广义合成偏应力椭球模型

本文从应力椭球的概念出发,建立了反映岩土类材料屈服与破坏的广义合成偏应力椭球屈服准则,该准则不仅反映了偏斜应力和静水应力对材料的屈服与破坏的贡献,而且反映了岩土类材料的屈服与破坏与静水应力呈非线性的关系以及静压屈服的特性。将该模型应用于混凝土,其结果与公开发表的文献和实验数据取得了很好的一致性。     

7050铝合金时效成形中应力松弛行为与回弹方程

通过自主设计的单向拉伸应力松弛装置研究7050铝合金时效成形过程中的应力松弛行为和回弹方程。结果表明:时效温度范围内7050铝合金的应力松弛曲线表现为典型的对数衰减曲线。该松弛过程可以分为应力快速下降,应力缓慢衰减和应力保持相对恒定3个阶段。随着温度的升高应力松弛极限逐渐降低。由于7050铝合金时效析出与应力松弛中位错蠕变的共同作用引起了松弛过程槛应力现象。通过解析7050铝合金应力松弛行为的特征和松弛曲线的泰勒方程得到该合金在时效温度范围内的应力松弛经验公式,以此获得该合金时效成形过程中的应力松弛方程,并利用该经验公式较好地预测时效成形后试样的回弹率。     

利用近饱和磁化产生的巴克豪森效应测量铁磁件二轴应力

讨论了一种检测铁磁材料的内部应力的无损检测新技术。利用该技术,以近饱和磁化产生的巴克豪森效应与应力的关系,测量了铁磁构件的二轴应力和焊接构件的残余应力。检测结果与传统的Ｘ射线检测法的结果相一致。该检测技术在工程检测中有广泛的适用性。     

玻璃应力检测仪校准方法的探索

提出了一种玻璃应力检测仪的校准方法并给出了相关标准器的设计思路,该标准器是根据玻璃各向异性的物理特性而设计的一种标准应力玻璃板。对标准应力玻璃板相应位置施加标准力值使其产生相应的标准玻璃内应力,再使用玻璃应力检测仪对其进行测量得出玻璃应力值,该测量应力值与玻璃板标准应力值进行对比,从而给出玻璃应力检测仪示值的误差。该校准方法和标准器为玻璃应力检测仪的量值溯源提供了一种可行方案,为玻璃生产中对产品质量控制提供了一定帮助。     

杆中导波声弹敏感模态与激励频率的确定方法

基于超声导波声弹性效应检测波导结构的应力水平具有潜在的优势。为实现超声导波声弹应力检测的关键技术——检测模态与激励频率的选取,提出一种基于Murnaghan超弹模型的有限元特征频率法。使用该方法计算预应力杆中的频散特性,得到反映不同激励频率应力敏感性的声弹频散曲线,与文献中的L(0,1)模态试验结果进行对比,趋势一致,说明该方法的适用性。为进一步验证该方法的可靠性,选取L(0,1)模态声弹敏感的几组频率,在自制拉伸试验平台上,对碳素钢杆进行超声导波声弹试验。试验结果表明:低应力区域误差较大,在高应力区域误差均低于10%,且声弹常数与理论结果趋势一致。研究表明该理论方法可指导超声导波声弹应力检测时频率与模态的选取。     

一种新的多轴高周疲劳模型

将疲劳强度以上加载等效为塑性应变,建立了塑性应变与加载应力呈线性关系的表达式,由此得到循环加载的塑性应变能。该塑性应变能使材料微观组织结构发生不可逆变化而引起等效宏观应力。假定该应力符合一种特定的分布函数,导出其最大应力与外加应力叠加达到材料本征断裂应力时的裂纹成核寿命,从而并由微裂纹引起上述两部分应力变化,得到继续加载直至宏观裂纹出现的疲劳寿命。所建立的多轴疲劳寿命公式由3个材料参数表达,并通过单轴疲劳试验数据确定。初步研究表明：该模型对所引用的多轴疲劳试验数据有很好的预测能力。     

基于坡面卸荷的土质边坡应力状态及稳定性分析

边坡稳定性分析中极限平衡法难以考虑土体应力状态,坡体滑面应力计算又长期停留在数值方法上。为解决这一问题,提出坡面卸荷应力等效思路,将坡面按半无限边界考虑后利用弹性理论求解坡体应力,并根据滑面应力进行稳定性安全系数计算,最后结合多个算例将潜在滑动面位置、滑面应力分布、安全系数与已有理论进行比较。研究结果表明:坡面卸荷应力等效思路概念清晰,符合边坡受力特征,且通过该思路求得的滑面应力与有限元分计算结果基本一致,搜索得到的潜在滑动面位置,以及对应的稳定性安全系数与有限元强度折减法、极限平衡法计算结果十分接近。此外,该计算方法还能有效与支护结构预应力结合,体现预应力的加固作用。     

