Ultrasonic Approach of Rayleigh Pitch-Catch Contact Ultrasound Waves on CFRP Laminated Composites

CFRP （carbon fiber reinforced plastics） composite materials have wide applicability because of their inherent design flexibility and improved material properties. However, impacted composite structures have 50%-75% less strength than undamaged structures. In this work, a CFRP composite material was nondestructively characterized in order to ensure product quality and structural integrity of CFRP and one-sided pitch-catch technique was developed to measure impacted-damaged area by using an automated-data acquisition system in an immersion tank. A pitch-catch signal was found to be more sensitive than normal incidence backwall echo of longitudinal wave under defect conditions in the composite.

Collapse behavior evaluation of hybrid thin-walled member by stacking condition

The recent trend of vehicle design aims at crash safety and environmentally-friendly aspect. For the crash safety aspect, the energy absorbing members should absorb collision energy sufficiently but for the environmentally-friendly aspect, the vehicle structure must be light weight in order to improve the fuel efficiency and reduce the tail gas emission. Therefore, the light weight of vehicle must be achieved in a securing safety status of crash. An aluminum or carbon fiber reinforced plastics (CFRP) is representative one of the light-weight materials. Based on the respective collapse behavior of aluminum and CFRP member, the collapse behavior of hybrid thin-walled member was evaluated. The hybrid members were manufactured by wrapping CFRP prepreg sheets outside the aluminum hollow members in the autoclave. Because the CFRP is an anisotropic material whose mechanical properties, such as strength and elasticity, change with its stacking condition, the effects of the stacking condition on the collapse behavior evaluation of the hybrid thin-walled member were tested. The collapse mode and energy absorption capability of the hybrid thin-walled member were analyzed with the change of the fiber orientation angle and interface number.

ULTRASONIC INFLUENCE OF POROSITY LEVEL ON CFRP COMPOSITE LAMINATES USING RAYLEIGH PROBE WAVES

It was found that a pitch-catch signal was more sensitive than normal incidence backwall echo of longitudinal wave to subtle flaw conditions in the composites （damages, fiber orientation, low level porosity, ply waviness, and cracks）. Both the strength and stiffness depend on the fiber orientation and porosity volume in the composites. The porosity content of a composite structure is critical to the strength and performance of the structure in general. The depth of the sampling volume where the pitch-catch signal came from was relatively shallow with the head- to-head miniature Rayleigh probes, but the depth can be increased by increasing the separation distance of the transmitting and receiving probes. Also, a method was utilized to determine the porosity content of a composite lay-up by processing micrograph images of the laminate. A free software package was utilized to process micrograph images of the test sample. The results from the image processing method were compared with existing data. Beam profile was characterized in unidirectional CFRP（carbon fiber reinforced plastics） using pitch-catch Rayleigh probes and the one-sided pitch-catch technique was utilized to produce C-scan images with the aid of the automatic scanner.

Crushing behavior of lightmass structural member

Carbon fiber reinforced plastic (CFRP) of the advanced composite materials is widely used in lightmass structural materials of air planes, ship and automobiles because of high strength and stiffness. In this study, experimental investigation was performed for each specimen. The square section members consist of aluminum, CFRP and hybrid (aluminum/CFRP) member, and hat-shaped section members consist of CFRP and hybrid (aluminum/CFRP) members specimen. Based on the collapse characteristics of aluminum square section member, the collapse characteristics and energy absorption capability of hat-shaped section members were analyzed. The axial static collapse tests were carried out for each section member. The collapse modes and the energy absorption capability of the members were analyzed. In the lightmass design aspect, the collapse characteristics and energy absorption capability of the members were compared.

ENERGY ABSORPTION CONTROL CHARACTERISTICS OF AL THIN-WALLED TUBES UNDER IMPACT LOAD

An experimental investigation was carried out to study the energy absorption characteristics of thin-walled square tubes subjected to dynamic crushing by impact loading to develop the optimum structural members. Here, the controller is introduced to improve and control the absorbed energy of thin-walled square tubes in this paper. When the controller were used, the experimental results of crushing of square tubes controlled by the controller＇s elements showed a good candidate for a controllable energy absorption capability in impact crushing.