复合材料开孔层合板有限元网格划分方法研究

对复合材料开孔层合板有限元建模过程中网格划分方法进行量化研究。应用参数化的方法建立多种板宽孔径比、多种铺层比例的开孔层合板模型,逐级调整网格密度,计算单轴拉伸载荷作用下孔边最大应力集中系数。根据有限元结果,结合牛顿插值的数值计算方法,模拟出开孔层合板合理的网格密度划分方程。然后,对该网格划分方程下计算的数值解进行试验验证与解析解验证。结果表明,这种网格密度划分方程能有效地降低计算误差,可以在板宽孔径比大于3的复合材料开孔层合板的有限元计算中广泛使用。     

45钢椭圆孔板应力集中的应变率效应

含孔板的应力集中问题一直是结构安全评估的重要研究课题。许多学者研究了线弹性孔板在静态载荷下的应力集中问题,包括孔的形状,材料的各向异性和加载方向等因素的影响。然而,当孔板承受动态载荷发生塑性变形时,应力应变关系的非线性和应变率效应会导致应力集中与线弹性结果有明显的不同。因此,基于Johnson-Cook模型,对45号钢含孔板孔边的动态应力集中问题进行了系统的有限元分析。研究结果表明,塑性应力集中系数不仅取决于加载大小(应变)而且还取决于加载速度(应变速率)。给定远端应变1%,在平面应力状态下:圆孔板在应变率6)ε∞=20/s下的应力集中系数比应变率6)ε∞=0. 1/s下的结果高10%;对于形状因子(短轴/长轴)为0. 5的椭圆孔板,在应变率6)ε∞=20/s下的应力集中系数比应变率6)ε∞=0. 1/s下的结果高11%。     

含孔复合材料层板的力学性能研究

对复合材料开口缝合补强结构进行了实验研究,测试了不同缝合参数(针距、行距、边距、单重和双重缝合)补强对含孔复合材料层板的破坏强度,研究了孔边应力集中和缝合补强对强度、模量等力学性能参数的影响,分析讨论了孔边及邻近区域应变集中及应变分布的规律,通过实验结果和分析讨论,对复合材料开口缝合补强结构提出合理的设计方法。     

连接结构的孔边强化层对复合材料含孔板失效过程的影响

在实际工程中,复合材料开口孔周围应力集中现象十分严重,使孔边极易发生破坏,且破坏形式多种多样.为提高含孔复合材料板的结构强度,可在孔边铺设一层一定厚度的材料,用来强化含孔板的承载能力.以三维逐渐损伤理论为基础,采用商用软件ANSYS的二次开发语言,建立对复合材料含孔板进行孔边结构强化的模型,在拉伸载荷下对具有强化结构的...     

连接件振动疲劳寿命分析的名义应力法

提出了采用名义应力法估算振动载荷下连接件疲劳寿命的方法。综合考虑连接件孔边的应力均方根集中程度、孔表面状况和填充系数的影响,给出了连接件在振动载荷激励下的应力均方严重系数,然后结合连接件孔边的动态特性给出了振动疲劳缺口系数的计算公式。设计并完成了两种激励谱下304不锈钢的连接件振动疲劳试验,结果表明该方法可以很好地预测连接件的振动疲劳寿命。     

折弯孔边距离的Deform模拟研究

针对板上预制孔在板材折弯过程中产生变形的问题，分析了板上预制孔产生变形的机理，介绍了避免预制孔产生变形的经验孔边距。并在此基础上，通过Deform一3D软件进行钣金折弯的模拟，验证了板厚、孔边距及孔变形间的关系。     

支撑板孔径对7A04-T6铝合金板冷挤压后孔周环向残余应力分布的影响

使用非线性有限元软件建立了含孔7A04-T6铝合金板的开缝衬套冷挤压模型,模拟了开缝衬套冷挤压过程,对冷挤压后孔周环向残余应力的分布进行了预测,并与实测结果进行对比,最后探讨了不同支撑板孔径下冷挤压后孔周环向残余应力的分布。结果表明:孔周环向残余应力的模拟结果与实测结果较为吻合;随着支撑板孔径增大,板件入口层处残余压应力有增大的趋势;当支撑板孔径小于11.74mm时,在孔边出口层会形成明显的凸台,造成残余压应力突变,出口层残余应力峰值出现在支撑板孔边所在处;随着支撑板孔径增大,板件出口层环向残余应力逐渐趋向平滑,凸台现象逐渐减缓。     

