Remaining useful life prediction based on nonlinear random coefficient regression model with fusing failure time data

Remaining useful life(RUL) prediction is one of the most crucial elements in prognostics and health management(PHM). Aiming at the imperfect prior information, this paper proposes an RUL prediction method based on a nonlinear random coefficient regression(RCR) model with fusing failure time data.Firstly, some interesting natures of parameters estimation based on the nonlinear RCR model are given. Based on these natures,the failure time data can be fused as the prior information reasonably. Specifically, the fixed parameters are calculated by the field degradation data of the evaluated equipment and the prior information of random coefficient is estimated with fusing the failure time data of congeneric equipment. Then, the prior information of the random coefficient is updated online under the Bayesian framework, the probability density function(PDF) of the RUL with considering the limitation of the failure threshold is performed. Finally, two case studies are used for experimental verification. Compared with the traditional Bayesian method, the proposed method can effectively reduce the influence of imperfect prior information and improve the accuracy of RUL prediction.

Mechanical model for failure modes of rock and soil under compression

The failure modes of rock and soil under compression are complex phenomena that have not been explained in a mechanical perspective. However, large amounts of studies indicate that the failure modes of rock and soil samples can be categorized into eight types. In this work, the inner tensile stress and the dissipation and conversion of energy of rock and soil under compression are analyzed, then the effective conversion coefficient of energy is deduced, thus the tensile failure criterion of rock and soil under compression is established. Combined with the shear strength criterion of Mohr–Coulomb, a tensile joint shear strength criterion for rock and soil under compression is built. Therefore, a mechanical criterion model concerning the failure modes of rock and soil under compression is established and verified by tests. This model easily explains the test results in the existing literature and many natural phenomena, such as collapse.

Non-Simultaneous Failure of Ice in Front of Multi-Leg Structures

Because the multi-leg jacket structure is the major type of offshore structures in the Bohai Sea, the study of non-simultaneous failure of ice on multi-leg structures is important. However, the non-simultaneous failure has not been considered in engineering design until now, obviously resulting in costly design and notable waste. To resolve this problem, this paper, by means of analysis of experimental data, calculates the coefficient of the non-simultaneous failure for the double-pile structure, the square four-leg structure, the single-line multi-pile structure, and the conical structure, respectively, and provides some reference criteria for engineering design.

Deformation and failure study of surrounding rocks of dynamic pressure roadways in deep mines

In order to understand the change rules of stress-displacement in surrounding rocks of dynamic pressure roadways in deep mines and to obtain a theoretical basis for analyses of roadway stability and designs of support, we established a coupling equation of adjacent rock strength, mining stress and supporting resistance on the basis of an elastic-plastic theory of mechanics. We obtained an analytical solution for stress and displacement distribution of elastic and plastic regions in surrounding rock of dy-namic pressure roadway.. Based on this theory, we have analyzed the changes in stress-displacement in elastic and plastic regions of surrounding rocks of dynamic pressure roadways in the Haizi Coal Mine. The results show that: 1) radial and tangential stress change violently within the first 4 m from the inner surface of a roadway after excavation; radial stress increases while tangential stress decreases within a range of about 6 m from the inner surface of the roadway as a function of q3; 2) radial and tangential stress increase with an increase in the mining pressure coefficient k; the increase in the rate of tangential stress is greater than that of ra-dial stress; 3) the radial displacement of the inner surface of roadways decreases with an increase in q3, provided that k remains unchanged.

Definition of failure criterion for frozen soil under directional shear-stress path

A series of directional shear tests on remolded frozen soil was carried out at 10°C by using a hollow cylinder apparatus to study failure criterion under a directional shear-stress path.Directional shear tests were conducted at five shear rates(10,20,30,40,and 50 kPa/min)and five intermediate principal stress coefficients(b=0,0.25,0.5,0.75,and 1),with the mean principal stress(p=4.5 MPa)kept constant.The results show that the torsional strength and the generalized strength both increase with the increase of the shear rates.According to the failure modes of frozen soil under different shear rates,the specimens present obvious plastic failure and shear band;and the torsional shear component dominates the failure modes of hollow cylindrical specimens.A shear rate of 30 kPa/min is chosen as the loading rate in the directional shear tests of frozen soil.The shape of the failure curve in theπplane is dependent on the directional anglesαof the major prin cipal stress.It is reasonable to use the strain-hardening curves to define the deviatoric stress value atγg=15%(generalized shear strain)as the failure criterion of frozen soil under a directional shear-stress path.

