Simulation on dynamic characteristics of TC4 cutting with crack defects

Titanium alloys play an important role in aerospace and other fields.However,after precision forging and cold rolling process,some defects will appear on the subsurface of titanium alloy bars,thus reducing the surface quality and precision of turning process.This study aimed at exploring the effect of crack defects on TC4 cutting.Firstly,the finite element cutting simulation model of TC4 material with crack defects was established in ABAQUS.Then,the cutting parameters such as cutting force,stress concentration,chip morphology,residual stress were obtained by changing the variables such as the size and height of crack defects.Finally,the turning experiment was carried out on centerless lathe.The results show that the cutting force changes abruptly when the defect position is located on the cutting path,the maximal stress occurs at the tip of the defect,and the mutation of stress value is more serious with the increase of defect size;the buckling deformation of chip morphology occurs and becomes less serious with the increase of the distance between the defect position and the workpiece surface;the surface residual stress near the defect is related to the stress when the tool is close to the defect,the larger defect size and the closer to the machined surface,the greater the residual stress.Therefore,under certain processing conditions,the TC4 material should avoid large size defects or increase the distance between defects and the machined surface,so as to obtain better and stable surface quality.

Characteristics of Welding Crack Defects and Failure Mode in Resistance Spot Welding of DP780 Steel

The mechanical properties of welded joints in resistance spot welding of DP780 steel were tested,and three different types of welding cracks in welded joints were investigated by optical microscopy,scanning electron microscopy and electron back-scattered diffraction.Finally,the failure mode of the welded joints in shear tensile test was discussed.It is found the shear tensile strength of welded joints can be greatly improved by adding preheating current or tempering current.The surface crack in welded joint is intergranular fracture,while the inner crack in welded joint is transgranular fracture,and the surface crack on the edge of the electrode imprint can be improved by adding preheating current or tempering current.The traditional failure mode criterion advised by American Welding Society is no longer suitable for DP780 spot welds and the critical nugget size suggested by Pouranvari is overestimated.

Elimination of cracks in stainless steel casings via 3D printed sand molds with an internal topology structure

The important supporting component in a gas turbine is the casing,which has the characteristics of large size,complex structure,and thin wall.In the context of existing 3DP sand casting processes,casting crack defects are prone to occur.This leads to an increase in the scrap rate of casings,causing significant resource wastage.Additionally,the presence of cracks poses a significant safety hazard after the casings are put into service.The generation of different types of crack defects in stainless steel casings is closely related to casting stress and the high-temperature concession of the sand mold.Therefore,the types and causes of cracks in stainless steel casing products,based on their structural characteristics,were systematically analyzed.Various sand molds with different internal topology designs were printed using the 3DP technology to investigate the impact of sand mold structures on high-temperature concession.The optimal sand mold structure was used to cast casings,and the crack suppression effect was verified by analyzing its eddy current testing results.The experimental results indicate that the skeleton structure has an excellent effect on suppressing cracks in the casing.This research holds important theoretical and engineering significance in improving the quality of casing castings and reducing production costs.

Analysis of the cause of crack in cold rolling of QSn6.5-0.1 strip

In order to know the cause of cracks in cold rolling of QSn6.5 0.1 copper alloy strip, a lot of experiments and analysis were done. The microstructure changes of QSn6.5 0.1 were investigated by means of metallurgical microscope. The morphology of cracks and surface defects were examined using scanning electron microscope. Macroscopic residual stresses produced in every process during manufacturing in the QSn6.5 0.1 strip were measured by X ray diffraction method and hole drilling method. The results show that the cracks in the QSn6.5 0.1 cold rolling strip were caused due to the derivation of metallurgical defects, such as SnO 2, S, fine looses,the inverse segregation unable to clear up when milling, and the accumulation of all kinds of resi dual stresses. When the accumulation of the residual stress reaches the material′s breaking strength, the cracks will be generated. Several measures to avoid the development of these kinds of cracks were put forward, such as: controlling the casting technology, improving homogenization annealing procedure (680 ℃/7 h) and milling quality(using the second milling when necessary), working out a more reasonable rolling technology to ensure intermediate annealing in time.