30CrMnSiA钢在循环载荷作用下冷挤压孔边残余应变场变化初探

用实测方法初步探讨了３０ＣｒＭｎＳｉＡ材料冷挤压强化孔边残余应变场在几种不同交变应力作用下的衰减变化情况。结果表明，３０ＣｒＭｎＳｉＡ材料的残余应变场没有随外加循环载荷作用衰减的特性，但存在一个临界值，当孔边实际最大应力超过这个临界值时，孔边材料将再次屈服；当孔边实际最大应力低于这个临界值时，孔边残余应变场保持稳定，这个临界值的实质是使孔边实际最大应力恰好达到材料屈服极限。     

孔口缝合补强对层间应力影响的数值模拟

使用空间杆单元模拟缝合线,对含孔复合材料层合板开口缝合补强结构进行有限元模拟计算。研究含孔复合材料层合板在轴向拉伸载荷作用下,圆孔附近各个铺层交界面处层间正应力和剪应力的分布情况,将缝合后的层间应力值与缝合前的相关数值进行比较,并研究不同缝合参数(针距、行距、边距、单缝合和双缝合)对孔边层间应力的影响。结果表明,缝合补强后孔边的层间应力明显减小。孔边附近层间应力的分布与相邻铺层的铺层角有很大关系,不同铺层之间的层间应力有显著差别。不同铺层之间的层间应力沿孔边区域存在应力转换点(即层间应力由正值变为负值)。     

低周疲劳载荷下裂缝及缺口尖端弹塑性应变场

在低周疲劳载荷作用下,对中心、双边裂纹和双边缺口试件进行实验研究.用云纹方法测量了在载荷循环周期内、不同应变水平下,裂纹和缺口尖端位移场、应变场和应变集中系数。对裂纹延长线上应变奇异性进行了分析。这些结果对研究裂纹体在低周循环载荷作用下,裂纹的起裂、扩展是有意义的。     

Rolling of I-section beams using lead as a model material: Some experimental results

Results of a series of tests rolling $\text{I-}\text{section}$ beams in the first two passes, using lead as a model material, are presented; they include measurements of relative spread, natural elongation, roll load, roll torque and the observed changes in deformation modes with variation in shape factors (height to width ratios) of the specimens and the relative draughts.A comparison of these results is made with those obtained using empirical formulae suggested by earlier research workers. The observed rolling loads are compared also with measurements made of the die loads when rectangular specimens with the same shape factors as in these rolling tests were compressed between shaped dies having grooves similar to that in rolling and compressed under conditions of plane strain and in open-die compression.     

Rolling of I-section beams using lead as a model material: Some experimental results

Results of a series of tests rolling I-section beams in the first two passes, using lead as a model material, are presented; they include measurements of relative spread, natural elongation, roll load, roll torque and the observed changes in deformation modes with variation in shape factors (height to width ratios) of the specimens and the relative draughts.A comparison of these results is made with those obtained using empirical formulae suggested by earlier research workers. The observed rolling loads are compared also with measurements made of the die loads when rectangular specimens with the same shape factors as in these rolling tests were compressed between shaped dies having grooves similar to that in rolling and compressed under conditions of plane strain and in open-die compression.     

凝胶色谱-固相萃取-气相色谱-串联质谱法测定水产品中9种三嗪类除草剂

建立了水产品中9种三嗪类除草剂的凝胶色谱 固相萃取-气相色谱-串联质谱(GPC-SPE-GC-MS/MS)分析方法。样品采用乙酸乙酯提取,凝胶渗透过滤,石墨化碳串联氨基柱净化,选择离子监测模式测定,外标法定量。结果表明：扑灭津、阿特拉津、特丁津、西玛津、扑草净在1.0~50.0 μg/L范围内线性良好,检出限均为1.0 μg/kg,在1.0~10.0 μg/kg添加水平,平均回收率为86.3%~119%,相对标准偏差为5.11%~10.1%;环草津、莠灭净、特丁净、西草净在2.0~100.0 μg/L范围内线性良好,检出限均为2.0 μg/kg,在2.0~20.0 μg/kg添加水平,平均回收率为87.6%~112%,相对标准偏差为5.27%~9.56%。该方法稳定、可靠,适用于水产品中9种三嗪类除草剂的同时测定。     

