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Tension–tension fatigue properties of SiC fiber reinforced Ti–6Al–4V matrix composite (SiC f /Ti–6Al–4V) at room temperature were investigated. Fatigue tests were conducted under a load-controlled mode with a stress ratio 0.1 and a frequency 10 Hz under a maximum applied stress ranging from 600 to 1200 MPa. The relationship between the applied stress and fatigue life was determined and fracture surfaces were examined to study the fatigue damage and fracture failure mechanisms using SEM. The results show that, the fatigue life of the SiC f /Ti–6Al–4V composite decreases substantially in proportion to the increase in maximum applied stress. Moreover, in the medium and high life range, the relationship between the maximum applied stress and cycles to failure in the semi-logarithmic system could be fitted as a linear equation: S max / μ = 1.381 − 0.152 × lgN f . Fractographic analysis revealed that fatigue fracture surfaces consist of a fatigued region and a fast fracture region. The fraction of the fatigued region with respect to the total fracture surface decreases with the increase of the applied maximum stresses. [ABSTRACT FROM AUTHOR]

An analytical model of the push-out test was developed to predict the interfacial fracture toughness of fiber-reinforced matrix composites. Elastic deformation, thermal residual stress, Poisson effect, and energy dissipation due to interfacial friction are all accounted for in the model based on a fracture mechanics approach and a general solution was derived from the analysis. In addition, finite element analysis was performed to validate the analyti-cal model. The results show that the predictions from the analytical model are in good agreement with the finite element results and experimental data on SiC-reinforced Timet-al834 composites. The effects of residual stress, the friction stress, and the debonding crack length on the interfacial fracture toughness were discussed for a better understanding of the interfacial phenomena in push-out test. The analytical model could be applied to other composite systems as well. [ABSTRACT FROM AUTHOR]

Abstract: The axisymmetric cell model consisting of interface, matrix and reinforced particle is used to simulate the tensile test of particle reinforced metal matrix composite for predicting the micro stress/strain field and macro tensile stress/strain curve. In simulation of the tensile test, the cohesive element model is selected to model interfacial crack growth. It mainly analyzed the effects of interfacial properties, reinforcement volume fractions and aspect ratios on the stress–strain states of particle reinforced metal matrix composite. The results show that the peak micro stress and plastic strain occur at the interface in which it is a certain angle from the tensile stress direction; with the interfacial fracture toughness and reinforcement volume fraction increasing, the flow stress increases firstly and then decreases. The tensile stress–strain properties of SiC/6064Al are good when the interfacial fracture toughness is equal to 60J/m and the reinforcement fraction volume is equal to 20%. Smaller reinforcement aspect ratio leads to smaller micro stress in composites. [Copyright &y& Elsevier]

The model based on fracture mechanics is developed to evaluate the fracture toughness Γ of the fiber/matrix interface in titanium alloys reinforced by SiC monofilaments. Theoretical model for single fiber push-out testing is obtained by shear-lag method. The influences of several key factors (such as the applied stress needed for crack advance, crack length, and interfacial frictional shear stress) are discussed. Using the model, the interfacial toughness of typical composites including Sigma1240/Ti-6-4, SCS-6/Ti-6-4, SCS-6/Timetal 834, SCS-6/Timetal 21s, SCS-6/Ti-24-11 and SCS-6/Ti-15-3 are successfully predicted compared with previous results of these composites. It is verified that the model can reliably predict the interfacial toughness of the titanium matrix composites as well as other metal matrix composites, due to interfacial debonding usually occurs at the bottom face of the samples in such composites. [ABSTRACT FROM AUTHOR]

• Graphene were excellently dispersed into alumina matrix by physical dispersion method. • The structural stability of graphene was analyzed by Raman spectroscopy. • The fracture toughness of the material was measured by the method of single edge notched beam (SENB). • The bending strength and the fracture toughness of the nanocomposites increased significantly at low graphene contents. • Different types of toughening mechanisms are observed. Monolithic Al 2 O 3 and graphene-reinforced Al 2 O 3 ceramic-matrix nanocomposites were fabricated with the help of spark plasma sintering (SPS). Density, hardness, bending strength, fracture toughness and microstructure of the sintered samples were studied. The contents of graphene were 0–1.6 wt%. The strengthening and toughening mechanisms of the composites were discussed in detail. The results showed that the density of the composites varied from 99.7% to 98.7%. 0.4–1.6 wt% of graphene was homogeneously distributed in the matrix. The structural stability of graphene was analyzed by Raman spectroscopy. The bending strength of the nanocomposite reached the maximum when graphene content was 0.4 wt%. The fracture toughness of the composites also increased when the addition of graphene was between 0.4 and 1.6 wt% as compared to monolithic alumina. Different types of toughening mechanisms were observed including; micro-cracks, graphene pull-out, crack deflection and crack bridging. [ABSTRACT FROM AUTHOR]