Crack Detection in Pipes with Different Bend Angles Based on Ultrasonic Guided Wave

Pipeline plays an indispensable role in process industries,because the progressing crack-like defects of in it may result in serious accidents and significant economic losses.Therefore,it is essential to detect the cracks occurred in pipelines.The axial crack-like defects in elbows with different angle are inspected by using the T(0,1)mode guided waves,in which different configurations including 45°,90°,135°and 180°(straight pipe)are considered respectively.Firstly,the detection sensitivity for different defect location is experimentally investigated.After that,finite element simulation is used to explore the propagation behaviors of T(0,1)mode in different bend structures.Simulation and experiment results show that the crack in different areas of the elbow can affect the detection sensitivity.It can be found that the detection sensitivity of crack in the middle area of the elbow is higher compared to the extrados and intrados of the elbow.Finally,the mode conversion is also investigated when the T(0,1)crosses the bend,and the results show that bend is a key factor to the mode conversion phenomenon which presents between the T(0,1)mode and F(1,2)mode.

Studies on the effect of weld defect on the fatigue behavior of welded structures

Structural integrity isstated as the science and technology of margin between safety and disaster. Systematic prediction of structural integrity of critical structures such ascombustion chambers,pressure vessels,nuclear reactor components,boilers etc.,ensures the human safety,environmental protection,and the economical considerations.The present work aims at prediction of fatigue behaviour of symmetric structures like pressure vessels in the presence of common welding defects such as lack of fusion( LOF),lack of penetration( LOP) and porosity.A ring type specimen which replicates the stress pattern in thepressure vessel is considered for the study of severity of weld imperfections. Initial dimensions of weld defects are arrived by performing NDT inspection.Crack growth analysis is carried out to determine the remaining life of the welded joint with defects.

针对背照式图像传感器加工工艺中Crack缺陷的分析与优化

阐述背照式CMOS图像传感器,是将硅片减薄后,在光电二极管photodiode背面搭建Color filter及Micro Lens形成的。相比前照式CMOS图像传感器,光线由背面射入,增大了光电元件感光面积,减少了光线经过布线时的损失,可以大幅提高CIS在弱光环境下的感光能力。在整个工艺中流程,深沟槽隔离DTI作为关键工艺步骤,防止光电二极管信号串扰。DTI刻蚀的形貌至关重要,决定能否顺利填充。目前业界有采用U和V型隔离槽。基于V型隔离槽形貌情况,结合填充能力,探讨加工晶圆中心区域存在Crack缺陷的问题,针对此问题,基于刻蚀角度优化V型隔离槽顶部的Bowling,通过实验对Bowling产生的机理和通过优化刻蚀菜单的方法,减小Bowling值,Bowling越小越有利于后续的填充,最终实现无Crack缺陷的方法。最终产品晶圆的良率将得到有效提高。

某电机齿轮冷挤压裂纹形成机理研究

针对材料为20Cr的某电机齿轮在冷挤压成形时内齿齿顶面上出现的裂纹缺陷,基于DEFORM-3D对其冷挤压过程进行了模拟,研究了其裂纹形成机理。有限元结果表明,内齿的金属流动速度小于中部及下部外齿的流动速度,内齿齿顶面上齿根处的金属流动速度最小,此处流动最不均匀,易产生应力集中;对齿面的最大主应力及损伤分布进行了分析,得出在内齿齿顶面上,中部及距离下端面1 mm左右的位置应力集中最明显,拉应力较大且大于材料抗拉强度,损伤值也较大且大于临界损伤值,会产生裂纹,与实际情况相符合。通过改变凹模入模角来控制成形缺陷情况,当凹模入模角为23°时,齿根处拉应力下降,损伤值减小,投入生产后次品率从原本的50%降为1%。

