探讨ADC芯片引脚与印制板之间的固封方式

通过故障分析,将某产品高温老炼试验过程中发生的性能异常现象定位于ADC芯片部分引脚焊点脱焊。为验证芯片引脚与印制板之间的固封方式对焊点受力的影响,分别对"底部灌封+四角固封"及"底部灌封+四边固封"固封方式进行试验验证及随机振动、热应力分析。根据分析结果,高温浸泡时"底部灌封+四边固封"方式下,焊点受力均匀,最大热应力低于3MPa;而"底部灌封+四角固封"固封方式下的焊点最大热应力约5.1MPa,导致了焊点的蠕变疲劳失效。为减少高温浸泡时焊点的热应力,设计了"底部不灌胶,四边固封但一角不封口"的固封方式,并顺利通过相应的验证试验,证明这是一种较为妥当的固封方式。     

民机非包容性转子失效危害防护设计研究

民用飞机的发动机转子非包容性失效给飞机的安全运行带来巨大的风险,为了将这种转子非包容性失效可能带来的危害降至最小,需要合理的评估碎片的危害水平,以及采取合理的安全预防措施。尽管在FAA(Federal Aviation Administration)用于评估碎片危害水平的UEDDAM(Uncontained Engine Debris Damage Analysis Model)软件工具中采用了加强防护设计以减少碎片危害,但是没有对具体的分析流程和碎片能量衰减的计算模型进行说明。为此,在现有的碎片危害分析方法的基础上,考虑到碎片在侵彻过程中会有能量衰减,分析了降低碎片危害的三种安全预防措施,通过对比确定了加强防护设计对于降低碎片危害的重要意义及其分析的流程。通过对飞机结构中关键区域定义的理解,明确了在飞机的不同部位需要采取不同的加强防护设计,并详细介绍了整体加强防护设计和局部加强防护设计的流程。     

直升机机载产品环境鉴定试验故障分析

目的探究机载产品在鉴定试验阶段故障频发的原因,并改进机载产品研制流程中的不足之处。方法收集某型直升机机载产品50项环境鉴定试验故障,并对环境试验故障进行分析。结果环境试验故障主要为三防及振动试验故障,其故障发生的原因主要为材料及表面处理方法选用不当、设计缺陷和质量控制程序不够严格。结论针对该分析结果提出机载产品在设计过程中,需要通过尽早安排环境研制性试验、建立环境数据库、模拟仿真进行环境适应性设计和加强质量管理等措施,避免机载产品在鉴定试验阶段故障频发的问题。     

圆环巴西试验的抗拉强度建议公式

目的改进Hobbs公式得到的计算值普遍较大这一问题,提出圆环巴西试验的抗拉强度建议公式。方法对巴西试验圆环的应力解进行分析,并引用砂岩的试验数据验证。结果得到圆环巴西试验的抗拉强度建议公式,使用Hobbs公式得到的抗拉强度σTT比巴西圆盘试验σT大6倍以上,利用建议公式得到的抗拉强度σθ与巴西圆盘试验σT十分接近,误差不到1%。结论当圆环内外径比ρ在0.05到0.15的范围内时,该建议公式可很好地用来计算岩石类等脆性材料的抗拉强度。     

小子样成败型产品可靠性评估方法研究

介绍了一种小子样成败型产品可靠性评估方法。基于"计量评估"理论原则,针对可用于评价产品的特征量的试验数据,依次运用了数据样本子样的概率分布拟合检验方法、样本数据的一致性检验和离群值识别等统计学方法,最终使用经检验的特征量试验数据完成产品的可靠性评估。使用实例数据,应用评估方法,完成了一类典型产品的可靠性评估,其中特别指出的是,在实际应用过程中,应该尤其关注离群值的识别和剔除。实例证明,此方法可用于特征量明确的小子样成败型产品的可靠性评估。     

Catastrophic Reproductive Failure, Terrestrial Survival, and Persistence of the Marbled Salamander

