Design of a Prognostics and Health Management System for Electromechanical Equipment Through Time Stress Analysis

Time stress includes all kinds of environment and operating stress such as shock, vibration, temperature and electric current that the electromechanical system suffers in the manufacture, transport and operating process. In this paper, the conception of time stress and prognostics and health management （ PHM） system are introduced. Then, in order to improve the false alarm recognition and fault prediction capabilities of the electromechanical equipment, a novel PHM architecture for electromechanical equipment is put forward based on a built-in test （BIT） system design technology and time stress analysis method. Finally, the structure, the design and implementing method and the functions of each module of this PHM system are described in detail.

TIME-TEMPERATURE-STRESS EQUIVALENCE AND ITS APPLICATION TO NONLINEAR VISCOELASTIC MATERIALS

Stress-dependence of the intrinsic time of viscoelastic materialsis investigated. The influence of stress level on the intrinsic timeis considered to be similar to that of temperature, pressure, solventcon- centration, damage and physical aging. Thetime-temperature-stress equivalence principle is proposed, byemploying which, the creep curves at different temperatures andstress level can be shifted into a master curve at referencetemperature and stress level.

Acoustic emission characteristics and stress release rate of coal samples in different dynamic destruction time

Considering the importance of the prediction of rock burst disasters, and in order to grasp the law of acoustic emission(AE) of coal samples in different dynamic destruction time, the SH-II AE monitoring system was adopted to monitor the failure process of coal samples. The study of the change rule of the AE numbers, energy, ‘b' value and spectrum in the micro crack propagation process of the coal samples shows that as dynamic damage time went by, AE presented high-energy counts and the accumulated counts increased during the compression phase. The AE energy and cumulative counts increased during the elastic stage. The AE blank area increased gradually and the blank lines were more and more obvious in the molding stage. The AE counts and energy showed a trend of decrease in the residual damage phase.AE ‘b' values gradually became sparse, and the large scale cracks percentage compared with micro cracks decreased and the degree of damage decreased. The AE frequency spectrum peak went from the residual damage phase to the molding phase, and finally it was nearly stable, besides the bandwidth of the main frequency is gradually narrowed. Also, the frequency peak changed from single peak frequency to bi-peak frequency and to the single peak frequency. Uniaxial compressive strength is more sensitive than the elastic modulus to dynamic damage time.

Time-sensitivity of the Kaiser effect of acoustic emission in limestone and its application to measurements of in-situ stress

Measuring in-situ stress by using the Kaiser effect in rocks has such advantages as timeefficiency, low cost and little limitation, but the precision of the method is dependent on rock properties and delay time of the measurement. In this paper, experiments on the Kaiser effect in limestones were performed, and it was found that the limestones had good ability to retain a memory of their recent stress history and high time-sensitivity. The longer the experiment was delayed from the extraction of the stone, the larger the Felicity ratio was. As the Felicity ratio approached l, significant Kaiser effect was observed. In-situ stress should be determined by the limestone measurements when the delay time was 40-120 days. Finally, the in-situ stress in a limestone formation could be successfully measured in practice.

Reference genes for quantitative real-time PCR analysis and quantitative expression of P5CS in Agropyron mongolicum under drought stress

Reference genes, stably expressing in different tissues and cells, are commonly used as the references in expression analysis. Selecting the optimum reference gene is crucial to the success of experiments. In this study, the expression stabilities of nine common reference genes, including ACT2, 18 S r RNA, APRT, EF-1α, RNA POL II, TUBα, TUBβ, GAPDH and TLF of Agropyron mongolicum, were studied under drought condition. Among them, 18 S r RNA was found to be the most optimum reference gene under drought stress by the analyzing of ge Norm and Norm Finder software. Quantitative expression levels of P5 CS using 18 S r RNA as the reference gene, and proline contents under drought stress in A. mongolicum were further operated, and we found the expression level of P5 CS gene and proline content had a significantly positive relationship（R^2=0.7763, P〈0.05）. This study established and validated 18 S r RNA as the reference genes in A. mongolicum under drought stress, providing a powerful tool for the quantitative expression analysis of drought genes in A. mongolicum.

