寿命服从威布尔分布产品相关失效数值分析

相关失效是降低并联系统可靠性的重要影响因素之一。由于相关失效存在，并联系统的实际寿命低于理想状态，在工程实际中必需加以考虑。威布尔分布具有较强的拟合能力，可以近拟表示各种常见分布函数，且便于计算分析，根据累积失效概率相等原理，提出了寿命从威尔分布产品的相关失效数值分析方法，可用于寿命且从威布尔分布产品的相关失效分析，可靠度分析和平均寿命分析，也可用威布尔分布近似表示的常用分布的相关失效分析，可靠性分析和平均寿命分析。

铝合金MIG焊缝的参数反求与高精度失效模拟

焊缝是车身及零部件CAE精确模拟的基础与关键,直接以力学试验获取焊缝的本构和失效参数有很大难度,且结果并不理想,基于铝合金本构模型和焊接接头分区的试验结果,构建铝合金MIG焊接接头数值仿真模型。根据仿真结果和铝合金MIG焊接接头特殊试样DIC拉伸试验结果,采用径向基函数法构建代理模型,以均方根误差作为优化目标,迭代反求出焊缝的材料参数,并进行验证,证明采用等效分区、迭代优化的焊缝参数反求构建焊接接头断裂失效数值模型方法的有效性。

汽车后框架柱承载力功能失效临界数值自动化测试研究

传统的测试方法对汽车后框架柱屈服强度分析不到位,导致测试的承载力功能失效临界数值不合理,为此研究汽车后框架柱承载力功能失效临界数值的自动化测试方法。该方法利用自动管理控制平台分解汽车框架,了解构框架柱的每一连接点以及连接紧密度,明确框架的总体结构。利用转角位移法定向分析有侧移的框架柱,计算纵向载力和水平载力影响下的弹性,通过二阶假定分析法计算框架柱弹性下的塑性变形程度,联立受压强度和抗拉强度公式计算框架柱屈服强度,实现载力功能失效临界数值的自动测试。实验结果表明,与传统测试相比,所研究的测试方法对框架柱屈服强度分析更加精准,测试到的失效临界数值更为合理。可见该测试更能满足汽车框架柱的承载力测试要求。

失效模式和效果分析法在儿童PICC安全管理中的应用及效果评价

[目的]建立适合儿童病人的安全管理模式,以减少各类安全问题的发生,使经外周静脉置入中心静脉导管(PICC)能更好地运用于临床。[方法]运用失效模式和效果分析(FMEA)法评估风险因素,列出所有的失效模式,选择其中长效模式优先风险数值(RPN)最高的6个失效模式并对其影响因素进行分析,制订完善的安全管理措施,建立安全管理模式。[结果]建立安全管理模式后RPN值较前降低,PICC导管的并发症及非计划拔管率较实施前显著下降(P<0.05)。[结论]应用FMEA将各种不安全因素进行提前评估,再根据评估结果建立标准化的安全管理模式,可有效杜绝在PICC风险问题,减少各种并发症及非计划拔管率。

Mechanical Behavior of a Glass-fiber Reinforced Composite to Steel Joint for Ships

The use of a glass-fiber reinforced composite in marine structures is becoming more common, particularly due to the potential weight savings. The mechanical response of the joint between a glass-fiber reinforced polymer （GRP） superstructure and a steel hull formed is examined and subsequently modified to improve performance through a combined program of modeling and testing. A finite-element model is developed to predict the response of the joint. The model takes into account the contact at the interface between different materials, progressive damage, large deformation theory, and a non-linear stress-strain relationship. To predict the progressive failure, the analysis combines Hashin failure criteria and maximum stress failure criteria. The results show stress response has a great influence on the strength and bearing of the joint. The Balsawood-steel interface is proved to be critical to the mechanical behavior of the joint. Good agreement between experimental results and numerical predictions is observed.

