Out-of-plane constraint effect on local fracture resistance of a dissimilar metal welded joint

An experimental investigation on effect and mechanism of out-of-plane constraint induced by specimen thickness on local fracture resistance of two cracks (A508 heat-affected-zone (HAZ) crack and A508/Alloy52Mb interface crack) located at the weakest region in an Alloy52M dissimilar metal welded joint (DMWJ) between A508 ferritic steel and 316L stainless steel in nuclear power plants has been carried out. The results show with increasing out-of-plane constraint (specimen thickness), the fracture mechanism of the two cracks changes from ductile fracture through mixed ductile and brittle fracture to brittle fracture, and the corresponding crack growth resistance decreases. The crack growth path in the specimens with different out-of-plane constraints deviates to low-strength material side, and is mainly controlled by local strength mismatch. For accurate and reliable safety design and failure assessment of the DMWJ structures, it needs to consider the constraint effect on local fracture resistance. The new safety design and failure assessment methods incorporating both in-plane and out-of-plane constraint effects need to be developed for the DMWJ structures.     

A novel robotic leg design with hybrid dynamics

A new leg mechanism is designed to achieve optimal behaviour in both the stance and swing phases. The leg is designed such that its dynamics and kinematics optimally mimic those of simpler mechanisms, namely the spring-loaded inverted pendulum (SLIP) and the double pendulum, for the stance and swing phase, respectively. Controllers based on the simpler mechanisms can thus be used, resulting in an effective control strategy that is simple and transparent.     

Electrochemical Study on the Reduction Mechanism of Uranium Oxide in a LiCl-Li2O Molten Salt

By means of a linear sweep voltammetry, a cyclic voltammetry and a chronopotentiometry, the electrolytic reduction of uranium oxide has been studied to establish the reduction mechanisms, which are based on a simultaneous uranium oxide reduction and a Li₂O electrowinning, and the formation and electrolysis of lithium uranate. From the voltammograms, the reduction potentials of the uranium oxide and Li₂O were obtained. From the chronopotentiometries based on the results of the voltammograms, the uranium oxide was reduced to uranium metal through the reduction mechanisms showing a more than 99% conversion. For a verification of the reduction mechanisms feasibility, basic data on the electrolytic reduction of the uranium oxide was obtained from the experiments and the characteristics of the closed recycle of Li₂O were discussed.     

草酸诱导大水沟碲矿溶解机制

随着社会的发展对碲需求量日益增加，低品位大水沟碲矿的开发利用受到了日益关注。利用草酸在常压下对大水沟碲矿进行溶解研究。结果表明，在草酸浓度0.25 mol/L、液固比15︰1、反应时间15 d的条件下，草酸对Fe、Mg、Ca、Al和Si的溶解量分别为662、187、610、686、64 mg/L，而Te富集到滤渣中。各矿相溶解的先后顺序为：白云石>磁黄铁矿>碲铋矿。结合计算模拟草酸与白云石、磁黄铁矿和碲铋矿之间的结合方式和电子转移机制，表明草酸通过其氢原子的酸解作用和氧原子的络合作用吸附于矿物表面，并且其电子从草酸向白云石表面转移，而磁黄铁矿和碲铋矿相反。     

Hot deformation behavior and microstructural evolution of as-forged Ti-44Al-8Nb-(W,B, Y) alloy with nearly lamellar microstructure

The hot deformation behavior and microstructural evolution of as-forged Ti-44Al-8Nb-(W, B, Y) alloy with nearly lamellar structure were investigated by means of uniaxial hot compression. Its stress exponent and activation energy are 3.81 and 494 KJ/mol, respectively. The efficiencies of power dissipation and instability parameters are evaluated, and processing maps at strains of 0.12, 0.25, and 0.5 are developed. It is demonstrated that the microstructural evolution is dependent on the temperature and strain rate. Moreover, the recovery and recrystallization of γ phases as well as the spheroidization of α phases play important roles in refining the microstructure. Reasonable parameters for secondary hot working are above 1150 °C with a strain rate of less than 0.25 s⁻¹ at a strain of 0.5. Additionally, the hot working window can be expanded to the region with lower temperature and higher strain rate at a strain of 0.12. Finally, crack-free TiAl sheets were successfully prepared by hot pack rolling. The as-rolled alloy is characterized by duplex microstructure with a mean grain size of 10 μm, exhibiting a failure strength of 1021 MPa with 0.78% ductility at room temperature. At 800 °C, the failure strength remains high: above 650 MPa.     

Optimisation of method for reducing residual stresses after cold bar drawing

Abstract

A new method to reduce the residual stresses after cold bar drawing has been proposed and optimised. This new method addresses the disadvantages of previous methods proposed by the authors, and needs neither the use of an extra finishing die nor an intricate die geometry. The application of axial tension to the bar or wire after drawing is all that is required, and by adjusting the magnitude of the tension it is possible to control the residual stresses in the final product. Axisymmetric elastic-plastic finite element analysis was carried out to examine quantitatively the influence of tension, followed by laboratory experiments using a thick, not thin, bar for convenience of measurement of residual stresses. The optimum value of tension was then determined. The applicability of the proposed method is discussed in the present paper. The new method is especially effective when applied to high speed cold drawing of an extremely thin wire, because the tension applied to the wire after finishing can be readily controlled simply by adjusting the peripheral speed of the rollers/pulleys.     

基坑降水造成地面变形的机理探讨

随着地下工程的蓬勃发展,由地面沉降引发的建筑物开裂等灾害也日益增多,降水是引发地面沉降的主要原因已得到大家的共识,然而其中的机理却依然复杂,因此,本文从地下水动力学降水涉及变形的理论公式的角度对降水引发地面变形机理进行探讨,考虑了时间因素的影响,最后对一个工程实例进行了应用。     

DN-YOLOv5的金属双极板表面缺陷检测算法

为解决氢燃料电池中金属双极板表面缺陷尺寸小，缺陷对比不明显、种类多造成的难以检测，易误检漏检以及缺陷检测模型复杂度太大难以部署等问题，提出一种改进版的金属双极板缺陷检测算法DN-YOLOv5,来探究缺陷检测在冲压成形的金属双极板视觉检测工作台场景下进行快速精准检测的可行性，从而实现智能检测，提升检测效率。本研究着重于修改YOLOv5主干网络Backbone部分，添加网络中模块数量，加入NAM注意力机制和使用深度可分离卷积模块来替代原来CSP/CBS主干网络卷积模块，并引入SIoU对损失函数重新进行了定义，极大的提升了主干网络的轻量化程度。结果表明，本算法的map@0.5可达0.988,每秒检测传输帧率为9.98,模型参数量降低了52.13%,在测试集75张缺陷图像中真检率达到了99.74%。该方法在保证模型较高检测率的同时，显著降低了模型复杂度和参数计算量。此外，该算法结合新的检测尺度设计特征融合网络，提升网络的小目标、多目标检测能力。该算法具有良好的稳定性和鲁棒性，综合性能较好，满足部署移动端场景进行缺陷检测的轻量化需求。