• Composites Research
• /
• v.16 no.3
• /
• pp.1-8
• /
• 2003

Densification occurs by the inelastic flow of the matrix materials during the consolidation processes at high temperature for MMCs, and the results depend on many process conditions such as applied pressure, temperature and volume fraction of fiber and matrix materials. This is particularly important in titanium matrix composites since material failure may occur by either the applied conditions or microstructural parameters through the processes, and thus a generic model based on micro-mechanical approaches enabling the evolution of density over time to be predicted has been developed. The mode developed is then implemented into FEM so that practical process simulation has been carried out. Further the experimental investigation of the consolidation behavior of SiC/Ti-6Al-4V composites using vacuum hot pressing has been performed, and the results obtained are compared with the model predictions.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.31 no.1
• /
• pp.62-67
• /
• 2011

Nanoparticles-coated and impact-damaged carbon-fiber reinforced plastics(CFRP) laminates were tested under compression-after-impact(CAI) mode and the propagation of damage due to compressive loading has been monitored by acoustic emission(AE). The impact damage was induced not by mechanical loading but by a simulated lightning strike. CFRP laminates were made of carbon prepregs prepared by coating of conductive nano-particles directly on the fibers and the coupons were subjected to simulated lightning strikes with a high voltage/current impulse of 10~40 kA within a few microseconds. The effects of nano-particles coating and the degree of damage induced by the simulated lightning strikes on the AE activities were examined, and the relationship between the compressive residual strength and AE behavior has been evaluated in terms of AE event counts and the onset of AE activity with the compressive loading. The degree of impact damage was also measured in terms of damage area by using ultrasonic C-scan images. From the results assessed during the CAI tests of damaged CFRP showed that AE monitoring appeared to be very useful to differentiate the degree of damage hence the mechanical integrity of composite structures damaged by lightning strikes.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2001.05a
• /
• pp.93-96
• /
• 2001

Structural polymer composites are susceptible to damage in the form of cracks, which form deep within the structure where detection is difficult and repair is almost impossible. A recent methodology for the damage repair of polymer composites using the self-healing technique is reported. The polymerization of the healing agent is triggered by contact with an embedded catalyst, being necessary to damage repair of polymer composites. For this purpose, the self-healing concept is introduced and the manufacturing process of microcapsule with the healing agent is briefly described. The polymerization between the healing agent and the catalyst is verified by the use of ESEM and IR spectroscopy. Finally the efficiency of the self-healing technique is investigated by measuring the critical load of TDCB specimen.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2001.10a
• /
• pp.174-178
• /
• 2001

The piezoelectric thin film sensor can be used to interpret variations in structural and material properties, e.g. for structural integrity monitoring and assessment. To illustrate one of this potential benefit, PVDF film sensors are used for monitoring impact damage initiation in Gr/Ep composite panel. Both PVDF film sensors and strain gages are surface mounted to the Gr/Ep specimens. A series of impact test at various impact energy by changing impact mass and height is performed on the instrumented drop weight impact tester. The sensor responses are carefully examined to predict the onset of impact damage such as matrix cracking, delamination, and fiber breakage, etc. Test results show that the particular waveforms of sensor signals implying the damage initiation and development are detected above the damage initiation impact energy. As expected, the PVDF film sensor is found to be more sensitive to impact damage initiation event than the strain gage.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2005.04a
• /
• pp.13-16
• /
• 2005

The mechanical properties of composite materials may degrade severely in the presence of damage. Especially, the high-velocity impact such as bird strike, a hailstorm, and a small piece of tire or stone during high taxing, can cause sever damage to the structures and sub-system in spite of a very small mass. However, it is not easy to detect the damage in composite plates using a single technique or any conventional methods. In this paper, the PYDF(polyvinylidene fluoride) film sensors and strain gages were used for monitoring impact damage initiation and propagation in composite laminates. The WT(wavelet transform) and STFT(short time Fourier transform) are used to decompose the sensor signals. A ultrasonic C-scan and a digital microscope are also used to examine the extent of the damage in each case. This research demonstrate how various sensing techniques, PVDF sensor in particular, can be used to characterize high-velocity impact damage in advanced composites.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2005.04a
• /
• pp.235-239
• /
• 2005

In this research, we investigated the frequency characteristic of low-velocity impact induced damage signals on graphite/epoxy composite laminates using high-speed fiber Bragg grating(FBG) sensor system. Appling the FBG sensors to damage assessment, we need to study the response of FBG sensors as the damage signals of the different incident angles because FBG shows different directional sensitivity. In order to discriminate an impact induced damage signal from that of undamaged case, drop impacts with different energies were applied to the composite panel with different incident angle to the FBG sensor. Finally, detected impact signals were compared using frequency distributions of wavelet detail components in order to find distinctive signal characteristics of composites delamination.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2002.10a
• /
• pp.118-121
• /
• 2002

