Flow characteristics and hot workability of a typical low-alloy high-strength steel during multi-pass deformation

Heavy components of low-alloy high-strength(LAHS) steels are generally formed by multi-pass forging. It is necessary to explore the flow characteristics and hot workability of LAHS steels during the multi-pass forging process, which is beneficial to the formulation of actual processing parameters. In the study, the multi-pass hot compression experiments of a typical LAHS steel are carried out at a wide range of deformation temperatures and strain rates. It is found that the work hardening rate of the experimental material depends on deformation parameters and deformation passes, which is ascribed to the impacts of static and dynamic softening behaviors. A new model is established to describe the flow characteristics at various deformation passes. Compared to the classical Arrhenius model and modified Zerilli and Armstrong model, the newly proposed model shows higher prediction accuracy with a confidence level of 0.98565. Furthermore, the connection between power dissipation efficiency(PDE) and deformation parameters is revealed by analyzing the microstructures. The PDE cannot be utilized to reflect the efficiency of energy dissipation for microstructure evolution during the entire deformation process, but only to assess the efficiency of energy dissipation for microstructure evolution in a specific deformation parameter state.As a result, an integrated processing map is proposed to better study the hot workability of the LAHS steel, which considers the effects of instability factor(IF), PDE, and distribution and size of grains. The optimized processing parameters for the multi-pass deformation process are the deformation parameters of 1223–1318 K and 0.01–0.08 s^(-1). Complete dynamic recrystallization occurs within the optimized processing parameters with an average grain size of 18.36–42.3 μm. This study will guide the optimization of the forging process of heavy components.

Derivation of Plastic Work Rate Done per Unit Volume for Mean Yield Criterion and Its Application

In Haigh Westergaard stress space linear combination of twin shear stress and Tresca yield functions is called the mean yield （MY） criterion. The mathematical relationship of the criterion and its plastic work rate done per unit volume were derived. A generalized worked example of slab forging was analyzed by the criterion and its corresponding plastic work rate done per unit volume. Then, the precision of the solution was compared with those by Mises and Twin shear stress yield criterions, respectively. It turned out that the calculated results by MY criterion were in good agreement with those by Mises criterion.

NEW PRINCIPLES OF WORK AND ENERGY AS WELLAS POWER AND ENERGY RATE FORCONTINUUM FIELD THEORIES

New principles of work and energy as well as power and energy rate with cross terms for polar and nonlocal polar continuum field theories were presented and from them all corresponding equations of motion and boundary conditions as well as complete equations of energy and energy rate with the help of generalized Piola's theorems were naturally derived in all and without any additional requirement. Finally, some new balance laws of energy and energy rate for generalized continuum mechanics were established. The new principles of work and energy as well as power and energy rate with cross terms presented in this paper are believed to be new and they have corrected the incompleteness of all existing corresponding principles and laws without cross terms in literatures of generalized continuum field theories.

Equal perimeter yield criterion and its specific plastic work rate: Development, validation and application

In order to overcome the nonlinearity of Mises criterion, a new linear yield criterion with a dodecagon shape of the same perimeter as Mises criterion was derived by means of geometrical analysis. Its specific plastic work rate expressed as a linear function of the yield stress, the maximum and minimum strains was also deduced and compared with that of Mises criterion. The physical meaning of the proposed yield criterion is that yielding of materials begins when the shear yield stress τs reaches the magnitude of 0.594σs. By introducing the Lode parameter, validation of evolution expressions of the proposed yield criterion with those based on Tresca, Mises and TSS criteria as well as available classical yield experimental results of various metals shows that the present results intersect with Mises results and coincide well with experimental data. Moreover, further application to the limit analysis of circle plate as an example is performed to demonstrate the effectiveness of the proposed yield criterion, and the subsequent comparison of limit loads with the Tresca analytical solutions and Mises numerical results shows that the present results are higher than the Tresca analytical results, and are in good agreement with the Mises numerical results.

Deduction of plastic work rate per unit volume for unified yield criterion and its application

A unified linear expression of plastic work rate per unit volume is deduced from the unified linear yield criterion and the associated flow rule. The expression is suitable for various linear yield loci in the error triangle between Tresca’s and twin shear stress yield loci on the π-plane. It exhibits generalization in which the different value of criterion parameter b corresponds to a specific linear formula of plastic work rate per unit volume. Finally, with the unified linear expression of plastic work rate and upper-bound parallel velocity field the strip forging without bulge is successfully analyzed and an analytical result is also obtained. The comparison with traditional solutions shows that when b=1/(1+ 3 ) the result is the same as the upper bound result by Mises’ yield criterion, and it also is identical to that by slab method with m=1, σ0=0.

