On the strength of polycrystalline tungsten monocarbide

The paper consists of analytical and applied parts. The mathematical means of mechanics of hexagonal polycrystals are used in the former. Here the correspondence of the published data on single crystal elastic constants of tungsten monocarbide to elasticity moduli of polycrystalline WC has been analyzed. The relationship between ultimate tensile stress and ultimate compressive stress of polycrystalline tungsten monocarbide has been established too. The dependence of ultimate tensile stress and ultimate compressive stress of polycrystalline tungsten monocarbide on mean grain diameter is considered in the applied part. Here the available experimental data are used.     

Energy Transfer Induced by TADF Polymer Enables the Recycling of Excitons in Perovskite Solar Cells

Formamidinium lead triiodide (FAPbI₃) has been demonstrated as the most efficient perovskite system to date, due to its excellent thermal stability and an ideal bandgap approaching the Shockley-Queisser limit. Whereas, there are intrinsic quantum confinement effects in FAPbI₃, which lead to unwanted non-radiative recombination. Additionally, the black α-phase of FAPbI₃ is unstable under room temperature due to the significant residual tensile stress in the film. To simultaneously address the above issues, a thermally-activated delayed fluorescence polymer P1 is designed in the study to modify the FAPbI₃ film. Owing to the spectral overlap between the photoluminescence of P1 and absorption of the above-bandgap quantum wells of FAPbI₃, the Förster energy transfer occurs at the P1/FAPbI₃ interface, which further triggers the Dexter energy transfer within FAPbI₃. The exciton “recycling” can thus be realized, which reduces the non-radiative recombination losses in perovskite solar cells (PSCs). Moreover, P1 is found to introduce compressive stress into FAPbI₃, which relieves the tensile stress in perovskite. Consequently, the PSCs with P1 treatment achieve an outstanding power conversion efficiency (PCE) of 23.51%. Moreover, with the alleviation of stress in the perovskite film, flexible PSCs (f-PSCs) also deliver a high PCE of 21.40%.     

龙滩碾压混凝土坝的温控研究

本文应用作者提出的模拟碾压混凝土成层浇筑过程一维温度场的解析解，对龙滩碾压混凝土南１２挡水上种不同的浇筑方案施工期最高温度场进行研究，给出了最高的温度变化时程曲线，计算了稳定温度场，根据容许温度和稳定温度确定浇筑温度，并提出了可供选择的温控方案。     

装甲钢温度-组织-应力耦合本构模型的建立及在焊接模拟中的应用

装甲钢焊接热循环过程中固态相变对焊接残余应力的演变及大小有着重要影响,而现有的有限元软件本构模型无法考虑固态相变的作用。在传热学、固态相变理论和连续介质力学的基础上,建立了温度－组织－应力耦合的本构模型,本构模型中综合考虑了固态相变引起的体积变化、力学性能变化和相变塑性对焊接残余应力的影响,采用ABAQUS子程序UMAT通过二次开发将该本构模型嵌入通用有限元软件中,对装甲钢平板对接焊进行研究,获得了装甲钢焊接热循环过程中温度、组织及残余应力变化规律。研究结果表明：装甲钢平板中断面表面宽度方向,在纵向残余应力表征上,耦合本构模型的模拟结果与X射线衍射测量结果具有较好的一致性,验证了耦合本构模型的正确性,并表明相变塑性对相变区的残余应力存在一定的松弛作用;对于装甲钢近缝区纵向残余应力大小：完全相变区＜部分相变区＜未发生相变区。     

二维超声磨削纳米复相陶瓷表面残余应力研究

采用二维超声振动磨削和普通磨削方式,利用X射线衍射仪,对纳米复相陶瓷和氧化锆陶瓷表面残余应力的性质及大小进行了研究。实验表明,残余应力是磨削条件、相变应力和裂纹释放应力综合作用的结果。得到结论:在相同的磨削条件下,超声磨削的切向残余拉应力比普通磨削方式的小,法向残余压应力则比普通磨削的大;磨粒尺寸越小,残余拉应力越小;材料以塑性方式去除时,残余应力表现为压应力;超声磨削的m相变率比普通磨削的小。     

