Investigation of Biaxial Properties of CFRP with the Novel-Designed Cruciform Specimens

Abstract

The biaxial loading properties of carbon-fiber-reinforced polymer (CFRP) are critical for evaluating the performance of composite structures under the complex stress state. There are currently no standardized specimens for the CFRP biaxial experiments. This work developed a new design criterion for the cruciform specimen coupled with the Hashin criterion. The finite element analysis was conducted to investigate the effect of geometric parameters on the stress distribution in the test area. The embedded continuous laying method (ECLM) was proposed to achieve the thinning of the center of the test region without introducing defects. The manufacturing quality of the cruciform specimens was verified by the ultrasonic C-scanning test. The biaxial test platform consisting of the biaxial loading system, digital image correlation (DIC) system, strain electrical measurement system, and acoustic emission detection system was constructed. The biaxial tensile tests under different biaxial loading ratios were conducted. The results showed that the biaxial failure efficiently occurred in the test area of the cruciform specimens designed and manufactured in this paper. The failure modes and morphology were characterized using macro/microscopic experimental techniques. The biaxial failure envelope was obtained. The results can be used to guide the design of composite structures under biaxial stress.

Fracture Behavior of a Unidirectional Carbon Fiber-Reinforced Plastic under Biaxial Tensile Loads

“…A cruciform specimen has been used for T-T loading tests on such laminates as cross-ply and angle-ply [ 26 , 27 , 28 , 29 , 30 ]. The present study applies this specimen to a unidirectional CFRP.…”

“…The present study applies this specimen to a unidirectional CFRP. According to these papers [ 26 , 27 , 28 , 29 , 30 ], conventional cruciform specimen shapes have a circular or square indentation referred to as ‘gauge area’ in the center. The authors also attempted to make this indentation and to fracture it at the center where the biaxial tensile load occurs, but it often broke prematurely at the arm.…”

“…Preceding fracture due to transverse crack Cruciform specimens are often used to determine the mechanical properties of CFRPs under biaxial tensile loading. However, most of the papers have been conducted on CFRP laminates, such as cross-ply and angle-ply [26][27][28][29][30], and there are few papers that apply the cruciform specimens to unidirectional CFRPs. The only reported paper is the case where the specimen was tensile-loaded from two transverse directions perpendicular to the fiber axis [31].…”