Tensile fracture and failure behavior of technical flax fibers

The apparent tensile strength of technical flax fibers was determined in single‐fiber tests at various clamping lengths (20, 40, and 80 mm) and the outcome was compared with literature data. It was demonstrated that the strength of flax at each clamping length obeyed the two‐parameter Weibull model. The failure mode and sequence were studied in situ (i.e., during loading) by SEM and acoustic emission (AE). The failure sequence (axial splitting of the technical fiber along its elementary constituents, radial cracking of the elementary fibers, multiple fracture of the elementary fibers) concluded reflected the hierarchical build‐up of the flax bast fibers. To the above failure events AE amplitude ranges were assigned. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3638–3645, 2003     

Stress Heterogeneity Effect on the Strength of Silicon Nitride

The experiments reported in this paper demonstrate the causes of the failure of monolithic ceramics. The specimens are made of silicon nitride and tested at room temperature. The stress field within the specimen is different for each of four series of tests that have been conducted. Fractographic observations have also been made to identify the causes of the failures. A size effect analysis is performed.     

Possibilities and extension of XRD material response analysis in failure research for the advanced evaluation of the damage level of Hertzian loaded components

Due to clearly distinguishable damage symptoms, it is differentiated between the surface and sub‐surface failure mode of rolling bearings. Material states red out by X‐ray diffraction (XRD) residual stress measurements point to a variety of loading conditions especially at raceway surfaces that are associated with several competing failure mechanisms. The corresponding lifetime reduction can range from the lower fatigue strength region to material ratcheting in extreme cases. Relevant position of the microstructural changes and nature of the failure mechanisms are characterized. The time alteration of the XRD material parameters measured at or near the surface and at the depth of the maximum equivalent stress correlates, in a different manner, with the statistical parameter of the 10 % bearing life. Both failure modes are illustrated by concrete examples. Contaminated lubricant and boundary lubrication, which represent practically important surface‐induced failures, are discussed in more detail. Gray staining, i.e. shallow pitting, often occurs without distinct indication of global material aging by means of XRD characteristics. Here, scanning electron microscopy observations and electron microprobe analyses point to corrosion fatigue as acting surface failure mechanism. The interaction between material and lubricant under complex loading regimes particularly of mixed friction and corrosion opens further failure research areas in the field of tribology.     

Evaluation of Slow Crack Growth Resistance in Ceramics for High-Temperature Applications

The slow (subcritical) crack growth (SCG) resistance of Si₃N₄ and SiC ceramics has been evaluated by a stepwise loading test on bending bars precracked by Vickers indentation. Three highly refractory materials were selected for the evaluation: i.e., (1) high-purity Si₃N₄ sintered by hot isostatic pressing (HIP) without additives and (2,3) α - and β - SiC pressureless sintered with B and C addition. Under the hypothesis of linear elastic behavior at high temperature, which was found satisfied in the present materials, the SCG resistance was expressed in terms of initial stress intensity factor critical for SCG failure within a predetermined lifetime. The present method was found useful in shortening the testing time and consistent with other traditional fatigue tests (e.g., static-fatigue test): It is recommended as a screening test for materials under research and development. Among the materials tested in the present study, the highest SCG resistance up to 1440°C was found in the high-purity Si₃N₄ without additives.     

弹簧钢棒线材质量投诉的分析研究

为分析研究某特钢厂用户投诉的原因及存在的问题，统计了其两年间的弹簧钢棒线材用户质量投诉，从缺陷类型及生产过程控制进行了分析，重点对多起断裂原因不明的投诉进行了深入的失效研究。结果表明，弹簧钢生产厂在设备工艺、过程控制和管理中存在很多不足，加上用户的使用工艺、材料的内外质量和规格等综合因素导致了材料的断裂失效。     

VCM压缩机曲轴断裂失效分析

介绍了锦化化工(集团)有限责任公司出现的VCM压缩机曲轴断裂事故，并从断口的部位、形貌特征，断轴的几何状态、受力状态及树料性能等方面分析了曲轴断裂的根本原因。     

多变量系统故障诊断和容错控制新方法及其在精馏过程中的应用

本文提出一种多变量系统的故障诊断和容错控制新方法，整个系统由四个神经元组成。将本文方法用于二元精馏塔顶和塔底组分的容错控制，仿真结果证实了本文方法的有效性。该方法可望在难以建模的复杂化工过程中得到应用。     

Knowledge-based diagnosis of drill conditions

One major bottleneck in the automation of the drilling process by robots in the aerospace industry is drill condition monitoring. This paper describes a system approach to solve this problem through the advancement of new machine design, sensor instrumentation, metal-cutting research, and intelligent software development. All drill failures can be detected and distinguished: chisel edge wear, flank wear, crater wear, margin wear, corner wear, breakage, asymmetry, lip height difference, and chipping at lips. However, in the real manufacturing environment, different workpiece materials, drill size, drill geometry, drill material, cutting speed, feed rate, etc. will change the criteria for judging the drill condition. The knowledge base used for diagnosing the drill failures requires a huge data bank and prior exhaustive testing. A self-learning scheme is therefore introduced to the machine in order to acquire the threshold history needed for automatic diagnosis by using the same new tool under the same drilling conditions.     

精轧油膜轴承密封失效机理的初步分析

对油膜轴承密封出现的进水、漏油现象作了大量的调查、测量和统计分析，找出了产生质量事故的根本原因，提出了解决措施。     

Fault-accommodation with intelligent sensors

Optimal sensor fault-accommodation is considered for faults modelled by an increase in measurement noise. This noise is taken to be bounded and its probabilistic properties unknown. It is assumed that intelligent (e.g. self-validating) instrumentation is in use and estimates of the noise bounds are available. The fault-tolerant controller is designed to optimize a noise rejection and a nominal reference tracking index and leads to a mixed norm minimization problem (l₁/l₂). We exploit known results and a particular feedback configuration to show that it is possible to optimize simultaneously without a trade-off the two performance indices. The results are applied to systems where the presence of auxiliary measurements allows for an optimal fault-accommodation strategy. Using properties of the optimal solution, we define a factorization for the optimal controller alternative to the Youla parametrization, leading to an algorithm which is optimal, transparent and efficient.