No abstract

This study proposes a numerical analysis for predicting fiber motion during injection molding of short-fiber-reinforced composites using the moving particle semi-implicit (MPS) method. Its meshless and Lagrangian nature enables us to track individual fibers and to easily represent free surfaces. In this study, the mechanism of fiber orientation in a T-shaped bifurcation was investigated experimentally and numerically. The fiber orientation of injection-molded glass-fiber/polypropylene composite was observed by X-ray CT. Despite the symmetric mold shape, there was asymmetric fiber orientation due to the mold filling process.Fiber motion in the bifurcation was then analyzed by the proposed simulation, and the fiber orientation was quantitatively evaluated in each small region. The prediction agreed well with the experiment, and the associated mechanism of fiber orientation is discussed. Furthermore, this approach explicitly demonstrates the interaction between fibers, which is an advantage of the proposed approach.

Tension‐tension cyclic‐fatigue tests of a two‐dimensional‐woven‐SiC‐fiber‐SiC‐matrix composite (SiC/SiC) prepared by chemical vapor infiltration (CVI) were conducted in air at room temperature and in argon at 1000°C. The cyclic‐fatigue limit (107 cycles) at room temperature was ∼160 MPa, which was ∼80% of the monotonic tensile strength of the composite. However, the fatigue limit at 1000°C was only 75 MPa, which was 30% of the tensile strength of the composite. No difference was observed in cyclic‐fatigue life at room temperature and at 1000°C at stresses >180 MPa; however, cyclic‐fatigue life decreased at 1000°C at stresses < 180 MPa. The fracture mode changed from fracture in 0° and 90° bundles at high stresses to fracture mainly in 0° bundles at low stresses. Fiber‐pullout length at 1000°C was longer than that at room temperature, and, in cyclic fatigue, it was longer than that in monotonic tension. The decrease in the fatigue limit at 1000°C was concluded to be possibly attributed to creep of fibers and the reduction of the sliding resistance of the interface between the matrix and the fibers.