Effects of Radial-Orientation-Die Structure Parameters on Properties of Short Fiber and Rubber Composite Material

The radial-orientation-die has special structure to make short fibers get radial orientation in rubber matrix during extrusion process,which means the physical and mechanical properties of short fiber and rubber composite material will be influenced by the die different structures. The effects of radial-orientation-die structure parameters on properties of short fiber and rubber composite were studied experimentally by different structure parameters, including expansion ratio, expansion angle, dam clearance, molding channel length, convergence angle, and transition channel length. The experimental results indicated that short fiber and rubber composite could get good properties with optimized radial-orientation-die structure parameter. And the optimized structure parameters are that expansion ratio is about 5with an expansion angle of 150°,dam clearance is about 4 mm,molding channel length is about 50 mm,convergence angle is about120°,and transition channel length is about 30 mm. Accordingly,the physical and mechanical properties of the composite can be remarkably improved,which give an obvious anisotropy.

Hybrid Composite Based on Natural Rubber Reinforced with Short Fibers of the Triumfetta cordifolia/Saccharum officinarum L.: Performance Evaluation

This article contributes to the development of the new class of fully biodegradable “green” composites by combining fibers (natural/bio) with biodegradable resin. The vegetable fibers (Triumfetta cordifolia and sugarcane bagasse) treated with NaOH and bleached were incorporated into a natural rubber matrix. The influence of the fiber ratio on the physical properties, tensile strength and surface hardness of the hybrid composites was analyzed. The results show that the addition of fibers in the natural rubber matrix increases the water absorption capacity but gradually reduces it with increasing fiber ratio. The hybrid composites of the NRT50-50B proportions show the best tensile strengths at 20 phr and a shore A hardness of 43.7 at 30 phr. The combination of two fibers has improved the physical and mechanical properties of the hybrid composites which can be used in engineering applications.

Aging behavior of Al_2O_3 short fiber reinforced Al-Cu alloy composites

Al2O3 short fiber reinforced Al-Cu composites containing 1%, 3%, 5% and 7% Cu were fabricated by a squeeze casting technique. The as-cast Al2O3/Al-Cu composites were solution treated at 535 ℃ and then aged at 170, 190 and 210 ℃, respectively. Age hardening behavior of the Al2O3/Al-Cu composites was analyzed by measuring the hardness of the samples at different aging temperatures and aging time. Microstructures of the composites were observed by transmission electron microscope(TEM). The results indicate that the hardness of the Al2O3/Al-Cu composites containing 7% Cu is much higher than that containing 1%-5% Cu because of the large amount of CuAl2 precipitant in the Al2O3/Al-Cu composite. With the increase of Cu content from 1% to 7%, the time needed for the appearance of peak hardness shortened, indicating that the addition of Cu can accelerate the kinetic of CuAl2 precipitation in the Al2O3/Al-Cu composites. The Al2O3/Al-Cu composite containing 7% Cu shows the highest increment of hardness by aging treatment. Therefore, in order to get a higher peak hardness, the Al2O3/Al-Cu composites need more Cu addition as compared with the un-reinforced Al-Cu alloys.

An Application of the Modified Shear Lag Model to Study the Influence of Thermal Residual Stresses on the Stiffness and Yield Strength of Short Fiber Reinforced Metal Matrix Composites

The modified shear lag model proposed recently was applied to calculate thermal residual stresses and subsequent stress distributions under tensile and compressive loadings. The expressions for the elastic moduli and the yield strengths under tensile and compressive loadings were derived which take account of thermal residual stresses. The asymmetries in the elastic modulus and the yield strength were interpreted using the derived expressions and the obtained results of the stress calculations. The model predictions have exhibited good agreements with the experimental results and also with the other theoretical predictions

Effects of Matrix Features on Stress Transfer of Short Fiber Composites

By employing the elastic and elastic plastic finite element method(FEM), the effects of matrix feature on the stress transfer mechanisms of short fiber composites are studied. In the calculation, the variations in matrix modulus, yield strength and hardening modulus are considered. It is concluded that large deformation of matrix is harmful to the improvement of the mechanical performances of the composites.

TENSILE STRENGTH OF RANDOM ORIENTED SHORT FIBER COMPOSITE

This paper shows a calculation model and a method for predicting the tensile strength of the random distributed short fiber composite.On the basis of Renjie Mao's model,the longitudinal tensile strength of the aligned short fiber composite is formulated.Considering the transverse tensile strength and in plane shear strength of the unidirectional fiber composite,and the stress transformation relations of two couples of axes,the stress of the unidirectional fiber composite when it is loaded at an arbitrary angle is obtained.With the aid of an equivalence relation,the calculation formulation of the tensile strength of the random short fiber reinforced composite is deduced.

