A. Mukherjee, H.S. Rao/Computational Materials Science 4(1995)249-262 4. ETect uf interface strength on toughening of CMC Material properties used for the present Al( iC CMC Property Matrix As discussed earlier, the whisker/matrix inter- face strength has an important bearing on the Youngs modulus )0.0 Gpa 600.0GPa oughening mechanics of the ceramic composites. 0.22 700 MPa The interface should not be too weak to effect a Tensile strength Radius 03μm tal whisker pull out at a very low stress. It should not be too strong to cause a brittle frac- ture. Therefore, the interface shear strength is to be engineered to an optimum level to ensure a crack deflection mechanism and a good work of matrix of 0.6 um width. These dimensions give a fracture. To demonstrate the effect of interface 33.3 percent of whisker reinforcement. The top shear strength on the toughening of CMCs, a matrix layer of 15 um length is provided to min single whisker quarter symmetry finite element imisc the local disturbances arising in the vicinity model of Al,O,(matrix)/SiC(whisker) ceramic of the load. on the mechanics of the interface. matrix-composite has been constructed(see Fig. The use of quarter symmetry required that the 9). This model has been analysed in(2-D) plane nodes along the axis of symmetry be fixed in x strain. Though the 2D analysis is an approxima- direction. This FE mesh consists of 150 matrix tion to the real 3D situation, but it still provides a and 75 whisker eight node quadrilateral ele- good insight. Material properties used in this ments. The whisker/matrix interface has been are modelled by 50 six-node isoparamctricintcrfacc The whisker has been modelled in quarter elements. Three interface elements are used at symmetry as having a half length of 30 um, and a the bottom axis of symmetry (y=0)as control half width of 0.3 um, and is connected to a elements. When the normal stress in these con- 个个个↑个 30 H m Matris whisker 06日l 0.3 Fig9(a)Quarter symmetry FE model of the Al,,/SiC ceramic composite (b)Finite element discretization of the CMc model.256 A. Mukherjee, H.S. Rao /Computational Materials Science 4 (1995) 249-262 4. Effect of interface strength on toughening of Table 1 CMC Material properties used for the present Al,O? /Sic CMC Property Matrix Whisker As discussed earlier, the whisker/matrix inter- (Al,O,) (SIC) face strength has an important bearing on the Young’s modulus 400.0 Gpa 600.0 GPa toughening mechanics of the ceramic composites. Poission’s ratio 0.22 0.22 The interface should not be too weak to effect a Tensile strength 700 MPa 6.89 GPa Radius total whisker pull out at a very low stress. It should not be too strong to cause a brittle frac￾ture. Therefore, the interface shear strength is to be engineered to an optimum level to ensure a crack deflection mechanism and a good work of fracture. To demonstrate the effect of interface shear strength on the toughening of CMCs, a single whisker quarter symmetry finite element model of Al,O, (matrix)/SiC (whisker) ceramic￾matrix-composite has been constructed (see Fig. 9). This model has been analysed in (2-D) plane strain. Though the 2D analysis is an approxima￾tion to the real 3D situation, but it still provides a good insight. Material properties used in this study are given in Table 1. The whisker has been modelled in quarter symmetry as having a half length of 30 km, and a half width of 0.3 pm, and is connected to a 0.3 pm Length 60 b matrix of 0.6 pm width. These dimensions give a 33.3 percent of whisker reinforcement. The top matrix layer of 15 pm length is provided to min￾imise the local disturbances arising in the vicinity of the load, on the mechanics of the interface. The use of quarter symmetry required that the nodes along the axis of symmetry be fixed in x direction. This FE mesh consists of 150 matrix and 75 whisker eight node quadrilateral ele￾ments. The whisker/matrix interface has been modelled by 50 six-node isoparametricinterface elements. Three interface elements are used at the bottom axis of symmetry (y = 0) as control elements. When the normal stress in these con￾Fig. 9. (a) Quarter symmetry FE model of the Al,O, /Sic ceramic composite. (b) Finite element discretization of the CMC model