Susceptible time window and endurable duration of cotton fiber development to high temperature stress

The development of the cotton fiber is very sensitive to temperature variation, and high temperature stress often causes reduced fiber yield and fiber quality. Short-term high temperature stress often occurs during cotton production, but little is known about the specific timing and duration of stress that affects fiber development. To make this clear, pot experiments were carried in 2014 and 2015 in a climate chamber using cotton cultivars HY370WR（less sensitive variety） and Sumian 15（heat sensitive variety）, which present different temperature sensitivities. Changes of the most important fiber quality indices（i.e., fiber length, fiber strength and marcironaire） and three very important fiber development components（i.e., cellulose, sucrose and callose） were analyzed to define the time window and critical duration to the high temperature stress at 34°C（max38°C/min30°C）. When developing bolls were subjected to 5 days of high temperature stress at different days post-anthesis（DPA）, the changes（Δ%） of fiber length, strength and micronire, as a function of imposed time followed square polynomial eq. as y=a＋bx＋cx^2, and the time around 15 DPA was the most sensitive period for fiber quality development in response to heat stress. When 15 DPA bolls were heat-stressed for different durations（2, 3, 4, 5, 6, 7 days）, the changes（Δ%） of fiber length, strength and micronire, as a function of stress duration followed logistic equations y=A_1-A_2/1＋（x/x_0）~p＋A_2. Referred to that 5, 10 and 15% are usually used as criteria to decide whether techniques are effective or changes are significant in crop culture practice and reguard to the fiber quality indices change range, we suggested that 5% changes of the major fiber quality indices（fiber length, fiber strength and micronaire） and 10% changes of fiber development components（cellulose, sucrose and callose） could be taken as criteria to judge whether fiber development and fiber quality have been significantly affected by high temperature stress. The key time window for cotton fiber development in response to the high temperature stress was 13–19 DPA, and the critical duration was about 5 days.

Stochastic transient analysis of thermal stresses in solids by explicit time-domain method

Stochastic heat conduction and thermal stress analysis of structures has received considerable attention in recent years.The propagation of uncertain thermal environments will lead to stochastic variations in temperature fields and thermal stresses.Therefore,it is reasonable to consider the variability of thermal environments while conducting thermal analysis.However,for ambient thermal excitations,only stationary random processes have been investigated thus far.In this study,the highly efficient explicit time-domain method(ETDM)is proposed for the analysis of non-stationary stochastic transient heat conduction and thermal stress problems.The explicit time-domain expressions of thermal responses are first constructed for a thermoelastic body.Then the statistical moments of thermal displacements and stresses can be directly obtained based on the explicit expressions of thermal responses.A numerical example involving non-stationary stochastic internal heat generation rate is investigated.The accuracy and efficiency of the proposed method are validated by comparison with the Monte-Carlo simulation.

TECHNOLOGY OF QUANTITATIVE ANALYSIS ON VIBRATORY STRESS RELIEF BASED ON ULTRASONIC TIME-OF-ARRIVAL METHOD

The effect of vibratory stress relief （VSR） is usually evaluated with the indirect method of observing the change of amplitude frequency response characteristics of structures. A new kind of evaluating method of VSR based on the ultrasonic time-of-arrival method （UTM）, which can obtain the residual stress directly through measuring the propagation time of ultrasonic wave in the material, is presented. At first, the principle of the measuring method of residual stress based on UTM is analyzed. Then the measuring system of the method is described, which is in virtue of ultrasonic flaw detector and high-sampling-rate digital oscillograph. And a set of calibration system that contains a piece of standard specimen is also introduced. Experimental results prove the relation between the residual stress and the propagation time of ultrasonic in workpieces. Finally, the measuring and calibration systems are applied in evaluating the effect of VSR. The final test results show that the method is effective.