高精度电磁标定力的产生及其特性分析

高精度标定力的产生是微推力高精度测量的关键之一。电磁力具有非接触、结构简单、容易控制等优势,成为微推力测量系统有效的标定力产生方法。针对微推力测量对于电磁标定力的性能要求,研究了磁铁与线圈之间相对位置变化对电磁力大小的影响关系,通过仿真计算得到了轴向距离、径向偏差、相对倾角变化下的电磁力输出特性:相对倾角、径向偏差不为0时,电磁力均会变大,且关于磁铁中心轴线具有对称性,沿轴向距离,电磁力先增大后减小。基于天平称重法,设计了可三维调节的电磁力测量装置,提出了轴向距离、径向偏差、相对倾角的归零调节方法;获得了电磁力较为完备的力学特性,通过分段拟合方法,解决了在较小标定力时相对误差较大的问题,确定了电磁力及电流的控制关系及相对位置变化范围;提出了不敏感角、不敏感径向偏差、不敏感轴向距离区间等新概念,为电磁力产生装置的性能表征提供了具体参数。     

Fracture of notched and perforated polymeric bars produced by longitudinal impact

An experimental investigation was executed to ascertain the stress intensity factors at the tip of stationary or moving cracks and the stress distribution at central holes in thin rectangular specimens of polymethyl methacrylate (PMMA) and polycarbonate of bisphenol (Lexan) as the result of longitudinal impact by 10 mm dia. steel spheres at velocities ranging from 15 to 130 m/s and by the hammers of standard Charpy impact testers. The initial and rebound velocities of the spheres as well as the strain histories in the specimens were measured. Crack kinematics, the stress intensity factor at the tip and the nominal stress at central holes were ascertained by means of a shadowgraphic technique using a 24-spark Cranz-Schardin camera.Stepwide propagation in the PMMA specimens, frequently found for low sphere-impact velocities, occurred at crack speeds of 250–340 m/s, while catastrophic failure in a single pass of the crack involved tip speeds from 625 to 700 m/s. For the Lexan samples, the velocities of all cracks whether moving intermittently or continuously, were observed to be between 435 and 510 m/s; thus, the average of the fast crack speeds corresponds to about 31% of the rod wave velocity for both materials. Dynamic stress intensity factors were found to be equal to or larger than corresponding static values of fracture toughness, and their variation with nominal stress in the bar followed different mechanical-optical paths during loading and unloading. Stress histories at holes in PMMA determined from strain gage data indicated a stress concentration when compared to those obtained from the shadowgraphs. Current analyses of the process based on static stress distributions in an infinite elastic plate under constant load require modification to provide an explanation of some of the phenomena observed. Such dynamic stress conditions in the vicinity of a crack or hole will also require an alteration of the photomechanical relations currently employed to ascertain crack tip intensity factors and stress conditions at circular holes determined from the geometry of shadow-graphic patterns.     

A flexible technique for calibrating relative position and orientation of two cameras with no-overlapping FOV

We propose a flexible new method to calibrate the relative position and orientation relationship of two cameras with no-overlapping field of view (FOV), which are called relative pose parameters in this paper. The objective of this method is to unify the local coordinate frames of the two cameras to be under one global coordinate frame. Additionally we design a flexible target composed of two short 1D bars with equally placed light spots and one long linking pole to assist the calibration. The target is adjustable according to the actual position and orientation of the two cameras, based on the principle that the two 1D bars can be shot clearly at the same time by their corresponding cameras, which will largely increase the calibration accuracy. The proposed approach consists of two steps. Firstly we use the invariant constraints on the angle and distance between the two short 1D bars to give a rough estimation on the relative pose parameters of the two cameras, then we use more restrictions on the invariant distances between light spots on the two 1D bars respectively to refine the estimation on both the relative pose parameters and the structure parameter of the targets. This technique offers a significant flexibility and tight space advantage compared to other calibration methods applying extremely large 2D or 3D targets for wide view calibration, which are inefficient in some conditions. And equally important, this approach still obtains acceptable calibration accuracy. Result of the experimental calibration shows that the system calibrated by this method reaches an accuracy of 0.108 mm when measuring a distance section of 1040 mm.     

