Y. Gowayed et aL/ Composites Science and Technology 70(2010)435-441 分AA Fig. 2(a) Film X-ray image of panel and(b) through transmitted ultrasound image of typical panel The white circle and the red dot are a tungsten marker placed on the anel. For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article. indication of any delamination and no large scale porosity was the stress-strain curve was reached, stress-strain data are fitted noted in the panels. In addition, each panel had two tensile bars ex to determine the modulus. validation of the stacked disks experi- tracted and tested at room temperature. All samples tested failed mental approach was carried out by using a rod of machineable above a 0.3% strain to failure requirement set to screen for process- monolithic glass ceramic MACOR [4]. A 28 mm long piece of the ing induced embrittlement. Since no anomalies were noted, these rod was tested in compression at room temperature to obtain panels were accepted into the experimental effort. the compressive elastic modulus which was determined to be Tensile tests were performed per EPM testing standards(equiv- 68.9 GPa. A series of disks were machined out of the rod with the alent to ASTM C1359)at room temperature and 1204C as a pos- same dimensions to be used in the testing of the CMC materiaL. sible operating temperature. Typical stress-strain curves are Testing was conducted at room temperature and the modulus of shown in Fig. 3. The elastic modulus was calculated as the slope the stacked disks was determined to be 66.0 GPa. This agreement of the stress-strain curve in the linear region between 13.79 and between the compressive elastic modulus of the rod and the 55. 16 MPa(2-8 Ksi) Strain gages were fitted to evaluate the Pois- stacked disks shows that the stacked disk method can be accepted sons ratio at room temperature. The shear modulus was deter- as a sound testing method ine/ s g biaxial extensometry on samples machined out of Nano-indentation experiments were carried out on the cross- nels at 45 and shear analysis was done consistent with section of samples to measure the in situ elastic moduli of the dis- D3518. The curves were fitted between 6.90 and crete phases of the composite [5]. This work was performed at 27.58 MPa(1-4 Ksi)in the linear shear region to be consistent with room temperature using a Nano-Indenter Il at Oak Ridge National the tensile modulus calculation Laboratory. The modulus was determined by analysis of the load A compressive test was performed on a series of stacked disks displacement recorded during nano-indentation as well as the va- to determine the through-thickness modulus at room temperature lue of the elastic modulus of the indentor [ 6]. The value of the elas in conformance with a recently developed technique [3. In this tic modulus of the iBN-Sylramic fiber measured using nano- experiment, each individual disk is ground flat to remove asperities indentation was found to be similar to that evaluated using a and enough disks are machined for a 2.54 cm extensometer to be tow testing techniques 5. A Hysitron's Tribo-lndenter was used flagged onto the sample. Through the center of each disk a hole to evaluate the elastic properties of the relatively compliant BN is machined so that a graphite rod could be inserted to hold the phase due to its ability to apply ultra-low load levels(a 400 HN stack in place and eliminate disk movement during initial loading. load was used in this case). Additionally, the Tribo-Indenter al- The rod is machined short so that it would not see any load that lowed in situ imaging by scanning probe microscopy as shown in could affect the measured modulus. Even though the disks are ma- Fig. 4. Up to the authors'knowledge this is the first time that chined flat, there is a typical initial compliance to the stack that the Young,s Modulus of the boron Nitride is measured within a had to be overcome by sufficient load. Once the linear region of systematic procedure to evaluate the in situ elastic moduli of con- stituent phases. The result of this nano-indentation work is listed aperature 3. Analysis of experimental data Nano-indentation experiments for constituent phases the in situ elastic modulus of the fiber as 394.9 GPa. the as 20.27 GPa. the sic-CVI as 438. 8 GPa. the sic-Sc as 405.6 GPa and the mi si metal as 164. 