裂缝小目标缺陷的轻量化检测方法

及时且准确捕获井壁出现的微小裂缝,对于井筒安全意义重大.轻量化检测模型是推动井壁裂缝自动检测的关键,打破现有方法聚焦于提取深层语义信息的局限,重视浅层特征表征的几何结构信息的应用,针对井壁裂缝提出轻量化检测模型E-YOLOv5s.首先融合普通卷积、深度可分离卷积和ECA注意力机制设计轻量化卷积模块ECAConv,再引入跳跃链接构建特征综合提取单元E-C3,得到骨干网络ECSP-Darknet53,它负责显著降低网络参数,同时增强对裂缝深层特征的提取能力.然后设计特征融合模块ECACSP,利用多组ECAConv和ECACSP模块组建细颈部特征融合模块E-Neck,旨在充分融合裂缝小目标的几何信息和表征裂缝开裂程度的语义信息,同时加快网络推理速度.实验表明,E-YOLOv5s在自制井壁数据集上的检测精度相较YOLOv5s提升了4.0%,同时模型参数量和GFLOPs分别降低了44.9%、43.7%.E-YOLOv5s有助于推动井壁裂缝自动检测的应用.

Experimental Study of Longitudinal and Circumferential External Defect in Pressured Cylindrical Shells

Two cylindrical vessels under internal pressure are used for this work in order to study the influence of the position and size of defects on their elastic and elastoplastic behavior. One contains two external longitudinal semi-elliptic defects of different dimensions realized diametrically opposed. The other contains the same defects but is circumferential. These defects are carried out by elect-erosion. Strain gauges are placed in the neighborhood of the defects of which the purpose is to obtain the strain distribution. This work also allows the comparison between two defects of different dimensions, which are of the same shape or different shapes. These defects are longitudinal and circumferential semi-elliptical. The position of these defects relative to the inner radius of a cylindrical pressure vessel is considered. The deformations results are discussed.

基于眼动追踪的视觉交互式裂缝检测方法

定期检测混凝土表面的缺陷对延长基础设施的使用寿命能够起到重要的安全保障作用.针对人工检测混凝土效率不高,计算机视觉方法在复杂场景中易出现误判的问题,将基于眼动追踪的视觉交互方法引入损伤检测,提出一种智能裂缝检测方法.首先利用眼动跟踪技术提取人眼信息,实现对疑似裂缝特征信息的定位交互;然后结合训练的深度神经网络模型对疑似裂缝区域进行精细化识别和分割,实现复杂场景图像下裂缝识别和提取.在桥梁损伤数据集CODEBRIM中的裂缝类集上进行眼动交互定位实验和裂缝识别实验,结果表明,所提方法的定位精度为90.6%,判别精度为83.1%,与其他方法相比精度更高,且定位识别效率和准确率高,可用于结构健康监测.

考虑残余应力影响的典型钢结构对接焊缝缺陷定位研究

对接焊缝为典型的钢结构焊缝形式,其位置处的裂纹和气孔型缺陷的准确检测对于钢结构维护有着重要的意义,使用磁记忆检测技术对焊缝裂纹和气孔型缺陷进行定位时,传统的零点极值理论由于焊接残余应力的影响,难以区分残余应力、焊接裂纹和气孔型缺陷所产生的磁信号,从而在实际检测中造成缺陷定位的误判和漏判,因此,从焊接裂纹和气孔型缺陷和残余应力所在区域磁信号产生机理的不同入手,开展考虑残余应力影响下的焊接裂纹和气孔型缺陷定位检测研究。首先对焊接残余应力与裂纹和气孔型缺陷产生磁信号的机理进行分析,提出采用三维磁模量梯度极值判定方式来区分残余应力与裂纹和气孔型缺陷产生的磁信号;其次再进行焊接缺陷有限元COMSOL模拟,将所得磁信号代入梯度极值特征公式中进行表征判断;最后为了验证模拟表征判断的准确性,人工制作焊接钢板,提取三维磁信号进行分析。研究结果表明,理论分析、数值模拟与试验结果相互吻合,三维磁模量梯度极值能定位焊接缺陷并定量表征缺陷的长度,且裂纹和气孔型的三维磁模量梯度值远远高于无缺陷残余应力区域的梯度值。

