Inverse approach to determine piston profile from impact stress waveform on given non-uniform rod

An essential problem in the design of mechanical impact systems is the impact of a piston on a rod. The impact of a semi finite cylindrical piston on a non uniform rod was studied. Based on wave mechanics and characteristic line theory, an inverse numerical approach to determine the piston profile was proposed, by means of which the geometry of an impact piston may be determined from the given stress waveform for a given rod profile. Numerical results show that the given stress waveform may be produced by means of the alternatives of design of piston and rod. There is good agreement between the experimental results and numerical results. [

Effect of non-uniform stress characteristics on stress measurement in specimen

There is a remarkable difference in stress distribution between a specimen and a plate removed from the specimen.The plate presents a uniform stress distribution whereas the specimen presents a non-uniform stress distribution.Firstly,the real stress distributions in plates with thickness of 30,40 and 50 mm and then in the specimens were obtained through simulation and X-ray surface stress measurement.Secondly,in order to study the impact of specimens shapes and processing ways on the results accuracy,two irregular shapes (parallelogram and trapezoid) and two processing ways (saw and electron discharge machining (EDM)) were compared and analyzed by simulation and experiment using layer removal method,then the specimen effects on measurement results were evaluated.The results show that:1) the non-uniform stress distribution characteristics of the specimen near the surface of the cut is significant,the range of non-uniform stress distribution is approximately one-thickness distance away from the cut,and it decreases gradually along the depth;2) In order to ensure the stability in the results,it is suitable to take the specimen plane size 2-3 times of its thickness;3) Conventional processing methods have little effect on experimental results and the average deviation is less than 5%.

Stress analytical solution for plane problem of a double-layered thick-walled cylinder subjected to a type of non-uniform distributed pressure

The stress state around circular openings,such as boreholes,shafts,and tunnels,is usually needed to be evaluated.Solutions for stresses,strains and ultimate bearing capacities of pressurized hollow cylinder are common cases.Stress analytical method for plane problem of a double-layered thick-walled cylinder subjected to a type of non-uniform pressure on the outer surface and uniform radial pressure on the inner surface is given.The power series method of complex function is used.The stress analytical solution is obtained with the assumption that two layers of a cylinder are fully contacted.The distributions of normal and tangential contact stress along the interface,tangential stress on the inner boundary and stresses in the radial direction at θ=0°,45° and 90°,are obtained.An example indicates that,when the elastic modulus of the inner layer of a double-layered thick-walled cylinder is smaller than that of the outer layer,the tangential stress is smaller than that in the corresponding point for a traditional cylinder composed of homogeneous materials.In that way,stress concentration at the inner surface can be alleviated and the stress distribution is more uniform.This is a capable way to enhance the elastic ultimate bearing capacity of thick-walled cylinder.

Numerical Study on Effect of Non-uniform CMAS Penetration on TGO Growth and Interface Stress Behavior of APS TBCs

The penetration of CaO-MgO-Al_(2)O_(3)-SiO_(2)(CMAS)is one of the most significant factors that induce the failure of air-plasma-sprayed thermal barrier coatings(APS TBCs).The direct penetration of CMAS changes the thermal/mechanical properties of the top coat(TC)layer,which affects the thermal mismatch stress behavior and the growth of thermally grown oxide(TGO)at the TC/bond coat(BC)interface,thereby resulting in a more complicated interface stress state.In the present study,a two-dimensional global model of APS TBCs with half of the TC layer penetrated by CMAS is established to investigate the effect of non-uniform CMAS penetration on the interface stress behavior.Subsequently,a local model extracted from the global model is established to investigate the effects of interface morphologies and CMAS penetration depth.The results show that non-uniform CMAS penetration causes non-uniform TGO growth in APS TBCs,which consequently causes the stress behavior to vary along the interface.Furthermore,the CMAS pen-etration depth imposes a significant effect on the TC/TGO interface stress behavior,whereas the interface roughness exerts a prominent effect on the stress level at the BC/TGO interface under CMAS penetration.This study reveals the mechanism associated with the effect of non-uniform CMAS penetration on the interface stress behavior in APS TBCSs.

Experimental Research on Damage Parameter of Concrete in Non-Uniform Stress Field

The damage variables of describing the material damage state should be chosen first when the research of concrete structures by use of theory of damage theory. The method of calculation of damage parameter by the measure of the change of the elastic modulus of concrete specimens is effectively. In this paper, the wedge splitting tests with double bearing of three groups of different initial crack lengths of concrete specimens were conducted, and the stress and the strain of the points with different distance from the initial crack tip measured and calculated, and the damage value with peak stress of the various points were calculated based on the stress-strain curves. From the results of the test, the damage parameter can be confirmed under the non-uniform stress field, and the initial crack length has some influence on the damage parameter, and the longer the initial crack length and the greater the damage parameter.

