Morphology and Mechanical Properties of Immiscible Polyethylene/Polyamide12 Blends Prepared by High Shear Processing

In this work, completely immiscible polyethylene/polyamidel2 （PE/PA12） blends were prepared by high shear extruder. The morphology and mechanical properties of the blends were investigated as a function of rotation speed. It was found that the high shear processing is an effective method to improve the dispersion of the PAl2 phase in PE matrix when PA 12 contents are 5 wt% and 10 wt%, and the dispersed phase particle size is reduced with the increase of rotation speed from 100 r/min to 500 r/min. However, with further increase of PAl2 content to 20 wt%, high shear processing has no effect on the phase morphology of the blends. Accordingly, a largely increased elongation at break and impact strength are observed for PE/PAl2/95/5 and PE/PA12/90/10 blends obtained at high rotation speeds but no effect on the property of PE/PAI2/80/20. Annealing experiment demonstrated that the obtained phase morphology is not stable thus compatibilizer should be introduced in the future work. This work could provide a guideline for the application of high shear processing in the preparation of polymer blends with huge polarity difference.

Three-dimensional analysis of the modified sloping cooling/shearing process

A self-designed setup of modified sloping cooling/shearing process was made to prepare the semisolid Al-3wt%Mg alloy. A three-dimensional simulation model was established for the analysis of preparing the semisolid Al-3wt%Mg alloy. Through simulation and experiment, it is shown that the sloping angle of the plate greatly affects temperature and velocity distributions, and the temperature and velocity of the alloy at the exit of the sloping plate increase with the increase of the sloping angle. The alloy temperature decreases linearly from the pouring mouth to the exit. The alloy temperature at the exit increases obviously with the increase of pouring temperature. To prepare the semisolid Al-3wt%Mg alloy with good quality, the sloping angle θ=45° is reasonable, and the pouring temperature is suggested to be designed above 650-660℃ but under 700℃.

Adiabatic Shear Mechanisms for the Hard Cutting Process

The most important consequence of adiabatic shear phenomenon is formation of sawtooth chip. Lots of scholars focused on the formation mechanism of sawtooth, and the research often depended on experimental approach. For the present, the mechanism of sawtooth chip formation still remains some ambiguous aspects. This study develops a combined numerical and experimental approach to get deeper understanding of sawtooth chip formation mechanism for Polycrystalline Cubic Boron Nitride（PCBN） tools orthogonal cutting hard steel GCr15. By adopting the Johnson-Cook material constitutive equations, the FEM simulation model established in this research effectively overcomes serious element distortions and cell singularity in high strain domain caused by large material deformation, and the adiabatic shear phenomenon is simulated successfully. Both the formation mechanism and process of sawtooth are simulated. Also, the change features regarding the cutting force as well as its effects on temperature are studied. More specifically, the contact of sawtooth formation frequency with cutting force fluctuation frequency is established. The cutting force and effect of cutting temperature on mechanism of adiabatic shear are investigated. Furthermore, the effects of the cutting condition on sawtooth chip formation are researched. The researching results show that cutting feed has the most important effect on sawtooth chip formation compared with cutting depth and speed. This research contributes a better understanding of mechanism, feature of chip formation in hard turning process, and supplies theoretical basis for the optimization of hard cutting process parameters.

Analysis of fracture process zone in brittle rock subjected to shear-compressive loading

An analytical expression for the prediction of shear-compressive fracture process zone(SCFPZ) is derived by using a proposed local strain energy density criterion, in which the strain energy density is separated into the dilatational and distortional strain energy density, only the former is considered to contribute to the brittle fracture of rock in different loading cases. The theoretical prediction by this criterion shows that the SCFPZ is of asymmetric mulberry leaf in shape, which forms a shear-compression fracture kern. Dilatational strain energy density along the boundary of SCFPZ reaches its maximum value. The dimension of SCFPZ is governed by the ratio of K_Ⅱ to (K_Ⅰ.) The analytical results are then compared with those from literatures and the tests conducted on double edge cracked Brazilian disk subjected to diametrical compression. The obtained results are useful to the prediction of crack extension and to nonlinear analysis of shear-compressive fracture of brittle rock.