Numerical investigation on interface enhancement mechanism of Ag-SnO_(2) contact materials with Cu additive

The electrical contact and mechanical performances of Ag-SnO_(2) contact materials are often improved by additives,especially Cu and its oxides.To reveal the improvement mechanism of metal additive,the effects of Cu nanoparticles on the interface strength and failure behavior of the Ag-SnO_(2) contact materials are investigated by numerical simulations and experiments.Three-dimensional representative volume element(RVE)models for the Ag-SnO_(2) materials without and with Cu nanoparticles are established,and the cohesive zone model is used to simulate the interface debonding process.The results show that the stress−strain relationships and failure modes predicted by the simulation agree well with the experimental ones.The adhesion strengths of the Ag/SnO_(2) and Ag/Cu interfaces are respectively predicted to be 100 and 450 MPa through the inverse method.It is found that the stress concentration around the SnO_(2) phase is the primary reason for the interface debonding,which leads to the failure of Ag-SnO_(2) contact material.The addition of Cu particles not only improves the interface strength,but also effectively suppresses the initiation and propagation of cracks.The results have an reference value for improving the processability of Ag based contact materials.

Numerical modeling of failure mechanisms in phyllite mine slopes in Brazil

This paper presents three case studies comprising failure mechanisms in phyllite mine slopes at Quadrila- tero Ferrifero, State of Minas Gerais, Brazil. Numerical modeling techniques were used in this study. Fail- ure mechanisms involving discontinuities sub parallel to the main foliation are very common in these mines. Besides, failure through the rock material has also been observed due to the low strength of phyl- lites in this site. Results of this work permitted to establish unknown geotechnical parameters which have significant influence in failure processes, like the in situ stress field and the discontinuity stiffness.

Failure mode and strength anisotropic characteristic of stratified rock mass under uniaxial compressive situation

A stratified rock mass model was founded by FLAC^3D. The failure mode and anisotropic characteristic of strength for stratified rock mass were analyzed. The analysis results show that the numerical simulation can visually reflect the failure modes of rock samples under different inclination angles β of structural plane. The stiffness of rock sample before peak strength changes in the compressive procedure. With the increase of β, the compressive strength σc of rock sample decreases firstly and then increases; when β is in the range of 20°-30° and 80°-90°, σc has the largest sensitivity to r; while β falls in the range of 30°-70°, σc varies little. When φj〈β〈90° （ φj is friction angle of structure plane）, the results obtained from numerical simulation and theoretical analysis are in almost the same values; while β〈 φj or β=90°, they are in great different values. The results obtained from theoretical analysis are obvious larger than those from numerical simulation; and the results from numerical simulation can reflect the difference of compressive strength of rock samples for the two situations of β≥φj and β=90°, which is in more accordance with the real situation.

The Qualitative Analysis of a Solution of a Series Maintenance System with Two Components

In this paper, firstly we study the series ma intenance system with two components, obtain its exsistence and uniqueness of a dynamic state nonnegative solution by strongly continuous semigroups of operator s theory. Then we prove that 0 is the eigenvalue of the system’s host operators, a nd finally we study the eigenvector of the eigenvalue 0.

Damage, failure and stability control of evolutionary process caused by re-exploitation of the residual resources

On the basis of considering the heterogeneity and using the finite element numerical simulation, this thesis investi- gates the damage of the roof and coal as well as the failure of evolutionary process during the re-exploitation of the residual coal. According to the analysis of the damage field, stress field and the failure process, it explores the damage evolution, stress distribution laws and the damage models. Besides, this thesis puts forward the idea of penetrating and establishing drilling steels aimed at solving the problem of wall carving and roof fall, meanwhile this suggestion accomplishes the successful appli- cation effect in the testing ground. This thesis demonstrates that the re-exploitation of the residual coal can be carried out and the safe production can be ensured by adopting some measures. What＇s more, the research result provides the theoretical and practical experience for the re-exploitation of the residual coal in the similar conditions.

The effect of diffusion loss on the time-varying giant Panda population

It has been certificated that corridors can help giant pandas to keep their habitat from fragmenting. However there are still losses during the process of moving along corridors. In this study, a mathematical model with Allee effect is carried out to describe the diffusion of giant pandas between n patches. Some criteria are obtained to keep the system persisting. It is proved that the system has a unique positive w-periodic solution which is globally asymptotically stable. The ecological meanings of these findings are discussed following the results. And some numerical simulations in the Qinling Mountain giant panda nature reservation area are also presented in the end.