Highlighting of two types of defects in 1300 nm PBC laser diodes

Laser diodes of PBC (p-substrate buried crescent) structure and emitting at 1300 nm, were subjected to calibrated electrostatic discharges (ESD). A failure analysis was then set up using a scanning optical microscope (SOM) and has allowed the localization of the damaged zones. The comparison of the results obtained with the electro-optical characteristics has highlighted two types of complementary defects: (i) a so-called optical type defect, since the optical power is significantly reduced, although leakage current has not occurred (active layer seriously damaged); (ii) a so-called electrical type defect, since the leakage current increases, although the optical power is barely reduced (active layer weakly damaged).     

Fabrication of Ta nanoparticles induced by nanosecond laser ablation in ethanol: the study of laser fluence effects

Tantalum nanoparticles (Ta NPs) were synthesized in ethanol solution by ablation with a 1064 nm Nd:YAG laser. Prepared NPs were investigated by UV-visible absorption spectroscopy, Transmission electron microscopy, X-ray diffraction and Photoluminescence measurement. The average sizes of NPs were calculated to be in the range of 12–18 nm. From the UV-visible studies, the plasmon peak position of Ta NPs was observed in the spectral range of 206–208 nm. The XRD spectra clearly showed the crystalline structure of NPs and various peaks of Ta and Ta₂O₅. Moreover, the UV region in the PL spectrum included the free exciton and the bound exciton emission correlated with the defect concentration. In fact, the laser ablation in the organic and inorganic solvents is a strong technique to obtain some NPs with particular structures, which are impossible to produce by conventional methods.     

Identification of microbiologically influenced corrosion (MIC) in industrial equipment failures

The present study demonstrates different approaches towards MIC identification in three real cases of technological equipment failures.

In the first case the failure of carbon steel heat exchanger as a result of tubes, lids, tube sheets, and connection pipes clogging was investigated. Chemical analysis of cooling water and precipitates, as well laboratory screening of deposits for bacteria, revealed that activity of iron-oxidizing bacteria present in cooling water led to heat exchanger blockage.

The second case is related to MIC detection on floating roofs made of magnesium–aluminum alloy following a 3-weeks hydro-test. Corrosion tests carried out on the original and sterilized water used in hydro-test confirmed MIC process.

In the third case the potential of MIC occurrence in engine cooling system made of cast aluminum alloy and filled with 20% ethylene glycol coolant solution was evaluated. The simulation tests allowed determining the real causes of the severe corrosion attack of examined system, including MIC high probability.     

Common root causes in recent failures of cranes

Catastrophic failure of cranes is a potentially very dangerous event and has often fatal consequences. The failures of two cranes are discussed in this study. Both cranes have different designs, but common root causes have been identified, related to deficiencies in the design and construction of their bases. Striking similarities in failure circumstances are discussed in this study. These include errors in the identification and interpretation of previous symptoms, in the mitigation measures undertaken and in the risks assumed by personnel, due to lack of information and training. The cranes are slender structures subjected to large loads that generate alternate stresses in the bases. The effects and implications of variable loads are often not completely understood or valued by builders and operators, which are used to deal with intrinsically static loads. A normative gap in the identification of responsibilities deriving from the equipment rent or sale contracts has been identified and is discussed. Finally, these failures stress the importance of early indications. Often, what appears to be a minor hitch turns out to be a deadly disaster.     

Survey of fatigue failures in helicopter components and some lessons learnt

The paper presents a comprehensive review of the failure investigations carried out within AgustaWestland Limited (AWL) over the last 30 years. The results of this survey show that fatigue accounts for approximately 55% of all failures in helicopter components. Although fatigue failures can occur in a wide range of components the types of factors responsible for initiation differ depending on the application of the part. This paper identifies the most common fatigue prone areas in the helicopter, how design considerations and certain key factors such as fretting can influence fatigue life. The importance of aircraft maintenance and quality control in the supply chain will also be discussed. Based on the survey, the paper will also illustrate several instances where fatigue failures have been eliminated through the application of novel surface engineering techniques, improvements in material & processes and modifications to the original design.     

A new failure analysis technique using the thermo-electromotive force induced by Laser irradiation

A new failure analysis technique based on the thermo-electromotive force induced by laser irradiation has been developed for evaluation of interconnects. This technique, which uses a high sensitivity OBIC (optical beam induced current) system, realizes the sensitive detection of defects, such as infant and advanced defects in aluminium (Al) interconnects, with no application of voltage or the removal of overlaid insulator films. This technique has been demonstrated in the analyses of many modes of interconnect failure.     

