A review of welding residual stress test methods

Due to local uneven heating during the welding process,the residual stress of the structure after welding affects the reliability of it.In order to ensure the reliability,it is of great significance to test the residual stress distribution of the welded joint.It has always been the focus to find a simple and feasible method for residual stress testing to quickly and accurately obtain the residual stress distribution of welded joints.The mechanical measurement method has high measurement accuracy,convenient and easy operation,but it will cause certain damage to the components.Physical measurement method can avoid damage to components,but its test cost is usually high,and its measurement accuracy can also be affected by the material microstructure characteristics of welded components.Based on the advantages and disadvantages of these two residual stress test methods,a modal test method is proposed.This method is a non-destructive measurement method.Based on the mathematical relationship between the residual stress of the welded structure and the natural frequency(mathematical model),the natural frequency is measured through the modal test to calculate the residual stress quickly.However,it is difficult to establish a mathematical model with this method,and it is not suitable for realization.

Dynamic test methods for natural frequency of footbridge

Using environmental random vibration as the excitation,traditional accelerometer method,non-contact video method and non-contact laser method were employed to determine the natural frequency of Kunyu River footbridge.All the results of these three methods are close to 2.70 Hz,which are concordant with each other and hence credible.

Test measurements for accuracy of absolute and relative GPS positioning

The paper, after the introduction, briefly outlines the principles of both absolute and relative GPS positioning. It deals with factors and error resources affecting the accuracy of these surveying procedures. It reviews the geodetic determination of a reference point and a base line used for the test measurements. The study describes the completed test measurements, and on the basis of results, it draws the conclusions for the accuracy of the investigated surveying methods. Finally, considering these accuracy measures, their possible application in mine surveying is also mentioned very shortly.

A Statistical Comparison of Traffic Measurements from the Moving versus Stationary Observer Methods

Data of traffic flow, speed and density are required for planning, designing, and modelling of traffic stream for all parts of the road system. Specialized equipments such as stationary counts are used to record volume and speed;but they are expensive, difficult to set up, and require periodic maintenance. The moving observer method was proposed in 1954 by Wardrop and Charlesworth to estimate these variables inexpensively. Basically, the observer counts the number of vehicles overtaken, the number of vehicles passed, and the number of vehicles encountered while traveling in the opposite direction. The trip time is reported for both travel directions. Additionally, the length of road segment is measured. These variables are then used in estimating speeds and volumes. In a westbound direction from Interstate Highway 30 (I-30) in the DFW area, this study examined the accuracy and feasibility of this method by comparing it with stationary observer method as the standard method for such counts. The statistical tests were used to test the accuracy. Results show that this method provides accurate volume and speed estimates when compared to the stationary method for the road segment with three lanes per direction, especially when several runs are taken.

Differences in Modified Morgan Phosphorus Levels Determined by Colorimetric and Inductively Coupled Plasma Methods

Phosphorus (P) fertilization is frequently needed for profitable crop production. Modified Morgan P (MMP) is a soil test P used to estimate plant available P in soils. The critical values of MMP for P fertilization and maintenance recommendations are based on the P concentrations measured by a common colorimetric molybdenum blue method although other P quantification methods have also been used for MMP measurements. In this study, we collected 120 surface soil samples of Caribou Sandy loam under potato cultivation or its rotation crops from Maine, USA, and 72 soil samples of Cecil sandy loam with cotton/corn crops under conventional tillage and no-till management with chemical and poultry litter fertilization in Georgia, USA. The MMP levels in all 192 dry samples were greater when they were measured by an inductively coupled plasma (ICP)-based method, compared to the corresponding data produced from colorimetry. Our results show the two sets of data were positively and significantly correlated (r = 0.93, P –1 with standard deviation of 12.9, compared to the average of colorimetric MMP level of 14.9 mg P kg–1 with standard deviation of 8.8. Based on the observations in this work, both colorimetric and ICP-based methods can be used for P fertilizer recommendation, but a conversion factor should be applied for ICP data as the current recommendation systems are based on colorimetric M&R data.

