基于DInSAR监测的动态地表移动变形数值模拟分析(英文)

合成孔径雷达干涉测量(DInSAR)技术是监测动态地表沉陷的新方法,能够大范围地监测地表下沉盆地的动态演化过程,可以较好地反映各阶段的地表下沉形态。但是受到噪声等因素的影响,基于DInSAR数据计算的倾斜、水平变形等曲线规律性较差,与实际偏差较大,而倾斜、水平变形又是研究地表受护对象是否安全的重要指标。基于DInSAR监测数据,采用数值模拟方法,对澳大利亚West Cliff煤矿长壁工作面32开采动态地表移动变形进行分析研究。结果表明,数值模拟得到的下沉曲线与DInSAR实测数据比较吻合,相关系数可达95%以上,且数值模拟方法求算的地表倾斜、曲率和水平变形与理论形态一致。因此,进行矿区地表及其附属建(构)筑物受采动影响分析时,应以DInSAR实测数据为基础确定模型参数,结合数值模拟方法揭示地表动态其他移动变形值的分布规律。研究表明,该方法具有良好的适用性,可为类似的情况提供参考。     

金属矿山岩移预计的损伤力学模型

矿山开采引起的岩层与地表移动是一个复杂的力学过程.根据地质采矿特点,把金属矿山的岩体看作经过变形、受过破坏的地质体,将岩层移动看作因开采产生再变形、再破坏的过程,提出了一个岩移预计的损伤力学模型,编制了考虑损伤的平面有限元程序,研究了金属矿山的岩移机制和规律;并在工程实用中取得了令人满意的结果.     

基于等价采高理论的固体充填采煤沉陷预计方法(英文)

在分析固体充填采煤岩层移动特征的基础上,提出固体充填采煤沉陷预计方法,并给出概率积分法参数选取方法。研究认为:与等价采高煤层垮落法开采下沉系数相比较,固体充填采煤沉陷预计参数中下沉系数可以根据垮落带、裂隙带的高度以及碎胀率计算得出;主要影响角的正切略小0.2~0.5,但不应小于1.0;出于安全考虑,拐点偏移距离可为零;水平移动系数和下沉影响角可不变。最后,利用基于等价采高理论的概率积分法模型计算了花园煤矿固体充填的地表沉陷。结果表明,该方法较为可靠地预测了固体充填的地表沉陷,最大下沉点的预计误差不超过5%。     

地下与露天复合采动效应下边坡破坏机制的数值分析

研究和探讨了地下与露天矿同期采动效应下边坡体的变形与破坏机制问题,在此条件下边坡的变形与破坏过程同时受两种开挖因素的影响,边坡体内的应力场分布规律及约束关系受两种采矿过程共同作用,并应用有限元法分析了叠加效应共同制约边坡体的变形与破坏过程。     

岩体初始应力实测值的各向异性球壳模型解析

提出了各向异性弹性球壳模型，并据此建立了岩体初始应力状态的解析式；得出了与全球实测应力值相吻合的解析结果，从自重应力理论的角度分析了岩体初始应力沿地表深度的分布特征。解析结果表明：岩体初始应力主要受岩体自重、地表位移、地温以及由岩体弹性参数Ｅ和μ间接表述的地质构造运动的影响；水平面内最大及最小正应力的差异主要取决于岩体各向异性特征     

GH4169高温合金的静态再结晶动力学

对GH4169高温合金在Gleeble-3500热模拟实验机进行了双道次和单道次热压缩实验。分析了变形温度、应变速率、间隔保温时间、变形量和初始晶粒尺寸对GH4169高温合金静态再结晶体积分数的影响。实验结果表明:变形温度越高、应变速率越大、道次间隔时间越长,变形量越大,初始晶粒度越小,静态再结晶体积分数越大。根据实验结果,建立了GH4169高温合金的静态再结晶模型,并将所建立的模型的预测结果和实验结果进行了对比分析,二者比较吻合。     

热变形对高强汽车钢组织及性能的影响

在Gleeble-3500热模拟试验机上对高强汽车钢进行了热变形处理,研究了热变形温度、应变速率、变形量和初始冷却速度对其应力应变曲线和显微组织的影响。结果表明,在相同的热变形温度下,应变速率越大,其同样应变量下的应力值越高;在相同应变速率下,随着热变形温度的升高,峰值应力逐渐降低;热变形温度、应变速率、变形量和初始冷却速度对实验钢中碳化物的微观结构和尺寸都有明显影响。     

