Engineering Failure Analysis最新文献

Buckling and failure mechanisms of asymmetric composite sandwich panels subjected to shear loadings 非对称复合夹芯板在剪切荷载作用下的屈曲和破坏机理

IF 4.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Engineering Failure Analysis

Pub Date : 2024-11-04 DOI: 10.1016/j.engfailanal.2024.109039

Asymmetric sandwich technology serves as an effective option for introducing loads into sandwich structures in lieu of conventional inserts and joints in lightweight design of thin-walled aeronautical applications. In this study, buckling and failure behaviors are investigated on asymmetric sandwich panels with tapered regions subjected to shearing, where the panels are composed of CFRP laminates as skins and PMI foam as the core. Experimental data and observations are analyzed regarding critical loads, strain distributions, macro- and micro-scaled failure mechanisms. Detailed damage evolution is captured with the developed material and structural models. The influence of the core thickness on stability, load-bearing capacity and failure mechanisms is further investigated. Results show that the shear failure is mainly induced by buckling with an extensive matrix splitting fracture along the diagonal direction for sandwich panels with thin cores. Nonlinearity is observed in strain and deflection responses. Fiber pull-out is formed due to losing support of neighboring matrix. The fracture morphology of fiber breakage roughly appears oblique, indicating that the failure is mainly caused by the combination of tension and shearing. For sandwich panels with a thicker core, i.e. 10 mm and 12 mm, the failure mode switches to pure shear failure. Due to the intensification of tapered edges, local bugling occurs simultaneously with ultimate failure. The ultimate load presents a mounting-up and declining trend with the increase of core thickness, other than a monotonic trend. Conclusively, optimal design parameters exist, such as 10 mm core thickness in the studied case, regarding the load-bearing capacity.

在薄壁航空应用的轻量化设计中，非对称夹层技术是将载荷引入夹层结构的有效选择，可替代传统的插入和连接方式。在本研究中，研究了具有锥形区域的非对称夹层板在受到剪切时的屈曲和失效行为，夹层板由 CFRP 层压板作为表皮和 PMI 泡沫作为芯材组成。实验数据和观察结果分析了临界载荷、应变分布、宏观和微观破坏机制。利用开发的材料和结构模型捕捉了详细的损伤演变过程。进一步研究了芯材厚度对稳定性、承载能力和破坏机制的影响。结果表明，对于夹芯板较薄的夹芯板，剪切破坏主要由屈曲引起，沿对角线方向存在广泛的基体分裂断裂。在应变和挠度响应中观察到非线性现象。由于失去了邻近基体的支撑，纤维拉出。纤维断裂的断口形态大致呈斜向，表明破坏主要是由拉伸和剪切共同造成的。对于芯材较厚的夹芯板，即 10 毫米和 12 毫米夹芯板，其破坏模式转变为纯剪切破坏。由于锥形边缘的加剧，局部翘曲与极限破坏同时发生。极限载荷随着芯材厚度的增加呈上升和下降趋势，而非单调趋势。总之，在承载能力方面存在最佳设计参数，例如在所研究的案例中，芯材厚度为 10 毫米。

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引用次数: 0

Research on TBM parameter optimization based on failure probability 基于失效概率的 TBM 参数优化研究

IF 4.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Engineering Failure Analysis

Pub Date : 2024-11-02 DOI: 10.1016/j.engfailanal.2024.109036

This study addresses the over-reliance on operator experience in Tunnel Boring Machine (TBM) operations by proposing a failure probability-based decision-making method to enhance the scientific accuracy and reliability of construction decisions. In large deformation soft rock zones, TBMs are significantly affected by surrounding rock stress and deformation, which can lead to reduced tunneling speed or even shield jamming, severely impacting construction progress and safety. To reduce subjective biases in operator decision-making, this study combines the stress release coefficient with a failure probability model to establish a limit equilibrium equation. Using Monte Carlo simulations, failure probabilities under varying geological conditions are evaluated, and the optimal tunneling parameters are selected by analyzing the cumulative effect over time. Additionally, the study incorporates a Bayesian updating method, dynamically adjusting model parameters based on periodic monitoring data, further reducing uncertainty and improving the accuracy of the decision support system. The results show that while higher tunneling speeds increase the instantaneous failure probability, considering the cumulative effect over time, the overall failure index decreases with increased speed. Conversely, lower speeds result in a lower instantaneous failure probability but prolonged exposure to high-risk conditions increases the overall failure index. With this decision-making method, operators can quantitatively and in real-time adjust tunneling parameters under complex geological conditions, minimizing failure risks and improving construction efficiency.

