An Assessment of Variability in the Average Tensile Properties of a Melt-Infiltrated SiC/SiC Composite

Journal of the American Ceramic Society

Yun

DiCarlo

2007

The tensile mechanical properties of ceramic matrix composites (CMC) in directions off the primary axes of the reinforcing fibers are important for architectural design of CMC components that are subjected to multi-axial stress states. In this study, 2D-woven melt- behavior, acoustic emission, and optical microscopy were used to quantify stressdependent matrix cracking and ultimate strength in the panels. It was observed that both off-axis loaded panels displayed higher composite onset stresses for through-thickness matrix cracking than the 2D-woven 0/90 panels loaded in the primary 0 o direction. These improvements for off-axis cracking strength can in part be attributed to higher effective fiber fractions in the loading direction, which in turn reduces internal stresses on critical matrix flaws for a given composite stress. Also for the 0/90 panel loaded in the 45 o direction, an improved distribution of matrix flaws existed due to the absence of fiber tows perpendicular to the loading direction. In addition, for the +67/0/-67 braided panel, the axial tows perpendicular to the loading direction were not only low in volume fraction, but were also were well separated from one another. Both off-axis oriented panels also showed relatively good ultimate tensile strength when compared to other offaxis oriented composites in the literature, both on an absolute strength basis as well as when normalized by the average fiber strength within the composites. Initial implications https://ntrs.nasa.gov/search.jsp?R=20070021762 2018-05-10T22:43:08+00:00Z 2 are discussed for constituent and architecture design to improve the directional cracking of SiC/SiC CMC components with MI matrices.

Section: Resultsmentioning

confidence: 99%

In‐Plane Cracking Behavior and Ultimate Strength for 2D Woven and Braided Melt‐Infiltrated SiC/SiC Composites Tensile Loaded in Off‐Axis Fiber Directions

Journal of the American Ceramic Society

Yun

DiCarlo

2007

“…To determine the onset for non‐linear stress–strain (proportional limit), the 0.002% and 0.005% offset strain stresses were measured (ASTM C1275) and compared for most of the fast‐fracture tests on as‐produced specimens, the initial loading curves of the creep tests, and the fast‐fracture tests for the after‐creep specimens. The 0.005% offset strain approach has been used at NASA Glenn Research Center for the Sylramic‐iBN § fiber reinforced MI composite system 15 . However, as evident below, the 0.005% offset strain stress was in some cases greater than the applied creep stress; therefore, the 0.002% offset strain stress was more useful for comparison of all the loading curves.…”

Section: Methodsmentioning

confidence: 99%

Creep and Stress–Strain Behavior after Creep for SiC Fiber Reinforced, Melt‐Infiltrated SiC Matrix Composites

Journal of the American Ceramic Society

Pujar²

2006

Silicon carbide fiber (Hi‐Nicalon Type S, Nippon Carbon) reinforced silicon carbide matrix composites containing melt‐infiltrated silicon were subjected to creep at 1315°C at three different stress conditions. For the specimens that did not rupture after 100 h of tensile creep, fast‐fracture experiments were performed immediately following the creep test at the creep temperature (1315°C) or after cooling to room temperature. All specimens demonstrated excellent creep resistance and compared well to the creep behavior published in the literature on similar composite systems. Tensile results on the after‐creep specimens showed that the matrix cracking stress actually increased, which is attributed to stress redistribution between composite constituents during tensile creep.

“…Table II shows the average values for the AE Onset Stress. Also shown are the 0.005% offset stresses, from the stress-strain curves, a common technique for determining the proportional limit [15], and often associated with matrix cracking strengths for these composites. As shown in Figure 4, the AE Onset Stress and 0.005% Offset Stress are close in magnitude; however, the 0.005% Offset Stress almost always exceeded the AE Onset Stress for the composites of this study.…”

Section: Room Temperature Stress Strain Behavior With Acoustic Emissionmentioning

confidence: 99%

“…7 Table II shows the average values for the AE onset stress. Also shown are the 0.005% offset stresses, from the stress-strain curves, a common technique for determining the proportional limit, 15 and often associated with matrix cracking strengths for these…”

Section: Room-temperature Stress-strain Behavior With Aementioning

confidence: 99%

Design Guidelines for In‐Plane Mechanical Properties of SiC Fiber‐Reinforced Melt‐Infiltrated SiC Composites

Int J Applied Ceramic Tech

Pujar²

2009

In-plane tensile stress-strain, tensile creep, and after-creep retained tensile properties of melt-infiltrated SiC-SiC composites reinforced with different fiber types were evaluated with an emphasis on obtaining simple or first-order microstructural design guidelines for these in-plane mechanical properties. Using the mini-matrix approach to model stress-strain behavior and the results of this study, three basic general design criteria for stress and strain limits are formulated, namely a design stress limit, a design total strain limit, and an after-creep design retained strength limit. It is shown that these criteria can be useful for designing components for high temperature applications.