Study on Large Power Tractor Driver's Heart Rate and Fatigue in Sowing Work

In order to reduce the driving fatigue in sowing work, this paper based on heart rate （HR） as the main indicator to survey, tested and analyzed the fatigue condition of the drivers of three imported tractors and one domestic tractor in sowing work. The results showed that when driving the imported tractors in sowing work, the HR increasing rate was 10.4%-14.3%, labor intensity belonged to the light level; when driving domestic tractor in sowing work, the HR increasing rate was 23.4%-33.0%, it was remarkably bigger than that of driving imported tractors （P〈0.05）, labor intensity belonged to the middle level. The main effects on driving fatigue included the control methods, tractors＇ cab environment, processing time, operating content, and so on. Finally, we proposed the concrete measures and suggestions to reduce driving fatigue and improve drivers＇ work condition.

On a cardiac work rate based on ventricular pressure measurement

We presented a cardiac work rate for one cycle cardiac based on the area of a Pressure Phase Plane, the velocity of activation and relaxation of the pressure curve, the interval of time and the variation of the pressure measurement on that cycle. We established an algebraic model to the Pressure Phase Plane area with a complete correlation of that model and the laboratory data for normal hypertensive and hypertrophied rat hearts (r = 0.99). We have obtained disjoint intervals for the cardiac work rate of the control group and the hypertrophied rat hearts as a consequence of the application of our algebraic model in those data acquisition.

The laparoscopic rating scale for the evaluation of working conditions for surgical treatment of super-obesity

In this technical note,a novel rating scale(abdominal integral index)was introduced for assessing the conditions of the working laparoscopic space based on linear measurements to select the optimal one or two-stage surgical treatment for super-obesity.Patients with the same height and similar BMI values had different rating scale scores,reflecting different conditions of laparoscopic bariatric surgery.The rating scale helps surgeons and patients make a safe option for surgery,depending on the experience of the surgeon and technical laparoscopic conditions.

考虑工作人群及不同防护措施的疫情传播速度仿真

本文主要针对疫情走势进行了分析,考虑了不同人群和不同防护措施对疫情走势的影响。针对此问题首先对传统的SEIR传染模型进行了优化,模拟出在公共场所内工作人员感染病毒后和普通人员感染病毒后的疫情传播情况;其次对比不同防护措施情况下的疫情传播情况,分析了物理防护和化学防护对疫情传播速率的影响。结果发现,初始潜伏者为工作人员时,疫情爆发的更加迅猛、快速;工作人员在分别采取物理防护和化学防护措施后会使得疫情发展速度有不同程度的降低。化学防护措施的防控效果相当于三级物理防护措施的防控效果,全国公共场所的工作人员在疫情防控工作下需要进行比普通人群更高等级的物理防护,也为后期疫情扩散期间的物资分配提供了依据。

液压伺服滑阀工作边冲蚀行为及影响因素

液压伺服滑阀阀口工作边易受油液中颗粒污染物的冲蚀作用,诱发伺服阀性能退化。采用阀口工作边淹没射流冲蚀可视化实验和固液两相流数值计算方法,研究颗粒冲击工作边的冲蚀行为及影响因素。结果表明:颗粒冲击工作边的冲蚀行为主要有刮擦-滑动、碰撞-滑动、悬浮-翻转以及边碰行为;1.05 MPa下,边碰行为颗粒的最大速度可达40.41 m/s,冲击能最高,且反弹速度最小仅4.59 m/s,对工作边产生的冲蚀破坏最大;1.2 MPa颗粒冲击比与边碰率比0.9 MPa和1.05 MPa更高,分别为46%和7%;冲击比和边碰率随粒径增大而增加;低黏度油液的冲击比和边碰率大于高黏度油液,黏度为0.01634 Pa·s时分别可达94%和17%。研究结果对揭示液压伺服滑阀冲蚀破坏机理及抗冲蚀设计具有重要意义。

负离子除尘技术在隧道中的应用与数值模拟研究

以武隆隧道为例,采用便携式负离子发生器进行现场测试,验证了负离子的消耗与除尘的有效性。对武隆隧道中应用负离子净化系统的除尘效果进行了数值模拟。结果表明:隧道内的电场以电极为中心呈环形分布且向外不断扩展;随着粉尘颗粒粒径的增大,荷电量增大,在电场力的作用下粉尘颗粒越容易发生偏移运动;在作用时间为600 s时,对2.5μm与10μm粉尘的除尘率分别为63.57%与99.00%;增大工作电压可以有效提高除尘率。

