酸腐蚀条件下石膏岩分数阶蠕变本构模型研究

为探究地下水对岩石的侵蚀损伤,通过开展酸腐蚀条件下的石膏岩单轴压缩蠕变试验和扫描电镜试验,研究了不同pH条件下石膏岩单轴压缩蠕变特性以及酸腐蚀前后试样的微观变化。结果表明：酸腐蚀加快了试样的蠕变速度,酸性越强,蠕变速率越快;试样主要以劈裂和剪切破坏形式为主,端部出现损伤破坏的现象,酸性越强,损伤破坏越明显。微观上,干燥试样结构完整;而酸腐蚀后的试样,随着酸性增强,孔隙增多、增大,结构疏松。为描述酸腐蚀条件下石膏岩蠕变过程,通过引入酸腐蚀劣化衰减系数β对变系数Abel黏壶进行改造,用改造后的变系数Abel黏壶元件代替西原体中黏塑性体部分的牛顿黏壶,建立了考虑酸腐蚀条件下的分数阶蠕变本构模型。通过试验数据与所建立的模型进行参数拟合,确定了模型中的参数,并对引入的参数β进行了敏感性分析。研究表明,所提出的模型能够很好地反映酸腐蚀条件下石膏岩的蠕变三个阶段,尤其是加速蠕变阶段。     

焊接管结构的非线性推覆简化模型

有限元分析方法中,采用三维实体单元对焊接管结构进行离散是最为精确的建模方法,但对三维实体模型分析时会划分大量单元,导致计算时间冗长。工程中常把焊接管结构简化为刚架模型,即刚性连接的杆系系统。这种建模方式忽略了节点的局部柔度,过高地估计了整体结构的刚度,使计算结果偏于危险。为解决上述问题,在节点处引入虚拟梁单元,使其等效模拟节点的局部变形,还原支管真实长度。为了验证节点柔度对焊接管结构的影响,对典型的焊接管结构缩尺,进行了推覆试验。分别采用壳单元模型、刚架模型及引入虚拟梁单元的简化模型进行有限元模拟,并与试验结果对比分析。结果表明,刚架模型会过高的估计焊接管结构的刚度,而简化模型计算结果与壳模型、试验结果较为吻合。     

聚脲加固砖填充墙抗爆性能的试验和分析方法研究

为了掌握聚脲喷涂加固砖填充墙的抗爆特性,基于一种改进的大型爆炸试验装置,开展了聚脲加固框架砖填充墙的原型爆炸试验,分析了爆炸荷载作用下加固砖墙的动力响应特征和破坏过程及模式,揭示了其失效破坏机理。研究结果表明,聚脲加固可大幅提升填充墙构件的抗爆性能,显著增加填充墙构件的变形延性;加固砖墙受爆炸荷载作用发生振动的过程其体系刚度不断变化,最高相差133%;随着比例距离降低,加固砖墙的破坏模式逐渐由弯曲破坏转为剪切破坏,聚脲厚度超过6 mm可以有效限制局部剪切破坏现象;基于砖墙和聚脲涂层的抗力函数建立的理论计算模型,可以较为准确地预测爆炸作用下背爆面加固双向砖墙的正向位移响应过程。     

AN EFFICIENT SEQUENTIAL DESIGN FOR SENSITIVITY EXPERIMENTS

In sensitivity experiments, the response is binary and each experimental unit has a critical stimulus level that cannot be observed directly. It is often of interest to estimate extreme quantiles of the distribution of these critical stimulus levels over the tested products. For this purpose a new sequential scheme is proposed with some commonly used models. By using the bootstrap repeated-sampling principle, reasonable prior distributions based on a historic data set are specified. Then, a Bayesian strategy for the sequential procedure is provided and the estimator is given. Further, a high order approximation for such an estimator is explored and its consistency is proven. A simulation study shows that the proposed method gives superior performances over the existing methods.     

恒定非均匀磁场调控下的强制对流传热数值研究

分别对雷诺数、磁场强度和磁纳米流体浓度进行了讨论，并将数字高程模型(DEM)应用到梯度磁场模型的建立，分析了磁场梯度大小和方向对传热效果的影响。结果表明：雷诺数、磁场强度和梯度与传热效果呈正相关，在磁场介入的情况下，磁纳米流体浓度对传热效果的影响存在一个最佳值；磁场梯度方向垂直于流动方向时对传热的强化效果最显著。以平均努塞尔数和压降为目标参数，利用正交试验设计的方法研究了各变量对传热效果影响的权重大小，得到各变量取值范围内的最佳组合。     

Precipitate Contribution to the Acoustic Nonlinearity in Nickel-Based Superalloy

The influence of γ′ precipitate on the acoustic nonlinearity is investigated for a nickel-based superalloy, which is subjected to creep deformation. During creep deformation, the cuboidal γ′ precipitate is preferentially coarsened in a direction perpendicular to the applied stress axis. The length and shape factor of the γ′ precipitate increase with creep time. The increase of relative acoustic nonlinearity with increasing fraction of creep life is discussed in relation to the rafting of γ′ precipitate, which is closely related to the scattering and distortion of the acoustic wave     

Improved free space optical communications performance by using time diversity

A laser beam propagating through turbulence experiences random amplitude and phase fluctuations, which can severely degrade the performance of free space optical communication systems. It this letter, time diversity is demonstrated as a technique which can decrease turbulence influence. Statistically, laser propagation along an atmospheric path is uncorrelated with an earlier-time path for a time interval greater than the atmospheric turbulence correlation time. To estimate time diversity system performance, a 2.2-km optical link is set up for comparing the fade probability of a system using time diversity with a system not using time diversity. The experimental results obtained under different turbulence conditions are shown which are in good agreement with the theory.     

高速铣削过程铣削力建模及析因试验分析

相对于常规切削，高速铣削时切削力的变化更为复杂，研究高速铣削过程中切削力的变化有助于优化切削参数，对实际生产有着重要的指导意义。     

W/Cu梯度功能材料的高热负荷性能研究

用等离子体喷涂和热压方法制作了W/Cu梯度功能材料(FGM)样品,用大功率ND∶YAG激光对其进行了高热负载模拟实验.结果表明,在100～400MW@m-2的瞬时(脉冲宽度为4ms)热负载下,经过200～700次热循环,未发现有W-Cu复合体开裂.在123MW@m-2的功率密度下作用700次,发现钨表面有再结晶现象及严重的晶界腐蚀和裂纹,再结晶的平均晶粒尺寸约为5～10μm,垂直于表面呈柱状结构,再结晶层厚度约20～30μm.由于激光的淬冷效应,晶粒生长的趋势并不明显.在398MW@m-2功率密度下出现了明显的腐蚀坑,坑内呈疏松的蜂窝结构,坑的边缘出现了明显沉积区,能谱分析表明沉积区集聚了大量的金属杂质.等离子体喷涂试样比热压试样更易产生晶界的断裂的裂纹.在相同的热负荷条件下,W/Cu FGM的重量损失低于石墨材料的重量损失.     

指数分布场合下步进应力加速寿命试验的Bayes分析

当寿命分布为指数分布时，本文给出了步进应力加速寿命试验的一种新的Ｂａｙｅｓ估计，为计算上的方便，本文还给出一种近似方法，数值例子表明，此方法简便可行。