MODIFIED LAYER REMOVAL METHOD FOR MEASUREMENT OF RESIDUAL STRESS DISTRIBUTION IN THICK PRE-STRETCHED ALUMINUM PLATE

The integrated structure parts are widely used in aircraft. The distortion caused by residual stresses in thick pre-stretched aluminum plates during machining integrated parts is a common and serious problem. To predict and control the machining distortion, the residual stress distribution in the thick plate must be measured firstly. The modified removal method for measuring residual stress in thick pre-stretched aluminum plates is proposed and the stress-strain relation matrix is deduced by elasticity theory. The residual stress distribution in specimen of 7050T7451 plate is measured by using the method, and measurement results are analyzed and compared with data obtained by other methods. The method is effective to measure the residual stress.

Impact Damage Identification of Aluminum Alloy Reinforced Plate Based on GWO-ELM Algorithm

As a critical structure of aerospace equipment,aluminum alloy stiffened plate will influence the stability of spacecraft in orbit and the normal operation of the system.In this study,a GWO-ELM algorithm-based impact damage identification method is proposed for aluminum alloy stiffened panels to monitor and evaluate the damage condition of such stiffened panels of spacecraft.Firstly,together with numerical simulation,the experimental simulation to obtain the damage acoustic emission signals of aluminum alloy reinforced panels is performed,to establish the damage data.Subsequently,the amplitude-frequency characteristics of impact damage signals are extracted and put into an extreme learning machine(ELM)model to identify the impact location and damage degree,and the Gray Wolf Optimization(GWO)algorithm is employed to update the weight parameters of the model.Finally,experiments are conducted on the irregular aluminum alloy stiffened plate with the size of 2200 mm×500 mm×10 mm,the identification accuracy of impact position and damage degree is 98.90% and 99.55% in 68 test areas,respectively.Comparative experiments with ELM and backpropagation neural networks(BPNN)demonstrate that the impact damage identification of aluminum alloy stiffened plate based on GWO-ELM algorithm can serve as an effective way to monitor spacecraft structural damage.

Influence of dent on residual ultimate strength of 2024-T3 aluminum alloy plate under axial compression

Drop-weight impact tests were conducted on 2024-T3 aluminum plates with five types of impactors, and then the effects of the dent on the residual ultimate strength of the 2024-T3 specimens were investigated through axial compression tests. Results indicate that with increase in dent depth, the five types of dents affect the ultimate strength of the plate in different trends. Nevertheless, other than the plate global deflection caused by impacting, the dent itself has unremarkable effect on the ultimate strength. The mathematical expressions are derived regarding the relationship between impact energy factor and the dent depth factor as well as the compressive ultimate strength reduction rate and the dent depth factor.

Relationship between microstructure and mechanical properties of 5083 aluminum alloy thick plate

The microstructure and mechanical properties of 105 mm thick 5083 aluminum alloy hot rolled plate were investigated by metallurgical microscope, scanning electron microscope and tensile testing machine, and three major characteristic problems in mechanical properties inhomogeneity were explained. The results show that the mechanical properties of the rolled plate are inhomogeneous along the thickness direction. From the surface to the center, the strength shows an inverted "N" shape change and the elongation presents a semi "U" shape change. Several similar structural units composed of long fibrous grains(LFG) and short fibrous grains bands(SFGB) exist in a special layer(Layer 2) adjacent to the surface. This alternating layered distribution of LFG and SFGB is conducive to improving the plasticity by dispersing the plastic deformation concentrated on the boundary line(BL) between them. However, their different deformability will cause the alternation of additional stresses during the hot rolling, leading to the strength reduction. The closer the location to the center of the plate is, the more likely the recovery rather than the recrystallization occurs. This is the possible reason for the unnegligible difference in strength near the central region(Layer 4 and Layer 5).

Effect of pre-deformation of rolling combined with stretching on stress corrosion of aluminum alloy 2519A plate

The effect of the pre-deformation of rolling combined with stretching on the stress corrosion cracking resistance of aluminum alloy 2519A was studied by means of the slow strain rate technique at 10-6 s-1. The tensile strength and stress corrosion index of the alloy plate with 7% rolling plus 3% perpendicular stretching were 481 MPa and 0.0429, respectively, showing better mechanical property and stress corrosion cracking resistance than those with 4% rolling plus 3% parallel stretching or 7% rolling plus 3% parallel stretching, which is due to its finer and denser precipitates within the grains, discontinuous grain boundary precipitates, as well as more narrow precipitate-free zone width. Such microstructure is attributing to the denser and more homogeneously distributed dislocations which are produced by the pre-deformation.