Abstract:  Wide variation in reproductive success is common among amphibians that breed in seasonal ponds, but persistence of adults can buffer against these fluctuations, particularly for long-lived species. We hypothesized that the frequent episodes of catastrophic failure of the marbled salamander ( Ambystoma opacum ) enhance the importance of high terrestrial survival. At Rainbow Bay in South Carolina reproductive success was poor (<1 metamorph/breeding female) in nearly half of the 22 years that the species bred. Complete failure occurred in 6 of 22 years. To study catastrophic failure, we adapted an age-structured, individual-based model with density-dependent growth and survival of larvae. The model was based on extensive data from local field studies and experiments. With consistently good survival in the pond stages, the simulated population required survival probabilities in the upland stages (juveniles and adults) near 0.5/year to persist and near 0.8/year to achieve the increases observed. Catastrophic failure, occurring randomly with probability 0.5/year, created additional fluctuations in the population, raised the thresholds of survival required for persistence, and caused extinction under conditions that were otherwise favorable. The marbled salamander at Rainbow Bay is not at great risk of extinction because of catastrophic failure, but the risk increases dramatically if life span is decreased or frequency of failure is increased. Any reduction in terrestrial survival will have deleterious consequences by reducing the breeding populations at equilibrium, even if it does not jeopardize persistence. Our model provides assessments of risk that can be applied to poorly studied species with similar life histories, such as the endangered flatwoods salamander ( A. cingulatum ).     

Corrosion failure probability analysis of buried gas pipelines based on subset simulation

Corrosion is the main reason for the failure of buried gas pipelines. For effective corrosion failure probability analysis, the structural reliability theory was adopted in this study to establish two calculation models for pipeline corrosion failure: the pressure failure model and von Mises stress failure model. Then, two calculation models for the corrosion failure probability were established based on a corrosion depth growth model obtained from actual survey data of soil corrosion characteristics. In an example, Monte Carlo simulation (MCS) and subset simulation (SS) were used to analyze the corrosion failure probability of pipelines, and the results were compared. SS can compensate for the shortcomings of MCS as it has higher computational efficiency and accuracy. Therefore, SS was adopted to simulate variations in the corrosion failure probability of buried pipelines with the service time for the two failure probability calculation models, which were applied to a natural gas pipeline located in a chemical industry park in Zhuhai, China. A sensitivity analysis was carried out on the relevant parameters that affect the failure probability. The results showed that multiple loads caused by the covering soil, residual stress, temperature differential, and bending stress have a non-negligible effect on the pipeline reliability. The corrosion coefficients gradually become the most important factors that affect the failure probability with increased service time. The proposed methodology considers the actual operating conditions of pipelines to provide a reliable theoretical basis for integrity management.     

在役管道防腐层的失效与维修

介绍了管道防腐层失效的原因和方式,指出水和氧气是防腐层失效的原因,含水量和含氧量决定腐蚀程度,提出对防腐层及时检查与修复等措施.     

某厂氩气纯化器失效分析及对策

某厂氩气纯化器是由1Cr18Ni9不锈钢制成,在使用过程中出现致密性的网状裂纹开裂。详细论述了氩气纯化器开裂失效的原因,并通过理论分析及实践摸索,找出了应对氩气纯化器失效的对策。并在实际运行中得到了验证,确保了新制氩气纯化器的安全可靠运行。     

双向聚能拉伸爆破及其在硐室成型爆破中的应用

针对当前定向断裂控制爆破存在的问题,结合某特大型硐室成型爆破工程的地质、工程条件,利用岩石耐压而怕拉的特性,提出了双向聚能拉伸爆破技术.对该技术的特点、破岩机理、力学模型作了详细介绍与分析.进行了现场双向聚能拉伸爆破基础试验研究.在此基础上,该技术被应用于硐室的方形断面(1个自由面)和岩锚梁(2个自由面)的成型爆破.现场试验及应用结果表明,双向聚能拉伸爆破工艺简单、操作方便,能有效地控制裂纹产生、发展方向及断裂面的形成,实现岩体的精确控制爆破,应用前景广阔.