飞秒激光加工SiC/SiC复合材料厚板的孔型特征研究

为了探究飞秒激光加工SiC/SiC复合材料厚板的孔型特征,采用光束同心圆填充扫描方式对厚度为4mm的SiC/SiC复合材料进行制孔实验,分析了飞秒激光加工参数对入口直径、孔深、锥度等孔型特征的影响规律和影响机理。结果表明,脉冲能量、重复频率、线重合度以及扫描速率对小孔入口直径影响较小,但对孔深和锥度影响较大;上述实验参数与光束扫描面积内的能量密度密切相关,小孔锥度随能量密度增大而减小,小孔深度则反之;当采用最大脉冲能量130μJ、最大重复频率100kHz、最小扫描速率100mm/s、最大线重合度77%以及最小进给量0.1mm时,小孔锥度达到最小值12.38°;上层材料对光束的遮挡以及排屑困难导致深孔加工锥度不易控制。该研究可以为今后SiC/SiC超快激光制孔应用提供参考。

磨料水射流去除等离子喷涂法热障涂层的试验研究

热障涂层技术在航空发动机中具有延长热端部件使用寿命、提高功率和减少燃油消耗的优点。对热障涂层金属构件进行电火花小孔加工时,需要先去除金属基体表面的热障涂层。针对等离子喷涂法(Air plasma spray,APS)制备的热障涂层进行了磨料水射流去除加工试验。采用直径为300μm的低压磨料水射流,在室温下开展APS涂层的盲孔加工试验,以期为后续的电火花穿孔加工提供可能性。结果表明,冲蚀孔径和孔深随磨料浓度、射流压力、冲孔时间和靶距的增加而增大,涂层去除速率随磨粒硬度和粒径的增加而提高,APS涂层的冲蚀效率明显高于EB‑PVD涂层。

激光精微打孔中工艺参数对孔型几何特征的影响规律

从实验研究角度探讨了激光精微打孔过程中孔深度方向上的几何特征随激光工艺参数的变化规律。为更精确描述深度方向上孔型几何特征的变化,采用不同深度位置上的孔直径、局部锥度作为激光成孔的几何量化指标并加以研究。实验工艺参数包括激光束的离焦量和脉冲个数。通过实验,建立了孔型几何参数与激光工艺参数之间的量化关系。研究发现,离焦量对孔型几何特征具有显著的影响,上锥度随离焦量的增加呈近似线性递减的趋势,最终趋于零锥度;而下锥度随离焦量的增加呈先下降后上升的趋势,在-0.5mm^+0.5mm的离焦量范围内出现零锥度。脉冲个数对孔几何形状的影响在大离焦的情况下才比较明显,并且一旦形成通孔,脉冲个数将不会对孔形状产生任何影响。

Pore characterization of different types of coal from coal and gas outburst disaster sites using low temperature nitrogen adsorption approach

To characterize the pore features of outburst coal samples and investigate whether outburst coal has some unique features or not, one of the authors, working as the member of the State Coal Mine Safety Committee of China, sampled nine outburst coal samples(coal powder and block) from outburst disaster sites in underground coal mines in China, and then analyzed the pore and surface features of these samples using low temperature nitrogen adsorption tests. Test data show that outburst powder and block coal samples have similar properties in both pore size distribution and surface area. With increasing coal rank, the proportion of micropores increases, which results in a higher surface area. The Jiulishan samples are rich in micropores, and other tested samples contain mainly mesopores, macropores and fewer micropores. Both the unclosed hysteresis loop and force closed desorption phenomena are observed in all tested samples. The former can be attributed to the instability of the meniscus condensation in pores,interconnected pore features of coal and the potential existence of ink-bottle pores, and the latter can be attributed to the non-rigid structure of coal and the gas affinity of coal.

Spatial Structure Characteristics Detecting of Landform based on Improved 3D Lacunarity Model

The spatial structure characteristics of landform are the foundation of geomorphologic classification and recognition.This paper proposed a new method on quantifying spatial structure characteristics of terrain surface based on improved 3D Lacunarity model.Lacunarity curve and its numerical integration are used in this model to improve traditional classification result that different morphological types may share the close value of indexes based on global statistical analysis.Experiments at four test areas with different landform types show that improved 3D Lacunarity model can effectively distinguish different morphological types per texture analysis.Higher sensitivity in distinguishing the tiny differences of texture characteristics of terrain surface shows that the quantification method by 3D Lacu-narity model and its numerical integration presented in this paper could contribute to improving the accuracy of land-form classifications and relative studies.

Development and application of an efficient gas extraction model for low-rank high-gas coal beds

To promote gas extraction in low-rank high-gas coal beds, the pore structure characteristics of the coal and their effect on gas desorption were studied. The results show that micropores are relatively rare in low-rank coal; mesopores are usually semi-open and inkpot-shaped whereas macropores are usually slit-shaped. Gas desorption is relatively easy at high- pressure stages, whereas it is difficult at low-pressure stages because of the ＇bottleneck effect＇ of the semi-open inkpot-shaped mesopores. A ＇two-three-two＇ gas extraction model was established following experimental analysis and engineering practice applied in the Binchang mining area. In this model, gas extraction is divided into three periods： a planning period, a transitional period and a production period. In each period, surface extraction and underground extraction are performed simultaneously, and pressure-relief extraction and conventional extraction are coupled to each other. After applying this model, the gas extraction rate rose to 78.8 %.

Comparative Leaves Anatomical Studies of Bouea, Mangifera and Spondias （Anacardiaceae） in Malaysia

Leaves anatomy of two species of Bouea, 11 species of Mangifera and two species of Spondias were studied in order to see the differences in stomata type, petiole, midrib and lamina anatomy and leaf venation. This study aims to use anatomical characters for species and genus identification. Common characters observed were the absence of trichomes, closed vascular bundles, uniseriate epidermal layers, resin canal in parenchyma cells, anticline wall pattems and druses crystals in leaf lamina transverse sections. All species displayed closed vascular bundles except Mangiferapajang which showed a combination of medullary vascular bundles. Uniseriate epidermal layer was observed in all species. All the species showed straight-wavy anticlinal walls. Druses crystals were found in the parenchyma cells of all the species. Four types of stomata were observed namely anomocytic, anisocytic, staurocytic and diacytic. Anomocytic, anisocytic and staurocytic stomata were observed in Mangifera, diacytic in Bouea and anomocytic in Spondias.