By using fatigue crack propagation testing and microstructural characterization, the crack fracture and propagation mechanisms of K4169 superalloy under various loads were investigated. The results demonstrate that the grain sizes of K4169 superalloy significantly increase, and the precipitation of the needle-like 8 phase and the Laves phase is observed. Voids and microcracks form at location of Laves phase enrichment, creating conditions for crack propagation. By the a-N (a is the crack length, and N is the number of cycles) relationship curve, the change in the fatigue crack growth rate with the increasing number of cycles progresses through three separate stages. The fracture process of K4169 superalloy under low-stress cyclic loading (3 kN) exhibits the ductile fracture. Subsequently, the fracture process starts to change from the ductile fracture to the brittle fracture as the stress increases to 4.5 kN. In the microstructures of fractures in both stress states, intergranular propagation is the mechanism responsible for crack propagation. Moreover, the Laves phase exists near the fracture crack, which is in line with the post-service structural phenomenon.

Springback compensation is a crucial approach to maintaining the accuracy of stamping parts with complex features. It has been challenging to determine the position of a characteristic point at the geometrical features during springback compensation. The currently available numerical approaches are not always sufficiently accurate and reliable, particularly when high-strength steels are increasingly used for lightweight structures. An enhanced hybrid method named springback path–displacement adjustment (SP-DA) method has been developed based on the well-known conventional displacement adjustment (DA) method to resolve the issue. A finite element method (FEM) model of stamping owning geometry complexity was established, and ST14F, BH300 and DP500, representing low, medium and high-strength steels, respectively, were selected for the study. Springback analyses were conducted, and the springback paths were acquired in the FEM simulation, based on which the spatial position of a node on the mesh of the compensation model was obtained using the SP-DA method. Its effectiveness was first verified numerically, and then, experiments were conducted to validate that the new SP-DA method could significantly increase the accuracy of springback compensation. Stamping of high-strength steels can benefit most from the proposed SP-DA method.

The aircraft engine casing, a pivotal component, is prone to early cracking during service, severely compromising the safety and lifespan of aerial vehicles. This study delved into the cracking mechanism at the lap component of aeroengine inner casing during service by examining the microstructural characteristics of specimens before and after service, alongside an analysis of microstructural evolution and mechanical properties under simulated service conditions. Experimental findings indicated that, post-service, a small number of locations in the specimens exhibited the adhesion of Mo-rich phases with Mo and Ti compound phases, accompanied by a notable increase in grain size compared to the original specimens. Under simulated high-temperature environments and thermomechanical loading conditions, Mo-rich phases precipitated after reaching 800 °C. Additionally, cracks emerged in the specimens under thermomechanical loading, leading to a transition in fracture behavior from ductile to brittle. In summary, the primary causes of cracking in aircraft engine casing materials were as follows: the aggregation of Mo and Ti compound phases and Mo-rich phases at grain boundaries, significant grain size enlargement, and a shift in the fracture nature of the alloy material. This study offers foundational research insights for the design and preparation of alloy materials for aircraft engine inner casings.

The microstructure evolution of the gamma ' ' precipitates in GH4720Li superalloy during the heat treatment processes of water quenching and subsequent aging at temperatures of 760 degrees C, 800 degrees C, and 850 degrees C was investigated with particular emphasis on the variation in the morphology, size, and size distribution of the precipitates and related mechanisms. Influence of aging temperature and time on the nucleation, growth, and coarsening behavior of the bimodal dispersion of secondary and tertiary gamma ' ' precipitates were discussed. Results showed that only spherical- shaped secondary gamma ' ' precipitates with sizes ranging from 10 to 50 nm formed during the cooling process of quenching. During aging, the nucleation of tertiary gamma ' ' precipitate, growth of both secondary and tertiary gamma ' ' precipitates follow the typical solid-diffusion-assisted precipitation mechanism, while the abnormal coarsening of the secondary precipitates occurs through coalescing adjacent particles. Aging temperature has a less effect on the precipitation of the tertiary gamma ' ' precipitate but substantially influences the coarsening of the secondary gamma ' ' precipitates. At higher aging temperatures such as 850 degrees C, the abnormal coarsening of the secondary gamma ' ' precipitates, which always takes place at 760 degrees C and 800 degrees C, are significantly suppressed. The aging time mainly influences the growth rate of the secondary gamma ' ' but shows little effect on the evolution of the tertiary gamma ' ' phase. Precipitates strengthen the alloy through strong coupling interaction mechanism. An optimal aging strategy heating at 850 degrees C for 8 h is proposed for the GH4720Li superalloy, yielding the best uniform dispersion of the precipitates, maximum hardness of the sample, and being considered time and energy-saving.