氧化物共晶陶瓷激光增材制造裂纹缺陷形成及抑制研究进展

氧化物共晶陶瓷以其优异的高比强度、耐高温、耐腐蚀、抗氧化和抗蠕变等独特性能,被认为是超高温氧化腐蚀等极端环境下长期稳定服役的理想材料之一,在新一代高推重比航空发动机高温热端结构部件中具有巨大的应用前景。激光增材制造技术已成为近年来制备高性能复杂结构部件最具潜力的前沿技术,然而陶瓷在激光快速凝固过程中,裂纹缺陷极易产生,严重影响构件的成形质量和性能,成为制约工程化应用的关键。本文综述了激光近净成形和激光粉末床熔融两种典型陶瓷激光增材制造技术,分析对比了两种技术制备的不同形状陶瓷样件的裂纹形态特征,重点从微观组织形态特征、应力状态等角度探讨了激光增材制造氧化物陶瓷裂纹的形成机理,并进一步从工艺参数优化、成分设计、外场辅助等三个方面改善微观组织与减小热应力以抑制裂纹进行系统总结。最后指出氧化物共晶陶瓷激光增材制造在粉末特性、成形主次因素、成形技术研究等方面的未来发展趋势及突破方向。

X80管道环焊缝可靠性及其影响因素分析

针对管道环焊缝裂纹缺陷特征建立含裂纹缺陷管道环焊缝的多重极限状态函数,结合参数统计特征,形成基于Monte Carlo的X80管道环焊缝可靠性计算方法。同时进行管道环焊缝敏感性分析,得到各个参数的灵敏度。结果表明,管道壁厚为18.4 mm,管道外径为1219 mm,焊接工艺为自保护药芯焊丝半自动焊的X80管道环焊缝的失效概率在基于应力的失效准则1,基于应力的失效准则2和基于应变的失效准则下分别为8.2×10^(-7),5.9×10^(-7)和3.5×10^(-7)。它们均处于可接受安全水平内,无需进行维修或更换。外载荷、缺陷深度、断裂韧性和屈服强度对管道环焊缝的失效概率影响较大,可以通过控制外载荷,减小管道缺陷尺寸,提高屈服强度和断裂韧性来增强管道环焊缝的可靠性,确保管道安全运行。

PBX内部裂纹水浸超声全聚焦成像方法研究

高聚物粘结炸药(PBX)的内部裂纹检测对其使用安全性和结构完整性评价具有重要意义和工程应用价值。为了提高PBX内部裂纹缺陷的成像检测精度和图像质量,研究了曲面修正水浸超声全聚焦成像方法,并在此基础上进一步结合了延迟乘和波束形成(DMAS)技术,通过水浸法对Φ100.0 mm的半圆柱PBX的底部裂纹缺陷进行了超声成像检测研究,实现了对曲面构形PBX底部裂纹缺陷的高精度成像表征。实验结果表明,传统全聚焦成像算法的裂纹缺陷高度测量误差为12.0%,图像信噪比为1.37 dB;曲面修正后的裂纹缺陷高度测量误差为3.6%,图像信噪比为2.13 dB;而曲面修正结合DMAS算法成像的裂纹缺陷高度测量误差仅为0.4%,图像信噪比为5.32 dB。

熔焊缺陷对镍基高温合金GH4065A疲劳行为的影响

采用SEM和EBSD显微分析手段研究镍基变形高温合金GH4065A熔焊焊点的缺欠组织,并对比研究无焊点、有密排焊点和疏散排布焊点3种GH4065A带中孔薄板试样分别在低周和低高周复合疲劳载荷下的寿命差异和断裂方式差异。结果表明:焊点组织中存在未熔合孔洞、凝固裂纹和液化裂纹,是导致含焊点试样低周和低高周复合疲劳寿命大幅下降的主要熔焊缺陷。这些熔焊缺陷的存在使得疲劳裂纹从无焊点试样的中孔内表面处转为在焊点处优先形成,导致700℃/700 MPa低周疲劳寿命的下降幅度可达44%~83%。在600℃和700℃低高周复合载荷(静应力700 MPa+动应力100 MPa)下,熔焊缺陷不仅使得裂纹源从中孔内表面处转为在焊点处优先形成,也改变了裂纹扩展方式,增大了沿晶扩展倾向。这使得低高周复合疲劳寿命在两种温度下均大幅下降超过85%。由于密排焊点因距离中孔结构更近,密排焊点试样低周疲劳寿命低于疏散排布焊点试样,但这种焊点情况差异对低高周复合疲劳寿命的影响不大。