Modeling of machine failures in a flexible manufacturing cell with two machines served by a robot

In this study, a stochastic model is developed to analyze performance measures of a flexible manufacturing cell (FMC) under different operational conditions, including machine failures and repairs. The FMC consists of two machines served by a robot for loading and loading purposes, and a pallet handling system. The model is based on Markov processes and determines closed-form solutions for the probabilities of system states that are used to calculate system performance measures, such as production output rate and utilizations of system components under different parametric conditions and equipment failures and repairs.     

Forecasting of failures in district heating systems

This work presents the method of failures forecasting in district heating systems on the basis of time series analysis.Statistical data concerning the frequency of damage in communal heat distribution networks from a ten-year time period have been used in the article. The data were subjected to statistical analysis. The methods of exponential smoothing, ARIMA, homologous period trend estimation and seasonal indicators were applied as the most adequate for this type of data. Four forecast models of damage in district heating systems were formulated and the best optimal model for the system was selected.After verification, the methods of failure prediction in district heating systems can be applied in the operating process of a heat supply system. These methods give us answers to many questions about planning of repairs, maintenance emergency service, planning of finances and purposefulness of operational control.     

Balancing burn-in and mission times in environments with catastrophic and repairable failures

In a system subject to both repairable and catastrophic (i.e., nonrepairable) failures, ‘mission success’ can be defined as operating for a specified time without a catastrophic failure. We examine the effect of a burn-in process of duration τ on the mission time x, and also on the probability of mission success, by introducing several functions and surfaces on the (τ,x)-plane whose extrema represent suitable choices for the best burn-in time, and the best burn-in time for a desired mission time. The corresponding curvature functions and surfaces provide information about probabilities and expectations related to these burn-in and mission times. Theoretical considerations are illustrated with both parametric and, separating the failures by failure mode, nonparametric analyses of a data set, and graphical visualization of results.     

Correlation between EMI-induced failures and large-signal response of fet-input opamps

Correlation between EMI susceptibility of opamp circuits and asymmetry in the slew-rates of the basic opamp is discussed with reference to FET-input devices. For the LF355 opamp the role played by an internal feedback loop on the common-mode, slew-rate and susceptibility performances is analysed. Other FET-input opamps, such as the OP42, which exhibit an almost symmetric slew-rate, have a very small EMI susceptibility.     

A study of uv preionization pulsed tea CO2 laser

Abstract

A uniform volumetric discharge was obtained by means of an auxiliary UV preionization in a home‐made TEA CO₂ laser. The maximum output pulse energy of this laser system was about 12J per pulse with a pulse duration of 80 ns. The ratio of electric field to neutral particle density (E/N) in this laser was 7.6×10^‐16 V cm². The peak power and pulse shape of the laser were studied. The time delay between the predischarge and the maindischarge during the stable operation of this laser system has also been studied. It was observed that the laser was operating with uniform glow discharges when the time delayed between the predischarge and the maindischarge was in the range of 1.0 μs to 6.0 μs. The spark array used as a preionizer for producing the UV radiation in this system is new, simple, durable, and can be easily fabricated.     

金属材料水导激光加工实验研究

金属材料的激光加工目前正向着低表面粗糙度、小热影响区及大深径比结构的趋势发展。新近发展了一种基于激光-水射流耦合原理的水导激光加工技术,本文阐述了水导激光加工技术的基本原理及其相对于传统激光加工方法的优势,基于激光-水射流耦合原理构建了一套水导激光加工设备,对多种金属材料进行了水导激光加工实验。利用超景深显微镜对加工工件表面进行了观测与分析,发现两种金属材料加工得到的盲孔边缘规则圆滑,切槽的边缘平直无毛刺,没有热影响区。实验结果说明对金属材料的水导激光精密加工具有可行性且有重要的应用价值。     

Low temperature annealing effects on the structure and optical properties of ZnO films grown by pulsed laser deposition