围绕板料在拉深过程中容易起皱的现象,引入强压工艺以消除板料的起皱,并探讨了强压压力与起皱程度的关系.为了定量分析强压压力与起皱的联系,通过研究起皱形态的表达,将起皱形成的波纹转化为标准波形进行计算,通过有限元软件仿真计算对应波形的强压压力.试验结果表明:有限元分析的强压压力与实际强压压力存在一致性,验证了计算结果的可靠性.

以航空发动机用不锈钢止动垫圈为典型研究对象,针对采用常规冲压成形方法零件精度低的问题,结合实验和有限元仿真分析,研究了高强度材质厚料窄边圈类零件冲压成形的特点、变形规律及尺寸误差来源、缺陷形成机理及避免措施,制定了合理的冲压工艺及模具方案.结果表明:两步法级进冲裁是获得高精度厚料窄边圈类零件的有效工艺方法,凹凸模间隙是影响零件塌角高度的重要因素,半冲裁过程施加下顶力可有效避免因外圈失稳变形引起的塌角和内径尺寸偏差.通过设定合理的模具间隙、下顶力、半冲裁厚度等关键参数,获得了符合设计图纸质量要求的止动垫圈零件.

The age hardening and precipitation behavior of the low-alloy content and widely used Al-Zn-Mg alloy during artificial aging was studied adopting methods of Vickers hardness testing and transmission electron microscopy. To meet with practical application of the production line conditions, the influence of natural aging (NA, at room temperature) on the precipitation behavior during subsequent artificial aging (AA, at 130 degrees C similar to 150 degrees C) and related mechanisms are discussed based on the classical nucleation theory. The results show that precipitates like solute clusters and GP zones will form during the NA process, which have a significant influence on the sub-sequent precipitation behavior during AA. These NA precipitates will dissolve at the initial stage of AA resulting in abundant localized supersaturated regions which are the favorable nucleation sites for eta ' phase. This positive effect is highly dependent on the temperature adopted during the AA process and the duration of NA. Higher AA temperatures result in a more noticeable increase in hardness compared to the samples without NA but require a longer duration of AA to achieve a relatively high and stable peak-aging hardness. However, an excessive long NA period can lead to a significant drop in hardness in the over-aging status. In the low-alloy content Al-Zn-Mg alloys, the actual nucleation rates of precipitation during the early stages of AA vary significantly with the AA temperature, which serves as the underlying cause of the observed NA effect. These results provide rather an important guidance for the production process of the 7003alloy and other aluminum alloys with similar chemical composition.

In order to comprehensively examine the premature crack sprouting phenomenon of the aero-engine hotend component, high-temperature tensile along with in-situ EBSD tests had been performed on alloy K4169. The microstructural and mechanical properties of K4169 high-temperature alloy under different temperature working conditions were also conducted. The results revealed that as the stress intensity factor increases, the stress-strain curve exhibits three distinct stages. With an increase in working temperature, the material's mechanical properties significantly deteriorate, the Laves brittle phase precipitates at the grain boundary, and voids begin to sprout. In-situ EBSD date, it has been discovered that the cracks start to sprout at the concentration of tiny voids formed inside the alloy. Subsequently, after the crack is expanded, it will propagate along the grain boundary, demonstrating the characteristics of intergranular cracks. The predominant type of fracture for the K4169 alloy during the tensile tests at 650 & DEG;C and 680 & DEG;C is ductile fracture. The fracture mechanism transitions from being ductile to a mixed ductile-brittle model at 710 & DEG;C, the operating temperature. This research aims to thoroughly reveal the aero-engine's failure cracking process, which significantly impacts how the engine genuinely operates.& COPY; 2023 Elsevier B.V. All rights reserved.

