Analysis and Modeling of Friction Stir Processing-Based Crack Repairing in 2024 Aluminum Alloy

Abstract A friction stir processing-based method was used to repair cracks in the 2024 aluminum alloy plates. The temperature field and plastic material flow pattern were analyzed on the basis of experimental and finite element simulation results. Microstructure and tensile properties of the repaired specimens were studied. The results showed that the entire crack repairing was a solid-phase process and plastic materials tended to flow toward the shoulder center and then resulted in the repairing of cracks. Meanwhile, the coarse grain structures were refined in repaired zone （RZ）, while the grains in thermal-mechanically affected zone and heat-affected zone were elongated and driven to grow up. Meanwhile, large phases are crushed into small particles and dispersed inside the RZ. Finally, the strength of the repaired specimens can be restored dramatically and their ductility can be partially restored. After heat treatment, the tensile properties of the repaired specimens can be further enhanced.

Computer-vision-guided semi-autonomous concrete crack repair for infrastructure maintenance using a robotic arm

Engineering inspection and maintenance technologies play an important role in safety,operation,maintenance and management of buildings.In project construction control,supervision of engineering quality is a difficult task.To address such inspection and maintenance issues,this study presents a computer-vision-guided semi-autonomous robotic system for identification and repair of concrete cracks,and humans can make repair plans for this system.Concrete cracks are characterized through computer vision,and a crack feature database is established.Furthermore,a trajectory generation and coordinate transformation method is designed to determine the robotic execution coordinates.In addition,a knowledge base repair method is examined to make appropriate decisions on repair technology for concrete cracks,and a robotic arm is designed for crack repair.Finally,simulations and experiments are conducted,proving the feasibility of the repair method proposed.The result of this study can potentially improve the performance of on-site automatic concrete crack repair,while addressing such issues as high accident rate,low efficiency,and big loss of skilled workers.

Repairing of Macroscopic Ceramic Cracks by Tiny Expansion Filling Composites

Using SiC, Al, Al_2O_3, ZrO_2 and Y_2O_3 as raw materials, based on chemical reactions those can cause expansion effect to compensate for the sintering shrinkage at elevated temperature among them, such as Al oxidizes to Al_2O_3, SiC converts to SiO_2, and their reaction productions react further to form mullite (3Al_2O_3·2SiO_2), a sort of tiny expansion composites were prepared and designed which can be used to repair macroscopic cracks of sintered ceramics. The total expanding extent can be adjusted by proportion of raw materials or control of sintering temperature. Filling this expandable ceramic ingredient in cracks of real ceramic part in a designed paste state, cracks could be repaired by a re-sintering process.

Fundamental Research of Repairing Macroscopic Cracking of Ceramic by Directed Metal Oxidation Method

This study focused on testing the possibility of formation of alumina ceramic phase using aluminum/alumina mixture with other low content sintered at high temperature. It was found from XRD and SEM that aluminium is oxidized to alumina completely and the samples formatted ceramic phase accompanying minute expansion. This research supplies a new method of repairing macroscopic cracking of ceramic.

Laser repairing surface crack of Ni-based superalloy components

Surface crack of components of the cast nickel base superalloy was repaired with twin laser beams under proper technological conditions. One laser beam was used to melt the substrate material of crack, and the other to fill in powder material to the crack region. The experimental results show that the surface crack with the width of 0.1 ～ 0.3?mm could be repaired under the laser power of 3?kW and the scanning speed of 6 ～ 8?mm/s. The repaired deepness of crack region is below 6.5?mm. The microstructure of repaired region is the cellular crystal, columnar crystal dendrite crystal from the transition region to the top filled layer. The phases in repaired region mainly consisted of supersaturated α Co with plenty of Ni, some Cr and Al, Cr 23 C 6, Co 2B, Co Ni Mo, Ni 4B 3, TiSi and VSi. The hardness of filled layer in repaired region ranged from HV 0.2 450 to HV 0.2 500, and the hardness decreases gradually from the filled layer to joined zone.

Formation mechanism of transverse crack in repair welding for thick plate of Q345 high strength steel

Transverse cracks occur usually in repair welding for thick plate of high strength steel. It needs multiple times of repair welding. The quality of production and deliver deadline will be influenced. Therefore, it is very significant to investigate the cause and control of transverse crack in repair welding. In this paper, both ends restraint crack experiment is developed to produce delay transverse crack for high strength steel. Metallographic results show that four types of cracks are found in repair welding metal zone and heat affected zone. Large chevron transverse cracks are found in repair welding zone. Lots of micro transverse cracks are found in inter-layer repair welding metal zone, root HAZ and two ends of repair welding individually. The distribution character and formation mechanism of the transverse crack are further analyzed through hardness testing and residual stress measurement.