T700碳纤维复合材料层合板面内剪切过程的声发射特性

为了研究碳纤维复合材料层合板面内剪切的破坏原理,对其损伤过程进行了声发射检测和有限元模拟。结果表明:碳纤维复合材料层合板面内剪切损伤形式和损伤演化过程与声发射特征参数(幅值、能量、撞击计数)具有相关性,损伤过程包括初始阶段、损伤累积阶段和断裂破坏阶段;在初始阶段和损伤累积阶段,损伤呈渐进式增长,试件具有一定的承载能力,在断裂破坏阶段,承载能力随大面积分层以及纤维断裂发生骤降。     

矿山地下开采对地表建筑物影响的评价方法研究

地下采空区造成地表建筑物破坏的问题是目前矿山安全生产领域普遍关注的地下工程问题之一.在总结关于地下开采过程中围岩变形和移动机理以及采动影响已有研究成果的基础上,研究了评价矿山地下开采对地表建筑物影响的"三带理论"、岩层移动角定性评价方法和基于有限差分数值模拟手段的定量评价方法.将上述评价方法应用于某矿采动对地表民房影响问题的研究中,基于对该矿采空区分布的实测成果,对其现有采空区和将来开采对附近民房安全的影响进行了计算和分析,指出了为保证地表民房安全该矿应采取的安全对策措施.     

煤系地层覆盖下铝土矿开采覆岩移动规律数值模拟研究

以山西某煤下铝土矿为研究对象，采用数值模拟方法研究煤下铝土矿开采覆岩移动变形规律。主要研究内容和成果如下：提取了影响煤下铝土矿开采覆岩沉降的主要控制因素，利用FLAC^3D数值模拟软件，分析煤下铝矿块式采场分区放顶开采条件下，不同主控因素的影响及控制作用。揭示了不同采场宽度、采场高度、放顶范围崩落体性质、上覆岩层性质条件下的覆岩移动规律。数值模拟的计算结果以及覆岩移动规律，为构建煤下铝协调开采覆岩裂隙带均匀沉陷控制技术体系提供了依据。     

Fracture behaviour of diffusion bonded titanium alloys with strength mismatch

Abstract

The present study considers the effect of strength mismatch on the fracture behaviour of diffusion bonded joints between commercially pure (CP) Ti and Ti-6Al-4V (Ti64), including dissimilar joints and sandwich structures with strength undermatching and overmatching. The aim of the investigation is to determine the influence of the interlayer thickness (for both higher and lower strength interlayers) and the bond quality on the deformation behaviour and fracture toughness of the joints. The influence of mechanical heterogeneity (strength mismatch) on the fracture behaviour of the interface in dissimilar joints was also investigated. Round bars of CP Ti and Ti64 having a diameter of 40 mm were diffusion bonded as dissimilar butt joints and sandwich structures containing lower strength (undermatching) and higher strength (overmatching) interlayers of different thicknesses. Round transverse tensile specimens and standard four point bend (single edge notch bend) specimens were extracted from the joints via spark erosion cutting. The four point bend specimens were fatigue precracked to introduce a sharp crack after introducing machine notches at the centre of the interlayers in the sandwich structures and at the interface in the dissimilar joints, and tested at room temperature. Some specimens were also prepared with the crack positioned away from the interface to determine the effect of notch position on fracture behaviour. The effect of strength mismatch on the crack tip opening displacement fracture toughness parameter of the joints has been evaluated. Crack initiation, crack growth, and crack deviation processes have been examined and fracture resistance curves (R curves) constructed for the joints. These results were used to explain the influence of mechanical heterogeneity of the joints and interlayer thickness on fracture behaviour.     

