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  • 1
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper examines the effects of loading rate on the Weibull stress model for prediction of cleavage fracture in a low-strength, A515-70 pressure vessel steel. Interest focuses on low-to-moderate loading rates (K˙I 〈 2500 MPa √m s−1 ). Shallow cracked SE(B) specimens were tested at four different loading rates for comparison with previous quasi-static tests on shallow notch SE(B)s and standard C(T)s. To utilize these dynamic experimental data, we assume that the Weibull modulus (m) previously calibrated using quasi-static data remains invariant over the loading rates of interest. The effects of dynamic loading on the Weibull stress model enter through the rate-sensitive material flow properties, the scale parameter (σu ) and the threshold Weibull stress (σw-min ). Rate-sensitive flow properties are modelled using a viscoplastic constitutive model with uniaxial, tension stress–plastic strain curves specified at varying plastic strain rates. The analyses examine dependencies of σw-min and σu on K˙I . Present results indicate that σw-min and σu are weak functions of loading rate K˙I for this pressure vessel steel. However, the predicted cumulative probability for cleavage exhibits a strong sensitivity to σu and, consequently, the dependency of σu on K˙I is sufficient to preclude use of the static σu value for high loading rates.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Jasmonic acid (JA) is known to be involved in the response of plants to environmental stresses such as drought, and betaine (glycinebetaine) is an osmopretectant accumulated in plants under environmental stresses including drought. However, it remains currently unclear whether JA is involved in the water-stress-induced betaine accumulation in plant leaves. The present experiment, performed with the whole pear plant (Pyrus bretschneideri Redh. cv. Suli), revealed that the exogenously applied JA induced a significant increase of the betaine level in the pear leaves when the plants were not yet stressed by drought, and when the plants were subjected to water stress, the ‘JA plus drought’ treatment induced a significant higher betaine level than did the drought treatment alone. Meanwhile, the ‘JA plus drought’ treatment induced higher levels of betaine aldehyde dehydrogenase (BADH, E C 1.2.1.8) and activities in the leaves than did the drought treatment alone. These results obtained in the whole plant experiments were supported by the results of detached leaf experiments. In detached leaves JA induced significant increases in betaine levels, BADH activities and BADH protein amounts in a time- and concentration-dependent manner. These data demonstrate that JA is involved in the drought-induced betaine accumulation in pear leaves.
    Type of Medium: Electronic Resource
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