Damage to n-MOSFETs from electrical stress Relationship to processing damage and impact on device reliability

The study reported herein examines and compares damage to n-channel and p-channel metal-oxide-silicon field-effect transistors (MOSFETs) from direct current (d.c.) and alternating current (a.c.) electrical stresses as well as the relationship of this damage to plasma processing damage in MOSFETs. The lightly-doped drain (LDD) MOSFETs used are of 0.5 μm channel length and with a 90 Å thick thermally grown gate oxide fabricated using a full flow CMOS process up to and including metal-1 processes and post-metallization annealing (PMA). The damage to MOSFETs is assessed using transistor parameter characterization and charge-to-breakdown measurements on the gate oxide. It is found that manifestations of d.c. stress-induced damage and a.c. stress-induced damage to transistors are fairly similar in that both forms of damage are passivated by PMA and are reactivated by a subsequent d.c. electrical stress. However, a.c. stress-induced damage is observed to occur at much lower electric fields across the gate oxide than those necessary for d.c. stress-induced damage to be significant. This is attributed to a.c. currents, caused by carrier hopping, occurring at relatively low electric fields. One implication of our results is that plasma-charging damage, often attributed to d.c. electrical stress alone, may comprise an a.c. electrical stress component too.     

On the formation of porosity and microchannels in growing scales

It is well known that oxide scales develop porosity and microchannels that permit inward transport of molecular species from the ambient gas even under conditions when there is no evidence of cracking of the scales. It is proposed that such porosity and microchannels develop as a result of grain growth and of plastic deformation (grain-boundary sliding, diffusion creep, etc.) under compressive stresses in the scales. The presence of small amounts of impurities enriched at grain boundaries in the scales may greatly affect deformation and mechanical and transport properties in scales.     

高速钢激光重熔后的组织与性能

研究了W18Cr4V高速钢激光重熔后的组织与性能。结果表明，常规淬回火组织经激光重熔后其硬度、韧性都有提高，熔化层的残余应力为技应力；经640℃回火后；由于残余应力的消除及重熔组织中马氏体的二次硬化和残余奥氏体的二次淬火效应其耐磨性能有了进一步地提高。     

压裂泵液力端阀箱内腔结构优化研究

压裂泵液力端阀箱内腔在加工完成后会自然形成相贯线,该相贯线位置存在严重的应力集中问题。这些位置也是液力端阀箱常见的开裂位置,虽然通过相贯线倒圆角的方式可以减小应力集中程度,但是应力减小的幅度不是十分明显。针对此问题,通过有限元仿真对比的方式进行了阀箱内腔优化研究,提出了减小阀箱内腔应力集中程度的技术方案,同时提出了应用该方案时应注意的一些问题。研究结果对于提高压裂泵液力端使用寿命及优化压裂泵液力端设计具有一定的指导意义。     

Axisymmetric and One-Dimensional Thermoelastic Fields of Radially Graded Bodies

In this paper, both Young's modulus and Poisson's ratio along with thermal expansion coefficient are allowed to vary across the radius in a solid ring and a curved beam. Effects of non-constant Poisson's ratio on the thermoelastic field in these graded axisymmetric and one-dimensional problems are studied. A governing differential equation in terms of stress function is obtained for general axisymmetric and one-dimensional problems. Two linearly independent solutions in terms of hypergeometric functions are then attained to calculate the stresses and the strains. Using Green's function method, a form of a solution for the stress functions in terms of integral equations for a curved beam and a solid ring are obtained. Specifically, closed form solutions for the stress functions, when Young's modulus and Poisson's ratio are expressed as power law functions across the radius, are calculated. The results show that the effect of varying Poisson's ratio upon the thermal stresses is considerable for the solid ring. In addition, a non-constant Poisson's ratio has significant influences on the thermal strain field in solid rings. The effect of varying Poisson's ratio upon the thermal stresses is negligible for the curved beam. However, non-constant Poisson's ratios have substantial effects on the thermal strain field in curved beams. Finally, the effects of varying Poisson's ratio on the thermal stresses in thick solid rings and curved beams are also investigated.