A novel approach of jet polishing for interior surface of small-grooved components using three developed setups

It is a challenge to polish the interior surface of an additively manufactured component with complex structures and groove sizes less than 1 mm.Traditional polishing methods are disabled to polish the component,meanwhile keeping the structure intact.To overcome this challenge,small-grooved components made of aluminum alloy with sizes less than 1 mm were fabricated by a custom-made printer.A novel approach to multi-phase jet(MPJ)polishing is proposed,utilizing a self-developed polisher that incorporates solid,liquid,and gas phases.In contrast,abrasive air jet(AAJ)polishing is recommended,employing a customized polisher that combines solid and gas phases.After jet polishing,surface roughness(Sa)on the interior surface of grooves decreases from pristine 8.596μm to 0.701μm and 0.336μm via AAJ polishing and MPJ polishing,respectively,and Sa reduces 92%and 96%,correspondingly.Furthermore,a formula defining the relationship between linear energy density and unit defect volume has been developed.The optimized parameters in additive manufacturing are that linear energy density varies from 0.135 J mm^(-1)to 0.22 J mm^(-1).The unit area defect volume achieved via the optimized parameters decreases to 1/12 of that achieved via non-optimized ones.Computational fluid dynamics simulation results reveal that material is removed by shear stress,and the alumina abrasives experience multiple collisions with the defects on the heat pipe groove,resulting in uniform material removal.This is in good agreement with the experimental results.The novel proposed setups,approach,and findings provide new insights into manufacturing complex-structured components,polishing the small-grooved structure,and keeping it unbroken.

Discussion on Reverse Design of Components with Complex Curved Surface and Computer Numerical Control Machining

With the continuous development and advancement of science and technology,the work of tool path planning has received extensive attention.Among them,curved surface generation and data processing are the focus of management and design,which necessitate the full application of reverse design of complex curved surface components to complete numerical control processing,effective optimization and upgrading,integration the tasks of point cloud data collection,and point cloud data processing to ensure that the corresponding computer numerical control machining model can exert its actual value.This paper briefly analyzes the basic principles of curved surface reconstruction as well as discusses the reverse design of complex curved components and the experimental processes and results that involved computer numerical control machining,which serves the purpose as reference only.

WEIGHTED LEAST SQUARE METHOD FOR S-N CURVE FITTING

An S-N curve fitting approach is proposed based on the weighted least square method, and the weights are inversely proportional to the length of mean confidence intervals of experimental data sets. The assumption coincides with the physical characteristics of the fatigue life scatter. Two examples demonstrate the method. It is shown that the method has better accuracy and reasonableness compared with the usual least square method.

ESTIMATION OF BLENDING RATIO OF TWO-COMPONENT FIBER BUNDLE FROM BUNDLE LOAD-ELONGATION CURVE

In this paper, two methods were developed to assess the blending ratio of two-componentfiber bundles. They were the peak-height method and the slope method. The relationship be-tween blending ratio and testing data was analysed, and the regression curves were obtained bystepwise regression method. It was pointed out that the testing errors of both methods were lessthan two percent. The validities of both methods were verified by experiments, All calculationsof both methods were completed by computer. The blending ratio was ascertained from the test-ing data of bundle fiber strength tester which was made by the authors themselves.

Analysis Approach to Durability Based on Material Initial Fatigue Quality and S-N Curve

Based on probabilistic fracture mechanics approach, a new concept of material initial fatigue quality （MIFQ） is developed. Then, the relation between S-N curve and crack propagation curve is studied. From the study, a new durability analysis method is presented. In this method, S-N curve is used to determine crack growth rate under constant amplitude loading and evaluate the effects of different factors on durability and then the structural durability is analyzed. The tests and analyses indicate that this method has lower dependence on testing, and higher accuracy, reliability and generality and is convenient for application.

Combine S-N curve and fracture mechanics for fatigue life analysis of welded structures

Based on the evolution of fatigue cracks in welded structures,the fatigue life of welded structures was defined as the sum of the crack initiation life Ni and the crack propagation life Np.Correspondingly,a fatigue-life analysis method combining S-N curves and fracture mechanics theory was proposed.The equivalent structural stress method and the lower 99%boundary of the master S-N curve were used to evaluate Ni,and cracks at the end of the initiation stage were considered as semi-elliptical surface cracks.Moreover,Paris equation and the stress intensity factor range of the cracks were used to evaluate Np.Furthermore,the fatigue test results obtained from the running girder of cranes were used as a reference for comparison and verification of the results.The results revealed that the equivalent structural stress is a good indicator for the crack initiation behavior of complex welded structures.In addition,the predicted fatigue life corresponded closely to the testing life.

