Kum Cheol Shin

Axial crush and bending collapse of an aluminum/GFRP hybrid square tube and its energy absorption capability

Abstract In this paper, energy absorption capability of axial crush and bending collapse of aluminum/GFRP hybrid tubes were investigated. Glass fiber–epoxy composite prepregs were wrapped around an aluminum tube and then cured completely in the autoclave under the recommended cure cycle. Bonding process between composite and aluminum tubes was performed by excess resin extracted from the composite tube during curing process. For comparing energy absorption characteristics of the hybrid tube with those of pure aluminum and composite tubes, tests were performed using specimens made of an aluminum alloy and a composite material, respectively. Failure mechanisms of the hybrid tube under the axial compressive load and the bending load were experimentally investigated. For calculating energy absorption capability of axial crush and bending collapse behaviors of the hybrid tube, the modified plastic hinge collapse model and the modified Kecmans model for hybrid tube were suggested, respectively. Two suggested models for the hybrid tube showed a good agreement with the experimental results.

A study on the lap shear strength of a co-cured single lap joint

In this paper, the lap shear strength of a co-cured single lap joint subjected to a tensile load was investigated by experimental analysis. Co-cured joint specimens with several different bonding parameters such as bond length, surface roughness, and stacking sequence of the composite laminate were fabricated and tested. The dependence of the lap shear strength of the co-cured joint on the bonding parameters was investigated from the experimental results. The failure mechanism of the co-cured single lap joint was partially cohesive failure. The lap shear strength of the co-cured single lap joint was significantly affected by the bond length and the stacking sequence of the composite laminate. However, the effect of surface roughness on the lap shear strength of the co-cured single lap joint was not so significant.

Tensile load-bearing capacity of co-cured double lap joints

The co-cured joining method has several advantages over the adhesively bonded joining method because both the curing and the joining processes for the composite structures are achieved simultaneously. In this study, the tensile load-bearing capacities of co-cured double lap joints were investigated experimentally and compared with the analytical results calculated by finite element analysis. Co-cured double lap joint specimens with several bond parameters such as bond length, surface roughness, and stacking sequence of the composite laminate were fabricated and tested. From the experimental results, it was found that the failure mechanism of the co-cured double lap joint was cohesive failure by delamination at the first ply of the composite laminate in the co-cured double lap joint. Finally, optimum values of several bond parameters were determined. Analytical tensile load-bearing capacities of the co-cured double lap joints were calculated by the three-dimensional Tsai-Wu failure criterion using stress distributions obtained from finite element analysis.

Prediction of the tensile load-bearing capacity of a co-cured single lap joint considering residual thermal stresses

In this paper, stress distributions in a co-cured single lap joint subjected to a tensile load were investigated using the finite element analysis. Residual thermal stresses, which resulted from the curing process of the co-cured single lap joint, were also considered. Since the adhesive layer in the co-cured single lap joint was about 10 μm thick, very thin compared with the thickness of both adherends, the interface between the steel and composite adherends was assumed to be perfectly bonded. The co-cured single lap joint was analyzed with respect to several bond parameters such as the bond length and stacking sequence of the composite adherend. The failure mechanism of the co-cured single lap joint was partial cohesive failure in the composite material, which was significantly affected by the interfacial tensile stress at the free edge of the co-cured single lap joint. Interfacial tensile stress was a primary factor that caused interfacial delamination between the steel and composite adherends in the co-cured single lap joint. Finally, tensile load-bearing capacities calculated from the Ye-delamination failure criterion were compared with the experimental results, and relatively good agreement was found.

The manufacturing process of co-cured single and double lap joints and evaluation of the load-bearing capacities of co-cured joints

Abstract The co-cured joining method, which is regarded as an adhesively bonded joining method, is an efficient joining technique because both the curing and joining process for the composite structures can be achieved simultaneously. In this paper, the manufacturing process of the co-cured joint was introduced and specimens of co-cured single and double lap joints of the plate type were fabricated and tested under a tensile load. The failure mechanism of co-cured single and double lap joints was discussed using stress distributions obtained from finite element analysis. Failure criteria of the co-cured single and double lap joints are proposed and verified by comparing the tensile load-bearing capacity calculated by failure criteria with tensile test results.

Fatigue characteristics of a co-cured single lap joint subjected to cyclic tensile loads

In this paper, the effect of bond parameters on the fatigue characteristics of a steel-composite co-cured single lap joint under cyclic tensile loads was experimentally investigated. We considered the surface roughness of the steel adherend and the stacking sequence of the composite adherend as bond parameters. A fatigue failure mechanism of the co-cured single lap joint was explained systematically by investigating the surfaces of failed specimens.

Adhesively bonded lap-joints for the composite-steel shell structure of high-speed vehicles

Abstract Recently the design and manufacture of lightweight train structures have become important in order to increase speed. Composite train structures have many advantages over conventional steel or aluminum train structures because of their high specific strength, modulus and high damping capacity, which is beneficial for NVH (noise, vibration and harshness). From the structures of high-speed trains, the upper car-body is a good candidate for composite structures which increase the stability of trains due to the low gravity center of vehicles. If the side body of the train is made of steel plates, then joining of composite structures to the steel structures is required. In this work, the adhesive joining method between the composite upper car-body structure and the steel side plates was investigated. A 1 10 -size model of a real train subjected to internal pressure was developed and tested statically and dynamically.

Effects of bond parameters on fatigue characteristics of a cocured double lap joint subjected to cyclic tensile loads

A cocured joint whose manufacturing process is simpler than that of an adhesively bonded joint is attractive for composite structures due to its several benefits. Fatigue behavior in the cocured joint is important because under alternating loads it will fail at stress levels much lower than it can withstand under monotonic loading. Although some researchers have recently reported on cocured joints, there are only a few articles published on the fatigue characteristics of cocured joints. In this article, effects of bond parameters on fatigue characteristics of a steel-composite cocured double lap joint under cyclic tensile loads were experimentally investigated. In order to observe stress distributions near the interface edge of the cocured double lap joint, finite element analysis was also performed. We considered the surface roughness of the steel adherend and the stacking sequence of the composite adherend as bond parameters. A fatigue failure mechanism of the cocured double lap joint was explained systematically by investigating the surfaces of failed specimens and stress distributions at the interface edge. Failure criteria of the cocured double lap joint under cyclic tensile loads were shown graphically.

Calculation of stress intensities at the interface corner of anisotropic/isotropic bonded joints with a wedge

The behavior of bonded joints is of interest in many engineering fields. In order to analyze the failure at the interface of a bi-material structure, it is important to investigate stress intensities at the interface corner. In this paper, the expanded Stroh formalism is used to determine asymptotic stress and displacement fields near the interface corner between anisotropic and isotropic adherends. This simple procedure makes it possible to obtain stress singularities more easily than before. Three examples are presented to help understand the method. To obtain stress intensities at the interface corner, a path-independent conservative line integral, derived from Bettis reciprocal principle, is used. Finally the method to calculate stress intensities at the interface corner of bonded joints is presented in detail.

Nonlinear Acoustoelastic Interactions of Lamb Waves with LiNbO3 Films Deposited on Sapphire Substrates

The influence of a biasing electric field on the propagation of the lowest-order antisymmetrical a0 Lamb wave modes in a bi-layered piezoelectric plate is investigated in this paper. It is found that the velocity shifts for the a0 mode due to presence of the bias field on the 10- µm LiNbO3 film structure are comparable with those observed in surface acoustic waves and Lamb waves in LiNbO3 plates. The fractional change in phase velocity of the layered piezoelectric structure is a linear function of the biasing electric field and can be used in voltage sensors.