Analytic model of non-uniform corrosion induced cracking of reinforced concrete structure

In order to perfectly reflect the dynamic corrosion of reinforced concrete (RC) cover in practical engineering,an analytic model of non-uniform corrosion induced cracking was presented based on the elastic-plastic fracture mechanics theory.Comparisons with the published experimental data show that the predictions given by the present model are in good agreement with the results both for natural exposed experiments and short-time indoor tests (the best difference is about 2.7%).Also it obviously provides much better precision than those models under the assumption of uniform corrosion (the maximal improved precision is about 48%).Therefore,it is pointed out that the so-called uniform corrosion models to describe the cover cracking of RC should be adopted cautiously.Finally,the influences of thickness of local rusty layer around the reinforcing steel bar on the critical corrosion-induced crack indexes were investigated.It is found that the thickness of local rusty layer has great effect on the critical mass loss of reinforcing steel,threshold expansion pressure,and time to cover cracking.For local rusty layer thickness with a size of a=0.5 mm,the time to cover cracking will increase by about one times when a/b (a,semi-minor axis;b,semi-major axis) changes from 0.1 to 1 mm.

NRT FILES镍钛根管锉预备对弯曲根管应力分布的仿真分析

背景:在根管治疗中,镍钛合金器械常因应力超过金属塑性变形的弹性极限或在根管弯曲处重复弯曲导致镍钛合金疲劳断裂。目的:探索新型镍钛锉NRT FILES在作为根管预备材料时对根管内壁存在的应力分布,明确应力集中区域。方法:利用Solidworks软件对NRT FILES进行三维建模,模拟还原器械在真实口腔环境中存在的状态。建立6组根管简化模型:①弯曲角度30°、弯曲半径5 mm、根尖弯曲;②弯曲角度30°、弯曲半径5 mm、根中弯曲;③弯曲角度30°、弯曲半径2 mm、根尖弯曲;④弯曲角度30°、弯曲半径2 mm、根中弯曲;⑤弯曲角度45°、弯曲半径5 mm、根尖弯曲;⑥弯曲角度45°、弯曲半径2 mm、根尖弯曲。将根管简化模型与根管锉模型进行组配,对根管内壁受力点及应力分布情况进行分析。结果与结论:①-⑥组根管锉最大应力分别为1 185,1 354,1 371,1 678,1 335,2 557 MPa,最大应变分别为0.010 36,0.013 54,0.013 79,0.016 48,0.013 45,0.022 03;根管弯曲部位的不同会影响根管锉所承受的应力大小,因此在根管治疗中,根管锉沿着根管越往下,根管锉与根管接触的半径越大、刚性越差,根管锉所承受的应力越大越容易发生断裂;根管弯曲半径越小,根管锉承受的应力越大;根管弯曲角度越小,根管锉所承受的应力越大。在根尖弯曲部位,根管锉在根管弯曲半径小的弯曲根管需要承受更大的应力,根管锉更容易发生断裂;同理,在根中弯曲部位,根管锉在根管弯曲半径小的弯曲根管亦承受更大的应力,因此要格外注意根管的弯曲程度,以此来选择合适的根管锉进行根管治疗。

A NEW NON-UNIFORM YIELD PHENOMENON AND ITS MECHANISM

A new non-uniform yield phenomenon is found during tension of austenite stainless steel at -190℃, which consists of elasto-plastic instability ξph and stress plateau ξL resulting from strain-induced martensite transformation. It is essentially different from non-uniform yield that is related to dislocation obstacles. The experimental results show that ξph and ξL increase with increaslng strain rate, and ξph, increases but ξL decreases with increasing prestmin.Tronsformation enengy of strain-induced martensite keeps a constant, 3.85×106J/m3, with increasing strain at the stages of both elasto-plastic instability and stress plateau.