Influence of Mineral Admixtures on the Electrodeposition Healing Effect of Concrete Cracks

Two types of solutions（Zn SO4, Mg SO4） were selected to study the influence of mineral admixtures on the electro-deposition healing effect of concrete cracks. Four parameters（i e, rates of weight gain, surface coating, crack closure and crack filling depth） were measured. The mineral composition of electro-deposits in the cracks was analyzed. The study shows that the healing effect of mortar specimens with 10% fly ash is the worst, while the healing effect of mortar specimens with 20% fly ash is better than that of the specimens without fly ash. The rates of weight gain, surface coating, crack closure and crack filling depth decrease with increasing content of the ground granulated blast-furnace slag（GGBS）. The mineral admixtures have no influence on the composition of deposits.

活性改性剂合成及其对环氧胶黏剂力学与界面粘接性能的影响

综合考虑环氧胶黏剂的施工性能、力学性能及与砂浆界面的粘接性能,利用三羟甲基丙烷三缩水甘油醚(TMPGE)与1,4-丁二醇(BDO),通过控制反应物物质的量比以及反应时间制备了四种低环氧值兼具高羟基含量的预聚体(PPM)。通过1H-NMR、盐酸-丙酮法及凝胶渗透色谱(GPC)对PPM进行了表征。进一步研究了PPM对改性环氧胶黏剂工作性能、固化力学性能、与水泥砂浆粘接强度以及表面性质的影响。结果显示:延长反应时间以及增加BDO用量使PPM的数均分子量更大、环氧值更低。四种PPM改性后,胶黏剂的放热峰值温度降低,可操作时间延长。同时,PPM使环氧固化物的延性显著增加。四种PPM改性后使环氧与水的接触角降低,固化物表面的极性组分升高。XPS分析表明,PPM使环氧固化物的羟基含量显著提高。最后,PPM使胶黏剂对湿砂浆基体的粘接强度提高了一倍以上。

Influence of Additives on the Formation of Electrodeposits in the Concrete Cracks

The electrodeposition method for rehabilitation of the cracked reinforced concrete,based on the electrochemical technique,was presented here.The aim of this study was to evaluate the influence of additive on the formation of electrodeposits in the concrete cracks.Cracked mortar specimens of size 40 mm×40 mm×160 mm were immersed in electrolyte solutions（ZnSO4,MgSO4）,and a constant current was applied between the reinforced steel and the external electrode for 15 days.Rate of surface coating,rate of crack closure and rate of crack filling depth were measured and the appearance of electrodeposits in the cracks was observed.The experimental results demonstrate that,under the experimental conditions,rate of surface coating and crack filling depth increase,while rate of crack closure decreases as the percengtage of additive increases.In addition,the electrodeposits become more denser and the microstructure varies with additive content,while the compositions of electrodeposits do not change.

Effect of Pulse Parameters on Deposition in Concrete Crack using Pulse Current Electro-deposition

To evaluate the effect of pulse parameters on the formation of electrodeposits in concrete cracks, five different types of pulse current were set up, and ZnSO_4 and MgSO_4 solutions were used as the electrolytes. The rate of weight gain, rate of surface coating, rate of crack closure and crack filling depth were measured. Scanning electron microscopy was used to assess the morphology of the electrodeposits, and energy dispersive spectroscopy was used to analyze the mineral composition of the electrodeposits in the cracks. The experimental results demonstrate that, among five different pulse parameters, when T_（on）/T_（off）=0.8 ms/0.8 ms, the healing effect of electro-deposition is the best. The pulse mode hardly affects the mineral composition of the electrodeposits but changes the micromorphology. In addition, for both ZnSO_4 and MgSO_4 solutions, when T_（on）/T_（off）=0.8 ms/0.8 ms, the crystal structure of the electrodeposits is the most uniform and the densest.

古建筑木构件开裂机制、评估与加固研究进展

开裂作为古建筑木构件最常见的残损类型之一,影响木构件的长期服役性能,是古建筑稳定性与安全性评估的重要考查内容。本文从古建筑木构件开裂情况、原因、影响,评估方法及修复加固等方面,系统梳理古建筑木构件开裂残损相关研究成果。分析发现我国古建筑木构件开裂的主要原因为木材干缩与受力破坏,主要类型为纵向开裂,开裂可降低木构件力学性能,也可为其他不利因素作用于木构件提供条件。目前主要通过实际试验与数值模拟评估开裂对木构件性能的影响,利用金属材料、纤维增强复合材料(fiber reinforced polymer,FRP)与高分子树脂材料对开裂木构件进行修复加固。然而,由于古建筑的特殊性与木材变异性,仍需进一步探索木构件的不同尺度开裂机制,开发适用于古建筑开裂木构件的检测、评估与加固方法,建立科学系统性的古建筑保护体系。