A Fast Product of Conditional Reduction Method for System Failure Probability Sensitivity Evaluation

Systemreliability sensitivity analysis becomes difficult due to involving the issues of the correlation between failure modes whether using analytic method or numerical simulation methods.A fast conditional reduction method based on conditional probability theory is proposed to solve the sensitivity analysis based on the approximate analytic method.The relevant concepts are introduced to characterize the correlation between failure modes by the reliability index and correlation coefficient,and conditional normal fractile the for the multi-dimensional conditional failure analysis is proposed based on the two-dimensional normal distribution function.Thus the calculation of system failure probability can be represented as a summation of conditional probability terms,which is convenient to be computed by iterative solving sequentially.Further the system sensitivity solution is transformed into the derivation process of the failure probability correlation coefficient of each failure mode.Numerical examples results show that it is feasible to apply the idea of failure mode relevancy to failure probability sensitivity analysis,and it can avoid multi-dimension integral calculation and reduce complexity and difficulty.Compared with the product of conditional marginalmethod,a wider value range of correlation coefficient for reliability analysis is confirmed and an acceptable accuracy can be obtained with less computational cost.

Evaluation of the Reliability Performance of Failure Criteria for Composite Structures

Evolution of materials, following the design requirements of special structures, has shifted interest towards development of composite members able to meet strength requirements “tailored” to specific applications. These members can provide appropriate, more cost effective structures, however absence of generic design guidelines raise constraints towards derivation of optimized structures. Reliability-based assessment can overcome this limitation by ensuring that acceptable levels of target reliability are achieved throughout their service life. This paper presents a methodology for reliability assessment of composite members based on appropriate limit state functions derived according to fundamental failure criteria, Tsai-Hill and Tsai-Wu, applicable to composite materials. The methodology that is proposed employs a Stochastic Response Surface Method (SRSM) which combines in discrete steps FEA modelling, numerical simulations and analytical probabilistic assessment techniques, allowing use of commercial and custom developed specialized numerical tools. Application of the proposed methodology on a complex composite structural geometry will illustrate its efficiency and evaluate the reliability performance of the limit states derived and examined.

The coefficient of variation representing the non-uniformity of the strain field and its implication to detect earthquake precursor

Before the major earthquake or rock damage occurs,it is often accompanied by a sudden change in the degree of non-uniformity of the strain field.In order to find a stronger non-uniformity signal before the rock failure,the coefficient of variation(Cv)is examined and reformed in this study.We test the Cv calculation way of the"normal-abnormal"model proposed in the previous studies.Based on the analysis of the physical process of rock failure and its relationship to the shear strain field,we construct a new way to calculate the Cv value.The variation of shear strain field on rock sample with the increase of stress is obtained by the digital speckle correlation method(DSCM).The new Cv value calculation way is used to study the non-uniformity of the spatial distribution for the shear strain field.The results show that this Cv calculation way can get more obvious abnormal signals.When the number of observation points are limited,the specific distribution of points can increase the signal strength,which may provide reference for the research on precursor detection of earthquakes.

Relationship between critical seismic acceleration coefficient and static factor of safety of 3D slopes

Many analytical methods have been adopted to estimate the slope stability by providing various stability numbers,e.g.static safety of factor(static FoS)or the critical seismic acceleration coefficient,while little attention has been given to the relationship between the slope stability numbers and the critical seismic acceleration coefficient.This study aims to investigate the relationship between the static FoS and the critical seismic acceleration coefficient of soil slopes in the framework of the upper-bound limit analysis.Based on the 3D rotational failure mechanism,the critical seismic acceleration coefficient using the pseudo-static method and the static FoS using the strength reduction technique are first determined.Then,the relationship between the static FoS and the critical seismic acceleration coefficient is presented under considering the slope angleβ,the frictional angleφ,and the dimensionless coefficients B/H and c/γH.Finally,a fitting formula between the static FoS and the critical seismic acceleration coefficient is proposed and validated by analytical and numerical results.

