Fracture behavior of advanced ceramic hot-gas filters Page: 4 of 13
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EVALUATION OF STRENGTH AND THERMAL-SHOCK
AND FATIGUE RESISTANCE
Filter strength was evaluated by both diametral compression testing of O-ring specimens
and by burst testing of short filter segments with rubber plugs.
O-Ring Compression Testing
One-inch-wide O-ring specimens were machined from each of the filters and then loaded
to failure in a diametral compression mode at a crosshead speed of 0.13 cm/min. Maximum
stress develops at the inner diameter across the load points, which simulates the thermal-shock
stresses developed during a pulse-cleaning cycle. The fracture stress 6f is given by Eq. 1.2
PK (1)
a, = ,()
where P is the fracture load, K is a function of the ratio of inner and outer diameters,2 b is the
outer radius of the specimen, and I is the length of the tube. Load displacement plots for the
filter specimens in as-fabricated condition indicated a nonbrittle failure mode for all composites
and brittle failure for the monolithic filters. A limited number of O-ring specimens machined
from one of the composite filters exposed in the Tidd demonstration plant for 1100 h were
tested in compression mode; strength was 7.72 1.13 MPa. The corresponding strength of
the unexposed filter was 19.47 2.11 MPa. This represents a strength loss of 60% during
filter exposure, which correlates very well with the strength loss of the reinforcing fibers and
may be related to in-situ fiber damage during filter exposure.3
Burst Testing
Burst testing was performed on 1-in.-wide O-ring specimens machined from a
Nextel/SiC composite filter in as-fabricated condition. As shown in Fig. 1, uniform radial
loading was applied to the O-rings through a rubber plug (slightly smaller in diameter than
O-ring) that was compressed between two aluminum plates. Figure 2 shows a typical load-
displacement plot for a specimen in as-fabricated condition.
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Singh, J.P.; Majumdar, S.; Sutaria, M. & Bielke, W. Fracture behavior of advanced ceramic hot-gas filters, report, May 1, 1996; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc670759/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.