全自动应变测试技术的探讨

本文主要对全自动应变测试技术进行探讨,并对全自动引伸计在试验机中的应用提出可操作性的见解。     

LGH-01型空气质量自动监测系统准确度检查方法探讨

LGH-01型空气自动监测系统因其独特的技术优势,在国内占有较大的市场份额,已广泛应用于城市环境空气质量监测.如何做好仪器的使用维护工作,保证监测结果的真实有效,是一线环境监测工作者每天必须面对的问题.本文针对DOAS系统准确度检查方法进行实验探讨,期望能提供给同行参考.     

漕河渡槽深厚卵石层钻探取芯样技术探讨

对深厚卵石层钻探完整取芯样问题一直是水电勘探中的一大难题,近十年来由于采取了SM植物胶金刚石钻进工艺,岩芯采取率和钻进效率都有一定的提高;随着实践经验的积累和技术参数、配制方法的不断调整,此钻进工艺得到了不断完善.槽河渡槽是南水北调中线工程河北省段最大的建筑物,河床段卵石层深厚且含砂量小,钻探取样难度极大;就漕河渡槽深厚卵石层勘探中钻具的选用、技术参数的选择及植物胶配制方法、注意事项、取芯样技术进行了较详细的叙述并进行了总结,可供以后类似地层勘探时参考.     

岩石动态劈裂试验的最优试件尺寸分析

利用有限元分析软件LS-DYNA对常规巴西圆盘、平台巴西圆盘和带孔巴西圆盘这三种最常用的劈拉试件,进行岩石SHPB动态劈裂试验的数值模拟,并依据模拟结果,采用平台巴西圆盘法,对花岗岩试样进行了动态劈裂试验。对比模拟与试验结果,得到了加载应变率与岩石动态抗拉强度的关系,探讨了用于岩石动态劈裂试验的最优试件尺寸。结果表明:平台巴西圆盘法可以较好地满足中心起裂条件,试验结果的可信度更高,而对于所采用的岩石参数,建议平台巴西圆盘试件的中心角取20°~24°;如采用带孔巴西圆盘试件进行动态劈裂试验,建议内外孔径比取0.4~0.5;岩石的动态劈拉强度随应变率的增大而增大,但增大速率越来越小,且这种增大趋势受到试件尺寸的显著影响。     

Weight functions and stress intensity factors for pin‐loaded single‐edge notch bend specimen

A recently developed pin‐loaded single‐edge notch bend specimen provides an alternative to the single‐edge notch tension specimen commonly used for small‐crack growth testing. In this paper, weight functions for pin‐loaded single‐edge notch bend specimen are derived by using two methods, the classical analytical weight function method and the newly developed numerical weight function complex variable Taylor series expansion method. Excellent agreement between the two methods is achieved. Based on these weight functions, accurate stress intensity factors for two load cases, that is, pin‐loading and Dugdale loading, which is required for plasticity‐induced crack‐closure analysis based on the strip‐yield model, are determined.     

Size independent fracture energy evaluation for plain cement concrete

The present work deals with the investigation of a robust analytical scheme to assess the size‐independent fracture energy of concrete. The study involves the numerical modelling of three‐point bend (TPB) concrete beams that are geometrically similar, having constant length to depth ratio with varying range of notch to depth (a/W) ratios. The unique nonlinear behaviour of concrete 1material is incorporated through fracture energy‐based strain‐softening model in the finite‐element numerical simulation. The International Union of Laboratories and Experts in Construction Materials, Systems and Structures (RILEM) fracture energy values are evaluated through numerical simulation of several set of experimentally observed load‐load line displacement response. The RILEM fracture energy values associated with geometrically similar beams have been utilised to develop a methodology for assessment of the size‐independent fracture energy of concrete. The numerically predicted and experimentally evaluated size‐independent fracture energy using the RILEM fracture energy values are found to be in close agreement.     