A New Modification to Shear Lag Model as Applied to Stiffness and Yield Strength of Short Fiber Reinforced Metal Matrix Composites

A new modification for the shear lag model is given and the expressions for the stiffness and yield Strength of short fiber metal matri×composite are derived. These expressions are then compared with our experimental data in a SiCw/Al-Li T6 composite and the published experimental data on different SiCw/Al T6 composites and also compared with the previous shear lag models and the other theoretical models.

SOLIDIFYING STRUCTURES OF Al_2O_3 SHORT FIBER／Al－Si ALLOY MATRIX COMPOSITE PREPARED BY SQUEEZE CASTING

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Solidification microstructures in a short fiber reinforced alloy composite containing different fiber fractions

The solidification microstructures and micro-segregation of a fiber reinforced Al-9 Cu alloy, containing different volume fractions of Al2O3 short fibers about 6μm diameter and made by squeeze casting have been studied. The results indicate that as volume fraction of fiber Vf. increases, the size of final grains becomes finer in the matrix. If λf 〉λ〉1, the fibers have almost no influence on the solidification behavior of the matrix, so the final grains grow coarse, where λf is the average inter-fiber spacing and A is the secondary dendrite arm spacing. While if λf/ 〈λ〈1, the growth of crystals in the matrix is affected significantly by the fibers and the grain size is reduced to the value of the inter-fiber spacing. The fibers influence the average length of a solidification volume element L of the matrix and also influence the solidification time 8, of the matrix. As a result of fibers influencing L and θl, the micro-segregation in the matrix is improved when the composite contains more fibers, although the level of the improvement is slight. The Clyne-Kurz model can be used to semi-quantitatively analyze the relationship between Vf and the volume fraction .fe of the micro-segregation eutectic structure.

STRAIN REGULARITY IN REINFORCERS OF SHORT-FIBER/ WHISKER REINFORCED COMPOSITE AND ITS APPLICATION

Based on the study of strain distribution in short-fiber/whisker reinforced metal matrix composites, a deformation characteristic parameter λ is defined as the ratio of the root-mean-square strain of reinforcers to the macro-linear strain along the same direction. Quantitative relation between λ and microstructure parameters of the composite is obtained. As an example of applying and verifying λ, the stress-strain curve of ［AlBO］w/Al composite under tensile loading is predicted and favorably compared with experiments. By using λ, the stiffness modulus of the composite with arbitrary reinforcer orientation under any loading condition is predicted from the microstructure parameters of material.

Silicon-Basing Ceramizable Composites Containing Long Fibers

Ceramization is a phenomenon which assures compactness of polymer-based composites in the case of their thermal degradation caused by open fire or exposure at high temperatures. This phenomenon is based on preventing volatiles of thermal decomposition of silicone rubber from evacuation by creation of ceramic layer. This ceramized structure is composed of mineral filer particles, connected by fluxing agent—glassy phase. The ceramic barrier created during firing is aimed to protect copper wire inside the cable from melting, being additionally strong enough to maintain integrity of electrical circuit. The paper presents experimental data on mechanical properties of silicone rubber composites strengthened additionally with long fibers of different types—aluminosilicate and polyamide (Kevlar) ones. Fibers were introduced into composites in oriented way. Mechanical properties were investigated taking into account fiber orientation anisotropy. Ceramization process of composites was described by observation of morphology and strengthen measurements of samples fired at 1000°C.

Sawdust Short Fiber Reinforced Epoxidized Natural Rubber: Insight on Its Mechanical, Physical, and Thermal Aspects

In this work,Epoxidized natural rubber/sawdust short fiber(ENR-50/SD)composites at different fiber content(5,10,15 and 20 phr)and size(fine size at 60–100μm and coarse size at 10–20 mm)were prepared using two-roll mill and electrical-hydraulic hot press machine respectively.Curing characteristics,water uptake,tensile,morphological,physical,and thermal properties of the composites were investigated.Results indicated that the scorch time and cure time became shorter whereas torque improved as SD content increase.Though the decline of tensile strength and elongation at break values,modulus,hardness and crosslinking density have shown enhancements with the increasing of SD content.The water uptake percentage of all samples has shown an increasing as SD content increase.However,the low SD content,particularly fine size have presented lower water uptake.The temperature of weight%loss(5 and 50 wt%loss)of 5 phr SD(low content)have recorded higher temperature compared to 20 phr SD(high content)in the rubber composites,which indicated higher thermal stability.The fine size of SD has recorded better overall properties than SD coarse size at same loading in the rubber composites.