自冲铆接凹模损伤对铆接质量的影响

采用了试验结合有限元仿真的方法,对自冲铆接(Self-Piercing Riveting,SPR)设备中的重要部件凹模出现的不同程度的损伤情况可能对SPR接头质量产生的影响进行了试验研究。对凹模的受损情况进行统计分类,根据凹模的受损程度将凹模分为早期受损、中前期受损等5个级别。使用不同受损程度的凹模对厚度为1. 5 mm的A6111铝板进行自冲铆接,测量铆接接头的外观质量与接头剖面几何参数。通过拉伸-剥离仿真试验,探究凹模断裂损伤对SPR铆接接头的连接质量的影响。试验结果表明:凹模损伤会对接头表面外观质量造成损伤,并且会随着凹模损伤程度的增加而增大;凹模没有发生断裂时,凹模损伤对接头剖面的几何参数不会产生太大影响;凹模发生断裂,会降低接头的连接质量。     

轧辊表面裂纹位置确定方法研究

轧辊是轧钢生产中的主要部件,在复杂应力下容易产生表面裂纹,对轧辊的使用寿命、轧材质量有严重的影响,因此轧辊表面裂纹检测至关重要。轧辊出现损伤时,其固有频率也会发生改变。采用振动法比较分析不同位置的表面裂纹对轧辊固有频率、位移模态、应变模态和一阶模态下轴向位移频响函数的影响。结果表明:一阶模态下的轴向位移对轧辊表面裂纹位置检测识别最敏感,可以作为裂纹位置判断的主要标识量。     

基于纳米压痕法的无铅BGA焊点的循环力学行为

采用纳米压痕法通过循环加载卸载方式研究了最大载荷、循环次数及保载时间对Sn-3.0Ag-0.5Cu和Sn-0.3Ag-0.7Cu 2种钎料BGA焊点循环性能的影响.结果表明,Sn-Ag-Cu系无铅BGA焊点的循环性能具有很大的载荷依赖性,随着最大载荷的增加,BGA焊点的损伤累积增加且前几周循环中损伤累积很大,其后逐渐减小并趋于稳定;循环次数增加,使BGA焊点抵抗变形的能力稍有降低;保载时间增加,蠕变位移不断增加,蠕变和疲劳共同作用会加速焊点失效;Sn-0.3Ag-0.7Cu钎料BGA焊点的能量损耗大于Sn-3.0Ag-0.5Cu钎料BGA焊点.     

剪切激励下润滑脂对螺栓连接结构松动行为的影响研究

目的 为了提高螺栓连接结构的可靠性,分析剪切激励下螺栓连接结构松动失效机理,并研究润滑脂对螺栓连接松动行为的影响。方法 基于自主设计的试验装置,开展了剪切激励下螺栓连接结构的松动试验,分析了两种润滑脂(MoS2润滑脂和锂基润滑脂)对螺栓连接结构松动行为的影响,试验结束后使用扫描电子显微镜分析螺纹表面的损伤情况。结果 在相同预紧力条件下,使用润滑脂的螺栓连接结构初始预紧力矩可降低30%~40%。螺栓连接结构所承受的剪切载荷存在门槛值,即当剪切载荷低于门槛值时,连接结构不会完全松动。在螺栓前三圈接触螺纹表面添加润滑脂(局部润滑),门槛值降低;在螺栓全部接触螺纹表面均添加润滑脂(完全润滑),门槛值进一步降低。当承受载荷幅值低于门槛值时,局部润滑有利于防松,螺栓连接结构的松动程度可降低20%以上。结论 螺纹接触界面的微观滑移和微动磨损是螺栓连接结构松动的主要原因,在螺纹接触界面添加润滑脂可有效减缓螺纹表面的微动磨损。     

Torsional fretting corrosion behaviours of Ti6Al4V alloys in Hank’s simulated body fluid

ABSTRACT

Torsional fretting corrosion in a physiological medium is one of the main reasons that artificial joints fail. In this study, we carried out experiments on torsional fretting corrosion in Titanium alloys (Ti6Al4V) against Zirconium dioxide (ZrO₂) ceramic balls under 37°C in a Hank’s simulated body fluid. During the tests, we recorded electrochemical corrosion parameters using an electrochemical analysis system in real-time. We analysed the torsional fretting dynamics behaviours, damage mechanisms, and electrochemical corrosion behaviours in detail using the micro-examinations of a scanning electron microscope (SEM), an energy-dispersive X-ray (EDX), a profilometer, and an X-ray photoelectron spectrometer (XPS). The results showed that the dynamics behaviours strongly depended upon the torsional angular displacement amplitude and the number of cycles. The friction torque increased with increases in the torsional angular displacement amplitude and normal load. We established a running condition fretting map (RCFM), which included three fretting running regimes: a partial slip regime (PSR), a mixed fretting regime (MFR), and a slip regime (SR). We determined that the influences of torsional fretting on electrochemical corrosion behaviours were strongly correlated to the angular displacement amplitude. Under large angular displacement amplitudes, the corrosion of the Ti6Al4V alloys in Hank’s simulated body fluids were accelerated by torsional fretting, especially during the initial stage of the test. However, when the angular displacement amplitude was smaller than 1°, the corrosion potentials and corrosion currents were almost invariable during the entire duration of the test. The damage to the Ti6Al4V alloy was the result of wear and corrosion. The wear mechanisms were attributable to delamination and abrasive wear in the three fretting regimes. We observed almost no damage on the contact centre and only slight scratches and wear on the contact edge in the PSR. In MFR testing, the damage zone extended to the contact centre and the sticking zone (which exhibited no damage) contracted to the contact centre with increases in the number of cycles. Ultimately, in MFR and SR testing, the damage mechanisms were primarily the result of abrasive wear, oxidation wear, tribochemical reactions, adhesion wear, and electrochemical corrosion.     

