• Journal of the Korean Society for Nondestructive Testing
• /
• v.13 no.2
• /
• pp.40-47
• /
• 1993

Composites composed of a precipitation harden 2124 alloy matrix reinforced by SiC whiskers, which are fabricated by powder metallugy, are suscepttible to fatigue damage due to the pile-up of moving dislocation and the microcrack initiation along SiC-Al interfaces, especially at the external surfaces of a body. The initial process, such as pile-up of dislocation or microcrack, that corresponds to the stage I during fatigue failure process are too small to be detected and characterized by conventional ultrasonic technique. This paper describes the applicability of an acoustic microscope with Line-Focus-Beam(LFB) lens of 225MHz to evaluate fatigue damage of SiC whiskers reinforced Al alloy. The specimens which were 6.6mm thick, 13mm wide, and 105mm long in the gage section were fatigued in tension-tension under load control. The velocity of leaky surface and leaky pseudosurface acoustic waves are obtained by FFT analysis technique from V(z) curve which is a record of output of piezoelectric transducer. These results are discussed with the change of number of fatigue cycles. The result obtained by acoustic microscope is compared with that by ultrasonic technique generated at 5MHz with conventional surface wave transducers.

• Composites Research
• /
• v.29 no.5
• /
• pp.306-314
• /
• 2016

In this study, to improve the thermal stabilities of the epoxy composite specimens in addition to the enhanced mechanical properties, those were reinforced with carbon nanotubes and micrometer-sized silica particles. To disperse the filler in matrix relatively simple physical process, specimens were fabricated using shear mixing and sonication. Tensile strength, coefficients of thermal expansion and thermal conductivity of the specimens were measured with varied contents of the two fillers. The mechanical and thermal properties were also discussed, and the experimental results of thermal expansion related to the thermal stability of the specimens were compared with those from several micromechanics models. The hybrid composites specimens incorporating 0.6 wt％ of carbon nanotubes and 50 wt％ of silica particles showed better mechanical properties than the others with increase in tensile strength up to 11％, with respect to those of the baseline specimens. As the silica contents were increased the thermal expansion was reduced down to 36%, and the thermal stability was improved with the decreased thermal deformation. Thermal conductivity of the epoxy composite specimens incorporating 50 wt％ of silica particles was enhanced, which demonstrate improvement of 72%. The mechanical and thermal properties of the hybrid composites specimens incorporating the two fillers were improved simultaneously.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2002.10a
• /
• pp.127-130
• /
• 2002

The 2.5 vol% TiNi/6061Al composites were fabricated by permanent mold casting, and its microstructures and tensile test for the cold rolled composites with maximum 50% reduction ratio were investigated. In the case of TiNi fiber with 2mm interval in preform, the interface bonding of fabricated composites were good. EPMA analysis results were found the small amount of Mg, Si segregated interface of diffusion layer. Transverse section of TiNi fiber was decreased with increasing reduction ratio and 40% reduction ratio was observed microcrack from TiNi fiber. And the tensile strength of composites at 38% reduction ratio was 194MPa. In the case of over 38% reduction ratio, the decrease of the tensile strength was due to TiNi fiber rupture by excess working. The fracture mode was appeared brittle fracture with increasing reduction ratio

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.67-71
• /
• 2003

A hot press method was used to create the optimal fabrication condition for a Shape Memory Alloy(SMA) composite. The bonding strength between the matrix and the reinforcement within the SMA composite by the hot press method was more increased by cold rolling. In this study, the objective was to develop an on-line monitoring system in order to prevent the crack initiation and propagation by shape memory effect in SMA composite. Shape memory effect was used to prevent the SMA composite from crack propagation. For this system an optimal AE parameter should be determined according to the degree of damage and crack initiation. When the SMA composite was heated by the plate heater attached at the composite, the propagating cracks could be controlled by the compressive force of SMA.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.14 no.6
• /
• pp.595-606
• /
• 2012

Utilization of fiber reinforced polymer(FRP) material has been increased to solve construction material problems such as corrosion, etc. However, there are still many problems in using a linear-shaped FRP material for a tunnel structure with curved section. In this study, the loading tests were performed on the curved FRP-concrete composite material to evaluate its behavior as tunnel support. These tests were based on the result from preliminary numerical analysis on FRP-concrete composite material. Also, additional numerical analysis considering interface characteristics between FRP and cement-concrete was conducted to compare the result of loading test on FRP-concrete composite material. From the results of the loading test and numerical analysis, the analysis method suggested from this study is reasonable to evaluate the mechanical behavior of FRP-concrete composite material.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.35 no.3
• /
• pp.218-224
• /
• 2007

