with lengths of 50mm in a fast-curing epoxy resin matrix. Unlike the complex molding methods such as the autoclave method, LFPS can produce products by simple molding method such as hot pressing. The main objective of this research is to design complex structures using LFPS and improve the adhesion strength of the hybrid structure of LFPS and metallic material.
Development of self-powered electroactive fabric sensors
Electroactive polymers are materials that respond to electrical stimulation by showing significantly large strains (a few hundreds %). Among ferroelectric polymers, polyvinylidene fluoride (PVDF) is one of the most promising electroactive polymers due to the relatively large and fast electro-mechanical response, high mechanical and chemical stability, flexibility, and low acoustic impedance close to water. Fabric sensor made of PVDF is promising with numerous potential applications in many industrial fields such as self-powered wearable devices, tools for structural health monitoring, and prediction system for natural or industrial disasters.
The main objective is to construct a flexible and durable fabric sensor made of PVDF fibers and ribbons and to develop main components of the fabric such as flexible electrode and PVDF fibers for high piezoelectric performance. Furthermore, electro-mechanical properties and correlation between frequency components and composite failure modeare also verified with various ways.
Health Monitoring Sensors based on filler reinforced polymer composite materials
Nanomaterials like SWCNTs, AgNWs and ZnSnO3 nanocubes are materials that show piezoelectric response when subjected to bending and tensile strains. These materials when used as nanocomposites with conductive polymers can form unique smart composites with high electrical and mechanical properties. These smart composites can be utilized in fabricating smart fabric sensors and stretchable strain sensors which are ideal to be used in promising applications such as human motion detection and health monitoring.
The main purpose of this research is to formulate unique set of nanocomposites which can be tuned for various applications and to obtain desired output signals based on the weight percentage of the filler contents. The fabricated sensors are mechanically and electrically stable and robust as tested by various electrical and mechanical tests.
Dynamic cell cultivation using smart actuator made
with electroactive polymers (EAPs)
Electroactive polymer (EAP) is a smart material that can get a larger strain than conventional materials in response to electrical stimulation. Furthermore, it is also called "artificial muscle" because it has flexibility similar to elasticity and damage, high energy density, vibration damping, and fracture toughness, and has similar workability to the muscles of living organisms. Although the in-vivo environment in which various cell tissues are active is mechanically flexible, the effect of this aspect on cell and vital tissue behavior and growth is very difficult to experimentally identify in an in-vitro environment. In this study, we used EAP to replace the static culture environment, which was the limitation of existing cell culture devices, and to apply the mechanical load transfer and various environmental conditions similar to the in-vivo environment even in the in-vitro environment The goal is to develop a new type of cell culture device that can be constructed similar to the in-vivo environment.
Estimation of mechanical properties of woven composites
experienced micro-scale deformation during draping process
Fiber-reinforced composites possess high specific stiffness, strength, and high fatigue life when compared with metallic materials and are therefore applied and studied in automotive and aerospace fields. Among them, fabric fiber-reinforced composites have higher formability due to in-plane shear deformation, and this is more advantageous in the process of fitting a two-dimensional prepreg to a complex three-dimensional curved surface (draping process) when compared with unidirectional composites. Macro deformation is possible to approximately predict the mechanical properties, but micro deformation simultaneously occur during the draping process. The prediction of the mechanical properties is limited if micro deformation is not considered. The main objective is to estimate of woven fabric composite material properties and behavior based on macro·micro structure deformation.
Design of high speed vehicles using fibrous composites
with high stiffness, high strength, high damping and lightweight
The metal structures was replaced by a high stiffness carbon/epoxy composite–aluminum hybrid structure to enhance the mechanical performance of the structures for high-speed vehicle. By considering driving conditions such as wide range of environmental temperatures, the composite laminates were applied to the inner surface of an aluminum structure. The bending stiffness of the existing structure was the most important mechanical performance criterion, which guarantee the higher stiffness, were tried to determine the mechanical performance and are therefore applied and studied in high performance vehicle and aerospace fields.
For obtaining lightweight, high stiffness, and damping characteristics of composite structures, carbon/epoxy composites have been used in metal structures, and for better performance which causes relative motion between structural materials, was introduced on composite hybrid structures for achieving high stiffness and high damping.
COMPOSITES HYDROGEN PRESSURE VESSEL
FOR FUEL CELL VEHICLES
To increase hydrogen storage efficiency for fuel cell vehicles high pressure vessel should be developed. High pressure vessels (over 70MPa) for hydrogen (Type III and Type IV) are composed of isotropic liner (aluminum or polymers) and carbon/epoxy composites and they are fabricated by a filament winding process. Non-linear stress analysis to find effective autofrettage pressure and strength analysis of composite-liner interface for fatigue failure are also in progress considering anisotropic behavior of composites and yielding of the liner structure. For the risk assessment of the structure experimental testing using FBG fiber optic sensors is also carried out. By using FBG fiber optic sensors real-time deformation and failure indication such as crack growth can be monitored for the safety of the structure.
BONDING CHARACTERISTICS OF COMPOSITE
ACCORDING TO ENVIRONMENTAL CONDITIONS
The filament winding is one of the manufacturing methods widely used in composite-related industries. At the interface of filament winding structures, residual stress generated in the thickness direction due to the wire tension. Our mission is to simulate this tension-generating residual stress with single lap joint for simple tests of bonding strength between different materials. We invented an additional pressure device with a steel jacket, epoxy block, strain gage, and so on. The additional pressure device was applied to the specimen for simulating wire tension-induced stress to the bonding interface of single lap joint during tensile tests under various temperature environments.
Strains corresponded to the expected residual stress according to the temperature were controlled. By consideration of the driving condition of automobiles -20℃, 25℃, 50℃ of temperature conditions were used. The failure mode and the onset of fracture were estimated by finite element analyses, and those analysis results were compared with the experimental results.
EVALUATION OF MECHANICAL PROPERTIES
OF POLYMER CONCRETES AND THEIR HEALTH MONITORING
Generally, Portland cement concrete is used to maintain a runway of airport because of their reasonable price and structural advantages. Cement concrete should be cured for 28 days to possess its maximum strength. But it is important to open the runway as fast as possible after repairing. To overcome the crucial drawback of the existing cement concrete on excessive time to be cured many researchers have been studying about the polymer concrete materials.
Polymer concretes are composed of aggregates and polymer material like epoxy and polyester. Epoxy resin has low shrinkage, better mechanical properties and coherence with aggregates than other polymer material. So, the polymer concrete which is made of epoxy resin has good strength and high bonding strength with an existing cement concrete. Furthermore, the necessity of real-time structure monitoring was emphasized to detect strains and material failures. The aim of our research is the evaluation of mechanical properties of polymer concrete under various conditions (various mixing ratio and temperature conditions) and the test results are used to construct repair system for a runway. FE analysis is followed to estimate stress distribution at the interface between polymer concrete and cement concrete under various environmental conditions.
MATERIAL CHARACTERIZATION OF TISSUES
The non-linear characteristics of living tissues are investigated by experimental approaches to develop the effective medical treatment. Soft tissues such as an anterior cruciate ligament (ACL) and an Achilles' tendon are easy to be injured during out-door activities, therefore effective way to reconstruction should be sought. In this research material characterization of soft tissues experiencing various medical treatments is examined and compared using animal testing. Biological environment of living tissues is provided by a bio-chamber to implement various in vivo and in vitro tests. The anisotropic and non-linear properties (creep and stress relaxation) of tissues are also investigated to find out the exact mechanical properties.
