基于激光测距的飞艇净重在线计算方法研究

通过对三维建模软件CATIA中的飞艇副气囊模型进行切片分割,获得了不同副气囊高度下的对应体积值,使用最小二乘法建立了副气囊中心点高度与副气囊体积的三次曲线拟合公式,采用相位式激光测距仪对副气囊中心高度测量,使用该公式可以估算出副气囊的实时体积大小,从而推算飞艇净重大小,掌握飞艇的压力高度和起降能力。使用某次飞行试验对副气囊高度测量的数据计算出的飞艇净重值,与多次地面称重数据一致性较好,验证了使用激光测距仪对大型飞艇净重进行在线评估的可行性,并使用该方法对某飞艇某次飞行试验过程中的净重进行了分析,对飞艇的压力高度进行了核算。     

Laser joining of CFRTP to titanium alloy via laser surface texturing

Grid pattern was textured on Ti-6Al-4V alloy (TC4) substrate surface by nanosecond laser system. Laser joining of carbon fiber reinforced thermoplastic composite (CFRTP) to TC4 joints were performed, and the effect of texture grid depth was investigated. The contact angle of molten CFRTP on textured TC4 surface was measured and the tensile-shear force was tested. The fracture surface and interface morphology were observed. The results indicated that the wettability of molten CFRTP on TC4 surface improved remarkably after laser textured TC4. Shear force of CFRTP/TC4 joints was increased by 156% after laser textured TC4 surface. When the depth of grid was deeper than 100 μm, contact angle increased and incomplete filling of molten CFRTP in grid occurred, the shear force thus decreased gradually. Resin-carbon fibers mixture was adhered on the fracture surface of TC4, and the variation tendency of adhesion ratio was consistent with that of shear force. TC4 matrix was exfoliated from substrate and adhered at the fracture surface of CFRTP, indicating stronger mechanical interlocking occurred at the joining interface after laser textured TC4 surface. Beside mechanical interlocking, compound layer consisted of CTi_0.42V_1.58 carburization phase was also confirmed at interface, suggesting that chemical bonding also occurred at the joining interface.     

Brazing diamond grits onto AA7075 aluminium alloy substrate with Ag–Cu–Ti filler alloy by laser heating

The brazing of diamond is a promising way to fabricate grinding wheels for efficient machining and precision grinding. This work investigated the feasibility of bonding diamond grits onto Aluminium Alloy 7075 (AA7075) substrate with a Ag–Cu–Ti filler alloy via laser fusion brazing. The interfacial microstructures and the strength of the brazed diamond joints were studied. The cross-section of the brazed diamond joint consists of a molten filler alloy layer, a molten pool, a heat effect zone, a columnar crystal zone and an equiaxed crystal zone. Within the interface of the filler alloy/substrate metal, microstructures observed possibly were Ag(s.s), Al(s.s), TixAl, Al2Cu and Mg intermetallic compounds. A layer of TiC with a thickness of about 30–50 nm was found at the bonding interface of the diamond/filler alloy. The averaged peak shear force of the brazed joints was found to be approximately 39.8 N. The abrasion grinding test indicated that the diamond/AA7075 brazed joint was adequate for grinding. However, the pulled-off of grit was found to be the primary failure of this type of brazed joint. This work broadened the brazing diamond technique and the range of applications of brazed diamond wheels for efficient grinding.     

Spin axis orientation of Ajisai determined from Graz 2 kHz SLR data

The Graz 2 kHz Satellite Laser Ranging (SLR) measurements allow determination of the spin axis orientation of the geodetic satellite Ajisai. The high repetition rate of the laser makes it possible to determine the epoch time when the laser is pointing directly between two corner cube reflector (CCR) rings of the satellite. Identification of many such events during a few (up to 3) consecutive passes allows to state the satellite orientation in the celestial coordinate system. Six years of 2 kHz SLR data (October 2003–October 2009) delivered 331 orientation values which clearly show precession of the axis along a cone centered at 14^h56^m2.8^s in right ascension and 88.512° in declination (J2000.0 celestial reference frame) and with an half-aperture angle θ of 1.405°. The spin axis precesses with a period of 117 days, which is equal to the period of the right ascension of the ascending node of Ajisai’s orbit. We present a model of the axis precession which allows prediction of the satellite orientation – necessary for the envisaged laser time transfer via Ajisai mirrors.     