本研究针对隧道掘进机（TBM）作业中过度依赖操作人员经验的问题，提出了一种基于失效概率的决策方法，以提高施工决策的科学性和可靠性。在大变形软岩区域，隧道掘进机受围岩应力和变形影响较大，可能导致掘进速度降低甚至盾构堵塞，严重影响施工进度和安全。为减少操作员决策中的主观偏差，本研究将应力释放系数与失效概率模型相结合，建立了极限平衡方程。通过蒙特卡罗模拟，对不同地质条件下的失效概率进行评估，并通过分析随时间变化的累积效应来选择最佳隧道参数。此外，该研究还采用了贝叶斯更新方法，根据定期监测数据动态调整模型参数，进一步降低了不确定性，提高了决策支持系统的准确性。结果表明，虽然较高的隧道掘进速度会增加瞬时故障概率，但考虑到随着时间推移的累积效应，整体故障指数会随着速度的增加而降低。相反，较低的速度会导致较低的瞬时故障概率，但长期暴露在高风险条件下会增加总体故障指数。有了这种决策方法，运营商就可以在复杂的地质条件下定量、实时地调整隧道参数，最大限度地降低故障风险，提高施工效率。

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引用次数: 0

Corrosion fatigue analysis of suspenders on continuous suspension bridge under combined action of wind and traffic 风和交通联合作用下连续悬索桥吊索的腐蚀疲劳分析

IF 4.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Engineering Failure Analysis

Pub Date : 2024-11-02 DOI: 10.1016/j.engfailanal.2024.109037

Suspenders and displacement-controlled device (DCD) are crucial force transmission components connecting the girder and the main cable in the continuous suspension bridge. These two structures will be subjected to environmental corrosion and fatigue loading simultaneously after the protection system fails. To investigate the safety of structure during the service, a comprehensive framework for corrosion fatigue analysis of continuous suspension bridge under the combined effects of wind and traffic flow was proposed. Taking a three-span continuous suspension bridge with DCD as engineering background, the wind-traffic combined load model was established and the fatigue life of the corroded suspenders was examined. Based on the Multilayer Perceptron algorithm, the impact of load form, environmental grade and DCD type on the corrosion fatigue performance of suspenders was analyzed. The results indicate that the fatigue life of suspender is significantly reduced due to uniform and pitting corrosion of the internal steel wires. The early failure mechanism of suspender is extremely sensitive to corrosion factors. Traffic load is the primary cause of fatigue damage to suspenders. Setting up DCD is beneficial for improving the corrosion fatigue life of the suspenders, and the selection of DCD type mainly depends on the topographical factors of the bridge site.

悬索和位移控制装置（DCD）是连接连续悬索桥梁和主缆的重要传力部件。保护系统失效后，这两个结构将同时承受环境腐蚀和疲劳载荷。为了研究结构在服役期间的安全性，提出了在风和交通流共同作用下连续悬索桥腐蚀疲劳分析的综合框架。以 DCD 三跨连续悬索桥为工程背景，建立了风-交通联合荷载模型，并考察了腐蚀悬索的疲劳寿命。基于多层感知器算法，分析了荷载形式、环境等级和 DCD 类型对吊带腐蚀疲劳性能的影响。结果表明，由于内部钢丝的均匀腐蚀和点状腐蚀，吊带的疲劳寿命明显缩短。悬挂装置的早期失效机制对腐蚀因素极为敏感。交通负荷是悬挂装置疲劳损坏的主要原因。设置 DCD 有利于提高悬挂装置的腐蚀疲劳寿命，而 DCD 类型的选择主要取决于桥址的地形因素。

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引用次数: 0

The impact of water contamination on the performance failure of lithium grease 水污染对锂基润滑脂性能故障的影响

IF 4.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Engineering Failure Analysis