ZnO thin films were deposited on glass substrates at room temperature (RT) ∼500 °C by pulsed laser deposition (PLD) technique and then were annealed at 150-450 °C in air. The effects of annealing temperature on the microstructure and optical properties of the thin films deposited at each substrate temperature were investigated by XRD, SEM, transmittance spectra, and photoluminescence (PL). The results showed that the c-axis orientation of ZnO thin films was not destroyed by annealing treatments; the grain size increased and stress relaxed for the films deposited at 200-500 °C, and thin films densified for the films deposited at RT with increasing annealing temperature. The transmittance spectra indicated that E_g of thin films showed a decreased trend with annealing temperature. From the PL measurements, there was a general trend, that is UV emission enhanced with lower annealing temperature and disappeared at higher annealing temperature for the films deposited at 200-500 °C; no UV emission was observed for the films deposited at RT regardless of annealing treatment. Improvement of grain size and stoichiometric ratio with annealing temperature can be attributed to the enhancement of UV emission, but the adsorbed oxygen species on the surface and grain boundary of films are thought to contribute the annihilation of UV emission. It seems that annealing at lower temperature in air is an effective method to improve the UV emission for thin films deposited on glass substrate at substrate temperature above RT.     

A study of parameters affecting the continuous CO2 laser cuts

Abstract

This work attempts to discover, by experimentation, some of the parameters governing cutting efficiency in perspex of a continuous CO₂ laser. The experimentation took the form of taking cuts in specimen pieces with the laser. While varying the parameters of speed of cut and position of the focal plane of the laser beam relative to the surface of the perspex, all other parameters were kept constant. These experiments produced conclusive ideas of the optimum position of the focal plane and the best speeds for cutting perspex at the same time producing the best cut quality obtainable. When the theoretically predicted minimum cut width is compared with the experimentally obtained results, the agreement is found to be almost exact.     

A parametric study of AlN thin films grown by pulsed laser deposition

High quality AlN thin films were grown at 200–450°C on sapphire substrates by laser ablation of Al targets in nitrogen reactive atmosphere. The nitrogen pressure was varied between 10⁻³ and 10⁻¹ mbar. The reactive gas pressure during irradiation and the temperature of the substrate were found to essentially influence the quality of the layers. X-ray diffraction analysis evidenced the formation of highly orientated layers for a very restrictive set of parameters. Other analysis techniques, like X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, optical transmission spectroscopy have been used to evidence the good stoichiometry and purity of the films. The characteristics of these films were compared with those of AlN thin films deposited in similar experimental conditions, on Si (100) and Si (111) substrates.     

皮秒激光切割AFRP复合材料实验研究

采用紫外皮秒激光(λ=355 nm)、绿光皮秒激光(λ=532 nm)和红外皮秒激光(λ=1064 nm)的三波长皮秒脉冲固体激光器,对1 mm厚芳纶纤维增强树脂基复合材料(Aramid fiber reinforced polymer,AFRP)进行单次扫描切割实验,用光学显微镜(OM)和SEM测量了上切缝宽度、切缝...     

Failure analysis of pin prick defects in galvannealed sheet – A case study

A peculiar type of pin prick spots/dents on the surface of some galvannealed sheets was observed, causing significant appearance problems in the finished product. In the present study, the surface defect was characterized by visual inspection, optical microscopy, microhardness, scanning electron microscopy and EDX to understand the source and mechanism of the defects. In the visual inspection, these peculiar defects were found to align in one direction. The SEM examination exhibited three distinct regions of the surface defect apart from the matrix: (1) particle, (2) a dense layer surrounding the particle, and (3) a crater region surrounding the particle. The EDX analysis of these regions indicated enrichment of Al and Fe and depletion of Zn in the particle. The microhardness measurements of the dense layer and the matrix indicated an increase in hardness in the dense layer compared to the matrix. Based on the preliminary results, the following hypothesis was made: Dross/zinc dust falling from snout wall or intermetallic phase or reaction product particles embed in the craters on the strip surface; during subsequent skin-pass rolling these particles peel out the zinc coating in the craters, thus densifying and flattening the region surrounding the particle. The paper presents the results of the investigation.     

激光熔覆化学处理钛合金表面改性的研究

采用两步走的方法实现了钛合金的表面改性，首先在钛合金表面进行激光熔覆CaO或CaCO3，得到冶金结合的复合涂层后，通过在磷酸等含磷酸根的溶液中浸泡CaOCa使涂层中的转变为磷酸盐，从而使钛合金表面具有生物活性。XRD和SEM分析表明，得到了活性涂层，涂层与基体的结合良好。