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Experimental analysis of single-fiber push-out for SiC fiber-reinforced titanium matrix composites (TMCs) is complicated by the incorporation of large thermal residual stresses, strong chemical bond of the fiber/matrix interface and matrix plastic deformation. This paper summarizes the development of push-out test and the characteristics of push-out test for TMCs such as crack initiating at the bottom face and theoretical analysis of the test. Moreover, it deeply analyzes the progresses of interfacial shear strength and fracture toughness, and work focus is pointed out in future. [ABSTRACT FROM AUTHOR]

Abstract: The deformation and fracture process in Al–Cu–Mg alloy were investigated by using the in situ straining transmission electron microscopy (TEM) method. Some major aspects of the fracture process, including dislocation emission and migration, thinning of dislocation free zone (DFZ), crack propagation (both in continuous and discontinuous manners) and slipping/twinning deformation, can be observed. The rod-like T dispersoids, which may increase the microcrack initiation sensitivity, also can effectively prevent the fast and continuous propagation of the crack. DFZ ahead of crack tip can be thinned in a mixed mode characterized by tearing and shear deformation, while nanovoids, which are typical characteristics in DFZ during discontinuous crack propagation, may originate from the enrichment of defects such as dislocations and vacancies. Deformation twinning at crack tip can slow down crack propagation and change crack propagation path, thus may be beneficial to the fracture toughness of the alloy. [Copyright &y& Elsevier]

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]

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]

Multiwalled carbon nanotube (MWCNT)-reinforced Al 2 O 3 -matrix nanocomposites were obtained by wet ball milling composite powders and spark plasma sintering. The mechanical and thermal properties of the nanocomposites with five different MWCNT concentrations from 0 to 2.0 wt% were studied. Results show that the matrix grain sizes of the composites decreased after MWCNT addition. The hardness, bending strength, and fracture toughness of 0.5 wt% MWCNT nanocomposite are the highest, which are 35.7%, 55%, and 182% higher than those of monolithic alumina, respectively. Errors of fracture toughness values obtained by the single-edge notch beam method are significantly smaller than those measured by the direct crack measurement method. With the addition of MWCNTs, the thermal conductivity of the nanocomposites decreases gradually, reaching the minimum of 12 W/mK in 2.0 wt% MWCNT composite at 300 °C. The thermal conductivity decreased owing to the agglomeration of MWCNTs and changes in the porosity and grain size of the composite matrix. No distinct difference is observed in thermal expansion behaviours between the nanocomposites and monolithic Al 2 O 3 owing to the low content of MWCNTs. [ABSTRACT FROM AUTHOR]

[Display omitted] • A low concentration of graphene (less than 0.4 wt%) was well dispersed into alumina matrix by physical dispersion method. • The hardness, bending strength and fracture toughness were increased significantly by 19.2%, 84.7% and 49.5%, respectively at low graphene contents. • Different types of toughening mechanisms are observed. • With the increase of graphene contents and temperature, thermal conductivity of the nanocomposites decreases. Graphene/CNTs-reinforced alumina ceramic composites were prepared by spark plasma sintering (SPS) method at 1500 °C. The distribution behaviors of graphene/CNTs reinforcements in alumina matrix composite were studied and mechanical properties of the composite were tested. The structural integrity of the graphene after sintering was analyzed by Raman spectroscopy. The composites show inter and trans-granular fracture behaviors. Many toughening mechanisms such as graphene and CNTs necking, crack bridging, crack deflection and crack branching were observed. The experiment-based calculation of heat capacity of the composite was presented in details. The thermal diffusivity and thermal conductivity of the nanocomposites were discussed. The thermal conductivity increased with the increase of grain size. The pure alumina had the highest thermal conductivity, which was 23.9 Wm−1 K−1. [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]