便携式锂钾分析仪现场测定热泉水中的锂

锂是绿色能源和轻质合金的理想原料,作为一种重要的战略性资源而备受各国重视。热泉水中富含锂,储量可观,然而热泉水主要分布在西藏、云南等偏远地区,样品运输与实验室测试成本高、效率低,锂资源勘查急需现场分析技术的支持。热泉水一般含有较高浓度的钠、钾等元素,基体效应显著。本文利用自主研发的便携式锂钾分析仪,搭配负性滤光片,选择锂的分析谱线波长670.78nm,通过优化测量条件,建立了标准曲线法与标准加入法现场测定热泉水中锂元素的分析方法。实验结果表明,当电解质是体积分数为1.5%的盐酸,工作电流为70mA,进样流速为3.0mL/min时,锂检出限为4.07μg/L,相对标准偏差(RSD)为1.03%。对热泉水样品进行加标测试,加标回收率为81.6%~115.9%。当热泉水样品基体组成较简单时,直接采用标准曲线法即可获得较准确的分析结果;当样品基体组成较复杂或者基体浓度高时,采用标准加入法可有效地减小基体效应,获得的分析结果相对更准确。本方法适用于不同类型基体的热泉水中锂含量的分析测试。

低渗致密气藏防水锁剂配方性能评价

基于吐哈油田低渗致密气藏,研发一种新型气藏防水锁剂GY-HE85,对其界面张力、表面张力和润湿性等基本性能进行研究,并分析了岩心渗透率恢复效果。实验结果表明,氟碳表面活性剂与碳氢表面活性剂复配后,碳氢表面活性剂除降低界面张力的作用之外,由于异电性亲水基之间强烈的静电吸引作用,表面活性剂分子在更低含量即可达到饱和吸附,还可降低表面活性剂的使用量。防水锁剂GY-HE85含量为0.1%~0.5%(w)的溶液时,表面张力为20.23~47.52 mN/m,随着溶液含量减小,拟黏附功逐渐降低,降幅呈“先快后慢”趋势,防水锁剂GY-HE85溶液优选含量为0.3%(w)。防水锁剂GY-HE85溶液具有较好的抗吸附性能,岩心渗透率恢复率在86.44%~91.20%,较好地预防了致密气藏储层“水锁”现象的发生。

玻璃纤维增强机制砂混凝土力学性能及收缩性能研究

为了解决机制砂性能不稳定、易收缩开裂的问题,提出了一种增强机制砂混凝土性能的方法,即采用耐腐蚀的玻璃纤维进行加固。以不同配合比的玻璃纤维增强机制砂混凝土为研究对象,制作试件共计180个,分别进行了坍落度测试、轴心抗压强度试验、抗折强度试验及收缩试验。通过对比机制砂对替代率和玻璃纤维掺量两个重要因素对玻璃纤维增强机制砂混凝土工作性能、力学性能及收缩性能的影响规律和作用原理,进一步确定机制砂对天然砂的最佳替代率和玻璃纤维最佳掺量,以推动机制砂玻璃纤维混凝土的发展与应用。

危废综合焚烧回转窑经济高效运行的技术难点及对策

随着国内危险废物处理产业化快速发展,回转窑综合焚烧技术得到了广泛应用,但其工业化应用存在回转窑工况不稳定、焚烧性能差、灰渣率高等问题,严重影响焚烧效率和运行成本。以危废综合焚烧的灰渣率为切入点,从回转窑焚烧机理、工艺设计、工艺控制、工艺运行等方面分析了灰渣率高的原因,并提出了相应的解决对策和建议,为危废综合焚烧回转窑经济高效运行和产业高质量发展提供参考和借鉴。

拉伸速率和转速位置对Nb47Ti合金拉伸测试的影响

利用万能试验机研究了拉伸速率和转速位置对Nb47Ti合金拉伸测试的影响,通过计算其真应力-应变曲线、加工硬化指数(n)和应变速率敏感系数(m)分析了Nb47Ti合金的力学行为。结果表明:Nb47Ti合金加工硬化能力十分有限,其屈强比接近1;随着拉伸速率的提高,加工硬化效果进一步减弱;拉伸速率对强度的影响较为显著,根据恒速率拉伸法计算其应变速率敏感系数为0.0263。转速试验中,随着拉伸速率的转换,应力值骤增。在加工硬化阶段的不同应变处转速时,突变幅值相对稳定,但整体随着应变量的增加而降低。本研究可为Nb47Ti合金拉伸测试时拉伸速率和转速点等参数的选取提供参考。