Experimental study on time-dependent stress and strain of in-plane shear(ModeⅡ) fracture process of rock

Shear-box test with strain measurement was used to study time-dependent stress and strain of in-plane shear(Mode Ⅱ) fracture process of rock and to reveal the mechanism of Mode Ⅱ fracture.Numerical results show that the maximum shear stress τmax at the crack tip is much larger than the maximum tensile stress σ1 and the ratio of τmax/σ1 is about 5,which favors Mode Ⅱ fracture of rock.Test results indicate that the strain-time curve comprises three stages:the linear deformation stage,the micro-cracking stage and the macroscopic crack propagation.The strain in the direction of the original notch plane is negative,due to restraining effect of compressive loading applied to the original notch plane.Both σ1 and τmax are increased as the load increases,but the slope of τmax is larger than that of σ1 and the value of τmax is always larger than that of σ1.Therefore,τmax reaches its limited value at peak load before σ1 and results in Mode Ⅱ fracture of rock.Shear-box(i.e.compression-shear) test becomes a potential standard method for achieving the true Mode Ⅱ fracture and determining Mode Ⅱ fracture toughness of rock.

The Effect of Unloading Positions and Times on Sheet Metal’s Stress-Strain Curve

The loading-unloading-reloading process could affect the tensile deformation of metals with the combined function of stress relaxation and work hardening, which has been reported in multiple experiments. Nevertheless, the effects of different unloading positions and unloading times have not been investigated. In this study, unloading-reloading tests on three materials (AL6061, HSLA and Q195) were conducted. The stress exhibits a rapid rise momentarily upon reloading and stabilizes afterward while the post stress-strain curve deviates up or down from the monotonic tensile curve. The ductility is enhanced by the unloading-reloading process in general. Different unloading positions and unloading times have different degrees of influence on the stretching of these metals. The effect of loading conditions on a medium manganese steel was further studied. The functions to modify the post stress-strain relationship after unloading-reloading were established.

Methods for Reliability Assessment under Irregular Time-Varying-Stress Degradation Testing

Degradation tests are often used to assess the reliability of products with long failure-time or few test units. Much of the previous work on reliability assessment methods has focused on constant-stress degradation test( CSDT) and accelerated degradation test( ADT), mainly under the constant, step or progressive stresses. However,in actual testing environments,some stresses are difficult to control and vary with time irregularly,which are quite different from the three stresses mentioned above. In this paper a new approach was presented for reliability assessment with degradation data under irregular time-varying-stress( ITVS).Firstly,the conventional degradation path modeling method was improved by taking into account the influences of the variable stress on the degradation variable. Then,an example was conducted to show the effectiveness of our improved model.

Development of a time-dependent energy model to calculate the mining-induced stress over gates and pillars

Generally, longwall mining-induced stress results from the stress relaxation due to destressed zone that occurs above the mined panel. Knowledge of induced stress is very important for accurate design of adjacent gateroads and intervening pillars which helps to raise the safety and productivity of longwall mining operations. This study presents a novel time-dependent analytical model for determination of the longwall mining-induced stress and investigates the coefficient of stress concentration over adjacent gates and pillars. The model is developed based on the strain energy balance in longwall mining incorporated to a rheological constitutive model of caved materials with time-varying parameters. The study site is the Tabas coal mine of Iran. In the proposed model, height of destressed zone above the mined panel, total longwall mining-induced stress, abutment angle, induced vertical stress, and coefficient of stress concentration over neighboring gates and intervening pillars are calculated. To evaluate the effect of proposed model parameters on the coefficient of stress concentration due to longwall mining, sensitivity analysis is performed based on the field data and experimental constants. Also, the results of the proposed model are compared with those of existing models. The comparative results confirm a good agreement between the proposed model and the in situ measurements. According to the obtained results, it is concluded that the proposed model can be successfully used to calculate the longwall mining-induced stress. Therefore, the optimum design of gate supports and pillar dimensions would be attainable which helps to increase the mining efficiency.