适宜水工混凝土内环境的矿化微生物梯度驯化优选

水工混凝土内部高碱性环境限制了微生物混凝土的自修复效能。利用梯度驯化方法可提高矿化微生物对高碱度的耐受性,优选出适宜混凝土孔隙内环境并具备高诱导矿化沉积能力的增强嗜碱型微生物。首先,在实验室高碱性环境下,对比巨大、科氏、枯草、巴氏等4种芽孢杆菌的活性及诱导矿化沉积量,初选耐碱性较好的微生物并对其开展耐碱性梯度驯化;随后,综合分析驯化微生物对混凝土力学性能、吸水性、渗透性和自愈能力的影响,通过扫描电子显微镜和X射线衍射对矿化产物微观形态和组成进行分析。结果表明:相较于巨大、科氏和枯草芽孢杆菌,巴氏芽孢杆菌在高碱性条件下表现出更强的活性,梯度驯化技术可进一步提高巴氏芽孢杆菌在高碱性环境中的活性,并证实通过该方法增强的耐碱性具有后代保留的特性;与掺未驯化微生物组试样相比,掺驯化微生物混凝土试样养护28 d的抗压强度提高了16.59%,吸水系数降低了37.74%,渗透系数减小了19.22%;掺驯化微生物混凝土试样的裂缝自修复试验得到裂缝最大修复宽度为0.57 mm,超过了未驯化微生物组的0.44 mm。本研究为基于微生物诱导矿化沉积技术的微生物水工混凝土研发和应用提供理论依据和技术支撑。

水工混凝土矿化微生物固载及自修复试验研究

直接内掺方式制备微生物自修复混凝土会因拌合的机械挤压摩擦、生存环境受限等因素影响矿化微生物的长期活性。本文选择巴氏芽孢杆菌为矿化微生物,以膨胀珍珠岩和陶粒为微生物载体,以水泥浆和偏高岭土浆液为载体包覆材料,通过试验优选有助于微生物释放和保护的载体及其合理粒径、包覆材料,并研究微生物固载对裂缝自修复效果的影响。结果表明:掺入定量的膨胀珍珠岩的水工混凝土试样劈裂裂缝处拉裂面积比更大,作为水工混凝土微生物固载材料时较陶粒更能有效释放矿化微生物;偏高岭土浆液较水泥浆更适合作为载体的包覆材料,其包覆的微生物14 d存活率为86.63%,有效保证了固载微生物的长期活性;对微生物进行膨胀珍珠岩固载和偏高岭土浆液包覆,修复养护90d裂缝最大修复宽度为0.616mm,高于直接内掺的0.453mm,有效改善了混凝土试件的裂缝自修复效果。

The Crack Self-healing Properties of Cement-based Material with EVA Heat-melt Adhesive

An experimental program was carried out to investigate whether EVA （ethylene vinyl acetate copolymer） heat-melt adhesive can potentially act as a self-healing agent in cement-based material. The effects of incorporation of EVA and heating on the properties of mortar were studied. Self-healing capacity of EVA specimens was also verified. The experimental results show that the addition of EVA would not greatly affect original characteristics of the matrix when EVA content was less than 5%; the interface between EVA and cement matrix was well improved after heating, which allows a significant improvement in flexural strength and toughness of specimen; pre-damaged specimens in various degrees （30%, 50% and 70%） were effectively repaired by EVA and the repair efficiency all exceeded 100%.

含裂纹油气管道CFRP修复数值研究

裂纹缺陷引发的管道强度下降是埋地油气管道的主要事故原因之一,而高强度、高模量、耐腐蚀的碳纤维增强树脂基复合材料(CFRP)可以很好地缠绕修复缺陷管段。针对有/无CFRP修复20钢含矩形裂纹缺陷管道,采用ANSYS有限元软件模拟内压载荷作用下含裂纹管道修复前后的响应过程,分析了裂纹角度、裂纹长度、裂纹深度、修复长度及修复厚度等参数对含裂纹管道强度的影响规律。研究表明,含裂纹管道的最大Mises等效应力随着裂纹与管道轴向夹角的减小、裂纹长度和深度的增大而增大,内压的增大加剧了缺陷参数对管道强度的影响程度。在工程中要严格控制裂纹在深度和长度方向的扩展,在内部减压后再维修含裂纹管道。CFRP修复厚度是修复后含裂纹管道强度的主要影响因素,随着修复厚度一定程度的增大,含裂纹管道最大Mises等效应力呈线性下降。

Corrosion Resistance of Steel in Cracked Reinforced Concrete after Electro-depositon Treatment

An electro-deposition method has been recently proposed to repair cracked reinforced concrete. To evaluate the corrosion resistance of the reinforcing steel in cracked concrete, three different parameters including type of auxiliary electrode, electrode distance, and current density were studied. Tafel polarization curve was used to evaluate the corrosion resistance of the steel. Self-corrosion potential and corrosion current of the steel were tested. The results indicate that the corrosion resistance improvement of the reinforcing steel is optimal as prism titanium mesh is applied as auxiliary electrode, followed by the flaky titanium mesh and the column titanium bar. When the electrode distance is 60 mm, the corrosion resistance improvement of the reinforcing steel is optimal, and with 80 mm electrode distance, the corrosion resistance improvement is the poorest. The property falls in between them when 40 mm electrode distance is used. Moreover, the corrosion resistance improvement of the reinforcing steel increases as the current density goes up.

