Volume Fraction Of Short Fibers Research Articles

Application of Embedded Element in the Short Fiber Reinforced Composite

The finite element analysis (FEA) is a numerical method for predicting the mechanical property of short fiber reinforced composite usefully. However, as we know, there is always a “jamming” limit when generating fiber architecture expecially in the cases of high volume fraction and high aspect ratio of short fiber. Even if the volume fraction and aspect ratio in finite element model meet the practical requirements, the problem of mesh deformity will always occur which would lead to unconverge of numerical computation. In this work, embedded element technique which will help to reduce the probability of the above two problems is employed to establish the finite element model of short fiber reinforced composite. The effect of edge size, thickness and mesh density of FE models on the elastic modulus were investigated. Numerical results show that the value of elastic modulus mainly depend on the edge size and fiber amount of FE model while the effect of thickness can be neglected. The elastic modulus takes to converge for high element number. An inverse method is proposed to calculate volume fraction of short fibers, by which numerical results agree well with the calculation results of empirical formula based on Halpin-Tsai equation.

Numerical simulation of the injection molding process of short fiber composites by an integrated particle approach

In this study, we propose an integrated particle approach based on the coupling of smoothed particle hydrodynamics (SPH) and discrete element method (DEM) to predict the injection molding process of discrete short fibers. The fibers in the coupled SPH-DEM model are treated as non-rigid bodies to allow deformation and fracture. The interaction between resin and fibers is solved by a physical model to take into consideration of drag forces. Two cases of injection molding process with different volume fractions of short fibers are studied to predict the flow behaviors of fibers and resin. The numerical results qualitatively agree with previous experimental studies. It is found that the velocity contour of resin flow is parabolic in shape due to the velocity gradient near the wall boundaries and consequently the moving direction of fibers is in parallel with the flow direction of resin. Fiber accumulation is found in the case with higher content of short fibers.

The Sources and Affecting Factors of Creep Threshold Stress of Magnesium-Based Composites

Tensile creep experiments were carried on AZ91D magnesium alloy and aluminum silicate short fiber-reinforced AZ91D magnesium matrix composite. The creep threshold stress of AZ91D composite depends on the Al atoms solute atmosphere, the bearing and transferring force of short fiber. Threshold stress decreases with temperature and increases with the short fiber volume fraction and the load transfer coefficient α, but the extent of increase drops with the amount of β-Mg17Al12 precipitation phase. The load transfer coefficient α characterizes the bearing and transferring capabilities of short fibers. As a result, the mathematical model of threshold stress in the magnesium matrix composite has been developed.

Effect of Fiber Volume Fraction on High Temperature Creep of Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub>(sf)/AZ91D Composite

Constant stress tensile creep tests were conducted on AZ91D–20 vol.%, 25 vol.%, and 30 vol.% Al2O3-SiO2short fiber composites and on an unreinforced AZ91D matrix alloy. The creep resistance of the reinforced materials is shown to be considerably improved compared with the matrix alloy. With the increasing volume fraction of short fibers, the creep resistance of AZ91D composites is improved, and their creep threshold stresses are also increased accordingly. Because of the increasing volume fraction of short fibers, loads of bearing and transmission of short fibers will increase, and thus the creep resistance of AZ91D composites further improves, but the precipitation of β-Mg17Al12precipitate increases in the number, it is easy to soften coarse, so that threshold stress of AZ91D composite does not increase greatly.

Short Fiber Reinforced Composite: The Effect of Fiber Length and Volume Fraction

The aim of this study was to determine the effect of short fiber volume fraction and fiber length on some mechanical properties of short fiber-reinforced composite (FRC). Test specimens (2 x 2 x 25 mm3) and (9.5 x 5.5 x 3 mm3) were made from short random FRC and prepared with different fiber volumes (0%-22%) and fiber lengths (1-6 mm). Control specimens did not contain fiber reinforcement. The test specimens (n=6) were either dry stored or thermocycled in water (x10.000, 5-55 degrees C) before loading (three-point bending test) according to ISO 10477 or statically loaded with a steel ball (Ø 3.0 mm) with a speed of 1.0 mm/min until fracture. A universal testing machine was used to determine the flexural properties and the load-bearing capacity. Data were analyzed using analysis of variance (ANOVA) (p=0.05) and a linear regression model. The highest flexural strength and fracture load values were registered for specimens with 22 vol% of fibers (330 MPa and 2308 N) and with 5 mm fiber length (281 MPa and 2222 N) in dry conditions. Mechanical properties of all test specimens decreased after thermocycling. ANOVA analysis revealed all factors were affected significantly on the mechanical properties (p<0.001). By increasing the volume fraction and length of short fibers up to 5 mm, which was the optimum length, the mechanical properties of short FRC were improved.

Fatigue Property and Fatigue Crack Propagation Behavior of Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;/A6061 MMCs at Room and Elevated Temperature

The rotating bending fatigue tests in high cycle region were carried out on alumina short fiber reinforced aluminum alloy composites (MMCs) at room and elevated temperatures of 200, 350, 400 and 450°C. The four kind of MMCs with 0%, 10%, 18% and 25% volume fraction were prepared in order to investigate the effects of alumina short fiber volume fraction on the fatigue property such as the fatigue strength, the crack initiation and propagation behaviors. As results, it was found that the fatigue strength at 107 cycles decreased with increase in the test temperature, but increased with an increase in alumina short fiber volume fraction at room and elevated temperatures. The crack initiation sites were large size alumina short fibers; some kind of cluster of short fibers and large size alumina particles (i.e. shots). And the crack growth paths were related to the distribution of the short fibers.

Ａｌ２Ｏ３／Ａ６０６１合金ＭＭＣの中高温疲労特性と疲労き裂進展特性

In order to investigate the effects of alumina short fiber volume fraction on the fatigue property at room and elevated temperature, the rotating bending fatigue tests were carried out on alumina short fiber reinforced aluminum alloy composites (MMCs). A6061 aluminum alloy and the three kinds of MMCs with 10%, 18% and 25% volume fraction were prepared and the five temperature conditions with room temperature, 200, 350, 400 and 450°C were performed. Fracture surface observation by FE-SEM of all specimens and surface crack observation using replication technique at room temperature and 200°C were performed.As results, the followings were found: The fatigue strength at 107 cycles increased with increase in alumina short fiber volume fraction at all test temperature conditions. Fatigue crack origins of all MMCs were large size alumina short fibers, some kinds of cluster of short fibers and large size alumina particles independently of the alumina short fiber volume fraction. The short fatigue crack of all MMCs propagated with avoiding the short fiber. But the da/dN-ΔK relation of all MMCs agreed with the A6061 one's. The effect on fatigue strength of short fiber compounding was more remarkable in the higher test temperature region.

K-0528 Al_2O_3/A6061合金の疲労き裂特性に及ぼすアルミナ短繊維体積含有率の影響(S04-4 非鉄金属の組織と疲労特性)(S04 金属材料の組織と疲労強度信頼性)

The effect of Al_2O_3 short fiber volume fraction on the fatigue crack initiation and growth of 6061 Al matrix composites was investigated. It was found that the fatigue strength at 10^7 cycles increased with an increase in volume fraction of short fibers. The surface replicas of the gage section of the specimen were taken throughout the fatigue tests to characterize the onset of crack initiation. As a result of the observation, the crack growth paths were related to the distribution of the short fibers. The cracks initiated at the part in which the short fibers were perpendicular to the compressive direction of manufacture. Moreover, the crack nucleation sites were also at the clusters of the fibers.