Reconstruction of probabilistic S-N curves under fatigue life following lognormal distribution with given confidence

When the historic probabilistic S-N curves are given under special survival probability and confidence levels and there is no possible to re-test, fatigue reliability analysis at other levels can not be done except for the special levels. Therefore, the wide applied curves are expected. Monte Carlo reconstruction methods of the test data and the curves are investigated under fatigue life following lognormal distribution. To overcome the non-conservative assessment of existent man-made enlarging the sample size up to thousands, a simulation policy is employed to address the true production where the sample size is controlled less than 20 for material specimens, 10 for structural component specimens and the errors matching the statistical parameters are less than 5 percent. Availability and feasibility of the present methods have been indicated by the reconstruction practice of the test data and curves for 60Si2Mn high strength spring steel of railway industry.

Explicit Topology Optimization Design of Stiffened Plate Structures Based on the Moving Morphable Component(MMC)Method

This paper proposes an explicit method for topology optimization of stiffened plate structures.The present work is devoted to simultaneously optimizing stiffeners’shape,size and layout by seeking the optimal geometry parameters of a series of moving morphable components(MMC).The stiffeners with straight skeletons and the stiffeners with curved skeletons are considered to enhance the modeling and optimization capability of the current approach.All the stiffeners are represented under the Lagrangian-description framework in a fully explicit way,and the adaptive ground structure method,as well as dynamically updated plate/shell elements,is used to obtain optimized designs with more accurate analysis results.Compared with existing works,the proposed approach provides an explicit description of the structure.Thus,a stiffened plate structure with clear stiffener distribution and smooth geometric boundary can be obtained.Several numerical examples provided,including straight and curved stiffeners,hierarchical stiffeners,and a stiffened plate with a cutout,validate the effectiveness and applicability of the proposed approach.

Structural Stress-Fatigue Life Curve Improvement of Spot Welding Based on Quasi‑Newton Method

ΔF-N curves are usually used to predict the fatigue life of spot welding in engineering,but they are time-consuming and laborious and not universal.For the purpose of predicting the fatigue life of spot welding accurately and efficiently,tensile-shear fatigue tests were conducted to obtain the fatigue life of spot-welded specimens with different sheet thicknesses combinations.These specimens were simulated by using the finite element method,and the structural stress was theoretically calculated.In the double logarithmic coordinate system,the structural stress-fatigue life(S-N)curve of spot welding was fitted by the least-squares method,based on the quasi-Newton method.The square of the correlation coefficient of the S-N curve was taken as the optimization objective,with the correction coefficients of force,bending moment,spot welding diameter,and sheet thickness as the variables.During the optimization process,three different ways were utilized to get three optimized spot welding S-N curves,which are suitable for different situations.The results show that the fitting effect of the S-N curve is improved,the data points are more compact,and the optimization effect is significant.These S-N curves can be used to predict the fatigue life,which provide the basis for practical engineering application.

Analysis of the Homogeneity of Wind Roses' Groups Employing Andrews’ Curves

The homogeneity of groups of 16-dimensional wind direction roses (obtained by hierarchical clustering in a previous report) is discussed through the application of Andrews’ Curves. Principal Component Analysis (PCA) is employed to reduce dimensionality and to provide an ordering of the variables to compute Andrews’ Curves. Our results suggest that Andrews’ Curves greatly facilitate the visualization of homogeneity as well as reveal information that allows improving the clusters’ arrangement. A combined analysis employing Andrews’ Curves and Calinkski and Harabasz’ approach (a method for determining the optimal number of groups) helps to assess the strength of the group structure of the data as well as to detect anomalies such as misclassified objects or atypical values. Furthermore, it allows finding out that the 24 original seasonal hourly roses (representing the “day”) become better represented by 6 groups (rather than by 5 as proposed in the previous report). The new group arrangement was consistent with the dendogram for another cut-off distance. As a result the wind occurrences are now represented by a more detailed and smooth pattern: there is a decrease in northern wind between midday and twilight while eastern winds become more important towards the evening. The methodology proposed is a subject to be considered to become part of an automated system.

