Lamb波在铝板缝类缺陷检测中的应用

为了研究Lamb波在缺陷板检测中的应用,建立非线性Lamb波检测系统。该系统用于检测具有不同深度裂纹的铝合金板和具有不同拉伸载荷循环的铝合金板。通过快速傅里叶变换(FFT)对获取的时域波形进行分析,得到两种缺陷对Lamb波非线性效应的影响。测试结果表明,对于裂纹缺陷,缺陷深度增加将增大试件超声非线性效应。当裂纹深度超过4 mm时,裂纹缺陷的非线性效应不会增加。对于疲劳裂纹缺陷,裂纹缺陷的出现也会加剧试件非线性效应,但是当试件疲劳断裂时,其宏观缺陷对非线性影响较小。     

熔石英元件抛光加工亚表面缺陷的检测

亚表面缺陷的准确检测是进行亚表面损伤研究的前提和基础,对保证光学元件加工质量至关重要.基于HF酸化学蚀刻法对熔石英元件抛光加工产生的亚表面水解层、缺陷层深度和亚表面损伤形貌进行了定量检测,并利用X射线荧光光谱法研究了熔石英抛光试件杂质元素的种类和元素含量沿深度分布规律,提出了熔石英元件抛光加工亚表面损伤深度的判定方法.研究表明:由于水解层和亚表面缺陷层的存在,熔石英抛光试件的蚀刻速率随着时间的增加呈现递减的趋势,且在蚀刻的初始阶段蚀刻速率下降尤为明显;当蚀刻深度超过某一特定值后,全部或部分覆盖在水解层以下的缺陷层将会被完全蚀刻去除,蚀刻速率基本保持不变;另外,熔石英抛光试件存在多种形式的表面及亚表面缺陷,在不同蚀刻深度,亚表面损伤形貌、划痕的宽度和深度也存在一定的差异.     

高温作用下混凝土动态力学性能时间效应试验研究

为研究混凝土的高温动态力学性能,采用ANSYS软件对C60混凝土试件加热过程中的温度场进行计算,以确定不同温度组试件的加热时间。利用SHPB试验装置和加热电阻炉进行高温下不同加热时间的混凝土抗冲击性能试验研究。试验结果表明:C60混凝土表现出明显的温度效应和时间效应,在不同高温下,随着加热温度的升高试件动态抗压强度先增大后减小,峰值应变增大,且在200℃左右动态抗压强度达到最大;在相同高温不同加热时间的条件下,随着加热时间的增加,试件动态抗压强度不断降低,峰值应变增大,弹性模量减小,且在500℃的稳态温度场中,当加热时间190 min时,试件动态抗压强度不再降低趋于稳定。     

基于ABAQUS的表面内嵌CFRP筋粘结滑移性能数值模拟分析

利用ABAQUS有限元软件,对混凝土、CFRP筋或板条以及粘结剂分别采用不同的单元类型,特别是运用Spring2非线性弹簧单元来模拟表面内嵌CFRP筋或板条混凝土的粘结作用,同时考虑材料各自的本构关系,对表面内嵌CFRP筋混凝土拉拔试件和内嵌CFRP板条加固混凝土梁试件进行有限元模拟,将模拟结果与已有试验结果进行对比验证。结果表明,利用数值模拟的方法可以得到较为准确的拉拔试件的极限值,也可以较为正确地模拟加固梁的受力过程。在验证模拟结果正确的基础上,进一步分析了拉拔试件CFRP筋应力、滑移、粘结应力随不同位置的变化规律以及加固梁CFRP板条粘结区域内应变和粘结应力的分布情况。研究结果表明,对于拉拔试件,不同荷载等级作用下,CFRP筋在粘结区域内不同位置处的应力呈非线性变化,而粘结应力峰值出现在距加载点20mm~40mm位置处,其随位置的变化曲线呈偏态曲线特点。对于表面内嵌CFRP板条加固梁,粘结区域内CFRP应变和粘结应力在梁屈服后激增,且呈非线性变化。     