复式钢管混凝土墩柱轴压性能及承载力提高分析

为提升矩形钢管混凝土独柱墩的工作性能,在其截面内套异心双圆钢管形成新型复式钢管混凝土墩柱。该文进行了7个墩柱轴压荷载试验,通过对比空钢管柱、矩形墩柱和夹层墩柱分析了新型墩柱的破坏形态、钢管应变发展及承载力和延性差异,最后利用钢管和混凝土的组合效应原理进行组合墩柱轴压承载力提高分析。研究得出新型复式钢管混凝土墩柱轴压破坏形态为鼓曲破坏,其极限承载力较夹层墩柱提高20%,较矩形墩柱提高22%,延性提高效果更为明显;新型墩柱内、外钢管应变发展充分,说明钢管较好地发挥了竖向承载和横向约束混凝土的能力;根据钢板的正则化宽厚比和屈曲后强度计算得出,内、外钢管在混凝土的支撑下承载力提高15%,混凝土在钢管的约束下承载力提高49%;根据约束组合效应得出,新型墩柱整体承载力提高31%;采用等效套箍系数计算的新型墩柱承载力与试验值绝对误差在4%以内,说明新型复式钢管混凝土墩柱符合钢管混凝土统一理论。研究结果表明,新型复式钢管混凝土墩柱在约束混凝土效应方面明显提高,构件的承载力较高、延性较好,具有较强的工程应用前景。

新型拉压复合型锚杆锚固性能研究Ⅳ:数值模拟

新型拉压复合型锚杆具有良好的锚固性能,在抗浮工程中优势明显并逐渐推广应用,但其荷载传递规律尚不明晰。基于此,针对已完成的现场试验,对拉压复合型锚杆的荷载传递机理开展了数值模拟研究。结果表明,拉压复合型锚杆筋体轴向拉力在承压锚固段保持不变,拉力传递至受拉锚固段后大幅降低,破坏时受拉承载系数略低于受拉长度系数。承压锚固段灌浆体受压,压应力向端头递减;受拉锚固段灌浆体受拉,拉应力先增大后减小,且最大拉应力显著低于全黏结型锚杆;优化拉压长度比,可以进一步减小受拉锚固段灌浆体受到的轴向拉应力。拉压复合型锚杆浆土界面剪应力在承载体处最大,向两侧减小;与全黏结型和压力型锚杆相比,相同拉力下,拉压复合型锚杆浆土界面剪应力显著减小,应力集中现象明显削弱,且分布更加均匀。

层间摩擦系数对非黏结柔性管抗拉铠装层轴压屈曲失效模式的影响研究

在柔性管运输、铺设安装和服役过程中,由于其抗拉铠装层钢带为柔性细长螺旋结构,当外部载荷超过临界值时,抗拉铠装层钢带容易发生屈曲失效。考虑非线性材料、几何大变形、层间接触和摩擦等非线性效应的影响,运用ABAQUS有限元软件建立了63.5mm典型非黏结柔性管8层完整结构模型,研究了在抗拉铠装层不同层间摩擦系数的情况下,非黏结柔性管在轴向压缩载荷作用下的力学性能和屈曲失效模式。研究结果表明,层间摩擦系数对非黏结柔性管的抗压刚度和抗拉铠装层屈曲失效模式有较大影响,层间摩擦系数以0.1和0.2为分界点,抗压刚度和屈曲失效模式均呈现出“三段式”变化规律。研究成果可为海洋非黏结柔性管的结构设计和屈曲失效评估提供技术参考。

贯通单裂隙北山花岗岩水-力耦合特性研究

为研究裂隙花岗岩的水-力耦合特性及其变形破坏过程中渗透特性的演化特征,以含倾角30°、45°和60°贯通单裂隙的花岗岩为研究对象,开展三轴压缩试验、围压分级加载的渗透试验以及三轴压缩耦合渗透测试的水-力耦合试验。结果表明:裂隙花岗岩的渗透系数随围压的增大而有所降低,随轴向应变的增大呈现出先降低后增大最后再降低的趋势。0.5 MPa渗透压差的水-力耦合条件会导致倾角30°、45°和60°裂隙花岗岩的抗压强度分别下降11.75%、25.42%和21.52%,弹性模量分别下降28.64%、40.15%和27.35%,但不会对其破坏形式造成显著影响。裂隙花岗岩的破坏形式分别为:穿裂隙面破坏(30°)、穿裂隙面破坏和沿裂隙面滑移并存的复合破坏(45°)以及沿裂隙面滑移破坏(60°)。