This study investigated the wear behavior of coated carbide tool with different tool nose radius under different cutting parameters when turning AISI 321 austenitic stainless steel. The full factorial turning experiments with three factors and two levels cutting parameters were carried out. The wear progression of the tool with cutting time was recorded. The tool wear mechanism and the influence of cutting parameters and tool nose radius on the tool wear behavior were analyzed. The results showed that the cutting tool mainly exhibited wear manners of abrasive wear, adhesive wear, and oxidation wear. The tool life varies a lot with the cutting parameters, with the feed rate the most sensitive. Decrease the nose radius makes the strength of the tool blade worsened, thereby increasing the tool life sensitivity to cutting parameters. However, decreasing the tool nose radius can effectively increase the tool life. The reason is that when the tool nose radius is reduced, the cutting temperature can be decreased and at the same time the chip breaking performance can be improved, which decrease the mechanical damage of chips to the tool and related wear, and thus resulting in a longer tool life.

为研究时序翻边曲线,设计了带U形槽的平面内凹和平面外凸的翻边模型,应用仿真计算,并结合近似模型及优化设计方法对翻边时序曲线进行了优化.结果表明,平面内凹翻边和平面外凸翻边优化计算的时序曲线分别为中间高、 两端低的弧形曲线和中间低、 两端高的弧形曲线.依据设计模型和优化结果进行了平面内凹、 平面外凸翻边及相应的时序优化翻边试验.结果表明,优化计算的时序曲线模具可以有效地减小平面内凹翻边时的拉伸效应及平面外凸翻边时的压缩效应,U形槽的开口变化程度得到了明显改善.

This study aims to experimentally explore the influences of stamping conditions on the variations in fiber yarn angle and material properties of continuous fiber reinforced thermoplastics (CoFRTP). First, the upright-orthogonal (O-), biased-orthogonal (B-) and non-orthogonal (N-) specimens were manufactured with thermo-stamping process. Second, the X-ray computed tomography (CT) was employed to characterize fiber yarn angle variations within each layer of thin-walled CoFRTP structures nondestructively. The results indicate that fiber yarn angle varied in different layers at the same position and also changed at different positions in the same layer for the N-specimens. In addition, the 6-ply, 8-ply and 10-ply N-specimens exhibited a similar average variation in fiber yarn angle. Finally, the tensile and three-point bending (TPB) tests were conducted to investigate the effects of stacking sequence and fiber yarn angle variations on material properties and structural performances of these consolidated CoFRTP specimens. In the off-axis tensile tests, the modulus, yield strength and failure strength of laminates decreased but the failure strain increased with increasing fiber yarn angle. In the TPB tests, the O-specimen showed the smallest failure displacement, the B-specimen presented the highest peak force, and the N-specimen exhibited the largest failure displacement. This study is anticipated to gain insights into the relationship between stamping process and forming characteristics as well as structural performances of CoFRTP structures.

Springback compensation is critical in sheet metal forming. Advanced techniques have been adopted in the design stage of various sheet metal forming processes, e.g. stamping, some of which are for complex shaped products. However, the currently available numerical approaches are not always sufficiently accurate and reliable. To improve the accuracy of springback compensation, an enhanced hybrid springback compensation method named Springback Path – Displacement Adjustment (SP-DA) method has been developed in this study based on the well-known conventional displacement adjustment (DA) method. Its effectiveness is demonstrated using FEM analysis of low, medium and high strength steels adopted in automobile industry, in which a symmetrical model owning geometry complexity similar to an auto body panel was established. The results show this new enhanced SP-DA method is able to significantly improve the accuracy of springback compensation comparing to conventional displacement adjustment technique.