瑞利波检测钢结构表面缺陷深度数值研究

本文介绍了一种利用瑞利波在表面缺陷处的传播时间规律检测材料表面缺陷深度的方法,该法比较适合检测材质均匀的金属材料表面缺陷深度.在超高频率的激励作用下,介质表面产生的瑞利波波长远小于钢结构表面缺陷深度,瑞利波会沿着表面缺陷两个侧面传播到上表面.本文分析了各应力波的衍射和模式转换,及其各自传播路径;通过位移几何关系计算不同应力波的传播时间,确定计算钢结构表面缺陷深度的理论公式,通过有限元数值计算验证理论分析的正确性;研究了钢结构表面缺陷的定位方法;讨论激励频率,激励源和观测点位置,实际构件边界对检测结果的影响.     

微细管道内表面光电检测及三维重构系统

基于位置传感器PSD和光学三角原理,开发了一种适于空间曲线型微细管孔内表面三维重构的检测系统.该系统主要由管道机器人、形貌检测器和曲率检测器等部分组成.形貌检测器可以采集管道内壁截面信息,并计算出截面环上的点在局部坐标系中的位置.曲率检测器负责测量管孔中心轴线在检测器采样位置处的局部几何性质,并完成管道中轴线的重构.在管道机器人的驱动下,根据上述两方面提供的数据以及其前进步距,可以实现管道内表面的三维重建.实验结果表明,利用该技术检测的管道时,管道曲率半径的相对检测精度可以达到±2%,内表面缺陷及内径的测量精度可以达到±0.1mm.     

高压电缆铝护套焊缝缺陷ACFM检测方法及检测系统的研究

针对在氩弧焊型高压电缆铝护套焊接过程中易出现表面漏焊、埋藏未焊透和焊穿等缺陷的问题,提出了焊缝缺陷的交流电磁场检测（alternating current field measurement, ACFM）方法。首先,利用COMSOL多物理场仿真软件建立高压电缆铝护套焊缝缺陷ACFM模型,研究U形磁芯上的励磁线圈在不同类型铝护套焊缝缺陷区域产生的感应电流的密度分布特点和和磁场信号特征;其次,设计了可获取缺陷长度和深度信息的正交式接收线圈,制作了带有缺陷的电缆铝护套焊缝试件及ACFM实验平台;最后,进行了不同类型铝护套焊缝缺陷的检测及结果分析。实验结果表明,ACFM方法能够有效用于3 mm厚的高压电缆铝护套焊缝表面漏焊和焊穿缺陷的检测,并且能够有效识别埋深为2 mm,长、宽、深分别为10,0.3,1 mm的埋藏未焊透缺陷。研究结果为高压电缆铝护套焊缝缺陷的识别和焊缝质量的评价提供了重要参考。     

基于矩形脉冲涡流传感器的表面缺陷定量评估及成像检测技术研究

本文介绍利用矩形脉冲涡流传感器的自差分特性来提高缺陷检测能力,并最终实现对表面缺陷的成像检测.采用ANSYS软件建立了矩形脉冲涡流传感器的仿真模型,对铝板表面涡流分布进行了仿真分析,结果表明:矩形传感器能够在铝板表面激励出均匀的感应涡流,当有缺陷存在时,提取Z向和Y向感应信号的幅值扫描曲线可以实现对表面缺陷长度和深度的定量.并对仿真结果进行了实验验证,得到了表面缺陷的成像结果.研究结果表明,该矩形脉冲涡流传感器可以很好的实现对表面缺陷的定量评估及成像检测.     