Pub Date : 2024-11-02 DOI: 10.1016/j.engfailanal.2024.109035

The performance of grease is significantly influenced by water contamination in humid environments, such as those found in mines and offshore wind farms. In this study, the impact of water contamination on the physicochemical properties, rheological properties, film thickness and tribological properties of lithium greases was evaluated using a series of instruments and techniques, including rheometer, ball-on-disc contact test rig, UMT tribometer and others. Results show that the water content of 2% can enhance both the shear resistance and the extreme pressure capacity of lithium-based grease. The shear viscosity and the structural recoverability increase when water content is below 4%. However, when the water content reaches 8%, the equilibrium of the grease-water composite system is disrupted, resulting in the formation of soap fiber surface breakage notches and a notable reduction in shear viscosity. Furthermore, grease with a water content of 2% to 4% is capable of forming a thicker multi-phase mixed lubrication film, wherein soap fibers, base oil and water coexist. Conversely, the film thickness is observed to diminish rapidly when the water content reaches 6% to 10%. Moreover, the oil–water mixture exhibits inadequate lubricating oil film recovery ability in boundary lubrication. The coefficient of friction of water-contaminated grease increases significantly, reaching 2–3 times that of the initial fully lubricated state at a certain point with severe surface wear. These findings provide technical support for the utilization of lubricants in humid environments and highlight the potential impact of water contamination on lubricant performance.

在潮湿的环境中，如矿井和海上风电场，润滑脂的性能会受到水污染的严重影响。本研究采用流变仪、球盘接触试验台、UMT摩擦磨损试验仪等一系列仪器和技术，评估了水污染对锂基润滑脂理化性能、流变性能、油膜厚度和摩擦学性能的影响。结果表明，2% 的含水量可以提高锂基润滑脂的抗剪切能力和极压能力。当含水量低于 4% 时，剪切粘度和结构恢复能力都会增加。然而，当含水量达到 8%时，润滑脂-水复合体系的平衡被打破，导致皂纤维表面形成断裂缺口，剪切粘度显著降低。此外，含水量为 2% 至 4% 的润滑脂能够形成较厚的多相混合润滑膜，其中皂纤维、基础油和水共存。相反，当含水量达到 6% 至 10% 时，油膜厚度会迅速减小。此外，油水混合物在边界润滑中的润滑油膜恢复能力不足。受水污染的润滑脂的摩擦系数会显著增加，在表面磨损严重的某个点，摩擦系数会达到初始完全润滑状态的 2-3 倍。这些发现为在潮湿环境中使用润滑油提供了技术支持，并突出了水污染对润滑油性能的潜在影响。

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引用次数: 0

Study on the impact toughness and crack propagation behavior of Ti microalloyed weathering steel laser-MAG hybrid welded joints 钛微合金耐候钢激光-MAG 混合焊接接头的冲击韧性和裂纹扩展行为研究

IF 4.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Engineering Failure Analysis

Pub Date : 2024-11-01 DOI: 10.1016/j.engfailanal.2024.109030

In this work, the effect of Ti microalloying on the impact toughness of weathering steel laser-MAG hybrid welded joints was investigated and the corresponding crack initiation and propagation mechanisms were revealed. The results show that the impact toughness of heat affect zone (HAZ) increased by 39.4% and weld metal (WM) by 70.9% compared to Ti-free weathering steel welded joints. The degree of improvement in impact toughness gradually increases with the direction from BM (base metal) to WM. In the WM, Ti element can refine the precipitations and reduce the shape and size of M−A constituents. Furthermore, the microstructure in the WM exhibits the obvious preferred orientations, i.e., the maximum IPF intensity value are concentrated around the [111] pole (the slip direction of BCC structure), which is more prone to slip under external forces. In the HAZ, the addition of Ti mainly plays a role in decreasing the size of precipitations, inducing AF precipitation and increasing the homogeneity of grain size. Therefore, the impact toughness of WM and HAZ for Ti microalloyed weathering steel welded joints is improved by hindering the crack propagation. In addition, in the WM, the main crack path is flatter and the number of secondary cracks is more than that in the HAZ, indicating that the impact toughness of WM is poorer.

本文研究了 Ti 微合金化对耐候钢激光-MAG 混合焊接接头冲击韧性的影响，并揭示了相应的裂纹萌发和扩展机制。结果表明，与不含 Ti 的耐候钢焊接接头相比，热影响区 (HAZ) 的冲击韧性提高了 39.4%，焊缝金属 (WM) 的冲击韧性提高了 70.9%。冲击韧性的改善程度随着从 BM（母材）到 WM 的方向逐渐增加。在 WM 中，Ti 元素可以细化析出物，减少 M-A 成分的形状和尺寸。此外，WM 中的微观结构表现出明显的优先取向，即最大 IPF 强度值集中在 [111] 极（BCC 结构的滑移方向）周围，在外力作用下更容易发生滑移。在 HAZ 中，Ti 的添加主要起到减小析出物尺寸、诱导 AF 沉淀和增加晶粒尺寸均匀性的作用。因此，Ti 微合金耐候钢焊接接头的 WM 和 HAZ 的冲击韧性可通过阻碍裂纹扩展而得到改善。此外，与 HAZ 相比，WM 的主裂纹路径更平坦，次裂纹数量更多，表明 WM 的冲击韧性更差。

