Fatigue Behavior of a Cross-Ply Ceramic Matrix Composite Under Tension-Tension and Tension-Compression Loading

A study was conducted which investigated the behavior of a cross-ply [0/90]2S Nicalon/Calcium-Aluminosilicate (Nicalon/CAS) ceramic matrix composite at room temperature under tension-compression fatigue loading. Material behavior and damage was recorded by stress-strain curves, elastic modulus, hysteretic energy density, and acetate replication techniques. Tension-tension fatigue tests at a load ratio R of 0.1 (R = σmin/σmax) were completed which determined that 140 MPa was the maximum stress allowable in which cycle runout (1,000,000 cycles) would occur. Above this value, transverse crack density increased with respect to cycles and failure ultimately occurred. Tension-compression tests were then performed at load ratios of -2.0, -1.5, and -1.0 with 140 MPa as the maximum tensile stress. In all cases, longitudinal cracks parallel to the loading direction developed. The greater the magnitude of the compressive load, the sooner these longitudinal cracks appeared. Failure always occurred in compression due to buckling of individual plies, thus indicating that tension-compression can significantly reduce fatigue life. Using the elastic modulus as a means of verifying damage was acceptable, but it did not reasonably predict specimen failure. on the other hand, the area under the stress-strain curve (hysteretic energy density) was a better indicator of probable failure since specimens which achieved cycle runout showed either a decreasing or constant energy density while those which failed always showed an increasing value

The Ethnic 'Other' in Ukrainian History Textbooks: The Case of Russia and the Russians

This paper examines portrayals of Russia and the Russians in two generations of Ukrainian history textbooks. It observes that the textbooks are highly condemning of Ukraine's main ethnic other in the guise of foreign ruler: the tsarist authorities and the Soviet regime are always attributed dubious and malicious intentions even if there is appreciation for some of their policies. By contrast, the books, certainly those of the second generation, refrain from presenting highly biased accounts of the ethnic other as a national group (i.e. Russians). Instances where negative judgements do fall onto Russians are counterbalanced by excerpts criticizing ethnic Ukrainians or highlighting conflicting interests within the Ukrainian ethnic group. The negative appraisal of the ethnic other as foreign ruler is clearly instrumental for the nation-building project as it sustains a discourse legitimating the existence of Ukraine as independent state. However, recent trends in history education, the paper concludes, suggest that the importance of nurturing patriotism as a national policy objective is diminishing