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951.
Dynamic steady-state crack growth has been analyzed under mode I plane stress, small-scale yielding conditions using a finite element procedure. A Perzyna type viscoplastic constitutive equation has been employed in this analysis. The viscoplastic work rate is converted into heat input and the temperature distribution is determined by solving the governing conduction/convection equation also by a finite element method. The Stream-line Upwinding Petrov-Galerkin formulation has been employed for this purpose because of the high Péclet number that results in such a type of analysis. The effect of strain rate sensitivity and crack speed on the temperature distribution near the crack tip is examined. 相似文献
952.
This paper proposes a modification of the Aggarwal et al. algorithm for reliability optimization by introducing a new heuristic criterion for selecting the subsystem where redundancy is to be added. This criterion accounts for the relative decrement in unreliability versus the largest of the relative increments in resources. The method applies to multiple separable constraint problems (which need not be linear) and to systems which may be complex or series. The method is simple, fast, and easily programmed. The results are compared with those of the Aggarwal et al. algorithm and are better in many problems. 相似文献
953.
954.
955.
Cool-down of cryogenic transfer lines is studied analytically and experimentally. Analytical expressions are derived for estimating cool-down time of uninsulated and vacuum insulated lines. The experimental results prove that for short sections the mass flow-rate does not affect the cool-down very significantly. It is also found that the analytical zero mass flow-rate cool-down curve predicts a reasonably accurate cool-down time for all mass flow-rates. The reverse annular flow theory explains many phenomena during cool-down. The cool-down curves are given for uninsulated glass, copper, aluminium and stainless steel pipelines. 相似文献
956.
957.
High temperature tensile creep behaviour of a directionally-solidified Ni3Al-based alloy is presented. The study involved selection of nine alloy systems based on Ni3Al. The alloys contained varying amounts of Cr and Ta, fixed amounts of 1·5 at.% Hf and 0·5 at.% Zr and doped with 0·2 at.%
each of C and B. The alloys were vacuum arc-melted into buttons and homogenized at 1050°C for 68 h. The test pieces of the
alloys were hot compression tested at 600, 700, 800 and 900°C. The yield strength data of some of the alloys were superior
to conventionally cast Mar-M 200, a cast nickel-base superalloy widely used in gas turbine structural applications. The best
alloy system was chosen based on consistent performance in the hot compression studies. The alloy so chosen was directionally
solidified and vacuum-homogenization-treated for 20 h at various selected temperatures. Optimum creep properties were observed
at 1120°C, 20 h treatment. The minimum creep rate data of the DS alloy showed relatively higher values even at lower temperatures
and stress levels as compared to Mar-M 200. Hence, the alloy is less promising in replacing nickel-based superalloys used
as structural materials in gas turbine applications. 相似文献
958.
Bayesian analysis combines the prior belief about the lifetime parameters with the experimental data. The present study develops Bayes estimates for the pointwise and interval availability of a system with constant failure and repair rates. Type I censored failure and repair information has been used in the estimation. 相似文献
959.
This paper reviews the evolution of off-line quality engineering methods with respect to one or more quality criteria, and
presents some recent results. The fundamental premises that justify the use of robust product/process design are established
with an illustrative example. The use of designed experiments to model quality criteria and their optimization is briefly
reviewed. The fact that most design-for-quality problems involve multiple quality criteria motivates the development of multiobjective
optimization techniques for robust parameter design. Two situations are considered: one in which response surface models for
the quality characteristics can be obtained using regression and considered over a continuous factor space, and one in which
the problem scenario and the experiment permit only discrete parameter settings for the design factors. In the former scenario,
a multiobjective optimization technique based on the reference-point method is presented; this technique also incorporates
an inference mechanism to deal with uncertainty in the response surface models caused by finite, noisy data. In the discrete-factors
scenario, an efficient method to reduce computational complexity for a class of models is presented. 相似文献
960.
An algorithm for computing recursively the exact system reliability of k-out-of-n systems is proposed. It is simple, easy to implement, fast, and memory efficient. It gives a reliability expression with minimal number of terms, C(k, n) and involves only a few multiplications. The reduction in number of terms and multiplications is over 50 percent compared to some methods. The recursive nature of the algorithm enables one to design easily the number of units in the system to meet a reliability target. An alternative representation of the algorithm which is easy to remember and good for manual computation is given. However, it involves a few more multiplications compared to the original one but fewer than those required with existing methods. 相似文献