失效模式与效应分析对达芬奇机器人手术器械清洗质量的影响研究

目的探讨失效模式与效应分析(FMEA)管理模式对达芬奇机器人手术器械清洗质量的影响。方法选取2023年3月至8月无锡市第二人民医院手术后需消毒供应中心清洗的机器人手术器械1842件(包括机器人手臂器械、光学目镜及机器人腔镜器械及辅助器械)为研究对象。2023年3月至5月采用常规管理模式对858件机器人手术器械清洗流程进行管理,设为对照组;2023年6月至8月采用FMEA管理模式对984件机器人手术器械清洗流程进行管理,设为观察组。比较两组手术器械清洗流程中4项主要潜在失效风险因素的风险系数(RPN)评分结果、器械清洗质量评价结果以及器械清洗时间。结果观察组中预处理不到位、器械未拆卸到最小单元、超声清洗温度不恒温、自动清洗机内器械叠放超载4个失效因素的RPN评分均明显低于对照组,差异有统计学意义(P<0.05);分别采用光源放大镜检测法、管腔器械内部照明装置检测法、ATP生物荧光检测法对两组器械清洗后的清洗质量进行检测,观察组3种检测方法清洗质量检测合格率均高于对照组,差异具有统计学意义(P<0.05);对两组机器人手术器械清洗时间进行比较,差异无统计学意义(P>0.05)。结论FMEA管理模式能有效提高达芬奇机器人手术器械的清洗质量,并保证器械良好功能,值得推广。

碳纤维增强复合材料黏结型锚固体系弯拉性能试验研究

为了研究碳纤维增强复合材料(CFRP)黏结型锚固体系的弯拉性能,对设计的锚固体系试件进行了10组轴向拉伸试验与12组弯拉试验。在锚固体系优化基础上研究了CFRP筋直径、弯曲半径改变下试件的极限承载力、破坏模式、锚固效率及CFRP筋荷载‒应变关系。结果表明,锚固体系的弯拉承载力折减量系数随CFRP筋弯曲半径的增大而减小,CFRP筋直径越大试件承载力折减量系数越大,并且CFRP筋横向约束有利于弯拉极限承载力的提高。此外,CFRP筋荷载‒应变曲线的非线性变化是试件失效前的典型特征。弯曲半径和CFRP筋直径的比值与锚固效率系数为线性关系,比值在2.4‰以下时试件的弯拉锚固效率系数小于80%,试件呈不均匀断裂和剪切的破坏形式。

计及邻近线路架设方向和屏蔽影响的密集输电通道防雷性能仿真分析

在调研了输电线路防雷设计的研究现状后,针对考虑密集输电通道中线路间屏蔽作用的绕击跳闸率计算问题提出了改进的电气几何模型法并验证其可行性,主要包括了计算思路的优化和地面倾角处理方式的修正。基于所提出的计算方法,针对3条输电线路并行工况进行了计算和规律分析,发现对线路间屏蔽效果占主导作用的为相邻线路,且屏蔽作用的强弱并非随线路间距线性变化,而是存在一个快速变化的区间范围。在此基础上,提出了考虑实际中线路走向和弧垂的线路间距和对地高度计算方法,基于所提出的方法对实际工程进行了计算,证明了方法的可行性,对输电线路的防雷改造具有一定的指导作用。

顺倾及反倾层状碎裂结构斜坡地震反应的大型振动台试验研究

西南艰险山区分布着大量的不同倾向的层状碎裂结构斜坡,地震作用下极易发生崩塌、滑坡等灾害,对在建的川藏铁路造成严重威胁。通过大型振动台模型试验,研究了强震条件下顺倾、反倾层状碎裂结构斜坡的动力响应、失稳破坏模式以及能量传递规律。试验结果表明:反倾斜坡的抗震性能显著优于顺倾斜坡;顺倾斜坡的破坏模式主要为拉裂-剪切-隆起-滑移型破坏,反倾斜坡的破坏模式主要为拉伸-弯曲-倾倒-崩塌型破坏;反倾斜坡的自振频率高于顺倾斜坡,顺倾斜坡的自振频率随震级的增加而逐渐降低,而反倾斜坡的自振频率在地震波幅值为0.4g~0.7g时出现反复震荡现象;顺倾斜坡存在明显的高程放大效应和趋表效应,反倾斜坡存在高程放大效应,其内部的加速度响应大于坡表。边际谱识别显示:顺倾斜坡的边际谱幅值(peak of marginal spectrum amplitude,简称PMSA)突变在坡腰上部最显著,说明该位置附近地震波的能量损失最大,反映出顺倾斜坡在坡腰上部附近形成了滑动破坏面;反倾斜坡的PMSA在坡肩处降低得最为显著,反映出坡肩部位损伤最为严重,易发生局部崩塌破坏。分析结果与试验现象能够较好地吻合,进一步揭示了不同结构类型层状碎裂结构斜坡在强震作用下的动力响应与失稳破坏模式,为川藏铁路的安全建设提供了依据。