变形量对冷拉拔低碳镀锌钢丝力学性能的影响

冷拉拔低碳镀锌钢丝以良好的耐蚀性能、焊接性能、与力学性能协同匹配的良好综合性能和低廉的价格广泛应用于轻工业及建筑行业,其中变形量是影响其力学性能、生产成本及良品率的关键因素。通过显微组织分析、力学性能测定、断口观察,研究了Q235冷拉拔低碳镀锌钢丝不同变形量下的加工硬化过程,并分析了断丝及钢丝表面出现箭头状裂纹的原因。结果表明:真应变从0增加到2.41的过程中,抗拉强度、横纵截面硬度随应变量增加呈抛物线状增加,抗拉强度从586.8 MPa增加到1157.1 MPa,横截面硬度比纵截面增加了5.8 HV。塑性变形初期,加工硬化率最大,为364.7 MPa。真应变从0增加到1.91过程中,加工硬化率从364.7 MPa降低到162.2 MPa,真应变从1.91增加到2.41的过程中,加工硬化率又增加到了172.0 MPa。钢丝中存在CaO夹杂物是导致钢丝出现断丝和表面箭头状裂纹的主要原因。

基于单缝法的混凝土工作应力微损测试

混凝土工作应力是相对于无应力状态的应力增量。为准确测定混凝土工作应力,基于“应变部分释放”的理念,提出一种用于混凝土工作应力的微损伤测试方法——单缝法。该方法通过切割一条较浅的弧形狭缝来释放应力,根据测试应变来计算应力。采用数值模拟验证了单缝法的有效性,并分析了混凝土弹性模量等参数对应变释放率的影响。应变释放率为切缝释放应变与混凝土初始应变的比值。通过试验研究了应力大小、切缝深度等参数对测试精度的影响。研究结果表明:应变释放率由切缝形状与大小唯一确定,与混凝土弹性模量、应力大小、切缝宽度等参数无关;给定切缝形状与大小,就可以借助数值模拟或试验确定相应的应变释放率。释放应变沿切缝两侧呈“M”形分布,远离切缝,释放应变呈先增加、后减小的趋势。应变片应尽量布置在应变较大且单调变化的位置,故建议选用50 mm的应变片,布置在距切缝边缘25 mm的位置。切缝深度越大,切割产生的扰动应变越大,当切缝深度小于35 mm,扰动应变为12~18με的压应变;扰动应变可在测试应变中扣除,以消除其对测试精度的影响。切缝深度越大,测试精度越高,但对混凝土的损伤也越大,若采用直径125 mm切割片,建议切缝深度控制在30~35 mm。单缝法能够有效测试混凝土工作应力且具有较高的精度,对于测试试样,测量误差少于8.5%。

“数字泰勒主义”影响下的外卖平台“计件工资制”研究

对工业生产中“计件工资制”的研究表明,薪酬制度不仅从经济维度影响劳动者的行为,更是形塑劳动者从纯劳动力意识向纯劳动意识转变的重要机制,是劳动力过度商品化的重要基础。本文通过对外卖平台“计件制”中的派单、奖励、惩罚等规则的梳理,提出平台“计件工资制”虽然在形式上承继了工业生产“计件制”“多劳多得”的简单累积逻辑,但根本上已经变成了高投入、高回报和高风险的企业家式博弈,以及本质上的加速积累逻辑。同时,通过对骑手个体经营意识、过渡意识、自由意识、平等意识等被薪酬制度所形塑的企业家式劳动主观意识的呈现,进一步提出外卖平台薪酬制度的变迁意味着平台劳动中的“数字泰勒主义”并非工业劳动经典“泰勒制”的自然延续,而是具备了主客观方面的独特特征。

一种迭代优化的联合播种机作业振动研究

为进一步提升我国联合播种机的综合播种效率,基于迭代计算模型理论针对其整机核心结构组件展开优化研究。通过搭建用于深度实现整机作业性能参数迭代优化的数学模型,考虑作业过程中部件振动与结构之间的关系,进行合理化的三维机构设计与振动仿真,并实施此迭代优化下的联合播种机实地作业试验。试验结果表明:经迭代优化后的联合播种机关键作业效能均得到明显改善,播种合格率和种子利用率分别相对提高了6.72%和8.79%,最佳作业频率阈值为14~16Hz,播种系统的作业稳定性与作业效率均提升至92%以上,可为种植装备的改进提供思路与方法。