Transverse stress-strain evolution during welding of thin aluminum alloy plate

The FE simulation results of transverse stresses and strains during welding of thin aluminum alloy plate are presented. The results indicate that restraint condition is the main factor that determines whether or not hot cracking will occur. With rigid restraint hot cracking (crater cracking) will occur at the arc-stopping end, and such cracking usually will not occur without external restraint. But under restraint-free condition it is easy for terminal cracks to occur.

High-velocity impact responses of 2618 aluminum plates for engine containment systems under combined actions of projectile form and oblique angle

Ballistic impact tests were carried out with examined projectiles of the Ti-6Al-4V titanium alloy to investigate the impact response of the 2618 aluminum plates at a nominal velocity of 210 m/s. The influence of projectile forms and oblique angles on damage formation was particularly discussed by applying different loading conditions such as multiple projectile forms and oblique angles. Additionally, the numerical simulation method was employed to provide further insight into the characteristics of damage and target responses. The Johnson-Cook(J-C)constitutive model with revised failure parameters was used to support the simulations to assess target responses and characteristics of the damage created from different impact conditions. Results show that there is a significant transition in the deformation mode as changes of the projectile form are applied. Moreover, the cracks on the back of the 2618 aluminum alloy plates impacted by the solid plate projectile and the hollow blade projectile tend to locate at different positions, which are supposed to be influenced by local bending and stretching. The work in this paper may provide guidance for the design of fan blade containment systems.

Residual stress in quenched 7075 aluminum alloy thick plates

The influence of quenching water temperature, pre stretching amount and aging temperature and times on residual stress in 7075 aluminum thick plate was studied by the measurement of residual stress using drilling hole method. The results indicate that residual stress decreases by 30% with increasing quenching water temperature from 40 ℃ to 80 ℃, 20% with increasing aging temperature from 100 ℃ to 180 ℃,and 20% with increasing aging times from 5 h to 25 h. Also, residual stress decreases to zero with increasing pre stretching amount to approximately 2%. Hence, residual stress in 7075 aluminum thick plate is reduced by the control of quenching water temperature at 80 ℃ and with pre stretching amount of about 2%. An optimal aging temperature and time should be systemically investigated to obtain combination of high mechanical performances and lower residual stress for manufacturing of 7075 aluminum alloy thick plates.

Influence of aluminum solid fraction on property of steel-mushy aluminum bonding plate

The interfacial shear property of steel-mushy aluminum bonding plate was studied, and the relationship between aluminum solid fraction and the interfacial shear strength of bonding plate was determined. The results showed that when aluminum solid fraction is 34.3 %, the maximum interfacial shear strength of bonding plate is 71 .0 MPa.

Multichip on Aluminum Metal Plate Technology for High Power LED Packaging

Multichip on Ahnnintnn Metal Plate（MOAMP） technology with simple structure and low thermal resistance is developed for effective heat reratrval of Light Emitting Diode（LED） p-n junction and LED lighting module to have high reliability. The thermal resistance of LED modules was numerical and experimental. Thermal resistance from the jtnction to aluminten metal plate, considering input power of IFD module using MOAMP technology, is 3.02 K/W, 3.23 K/W for the measured and calculated, respectively. We expect that the reported MOAMP technology with low thermal resistance will be a promising solution for high power LED fighting modules.

Immersing Treatment of Steel Plate Surface in Steel-Aluminum Solid to Liquid Bonding

The interfacial status of the steel-aluminum solid to liquid bonding plates (their steel plate surfaces were or were not immersed in flux aqueous solution) were measured by using SEM (Scanning Electron Microscope) and X-ray diffraction . The results showed that the layer of flux (the minimum thickness was 15 μm on the steel plate surface) could protect the steel plate surface from oxidizing effectively at high temperature in solid to liquid bonding. The melt temperatUre of the flux should be lower than 580 ℃ so that it could be melted and removed completely. No. 1 flux (patent product made by the author) made up of halogeindes could also force liquid aluminum to infiltrate into steel plate surface and thus the interfacial shear strength of the bonding plate was rather large.

