Mechanical Properties Of Particulate Reinforced Composites Research Articles

Particulate‐Reinforced Precursor‐Derived Si–C–N Ceramics: Optimization of Pyrolysis Atmosphere and Schedules

Surface oxidation occurred during pyrolysis of SiC particulate‐reinforced composites (PRCs) with a precursor‐derived Si–C–N matrix. In contrast, such an oxidation was not observed in pure Si–C–N ceramics. The present investigation discusses the possible reasons for this, and reports on the influence of such an oxidation on the microstructure and the mechanical and thermal properties of PRCs by the precursor‐impregnation and pyrolysis method. The high‐temperature mass stability of the PRCs in Ar deteriorated owing to the decomposition of SiO2 formed by oxidation. The effects of the pyrolysis schedule on the processing and mechanical properties of PRCs are also investigated.

Interface effects on mechanical properties of particle-reinforced composites

Objectives: Effective bonding between the filler and matrix components typically improves the mechanical properties of polymer composites containing inorganic fillers. The aim of this study was to test the hypothesis that composite flexural modulus, flexure strength, and toughness are directly proportional to filler–matrix interfacial shear strength. Methods: The resin matrix component of the experimental composite consisted of a 60:40 blend of BisGMA:TEGDMA. Two levels of photoinitiator components were used: 0.15, and 0.5%. Raman spectroscopy was used to determine degree of cure, and thermogravimetry (TGA) was used to quantify the degree of silane, rubber, or polymer attachment to silica and glass particles. Filler–matrix interfacial shear strengths were measured using a microbond test. Composites containing glass particles with various surface treatments were prepared and the modulus, flexure strength, and fracture toughness of these materials obtained using standard methods. Mechanical properties were measured on dry and soaked specimens. Results: The interfacial strength was greatest for the 5% MPS treated silica, and it increased for polymers prepared with 0.5% initiator compared with 0.15% initiator concentrations. For the mechanical properties measured, the authors found that: (1) the flexural modulus was independent of the type of filler surface treatment, though flexural strength and toughness were highest for the silanated glass; (2) rubber at the interface, whether bonded to the filler and matrix or not, did not improve toughness; (3) less grafting of resin to silanated filler particles was observed when the initiator concentration decreased. Significance: These findings suggest that increasing the strength of the bond between filler and matrix will not result in improvements in the mechanical properties of particulate-reinforced composites in contrast to fiber-reinforced composites. Also, contraction stresses in the 0.5 vs 0.15% initiator concentration composites may be responsible for increases in interfacial shear strengths, moduli, and flexural strengths.

Constitutive relation of particulate-reinforced viscoelastic composite materials with debonded microvoids

In this paper, the constitutive relation of particulate-reinforced viscoelastic composite materials is studied by considering the evolution of microvoids. Owing to the difference in mechanical properties between matrix and second phase particles, debonding of particle-matrix interface may occur under the condition of high stress triaxiality. This kind of damage will lead to the nucleation and growth of microvoids. The reinforcing effect due to rigid particles and the weakening effect due to microvoids caused by debonding on the overall mechanical properties of particulate-reinforced composites are investigated. Using the energy criterion of interfacial debonding, an expression for the nucleation rate of microvoids is suggested. Then, the growth of these voids is studied by means of Eshelby’s equivalent inclusion method. It is shown that the strain of the microvoids depends not only on the remote strain history but also on their nucleation time. By considering the effect of nucleation time, a new definition of an average strain of microvoids is given. According to the Mori–Tanaka scheme, a macroscopic constitutive relation of the composite material is finally derived. The results show that macroscopic strain rate, particle-size dispersity, relaxation time of matrix, and interface adhesive strength all play key roles in the overall mechanical properties of particulate-reinforced composites.

MICROMECHANICS FOR PARTICULATE-REINFORCED COMPOSITES

A set of micromechanics equations for the analysis of particulate-reinforced composites is developed using the mechanics of materials approach. Simplified equations are used to compute homogenized or equivalent thermal and mechanical properties of particulate-reinforced composites in terms of the properties of the constituent materials. The microstress equations are also presented here to decompose the applied stresses on the overall composite to the microstresses in the constituent materials. The properties of a “generic” particulate composite as well as those of a particle-reinforced metal matrix composite are predicted and compared with other theories as well as some experimental data. The micromechanics predictions ate in excellent agreement with the measured values.