Formation and Evolution of Non-dendritic Microstructures of Semisolid Alloys Prepared by Shearing/Cooling Roll Process

The shearing/cooling roll （SCR） process was adopted to prepare semi-solid A2017 alloy. The formation and evolution of non-dendritic microstructures in semi-solid A2017 alloy were studied. It is shown that the microstructures of semi-solid billets transform from coarse dendrites into fine equiaxed grains as the pouring temperature of molten alloy decreases o.r roll-shoe cavity height is reduced. From the inlet to the exit of roll-shoe cavity, microstructure of semi-solid slurry near the shoe surface is in the order of coarse dendrites, degenerated dendrites or equiaxed grains, but fine equiaxed grains are near the roll surface. Microstructural evolution of semi-solid slurry prepared by SCR process is that the molten alloy nucleates and grows into dendrite firstly on the roll and shoe＇s surface. Under the shearing and stirring given by the rotating roll, the dendrites crush off and disperse into the melt. Under the shearing and stirring on semi-solid slurry with high volume fraction of solid, the dendrite arms fracture and form equiaxed grain microstructures.

铁基非晶纳米晶合金带材滚剪加工过程分析

在生产现场采用跟踪统计方法,归纳分析铁基非晶纳米晶合金带材滚剪加工过程以及滚剪刀耐用度、刀具刃磨等问题,统计分析不同宽度滚剪刀的加工情况发现,滚剪刀有效工作时间比率为65%~88%,平均有效工作时间比率为76.1%,有效工作时间不稳定;滚剪刀剪切行程处于3700~4200m之间,平均剪切行程为3839.74m,刀具耐用度存在较大差异,剪切宽度越大滚剪刀耐用度越长;滚剪刀刃磨时刀具径向去除量在80~150μm之间,平均刃磨去除量为106μm,刀具刃磨工艺对刀具耐用度有决定性影响。最后针对滚剪刀磨损检测问题,提出采用声发射信号对滚剪刀状态进行在线检测的技术方案。

Numerical simulation of direct shear tests on mechanical properties of talus deposits based on self-adaptive PCNN digital image processing

The macro mechanical properties of materials with characteristics of large scale and complicated structural composition can be analyzed through its reconstructed meso-structures.In this work,the meso-structures of talus deposits that widely exist in the hydro-power engineering in the southwest of China were first reconstructed by small particles according to the in-situ photographs based on the self-adaptive PCNN digital image processing,and then numerical direct shear tests were carried out for studying the mechanical properties of talus deposits.Results indicate that the reconstructed meso-structures of talus deposits are more consistent with the actual situation because the self-adaptive PCNN digital image processing has a higher discrimination in the details of soil-rock segmentation.The existence and random distribution of rock blocks make the initial shear stiffness,the peak strength and the residual strength higher than those of the "pure soil" with particle size less than 1.25 cm apparently,but reduce the displacements required for the talus deposits reaching its peak shear strength.The increase of rock proportion causes a significant improvement in the internal friction angle of talus deposit,which to a certain degree leads to the characteristics of shear stress-displacement curves having a changing trend from the plastic strain softening deformation to the nonlinear strain hardening deformation,while an unconspicuous increase in cohesion.The uncertainty and heterogeneity of rock distributions cause the differences of rock proportion within shear zone,leading to a relatively strong fluctuation in peak strengths during the shear process,while movement features of rock blocks,such as translation,rotation and crossing,expand the scope of shear zone,increase the required shear force,and also directly lead to the misjudgment that the lower shear strength is obtained from the samples with high rock proportion.That,however,just explains the reason why the shear strength gained from a small amount of indoor test data is not consistent with engineering practice.