基于主成分自组织神经网络法的测井曲线分层技术

在砂岩型铀矿找矿工作中,提高测井岩性分层效率和精度至关重要。为提高砂岩型铀矿岩性分层效果,本文采用主成分分析法对多个测井曲线进行降维处理,将主成分分析法的第一主成分、第二主成分、第三主成分作为自组织神经网络的样本数据,进行自组织神经网络训练,将训练好的网络模型用于砂岩型铀矿岩性的自动化分层。实验结果显示:主成分自组织神经网络法岩性分层精度可达到85%以上,高于传统自组织神经网络算法78%的分层精度,具有更好的测井岩性分层效果。因此,主成分自组织神经网算法的岩性分层方法有效减少了输入样本的种类,简化了自组织神经网络结构,其自动化分层效果要优于传统的自组织神经网络算法。本文的研究结果表明,主成分自组织神经网算法在砂岩型铀矿领域岩性识别工作中具有较好的应用效果。

六分量地震观测在工程勘查中的应用试验

利用面波频散曲线反演地下介质的S波速度结构,是浅层工程地震领域一种重要的方法技术.传统的面波法包括主被动源的面波多道分析方法(MASW)和被动源的空间自相关(SPAC)方法,均需要多台地震仪同时记录地面振动;而记录平动和旋转运动的单台站六分量地震数据理论上也可以获得面波频散曲线.本文以河北唐山城区煤矿采空区浅层工程勘探实际六分量地震数据为例,对比了利用单台站六分量地震数据与主、被动源法多台站提取的Rayleigh波频散曲线.试验结果表明利用纵波扫描可控震源时,30 Hz以下频段利用单台站六分量地震数据提取的基阶Rayleigh波频散曲线与主、被动源MASW方法提取的频散曲线结果一致,说明在浅层工程地震勘查中,利用单物理点的六分量地震观测反演浅层横波速度是可行的.

曲面构件阵列超声频域逆时偏移成像方法研究

曲面构件因其独特的结构和力学特性,广泛应用于航空航天领域。然而,未知的曲面形状导致阵列超声检测时,声传播延时计算不准确,影响缺陷检测的精度。为解决这一问题,提出了一种不依赖声传播延时的适用于曲面构件的阵列超声频域逆时偏移成像方法。首先,利用阵列超声全聚焦方法对曲面构件表面进行成像;然后,对成像结果进行阈值分割和曲线拟合,重构构件表面形状并建立二维声学特性分布模型;最后,通过频域逆时偏移将来自超声波源的正向传播波场与缺陷反射体的反向传播波场进行互相关成像。实验结果表明,所提出的方法可以有效实现曲面构件内部缺陷成像,与传统的阵列超声全聚焦方法相比,缺陷的成像质量提升66%以上,缺陷定量平均误差降低37.04%以上。

高含量重密度组分煤重介质旋流器分选特性研究

为了提高重介质旋流器对高含量重密度组分难选原煤的分选效率,设计了新型重介质旋流器模型装置,建立了颗粒在离心旋转流场中沉降分离数学模型,采用试验与理论分析相结合的方法研究新型重介质旋流器的分选特性,揭示高含量重密度组分难选煤分选特性随工艺参数的变化规律,探索影响新型重介质旋流器流场工作悬浮液动态稳定性的因素及重产物排料输运机制。研究结果表明,新型重介质旋流器分选高含量重密度组分煤时,底流重产物排料能力强、处理量大;离心旋流场中的悬浮液密度梯度分布小、密度相对均匀,底流与溢流密度差值较低,流场中悬浮液稳定性更强;入料的压力与悬浮液动态稳定性、分选精度及重产物排料效率直接相关,随着入料的压力增大,底流、溢流口排出悬浮液密度差值增大,可能偏差E值降低,分选精度提高,重产物排出量升高;当入料的压力为25 kPa时,实际分选密度为1.666 g/cm^(3),可能偏差E值为0.09 g/cm^(3),重产物产率为75.23%。本研究为高含量重密度组分煤的分选提供了新的思路。

商业银行普通金融债超额收益影响因子研究

商业银行普通金融债是我国债券市场的重要品种,近年来发行交易较为活跃。本文运用小样本稳健的自助法,以2010年至2021年我国商业银行普通金融债收益率和超额收益为对象进行研究,发现政策性银行债收益率曲线前三个主成分(水平、斜率和曲率)以及社会融资规模增速波动项对商业银行普通金融债超额收益具有显著影响,而收益率曲线更高阶主成分、通货膨胀趋势、债券供给的影响并不显著。实证结果表明,社融增速波动项可能是商业银行普通金融债超额收益定价因子,与超额收益呈负相关关系。本文的结论为新兴市场债券定价以及金融债定价的相关研究提供了有益补充。建议商业银行和市场投资者综合考虑收益率曲线形态和社融增速,合理评估金融债供给波动的短期影响,妥善安排债券发行和投资。