有限长厚壁圆筒康托洛维奇应力变分解端部偏差的修正

本文指出文献[4]、[5]在用康托洛维奇应力变分法解有限长厚壁圆筒轴对称问题时存在的端部应力偏差;提出一个消除该偏差的反向端部效应的问题;通过简单计算推导出满足其全部应力边界条件与平衡微分方程的应力表达式,并用应力变分法求得其解答;数值计算结果表明,该解答较好地修正了文献[4]中端部附近应力的偏差。     

承受单向静拉应力的有限宽板双边对称裂纹尖端I_1/σ_(mises)的分布函数

采用线弹性有限元方法分析了承受单向静拉应力的有限宽板双边对称裂纹尖端的Mises应力和应力第一不变量I1的分布特性及其影响因素,在此基础上建立了裂纹尖端I1/σmises的分布函数,该函数仅与泊松比和裂纹长度相关,与板厚、弹性模量和加载名义应力无关;应用该分布函数可很好的解释厚板断裂行为特征。     

基于人工神经网络的Mg-Zn-Zr-Ce合金热压缩变形研究

为研究含稀土元素铈的镁合金中高温流变行为,利用热模拟试验机对Mg-6Zn-0.5Zr-1.5Ce合金在变形温度523～673 K、应变速率0.001～1 s-1范围内进行热压缩实验.基于真应力真应变实验数据构建了单隐层前馈误差反向传播人工神经网络模型,利用该模型对ZK60-1.5Ce合金的流变应力行为进行预测,并分析了变形温度、应变速率与真应变对流变应力的影响.研究表明:Ce添加可显著细化晶粒;该镁合金的流变应力随变形温度降低和应变速率升高而增加;其流变应力行为可用双曲正弦函数进行描述,依据峰值应力拟合求得该合金的表观激活能为161.13 kJ/mol;变形温度和应变速率对流变应力的影响高于真应变.所建立的人工神经网络模型可以很好地描述该镁合金的流变应力,其预测值与实验数值吻合良好.     

高精度激光准直技术的研究（一）

论述了激光准直技术的发展及共性的技术关键问题，系统介绍了对单位在高精度激光准直技术方面的研究成果，从理论到实践较好地克服激光漂移，大气环境对激光准直的严重影响。研制成功的激光光纤准直仪，激光双频同轴度仪及激光旋光准直仪具有当前高精度激光准直技术的代表性，并且均达到国内外先进水平。     

In situ TEM near-field optical probing of nanoscale silicon crystallization

Laser-based processing enables a wide variety of device configurations comprising thin films and nanostructures on sensitive, flexible substrates that are not possible with more traditional thermal annealing schemes. In near-field optical probing, only small regions of a sample are illuminated by the laser beam at any given time. Here we report a new technique that couples the optical near-field of the laser illumination into a transmission electron microscope (TEM) for real-time observations of the laser-materials interactions. We apply this technique to observe the transformation of an amorphous confined Si volume to a single crystal of Si using laser melting. By confinement of the material volume to nanometric dimensions, the entire amorphous precursor is within the laser spot size and transformed into a single crystal. This observation provides a path for laser processing of single-crystal seeds from amorphous precursors, a potentially transformative technique for the fabrication of solar cells and other nanoelectronic devices.     

不锈钢表面激光熔覆抗空蚀涂层技术研究进展

综述了国内外不锈钢抗空蚀激光表面熔覆技术的研究现状,介绍了该技术的特点,设备和抗空蚀熔覆粉末体系.并对激光熔覆层结构及性能作了较详细的介绍,阐述了熔覆层的抗空蚀性、耐磨蚀性和耐腐蚀性等.还简要介绍了该技术的应用现状,并提出了其今后的发展前景及方向.     

Laser phase noise reduction for industrial interferometric applications

Laser ultrasound is a technique used for the ultrasonic inspection of composites during manufacturing of advanced jet fighters. With this technique laser interferometry is used to detect ultrasonic displacements generated by a laser. In theory, the signal-to-noise ratio is proportional to the square root of the collected detection light. In practice, laser phase noise limits the signal-to-noise ratio above a certain collected light level. Two techniques are presented to decrease effects due to laser noise. In one technique the dual-cavity Fabry-Perot currently used is replaced by an interferometer based on a photorefractive crystal. The other technique has a high-finesse Sagnac cavity that filters the phase noise from the detection laser. Experimental results demonstrate that these two techniques significantly reduce limitations due to laser noise.     