电子束熔丝沉积快速制造成型技术与组织特征

利用电子束熔丝沉积快速制造技术制备了TC4钛合金薄壁结构和实体结构试样,分析了成型技术特点,探讨了组织形貌特征及形成机制。研究表明:对于薄壁结构,采用合理的工艺参数,获得的熔积层的宽度为7.4mm,层高为1.5mm;结构纵截面的组织形貌特征是原始β柱状晶与沉积高度方向大约成15°角,较为粗大,宽3～5mm,单个柱状晶贯穿几层到十几层熔积层不等。对于实体结构,熔积间距为4.7mm时得到的试样表面较为平整,熔积高度基本一致;试样纵截面可观察到明显的层带,而原始β柱状晶垂直向上生长。     

脉冲激光推进的能量相似律理论研究

激光推进的能量相似律,指确定的激光能量有与之相对应的最佳喷管尺寸,使得冲量耦合系数最大且不变的规律。用大气高度参数、入射的激光能量、喷管几何参数构造了无量纲因子,建立了圆锥形喷管在单脉冲条件和一维球对称点聚焦情况下的能量相似律。结果表明:当锥角固定时,冲量和冲量耦合系数存在极大值,极大值对应的无量纲因子仅与气体比热比相关;当无量纲因子固定时,冲量随入射激光能量增加而单调增大,冲量耦合系数则与能量无关。本文的研究结论和规律性认识,对目前可实现和以后工程化放大的激光能量范围,均能给出可信可靠的喷管优化尺寸。     

连续波激光推力器稳定工作条件的解析计算模型

连续波激光推力器工作需要稳定的等离子体以吸收激光。为得到推力器中等离子体稳定维持的参数条件,根据吸收室内绕等离子体区域流动的流场特征,考虑高温状态下工质的热物理性质、激光吸收和辐射效应,建立了推力器吸收室内的能量平衡模型,该模型包含入射激光功率、推力室压强、等离子体区核心温度以及工质质量流量等参数。计算表明,该模型所得稳定质量流量随压力、激光功率的变化趋势与实验结果一致,并解释了稳定质量流量区间存在的原因。     

光电跟踪仪激光测距器性能检测方法研究

介绍了光电跟踪仪激光测距器的特点,提出了其重要性能指标一测距能力和精度的检测方法。采用半实物仿真技术测试反映测距能力的消光比参量;采用精密延时法,实现了测距精度的测量。检测装置的耦合透镜部件放置于平行光管靶面,容易与测试光电跟踪设备其它模块的装置进行集成。     

大型机翼整体壁板时效成形技术

 分析了单级时效、双/多级时效、振动时效以及应力位向效应等工艺措施和因素对铝合金机翼整体壁板材料时效成形特性的影响,得到以下结论：应采用双/多级时效处理,以提高成形后壁板材料的综合性能;应采用振动时效应力松弛,以加速应力松弛,降低回弹,并提高成形后壁板材料的抗疲劳性能;对时效过程中存在应力位向效应的铝合金,应设计合适的时间温度曲线与加载曲线,以避免壁板材料因应力位向效应产生各向异性,导致材料屈服强度降低。提出了大型机翼整体壁板时效成形的工艺流程,给出了成形过程中热压罐内的温度时间曲线和气压时间曲线;提出了成形工装的模块化、标准化与柔性化设计以及解决壁板时效成形回弹问题的有限元方法,并对中国研究发展大型机翼整体壁板时效成形技术提出了建议。     

激光多普勒测量技术及其应用

从光学结构、信号处理、方向辨别三个方面综述了激光多普勒测量技术的研究,最后讲述了激光多普勒测量技术在散射体位移测量中的一个实际应用──空间滤波的仿光栅散射体多普勒测量。