Mechanical behavior and damage development during cyclic fatigue 3.2.4 Microstructural observations plane parallel to the load axis in the middle of the spe- The study of the microstructure is madc on spccimcns cimcn width, the damage bcing cxamined along the tested by cyclic fatigue at different temperatures with a specimen thickness peak stress at 230 MPa. The observations are made on a Matrix cracking(perpendicular to the tensile direc tion). The broken and unbroken specimens, after face between a fifth and a third of that of the untested material (267 117 um initial crack spacing ≌30 to 80=+50 um after cyclic tensile testing at 1500C) If we compare this crack spacing with that exhibited by a specie men s objected to a tensile rve 100c 10 a very small change, a factor of I·2(89±80um and 122+80 um, respectively, after cyclic tensile loading and fatigue tests at 1000C)for the unfailed specimens(tested at 600 and 1000oC)and lOg (NUMBER OF CYCLES) smaller by a factor 0-65 for the fatigue failed spe cimens (tested at room temperature and 1500 Fig. 6. Hysteresis changes during cyclic fatigue tests at differ (126±82{mand80±50um, respectively, after 220 MPa) tensile cyclic loading and fatigue testing at 1500oC) Fig. 9. Damage accumulated during cyclic fatigue testing at Fig. 7. The as-received 2- SD C/SiC composite 600C(omax=230 MPa, in a horizontal loading direction) Fig 8. Damage accumulated during cyclic fatigue testing at 230 MPa, in a horizontal loading Fig 10. Damage accumulated during cyclic fatigue testing atMechanical behavior and dumage development during cyclic fafigue 697 3.2.4 Microstructural observations The study of the microstructure is made on specimens tested by cyclic fatigue at different temperatures with a peak stress at 230 MPa. The observations are made on a em T EW ‘C 0 / ~~ ~~_ 1 10 10’ 10’ 101 IO’ IOh log (NUMBER OF CYCLES) Fig. 6. Hysteresis changes during cyclic fatigue tests at differ￾ent temperatures (umaX = 220 MPa). Fig. 7. The as-received 2-5D C/Sic composite. Fig. 8. Damage accumulated during cyclic fatigue testing at room temperature ((T,,, = 230MPa, in a horizontal loading direction). plane parallel to the load axis in the middle of the spe￾cimen width, the damage being examined along the specimen thickness. Matrix cracking (perpendicular to the tensile direc￾tion). The broken and unbroken specimens, after fatigue testing, exhibit crack spacings at the sur￾face between a fifth and a third of that of the untested material (267 f 117 pm initial crack spacing to 80 l 50 firn after cyclic tensile testing at 1500°C). If we compare this crack spacing with that exhibited by a specimen subjected to a tensile test, we observe a very small change, a factor of 1.2 (89i 80pm and 122 f 80 Km, respectively, after cyclic tensile loading and fatigue tests at 1000°C) for the unfailed specimens (tested at 600 and 1OOOC) and smaller by a factor 0.65 for the fatigue failed spe￾cimens (tested at room temperature and 15OO’C) (126 f 82 pm and 80 f 50 pm, respectively, after tensile cyclic loading and fatigue testing at 1 SOO’C). Fig. 9. Damage accumulated during cyclic fatigue testing at 600°C (o,,, = 230 MPa, in a horizontal loading direction). Fig. 10. Damage accumulated during cyclic fatigue testing at 1500°C (urnax = 230 MPa, in a horizontal loading direction)