面向应力分析的LNG船舶管路三维协同设计方法

针对在天然液化气(Liquefied Natural Gas,LNG)管道生产设计与应力分析中串行工作模式带来的数据格式不兼容、设计返工频繁等问题,构建管路信息模型,并基于标准管道组件文件(Piping Component File,PCF)格式进行模型的表达;通过二次开发实现船舶计算机辅助设计(Computer Aided Design,CAD)环境下管路部件信息的提取;建立管路参数化模型,支持管路应力分析模型的自动创建;并基于管路信息模型实现应力分析结果的CAD环境集成。应用案例验证表明,基于应力分析的复杂LNG管路设计协同工作模式可以大大提高设计效率与质量。

华北地区构造应力场非均匀特征与煤田深部应力状态

将华北地区分成11个应力小区,依据华北地区近期1111条中小地震震源机制解数据,利用格点尝试法分析华北地区主应力方向的分布特征,结果显示,华北地区现今构造应力场以水平作用为主,其中,唐山和晋南地区最大主应力方向为近EW向,其他地区最大主应力方向均为NEE向,方位为NE60°～80°。鲁西南万福煤矿深部水压致裂原地应力测试结果显示,水平最大主应力方向的为NE40°～80°,与鲁西南地区中小地震震源机制解的分析结果十分接近。通过构造类比,认为万福煤矿深部应力状态受控于鲁西南地区区域构造应力场。

鄂尔多斯盆地大牛地气田致密砂岩气层应力敏感性综合研究

致密砂岩气藏开发过程中有效应力增加所带来的渗透率应力敏感损害是导致气井产量快速递减的根本原因,故对应力敏感性损害机理研究能够为气层保护工作提供合理依据。在考虑岩石组分、裂缝、温度、含水饱和度和施压次数等因素的同时,对大牛地气田致密砂岩应力敏感性进行了评价,指出随岩屑含量增加和温度升高,致密砂岩应力敏感性增强,温度与有效应力联合作用使致密砂岩应力敏感性更强,水的存在对致密砂岩应力敏感性具强化作用;重复施压过程造成致密砂岩渗透率不断降低,裂缝岩样的渗透率应力敏感程度远大于基块;采用屏蔽暂堵储层保护工作液技术能够减轻致密砂岩气层的应力敏感性损害。

膨胀剂掺量和应力比对钢管混凝土徐变性能的影响

为了研究膨胀剂掺量和应力比对钢管混凝土徐变性能的影响,进行膨胀剂掺量分别为4%,8%和12%共3种情况下的钢管混凝土徐变应变试验,测试钢管与混凝土整体纵向变形随时间的分布规律。同时进行应力比分别为0.15,0.31,0.33,0.37和0.74共5种情况下的徐变试验,测试在相同荷载下,不同应力比钢管混凝土应变变化规律。研究结果表明:膨胀剂掺量对钢管混凝土徐变应变的影响由小到大依次为12%,8%和4%,但是徐变应变并不是随着膨胀剂掺量的增加而呈比例减少;徐变应变随着应力比的增加而增加。应用扫描电镜二次电子成像观测及能谱成分分析膨胀剂的作用机理,得出膨胀剂反应生成钙矾石,其微膨胀可以补偿收缩;同时钙矾石填充在结构孔隙中,使水泥石更加致密。通过应力比对钢管混凝土徐变影响的机理分析,得出混凝土应力随着应力比的增加而增大,同时随着壁厚的增加,钢管对混凝土的侧向约束增加,限制了混凝土徐变变形。

ANSYS三维地应力场数值模拟方法应用研究

初始地应力场由自重应力场和构造应力场叠加而成,是深部地下工程分析必须考虑的重要因素。针对目前常用的三维地应力场数值模拟方法在维持地应力场分布规律和避免附加位移方面存在的缺陷,进行了ANSYS地应力场模拟方法的比较研究。用java语言编写了针对不同ANSYS版本的初始应力文件合并程序,提出了高版本ANSYS初始应力文件合并的EXCEL简易方法,实现了不需编写任何其他程序、对所有类型单元通用的ANSYS初始应力平衡等效节点反力法,构建了一套实用的ANSYS三维地应力场模拟方法流程。

岩石抗拉强度特性的劈裂试验分析

采用钢丝垫条、直接加压、弧形模具的加载方式,对砂岩、泥岩进行了大量的劈裂试验。结果表明:采用不同的加载方式,测定的岩石抗拉强度差别很大。其中,弧形模具加载测得的抗拉强度最大,其次是直接加压的方式,钢丝垫条加载方式测得的抗拉强度最小。通过对劈裂试验试件内应力场的分析,用MATLAB程序绘制出试件内应力场解析解的分布图,结合FLAC2D的模拟结果,认为对于不同的岩石,试件的破坏方式不同,硬岩不一定是从试件中心首先破坏,而是试件轴线上的某个部位;软岩和层状岩石则因不同的加载方式有不同的破坏方式。不同加载方式测试结果产生差别主要是因为加载板和试件间存在摩擦力等因素影响,随后给出了硬岩不同加载方式时抗拉强度的计算公式。

异侧竖缝式鱼道水力特性试验研究

对异侧竖缝式鱼道的水力特性进行了试验研究.在试验室的水槽中,通过三维超声波流速仪(ADV)测得鱼道池室中的流速数据,对流量为5.61L/s和9.31L/s池室中不同水深时的流速场、紊动能和雷诺剪切应力等水力参数进行了初步分析研究.结果表明:鱼道池室中流速沿垂向的分量很小,几乎为零;同等流量下随着水深的增加,流速有减小的趋势,而紊动能和雷诺剪切应力有增大的趋势;而随着流量的增加,池室中相同部位的流速、紊动能和雷诺剪切应力也会相应的增大.

