CERAMIC COMPOSITE INTERFACES 507 (Figure 4d) relying on an indenter for loading, pullout tests(Figure 4c), and microcomposite tests(Figure 4b) Indentation Push-in and Push-through Techniques Indentation tests receiving the greatest attention due to their simplicity involve a sharp(26, 27)or blunt(27)indenter that is used to push in a fiber in a composite or push through a fiber in a composite of thin cross-section. First developed by Marshall (26), a sharp indenter was used to displace a fiber into a matrix, and the residual displacement could be ascertained from impressions left in the matrix in he near vicinity of the fiber. Marshall Oliver(28)used a nanoindenter for the same purpose and instrumented the test to provide a continuous measure of the force and displacement during loading, unloading, and load cycling. Analysis of the force-displacement results allowed upper bound estimates of the debond fracture energy and frictional sliding stress, in contrast to the original push-in or push-through test, which was limited to frictional stress evaluation. A further variation of the push-through technique uses a cylindrical indenter that allows no contact with the matrix(29) Elegant analysis of the experiment has been presented by Zhou Mai( 32), who include the radial constraint imposed by neighboring fibers on their analysis of stress transfer and frictional push-out in such a test and have recently included roughness effects(33). Not surprisingly, the frictional push-out stress increases with reinforcement volume fraction. and radial constraints of sur- increase as the embedded length increases More recently, the push-out test has been used for arrays of fibers by Mackin zok(34). protruding fibers, 10 to 15 um in height, trolled etching of the matrix and form the push surface. A displacement piston n the underside of the sample measures displacement. The and the number of fibers displaced Pullout Techniques Conventional pullout tests are prepared with an end of the fiber protruding from the matrix material, which is gripped directly to the loading apparatus (35), a variation of Figure 4c. The free length of the fiber provides a processing challenge, an alignment challenge during mechanical testing, and an enhanced compliance in the system that may prove undesirable for unstable debond crack initiation. The matrix crack is replaced by a matrix surface, which may pos an artificial barrier to debond crack initiation and, hence, unstable debonding Despite this, evaluations by Bright et al (36) showed that sliding resistance measurements on a SiC fiber-reinforced borosilicate glass made via pullout and push-out tests were equivalent. However, constant friction shear stress over theP1: ARK/MBL/rkc P2: MBL/vks QC: MBL/agr T1: MBL May 16, 1997 13:47 Annual Reviews AR034-16 CERAMIC COMPOSITE INTERFACES 507 (Figure 4d) relying on an indenter for loading, pullout tests (Figure 4c), and microcomposite tests (Figure 4b). Indentation Push-in and Push-through Techniques Indentation tests receiving the greatest attention due to their simplicity involve a sharp (26, 27) or blunt (27) indenter that is used to push in a fiber in a composite or push through a fiber in a composite of thin cross-section. First developed by Marshall (26), a sharp indenter was used to displace a fiber into a matrix, and the residual displacement could be ascertained from impressions left in the matrix in the near vicinity of the fiber. Marshall & Oliver (28) used a nanoindenter for the same purpose and instrumented the test to provide a continuous measure of the force and displacement during loading, unloading, and load cycling. Analysis of the force-displacement results allowed upper bound estimates of the debond fracture energy and frictional sliding stress, in contrast to the original push-in or push-through test, which was limited to frictional stress evaluation. A further variation of the push-through technique uses a cylindrical indenter that allows no contact with the matrix (29). Elegant analysis of the experiment has been presented by Zhou & Mai (30– 32), who include the radial constraint imposed by neighboring fibers on their analysis of stress transfer and frictional push-out in such a test and have recently included roughness effects (33). Not surprisingly, the frictional push-out stress increases with reinforcement volume fraction, and radial constraints of sur￾rounding fibers increase as the embedded length increases. More recently, the push-out test has been used for arrays of fibers by Mackin & Zok (34). Protruding fibers, 10 to 15 µm in height, are created through a con￾trolled etching of the matrix and form the push surface. A displacement piston on the underside of the sample measures displacement. The average interface sliding stress is determined from the applied load, the measured displacement, and the number of fibers displaced. Pullout Techniques Conventional pullout tests are prepared with an end of the fiber protruding from the matrix material, which is gripped directly to the loading apparatus (35), a variation of Figure 4c. The free length of the fiber provides a processing challenge, an alignment challenge during mechanical testing, and an enhanced compliance in the system that may prove undesirable for unstable debond crack initiation. The matrix crack is replaced by a matrix surface, which may pose an artificial barrier to debond crack initiation and, hence, unstable debonding. Despite this, evaluations by Bright et al (36) showed that sliding resistance measurements on a SiC fiber-reinforced borosilicate glass made via pullout and push-out tests were equivalent. However, constant friction shear stress over the