Standard Test Method for Open-Hole Tensile Strength of Fiber-Reinforced Advanced Ceramic Composites

Importancia y uso:

5.1 Open-hole tests of composites are used for material and design development for the engineering application of composite materials (5-11). The presence of an open hole in a composite component reduces the cross-sectional area available to carry an applied force, creates stress concentrations, and creates new edges where delamination may occur. Standardized open-hole tests for composite materials can provide useful information about how a composite material may perform in an open-hole application and how to design the composite for notches and holes.

5.2 The test method defines two baseline test specimen geometries and a test procedure for producing comparable, reproducible OHT test data. The test method is designed to produce OHT strength data for structural design allowables, material specifications, material development and comparison, material characterization, and quality assurance. The mechanical properties that may be calculated from this test method include:

5.2.1 The open-hole (notched) tensile strength (S_OHTx) for test specimen with a hole diameter x (mm).

5.2.2 The net section tensile strength (S_NSx) for a test specimen with a hole diameter x (mm).

5.2.3 The proportional limit stress (σ₀) for an OHT specimen with a given hole diameter.

5.2.4 The stress response of the OHT test specimen, as shown by the stress-time or stress-displacement plot.

5.3 Open-hole tensile tests provide information on the strength and deformation of materials with defined through-holes under uniaxial tensile stresses. Material factors that influence the OHT composite strength include the following: material composition, methods of composite fabrication, reinforcement architecture (including reinforcement volume, tow filament count and end-count, architecture structure, and laminate stacking sequence), and porosity content. Test specimen factors of influence are: specimen geometry (including hole diameter, width-to-diameter ratio, and diameter-to-thickness ratio), specimen preparation (especially of the hole), and specimen conditioning. Test factors of influence are: specimen alignment and gripping, speed of testing, and test temperature/environment. Controlled stress states are required to effectively evaluate any nonlinear stress-strain behavior which may develop as the result of cumulative damage processes (for example, matrix cracking, matrix/fiber debonding, delamination, fiber pull-out and fracture, etc.) which may be influenced by testing mode, testing rate, processing effects, or environmental influences. Some of these effects may be consequences of stress corrosion or slow (subcritical) crack growth. Stress corrosion and slow crack growth factors can be minimized by testing at sufficiently rapid rates as described in 12.1.7.

Subcomité:

C28.07

Volúmen:

15.01

Número ICS:

81.060.30 (Advanced ceramics)

Palabras clave:

ceramic composite materials; notch sensitivity; notch strength; open-hole tensile strength; stress concentration; tensile testing;