Aluminum or CFRP (Carbon Fiber Reinforced Plastics) tube subjected to axial loading sustains load, and absorbs energy during axial collapse. The aluminum tube absorbs energy by stable plastic deformation, while the CFRP tube with higher specific strength and stiffness than those of the aluminum tube absorbs energy by unstable brittle failure. To achieve a synergy effect by combining the two members, aluminum/CFRP compound tubes were manufactured, which are composed of aluminum tubes wrapped with CFRP outside aluminum tubes with different fiber orientation angle of CFRP and number of plies. The axial quasi-static collapse tests were performed for the tubes. The collapse characteristics of the tubes were compared with those of respective aluminum tube and CFRP circular tube. Test results showed that the collapse of the aluminum/CFRP tubes complemented unstable brittle failure of the CFRP tube due to the ductile characteristics of the inner aluminum tube. The collapse modes and the absorbed energy were influenced by the fiber orientation angle of CFRP and the number of plies. The absorbed energy per unit mass, which is in the light-weigh aspect, was higher in the aluminum/CFRP compound tube than in the aluminum tube or the CFRP tube alone.
Since layup orientation of the laminates greatly influences its properties, an NDE technique for layup orientation determination would be very beneficial. It is desirable to perform contact-less nondestructive evaluation to assess material properties and defects of composites because of permeation of coupling medium such as water. An ultrasonic technique would be very useful, which could be used to test the part after and before curing laminates and requires less time than the optical test. First of all, conventional ultrasonic experimentations were conducted using water as a transmitting medium. In contrast, air-coupled ultrasound is non-contact and has clear advantages over water-coupled testing. Therefore ultrasonic systems for air-coupled and conventional ultrasound were set out for different measurement modalities for acquiring ultrasonic signals as a function of in-plane azimuthal angle. Firstly, a manual scanner was built for making transmission measurements using a pair of normal-incidence shear wave transducers to find the effect of fiber misorientations of orthotropic composite laminates. With the transmitter and receiver on the same side of a laminates, Lamb waves were generated and used for the amplitude magnitude. As a result, it was confirmed that the influence of fiber direction in the laminates could be detected by the non-contacting or contacting inspection from one-side and the detectability was improved by using shaped tube for reducing the specular reflection on transmitting. Furthermore, a vector decomposition model was utilized for lay-up error of the orthotropic laminates. Finally, aircoupled results well corresponded somewhat to those of contact ultrasonic examination in the orthotropic laminates.
Currently, stacking condition related to the energy absorption of composite materials is being considered as an issue for the structural efficiency and safety of automobiles, aerospace vehicles, trains, ships even elevators during collision. In particular, CFRP (carbon fiber reinforced plastics) composite materials have found wide applicability because of their inherent design flexibility and improved material properties. The most important objective in designing automobiles is currently to focus on environment-friendly aspect and safety performance aspect. Therefore, the designing automobile should be more concerned on the aspect of securing safety performance, but at the same time, it also should consider reducing weight of automobile structural member. In this study, CFRP (Carbon Fiber Reinforced Plastics) side members with single-hat-section shaped were manufactured. The axial static collapse tests were performed for the members using universal testing machine, and the collapse mode and energy absorption characteristics were analyzed according to stacking condition such as fiber orientation angle and shape of the section.
Because the layup of composite laminates influences there properties, the strength of composites depends on layup sequence of CFRP laminates. They could result in the part being rejected and discarded if the layup orientation of a ply is misaligned. A nondestructive technique would be very beneficial, which could be used to test the part after curing and requires less time than the optical test. Scanners were set out for different measurement modalities for acquiring ultrasonic signals as a function of in-plane azimuthal angle. The first motorized scanner was built for making transmission measurements using a pair of normal-incidence shear wave transducers. A scanner was built for the acousto-ultrasonic configuration using contact transducers. And a ply-byply vector decomposition model has been developed, simplified, and implemented for composite laminates fabricated from unidirectional plies. We have compared the test results with model data. It is found that high probability shows between tests and the model developed in characterizing cured layups of the laminates.
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