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811.
Hopkinson bar techniques have played an important role in the study of high-rate deformation and fracture behavior of materials.
In the current work, a split Hopkinson pressure bar was developed for dynamic four-point bend fracture testing, referred to
as a “two-bar (incident and transmitted bars)/four-point” (2-bar/4-pt) bend test. To further understand some fundamental issues
regarding stress wave propagation in this 2-bar/4-pt bend testing system, dynamic fracture tests were performed in pulse-shaped
and unshaped pulse testing conditions. The effect of the pulse shaper on the incident pulse characteristics (rise time and
duration), specimen’s dynamic response (load and loading point displacement), crack initiation time and stress-state equilibrium
were investigated experimentally in the current work. The present results show that stress state equilibrium can be achieved
prior to fracture initiation in notched and precracked specimens. In the pulse-shaped bending test, the specimen is more likely
to attain stress-state equilibrium than in an unshaped incident pulse test. The crack initiation time was extended and the
time required for attaining stress equilibrium was reduced by pulse shaping due to the tailored incident pulse having a longer
rise time, which ensures that stress equilibrium is achieved prior to crack initiation.
This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during
the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals,
Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee. 相似文献
812.
Aluminum casting alloys exhibit creep behavior when the materials are exposed to high temperature and load. In this article,
the stress- and temperature-dependent creep behavior of a die casting A380-T5 aluminum alloy was simulated using a classical
constitutive model. The bolt-load retention behavior of the material was analyzed in a head bolt joint in an aluminum engine
under thermal cycle condition using the finite element method. In this simulation, transient thermal analysis was performed
first to calculate the metal temperature at the head bolt joint as a function of time during engine thermal cycling. This
temperature was then input as the thermal loading in the subsequent structural analysis to calculate its effect on the bolt-load
retention. The finite element analysis (FEA) model for the bolt-load retention simulation includes not only the plasticity
in all metal components but also the creep properties of head bolt threads in the cast aluminum engine block. The FEA model
was validated by good correlation between the predicted head bolt-load loss and the experimental measurement during engine
thermal cycling. The simulation results also indicated that creep in the head bolt threads of cast aluminum engine block was
mainly responsible for the load loss in the head bolt joint.
This article is based on a presentation given in the symposium entitled “Simulation of Aluminum Shape Casting Processing:
From Design to Mechanical Properties” which occurred March 12–16, 2006 during the TMS Annual Meeting in San Antonio, Texas
under the auspices of the Computational Materials Science and Engineering Committee, the Process Modeling, Analysis and Control
Committee, the Solidification Committee, the Mechanical Behavior of Materials Committee, and the Light Metal Division/Aluminum
Committee. 相似文献
813.
量子卡诺制冷机制冷率与熵产率的协调优化性能 总被引:3,自引:2,他引:1
研究了内可逆谐振子量子卡诺制冷机的整体最优性能。得到了协调优化目标函数E最大时量子制冷机的制冷系数以及最佳制冷率和熵产率。 相似文献
814.
815.
本系统是一个较完整的由单片机控制的消防系统,其功能是在查到消防报警信号后,通过串行通讯口给各控制点发出控制信号如起动加压水泵,打开喷水龙头的电磁阀或灭火器的气体阀等等。讯号由键盘发出。各被控点如已正确动作,在控制板上会有所显示。误动作或未动作也可显示在控制板上。控制的时间和路数可由打印机记录下来、相应的软件有数据处理、显示、通讯、结果打印等。 相似文献
816.
纺织品印染后整理剂Fs系多羟基多胺的阳离子树脂型缩合物,不含游离甲醛。本文介绍了纺织品印染后整理剂Fs的合成方法和应用条件。 相似文献
817.
布尔函数的对偶性和线性点 总被引:5,自引:1,他引:4
本文主要讨论了部分自对偶和部分反自对偶函数、部分线性函数以及具有线性点的函数的性质。 相似文献
818.
The cellular localization of protein kinase C (PKC) is intimately associated with the regulation of its biological activity. Previously we have demonstrated that the redistribution of PKC to the plasma membrane in response to physiological stimuli is followed by a rapid returning of PKC back to the cytoplasm (Feng, X., Zhang, J., Barak, L. S., Meyer, T., Caron, M. G., and Hannun, Y. A. (1998) J. Biol. Chem. 273, 10755-10762). Although the process of PKC membrane targeting has been extensively studied, the molecular mechanism underlying the dissociation of membrane-bound PKC remains unclear. In the present study, by examining the dynamic distribution of wild-type PKC betaII and its kinase-deficient mutant (K371R), we demonstrate that kinase activity is required for PKC membrane dissociation. Moreover, the inability of PKC betaII(K371R) to dissociate from the plasma membrane in cells overexpressing wild-type PKC betaII suggests that autophosphorylation activity of the kinase might be essential for its membrane dissociation. This was further supported by mutational analysis of two in vivo autophosphorylation sites on PKC betaII. The replacement of Ser660 or Thr641 by alanine (S660A or T641A) was found to synergistically reduce the reversal of PKC betaII membrane translocation, whereas the replacement of the same amino acids by glutamic acid (S660E or T641E), an amino acid commonly used to mimic phosphate, results in mutants behaving similar to wild-type PKC betaII. These findings point to an essential role for autophosphorylation in the dissociation of activated PKC from the plasma membrane and suggest that, like PKC membrane translocation, the returning of PKC to the cytoplasm after its activation is also delicately regulated. 相似文献
819.
Investigation on Ballistic Performance of Armor Ceramics against Long-Rod Penetration 总被引:1,自引:0,他引:1
A series of depth-of-penetration (DOF) tests are carried out to investigate the ballistic performance of armor ceramics. Based
on the experimental results, an improved differential efficiency factor (DEF) is presented, which demonstrates that the general
ballistic efficiency index is independent of the ceramic thickness. It is also shown that the density, internal friction,
and compression strength of ceramics are crucial factors that affect the ballistic performance of ceramics significantly through
the interaction between the long-rod projectiles and thick-tile armor.
This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during
the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals,
Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee. 相似文献
820.
This paper explores different means of representation for algebraic transductions, i.e., word relations realized by pushdown transducers. The relevance of this work lies more in its point of view rather than any particular result. We are aiming at giving specific techniques for obtaining, or perhaps explaining, decompositions of algebraic (and incidentally, rational) relations, relying solely on their “machine” definition rather than some complex algebraic apparatus. From this point of view, we are hoping to have demystified the heavy formalism employed in the present literature. Some of the novelties of our work are: the use of “stack languages” and “embeddings,” which eliminate the need of arbitrary context-free languages in our characterizations, the study of uniformizations for algebraic transductions and the use of the so-called stack transductions for exposing the anatomy of pushdown transducers.This work was supported by the Natural Science and Engineering Research Council of Canada grants R220259 and OGP0041630. 相似文献