矿用喷涂堵漏风自修复材料性能研究及工程应用

喷涂堵漏风是防止煤自燃的有效手段之一。针对传统水泥基喷涂堵漏风材料脆性大、易开裂、堵漏风效果差的弊端,提出以微生物及结晶矿物为自愈合剂,研制出生物胶囊和矿物胶囊以及一种生物–矿物–纤维协同自修复材料。研究了不同养护湿度和养护时间对材料裂缝自修复能力的影响。结果表明:当养护湿度为100%相对湿度、养护时间为35 d时,研制的生物胶囊和矿物胶囊可以将裂缝完全修复,裂缝最大修复宽度为1260μm。采用扫描电子显微镜(SEM)和X射线能谱仪(EDS)探究了自修复材料裂缝区域修复产物的晶型及元素组成,发现裂缝处的修复产物为球碳镁石、花瓣状的水菱镁矿以及大量由细菌矿化产生的球形方解石,这些修复产物在一定程度上起到了密闭裂缝的作用;EDS能谱分析证实了修复产物为MgCO_(3)和CaCO_(3)。当养护湿度为100%时,材料具有最高的堵漏风率(97.15%),比同养护条件的对照组试样高出73.62%。最后将自修复材料用于沿空煤柱喷涂堵漏风,结果显示该材料在6个月内未发现明显裂隙,与传统水泥砂浆相比,该材料具有更长的使用寿命和更好的预防效果。

Fe-SMA主动加固钢桥面横隔板弧形切口疲劳裂纹实桥应用研究

为确定铁基形状记忆合金(Fe-SMA)主动加固正交异性钢桥面板横隔板弧形切口疲劳裂纹的可行性,以某在役钢箱梁斜拉桥为背景进行实桥加固研究。根据现场横隔板弧形切口的开裂特征,在对裂纹钻孔止裂的基础上,提出利用Fe-SMA材料对横隔板弧形切口裂纹进行粘贴加固的方案,并进行加固施工。通过现场测试得到Fe-SMA板条热激活过程的应变和温度变化,分析Fe-SMA板条和钢板之间的相互作用及加固机理。结果表明:粘贴Fe-SMA板利用Fe-SMA热驱动形状记忆效应可有效便捷地为结构施加预压应力,实现对受损部位的主动加固;经过Fe-SMA联合止裂孔修复后,热驱动作用下的Fe-SMA可以产生200~240 MPa的预拉应力,并在钢板止裂孔边缘施加43~90 MPa的压应力,可有效阻止裂纹进一步扩展;加固体系在加热激活过程完好可靠,当控制一侧加热区域中部温度为200℃时,热传导作用下非加热区域中部的温度为60℃以下,而背面总体温度基本在90℃以下。

基于微生物矿化的水泥基材料表面防护及裂缝修复

微生物诱导碳酸钙沉淀技术是一种比较新颖、绿色环保的混凝土修复技术。针对混凝土工程裂缝等缺陷,试验研究微生物水泥对混凝土表面及裂缝的修复防护效果。研究表明,试件表面先涂覆菌液再喷洒营养液,经多次修复后,试件表面均被沉积的碳酸钙膜层覆盖,表面裂缝也均被封闭,覆膜层坚硬、致密。试件毛细吸水系数得以大幅降低,降低率达90%以上,修复效果的表征应采用毛细吸水系数及毛细吸水系数降低率综合评价。裂缝中填入石英砂(粉)作为修复基材,经微生物水泥多次注入后抗折强度均得到了不同程度的提高,特别是缝宽3.0 mm试件修复后的抗折强度最高恢复至原基准试件的78%,抗折强度提高了74%,修复效果明显;其他缝宽试件的抗折强度恢复率为60%~68%,提高率为18%~30%,裂缝越宽,修复效果相对越好。

PROBABILITY OF RANDOM EVENTS OF INSPECTION AND REPAIR AND MAINTAINING RELIABILITY OF STRUCTURES

Reliability analysis of the inspected and repaired structure requires dealing with a large number of complex random events. Considering many kinds of random factors, a probability of these random events existing possibly in the inspection and repair process and reliability analysis methodologies are proposed. A systematic dynamic reliability model is given for structures in service under the scheduled inspection and repair.