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A hybrid composite train carbody with length of 23m was developed. Static, fatigue and fire resistance tests were conducted to evaluate the structural and fire safety. We have achieved approximately 40% weight saving by application of the sandwich composite structure instead of aluminum. In addition, the manufacturing process of 50% was reduced by manufacturing the bodyshell as a one body.
(Published on May 2008 – JEC Magazine #40)
DR. JUNG-SEOK KIM SENIOR RESEARCHER ADVANCEDMATERIAL TILTING TRAIN SYSTEM RESEARCH CENTER KOREA RAILROAD RESEARCH INSTITUTE
The Korea Railroad Research Institute (KRRI) and Hankuk Fiber Glass Company have developed Korean tilting train with maximum design speed of 200km/h (figure 1). The objective of the train is to increase speed of conventional lines where are high percentage of curves.
The carbody of it has been developed using a hybrid design concept combined with a sandwich composite structure for bodyshell and a stainless steel structure for the underframe to match the challenging demands with respect to cost efficient lightweight design for railway carriage structures.
The sandwich composite structure was used to minimize the weight, while the steel underframe was used for the easy installation of the electrical equipment and design modification.
The tilting train employed the composite sandwich structure because the sandwich structure offers many advantages over more traditional stiffened skin structures. The sandwich structure can be made sufficiently stiff without the need for additional stiffeners. This reduces the number of parts required, simplifies assembly, and usually offers a more lightweight design. The carbody structure consists of a bodyshell made of aluminum honeycomb sandwich structure with CF1263 woven fabric carbon/epoxy face, inner reinforced frames made of mild steel and an underframe structure made of stainless steel.
The composite carbody structure was 23 meters long, 3 meters wide and 2.7 meters high, and cured as one body in large autoclave equipment with length of 30 meters and diameter of 5 meters. Figure 2 shows the carbody structure with the aluminum honeycomb core and the woven fabric carbon/epoxy face. The thickness of the aluminum honeycomb core is 40mm and the thickness of the inner face and outer face are 1.5mm and 3.5mm, respectively. The carbon/epoxy face and the aluminum honeycomb core were bonded using BONDEX®606 adhesive film.
The carbody has been manufactured using large autoclave equipment. It has the length of 30 meters and the diameter of 5 meters (figure 3). Operating temperature is in a range of room temperature ~ 180°C, and maximum pressure level is 7bar. The autoclave curing method was selected because complex shapes including double contours and relatively large parts can be readily handled and manufactured as one body. We have achieved approximately 40% weight saving by application of the sandwich composite structure instead of aluminum. In addition, the manufacturing process of 50% was reduced by manufacturing the bodyshell as a one body.
Performance tests: static tests
The static tests such as vertical load test, end compressive load test, torsional test and 3-point support test were conducted for evaluation of structural safety and behavior (figure 4). By these tests, stress distribution and location of maximum stress point were investigated for these load cases. In addition, maximum deflection and equivalent bending stiffness of the composite carbody were measured and calculated as Table 1. From the test results, the stiffness of the composite carbody met the specified design requirement.
In order to evaluate fatigue strength of the composite carbody, it was excited by two 50-ton capacity hydraulic actuators installed under the body bolster. The excitation frequency was determined by natural frequency evaluation test under full weight condition and was 5 Hz. The fatigue test was conducted for 3x106cycles. During the fatigue test, the nondestructive tests using X-ray (figure 5) and liquid penetrant was performed to evaluate the fatigue cracks. From the test, there were no fatigue cracks.
Fire resistance test
Fire resistance test of the carbody using a large scale mock-up were performed to evaluate the fire safety of the composite train carbody. The fire test was conducted under the real fire accident scenario based on the Daegu subway accident. In the accident, an arsonist poured thinner of 4 litters onto the floor and seat, and then lit. In this test, several sheets of paper were placed on the floor and seats and then, the flammable liquid of 4 litters were poured on the floor (2 litters) and seats (0.5 litters for each seat set) uniformly. The temperature on surface and inside of the body was measured using thermocouple of twenty four.
Figure 6 shows the fire test result for the composite carbody installed the interior parts. In this case, the flame was strongest between 20 seconds and 40 seconds after ignition. The flame started to sink down after 40 seconds and it was extinguished naturally after 290 seconds.
From the results, the maximum surface temperature of the interior and the composite carbody were 156.3°C and 307.2°C, respectively. These values were lower than the ignition temperature of them. Therefore, it could be ensured that the composite carbody has fire resistance under the severe test scenario.
Main line tests
The tilting train with the hybrid composite train carbody launched the main line test on conventional lines at 4 April 2007. The mileage of it was twenty thousand kilometers at the end of 2007. In the tests, reliability and safety of the train have been evaluated.
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