页岩储层应力敏感性的时间效应

有效应力及其作用时间是控制岩石孔隙和裂缝变形的重要外部因素。页岩储层的多尺度孔隙结构特征及孔缝配置关系使得其应力敏感时间效应具有特殊性,然而,以往研究尚未考虑有效应力加载及卸载时间对页岩应力敏感行为的影响。以川南威荣气田龙马溪组页岩气藏为研究对象,钻取不同孔缝发育程度的页岩样品,设计并测试了变有效应力状态下变加载及卸载持续稳定时间对岩样渗透率的影响实验。结果表明:1)有效应力从5 MPa升至35 MPa时,微裂缝岩样和基块岩样渗透率分别降低了66.82%和27.19%,卸载过程中渗透率恢复率为74.73%和79.82%。页岩渗透率越低,有效应力滞后效应越显著;2)恒定有效应力加载持续稳定时间从2.5 h延长至10.0 h,应力敏感系数增加3.76%∼80.17%,且当有效应力较小时的时间效应更显著。研究认为,页岩组分及多尺度孔缝结构是导致其孔缝变形行为差异性的主因。基于实验研究结果,推荐页岩样品老化处理为6.0 h,提出了优化页岩储层敏感性评价实验方案和优化气井工作制度的建议。

THE ANALYSIS OF DYNAMIC STRESS INTENSITY FACTOR FOR SEMI-CIRCULAR SURFACE CRACK USING TIME-DOMAIN BEM FORMULATION

The time-domain BEM was developed to analyze the dynamic stress intensity factor ( DSIF) of 3-D elastodynamic crack problems. To simulate the stress singularity along the front of a crack, eight-node isoparametric singular elements were used, and the DSIF for a semi-circular surface crack was firstly calculated based on displacement equation using the time-domain BEM formulation. The new scheme to determine the time step was brought forward. By the dynamic analysis program of time-domain BEM compiled by its, several numerical examples are presented, which demonstrate the unconditional stability and high accuracy of time-domain BEM applied to 3-D elastodynamic crack problems.

Modeling of Surface Waves in a Fluid Saturated Poro-Elastic Medium under Initial Stress Using Time-Space Domain Higher Order Finite Difference Method

In this present context, mathematical modeling of the propagation of surface waves in a fluid saturated poro-elastic medium under the influence of initial stress has been considered using time dependent higher order finite difference method (FDM). We have proved that the accuracy of this finite-difference scheme is 2M when we use 2nd order time domain finite-difference and 2M-th order space domain finite-difference. It also has been shown that the dispersion curves of Love waves are less dispersed for higher order FDM than of lower order FDM. The effect of initial stress, porosity and anisotropy of the layer in the propagation of Love waves has been studied here. The numerical results have been shown graphically. As a particular case, the phase velocity in a non porous elastic solid layer derived in this paper is in perfect agreement with that of Liu et al. (2009).

退火处理对热轧Al/Mg/Al复合板界面微观组织与性能的影响

采用1 mm Al+3 mm Mg+1 mm Al的组坯方式,轧制温度为400℃,压下率为35%,热轧得到6061/AZ31B/6061复合板。在退火温度为200℃的条件下,研究了不同退火时间对复合板拉伸性能、界面结合、微观组织以及表面残余应力的影响。在保温时间分别为0、0.5、1和1.5 h情况下,分别进行拉伸实验、能谱分析、微观组织观察和残余应力测试。结果表明,当轧制压下率为35%时,6061铝合金和AZ31B镁合金能够通过热轧方法得到很好的复合;随着退火时间的增加,6061/AZ31B/6061复合板的拉伸强度、伸长率和界面扩散厚度显著增加,且铝合金表面残余应力也增大。