裂纹-孔洞缺陷下PVC涂层织物类膜材的撕裂行为

膜结构节点和边界处往往需要通过膜面开孔来实现关键部位的连接,孔洞边缘的应力集中会影响膜面的撕裂行为。为探究聚氯乙烯(polyvinyl chloride,PVC)涂层织物类膜材中孔洞对裂纹扩展行为的影响,开展了含有裂纹-孔洞缺陷的PVC涂层织物类膜材的单轴拉伸试验,分析了裂纹扩展全过程和撕裂机理,提出了适用于含裂纹-孔洞多缺陷PVC涂层织物类膜材撕裂强度的预测模型,并验证了模型的适用性。研究结果表明:含裂纹-孔洞缺陷的PVC涂层织物类膜材在中心撕裂过程中存在裂纹端扩展和孔端再扩展两阶段;定义了裂纹端临界撕裂荷载、裂纹端峰值撕裂荷载、孔端临界撕裂荷载和孔端峰值撕裂荷载4项撕裂特征指标,以衡量含裂纹-孔洞缺陷膜材的抗撕裂性能;孔洞的存在导致试样在孔端再扩展阶段的承载力提升,但随着孔洞尺寸增大,孔端的承载力提升效应减弱,裂纹端峰值撕裂荷载逐渐变为控制试样破坏的极限荷载;所提出的二次函数-指数函数应力场模型能有效地预测膜材的裂纹端临界撕裂应力和孔端临界撕裂应力。

火力发电厂蒸汽管道ZG15Cr1Mo1V铸造水压堵阀裂纹缺陷成因分析

铸造水压堵阀裂纹缺陷已是火电金属监督检验典型问题之一,为探究裂纹缺陷成因,指导现场检验和缺陷处理,本文以ZG15Cr1Mo1V主汽和再热热段堵阀大规模裂纹缺陷为研究对象,从材料特性、水压堵阀结构特征、制造工艺、服役特点等方面展开分析。结果表明:堵阀制造阶段已存在微小原始缺陷,运行服役后扩展形成裂纹缺陷;材料特性和制造工艺决定其存在原始缺陷的倾向较大;分型铸造方式导致阀体两侧缺陷差异明显;水压试验时堵阀仅前侧受力的状况造成阀体前后侧裂纹缺陷差异;相贯线过渡区域、口环连接区域易形成缩松、微裂纹等缺陷,且过渡区域多为应力集中区,导致裂纹缺陷易在此富集与扩展;制造热处理和运行服役阶段温度、压力的作用,促使裂纹缺陷的生成与扩展。

近表面疲劳裂纹的水浸式非共线横波混频检测方法研究

针对近表面疲劳裂纹检测问题,开展了水浸式非共线横波混频检测方法研究。在材料非线性、水/试件界面和疲劳裂纹不同非线性源情况下,分析相互作用角和频率比对混频非线性效应的影响规律。在此基础上,对有无近表面疲劳裂纹试件沿着深度方向进行扫查检测。结果表明,在不同非线性源情况下,混频特征图具有显著差异,根据混频特征图中和频纵波峰值及其对应相互作用角可对试件近表面疲劳裂纹进行检测;水/试件界面对近表面疲劳裂纹非共线横波混频检测具有一定影响,去参考检测方法可显著降低水/试件界面的影响,实现对近表面疲劳裂纹的有效检测。

CrMoV与NiCrMoV异种钢焊接接头的高周疲劳性能及寿命模型

对CrMoV与NiCrMoV异种钢焊接接头开展室温及400℃下的高周疲劳试验,并对失效试样进行断口分析,研究异种钢焊接接头的高周疲劳失效机理.结果表明,接头疲劳S-N曲线呈现连续下降形式,在高周疲劳过程中未见疲劳极限平台,失效位置均位于焊缝金属区域,并且集中在显微硬度值最低的结构弱区;随着应力幅值的下降,裂纹萌生模式由表面和内部萌生的竞争转变为内部微缺陷萌生占主导,内部焊接气孔微缺陷是主要裂纹萌生源;根据Murakami模型得到的疲劳极限分散性较大,与高周疲劳寿命未呈现出明显规律,通过引入Z参量模型,指出焊接接头的高周疲劳寿命由应力水平、微缺陷有效尺寸和相对深度等因素共同决定,Z参量与高周疲劳寿命具有很好线性关系.