Modeling of failure mode of laser welds in lap-shear specimens of HSLA steel sheets

Failure mode of laser welds in lap-shear specimens of high strength low alloy (HSLA) steel sheets is investigated in this paper. The experiments for laser welds in lap-shear specimens under quasi-static loading conditions are briefly reviewed first. The experimental results showed that the laser welds failed in a ductile necking/shear failure mode and the ductile failure was initiated at a distance away from the crack tip near the boundary of the base metal and heat affected zone. In order to understand the failure mode of these welds, finite element analyses under plane strain conditions were conducted to identify the effects of the different plastic behaviors of the base metal, heat affected zone, and weld zone as well as the weld geometry on the ductile failure. The results of the reference finite element analysis based on the homogenous material model show that the failure mode is most likely to be a middle surface shear failure mode in the weld. The results of the finite element analysis based on the multi-zone non-homogeneous material models show that the higher effective stress–plastic strain curves of the weld and heat affected zones and the geometry of the weld protrusion result in the necking/shear failure mode in the load carrying sheet. The results of another finite element analysis based on the non-homogeneous material model and the Gurson yield function for porous materials indicate that the consideration of void nucleation and growth is necessary to identify the ductile failure initiation site that matches well with the experimental observations. Finally, the results of this investigation indicate that the failure mode of the welds should be examined carefully and the necking/shear failure mode needs to be considered for development of failure or separation criteria for welds under more complex loading conditions.     

A Biaxial Fatigue Specimen for Uniaxial Loading

Abstract: The aim of this paper is to present a novel un‐notched fatigue test specimen in which a biaxial stress state is achieved using a uniaxial loading condition. This allows the problem of multi‐axial fatigue to be studied using relatively common one‐axis servo‐hydraulic testing machines. In addition the specimen presented here is very compact and can be made using a small volume of material (100 × 40 × 4.5 mm). For this specimen, the degree of biaxiality, defined by the parameter is equal to approximately 0.45. The specimen geometry was optimised using the Dang Van multi‐axial fatigue criterion. In addition to use as a fatigue specimen, it has been demonstrated that the biaxial specimen presented here is also suitable for biaxial tensile tests, to determine the rupture strength of a material in a biaxial stress state. Two different materials have been investigated: The first was wrought aluminium 2024‐O in the form of 5 mm sheets. The second was a cast aluminium‐silicon alloy AlSi7Cu0.5Mg0.3, commonly used in automotive and aeronautical applications. The fatigue strengths were determined at 2 × 10⁶ cycles and at various R‐ratios using a staircase procedure. For the aluminium 2024, it is shown that the biaxial stress state increases the maximum permissible first principal stress when compared to the uniaxial condition. However, in terms of the cast aluminium alloy, it has been demonstrated that this type of fatigue specimen is not suitable for materials containing casting defects, in particular micro‐shrinkage pores, because the volume of material, in which the stress state is biaxial, is not large enough.     

XRF法快速测定铝土矿火车样

采用压样法,使用国产便携式Ｘ射线光分析仪快速测定铝土矿火车样中的铝、硅、磷、硫、钾、钙、铁、钛８个元素。文章对标样的采集、制样、仪器某些性能的改进,各种影响因素的校正（如基体效应、谱叠加干扰等）、数学模型的研究开发等作了简要说明,提出了解决问题的基本原则,在小型仪器上攻克了铝土矿火车样工业分析的难题。该技术具有准确、快速、成本低的优点。     

航空发动机燃烧室机匣破裂安全性预测方法

针对航空发动机燃烧室机匣安装座环焊缝疲劳寿命的研究,提出了一种安装座焊接结构双轴拉伸模拟件的设计方法。首先,通过分析机匣安装座的载荷工况及几何特征,给出了相应的设计准则和几何等效分析,同时设计出模拟件的雏形。然后,根据优化目标提出了一种优化数学模型,以有限元计算的方式讨论了模拟件在中心试验区直径D₁,夹持臂楔形角度ω,安装座通孔直径D₂的3种尺寸变量下的应力变化规律,进而确定了模拟件的最终尺寸。最后,采用该模拟件进行双轴拉伸疲劳试验。试验结果表明,裂纹源出现在模拟件试验区的焊缝处,并且沿着焊缝向两侧进行扩展,证明了该设计的合理性。