Although piezoelectric materials such as PZT have been widely used as actuators in the field of active vibration suppression, the use of bare PZT as an actuator may cause some drawbacks such as critical breaks in the installation process, short circuits in the host material and low fatigue performance. The LIPCA-C2 (lightweight piezocomposite actuator) was developed to alleviate these problems. We implemented the LIPCA as an actuator to suppress the vibration of an aluminum cantilever beam with a tip mass. In our test, we used positive position feedback control algorithm. The filter frequency for this type of feedback should be tuned to the natural frequency of the target mode. The first three experimental natural frequencies of the aluminum cantilever beam agree well with the results of finite element analysis. The effectiveness of using the LIPCA as an actuator in active vibration suppression was investigated with respect to the time and frequency domains, and the experimental results show that LIPCAs with PPF control can significantly reduce the amplitude of forced vibrations and the settling time of free vibrations. For a case study, the forced vibration control of several beams with different thicknesses were performed.

• Composites Research
• /
• v.30 no.5
• /
• pp.316-322
• /
• 2017

Carbon fiber is a material with excellent mechanical, electrical and thermal properties, which is widely used as a composite material made of a polymer matrix. However, this composite material has a weak point of interlaminar delamination due to weak interfacial bond with polymer matrix compared with high strength and elasticity of carbon fiber. In order to solve this problem, it is essential to use reinforcements. Due to excellent mechanical properties, graphene have been expected to have large improvement in physical properties as a reinforcing material. However, the aggregation of graphene and the weak interfacial bonding have resulted in failure to properly implement reinforcement effect. In order to solve this problems, dispersibility will be improved. In this study, functionalization of graphene nanoplatelet was proceeded with melamine and mixed with epoxy polymer matrix. The carbon fiber reinforced polymer composites were fabricated using the prepared graphene nanoplatelet/epoxy and flexural properties and interlaminar shear strength were measured. As a result, it was confirmed that the dispersibility of graphene nanoplatelet was improved and the mechanical properties of the composite material were increased.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.23 no.5
• /
• pp.418-428
• /
• 2003

Fiber fracture is one of the dominant failure phenomena affecting the total mechanical Performance of the composites. Fiber fracture locations were measured through the conventional optical microscope and the nondestructive acoustic emission (AE) technique and then were compared together as a function of the epoxy matrix modulus and the fiber surface treatment by the electrodeposition method (ED). Interfacial shear strength (IFSS) was measured using tensile fragmentation test in combination of AE method. ED treatment of the fiber surface enlarged the number of fiber fracture locations in comparison to the untreated case. The number of fiber fracture events measured by the AE method was less than optically obtained one. However, fiber fracture locations determined by AE detection corresponded with those by optical observation with small errors. The source location of fiber breaks by AE analysis could be a nondestructive, valuable method to measure interfacial shear strength (IFSS) of matrix in non-, semi- and/or transparent polymer composites.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2001.04a
• /
• pp.692-696
• /
• 2001

Thermo-mechanical behavior and mechanical properties of intelligent polymer matrix composite with SMA fiber are experimentally studied. It is found that increments of compressive thermal strain is observed as the pre-strain and TiNi volume fraction increase. The smartness of the SMA is given due to the shape memory effect of the TiNi fiber which generates compressive residual stress in the matrix material when heated after being prestrained. In the paper, alloy is based on the general purpose commercial code ANSYS. And for the purpose of easy and fast user's analysis, it is developed the Graphical User Interface by using Tcl/Tk language.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.2
• /
• pp.237-247
• /
• 1993

Carbon fiber reinforced plastics(CFRP) have gained increased application in aerospace structures because of their specific strength and stiffness, but are sensitive to impact-induced damage. An experimental investigation was carried out to evaluate the impact resistance of CFRP according to the ply angle. The specimens of angle ply laminate composites were employed with [0.deg. $_{6}$/ .deg.$_{10}$/0.deg.$_{6}$], in which 6 kinds of ply angle such as .deg.=15.deg., 30.deg., 45.deg., 60.deg., 75.deg. and 90.deg. were selected. The impact tests were conducted using the air gun type impact testing machine by steel balls of diameter of 5 mm and 10 mm, and impact-induced damages were evaluated under same impact speed of V=60m/s. The impact damaged zones were observed through a scanning acoustic microscope (SAM). The obtained results were summarized as follows: (1) Delaminations on the interfacial boundaries showed th directional characteristics to the fiber directions. The delamination area on the impact side (interface A) was considerably smaller compared to that of the opposite side (interface B). (2) Cracks corresponding to other delaminations than those mentioned in SAM photographs were also seen on the impact damaged zone. (3) The delamination patterns were affected by the ply-angle, the dimensions of the specimen, and the boundary conditions. (4) The impact damaged zone showed zone showed the delamination on the interfacial boundaries, transverse shear cracks of the surface layer, and bending cracks of the bottom layer.r.r.r.