• Journal of the Korean Society for Nondestructive Testing
• /
• v.21 no.3
• /
• pp.251-260
• /
• 2001

Damage Profess of CFRP laminates under monotonic tensile test was characterized by the correlation between Acoustic Emission(AE) and Ultrasonic Test(UT). The amplitude distribution of AE signal from a specimens is an aid to the determination of the extent of the different fracture mechanism such as matrix crack, debonding, fiber pullout and fiber fracture as load is increased. In addtion, the characteristics of ultrasonic amplitude attenuation are useful lot analysis of the different type of fracture mechanism. Different orientation of carbon fiber reinforced plastic specimens were used to investigate the AE amplitude range and ultrasonic amplitude attenuation. Finally, loading-unloading tests were carried out to check Felicity effect. During the tests, ultrasonic amplitude attenuation was investigated at the same time and compared with AE parameters. The result showed that two parameters of both AE and UT could be effectively used for analysis of fracture mechanism in CFRP laminates.

• Composites Research
• /
• v.26 no.2
• /
• pp.141-145
• /
• 2013

The mode II interlaminar fracture toughness was evaluated for CFRP laminates with different types of nonwoven tissues and the source of increased mode II interlaminar fracture toughness was examined by SEM analysis in this paper. The interlaminar fracture toughness in mode II is obtained by an end notched flexure test. The experiment is performed using three types of non-woven tissues: 8 $g/m^2$ of carbon tissue, 10 $g/m^2$ of glass tissue, and 8 $g/m^2$ of polyester tissue. On the basis of the specimen with no non-woven tissue, interlaminar fracture toughness on mode II at specimens inserted with non-woven carbon and glass tissues and polyester tissues increases as much as 166.5% and 137.1% and 157.4% respectively. The results show that mode II interlaminar fracture toughness of CFRP laminates inserted with nonwoven tissues increased due to the fiber bridging, fiber breakage, and hackle etc. by SEM analysis.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2011.06a
• /
• pp.1005-1006
• /
• 2011

• Steel and Composite Structures
• /
• v.18 no.5
• /
• pp.1145-1160
• /
• 2015

An experimental study was conducted for the effectiveness of steel-CFRP composite (CFRP laminates sandwiched between two steel strips) as stirrups in concrete beam to carry shearing force and comparison was made with conventional steel bar stirrups. A total numbers of 8 concrete beams were tested under four point loads. Each beam measured 1,600 mm long, 160 mm width and 240 mm depth. The beams were composed of same grade of concrete, with same amount of flexural steel but different shear reinforcements. The main variables include, type of stirrups (shape of stirrups and number of CFRP layers used in each stirrup) and number of stirrups used in shear spans. After getting on an excellent closeness between the values of ultimate shear resistance and ultimate tensile load of steel-CFRP stirrups, it could be concluded that the steel-CFRP stirrups represent the effective solution of premature failure of FRP stirrups at the bends.

• Journal of the Korean Society for Advanced Composite Structures
• /
• v.2 no.2
• /
• pp.13-19
• /
• 2011

This paper presents the stress distribution of the damaged butt joint of steel plate using CFRP laminates when the flange in tension zone of steel box girder is welded by butt welding. When CFRP sheets are patched on tension flange of steel-box girder, the stress distribution of a vertical and normal direction on damaged welding part is shown as parameters such as a variation of the thickness of adhesive, the overlap length with steel, and the modulus of elasticity of CFRP sheets. For the study, we wrote the computer program using the EAS(Enhanced assumed strain) finite element method for plane strain that has a very fast convergency and exact stress for distorted shape.

• Journal of Advanced Marine Engineering and Technology
• /
• v.34 no.5
• /
• pp.686-694
• /
• 2010

Continuing progress in high technology has created numerous industrial applications for new advanced composite materials. Among these materials, carbon fiber-reinforced plastic (CFRP) laminate composite is typically used for low-weight carrying structures that require high specific strength. In this study, the damage mechanism of a compact tension (CT) specimen of woven CFRP laminates is described in terms of strain and displacement changes and crack growth behavior. The digital image correlation (DIC) method (which is employed here as a computer vision technique) is analyzed. Acoustic emission (AE) characteristics are also acquired during fracture tests. The results demonstrate the usefulness of these methods in evaluating the damage mechanism for woven CFRP laminate composites. From the results, we show these methods are so useful in order to evaluate the damage mechanism for woven CFRP laminate composites.