牛粪和核桃果枝混合发酵理化特性试验及设备工艺优化

通过鲜牛粪、牛粪与核桃果枝、牛粪核桃果枝加发酵菌剂三个不同配比的堆肥试验,开展牛粪和核桃果枝的化学特性参数试验;同时,参照土壤力学试验方法,对有机肥发酵各阶段的含水率、电导率、硬度、湿密度、抗剪强度等物理特性参数进行试验研究。试验结果表明,三种堆体有机质质量分数、总氮、总磷和总钾质量分数在堆肥初期都有所下降,随后缓慢上升,最后趋于平稳,分别稳定在32%、39%、40%,6.33%、9.48%、9.53%,0.95%、1.26%、1.29%和1.71%、2.59%、2.48%,添加果枝和菌剂的堆肥营养物质损失最少。三个堆体EC值的变化趋势基本一致,逐步升高,随着CO_(2)、NH_(3)的挥发,EC值开始缓慢下降,三个堆体EC值最终分别稳定在5.44ms/cm、5.94ms/cm、5.54ms/cm。3个堆体的湿密度在堆肥过程中都随着堆肥天数的增加总体呈下降趋势,堆肥结束时,三个堆体湿密度分别是0.71g/cm^(3)、0.65g/cm^(3)、0.45g/cm^(3)。

基于QAR飞参数据飞行员风切变处置能力评价模型

为提高飞行员处置风切变的能力,本文基于快速存取记录器(QAR,quick access recorder)飞参数据建立了飞行员风切变处置能力评价模型。首先,将飞行员风切变处置能力分为处置决策及时性、程序合规性以及航迹管理能力3个维度;其次,基于层次分析法(AHP,analytic hierarchy process)建立飞行员风切变处置能力评价体系,并融合专家经验构建风切变处置能力定量评价模型;最后,基于QAR采集的飞参数据验证该模型的实用性和可行性。实验结果表明,本文所构建的定量评价模型可以较好地判别飞行员风切变处置能力的优劣,定位出其处置不当的指标,并给出操纵建议。该评价模型可为改进飞行训练提供参考,具有一定的实用价值。

适用于共晶焊的肖特基二极管背面金属化工艺优化

[目的]为了降低成本,减少污染,提高工艺效率,对肖特基二极管背面金属化工艺进行研究,探索锡锑合金替代金系合金的最佳不持温镀膜金属化工艺.[方法]通过持温镀膜与不持温镀膜对比实验,分析电子束蒸发镀膜基片温度对阴极金属层间黏附性和导电性,以及薄膜厚度对空洞率的影响,得到适用于批量共晶焊的肖特基二极管背面金属化最优工艺参数.[结果]当基片温度为180℃时,不持温镀膜的剪切力为64.53 N,高于持温镀膜的剪切力;当金属化锡锑合金膜厚为3μm时,共晶焊的空洞率低于5%,符合共晶焊要求;电子束蒸发镀膜背面金属层方块电阻随基片温度升高先减小后增大,温度在180~240℃之间,方块电阻随基片温度的变化不大.[结论]用于共晶焊的肖特基二极管背面金属化的最优工艺为基底温度升到180℃后在自然降温的同时进行多层金属镀膜,锡锑合金镀膜厚度为3μm.

DH590冷轧板及镀锌板电阻点焊工艺窗口及点焊一致性的研究

采用电阻点焊对DH590冷轧板及其镀锌板进行工艺窗口和焊点一致性试验,对焊点进行了拉剪试验和十字拉伸试验,分析了点焊接头的显微组织、硬度分布以及断口形貌。结果表明:相比于冷轧板,DH590镀锌板焊接工艺窗口向右移动(增大)约2 kA,同时工艺窗口范围变窄,熔核形成更加充分,发生飞溅时的熔核直径更大。两种点焊接头熔核区组织为板条马氏体,但镀锌板熔核区的平均硬度更高。点焊一致性试验中,熔核直径均达到标准要求,未见明显波动。工艺窗口内的焊点失效模式以拔出断裂为主,从断口观察到大量的剪切韧窝,呈现出塑性断裂的特点。

