The dependence of structure and properties of polycrystalline diamonds (PCD) on the conditions of their production

Abstract

AES and SIMS were used to analyze the diamond powders surface composition using LAS-3000 device. It is found that impurities on diamond particles surfaces have a detrimental effect on the PCD sintering and physico-mechanical properties of the product.     

套管外压挤毁强度分析与计算

在对大量的套管全尺寸挤毁试验结果分析的基础上，提出套管外压失稳机理：实际工程中的套管截面不是理想圆，在外压作用下的非圆套管圆周方向上环向应力分布不均匀，有附加弯矩效应；随外压增加，在最大压缩环向应力处达到屈服；当屈服逸到一定程度时，材料由于强度承载力不足而失效，导致套管发生失稳挤毁。基于上述套管强度挤毁准则，分析了理想弹塑性套管在轴向载荷作用下的抗挤强度计算方法，得到较保守的套管挤毁压力计算公式。与试验结果对比表明：导出的计算公式偏差较小，计算精度满足工程要求，失稳强度准则是适用的。     

Imaginary quadratic function fields

In Bautista-Ancona and Diaz-Vargas (2006) [B-D] a characterization and complete listing is given of the imaginary quadratic extensions K of k(x), where k is a finite field, in which the ideal class group has exponent two and the infinite prime of k(x) ramifies. The objective of this work is to give a characterization and list of these kind of extensions but now considering the case in which the infinite prime of k(x) is inert in K. Thus, we get all the imaginary quadratic extensions of k(x), in which the ideal class group has exponent two.     

Stress distribution in poly‐p‐phenylenebenzobisoxazole (PBO) fiber estimated from vibrational spectroscopic measurement under tension. II. Analysis of inhomogeneous stress distribution in PBO fiber

Fourier transform Raman spectra were measured for poly‐p‐phenylenebenzobisoxazole (PBO) fiber subjected to a tensile stress, and the Raman shift factor (the frequency shift caused by 1 GPa tensile stress) depended strongly on the sample‐preparation condition. To clarify the reasons of this dependency, a mechanical series parallel model was adopted that could successfully and quantitatively explain the observed Raman shift factors and gave a concreate heterogeneous stress distribution in the PBO fibers. As a result, a mechanical series model was reasonable for PBO fiber. Broadening of Raman bands, which was observed when the PBO fiber was tensioned, could also be interpreted on the basis of an idea of heterogeneous stress distribution. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1281–1287, 2002     

Creep and Long-Term Strength of Press-Powder Composites

The mechanical state of a press-powder filler for pyroautomatics system units of aerospace equipment during their long-term storage is investigated. With the use of the endochronic approach, the rheological properties of a dispersedly reinforced composite are simulated based on the conceptions of linear and nonlinear creep. Analytical expressions of constitutive relations of creep and strength for the composites are obtained. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 6, pp. 803–818, November–December, 2005.     

孔洞受压的统一极限分析

采用俞茂宏统一强度理论分别就平面应变和平面应力总是对受压孔洞进行了极限分析，得到了各自的统一解形式。以往的基于Ｔｒｅｓｃａ、Ｍｉｓｅｓ、双剪屈服准则以及Ｍｏｈｒ－Ｃｏｕｌｏｍｂ强度理论的极限解均为本文统一解的特例。此解可以适应于广泛的不同性质的各灯材料，合理也得出不同材料的相应解。     

STRENGTH ANALYSIS OF CLAMPING IN MICRO/NANO SCALE EXPERIMENTS

Two kinds of clamping in micro/nano scale experiments are investigated in this paper, one based on electron-beam-induced deposition, and the other on the van der Waals interaction. The clamping strength and mechanism are analyzed both theoretically and experimentally. The influence of relative humidity on the micro/nano clamping and the method of electrostatic clamping are discussed. The clamping strength and performance of different clamping methods are compared considering the size and material of the clamped objects, and the application environments.     

交连续dcpo的遗传性和不变性

讨论了交连续dcpo的遗传性和不变性,证明了如下结论:(1)交连续dcpo对于开子空间和闭子空间都是可遗传的;(2)交连续dcpo在加最大元和去最小元运算下保持交连续性;(3)交连续dcpo的收缩核为交连续dcpo.另外,给出了交连续的主理想刻画的一个直接证明;构造了反例说明交连续dcpo对于主滤子是不可遗传的;也构造了反例说明所有主滤子都交连续的一个dcpo,自身不必是交连续的.     

Role of weak interface to retain high strength of fiber in monofilamentary SiC fiber/titanium-aluminide composite

The tensile strength of monofilamentary weakly bonded SiC fiber/γ-TiAl intermetallic compound matrix composite, prepared by the sputtering method, was measured and analysed using a fracture mechanical technique. The main results are summarized as follows: (1) The fracture of TiAl occurred prior to that of fiber, resulting in formation of circumferential cracks on the fiber. Interfacial debonding occurred during tensile test, resulting in long pull-out of the fiber. (2) The strength of the fiber in the TiAl matrix was nearly the same as that of the bare fiber. (3) The fracture mechanical analysis showed that (i) the interfacial debonding grows unstably upon initiation and (ii) the stress distribution in the fiber in the cross-section, where the matrix is fractured, approaches to that of bare fiber with increasing debonded length. The reason why the fiber strength was maintained in spite of the formation of cracks on the fiber surface due to the premature fracture of the matrix was accounted for by the fully blunted crack-tip from the above calculation result.     

Anchorage strength models for end-debonding predictions in RC beams strengthened with FRP composites

The increase in the flexural capacity of RC beams obtained by externally bonding FRP composites to their tension side is often limited by the premature and brittle debonding of the external reinforcement. An in-depth understanding of this complex failure mechanism, however, has not yet been achieved. With specific regard to end-debonding failure modes, extensive experimental observations reported in the literature highlight the important distinction, often neglected in strength models proposed by researchers, between the peel-off and rip-off end-debonding types of failure. The peel-off failure is generally characterized by a failure plane located within the first few millimetres of the concrete cover, whilst the rip-off failure penetrates deeper into the concrete cover and propagates along the tensile steel reinforcement. A new rip-off strength model is described in this paper. The model proposed is based on the Chen and Teng peel-off model and relies upon additional theoretical considerations. The influence of the amount of the internal tensile steel reinforcement and the effective anchorage length of FRP are considered and discussed. The validity of the new model is analyzed further through comparisons with test results, findings of a numerical investigation, and a parametric study. The new rip-off strength model is assessed against a database comprising results from 62 beams tested by various researchers and is shown to yield less conservative results. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 3, pp. 373–388, May–June, 2008.