Excimer laser micromachining of oblique microchannels on thin metal films using square laser spot

Excimer laser micromachining of thin metal films with a sacrificial polymer coating is a novel technique that produces features with smooth edges. Using this technique, oblique microchannels are fabricated by workpiece dragging and using a square laser spot, where the axis of traverse of the workpiece is not parallel to the edges of the square laser spot. The microchannels have serrated edges that are particular to the shape of the mask producing the spot. The edge roughness of the channels, machined with a square laser spot of side 100 μm, is found to be most affected by the fluence–spot overlap interaction, and the channel width by spot-overlap and the angle of tilt of the traversed path. Polymer coated metal films underwent close to ideal machining, aided by the clamping action of the polymer layer. Through this technique of machining post polymer coating, the edge roughnesses of the microchannels have been curtailed to less than 10 μm, and channel widths to 150 μm. This technique may be used in fabrication of oblique and circular patterns using excimer laser micromachining with rectangular and square laser spots.     

激光熔覆技术研究进展

首先从激光熔覆用设备与材料、熔覆层的性能以及工业应用等方面,综述了国内外激光熔覆技术的研究动态与进展.其中,着重介绍了激光熔覆层的性能,如耐磨、耐蚀、耐高温等.随后指出了激光熔覆技术目前存在的一些技术难题,如熔覆层的开裂与剥落、工件的变形、不完整的熔覆层材料体系以及轻金属的熔覆质量等问题.最后展望了激光熔覆技术的发展前景,并针对目前该技术存在的问题指明了今后的发展方向.     

Operational stabilization of a high-power ultrashort dye oscillator-amplifiers laser chain

Stable operation of a high-power ultrashort dye laser chain is achieved with an inexpensive heating technique. The femtosecond oscillator and its pumping laser are separately covered with boxes to isolate them from external temperature fluctuations. Both laser-isolating boxes are lined with a heating pellicle that permanently and uniformly warms the lasers to preset operating temperatures. The power, spectrum, and duration of the laser-chain output pulse remain constant from day to day. This technique could be applied to other ultrafast laser devices that require long-term performance stability.     

Single-multiple Scattering Technique to Simulate a Time-dependent Signal of a Pulse Laser Radar with Separately Located Illuminating and Receiving Platforms

A technique for calculating the time-dependent signal of a laser radar with a narrow angle of the field of view and separately located receiver and laser is proposed. The laser is assumed to have a short pulse and the results are valid for relatively uniform meteorological situations. This technique is based on the use of a single-multiple scattering model of the aerosol space and 'weighted' influence energetic coefficients of elementary volumes of aerosol space, taking account of spatial, energetic, temporary and other parameters of a radiation source and receiver. Taking into consideration a number of approximations, a relatively simple engineering technique to estimate a laser radar signal is described.     

Femtosecond laser machining for characterization of local mechanical properties of biomaterials: a case study on wood

Abstract

The standard preparation technique for micro-sized samples is focused ion beam milling, most frequently using Ga⁺ ions. The main drawbacks are the required processing time and the possibility and risks of ion implantation. In contrast, ultrashort pulsed laser ablation can process any type of material with ideally negligible damage to the surrounding volume and provides 4 to 6 orders of magnitude higher ablation rates than the ion beam technique. In this work, a femtosecond laser was used to prepare wood samples from spruce for mechanical testing at the micrometre level. After optimization of the different laser parameters, tensile and compressive specimens were produced from microtomed radial-tangential and longitudinal-tangential sections. Additionally, laser-processed samples were exposed to an electron beam prior to testing to study possible beam damage. The specimens originating from these different preparation conditions were mechanically tested. Advantages and limitations of the femtosecond laser preparation technique and the deformation and fracture behaviour of the samples are discussed. The results prove that femtosecond laser processing is a fast and precise preparation technique, which enables the fabrication of pristine biological samples with dimensions at the microscale.     

Deconvolution of long-pulse lidar signals with matrix formulation

A deconvolution technique for deriving more resolved signals from lidar signals with typical CO(2) laser pulses is proposed, utilizing special matrices constructed from the temporal profile of laser pulses. It is shown that near-range signals can be corrected and small-scale variations of backscattered signals can be retrieved with this technique. Deconvolution errors as a result of noise in lidar data and in the laser pulse profile are also investigated numerically by computer simulation.