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引用次数: 0

The deteriorated tribological and noise performances of copper-based brake pads induced by the increased content of flake graphite 鳞片石墨含量增加导致铜基刹车片的摩擦学性能和噪音性能下降

IF 4.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Engineering Failure Analysis

Pub Date : 2024-11-01 DOI: 10.1016/j.engfailanal.2024.109033

Enhancing the lubricity of copper-based brake pads has been viewed as a crucial strategy to boost braking performance. Flake graphite and the oxide film are two substances that are widely concerned with providing lubrication at the friction interface. However, the results from full-scale dynamometer in this work indicate that the increased content of flake graphite with stronger lubrication and iron particles that accelerate the generation of oxide film lead to a deterioration in tribological and noise performance. This is manifested by high sensitivity to clamping force, significant fading behavior, increased sound pressure level and high-frequency noise. The evidence from the worn surface suggests that flake graphite is susceptible to peeling off from the friction surface, thereby amplifying the instability of the friction surface. The unstable existence of both flake graphite and oxide film during emergency braking actually diminishes the lubrication of the friction interface, likely resulting in the degraded braking performance. The indication suggests that the development of high-performance copper-based brake pads should aim to achieve a harmonization of diverse properties, rather than emphasizing only specific aspects.

增强铜基刹车片的润滑性一直被视为提高制动性能的关键策略。鳞片石墨和氧化膜是在摩擦界面提供润滑的两种广受关注的物质。然而，这项工作中的全尺寸测功机结果表明，润滑性更强的鳞片石墨和加速氧化膜生成的铁颗粒含量的增加会导致摩擦学性能和噪音性能的下降。具体表现为对夹紧力的敏感度高、衰减明显、声压级和高频噪声增加。磨损表面的证据表明，鳞片状石墨很容易从摩擦表面剥落，从而加剧了摩擦表面的不稳定性。在紧急制动时，鳞片状石墨和氧化膜的不稳定存在实际上降低了摩擦界面的润滑性，可能导致制动性能下降。这些迹象表明，开发高性能铜基刹车片的目标应该是实现各种性能的协调，而不是只强调特定方面。

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引用次数: 0

Solder joint lifetime model using AI framework operating on FEA data 使用基于有限元分析数据的人工智能框架建立焊点寿命模型

IF 4.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Engineering Failure Analysis

Pub Date : 2024-11-01 DOI: 10.1016/j.engfailanal.2024.109032

The thermo-mechanical reliability of electronic systems is often limited by the crack growth within the solder joints. Addressing this issue requires careful consideration of the design of the package and solder pads. Finite Element Analysis (FEA) is widely used to predict crack growth and to model their lifetime. Traditionally, FEA post-processing methods rely on human expertise to select appropriate regions for evaluating plastic and creep strain at critical locations and correlating these values with experimental data using the Coffin-Manson equation, which predicts fatigue lifetime based on cyclic plastic strain. This study introduces a novel method for FEA post-processing of surface-mounted devices (SMD) on printed circuit boards (PCB) using artificial intelligence. The method transforms the FEA data into a 2D grid map of creep strain values and employs a Convolutional Neural Network (CNN) for automatic feature extraction. Afterwards, a fully connected layer correlates the extracted features with the experimental measured solder joint lifetime, effectively capturing nonlinear relationships.

The study focuses on the development of the concept of crack formation in the solder interconnects of ceramic based high-power LED packages used in the automotive industry for headlights. The validated FEA model is based on an extensive data set of 1800 LED packages including seven different ceramic-based LED packages and five different solders. The design of the ceramic LED package covers two-pad and three-pad footprint for soldering and thin film and thick film metallized ceramic carriers. Results show a strong agreement (R² Score is 99.867 %) between simulations and experimental data for ceramic LED packages. This automatic feature extraction from FEA data sets a new benchmark for improving solder reliability predictions, and it has proved to be better than established methods for lifetime prediction of solder joints.