DETERMINATION OF LEAD(II) BY FLOW-INJECTION ANALYSIS USING LUMINOL-POTASSIUM PERIODATE POST-CHEMILUMINESCENCE REACTION

The post-chemiluminescence (PCL) phenomenon arising from the potassium periodate–luminol reaction induced by lead(II) was investigated. A strong PCL signal was observed when lead(II) was injected into the mixture of potassium periodate and luminol in a flow-cell. The influencing factors on the PCL intensity of the system were investigated. Under the optimum experimental conditions, the present method allowed the determination of lead(II) in the concentration range of 1.0 × 10^?8 to 1.0 × 10^?5 mol/L and the detection limit for lead(II) was 2.3 × 10^?10 mol/L. The relative standard deviation was 3.2% for 11 replicate analyses of 1.0 × 10^?6 mol/L lead(II). Combined with cotton cellulose xanthate for separation, the proposed method was applied to the determination of lead(II) in real water samples with satisfactory results.     

On the effects of friction on free volume holes in PTFE

Since the macroscopic properties of materials are relevant to their micro structure, the detection of microscopic defects or their changes in size and concentration is an interesting topic in materials science. The positron annihilation lifetime (PAL) method used here is established as a unique technique that can provide information about the size and concentration of free volume holes directly without significantly intervening in the bulk properties of the specimens. To our knowledge, this is the first time that PAL techniques have been used to study the wear mechanism of macromolecular tribomaterials. Here we present the results of a study in which the correlation between the fretting wear behaviour of polytetrafluorethylene (PTFE) and the changes in its free volume size and concentration in amorphous-crystal interface regions was found to be δω =A.δτ₃, where δω is the wear loss of PTFE under fretting wear conditions, A is a constant, and δτ₃ represents the relative change in the third lifetime components after the friction test. The results indicate that fretting mainly influences the characteristics of atomic-scale free volume holes in the amorphous-crystal region in PTFE, and under high-load fretting wear conditions the ductile polymer PTFE possesses a self-curing function for its defect-free micro volume holes.     

Cylindrical three-hole pressure probe calibration for large angular range

This paper presents a brand new method to calibrate a Cylindrical Three-Hole Probe (CTHP) in a “non-nulling” operating mode. This calibration method employs the definition of a new normalization factor used in the calibration coefficients of the probe. By means of this new normalization, singular points are prevented from appearing in the calibration coefficients. In addition, the angular range attainable when using this new calibration is ±70^°, while the typical angular range of traditional calibration is approximately ±30^°. To validate this study, an uncertainty analysis of the probe using this new method is carried out, resulting in significantly low uncertainties for the whole angular range of the probe. Complementarily, the influence of the angular distance between the holes of the probe on both angular range and maximum uncertainties is also performed in the paper. From this analysis, it is established that the optimal angular separation for the holes should be chosen to be between 50 and 60 degrees. Finally, to illustrate the usefulness of this procedure, a set of experimental measurements were conducted downstream of the rotor of an axial turbomachine, using the new normalization factor in a CTHP with an angular distance of 60 degrees between the holes. The results revealed that the complex, unsteady flow within the blade passages can be perfectly captured, including those regions with high variations in the flow angle, like the shear layers of the wake fluid or both casing and hub boundary layers. In summary, this newly developed calibration method enables the measurement of large variations of the flow angle, in particular, up to 140 degrees, increasing in 80 degrees the typical angular range of the traditional calibration.     

基于灰色理论镍基单晶合金多轴非比例加载低周疲劳研究

基于灰色理论研究DD3镍基单晶合金高温多轴非比例加载低周疲劳特性,对等效应变范围、温度、应变路径角、拉/扭载荷相位角和轴向应变比等影响疲劳寿命的因素进行灰色关联度分析,并引入损伤参量Q表征非对称循环特性和拉/扭多轴效应,以参量Q、等效应变范围Δεe和Mises等效应力范围Δσe构造疲劳损伤参量,建立低周疲劳寿命GM(1, N)预测模型。结果表明,各影响因素与多轴低周疲劳寿命的关联度等级依次为等效应变范围、温度和应变路径角为一级,拉/扭载荷相位角为二级,轴向应变比为三级;680 ℃和850 ℃温度下的GM(1, N)疲劳寿命模型的预测寿命与试验寿命的绝对关联度分别为0.97、0.86,平均相对误差分别为4.9%、6.0%;两种温度的试验数据几乎分别落在1.93、2.13倍偏差分布带内。