A. Morales-Rodriguez et al. Journal of the European Ceramic Sociery 27(2007)3301-3305 Table I List of MTT-deformed specimens indicating the solicitation conditions, strengths, final strains and Youngs moduli Specimen Loading rate(N/min) OUTs(MPa) Efna(%) Ec(MPa 0.48 The fracture behavior at room temperature in air has been investigated under different uniaxial tensile conditions. mono- tonic load (MTT, Monotonic Tensile Test) and after static fatigue #1 at various stress levels to explore the residual properties(RTT, Residual Tensile Test). The mechanical tests have been per #2 formed on a servohydraulic machine(INSTRON model 8502) using samples with bone-shape of rectangular section(calibrated length: 8 mm x 3 mm x 40 mm). Samples and test conditions ￡(% are summarized in Tables 1 and 2 Fractured specimens were examined using a conventional Fig. 1. Monotonic tensile behavior of original specimens loaded at 100N/min scanningelectronic microscope(SEM, model JEOL JSM-840A) (dashed line)and at 500N/min(solid line) at room temperature in air. to investigate the characteristic fracture surface morphology of the fibers in order to estimate in situ fiber strength. Pull out lengths have been measured to estimate the shear stress developed during fiber/matrix sliding before the final fracture. 6 Surfaces parallel to the loading axis have been cut using a slow speed saw, polished up to 1 um diamond paste and chem ically etched by the Murakami procedure to exhibit the matrix 3. Experimental results ig. I presents a-e plots corresponding to the initial monotonic tensile behavior of 2D-SiC/Sic composites. The mechanical properties obtained from these tests are collected in Table 1. It is observed that these composites are able to achieve UTS values of 228 MPa and final deformations up to 0.7%.Fig. 2 shows a-E plots corresponding to RTT after static loading at two different stress levels of 70%(dashed line) and 90% or(solid line) where the maximal strength measured in MTT has been Fig. 2. a-c plots from RTT after two different loading conditions in fatigue of considered as the reference strength, oR, for these composites 70%(dashed line)and 90%0 OR(solid line) at room temperature in air. These The changes observed in o-E slopes after static fatigue tests, Et, plots show the loading, the static fatigue and the final residual tensile curves comparing with the first loading slopes, EC, indicate that dam- aging processes are developed during static fatigue, decreasing for as-received specimens. In contrast, an enhancement of the the elastic modulus(EC< EF). Youngs modulus evolution is residual properties is observed after loading at 90% of rupture negligible up to 60% OR static loading conditions(Fig. 2, #5). stress level; higher strength and larger final deformation have The mechanical properties obtained from RTTs are collected been achieved in"high-stress"post-fatigued composites(solid in Table 2. Note that the strength after static loading at low line). This enhancement of residual properties has not been noted stress(dashed line) is limited to the monotonic strength found previously after static fatigue Table 2 List of RTT-deformed specimens indicating the static fatigue conditions, strengths, final strains and Youngs moduli(F: first loading and D: damaged after static Specimen Fatigue conditions OUTS(MPa) Final(%o) (MPa) (MPa) 100h,70%aR 6 h,90% Loading rates of 500N/min were imposed during monotonic tensile steps3302 A. Morales-Rodr´ıguez et al. / Journal of the European Ceramic Society 27 (2007) 3301–3305 Table 1 List of MTT-deformed specimens indicating the sollicitation conditions, strengths, final strains and Young’s moduli Specimen Loading rate (N/min) σUTS (MPa) εfinal (%) EC (MPa) #1 500 228 0.66 189 #2 100 202 0.48 178 #3 100 225 – – The fracture behavior at room temperature in air has been investigated under different uniaxial tensile conditions: mono￾tonic load (MTT, Monotonic Tensile Test) and after static fatigue at various stress levels to explore the residual properties (RTT, Residual Tensile Test). The mechanical tests have been per￾formed on a servohydraulic machine (INSTRON model 8502) using samples with bone-shape of rectangular section (calibrated length: 8 mm × 3 mm × 40 mm). Samples and test conditions are summarized in Tables 1 and 2. Fractured specimens were examined using a conventional scanning electronic microscope (SEM, model JEOL JSM-840A) to investigate the characteristic fracture surface morphology of the fibers in order to estimate in situ fiber strength. Pull￾out lengths have been measured to estimate the shear stress developed during fiber/matrix sliding before the final fracture.6 Surfaces parallel to the loading axis have been cut using a slow speed saw, polished up to 1 m diamond paste and chem￾ically etched by the Murakami procedure to exhibit the matrix cracks. 3. Experimental results Fig. 1 presents σ–ε plots corresponding to the initial monotonic tensile behavior of 2D-SiCf/SiC composites. The mechanical properties obtained from these tests are collected in Table 1. It is observed that these composites are able to achieve UTS values of 228 MPa and final deformations up to 0.7%. Fig. 2 shows σ–ε plots corresponding to RTT after static loading at two different stress levels of 70% (dashed line) and 90% σR (solid line) where the maximal strength measured in MTT has been considered as the reference strength, σR, for these composites. The changes observed in σ–ε slopes after static fatigue tests, ED C, comparing with the first loading slopes, EF C, indicate that dam￾aging processes are developed during static fatigue, decreasing the elastic modulus (ED C < EF C). Young’s modulus evolution is negligible up to 60% σR static loading conditions (Fig. 2, #5). The mechanical properties obtained from RTTs are collected in Table 2. Note that the strength after static loading at low stress (dashed line) is limited to the monotonic strength found Fig. 1. Monotonic tensile behavior of original specimens loaded at 100 N/min (dashed line) and at 500 N/min (solid line) at room temperature in air. Fig. 2. σ–ε plots from RTT after two different loading conditions in fatigue of 70% (dashed line) and 90% σR (solid line) at room temperature in air. These plots show the loading, the static fatigue and the final residual tensile curves. for as-received specimens. In contrast, an enhancement of the residual properties is observed after loading at 90% of rupture stress level; higher strength and larger final deformation have been achieved in “high-stress” post-fatigued composites (solid line). This enhancement of residual properties has not been noted previously after static fatigue. Table 2 List of RTT-deformed specimens indicating the static fatigue conditions, strengths, final strains and Young’s moduli (F: first loading and D: damaged after static fatigue) Specimen Fatigue conditions σUTS (MPa) εfinal (%) EF C (MPa) ED C (MPa) #4 100 h, 70% σR 225 0.6 197 115 #5 120 h, 90% σR 265 0.9 171 82 #6 120 h, 90% σR 256 – – – Loading rates of 500 N/min were imposed during monotonic tensile steps.