Monte Carlo Simulation of Sudden Death Bearing Testing

Monte Carlo simulations combined with sudden death testing were used to compare resultant bearing lives to the calculated bearing life and the cumulative test time and calendar time relative to sequential and censored sequential testing. A total of 30,960 virtual 50-mm bore deep-groove ball bearings were evaluated in 33 different sudden death test configurations comprising 36, 72, and 144 bearings each. Variations in both life and Weibull slope were a function of the number of bearings failed independent of the test method used and not the total number of bearings tested. Variations in L ₁₀ life as a function of number of bearings failed were similar to variations in life obtained from sequentially failed real bearings and from Monte Carlo (virtual) testing of entire populations. Reductions up to 40% in bearing test time and calendar time can be achieved by testing to failure or the L ₅₀ life and terminating all testing when the last of the predetermined bearing failures has occurred. Sudden death testing is not a more efficient method to reduce bearing test time or calendar time when compared to censored sequential testing.     

Effect of Silicon Nitride Balls and Rollers on Rolling Bearing Life

Three decades have passed since the introduction of silicon nitride rollers and balls into conventional rolling-element bearings. For a given applied load, the contact (Hertz) stress in a hybrid bearing will be higher than that of an all-steel rolling element bearing. The silicon nitride rolling-element life as well as the lives of the steel races were used to determine the resultant bearing life of both hybrid and all-steel bearings. Life factors were determined and reported for hybrid bearings. Under nominal operating speeds, the resultant calculated lives of the deep-groove, angular-contact, and cylindrical roller hybrid bearings with races made of post-1960 bearing steel increased by factors of 3.7, 3.2, and 5.5, respectively, from those calculated using the Lundberg-Palmgren equations. An all-steel bearing under the same load will have a longer life than the equivalent hybrid bearing under the same conditions. Under these conditions, hybrid bearings are predicted to have a lower fatigue life than all-steel bearings by 58% for deep-groove bearings, 41% for angular contact bearings, and 28% for cylindrical roller bearings.     

Reevaluation of Rolling Element Bearing Load-Life Equation Based on Fatigue Endurance Data

The load-life exponents used in the modified life rating equation for rolling element bearings were determined by statistical analysis of the experimental data generated in the 1940s, following Lundberg and Palmgren's seminal work. Based on fracture mechanics arguments, the fatigue life is known to be inversely proportional to the square root of the size of the nonmetallic inclusions. However, modern high-performance vacuum induction melt–vacuum arc remelt (VIMVAR) bearing steels are clean and nonmetallic inclusions are no longer the weak link. Fatigue life predictions (L₁₀ life) for modern bearings using the modified load-life relations greatly underpredict observed life. Hence, there is a need to update parameters of these equations using more recent life data. Based on the endurance data reported in Harris and McCool (1), validation analysis of the modified life rating equation was performed to reevaluate the values of load-life exponent for both ball and cylindrical roller bearings. The results from this study indicate that the load-life exponent for ball bearings should be 4.1, instead of 3, and for roller bearings it should be 5.5, instead of 3.33. Bearing L₁₀ life calculated using the corrected load-life exponents values shows better agreement with observed life. Details of the sampling technique used for reducing epistemic uncertainty in experimental data and the process of statistical reevaluation using Bayesian updating are discussed in detail. The accuracy of reevaluated results is presented using logarithmic plots of the ratio of predicted to actual fatigue lives for all data samples.     

Comparison of Models for Ball Bearing Dynamic Capacity and Life

Generalized formulations for dynamic capacity and life of ball bearings, based on the models introduced by Lundberg and Palmgren and Zaretsky, have been developed and implemented in the bearing dynamics computer code ADORE. Unlike the original Lundberg-Palmgren dynamic capacity equation, where the elastic properties are part of the life constant, the generalized formulations permit variation of elastic properties of the interacting materials. The newly updated Lundberg-Palmgren model allows prediction of life as a function of elastic properties. For elastic properties similar to those of AISI 52100 bearing steel, both the original and updated Lundberg-Palmgren models provide identical results. A comparison between the Lundberg-Palmgren and the Zaretsky models shows that at relatively light loads the Zaretsky model predicts a much higher life than the Lundberg-Palmgren model. As the load increases, the Zaretsky model provides a much faster drop-off in life. This is because the Zaretsky model is much more sensitive to load than the Lundberg-Palmgren model. The generalized implementation, where all model parameters can be varied, provides an effective tool for future model validation and enhancement in bearing life prediction capabilities.     