Drawing process represents a significant area of production technology since it influences the feasibility of producing auto-body die panels. In the drawing process, the plastic deformation of blank is not uniform due to the intermittent deformation behavior of the material. This primes a non-uniform thickness distribution in the formed panels, which directly affects the die life and the quality of panels. In the presented study, a new algorithm was proposed for constructing the numerical control machining tool path for the new die surface obtained from FEM simulation and mesh mapping. The commercial package LS-DYNA was employed for the FEM simulation and to calculate the thickness distribution in the drawn workpiece. In order to construct the new numerical control machining tool path according to the new die surface, the positions of all cutter location points relative to the movement of new die mesh were determined. A set of forming die was machined using the proposed algorithm to fabricate a real workpiece of steel DC04. A comparison between the measured thicknesses in the fabricated workpiece and the FEM simulation results shows that they agree with each other very well, which directly validates the proposed algorithm. The developed method can improve product quality, increase production efficiency, and reduce labor intensity.

传统的压边力计算公式由于考虑的因素较少,因而精度较低.利用数值模拟技术和响应面法,建立筒形件最佳压边力与板料几何参数、材料性能参数和模具几何参数之间的关系函数.根据所得的关系函数,针对具体的材料、板料和模具,可以快速计算出相应的最佳压边力,以达到成形质量提高的最佳效果.

基于分段线性硬化假设和J2流动法则,建立了某高强度钢的弹塑性本构模型.采用隐式向后Euler径向返回算法进行应力更新,推导了材料平面应变Jacobian矩阵,编写了相应的适合冲压成形的分段线性硬化高强度钢平面应变用户材料子程序UMAT_ PL.分别使用ABAQUS自带的各向同性硬化本构模型、利用最小二乘法拟合的线性硬化模型用户材料子程序UMAT_L以及分段线性硬化平面应变用户材料子程序UMAT_ PL,对某高强度钢槽形件进行了冲压成形分析.结果 表明,利用该分段线性硬化UMAT_ PL获得的应力计算结果,和ABAQUS自带的各向同性硬化本构模型得到的应力计算结果是一致的.与线性硬化模型相比,分段线性硬化模型能获得更加满意的应力计算精度.

基于差厚拼焊板成形时由于板料发生塑性变形从而不可避免地会出现焊缝线偏移现象,采取预先对坯料焊缝线进行调整优化的方式来缩小成形后焊缝线与设计焊缝线的偏差.先在压料面或填补的孔洞上延伸合并分离的焊缝线,然后将焊缝线离散成系列点后通过网格映射法建立设计焊缝线、坯料焊缝线及成形后焊缝线三者之间的位置映射关系,然后通过仿真计算获取成形后焊缝线与设计焊缝线各对应离散点之间的偏差,并依据偏差值对坯料焊缝线离散点进行相应的偏移,获得坯料理想的曲线焊缝.在此基础上对曲线焊缝直线化,并根据直线焊缝坯料的仿真计算结果对坯料焊缝进行适当的偏转和平移,从而缩小成形后焊缝线相对于设计焊缝线的偏差.冲压试验结果表明该方法是有效的,同时也揭示了成形后焊缝线相对于设计焊缝线有偏差主要是因为坯料选用了直线焊缝.

由于航空发动机排气短管壁薄、深度深、型面复杂,使得成形比较困难.本文提出了一种带下压板冲压的成形工艺方案,通过DIC(数字图像相关)技术测试了零件材料的力学性能,通过冲压仿真获得了材料三种不同流动方式下的成形结果,并与传统冲压方式进行了对比.结果 表明,带下压板的冲压成形比传统冲压成形能有效地改善材料流动性,减小零件最大减薄率,获得更优的成形质量.同时,不同的材料流动方式也对零件最终的减薄率产生较大的影响.