螺纹钢切分轧制采用控轧控冷工艺生产实践

螺纹钢生产采用切分工艺,可以降低能耗和提高产能,采用控轧控冷工艺又可以显著降低钢坯合金成本,采用三切分工艺与控轧控冷工艺相结合,会增加技术难度。文章介绍了普通螺纹钢产线对传统三切分工艺进行优化后,与控轧控冷工艺相结合,解决了切分后进行飞剪切头控制稳定性差的问题;并通过进行多次控轧控轧工艺试验,摸索出各处关键温度控制范围,稳定了控轧控冷工艺产品的性能,保证产能与效率的同时降低了合金成本。

填料对碳纤维-环氧树脂拉挤板层间剪切性能的影响

在碳纤维含量相同条件下,研究了填料种类、粒径、用量对碳纤维-环氧树脂拉挤板(简称拉挤碳板)层间剪切性能的影响。结果表明:除聚乙烯微蜡粉外,重质碳酸钙、轻质碳酸钙、高岭土、氢氧化铝粉和滑石粉的加入都能有效提升拉挤碳板的层间剪切性能。其中,效果最好的是氢氧化铝粉,使拉挤碳板的层间剪切强度提升近13%;最适合拉挤碳板的填料粒径是6.5~11.5μm;粒径为6.5μm的氢氧化铝粉填料用量为4 phr时,拉挤碳板的层间剪切强度最大,达66.51 MPa;此外,加入氢氧化铝粉后,拉挤碳板0°拉伸性能有所降低。

40Cr热轧圆钢剪切开裂原因分析及改进工艺探析

某钢厂在生产Φ75 mm的40Cr圆钢时,在剪切下料过程中容易出现横向开裂问题,影响企业整体生产。为此,在了解40Cr热轧圆钢的生产工艺后,从样品的化学成分、金相组织、显微硬度等方面入手,分析开裂原因,进而明确裂纹原因主要为圆钢中存在夹渣缺陷;从石灰量、化渣剂、保护渣碱度等参数指标出发,针对性提出冶炼改进方案;对优化方案进行实践应用,结果表明,该优化方案可有效处理铸坯夹渣的问题,且使得对应轧材的表面缺陷率大幅度降低,能保证圆钢的生产质量,满足钢厂发展需要。

机械振动对磨粒流抛光TC4钛合金加工效率及质量的影响

为进一步提高磨粒流抛光TC4钛合金的加工效率及质量,提出机械振动辅助磨粒流抛光方法,进行磨粒流抛光TC4钛合金试验,探究机械振动对工件的材料去除效率、表面粗糙度和表面形貌的影响,分析其变化规律。结果表明:在抛光过程中,对工件施加机械振动辅助,抛光液“剪切增稠”效应增强,磨粒去除工件表面材料的能力增加;相比于无机械振动,有机械振动条件下工件的材料去除效率提高19.90%,表面粗糙度降低19.58%,工件表面划痕、凹陷等加工缺陷减少,提高了表面质量,为实际的生产加工积累经验和提供基础数据。

基于内聚力模型的无针搅拌摩擦点焊-胶接混合连接接头拉剪性能研究

针对铝合金薄板的连接,提出了一种无针搅拌摩擦点焊-胶接混合连接工艺。基于内聚力模型,利用有限元软件ABAQUS模拟无针搅拌摩擦点焊-胶接混合接头的拉剪失效过程,研究了不同焊点排布方式及胶粘剂种类对混合接头力学性能的影响。结果表明,焊点排布方式对混合接头的拉剪载荷没有明显影响,但会影响混合接头内的裂纹扩展行为;使用柔性胶2015混合接头的拉剪峰值载荷和破坏位移均大于脆性胶AV138混合接头。该混合连接工艺为铝合金薄板提供了一种高强度、低变形的连接方案,在汽车轻量化领域具有应用前景。

沉管隧道管节接头钢剪力键制作及安装工艺

随着我国海底隧道工程建设的快速发展,沉管法海底隧道施工技术得到更多应用。沉管隧道管节接头作为沉管连接的关键部位,也是薄弱部位,管节接头止水与剪力键体系对沉管隧道结构的安全性有重要影响。为高质量完成管节接头施工,保证沉管的安全性,文章通过大连湾海底隧道管节接头钢剪力键施工,总结钢剪力键制作及安装技术的具体操作步骤及施工要点,积累沉管隧道管节接头剪力键施工经验,为后续施工提供参考。