9 gPa as listed in table 1. results for the in situ modulus for the fiber, the Sic phases and the Si metal did not change much from their values for stand-alone phases. Up to the authors'knowledge, the value for the in situ modulus of the bn coat has not been previously reported in literature. Typical stress-strain curves at room temperature and 1204C for the Sic/SiC composite material are shown in Fig 3. It strain o0o 0s 0, seen for both temperatures, that at low load levels there is a linear Fig 3. Tensile stress-strain curves at room temperature and 1204 is followed by a knee in the curve and another linear regionindication of any delamination and no large scale porosity was noted in the panels. In addition, each panel had two tensile bars ex￾tracted and tested at room temperature. All samples tested failed above a 0.3% strain to failure requirement set to screen for process￾ing induced embrittlement. Since no anomalies were noted, these panels were accepted into the experimental effort. Tensile tests were performed per EPM testing standards (equiv￾alent to ASTM C1359) at room temperature and 1204 C as a pos￾sible operating temperature. Typical stress–strain curves are shown in Fig. 3. The elastic modulus was calculated as the slope of the stress–strain curve in the linear region between 13.79 and 55.16 MPa (2–8 Ksi). Strain gages were fitted to evaluate the Pois￾son’s ratio at room temperature. The shear modulus was deter￾mined using biaxial extensometry on samples machined out of the panels at 45 and shear analysis was done consistent with ASTM D3518. The curves were fitted between 6.90 and 27.58 MPa (1–4 Ksi) in the linear shear region to be consistent with the tensile modulus calculation. A compressive test was performed on a series of stacked disks to determine the through-thickness modulus at room temperature in conformance with a recently developed technique [3]. In this experiment, each individual disk is ground flat to remove asperities and enough disks are machined for a 2.54 cm extensometer to be flagged onto the sample. Through the center of each disk a hole is machined so that a graphite rod could be inserted to hold the stack in place and eliminate disk movement during initial loading. The rod is machined short so that it would not see any load that could affect the measured modulus. Even though the disks are ma￾chined flat, there is a typical initial compliance to the stack that had to be overcome by sufficient load. Once the linear region of the stress–strain curve was reached, stress–strain data are fitted to determine the modulus. Validation of the stacked disks experi￾mental approach was carried out by using a rod of machineable monolithic glass ceramic MACOR [4]. A 28 mm long piece of the rod was tested in compression at room temperature to obtain the compressive elastic modulus which was determined to be 68.9 GPa. A series of disks were machined out of the rod with the same dimensions to be used in the testing of the CMC material. Testing was conducted at room temperature and the modulus of the stacked disks was determined to be 66.0 GPa. This agreement between the compressive elastic modulus of the rod and the stacked disks shows that the stacked disk method can be accepted as a sound testing method. Nano-indentation experiments were carried out on the cross￾section of samples to measure the in situ elastic moduli of the dis￾crete phases of the composite [5]. This work was performed at room temperature using a Nano-Indenter II at Oak Ridge National Laboratory. The modulus was determined by analysis of the load– displacement recorded during nano-indentation as well as the va￾lue of the elastic modulus of the indentor [6]. The value of the elas￾tic modulus of the iBN-Sylramic fiber measured using nano￾indentation was found to be similar to that evaluated using a tow testing techniques [5]. A Hysitron’s Tribo-Indenter was used to evaluate the elastic properties of the relatively compliant BN phase due to its ability to apply ultra-low load levels (a 400 lN load was used in this case). Additionally, the Tribo-Indenter al￾lowed in situ imaging by scanning probe microscopy as shown in Fig. 4. Up to the authors’ knowledge, this is the first time that the Young’s Modulus of the Boron Nitride is measured within a systematic procedure to evaluate the in situ elastic moduli of con￾stituent phases. The result of this nano-indentation work is listed in Table 1. 3. Analysis of experimental data Nano-indentation experiments for constituent phases reported the in situ elastic modulus of the fiber as 394.9 GPa, the BN coat as 20.27 GPa, the SiC-CVI as 438.8 GPa, the SiC-SC as 405.6 GPa and the MI Si metal as 164.9 GPa as listed in Table 1. Results for the in situ modulus for the fiber, the SiC phases and the Si metal did not change much from their values for stand-alone phases. Up to the authors’ knowledge, the value for the in situ modulus of the BN coat has not been previously reported in literature. Typical stress–strain curves at room temperature and 1204 C for the SiC/SiC composite material are shown in Fig. 3. It can be seen for both temperatures, that at low load levels there is a linear relationship between stress and strain until around 170 MPa. This is followed by a knee in the curve and another linear region. Fig. 2. (a) Film X-ray image of panel and (b) through transmitted ultrasound image of typical panel. The white circle and the red dot are a Tungsten marker placed on the panel. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) 0 100 200 300 400 500 600 0 0.001 0.002 0.003 0.004 0.005 0.006 Stress (MPa) Strain Room Temperature 1204ºC Fig. 3. Tensile stress–strain curves at room temperature and 1204 C. Y. Gowayed et al. / Composites Science and Technology 70 (2010) 435–441 437