一种非接触式R-test测量仪球心坐标计算方法

R-test测量仪是用于五轴数控机床转动轴结构误差测量的专用设备,其通过测量球相对测量坐标系的位置变化进行误差辨识。在测量坐标系中,测量球球心坐标计算的准确性和稳定性是保证测量精度的重要前提。为进行测量球球心坐标的精确计算,构建了非接触式R-test测量仪的结构模型并建立了球心坐标计算方程组。以球心坐标计算方程组为基础,简化得到用于球心坐标求解的非线性方程组并构建其目标函数,然后采用差分进化算法提高球心坐标求解的精度。最后,在GF Mikron UCP800五轴机床上进行对比实验,将测量球球心坐标的计算结果与机床实际坐标进行对比,验证所提出球心坐标计算方法的精度和可靠性。

Quantitative Testing of Defect for Gun Barrels

The magnetic flux leakage (MFL) method is commonly used in the nondestructive evaluation (NDE) of gun barrels. The key point of MFL testing is to estimate the crack geometry parameters based on the measured signal. The analysis of magnetic leakage fields can be obtained by solving Maxwell’s equations using finite element method (FEM). The radial component of magnetic flux density is measured in MFL testing. The peak-peak value, the separation distance between positive and negative peaks of signal and the lift-off value of Hall-sensor are used as the main features of every sample. This paper establishes the multi-regression equations related to the width (the depth) of crack and the main characteristic values. The regression model is tested by use of the magnetic leakage data. The experimental results indicate that the regression equations can accurately predict the 2-D defect geometry parameters and the MFL quantitative testing can be achieved.

盾构隧道下穿高铁路基变形影响规律及加固优化研究

为研究盾构隧道下穿高铁路基施工时对路基的影响规律,探究在隧道开挖过程中运用不同加固措施对既有高铁路基的影响程度。以西安市某地铁工程为依托,利用室内模型试验对比分析盾构隧道下穿高铁CFG桩复合路基过程中,无加固、超前管幕工法加固与地表袖阀管注浆加固3种隧道施工条件下,地表沉降值和沉降槽的空间分布规律;采用数值模拟分析验证超前管幕工法加固工况下盾构隧道下穿时,高铁路基、道床的位移变化规律。室内模型试验结果表明:盾构隧道施工中采用管幕工法加固后复合地基正上方的地表沉降最大值减小28.6%,采用袖阀管注浆加固后减小18.0%,并且采用两种加固措施后的CFG桩最大附加轴力均减小20%以上。因此,在隧道掘进过程中采用一定加固措施,可改善围岩稳定性,其中管幕工法加固效果更为显著。数值模拟分析表明:采取管幕工法加固施工与不采取加固措施相比,路基最大沉降量减少33.78%,道床最大沉降量减少45.08%。因此,管幕工法加固能够有效减小对既有高铁路基的影响。

偏心拉伸实验的理论分析与实验研究

偏心拉伸实验是一种综合性、研究性的材料力学实验项目。为了增加材料力学实验课程的难度和深度,通过理论分析推导偏心拉伸应力公式,并指出偏心拉伸试样的实际中性层并不再是几何中性层;利用ABAQUS软件模拟了偏心拉伸试样的应力分布;通过自制的一种可以在电子万能试验机上进行偏心拉伸实验的装置并利用电测法测试了试样横截面上各点的应变。结果表明:偏心拉伸实验的理论计算结果、实验结果和模拟结果基本吻合,3种数据之间的偏差较小;而且,应力在试样横截面上几乎呈线性分布,左边受压缩,右边受拉伸,左边的应力最小,右边的应力最大。