With expanding use of multi-materials in vehicle components for attaining light-weighting structures, growing interests have been refilled in the adhesive bonding technique attributable to its compelling advantages to bond dissimilar materials, especially for carbon fiber reinforced plastic (CFRP) composite and metals. A significant issue related to the bonding of dissimilar materials is, nevertheless, that there are substantial differences between adherend material properties, which often lead to different structural and fracture responses. This study aimed to investigate the effects of adherend thickness and adherend material types (e.g. steel, aluminum, CFRP composite) on the fracture behavior of the joints. The adherend deformation and fracture processes of the joints were monitored by the charge couple device (CCD) cameras during the tensile tests. A digital image correlation (DIC) technique was used to capture full-field, out-of-plane deformation of the adherend, the strain distribution and strain evolution along the bondline so that the fracture process can be characterized visually. The microscopic and macroscopic studies on the fracture surface were also carried out to explore the influences of adherend thickness and material types on the failure modes of the joints quantitatively. The results divulged that the joint strength increased with increasing adherend thickness; and the sensitivity of adherend thickness on the joint strength depended on the joint material types. When the adherends underwent the elastic deformation, adherend stiffness affected the joint stiffness and joint fracture process. Adherend yield strength determined the joint strength, fracture state and failure modes when the failure occurred with yielding in the adherend. The fracture processes and strain evolutions in the bondline were found to be symmetric for the joints with the same adherends, while the maximum strain and crack appeared first on the lap end of the lower yield strength adherend for the joints with dissimilar materials. The study is expected to provide new insights into the design of multi-material joints with different thicknesses.

To meet the growing demands for structural lightweight and safety, metal-foam-composite hybrid tubular sandwich structures, which combine low-cost metallic materials and high-strength composites with low-density cellular materials, have been recently introduced to be a class of energy absorber configurations for automotive engineering. This study proposed four different hybrid sandwich tubes and investigated their crashworthiness and performance to cost ratio under quasi-static axial condition. For a comparative purpose, individual carbon fiber reinforced plastic (CFRP) tube, aluminum tubes and aluminum foam were also tested here. From the energy absorption perspective, it is found that all the hybrid specimens exceeded the sum of the individual components. Of different configurations, specimen C-F-C (i.e. outer CFRP tube + aluminum foam + inner CFRP tube) had the highest energy absorption capacity (in energy absorption): 6.70 kJ, specific energy absorption (SEA): 37.32 kJ/ kg, improvement of energy absorption: 39.1%, and material cost 6.877 pound, respectively. The specimen C-F-A (i.e. outer CFRP tube + aluminum foam + inner aluminum tube) exhibited the highest crushing force efficiency (0.87) and value-added performance of energy absorption (0.325 kJ/) pound. The specimen A-F-A (i.e. outer aluminum tube + aluminum foam + inner aluminum tube) exhibited the lowest peak crushing force (63.56 kN) and lowest material cost (2.227 ) pound. Further, the finite element (FE) model was established to analyze the crashworthiness characteristics of hybrid sandwich tubes through validating the simulation results with the experimental data, which provided a basis for further parametric analysis and structural optimization.

As an effective way to control springback, compensation technology is widely used in the field of automotive panel stamping. It is hard to reconstruct the whole tool mesh model containing addendum surface and binder surface in the compensation process, because the springback calculation is always carried out after trimming. A method for reconstructing the whole tool mesh automatically during springback compensation is proposed in this study. The method is based on the Displacement Adjustment (DA) compensation, and in the reconstructing process the blank mesh is split into two parts: the trimmed product and the addendum surface in trimming process. Base on this method, the changes of the reconstructed tool mesh can be avoided to ensure the accurate description of the tool surface. The reconstructed whole tool mesh can be used not only for the following stamping simulation but also for the springback compensation of automotive stamping parts.