基于能量系数的电力变压器热故障严重性评估方法

运行电力变压器内部的热点温度直接影响其使用寿命和运行可靠性。为准确评估电力变压器内部过热故障的严重程度,文章借助焓变理论提出一种计算故障能量系数的方法,为故障赋予一定的权值系数;并基于能量系数这一概念,以电力变压器各类不同程度的热故障为研究对象,建立其严重程度分级评估基准,此基准是以563组电力变压器热故障油色谱分析数据所计算出的能量系数值作为样本数据,利用最大熵原理得出最符合实际分布的电力变压器热故障能量系数概率分布函数,并求取其分位值Q_(20)、Q_(70)和Q_(95)作为热故障严重程度的分级评估值。经实际算例分析,采用文中所提方法,不仅可以实现对热故障严重程度的量化评估,还可以合理地划分其严重等级,可为检修人员制定和执行维护计划提供参考。

基于渐进破坏理论的顺层岩质边坡稳定性解析

顺层岩质边坡的坡脚开挖扰动后易发生牵引式失稳滑移。为研究不同破坏阶段的顺层岩质边坡稳定性,采用半无限楔形体模型计算坡体开挖面应力,然后赋予滑面陡降型应变软化模型,对不同破坏阶段顺层岩质边坡的开挖释放应力、滑面应力状态、滑面位移和边坡稳定系数等状态特征进行量化解析,形成了临界荷载求解、渐进破坏阶段界定和稳定系数解析3步走的系统解析流程;探讨了顺层岩质边坡首次滑移长度的确定方法,最后通过工程实例进行分析验证。结果表明,顺层岩质边坡的渐进破坏可划分为峰前应力阶段、峰前-残余应力阶段和残余应力阶段;提出不同阶段的稳定系数解析方法,建立了顺层岩质边坡首次滑移长度的应力计算式。首次滑移长度参考值较实际值相差9.3%,所得解析结果可为工程设计提供参考。

Shear mechanical properties and fracturing responses of layered rough jointed rock-like materials

This study aims to investigate mechanical properties and failure mechanisms of layered rock with rough joint surfaces under direct shear loading.Cubic layered samples with dimensions of 100 mm×100 mm×100 mm were casted using rock-like materials,with anisotropic angle(α)and joint roughness coefficient(JRC)ranging from 15°to 75°and 2-20,respectively.The direct shear tests were conducted under the application of initial normal stress(σ_(n)) ranging from 1-4 MPa.The test results indicate significant differences in mechanical properties,acoustic emission(AE)responses,maximum principal strain fields,and ultimate failure modes of layered samples under different test conditions.The peak stress increases with the increasingαand achieves a maximum value atα=60°or 75°.As σ_(n) increases,the peak stress shows an increasing trend,with correlation coefficients R² ranging from 0.918 to 0.995 for the linear least squares fitting.As JRC increases from 2-4 to 18-20,the cohesion increases by 86.32%whenα=15°,while the cohesion decreases by 27.93%whenα=75°.The differences in roughness characteristics of shear failure surface induced byαresult in anisotropic post-peak AE responses,which is characterized by active AE signals whenαis small and quiet AE signals for a largeα.For a given JRC=6-8 andσ_(n)=1 MPa,asαincreases,the accumulative AE counts increase by 224.31%(αincreased from 15°to 60°),and then decrease by 14.68%(αincreased from 60°to 75°).The shear failure surface is formed along the weak interlayer whenα=15°and penetrates the layered matrix whenα=60°.Whenα=15°,as σ_(n) increases,the adjacent weak interlayer induces a change in the direction of tensile cracks propagation,resulting in a stepped pattern of cracks distribution.The increase in JRC intensifies roughness characteristics of shear failure surface for a smallα,however,it is not pronounced for a largeα.The findings will contribute to a better understanding of the mechanical responses and failure mechanisms of the layered rocks subjected to shear loads.