Anisotropic Thermal Diffusivity Measurements in High-Thermal-Conductive Carbon-Fiber-Reinforced Plastic Composites

This paper presents the temperature dependence of in-plane thermal diffusivity and anisotropy distribution for pitch-based carbon-fiber-reinforced polymers (CFRPs). The measurement was performed using the laser-spot periodic heating method. The samples were unidirectional (UD) and crossply (CP) CFRPs. All carbon fibers of the UD samples ran in one direction, while those of the CP samples ran in two directions. In both UD and CP CFRPs, from -80°C to +80°C, temperature dependence of thermal diffusivity values increased as temperature decreased. In this temperature range, the anisotropic ratio between the fiber direction and its perpendicular direction of the UD CFRP was 106 - 124. During the anisotropy distribution measurement, it was found that thermal anisotropy can be visualized by scanning the laser in a circle on the sample. The thermal diffusivity of the UD CFRP in the fiber direction was 17 times larger than that in the 15°direction, and the thermal diffusivity in the other directions was lower than that in the 15°direction. The anisotropy distribution for the CP CFRP reflected its inhomogeneous structure.

Achieving superior mechanical properties in friction lap joints of copper to carbon-fiber-reinforced plastic by tool offsetting

It is a challenge to achieve a sound welded metal/carbon-fiber-reinforced thermoplastic（CFRTP） joint with high strength and few bubbles. In this study, sound lap joints of Cu and CFRTP were obtained by friction lap joining（FLJ） directly at rotation rates of 600-2000 rpm, with the welding tool at the joint center and offsetting the tool 7 mm away from the center toward the retreating side, respectively. Tool offsetting reduced the non-uniform temperature distribution in the lap joints resulting from the high conductivity of Cu, which not only enhanced the tensile shear force from 0.89-2.25 kN to 1.71-3.54 kN,with the maximum increasing rate of 135%, but also reduced the bubble area to only 19% of the original level of 2000 rpm. It is the first time to report a high-quality Cu/CFRTP joint with a high strength and few bubbles. The large increase of the strength after tool offsetting was attributed to the increase of the joining area, the decrease of bubbles and the decrease of the CFRTP degradation. The details on the generation,quantitative distribution and expulsion of the bubbles in the FLJ joints were discussed.

Dynamic Biaxial Compression of CFRP Laminates Using Electromagnetic Loading

The dynamic biaxial compression test for carbon-fiber-reinforced polymer(CFRP)laminates was carried out via synchronous electromagnetic loading in this study.During the experiments,four stress pulses transmitted along four incident bars,loading the square specimen simultaneously from four directions to keep the center of the specimen still.The dynamic mechanical behavior of CFRP was obtained employing the one-dimensional wave propagation theory,and the deformation and failure processes of the specimens were recorded by a high-speed camera.The effects of various biaxial stresses on the compressive strength were investigated in three biaxial and one uniaxial loading cases.For the CFRP laminates,the dynamic transverse compressive stress showed little effect on the longitudinal ultimate compressive strength.Numerical simulations were performed to understand the dynamic stress wave propagation.It showed that the employed loading device could guarantee good biaxial loading conditions until the ultimate failure of the specimens.This approach allows for the dynamic biaxial compression testing of various materials,which is of great significance in evaluating the dynamic impact performance of aeronautical composites.