Papers by Author: Ho Chel Yoon

Abstract: Failure strength evaluation on resistance welding mixed adhesive bonding was studied. Tensile-shear tests were carried out with the single-lap specimen, using both resistance welding and adhesive bonding. Peel tests were also carried out with DCB specimen. Composites were manufactured using the polyester as a matrix and bamboo natural fiber layer as a reinforcement. Adhesive bond, having bonding strength that remains unaffected by heat at resistance welding, were selected. Generally, adhesive bond require a long curing time and have little strength before hardening. Resistance welding helps weakness of adhesive bond both curing time and peel strength. And the spew fillet of adhesive bonding also helps to release stress intensity of edge of joining. The failure mechanism was discussed in order to explain higher peel and tensile-shear strength of resistance welding mixed adhesive bonding.

Abstract: Structure adhesive bonding method is widely used in the industry because it is possible to joint complex shape and dissimilar materials. Especially in the car industry, requests of lightweight car have adhesive bonding method be applied in the many parts. Also it is possible for stress to distribute uniformly through the adhesive layer, and stress concentration is released. Since strength, stiffness durability is much better, this method is determined as the technique replaced weld defect. But, it has much shorter history then other joint method such as spot weld and mechanical joint method. Evaluation of strength and durability is not established. As the fundamental research of design of adhesive bonding joints, considers over-lap length, adhesive thickness, surface treatment and environment which affect strength and durability of single-lap joints. In this research, a real part of bus folding door was used and tested to compare durability of spot welding and adhesive bonding.

Abstract: This research is concerned with a study of failure strength of natural fiber composite. Tensile-shear tests were carried out with the single-lap resistance welded joined specimens consisting of composite materials. Composite materials were manufactured using the polyester as a matrix and bamboo natural fiber layer as a reinforcement. Two types of specimen with different reinforcement positions were tested to evaluate the failure strength of natural fiber reinforced composite resistance welded joined specimens. The test results were presented by tensile-shear strength. The failure mechanism was discussed in order to explain the lower tensile-shear strength of composite and position of bamboo natural fiber layer on the failure strength properties were explained

Abstract: This research was concerned with study of fracture strength of adhesive-lap-joined composites. The tensile and peel tests were carried out with specimens manufactured hybrid stacked composites, because the orientation of fiber and the interfacial fracture between the matrix and the reinforcement had influence on failure strength of composites. Bamboo natural fiber layer was located between polyester layers. The objective of this study was to evaluate the effect of fiber orientation on failure strength properties of composites. The test results were presented by load-displacement graph and finite element analysis. As a result, the load-directional orientation and the thinner thickness of bamboo natural fiber layer have a good effect on peel and tensile-shear strength and failure shape of adhesive-joined hybrid stacked composite.

Abstract: This research was concerned with study of failure strength of natural fiber reinforced composites. Tensile-shear tests were carried out with single-lap-adhesive-joined specimens consisting of polyester lap and composite lap. Composites were manufactured using the polyester as matrix and bamboo natural fiber layer as reinforcement. Two types of specimens with different reinforcement positions were tested to evaluate the failure strength of adhesive-single-lap-joined natural fiber reinforced composites. The test results were presented by tensile-shear strength graph comparing with finite element analysis. The failure mechanism was discussed in order to explain the lower tensile-shear strength of composite, and effect of position of bamboo natural fiber layer on the failure strength properties were explained.

Abstract: There is an increasing interest in developing fully biodegradable materials for industrial applications. Composite combining biodegradable polymer and natural fiber could be a fully biodegradable material. This work focus on the investigation on China jute fiber reinforced PLA composites. Composites with three different fiber volume fractions were fabricated by film stacking hot press method. Mechanical properties have been investigated and the microstructure of the composites was observed. Fiber surface treatment by silane was applied in order to investigate the effects on the properties of the composites. The moisture absorption rates in a hygrothermal environment were also measured.

Abstract: The bonding strength of adhesive joints is influenced by the surface roughness of the joining parts. However, the magnitude of the influence has not yet been clarified because of the complexity of the phenomena. In this study, it is showed that surface treatment affects adhesive strength and durability of aluminum/polycarbonate single-lap joints, and loading speed affects tensile-shear strength of adhesive joints. To evaluate the effect of surface treatments on the adhesive strength, several surface treatment methods are used, that is, cleaning, grinding, SiC polishing and sand blasting. It is showed that an optimum value of the surface roughness exists with respect to the tensile-shear strength of adhesive joints. The adhesive strength shows linear relationship with the surface roughness and loading speed. And the mechanical removal of disturbing films of lubricants, impurities and oxides make adhesive strength increase significantly.

Abstract: Ceramics are significantly used in many industrial applications due to their excellent mechanical and thermal properties such as high temperature strength, low density, high hardness, low thermal expansion and good corrosion properties. To combine the specific advantages of ceramics with that of metals, they are often used together within one composite component. In this study, the effect of temperature on fracture characteristics of silicon nitride joined to 304 stainless steel brazed with Ti active alloy are investigated in room and high temperature regions. And analytical studies on the residual stress of dissimilar brazed joint are performed by the finite element method. Four-point bending strength and deflection of interlayer increase with increasing strain rate in room temperature. As the test temperature increases, the bending strength decreases, but the deflection of interlayer is almost constant. The residual stresses redistribute after cutting of joint and the maximum tensile stress occurs on the new free surface at the ceramic near the interface. The singularity of residual stresses at the ceramic near the interface is characterized by elastic-plastic properties of ceramic and inserted materials.­