Korrosionsunterstützte Schädigungsmechanismen an SMD-Bauelementen

Failure mechanism under corrosion on surface mounted devices During the fabrication of electronic systems residues could occur. Together with atmosphere influences these residues cause corrosion effects, which lead to a failure of the electronic systems. Due to the increasing miniaturisation and the decreasing distance between the pins corrosion products with small dimensions are sufficient to cause damage on electronic components. Very critical are flux residues, which stay after the soldering process. By the influence of moisture the solder surface can be disturbed or jumpers between the solder joints can be formed. Another damage can occur due to a insufficient tightness of the packages of electronic components.     

Mechanisms of damage initiation in a titanium alloy subjected to water droplet impact during ultra-high pressure plain waterjet erosion

Impingement of ultra-high pressure plain waterjets (PWJ) has been considered as a promising surface treatment technology (e.g. peening, milling, cleaning) for some difficult-to-machine engineering materials (such as titanium alloys). However, a comprehensive understanding of the mechanisms of damage initiation on such materials under PWJ impingement has not been established. This paper presents an in-depth investigation into the initial material damage mechanisms which are observed during impingement of a PWJ onto polished samples of an α?β titanium alloy—Ti–6Al–4V, and the influence of the microstructure of the alloy on the initial damage modes. A series of single-track erosion trials were carried out and scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to examine the resulting damage. It was found that the microstructural features of Ti–6Al–4V influence the development of damage, with grain boundaries exhibiting lower resistance to damage than grains themselves. Under waterjet impingement, the initial stage of damage is associated with deformation resulting in grain tilting; a combination of impact damage and lateral outflow jetting then results in preferential damage to the grain boundary regions. Hydraulic penetration into the damaged grain boundaries results in the formation and expansion of microvoids and pits, firstly along the grain boundaries and then across the grains. The subsequent damage is linked with the effects of both hydraulic penetration and lateral outflow jetting on the increasingly roughened surface.     

车用扭杆端头镦粗工艺参数对其表面损伤的影响

针对车用扭杆端头在镦粗加工时,其始锻温度、锻造方式以及锻机进给速度等工艺参数对端头的表面质量影响较大的问题,采用有限元法,建立车用扭杆及端头的有限元模型,利用Deform-3D软件对扭杆及其端头进行网格划分以及边界条件设置,对其镦粗过程进行仿真,考虑了热交换模型,对不同的始锻温度和进给速度下,扭杆端头所产生的轴向应力、轴向应变以及表面损伤进行探究,得出了适用于车用扭杆端头镦粗工艺的相关规律。结果表明:始锻温度在1150~1200℃之间、锻机进给速度为1 mm·s-1时,车用扭杆端头的表面损伤最小,工件性能较好。     

P92钢焊接接头蠕变损伤与裂纹扩展数值模拟

高温焊接接头由于蠕变损伤而提前失效的案例频频发生,准确预测焊接接头的蠕变损伤和裂纹扩展行为对于保证高温装备的结构完整性具有重要意义.文中基于延性耗竭模型并结合有限元方法,考察了结构因素对厚壁圆管焊接接头蠕变失效行为的影响.结果表明,蠕变裂纹萌生/扩展行为受热影响区宽度影响,细晶热影响区宽度对蠕变裂纹的萌生时间影响不大,但会改变裂纹萌生位置;相比之下,粗晶热影响区的宽度变化对裂纹萌生时间影响略大.不同坡口形式展现出不同的裂纹萌生/扩展行为,而X形坡口是四种坡口形式中的较优选择.