基于成熟度的大体积混凝土早期温度应力场有限元分析

引入成熟度的概念对传统的早期混凝土温度应力有限元计算方法进行了改进。该方法考虑了温度和龄期对水泥放热速率和混凝土弹性模量发展的影响。通过对某大体积混凝土桩承台的现场测温以及温度应力的有限元实例分析 。

X80管线钢焊接接头氢分布的数值模拟

利用ABAQUS有限元软件,建立了三维有限元模型,对X80管线钢焊接接头的氢扩散行为进行了模拟.通过对不同焊接条件下温度场、应力场、氢扩散的三场耦合模拟,研究了焊接工艺参数对焊接接头中氢扩散及分布的影响.结果表明,焊接热影响区残余应力水平最高,是整个接头的应力集中部位,也是焊接接头中的富氢地带.适当地提高预热温度和焊接热输入,均有利于焊接接头中氢的扩散逸出,降低氢在焊接热影响区的聚集程度,从而降低氢致裂纹的敏感性.

中国大陆现今构造应力场的回归分析研究

叙述了应用有限元方法和回归分析理论,依据实际应力观测资料,结合中国大陆构造地质资料反演中国大陆现今构造应力场的研究成果。计算中考虑了地壳结构在纵向上和横向上的非均匀性和现今活动断层的影响,采用接触分析方法模拟了板块边界的作用。计算结果表明,通过回归分析得到中国大陆现今构造应力场特征与实际观测结果是一致的:(1) 在中国大陆现今水平最大主压应力轴走向以青藏高原为中心,呈辐射状分布;(2) 在中国大陆现今水平最大主压应力总体表现为由西向东逐渐降低的趋势;(3) 中国大陆东南的台湾海峡区域水平最大主压应力有局部升高的现象。

大田玉米水分胁迫指数经验模型建立方法

作物水分胁迫指数(Crop water stress index,CWSI)经验模型的建立与气候和种植条件密切相关。以内蒙古自治区鄂尔多斯市达拉特旗大田玉米为对象,研究了CWSI的最优经验模型。玉米在营养生长阶段(Vegetative stage,V期)、生殖期(Reproductive stage,R期)和成熟期(Maturation stage,M期)分别进行不同灌溉水平的处理,采用红外测温传感器采集玉米冠层温度。分别结合田间和实验地旁标准气象站空气温湿度数据建立了CWSI经验模型的无水分胁迫基线。基于2种无水分胁迫基线,分别利用饱和水汽压梯度获取的无蒸腾作用基线和5℃无蒸腾作用基线建立了4种CWSI经验模型,得出反映大田玉米水分胁迫状况的关系曲线,并进行对比。结果表明,基于实验地旁标准气象站空气温湿度数据建立的CWSI经验模型具有很大的波动性,并不能很好反映玉米的水分胁迫状况,其值常常超出正常范围(0~1)。而基于田间空气温湿度数据建立的CWSI经验模型则可以很好地监测内蒙古自治区大田玉米水分胁迫状况,M期3种不同水分处理100%、52%和28%具有较好的CWSI数值梯度,分别为0.03、0.14和0.32。相比于基于饱和水汽压梯度获取的无蒸腾作用基线,以5℃作为无蒸腾作用基线时得到的CWSI数值较小,可以较好地反映水分胁迫状况,对应上述M期3种不同水分处理CWSI值分别为0.02、0.10和0.22,具有较为合理的梯度。经过初步检验和分析,认为基于田间空气温湿度数据建立的CWSI经验模型较为合理,可以有效监测大田玉米水分胁迫状况。

充填采矿法胶结充填体力学作用分析

结合某矿山应用胶结充填采矿法的试验 ,测试胶结充填体的力学参数 ,采用数值模拟方法研究胶结充填体的受力情况和变形特征。结果表明 :尾砂胶结充填体 ,具有独特的支护特性和力学特征、良好的可塑性和较高的残余强度 ;尾砂胶结充填体受动态载荷作用的动态强度、动态弹性模量均高于受静态载荷的静态值 ;胶结充填体的支护作用是对围岩的限制和与围岩的共同承载。