Effect of Interfacial Bonding on the Toughening of Al_2O_3/Ni Ceramic Matrix Composites

The main Iimitation to the toughening of the α-Al2O3/Ni composite is the poor bonding atthe interface. which causes the nickel particles to be pulled-out during crack propagation with-out obvious plastic deformation. A proper control of oxygen content at the Al2O3-Ni interfacecan promote wetting at the intedece, and produce a mechanically interlocked and chemically strengthened intedece, causing most of the nickel particles to be stretched to failure and to expe-rience severe plastic deformation during crack propagation in the composite. Fracture toughnesstesting using a modified double cantilever beam method with in situ observation of crack prop-agation in a scanning electron microscope shows that the composite with the strengthenedinterface has a more desirable R-curve behaviour and a higher fracture toughness value than thenormal composite.

Fracture behavior of hybrid epoxy nanocomposites based on multi-walled carbon nanotube and core-shell rubber

The dispersion of nanoparticles plays a key role in enhancing the mechanical performance of polymer nanocomposites.In this work,one hybrid epoxy nanocomposite reinforced by a well dispersed,zinc oxide functionalized,multi-wall carbon nanotube (Zn O-MWCNT) and core-shell rubber (CSR) was prepared,which possesses both high modulus and fracture toughness while maintaining relatively high glass transition temperature (Tg).The improved fracture toughness from 0.82 MPa mfor neat epoxy to 1.46 MPa mfor the ternary epoxy nanocomposites is resulted from a series of synergistic toughening mechanisms,including cavitation of CSR-induced matrix shear banding,along with the fracture of MWCNTs and crack deflection.The implication of the present study for the preparation of high-performance polymer nanocomposites is discussed.

Well-posedness of two-phase local/nonlocal integral polar models for consistent axisymmetric bending of circular microplates

Previous studies have shown that Eringen’s differential nonlocal model would lead to the ill-posed mathematical formulation for axisymmetric bending of circular microplates.Based on the nonlocal integral models along the radial and circumferential directions,we propose nonlocal integral polar models in this work.The proposed strainand stress-driven two-phase nonlocal integral polar models are applied to model the axisymmetric bending of circular microplates.The governing differential equations and boundary conditions(BCs)as well as constitutive constraints are deduced.It is found that the purely strain-driven nonlocal integral polar model turns to a traditional nonlocal differential polar model if the constitutive constraints are neglected.Meanwhile,the purely strain-and stress-driven nonlocal integral polar models are ill-posed,because the total number of the differential orders of the governing equations is less than that of the BCs plus constitutive constraints.Several nominal variables are introduced to simplify the mathematical expression,and the general differential quadrature method(GDQM)is applied to obtain the numerical solutions.The results from the current models(CMs)are compared with the data in the literature.It is clearly established that the consistent softening and toughening effects can be obtained for the strain-and stress-driven local/nonlocal integral polar models,respectively.The proposed two-phase local/nonlocal integral polar models(TPNIPMs)may provide an efficient method to design and optimize the plate-like structures for microelectro-mechanical systems.

On the consistency of two-phase local/nonlocal piezoelectric integral model

In this paper,we propose general strain-and stress-driven two-phase local/nonlocal piezoelectric integral models,which can distinguish the difference of nonlocal effects on the elastic and piezoelectric behaviors of nanostructures.The nonlocal piezoelectric model is transformed from integral to an equivalent differential form with four constitutive boundary conditions due to the difficulty in solving intergro-differential equations directly.The nonlocal piezoelectric integral models are used to model the static bending of the Euler-Bernoulli piezoelectric beam on the assumption that the nonlocal elastic and piezoelectric parameters are coincident with each other.The governing differential equations as well as constitutive and standard boundary conditions are deduced.It is found that purely strain-and stress-driven nonlocal piezoelectric integral models are ill-posed,because the total number of differential orders for governing equations is less than that of boundary conditions.Meanwhile,the traditional nonlocal piezoelectric differential model would lead to inconsistent bending response for Euler-Bernoulli piezoelectric beam under different boundary and loading conditions.Several nominal variables are introduced to normalize the governing equations and boundary conditions,and the general differential quadrature method(GDQM)is used to obtain the numerical solutions.The results from current models are validated against results in the literature.It is clearly established that a consistent softening and toughening effects can be obtained for static bending of the Euler-Bernoulli beam based on the general strain-and stress-driven local/nonlocal piezoelectric integral models,respectively.

A novel route to enhance high-temperature mechanical property and thermal shock resistance of low-carbon Mgo-C bricks by introducing ZrSiO_(4)

Conventional MgO-C bricks(graphite content>14 wt.%)produce a great deal of greenhouse gas emission,while low-carbon MgO-C bricks have serious thermal shock resistance during high-temperature service.To enhance the high-temperature mechanical property and thermal shock resistance of low-carbon MgO-C bricks,a novel route of introducing ZrSiO_(4) powder into low-carbon MgO-C bricks was reported in such refractories with 2 wt.% flaky graphite.The results indicate that the low-carbon MgO-C brick with 0.5 wt.%ZrSiO_(4) addition has the maximum hot modulus of rupture at 1400℃ and the corresponding specimen fired in the carbon embedded atmosphere has the maximum residual strength ratio(98.6%)after three thermal shock cycles.It is found that some needle-like AlON and plate-like Al_(2)O_(3)-ZrO_(2) composites were in situ formed in the matrices after the low-carbon MgO-C bricks were coked at 1400℃,which can enhance the high-temperature mechanical property and thermal shock resistance due to the effect of fiber toughening and particle toughening.Moreover,CO_(2) emission of the newly developed low-carbon MgO-C bricks is reduced by 58.3% per ton steel after using them as the working lining of a 90 t vacuum oxygen decarburization ladle.