X80管线钢不同缺陷类型的磁记忆检测试验研究

为探究X80管线钢不同缺陷类型的力磁耦合特性,设计了平板试件与穿孔、边缘切槽3种不同试件,通过金属磁记忆检测方法对X80管线钢试件不同缺陷类型的磁记忆信号特征进行了试验研究.采用材料试验机对试件导入不同程度的塑性损伤与应力集中,通过光学应变测量系统获取试件表面的实时应变情况,同时采用磁记忆检测仪对试件表面诱发磁场的法向分量与切向分量进行卸载离线检测.结果表明:随着塑性损伤程度的增加,无缺陷试件的磁记忆信号法向分量与切向分量从平缓趋向波动,但未出现明显的峰值;含穿孔与切槽试件磁记忆信号法向分量在缺陷处出现过零点与反对称双峰,切向分量出现单峰值,并且渐趋明显.初步探究了X80管线钢塑性损伤与磁记忆信号之间的关联性,为油气管道塑性损伤程度的无损定量评价奠定了基础.     

砼回弹仪弹击拉簧失效分析

砼回弹仪是利用回弹法无损检测工业与民用一般建筑物混凝土的抗压强度的一种仪器.其工作原理是用弹簧驱动弹击锤,通过弹击杆弹击试样表面所产生的瞬时弹性形变的恢复力,从而带动指针弹回并指示出回弹距离,以回弹值作为评定混凝土抗压强度的相关指标之一,其检测结果反映的是混凝土试件硬度与强度间的相关关系.     

Thermal Response of Steel–Steel Composite Metal Foams under Small-Scale Torch-Fire Conditions

Steel–steel composite metal foam (S–S CMF) is a novel metal matrix composite material characterized by its high strength-to-weight ratio and unique mechanical and thermal properties. It is made up of hollow stainless-steel spheres, embedded in stainless steel matrix, with 65–70% air in the structure making it effective as an insulating material. S–S CMF is being explored for use in tank cars carrying hazardous materials (HAZMATs) as a potential partial replacement for conventional carbon steel and thermal insulating material currently being used. In this study, S–S CMF material is numerically and experimentally evaluated for its thermal protection performance. Experimental studies are conducted in scaled-down jet fire condition while numerical studies are conducted using fire dynamics simulator (FDS). Based on experimental and modeling results, as well as uncertainty studies, 13–15 mm thick S–S CMF ranging in density of about 2.5 g cc⁻¹ tested as novel structural/insulating material meets the acceptance criterion for small-scale simulated torch-fire testing. Further success is anticipated in future full-scale evaluation of 122 × 122 cm samples. The outstanding fire resistance and thermal protection of S–S CMF is attributed to the substantial volume of air trapped within the material, which correlates to its total density.     

钨铜粉末药型罩射孔弹对钢靶侵彻的数值模拟

利用Ansys/Ls-Dyna软件对钨铜粉末药型罩射孔弹侵彻钢靶过程进行了数值模拟。运用混合物的叠加原理对钨铜混合材料的状态方程参数进行了计算,得到钨铜(20W80Cu)粉末药型罩的参数。采用多物质ALE算法,模拟了钨铜药型罩射流的形成及侵彻钢靶的过程,模拟89型号射孔弹作用45#钢靶,穿深为153mm,孔径为9.6mm,并与实际情况对比,数值模拟结果与实验结果差别在5%以内。     

Shallow Buried Defect Testing Method Based on Ultrasonic TOFD

Ultrasonic time of flight diffraction (TOFD) suffers from the shortcoming of lack of near surface resolution, primarily owning to the superposition of the lateral wave and the shallow buried defect (SBD) wave, and the insensitive region beneath the inspection surface because of the restricted beam width of the probes. This paper presents a method for the detection of SBD based on conventional TOFD. The method is named as TOFDW because it employs a three-fold reflected longitudinal wave whose propagation path in the testing piece looks like the letter “W”. Based on Pythagoras’s theory, mathematical models are developed to locate SBD. In TOFDW mode, the time difference between the lateral wave and the SBD wave can be enlarged greatly so that they would never be superposed. In addition, through reflecting the incident longitudinal wave by bottom surface, the near surface region of the testing piece is covered with an intense acoustic field, making TOFDW free of the restriction of the probes’ beam width. These contribute to the improvement of the near surface resolution. The experiments show that with the proposed TOFDW and mathematical models, the artificial defect tip with the buried depth of 1 mm can be detected, and the tips can be measured within an error of 0.3 mm; the weld defect with the buried depth of 2 mm can be identified effectively, and the location can be measured within an error of 0.5 mm.     

