The fiber-reinforced composite materials have been advanced for various applications because of their excellent mechanical and electromagnetic properties. On their manufacturing processes, however, thermo-curing inherently produces the undesired thermal deformation mainly from temperature drop from the process temperature to the room temperature, so called spring-back. The spring-back must be understood especially in the hybrid composites in order to design and fabricate desired shape. In this research, (glass fiber / epoxy) + (carbon fiber / epoxy) unsymmetric hybrid composites were fabricated under various conditions such as cure cycle, laminate thickness, stacking sequence and curing sequence. Coupons were made and spring-back were measured using coordinate measuring machine (CMM). Using the Classical Lamination Theory (CLT) and finite element analysis (ANSYS), the behavior of spring-back were predicted and compared with the experimental data. The results from CLT and FEA agreed well with the experimental data. Although, the spring-back could be reduced by lowering curing temperature, at any case, the spring-back could not be removed completely.

With the wide applications of fiber-reinforced composite material in aero-structures and mechanical parts, the design of composite joints have become a very important research area because the joints are often the weakest areas in composite structures. This paper presents an analytical study of the stress distributions in mechanically single-fastened and multi-fastened composite laminates. The finite element models which treat the pin and hole contact problem using a contact stress analysis are described. A dimensionless stress concentration factor is used to compare the stress distributions in composite laminates quantitatively In the case of single-pin loaded composite laminate, the effects of stacking sequence, the ratio of a hole diameter and the width of a laminate (W/D ratio), the ratio of hole diameter and distance from edge to hole (E/D ratio), friction coefficient and clamping force are considered. In the case of multi-pin loaded composite laminate, the influence of the number of pins, pitch distance, number of rows, row spacing and hole pattern are considered. The results show that P/D ratio and E/D ratio affect more on stress distributions near the hole boundary than the other factors. In the case of multi-pin loaded composite laminate, the stress concentration in the double column case is better than the other cases of multi-pin loaded composite laminate.

This paper has performed an experimental study on the hybrid composite carbody of Korean tilting railway vehicle. The hybrid composite carbody has the length of 23m and is comprised of a 40mm-thick aluminium honeycomb core and 2mm-thick woven fabric carbon/epoxy face sheet. In order to evaluate the structural behavior and safety of the hybrid composite carbody, the static load tests such as vertical load, end compressive load, torsional load and 3-point support load tests have been conducted. The test was performed under Japanese Industrial Standard (JIS) 17105 standard. from the tests, the maximum deflection was 12.3mm and the equivalent bending stiffness of the carbody was . The maximum strain of the composite body was below of failure strain of the carbon/epoxy face sheet.

The mechanical properties of composite materials may severely degrade 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 considerable 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 PVDF(polyvinylidene fluoride) film sensors were used for monitoring high-velocity 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 shows how various sensing techniques, PVDF sensor in particular, can be used to characterize high-velocity impact damage in advanced composite.

In this study, we analyzed the relation between physical/mechanical properties and ballistic properties for several engineering ceramics that were expected to use as armor material. After physical/mechanical measurement, we measured ballistic properties about KE(Kinetic Energy, L/D=10.7, tungsten heavy alloy) and HEAT(High Explosive Anti-Tank, K215) projectiles. Increasing Young's modulus/density, hardness/density and flexural strength/density ratios, ballistic properties were generally increased. Especially it appeared that the ballistic property about KE projectile was lineally increased, as HEL/density ratio increased.

In this study, we tried to invent ceramic armor material with brilliant ballistic properties by the silica of the high compression-expansion ratio and based on alumina that has the most economical and higher ballistic efficiency. After we choose three compositions, proper sintering temperature for each composition was decided. After physical/mechanical measurement, we measured ballistic properties about KE(Kinetic Energy, L/D=10.7, tungsten heavy alloy) and HEAT(High Explosive Anti-Tank, K215) projectiles. As a result, of three compositions had the highest ballistic efficiency md better properties than alumina.

In this study, to improve the ballistic efficiency of very brilliant alumina-silica armor material, forming press and sintering temperature were changed. After physical/mechanical measurement, we measured ballistic properties about KE(Kinetic Energy, L/D=10.7, tungsten heavy alloy) and HEAT(High Explosive Anti-Tank, K215) projectiles and analyzed them. As a result, in , it appeared the highest ballistic efficiency about HEAT and it improved ballistic efficiency, better than invented alumina-silica armor material before.