Evaluation Of Notched Tensile Strength Of CFRPEN Based On Linear Notch Mechanics

Abstract

Notched tensile strength of short carbon fiber reinforced plastics were characterized. The materials used are short carbon fiber reinforced polyethemitrile (CFRPEN), in which the short carbon-fibers were randomly combined in a PEN resin matrix with a fiber content of 15%, 30% and 40% (by weight). Tensile tests of a strip with double edge notches were carried out for a wide range of notch root radii and depths under the condition of constant specimen thickness. The results were discussed based on linear notch mechanics. The nominal stress for fracture in the sharply notched specimens having the same notch depth and the same minimum section is nearly constant independent of the value of notch root radius. This is due to the fact that in those specimens the stable crack growth can be recognized before final fracture. The fracture of CFRPEN specimen is controlled by the maximum elastic stress and the notch root radius alone, independent of the other geometrical conditions. INTRODUCTION Fiber reinforced plastics (FRP) are being used increasingly for engineering applications by reason of the higher specific strength and specific modulus. Especially short fiber reinforced plastics molded by injection mold are in high demand, because unnecessary of cutting work reduces the cost of components. To increase the demand further, it is important to investigate the fracture criteria and the prediction method of fracture strength in consideration of stress concentration for the requirement of reliability in the component. In this paper the notched tensile fracture criterion and the effect of fiber content on the notch sensitivity were discussed based on the linear notch mechanics, which was proposed by one of the authors [1]. Transactions on Engineering Sciences vol 6, © 1994 WIT Press, www.witpress.com, ISSN 1743-3533 514 Localized Damage MATERIALS AND EXPERIMENTAL PROCEDURE The materials used are carbon fiber reinforced polyethernitriles (CFRPEN) in which the short carbon-fibers having a diameter of 7//m and mean length of 100/zm were randomly combined in a PEN resin matrix. Fiber content is 15%, 30% and 40%. The mechanical properties of the materials used are tabulated in Table 1. Figure 1 shows the specimen configurations of CFRPEN. Tensile test of a strip with double edge notches were carried out for a wide range of notch root radii and two notch depths under the condition of constant specimen thickness. It was performed at room temperature under a constant cross-head speed of 0.5mm/min. The initiation and propagation processes of cracks were observed successively by the replication technique. The observations of fracture surfaces were also carried out by a scanning electron microscope. Table 1 : Mechanical properties of PEN and CFRPEN.