不同含水状态下煤样蠕变实验研究

通过保持结构完整性浸水装置、X射线衍射仪及电液伺服加载煤岩体三轴蠕变渗流实验平台,实验得到上湾煤矿煤样的饱水曲线、不同含水状态下微观组分变化及蠕变特征。实验结果表明:煤样含水率与浸水时间呈负指数函数关系,含水率变化可分为加速增长、减速增长及稳定3个阶段;1次饱和过程中,随着含水率增加,煤样石英含量几乎保持不变,而高岭石等黏土矿物含量在这一过程中减少较多;干湿循环过程中,煤样石英含量衰减与循环次数成正比;随着含水率及干湿循环次数增加,煤样进入稳态蠕变及加速蠕变所需轴向荷载降低。

双层曲母线锥壳构件整体液压成形工艺研究

为解决传统分块成形-拼焊工艺制造双层薄壁锥壳构件时存在的型面精度低、内外层贴合不严等问题,本文提出一种双层曲母线锥壳构件整体液压成形新工艺。通过控制内压与合模力使内、外层筒坯同步胀形,孪生整体成形出双层锥壳构件。采用数值模拟与实验的方法研究了双层曲母线锥壳构件液压成形的贴模过程,并对最终获得的双层锥壳构件的型面轮廓精度及壁厚分布规律进行了分析。结果表明:整体液压成形过程中内、外层锥形筒坯同步发生变形,在凹模型腔两端率先贴模,之后随着内压增大开始从大端向小端逐渐贴模。双层锥壳构件型面直径偏差控制在[-0.5 mm,+1.5 mm]以内,最大偏差发生在大端。此外,液压成形过程中双层锥形筒坯大端发生缩径变形并流入型腔,产生自补料作用缓解构件壁厚减薄,最大壁厚减薄率为3.68%。

端板支承式多肋预制底板承载力试验研究

端板支承式多肋叠合板是一种主肋在端部收齐,端部主筋弯起,再焊以抗剪角钢部件后设计的新型叠合板,主要应用于现代物流仓储等承载力大、对空间要求较高的场景.为研究多肋预制底板在施工过程中的受力及破坏特征,设计了多肋预制底板的简支均布静载试验来分析预制底板的承载力、支座受力特征等.试验表明,随着荷载的增加,多肋混凝土预制底板的抗弯强度呈下降趋势,达到最大承载力时,支座位置出现断裂,此时角钢达到屈服应变;且该多肋混凝土预制底板的破坏特征与适筋梁破坏形式类似,构件的破坏过程均可分为3个阶段.最后,通过有限元模拟软件ABAQUS对角钢的变形状态以及在加载的4个阶段对不同部位的纵筋应变进行分析,将试验结果与ABAQUS模拟结果进行对比研究,得出有限元软件可较好模拟并呈现多肋混凝土预制底板破坏形态的结果,这一结果可为后续叠合板的研究提供一定的依据.

材料表面润湿性对超微量胶液分配及封装效果的影响

为了在微纳元件的封装中实现pL级超微量胶液的分配,根据不同材料表面具有不同表面润湿性的性质,提出了一种微纳量级的点胶方法。首先,使用自主搭建的超微量点胶系统进行pL级胶液分配实验,该系统点样的平均体积误差≤±1.1%,转移液滴的最小体积约为19.6 pL;然后,通过改变表面润湿性的单因素实验分析接触角对胶液转移量的影响,实验结果表明,接触角可以直观反映材料表面的润湿程度,即接触角越小,表面润湿性越好,转移液滴体积越大;最后,根据接触角与转移液滴体积的实验数据进行非线性曲线拟合,推导出了转移液滴体积预测公式,利用该公式预测的转移液滴体积与实测体积之间的平均差异率为2.32%。

基于部件组合的连衣裙款式图快速生成研究

款式图作为真实服装的一种平面表达方式,在服装生产过程中起着重要的作用。为了简化服装款式设计过程,提高款式设计的效率与服装信息表达的准确率,并针对不同体型生成个性化的款式图,以连衣裙为对象,基于部件数字化对款式图快速生成进行了研究。首先,采用薄板样条插值算法以使服装款式图拟合不同人体体型,使衣身能够快速达到满足特定体型的尺寸;其次,通过基于关键点的矩阵变形实现部件之间的自适应组合;最后,选用参数驱动和交互式修正关键点2种方法实现对服装款式细节的调整。以连腰鱼尾裙为例,阐述并实现了连衣裙款式图快速生成过程,验证了基于部件组合的款式图快速生成的可行性,为个性化定制和智能化款式设计提供理论支持。