区段煤柱变形光纤光栅监测应用研究

针对近距离煤层下伏工作面过上覆遗留煤柱时,发生动静载叠加诱发强矿压显现,导致区段煤柱发生变形失稳造成人员伤亡和设备破坏。为探索基于光纤光栅实时监测区段煤柱变形发育特征,分析进、出遗留煤柱阶段矿压显现机理,将FBG、光栅应力计的光测方法相结合,结合现场实测的区段煤柱变形应力应变水平参量变化规律,研究煤柱应变空间分布规律及回采过程中工作面前方煤柱内部应变时域响应特征,验证光测方法在煤体应变水平观测的可行性。结果表明:工作面回采经过上覆遗留煤柱期间,区段煤柱顶板受集中应力影响,上部岩层块体破断并发生回转导致煤柱载荷增加,随着工作面推进覆岩断裂进一步向上传递,关键层断裂回转发生导致工作面来压,最终导致区段煤柱变形失稳。根据现场光栅应变增量幅度判断煤柱内局部变形的剧烈程度,在集中应力作用下,区段煤柱变形时发生最大应变为650×10^(-6),上覆岩层集中应力造成煤柱应变水平峰值位置为煤柱宽度11.5 m,沿煤柱宽度方向应变表现出先增加后减小然后趋于稳定的趋势,内部应变随采动过程中影响范围在5 m左右。综合研究工作面回采经过上覆遗留煤柱时应变对区段煤柱发生变形失稳的特点和规律,以及应变水平变化和煤柱物理力学性质,得到煤柱破坏的前兆特征,在外力作用下达到变形峰值前对煤柱提前进行卸压和防护的安全处理。

不同应力波形下饱水红砂岩动力学特性

应力波幅值及能量耗散时空演化规律在冲击地压等煤岩动力灾害防治工作中往往被忽略,为研究冲击脉冲波形状对岩石的动力学特性影响,利用分离式霍普金森杆实验系统(SHPB),采用多种长度和纺锤形撞击杆(子弹)对干燥和饱和水红砂岩进行不同应变率下的动态压缩实验。结果表明:应力波持续时间对岩石的应变率和动态强度产生显著影响,当撞击杆长度大于300 mm时,应变率-时程曲线产生“双峰”现象,岩石动态强度与持续时间呈线性关系;当应变率小于300 s^(-1)时,透射能随应变率增大而增加,当应变率大于300 s^(-1),撞击杆长度大于300 mm时,岩石的透射能力随应变率变大而降低;能耗率拟合曲线随应变率增大表现为先增大后降低趋势。

考虑椭圆模型M_W≥5.5地震震源参数时域计算方法

为提高时效性,地震预警系统对震源的处理一般采用“点源”假定,不考虑震源尺度、破裂方向和震源区应力降,对震源参数简化处理使得预测地震动参数分布过于粗略,特别是对破坏性大震.本文应用日本地震(M_W≥5.5)强震动数据,考虑椭圆震源模型,提出了一种适用于中、大地震矩震级、拐角频率和应力降等震源参数时域计算方法,并分析了场地效应、地震动传播衰减、震源效应和滤波频带等因素对时域方法的影响.结果表明,该方法能利用P波信息快速获取震源能量释放过程,量化随破裂传播震源谱拐角频率、应力降和破裂面积的演化过程,为地震动预测提供更多重要的震源参数.

鲜水河构造带隧道高地应力区岩爆特性分析

研究目的:青藏高原持续隆升,导致鲜水河构造带及邻区高地应力特征突出,地应力场极其复杂,研究高地应力的孕灾特征有助于隧道岩爆的风险防控,特别是时滞型岩爆的孕灾和致灾机理的研究。本文阐述鲜水河构造带地貌、地层岩性、构造及地应力场特征的孕灾总体认识,通过对该区域隧道近10 km约1300次岩爆统计,从发生概率、等级、埋深、位置、时间、距离等多角度研究岩爆特征,对发生的5次时滞型岩爆和隧道时效性变化特征进行分析,展望后续岩爆研究的重点。研究结论:(1)鲜水河构造带及邻区受高地应力影响,隐伏小微构造发育且无规律,为岩爆创造了特殊的孕灾环境,岩爆发生的随机性大;(2)该区域隧洞岩爆等级以轻微岩爆为主,具有“分区破裂”和脆性变形特征,时滞型岩爆一定程度上具有“继承性”;(3)建议加强沟谷应力场低埋型岩爆和滞后型岩爆或硬岩潜在时效破坏的监测研究;(4)本文研究成果可为类似高地应力环境下岩爆预测和防控提供借鉴。