Effects of Matrix Porosity on the Mechanical Properties of a Porous‐Matrix, All‐Oxide Ceramic Composite

Abstract

The effects of matrix porosity on the mechanical properties of an all-oxide ceramic composite are investigated. The porosity is varied through impregnation and pyrolysis of a ceramic precursor solution. Mechanical tests are performed to assess the role of the matrix in both matrix-dominated and fiberdominated loading configurations. The results demonstrate a loss in damage tolerance and tensile strength along the fiber direction as the porosity is reduced. Concomitantly, some improvements in interlaminar strength are obtained. The latter improvements are found to be difficult to quantify over the entire porosity range using the standard short beam shear method, a consequence of the increased propensity for tensile fracture as the porosity is reduced. Measurements of interlaminar shear strength based on the double-notched shear specimen are broadly consistent with the limited values obtained by the short beam shear method, although the former exhibit large variability. In addition, effects of precursor segregation during drying on through-thickness gradients in matrix properties and their role in composite performance are identified and discussed. An analysis based on the mechanics of crack deflection and penetration at an interphase boundary is presented and used to draw insights regarding the role of matrix properties in enabling damage tolerance in porousmatrix composites. Deficiencies in the understanding of the mechanisms that enable damage tolerance in this class of composites are discussed.

Fabrication and properties of 3D oxide fiber-reinforced Al2O3–SiO2–SiOC composites by a hybrid technique based on sol–gel and PIP process

“…Besides, the matrix density in the near-surface region is higher than that in the interior. The observation is coincident with the results of all-oxide composites reported by Mattoni [20]. A suitable explanation is that multiple infiltrations may produce a gradient in matrix density from outside to inside.…”

“…The differences for the shear strength of the composites with different densification cycles mainly originated from the different fracture modes. According to Zok, the failure of the porous composites will gradually change from shear mode to tensile mode, with the matrix densification degree enhancing [20]. The SBS response for N440/ASS2 composites showed more thermal stability, even after thermal aging at 1000 1C for 100 h. ( analysis revealed that the matrix pore even inner fiber bundle was filled with PDC-SiOC.…”

“…The interlaminar shear strength (ILSS) was measured using the short beam shear (SBS) test [20]. Sample geometry was 45 l  5 w  3 t mm 3 , while the span and velocity of the crosshead were 15.5 mm and 0.5 mm/min, respectively.…”

Effects of Steam Environment on Creep Behavior of Nextel™610/Monazite/Alumina Composite at 1,100°C

“…Resulting oxide/ oxide CMCs exhibit damage tolerance combined with inherent oxidation resistance. In this case, there is a strong bonding between the fiber and matrix; consequently, a minimum matrix porosity is needed for this concept to work [14]. An extensive review of the mechanisms and mechanical properties of porous-matrix CMCs is given in [1,15].…”

Notch Sensitivity of Ceramic Composites with Rising Fracture Resistance

“…The matrix was introduced in two steps: (i) pressure-assisted infiltration of a mullitealumina slurry through the fiber preform and (ii) impregnation and pyrolysis of an Al 2 Cl(OH) 5 solution (an alumina precursor). Processing details were essentially identical to those described earlier 11 with two exceptions. First, the concentration of the precursor solution was increased to give a volumetric yield of 6.4%, compared with 3% in previous studies.…”