舰载飞机着舰撞击载荷实测技术研究

针对国内飞机起落架载荷测量中普遍存在的静标动测问题,从理论和机理上分析了静标定的应变法实测动态载荷存在问题的原因。同时,考虑到舰载飞机因定点着舰方式遭受严重的动态载荷,重点研究了舰载飞机着舰撞击载荷的静标动测问题。通过动态落震试验模拟飞机着舰过程,根据测力平台的实测载荷分析,获取了应变法实测载荷精度受动态影响的程度,提出一种改进的惯性修正方法,即:通过落震试验数据辨识质量矩阵,通过辨识的质量矩阵和实测加速度修正应变法的实测载荷。试验结果表明,改进的惯性修正方法进一步提高了垂向载荷的测量精度,显著提高了航向和侧向载荷的实测精度。

Scanning Hartmann test method and its application to lens aberration measurement

A scanning Hartmann test method is proposed and its measurement principle is described. The scanning Hartmann test setup is formed by modifying the Hartmann screen of the conventional Hartmann test setup. With the rotation of the scanning Hartmann screen and the improved hole arrangement, the whole information of the lens to be tested in the full aperture can be obtained. The measurement accuracy of the aberration is improved and the local error of the lens can be got. In the method, no change of the Hartmann screen is needed for measuring the lenses of different aperture sizes. Experimental results of aberration measurements of two lenses are given to verify the usefulness of the setup.

考虑负摩阻力的桩基设计研究

以广东省广州市南沙区的房屋建筑工程为例,对复杂地质情况下桩周负摩阻力的桩基设计进行研究,详细分析了桩侧阻力的计算方法、桩基静载试验检测要点,探讨了桩侧阻力成因和影响因素,并提出负摩阻力防治措施。经过在复杂地质条件下的工程应用,表明本工程所提出的方案具有良好的实践效果,证明未能正确考虑桩周负摩阻力的桩基设计存在较大的安全风险,必须全面掌握桩周负摩阻力的成因、计算方法,有效进行桩基静载试验检测,采取有效的防治措施,才能确保桩基设计的安全和良好的经济效益。

基于拟合椭圆的等震线长短轴测量方法

提出了一种改进的拟合椭圆算法用于测量等震线长短轴,即将等震线测量的模式和直接测量算法的概念以约束的形式加入拟合椭圆算法,并使用最小二乘法求解椭圆系数,在与传统等震线测量方法保持一致的基础上,减少了直接测量方法的主观不确定性。在此基础上讨论了拟合椭圆算法的适用性和鲁棒性,将等震线长短轴的测量结果与前人的结果进行了对比。结果表明:拟合椭圆算法的适用性较好,可用于等震线的拟合;拟合椭圆算法的鲁棒性较好,计算结果较为稳定;对于未闭合且形状复杂的等震线,计算结果相对离散,要单独验证结果是否合理;利用拟合椭圆算法得到的等震线长短轴结果与前人的结果较为一致,可用于建立烈度衰减关系。

大口径异型方管风量测量数值仿真分析及试验验证

针对1 m以上大口径异型方管转弯部分长度较短、前后段没有较长的直管,管道内部流场复杂、需准确测量管道流量的问题,进行了数值模拟分析。提出了一种基于变差系数的平均速度评价方法,选出多点最接近管道平均流速的位置,明确传感器插入深度和多个测量点的权重系数,拟合出1个以截面平均速度为函数,流场中多点的流速值为自变量的计算公式。在风洞实验台进行流量测量试验,并与数值分析拟合的公式计算值进行比较,满量程相对误差小于0.54%。

基于测压风洞试验的钢桁梁上列车二维气动导纳研究

基于节段模型测压方法,建立了列车二维气动导纳的识别方法。在紊流场风洞试验中,获取了0°攻角时钢桁梁上列车抖振力的展向相关性;识别了钢桁梁上列车中车的三维气动导纳,探究了钢桁梁上列车中车三维气动导纳与二维气动导纳的关系。可知,随无量纲折减频率及展向间距的增大,抖振力的展向相关性逐渐减小,列车抖振力展向相干函数可用Jakobsen模型较好地拟合。当k_(1)B/2小于0.3时,二维气动导纳值为1,三维气动导纳会明显低估列车的气动导纳值。当k_(1)B/2大于0.3时,三维气动导纳会明显地高估二维气动导纳函数值,且随着折减频率的增大,气动导纳值减小。最后,给出了列车二维气动导纳函数及相干函数的数学表达式。研究成果可为风-列车-桥梁耦合振动计算分析提供参数。