粘铝合金板加固RC梁抗弯性能试验及正截面承载力

为了探讨铝合金板厚度与端部U形铝合金箍板构造对RC梁破坏机理及抗弯性能的影响,对16根铝合金板加固RC梁进行了4点弯曲静力加载试验。在试验梁底铝合金板的表面以及试验梁跨中截面的顶面、侧面粘贴应变片,在试验梁底跨中、梁顶两端支座布置百分表。为了推导铝合金板加固RC梁的正截面承载力计算式,基于试验得到的破坏机理,通过引入6个基本假定,分析了5种不同破坏模式的相对受压区高度。建立了各破坏模式下铝合金板加固RC梁的正截面承载力计算式,并将其与引入文献中的试验结果进行了对比分析。结果表明:试件破坏形态包括适筋破坏、端部铝合金板与结构胶剥离、端部铝合金板与梁剥离及中部铝合金板剥离4种情况;当端部设置U形铝合金箍板时,可有效抑制端部铝合金板发生剥离,使钢筋与铝合金板的材料性能得到充分发挥,试件承载力与延性明显提升;当铝合金板厚度分别为2~6 mm时,试件承载力随铝合金板厚度的增加而提高;端部设置U形铝合金箍板可有效防止端部铝合金板发生剥离,但试件仍可能会出现中部铝合金板剥离现象;当试件出现适筋破坏特征时,试件抗弯承载力的计算值与试验值比值均在1以下。本研究所提计算式具有明显的规律性和适用性,可为工程实际设计提供参考。

2023年积石山地震重要公共建筑吊顶震害调查分析

对2023年6.2级积石山地震中公共建筑内部吊顶开展了震害调查及分析,并以积石山县大河家镇大河家中学教学楼、中西医结合医院门诊楼以及中国邮政银行会议室3处典型震害为例,分析了在以往的公共建筑吊顶震害调查及研究中较少涉及的铝扣板吊顶、间接悬挂式吊顶的新震害现象及典型震害特征。研究表明:铝扣板边角锋利,卡入式连接对龙骨网格平整度要求较高,此类吊顶如若用于抗震要求较高或人员较为密集的建筑内,建议进行专门的抗震分析,以避免坠板伤人或妨碍人员逃生。此外,在吊顶地震损伤评估中,除坠板率外,还应考虑龙骨网格变形等因素。应加强吊顶中照明单元与主体结构连接的可靠性以避免其在地震中出现大量坠落。研究结果可为公共建筑吊顶抗震研究与工程应用提供参考。

大厚度铝合金板疲劳裂纹扩展特性研究现状及关键问题探讨

试样厚度增加引发的裂纹扩展“马鞍效应”是厚度与三维裂纹端部应力应变场内在联系的表象反映,在未得出这种内在联系机理与规律的情况下,基于传统模型对大型机械设备中的厚板及变厚度板进行损伤容限评定必然存在很大的风险。以大厚度铝合金板为研究对象,从三维裂纹端部应力应变场与裂纹扩展形貌之间的关系、疲劳裂纹扩展的厚度效应、腐蚀与疲劳共同作用下裂纹扩展机理与模型等三个方面,对裂纹扩展相关问题的研究现状进行了总结分析,对大厚度铝合金板疲劳裂纹扩展特性研究的关键问题进行了探讨。

基于电接触强化的铝合金表面电刷镀镍层改性研究

[目的]对铝合金进行表面处理可提高其硬度和耐磨性,拓宽铝合金材料在机械零件方面的应用。[方法]采用电刷镀技术在1060铝合金表面制备Ni镀层,再通过电接触强化技术对Ni镀层进行改性。采用扫描电子显微镜和维氏硬度计考察了Ni镀层电接触强化前后的微观组织和显微硬度。通过摩擦磨损试验对比了1016铝合金及Ni镀层电接触强化前后的耐磨性。[结果]经电接触强化后,Ni镀层内部的裂纹及孔洞类缺陷减少,晶粒间隙减小,致密性提高,显微硬度增大到524.4~560.3 HV0.1范围内。1016铝合金在摩擦磨损试验后存在较深的犁沟和剥落,耐磨性较差。Ni镀层的耐磨性优于1016铝合金,但在摩擦过程中会发生剥落。经电接触强化的Ni镀层在摩擦过程中摩擦因数平稳,表面只是轻微擦伤,耐磨性最佳。[结论]结合电刷镀镍和电接触强化技术可显著提高铝合金的表面性能。

基于Lamb波与虚拟时间反转的延时叠加成像算法

针对传统的延时叠加成像容易产生伪像而导致缺陷不易识别且成像清晰度差的问题,提出采用虚拟时间反转技术与椭圆定位法初步定位损伤区域,进而在对应的时间窗内截取差信号,最后结合延时叠加成像技术解决了伪像和清晰度问题。以ABAQUS软件仿真的方式模拟Lamb波在损伤铝板中的传播过程,首先利用虚拟时间反转法对初次响应信号进行处理而获得聚焦重构信号,然后利用准确的时间延时作椭圆以初步定位范围,从而得到对应的时间窗来截取差信号,最后结合延时叠加成像技术对损伤进行成像。仿真和试验结果表明:该方法降低了操作难度,提高了成像清晰度,能准确有效地识别损伤位置,提高了铝板的损伤定位检测精度。