Transient Eddy Current NDE System Based on Fluxgate Sensor for the Detection of Defects in Multilayered Conducting Material

This paper describes a novel transient eddy current non destructive evaluation (NDE) system for the detection of defects in a multilayered conducting material by using fluxgate magnetometer as a sensor. In conventional eddy current NDE, the depth of defect detection is restricted due to the excitation frequency and its associated skin depth. Similarly, in conventional pulsed eddy current testing the time derivative of the secondary magnetic field, which decays much faster than the magnetic field itself, is measured by the induction coil. However, in this work we use fluxgate magnetometer which measures magnetic field directly and double “D” differential excitation coil in order to enhance the depth of investigation. In addition to this, the other instruments such as transmitter, transmitter controller and data acquisition system used for this work are the same one used for TEM based geophysical applications. The system has been used for the detection of an artificially engineered defect in an aluminum plate at a depth of 2 mm as well as 20 mm below the surface.     

等离子弧焊接熔池和小孔形成过程数值分析

目的 研究等离子弧焊接穿孔过程中熔池内部的金属流动情况和小孔动态变化过程。方法 通过“传热-熔池流动-小孔”之间的相互耦合关系,建立了等离子弧焊接穿孔过程的数值分析模型,通过VOF方法追踪了小孔界面,采用FLOW-3D软件模拟了等离子弧焊接熔池和小孔的形成过程,定量计算了等离子弧焊接温度场、熔池流场及小孔形状;分析了等离子弧焊接熔池和小孔行为;并通过等离子弧焊接实验数据验证了模拟结果。结果 当焊接时间为0~1.0 s时,小孔深度曲线与熔深曲线几乎相同,小孔底部紧贴熔池底部;在2.8 s以后,小孔深度曲线与熔深曲线有一定距离,小孔深度曲线在一定范围内波动,等离子弧焊接电弧挖掘作用到达极限,电弧压力与其他力达到平衡状态。模拟的焊缝熔深为8.04 mm、熔宽为13.20 mm,实验测得的焊缝熔深为8.00 mm、熔宽为13.42 mm。结论 构建的随小孔动态变化的曲面热源模型和电弧压力模型可以描述等离子弧焊接过程中的电弧热-力分布;模拟出了等离子弧焊接熔池和小孔动态演变过程;模拟得到的等离子弧焊接焊缝形貌与实验测得的焊缝形貌基本吻合。     

Volumetric inspection of moderately thick austenitic stainless steels by multifrequency eddy currents

This paper describes the initial phase of a project to develop eddy-current methods to inspect welds joining sections of austenitic stainless steel pipe having walls up to 13 mm (0.5 in.) thick. The objective of this phase was to demonstrate the feasibility of detecting and characterizing flaws in austenitic stainless steel base metals. These materials and welds present challenging eddy-current problems because of their relatively large thickness and ferromagnetism. Multiparameter analysis shows that a reflection coil probe operated with three discrete driver frequencies and phase detection can locate and size a cracklike defect in a single conductor in the presence of variations in conductor resistivity, permeability, and thickness and in the probe-conductor spacing (liftoff). Experiments were performed with a modular three-frequency instrument. Flat-plate specimens of types 304L and 347 stainless steel machined to 12.7 to 15.9 mm thickness simulated pipe walls; saw-cut slots 10 to 30% of nominal specimen thickness simulated cracklike defects. The same slots were used in duplicate experiments as near-side (directly under the test probe) or far-side (in the face opposite the probe) defects. Flaw detection and characterization capability was demonstrated by a series of experimental measurements fitted to specimen properties by least squares techniques. The quality of the fit determined the expected accuracy of measurement. Comparison of accuracy estimates determined the best choice of operating frequencies. From the 1,2,5 sequence of frequencies between 0.5 and 20 kHz, the optimum set of operating frequencies was selected to be 0.5, 2, and 10 kHz. Estimates of measurement accuracy for combined near- and far-side defect cases were: plate thickness, 0.74 mm; probe liftoff, 0.03 mm; defect location (depth of material above defect), 3.48 mm; and defect size (vertical slot depth), 1.09 mm. A few property values were back-calculated from instrument readings; the errors in these values were somewhat larger than the measurement accuracy estimates because of instrument drift and the absence of calibration circuits.     