Effect of Al2O3sf addition on the friction and wear properties of (SiCp+Al2O3sf)/Al2024 composites fabricated by pressure infiltration

Aluminum(Al) 2024 matrix composites reinforced with alumina short fibers(Al_2O_(3sf)) and silicon carbide particles(SiC_p) as wear-resistant materials were prepared by pressure infiltration in this study. Further, the effect of Al_2O_(3sf) on the friction and wear properties of the as-synthesized composites was systematically investigated, and the relationship between volume fraction and wear mechanism was discussed. The results showed that the addition of Al_2O_(3sf), characterized by the ratio of Al_2O_(3sf) to SiC_p, significantly affected the properties of the composites and resulted in changes in wear mechanisms. When the volume ratio of Al_2O_(3sf) to SiC_p was increased from 0 to 1, the rate of wear mass loss(K_m) and coefficients of friction(COFs) of the composites decreased, and the wear mechanisms were abrasive wear and furrow wear. When the volume ratio was increased from 1 to 3, the COF decreased continuously; however, the K_m increased rapidly and the wear mechanism became adhesive wear.

Distribution and segregation of solute in Al_2O_3 short fiber reinforced Al-5%Cu alloy containing La by squeeze casting

Al2O3 short fiber reinforced La-bearing Al-5%Cu alloy was fabricated by squeeze casting, and the solidified structure and the solute segregation during alloy solidification were studied. The results indicated that La has been enriched near the interface which is favorable to improve the wettability between the fiber and At alloy, but the RE-rich phase was not formed at the interface. At the end of the solidification of the composites, the change of the solute in the surplus liquid phase results in the type of matrix alloy being changed because of the selective crystallization, and the segregation at the interface is finally formed. There is no special influence by La on the Cu segregation in the matrix alloy.

Fabrication of Short Carbon Fiber Reinforced AZ91D Alloy by Infiltration-Extrusion Integrated Technique

Short carbon fiber reinforced AZ91D alloy (Csf/AZ91D) was fabricated by the infiltration-extrusion method. The short carbon fiber preform was infiltrated with melted AZ91D alloy under the assistant of gas pressure. The extrusion processing was applied following the infiltration processing directly. The tensile property and microstructure of the Csf/AZ91D and that of the die-casting and extruded AZ91D alloy was compared. The results show that the short carbon fiber reinforced AZ91D alloy present excellent tensile property. The tensile strength and modulus of elasticity of Csf/AZ91D is about 50% and 18% higher than that of cast AZ91D alloy, respectively. The elongation to fracture of Csf/AZ91D is about 50% lower than that of AZ91D alloy.

Micro-yield behaviors of Al_2O_3-SiO_(2(sf))/Al-Si metal matrix composites

Effects of the volume fraction and the size of crystallized alumina silicate short fibers as well as heat treatment processes on micro-yield strength(MYS) of Al2O3-SiO2(sf)/Al-Si metal matrix composite(MMC) that was fabricated by squeezing cast, were investigated by using continuous loading method on an Instron 5569 tester with a special extensometer with an accuracy of 10?7. The results show that MYS of MMC decreases with the increase of volume fraction and length of the alumina silicate short fibers in the metal matrix composite, respectively. MYS of quenched Al2O3-SiO2(sf)/Al-Si MMC is the lowest, MYS of the MMC through peak-aging treatment is higher than that through other heat treatment methods. And before the peak-aging, MYS of MMC aging treated gradually increases with the increase of the aging time. Aging treatment after solution treatment is a preferred way that enhances micro and macro-yield strength of Al2O3-SiO2(sf)/Al-Si MMC.

THE FRACTURE CHARACTERISTICS OF δ-Al_2O_3/AlALLOY COMPOSITES

The initial location of the crack and the controlling factor of the fracture in the squeeze casting composites δ-Al2 O3/Al-5.5Zn, δ-Al2 O3/Al-5.5Mg and δ-Al2 O3/Al-cSi were studied by microscopic observation and finite element analysis(FEA). The in situ failure processes were obseroed bU the scanning electronic microscope mp. The distributions of stress components along the fiber length in matta, and the tnean axial stresses of fiber and matrix were calculated by three-dimensional elasto-plastic FEA.It is found that the failure modes of short fiber reiwtreed metal matrix composites change with the variations of the micro-structurnl characteristics of composites, such as fiber orientation, matrix strength and intedecial bonding, etc.

Preparation and microwave dielectric properties of C_(sf)/Si_3N_4 composites

The Csf/Si3N4 composites were prepared by hot-press sintering method using α-Si3N4 power,short carbon fibers and La2O3-Y2O3 sintering additives. The mechanical and microwave dielectric properties of Csf/Si3N4 composites were studied and discussed. The results show that the addition of the short carbon fibers can not destroy the relative density of the sintered samples,but it deteriorates the flexural strength of the sintered samples,so the flexural strength of the silicon nitride matrix is the highest among the samples. The real part(ε′) and the imaginary part(ε″) of the permittivity of Csf/Si3N4 composites greatly increase with increasing volume fraction of the short carbon fibers,achieve the maximum 73.1 and 101.5,respectively. A strong frequency dependence of the imaginary part(ε″) of the permittivity is observed.