• Steel and Composite Structures
• /
• v.10 no.3
• /
• pp.281-295
• /
• 2010

An experimental and a non linear finite element investigation on the behavior of steel-concrete composite beams stiffened in hogging moment region with Carbon Fiber Reinforced Plastics (CFRP) sheets is presented in this paper. A total of five specimens were tested under two-point loads. Three of the composite beams included concrete slab while the other two beams had composite slabs. The stiffening was achieved by attaching CFRP sheets to the concrete surface at the position of negative bending moment. The suggested CFRP sheets arrangement enhanced the overall beam behavior and increased the composite beam capacity. Valuable parametric study was conducted using a three dimensional finite element model using ANSYS program. Both geometrical and material nonlinearity were included. The studied parameters included CFRP sheet arrangement, concrete strength and degree of shear connection.

• Journal of the Korean Society of Safety
• /
• v.33 no.2
• /
• pp.8-13
• /
• 2018

The light weight composite materials have been replacing in high performance structures. The object of this study is to examine the effects of the initial crack location about a delamination in a PVC foam cored sandwich composite that is used for the strength improvement of structures. The initial crack location and fiber laminates thickness were changed with several types. The MMB specimen was used for evaluating the fracture toughness and crack behaviors. The material used in the experiment is a commercial twill carbon prepreg in CFRP material and Airex in PVC foam core. Sandwich laminate composites are composed by PVC foam core layer between CFRP face sheets. The face sheets were fabricated as 2 types of 5 and 8 plies. The initial cracks were located in a PVC form core and the interface of upper CFRP sheet. From the results, the crack initiation was affected with the location of the initial crack inserted in the PVC foam core. Among them, the initial crack at 1/3 of the upper part of the PVC foam core was the most rapid progression. And the critical energy release rate was $0.40kJ/m^2$, which is the lowest value when the initial crack was inserted into the interface between a PVC foam core and CFRP laminated with 5 plies. Meanwhile, the highest value of $1.27kJ/m^2$ was obtained when the initial crack was located at the center line in case of the 8 plies.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.50 no.5
• /
• pp.309-316
• /
• 2022

This paper presents nonlinear numerical analysis results which were compared with the tested tensile strengths of CFRP(Carbon Fiber Reinforced Plastic) laminates with 14 different stacking sequences. The composite laminate coupons were cured under an autoclave pressure using resin-impregnated unidirectional tapes. The nonlinearity of the matrix was considered for the analysis, which was obtained from lamina tests. The Hashin failure criteria and progressive failure analysis were used for the nonlinear finite element analysis. The comparison results show that the current approach is acceptable to predict the tensile strengths of the CFRP laminate coupons with various stacking sequences and no damage. However, it is not acceptable to predict the tensile strengths of the laminate specimens with a center hole.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2001.05a
• /
• pp.69-73
• /
• 2001

Damage induced by low-velocity impact on the curved composite laminates was experimentally evaluated for CFRP cylindrical shells with the radius of curvatures of 50, 150, 300, and 500 mm. The result was then compared with that of flat laminates. The radius of curvatures and the effective shell stiffness appeared to considerably affect the dynamic impact response of curved shells. Under the same impact energy level, the maximum contact force increased with the decreasing radius of curvatures, with reaching 1.5 times that for plates at the radius of curvature of 50 mm. Since the maximum contact force is directly related to the impact damage, curved laminates can be more susceptible to delamination and less resistant to the low-velocity impact damage. The distribution of delamination along the thickness direction of curved laminates are also different from that of flat plates. Delamination was distributed rather even]y at each interface along the thickness direction of curved laminates. This implies that the effect of curvatures has to be considered for the design of a curved composite laminate.