基于图像处理的破片场三维测试方法

针对靶板法人工检靶效率低、人为误差大以及无法实现破片场三维测试的问题,利用摄影测量技术,提出灰度加权重心法计算破片穿孔位置坐标,采用基于单点标志的靶板轮廓识别和编码标志的大范围、位姿改变靶板三维拼接,二维坐标到三维空间坐标转换,实现了破片场的三维空间测量,通过设计试验,验证了方法的可靠性,结果表明:采用该方法破片尺寸大于3 mm识别率为100%,且准确获取了破片相对于爆心位置的三维坐标,实现了破片场三维测试,与人工检靶比较测试效率提高了10倍以上。此结论可为破片战斗部爆炸威力场的精确测试提供技术支撑,具有一定的工程应用价值。

行星传动系统均载与动载系数试验测量改进设计

试验测量行星传动系统均载与动载系数的精准度是评价系统动态性能的基础。针对现有行星传动系统均载与动载系数测量方法存在灵敏度与精度欠佳、系数测试算法缺失、测试应力点存误等问题,本文提出了一种方便、实用且具有高精度的行星传动系统均载与动载系数测试方法,定义了系统系数的测试算法与概念,明确了精确应力测试位置点及不同位置间差异性,采用应变片电桥传感器串并联设计,实现了拉压应力叠加、温度补偿以及繁琐标定免除等优点,为精准测取行星传动系统均载与动载性能提供了重要的理论基础和技术手段。

生成式人工智能创作使用作品的合理使用调适

技术迭代易造成规则失范,随着生成式人工智能技术与创作的深度融合、著作权权利边界的不断扩张,以及著作权领域不同利益之间的杂糅、冲突与博弈,对于生成式人工智能创作使用作品的法律规制已迫在眉睫。从合理使用的制度功能出发,生成式人工智能创作过程吸纳合理使用具备了相当程度的正当性与可行性。但是,合理使用的适用过程也面临着利益平衡格局受损、现有规定适用困难以及与技术措施协调不足等现实梗阻,而这也对合理使用的适应性、柔韧性和包容性提出了新要求。未来,可从专门例外、三步检测法、技术措施、配套措施等方面进行完善,以调适著作权领域相关主体差异化的利益诉求,实现产业发展、私权保护与公共利益的良性互动。

CTD海上剖面测量性能综合评定方法研究

随着国产温盐深剖面仪(Conductivity-Temperature-Depth profiler,CTD)测量性能的不断提高,其使用范围和规模也逐步扩大,需要规范CTD海上剖面测量性能评定方法。在威海附近海域开展基于锚泊式平台CTD海上比对试验,通过改变同架比对CTD数量、引入相关系数和平均差数据处理方法研究海上比对试验效果,提出以精准度和灵敏度为目标层的CTD海上剖面测量性能评价指标体系,实现了对被测CTD海上剖面测量性能相对全面的评价,准确量化了被测CTD在实际海洋环境中的剖面测量性能,为国产CTD海上剖面测量性能的优化提供依据。

基于PBL教学方式的汽车检测实训课程教学研究

汽车检测实训课程是汽车检测与维修技术专业的必备课程,是汽车检测与维修技术专业人才培养方案中的核心实践课程,是汽修行业汽修专业人才的必修课程。问题导向学习(PBL)教学方法普适于高职教学,文章分析了PBL教学法存在的不足,提出教学改进措施,并设计了PBL教学方式应用于汽车检测实训课程教学案例。通过教学有力增强了学生的问题解决能力,掌握实用技能,提高了团队合作技能和动手能力,提升了自主学习能力和深层学习能力等,为高职汽车检测实训课程教学改革研究提供参考。