The Effect of Adapter Crown Wear on Rated Fatigue Life of a Railroad Tapered Roller Bearing

A model is developed to describe the effects of adapter crown wear on the misalignment of a railroad tapered-roller bearing. Wear of the crowned surface results in a flat on top of the adapter. This flat, in contact with the wear plate, is shown to have the capacity to transmit a moment between the bearing and the side-frame of the truck. The magnitude of the moment transmitted is dependent on the length of the flat. These analytical results are coupled with model results from a bearing manufacturer, which give the relationship between bearing misalignment, and thus transmitted moment, and reduction in fatigue life of the bearing. The analysis indicates that a slightly worn adapter has no appreciable effect on the rated fatigue life of the bearing, but once a threshold level in adapter crown wear is reached, the bearing fatigue life will begin to decrease. Large amounts of adapter crown wear will result in significant bearing misalignment and a corresponding reduction in the fatigue life of the bearing.     

Life‐Cycle Assessment of Ammunition Demilitarization in a Static Kiln

The demilitarization of ammunition that has reached the end of life (or become obsolete) has to be carried out with minimum energy and environmental impacts. The Portuguese Armed Forces have significant amounts of ammunition that need to be eliminated. In order to assess and improve ammunition demilitarization, a life‐cycle approach must be adopted. The main goal of this article is to present a comprehensive life‐cycle assessment (LCA) of the ammunition demilitarization performed by the Portuguese company IDD (Industria de Desmilitarização e Defesa). A life‐cycle model was developed for the entire demilitarization process, which involves ammunition dismantling, discharging, the incineration of energetic material, and the subsequent flue gas treatment. A detailed inventory was based on data collected from the IDD. A life‐cycle impact assessment was carried out, based on three complementary methods used to assess a total of ten impact categories: cumulative energy demand (primary energy); CML 2001 (six environmental impact categories) and USEtox (three toxicological categories). The results show that the main contributor in nine out of the ten impact categories is the incineration and gas treatment process, due to the high energy requirements (electricity and propane). Nevertheless, equipment manufacture also has a significant impact in the Human Toxicity (non‐cancer) category, mainly related to the manufacture of the static kiln. These findings enhance our understanding of demilitarization using a static kiln, showing that the associated impacts are significant and should be reduced.     

基于动力学优化的航空管道DFR疲劳寿命分析

基于动力优化的有限元分析方法,以避开系统共振频率为目标函数,支撑位置为设计变量,对某型航空管道进行动力优化,得到该型管道支撑最佳位置;将最佳支撑位置优化结果与管道实际承受的载荷相结合,基于DFR法,对管道进行疲劳可靠性寿命分析并进行评估。结果表明:支撑位置对管道系统各阶固有频率影响较大,避开的系统共振频率不同,优化支撑位置也不同;基于最优结果的DFR法疲劳寿命分析可以为管道安全运行提供指导且该型管道疲劳寿命满足要求。     

铝液除气机中的石墨转子强化工艺研究

采用氧化铝和正磷酸加热反应制得磷酸二氢铝,对铝液除气机中的石墨转子在真空条件下进行浸渍、加压、固化处理,使石墨转子的密度由原来的1.6g/cm3提高到1.7g/cm3,其使用寿命比原未处理的石墨转子提高5倍以上,而成本仅提高1%,增强了石墨转子的强度,提高了石墨转子在铝液净化过程中的使用寿命。     

生命周期评价中的时间折扣研究

生命周期评价(Life Cycle Assessment,LCA)是评价产品生命周期环境影响和资源消耗的有效工具。但是现行的LCA并没有考虑清单数据的时间差异,导致了生命周期影响评价结果的不准确性。研究了LCA中的时间差异和生命周期排放模式,引入生命周期平均排放速率函数,以连续排放的模式代替现有研究的脉冲排放模式。在此基础上运用一级衰减模型建立了LCA中的时间折扣计算方法。最后,以国内某企业生产的洗碗机产品进行实例研究,说明LCA时间折扣的应用,表明应用时间折扣方法后CO2排放的变化。     

沈抚新城“生命之环”钢结构安装施工技术

沈抚新城"生命之环"结构新颖复杂,主体结构为三角形变截面钢管桁架组成的指环形体系,具有结构超高、形体新颖、结构复杂等特点。基于这些特点,采用超大型履带式起重机进行大节段预拼及吊装,格构式钢支撑作为承重结构,大跨度跨中段整体提升的钢结构施工技术路线。并通过全过程施工仿真分析,预测建造过程中结构的应力和位移,并使施工完成后的结构受力和变形趋于设计状态,为合理施工提供技术支持。