前箱熔体温度对8011铝合金铸轧板坯组织性能的影响

为了稳定提高双零铝箔用铸轧坯料质量,使用电解铝液配料生产规格为7.0 mm×1300 mm的8011铝合金铸轧铝板卷,并利用光学显微镜(OM)、扫描电镜(SEM)、能谱仪(EDS)及电子万能拉伸试验机等手段,研究了不同前箱铝熔体温度(680,690,700,710℃)对8011铝合铸轧板坯微观组织和力学性能的影响.结果表明:随着前箱熔体温度的升高,铸轧板坯晶粒的尺寸呈略微增大再急剧变大的趋势,其抗拉强度和断后伸长率均呈先缓慢降低后急剧下降的趋势;当前箱熔体温度控制在680~700℃时,可获得综合力学性能较佳的铸轧板坯,其平均纵向抗拉强度和横向抗拉强度分别不低于141.87 MPa和138.84 MPa,平均纵向断后伸长率和横向断后伸长率分别不低于29.8%和26.4%.

高精度铝板矫直机辊系拉力条件提升方案

结合高精度铝板矫直机的辊系参数特点,分析了辊系拉力条件对设备矫直能力的影响,介绍了采用夹送辊装置改善拉力条件、提升矫直能力的技术方案。

表面改性对铁基非晶合金微波吸收性能的影响

目的旨在调节铁基非晶合金(IAA)粉体复合材料的微波吸收性能。方法先在铁基非晶合金粉体表面采用磁控溅射局部覆盖铝膜,再使用KH560硅烷偶联剂对粉体进行绝缘包覆。通过XRD、SEM和FT-IR分别对粉体进行材料表征,采用VSM和传输反射法分别测试样品的电磁性能。结果镀铝后铁基非晶合金粉体的复介电常数实部εʹ提高了56.1%,复介电常数虚部εʺ提高了132.4%。绝缘包覆后铁基非晶合金粉体的εʹ降低变为铁基非晶合金的32.6%,εʺ变为铁基非晶合金的25.1%。镀铝再包覆KH560的铁基非晶合金粉体的εʹ和εʺ则分别变为铁基非晶合金的43.5%和36.6%,其复介电常数实部和虚部比镀铝后的样品低,比单纯用KH560包覆后的样品高,显示出镀铝可补偿因KH560绝缘包覆而带来的介电损耗能力下降,有利于调节KH560绝缘包覆的粉体材料的电磁性能。结论对铁基非晶合金粉体的绝缘包覆,改善了相应材料的高频吸收性能,但牺牲了其低频吸收性能,为了弥补这个不足,提出在铁基非晶合金粉体表面局部覆盖铝膜,再进行绝缘包覆,期望在绝缘包覆后,粉体仍有较高的介电损耗能力,达到调节材料中低频电磁波吸收能力的目的。样品模拟反射率曲线显示,样品厚度在2~3 mm时,铁基非晶合金/Al/KH560样品最低峰对应频率低于铁基非晶合金/KH560的相应峰位,铁基非晶合金粉体表面镀铝可明显改善其复合材料的低频微波吸收特性。

电压对纯铝板陶瓷膜层显微组织及其性能的影响

分别采用恒定电压和阶梯电压在纯铝板表面制备陶瓷膜层,研究不同电压模式对陶瓷膜层组织和性能的影响。借助扫描电子显微镜、X射线衍射仪、显微硬度计和电化学工作站等,研究纯铝板表面陶瓷膜层的微观形貌、物相、显微硬度和耐腐蚀性能,并分析陶瓷膜层形成机理。结果表明:纯铝板表面陶瓷膜层是非晶态Al2O3相,与恒定电压相比,采用阶梯电压制备的陶瓷膜层孔洞、裂纹等缺陷较少。恒定电压和阶梯电压为26 V时,陶瓷膜层显微硬度均达到最大,分别为520.2 HV和570.2 HV。阶梯电压为26 V时,陶瓷膜层耐腐蚀性能最佳,自腐蚀电位和极化电阻分别为-0.429 V和113173.9Ω。采用阶梯电压在纯铝板表面制备陶瓷膜层时,每次电压升高都会加速化学反应速率,在纯铝板表面生成致密均匀的内部阻挡层,从而提高陶瓷膜层的显微硬度和耐腐蚀性能。