电子系统的热机械可靠性往往受到焊点裂纹增长的限制。要解决这个问题，就必须仔细考虑封装和焊盘的设计。有限元分析 (FEA) 被广泛用于预测裂纹的生长并建立其寿命模型。传统的有限元分析后处理方法依赖于人类的专业知识来选择适当的区域，以评估关键位置的塑性应变和蠕变应变，并使用 Coffin-Manson 方程将这些值与实验数据关联起来，该方程根据循环塑性应变预测疲劳寿命。本研究介绍了一种利用人工智能对印刷电路板（PCB）上的表面安装器件（SMD）进行有限元分析后处理的新方法。该方法将有限元分析数据转换为蠕变应变值的二维网格图，并采用卷积神经网络（CNN）进行自动特征提取。之后，一个全连接层将提取的特征与实验测量的焊点寿命相关联，从而有效地捕捉非线性关系。该研究的重点是开发汽车行业前大灯使用的基于陶瓷的大功率 LED 封装的焊料互连中裂纹形成的概念。经过验证的有限元分析模型基于 1800 个 LED 封装的广泛数据集，其中包括 7 种不同的陶瓷 LED 封装和 5 种不同的焊料。陶瓷 LED 封装的设计涵盖用于焊接的双焊盘和三焊盘基底以及薄膜和厚膜金属化陶瓷载体。结果表明，陶瓷 LED 封装的模拟和实验数据之间具有很高的一致性（R2 分数为 99.867 %）。这种从有限元分析数据中自动提取特征的方法为提高焊点可靠性预测设定了新的基准，而且事实证明它优于现有的焊点寿命预测方法。

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引用次数: 0

Understanding surface morphology changes in stainless steel through stepwise cavitation erosion: A comprehensive study 通过逐步空化侵蚀了解不锈钢表面形貌的变化：综合研究

IF 4.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Engineering Failure Analysis

Pub Date : 2024-11-01 DOI: 10.1016/j.engfailanal.2024.109017

Cavitation damage, evolution, and features with time are serious problems confronting designers and users of high-speed hydraulic machines. The stepwise erosion technique clarifies the evolution of cavitation damage and its features over time. The technique involves exposing a test sample to repeated very low durations of erosion, followed by accurate relocation in the SEM. This allows fora detailed study of the actual wear processes within a material, providing a solid foundation for understanding material failure. The experiments were conducted using an ultrasonic vibratory horn functioning at 19.5 kHz frequency and 50 µm ± 0.2 um peak-to-peak amplitude. The tested material was cold-rolled austenitic stainless steel SUS 304 (18 Cr-8 Ni). The results show that the slip bands formed due to shock waves’ impact are the preferential sites for early material removals. Material removal starts gradually along the slip bands that form at the grain boundary and then progresses into the grain. The results also showed that the microjets formed pits that were a few micrometers in size and separated from one another. These pits have remained the same shape and size over time, confirming their limited role in the evolution of cavitation damage. The initiation and progression of inherent cracks resulting from plastic deformation, as well as the characteristics of dislodged particles, strongly support the conclusion that shockwave impacts cause fatigue failure as the mechanism of cavitation erosion.

气蚀破坏、演变和随时间变化的特征是高速液压机设计者和使用者面临的严重问题。分步侵蚀技术可明确气蚀损伤随时间的演变及其特征。该技术包括将测试样品反复暴露于持续时间极短的侵蚀中，然后在扫描电子显微镜中进行精确定位。这样就可以详细研究材料内部的实际磨损过程，为了解材料失效提供坚实的基础。实验使用频率为 19.5 kHz、峰-峰振幅为 50 µm ± 0.2 um 的超声波振动喇叭进行。测试材料为冷轧奥氏体不锈钢 SUS 304（18 Cr-8 Ni）。结果表明，冲击波冲击形成的滑移带是早期材料去除的首选部位。材料去除是沿着晶界处形成的滑移带逐渐开始的，然后进入晶粒内部。结果还显示，微射流形成的凹坑只有几微米大小，而且彼此分离。随着时间的推移，这些凹坑的形状和大小保持不变，这证实了它们在空化损伤演变过程中的作用有限。塑性变形导致的固有裂纹的产生和发展，以及脱落颗粒的特征，都有力地证明了冲击波撞击导致疲劳破坏是空化侵蚀机制的结论。

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引用次数: 0

Effects of irregular holes on load-bearing mechanism and capacity in prestressed concrete cylinder pipes 不规则孔洞对预应力混凝土圆筒管承重机理和承载能力的影响

IF 4.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Engineering Failure Analysis