A Preliminary Magnetoinductive Sensor System for Real-Time Imaging of Steel Reinforcing Bars Embedded Within Concrete

This paper studies the feasibility of using solid-state magnetoinductive probes for detecting and imaging steel reinforcing bars embedded within prestressed and reinforced concrete. Changes in the inductance of the sensor material are directly proportional to the strength of the measured magnetic field parallel to the sensor. Using a square coil of 300 mm times 300 mm times 2.5 mm, 10-mm rebars can be imaged down up to a depth of 100 mm. Experimental results obtained by scanning steel bar specimens are presented. General performance characteristics and sensor limitations are also investigated.     

热模拟2205DSS焊接HAZ的点蚀实验研究

采用热模拟法模拟焊接热过程,研究了2205双相不锈钢(DSS)的模拟焊接粗晶区的耐点蚀性能和金相组织的关系,探讨了冷却时间t8/5对模拟热影响区(HAZ)组织与点蚀性能的影响.结果表明:冷却时间t8/5对组织及点蚀性能有较大的影响,随冷却时间t8/5的增加,铁素体含量减少,奥氏体含量增加,模拟HAZ的点蚀率和点蚀相对面积降低,但仍大于母材,而最大点蚀深度增大,但低于母材.当冷却时间t8/5为100s左右时,模拟HAZ的抗点蚀性能接近母材的抗点蚀性能.     

Improvement in the fatigue strength of chromium electroplated AISI 4340 steel by shot peening

In landing gear, an important mechanical component for high responsible applications, wear and corrosion control is currently accomplished by chrome plating or hard anodising. However, some problems are associated with these operations. Experimental results have also shown that chrome‐plated specimens have fatigue strength lower than those of uncoated parts, attributed to high residual tensile stress and microcracks density contained into the coating. Under fatigue conditions these microcracks propagate and will cross the interface coating‐substrate and penetrate base metal without impediment. Shot peening is a surface process used to improve fatigue strength of metal components due to compressive residual stresses induced in the surface layers of the material, making the nucleation and propagation of fatigue cracks difficult. This investigation is concerned with analysis of the shot peening influence on the rotating bending fatigue strength of hard chromium electroplated AISI 4340 steel. Specimens were submitted to shot peening treatment with steel and ceramic shots and, in both cases, experimental results show increase in the fatigue life of AISI 4340 steel hard chromium electroplated, up to level of base metal without chromium. Peening using ceramic shot resulted in lower scatter in rotating bending fatigue data than steel shots.     

浇注式沥青混凝土现状与发展

为进一步确定浇注式沥青混凝土科学合理的性能评价指标及要求,全面梳理了国内外浇注式沥青混凝土相关规范,对比评价了不同规范中的技术指标要求及级配范围,系统地调查了大量实体工程及研究动态,厘定了浇注式沥青混凝土钢桥面铺装结构层组合、原材料类型和技术指标要求及级配类型,为浇注式沥青混凝土规范完善与质量控制奠定了基础.结果表明:推荐钢桥面铺装结构层组合为30~35 mm GA-10+35~40 mm SMA-10,GA基础沥青为SBS改性沥青+TLA(15%~30%),采用2%降粘剂;推荐性能评价指标要求范围为油石比7.9%~8.5%、流动度10~17 s、贯入度1.4~2.5 mm、贯入度增量不超过0.25 mm、弯拉应变不小于7 000με、动稳定度不小于1 000次/mm(参考指标);疲劳性能试验以控制应变模式进行,结果以实测为准.