Polyvinylidene di-fluoride (PVDF) film sensor appeared to be practically useful for the structural health monitoring of composite materials and structures. PVDF film sensors were either attached to or embedded in the graphite/epoxy composite (CFRP) samples to detect the fatigue damage at the bondline of single-lap joints or the tensile failure of unidirectional laminates. PVDF sensors were sensitive enough to detect and determine the crack front in linear location since composites usually produce very energetic acoustic emission (AE). PVDF sensors are extremely cost-effective, as flexible as other plastic films, in low profile as thin as a few tens of microns, and have relatively wide-band response, all of which characteristics are readily utilized for the structural health monitoring of composite structures. Signals due to fatigue damage showed a characteristics of mode II (shear) type failure whereas those from fiber breakage at DEN notches showed that of mode I (tensile) type fracture.

• Journal of Environmental Impact Assessment
• /
• v.28 no.4
• /
• pp.387-399
• /
• 2019

This research aimed to prepare the classification of the damage types and the damage rating system of noise barriers for expressway noise barriers and to develop deterioration evaluation method of noise barriers by reflecting them. The noise barrier consists of soundproof panels, foundations and posts and the soundproof panels with 10 different types of materials are used in a single or mixed form.In this paper, damage of soundproof panel shows a single or composite damage, and thus a evaluation model of deterioration has been developed for noise barriers that can reflect the characteristic of noise barriers. Materials used mainly for soundproof walls were divided into material types for metal, plastic, timber, transparent and concrete. And damage types for noise barrier were classified into corrosion, discoloration, deformation, spalling and dislocation and damage types were subdivided according to the noise barrier's components and materials. Damage rating was divided into good, minor, normal and severe for each major part of noise barrier to assess damage rating of soundproof panel, foundation and post. The deterioration degree of noise barrier was evaluated comprehensively by using the deterioration evaluation method of whole noise barrier using weighted average. Deterioration evaluation method that can be systematically assessed has been developed for noise barrier using single or mixed soundproof panel and noise barrier with single or complex damage types. Through such an evaluation system, it is deemed that the deterioration status of noise barrier installed can be systematically understood and utilized for efficient maintenance planning and implementation for repair and improvement of noise barriers.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• v.y2005m4
• /
• pp.31-34
• /
• 2005

Hygrothermal aging of the laminates of $Avimid^{R}$ K3B/IM7 in $80^{\circ}C$ water was studied as a function of immersion time prior to forming microcracks. The factors causing the $80^{\circ}C$ water to degradation of the laminates could be the degradation of the matrix toughness, change in residual stresses or interfacial damage between the fiber and matrix. The times to saturation in $80^{\circ}C$ water for the laminates and the neat resin are 100 hours and 500 hours. After 500 hours aging of the neat resin in $80^{\circ}C$ water, the glass transition temperature was changed less than $1\%$ by DSC test and the weight gain was $1.55\%$ increase. After 500 hours aging, the fracture toughness of the neat resin was decreased about $37\%$ by 3-point bending test. After 100 hours aging of the [+45/0/-45/90]s K3B/IM7 laminates in $80^{\circ}C$ water, the weight gain was $0.41\%$ increase. The $80^{\circ}C$ water diffusion rate into the neat resin was faster than into the laminates. In 100 hours, the loss of the microcracking toughness of the laminates was $28\%$ of the original toughness by our own microcracking fracture toughness criterion.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.35 no.5
• /
• pp.332-340
• /
• 2015

Acoustic emission (AE) is an effective nondestructive test that uses transient elastic wave generated by the rapid release of energy within a material to detect any further growth or expansion of existing defects. Over the past decades, because of environmental issues, the use of compressed natural gas (CNG) as an alternative fuel for vehicles is increasing because of environmental issues. For this reason, the importance and necessity of detecting defects on a CNG fuel tank has also come to the fore. The conventional AE method used for source location is highly affected by the wave speed on the structure, and this creates problems in inspecting a composite CNG fuel tank. Because the speed and dispersion characteristics of the wave are different according to direction of structure and laminated layers. In this study, both the conventional AE method and the energy based contour map method were used for source location. This new method based on pre-acquired D/B was used for overcoming the limitation of damage localization in a composite CNG fuel tank specimen which consists of a steel liner cylinder overwrapped by GFRP. From the experimental results, it is observed that the damage localization is determined with a small error at all tested points by using the energy based contour map method, while there were a number of mis-locations or large errors at many tested points by using the conventional AE method. Therefore, the energy based contour map method used in this work is more suitable technology for inspecting composite structures.