基于SAM&ImageJ图像处理的堆石混凝土坝层面露石率研究

堆石混凝土坝层面的外露块石为上下层提供了重要的啮合作用,其投影面积比例是科学评价层间抗剪性能的重要指标。采用国际最新Meta AI模型segment anything model(SAM)对层面外露堆石进行自动图像分割,并基于ImageJ软件对SAM识别后的图片进行再加工与图像计算,利用平滑、差分算法、中值滤波等方法精准标定外露堆石,二值化后计算得到层面露石率。结果表明:SAM图像预分割可识别约90%的外露堆石,经过ImageJ二次图像处理后可有效提高小粒径堆石的识别精度,对比手动标注结果误差在±3%以内。以贵州省两座水库的工程应用为例,对浇筑仓面进行分区预处理,结果发现靠近上游、中部、下游不同区域的露石率差别较大,计算得到的层面露石率以10%~30%居多,其中堆石入仓运输通道区域的露石率较低。研究内容与结论可为堆石混凝土结构层间界面抗剪力学性能和大坝蓄水安全稳定的研究提供参考与借鉴。

On a general theory for compressing process and aeroacoustics:linear analysis

Of the three mutually coupled fundamental processes （shearing, compressing, and thermal） in a general fluid motion, only the general formulation for the compress- ing process and a subprocess of it, the subject of aeroacous- tics, as well as their physical coupling with shearing and thermal processes, have so far not reached a consensus. This situation has caused difficulties for various in-depth complex multiprocess flow diagnosis, optimal configuration design, and flow/noise control. As the first step toward the desired formulation in fully nonlinear regime, this paper employs the operator factorization method to revisit the analytic linear theories of the fundamental processes and their decomposi- tion, especially the further splitting of compressing process into acoustic and entropy modes, developed in 1940s-1980s. The flow treated here is small disturbances of a compressible, viscous, and heat-conducting polytropic gas in an unbounded domain with arbitrary source of mass, external body force, and heat addition. Previous results are thereby revised and extended to a complete and unified theory. The theory pro- vides a necessary basis and valuable guidance for developing corresponding nonlinear theory by clarifying certain basic issues, such as the proper choice of characteristic variables of compressing process and the feature of their governing equations.

软-硬互层岩体节理峰前循环剪切疲劳损伤机理研究

三峡库区频发微小地震下岩体节理循环剪切疲劳损伤对边坡动力稳定性具有重要影响。通过室内峰前循环剪切试验和PFC2D细观数值计算,研究了考虑一阶起伏角、含水率、剪切速率、剪切幅度、法向应力及循环剪切次数影响的软-硬互层岩体节理宏细观疲劳损伤机理。研究表明:①岩体节理剪切应力-剪切位移曲线历经初始非线性压剪变形、近似线弹性压剪变形、循环剪切疲劳损伤变形、应力缓升压剪变形、应力陡升压剪变形及应力脆性跌落压剪变形六个演化阶段。②岩体节理峰值(残余)剪切强度和疲劳剪切(法向)位移在相同一阶起伏角、含水率、剪切速率、剪切幅度或法向应力下随循环剪切次增多而分别降低和增大;且其在相同循环剪切次数下随一阶起伏角或法向应力变大而分别增大和降低,而随含水率、剪切速率或剪切幅度变大则分别降低和增大。③宏细观结果总体上吻合较好,且岩体节理细观剪切疲劳损伤裂纹数量随剪切位移变化呈前期微增-陡增、中期缓增及后期陡增-缓增-陡增的发展特征,而其随循环剪切次数变化则呈前期陡增和后期缓增的发展特征。④岩体节理宏细观剪切疲劳损伤典型演化过程可概述为压密-起裂破坏、循环错动-贯通破坏及分离-啃断破坏3个渐进性发展阶段,且宏细观剪切疲劳损伤裂纹近似呈“倒U形”密集分布于岩体节理附近。