Standard Test Method for Hoop Tensile Strength of Continuous Fiber-Reinforced Advanced Ceramic Composite Tubular Test Specimens at Ambient Temperature Using Elastomeric Inserts

Importancia y uso:

5.1 This test method (also known as overhung tube method) may be used for material development, material comparison, material screening, material down selection, and quality assurance. This test method is not recommended for material characterization, design data generation, material model verification/validation, or combinations thereof.

5.2 Continuous fiber-reinforced ceramic composites (CFCCs) are composed of continuous ceramic-fiber directional (1D, 2D, and 3D) reinforcements in a fine-grain-sized (<50 µm) ceramic matrix with controlled porosity. Often these composites have an engineered thin (0.1 to 10 µm) interface coating on the fibers to produce crack deflection and fiber pull-out.

5.3 CFCC components have a distinctive and synergistic combination of material properties, interface coatings, porosity control, composite architecture (1D, 2D, and 3D), and geometric shape that are generally inseparable. Prediction of the mechanical performance of CFCC tubes (particularly with braid and 3D weave architectures) cannot be made by applying measured properties from flat CFCC plates to the design of tubes. In particular, tubular components comprised of CMCs material form a unique synergistic combination of material and geometric shape that are generally inseparable. In other words, prediction of mechanical performance of CMC tubes generally cannot be made by using properties measured from flat plates. Strength tests of internally pressurized CMC tubes provide information on mechanical behavior and strength for a multiaxially stressed material.

5.4 Unlike monolithic advanced ceramics which fracture catastrophically from a single dominant flaw, CMCs generally experience “graceful” fracture from a cumulative damage process. Therefore, while the volume of material subjected to a uniform hoop tensile stress for a single uniformly pressurized tube test may be a significant factor for determining matrix cracking stress, this same volume may not be as significant a factor in determining the ultimate strength of a CMC. However, the probabilistic nature of the strength distributions of the brittle matrices of CMCs requires a statistically significant number of test specimens for statistical analysis and design. Studies to determine the exact influence of test specimen volume on strength distributions for CMCs have not been completed. It should be noted that hoop tensile strengths obtained using different recommended test specimens with different volumes of material in the gage sections may be different due to these volume effects.

5.5 Hoop tensile strength tests provide information on the strength and deformation of materials under biaxial stresses induced from internal pressurization of tubes. Nonuniform stress states are inherent in these types of tests and subsequent evaluation of any nonlinear stress-strain behavior must take into account the unsymmetric behavior of the CMC under biaxial stressing. This nonlinear behavior may develop as the result of cumulative damage processes (for example, matrix cracking, matrix/fiber debonding, fiber fracture, delamination, etc.) which may be influenced by testing mode, testing rate, processing or alloying effects, or environmental influences. Some of these effects may be consequences of stress corrosion or subcritical (slow) crack growth that can be minimized by testing at sufficiently rapid rates as outlined in this test method.

5.6 The results of hoop tensile strength tests of test specimens fabricated to standardized dimensions from a particular material or selected portions of a part, or both, may not totally represent the strength and deformation properties of the entire, full-size end product or its in-service behavior in different environments.

5.7 For quality control purposes, results derived from standardized tubular hoop tensile strength test specimens may be considered indicative of the response of the material from which they were taken for, given primary processing conditions and post-processing heat treatments.

5.8 The hoop tensile stress behavior and strength of a CMC are dependent on its inherent resistance to fracture, the presence of flaws, or damage accumulation processes, or both. Analysis of fracture surfaces and fractography, though beyond the scope of this test method, is highly recommended.

Subcomité:

C28.07

Volúmen:

15.01

Número ICS:

81.060.30 (Advanced ceramics)

Palabras clave:

ceramic matrix composite; CMC continuous fiber composite; hoop tensile strength; internal pressure test; tubes;