Pub Date : 2024-10-31 DOI: 10.1016/j.engfailanal.2024.109006

This study investigates the effects of irregular holes on the load-bearing mechanism and capacity of prestressed concrete cylinder pipes (PCCP). An internal pressure test was performed on a PCCP specimen containing multiple irregular holes, and a finite element numerical simulation was conducted to explore the impact of these holes. The results indicated that the presence of irregular holes caused significant anisotropic stress distribution, particularly at the inner wall of the concrete core, with stress concentrations around the holes. Cracks were initiated near the spigot end and propagated axially as the internal pressure increased. The load-bearing process of the PCCP evolved in three stages: (1) the prestressed wires bore the majority of the load, (2) the concrete began sustaining a portion of the load as it experienced tensile stress, and (3) the concrete underwent plastic damage, transferring the load to the steel cylinder and prestressed wires. The internal pressure of PCCP model with multiple irregular holes associated with the serviceability limit-states was 0.23 MPa, representing only 26.4 % of the intact model, which was 0.87 MPa. However, the difference in ultimate load-bearing capacity between the two models was minimal. These findings underscore the necessity of timely repairs to prevent the worsening of erosion in PCCPs with irregular holes.

本研究探讨了不规则孔洞对预应力混凝土圆筒管（PCCP）承载机理和承载能力的影响。对含有多个不规则孔洞的 PCCP 试样进行了内压试验，并进行了有限元数值模拟，以探讨这些孔洞的影响。结果表明，不规则孔洞的存在造成了明显的各向异性应力分布，尤其是在混凝土芯的内壁，孔洞周围应力集中。裂缝在拉钉端附近产生，并随着内压的增加向轴向扩展。PCCP 的承载过程分为三个阶段：(1) 预应力钢丝承受大部分荷载；(2) 混凝土在承受拉应力时开始承受部分荷载；(3) 混凝土发生塑性破坏，将荷载转移到钢筒和预应力钢丝上。带有多个不规则孔洞的 PCCP 模型在使用极限状态下的内部压力为 0.23 兆帕，仅为完整模型（0.87 兆帕）的 26.4%。不过，两种模型的极限承载能力差别很小。这些发现强调了及时修复的必要性，以防止带有不规则孔洞的 PCCP 侵蚀恶化。

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引用次数: 0

Role of residual stress in the failure of the bend of superheater Cr-Mo steel tube working in high-temperature conditions 残余应力在高温条件下工作的过热器铬钼钢管弯曲失效中的作用

IF 4.4 2区工程技术 Q1 ENGINEERING, MECHANICAL

Engineering Failure Analysis

Pub Date : 2024-10-29 DOI: 10.1016/j.engfailanal.2024.109018

This study deals with the material analysis of a Cr-Mo steel superheater at the bending point. The crack occurred on the inside of the bend after 4,300 h of boiler operation, which resulted in a leak of the working medium and a forced device shutdown. The planned service life of the superheater tubes was 34,000 h. The operating parameters of the boiler were as follows: steam output pressure 3.2–3.6 MPa, steam output temperature 440–450 °C. Cracks were found on the lateral surfaces of the bends of the superheater lower tubes. Visual, microscopic, and EDS SEM analyses were performed to determine the cause of the damage. Microscopic analysis showed that crack initiation occurred near the maximum bend on the inner surface of the tubes, where the present pits acted as stress concentrators. EDS SEM confirmed that the predominant iron content in the corrosion layer was related to the formation of tubercles above the corrosion pits, which participated in the corrosion-mechanical nature of the failure. The calculated residual stress values were significant and concentrated in both the intrados and extrados bending regions of the tube. Finite element model (FEM) was used to locate the post-bending stress distribution of the tube and confirmed that a combination of post-bending residual stresses, steam pressure and temperature, and steel tube pitting caused cracks to form and propagate. The distribution of local mechanical stresses through a cross-section of the wall thickness of the superheated tube was experimentally carried out using an electron backscattered diffraction (EBSD) analysis. The obtained results were correlated with the Mises residual stress.

本研究涉及铬钼钢过热器弯曲点的材料分析。锅炉运行 4 300 h 后，在弯曲内侧出现裂缝，导致工作介质泄漏，设备被迫停机。锅炉的运行参数如下：蒸汽输出压力 3.2-3.6 MPa，蒸汽输出温度 440-450 °C。在过热器下管弯曲处的侧表面发现了裂纹。为确定损坏原因，进行了目视、显微和 EDS SEM 分析。显微分析表明，裂纹起始点位于管子内表面最大弯曲处附近，此处存在的凹坑起到了应力集中器的作用。EDS 扫描电子显微镜证实，腐蚀层中主要的铁含量与腐蚀坑上方形成的小瘤有关，这些小瘤参与了失效的腐蚀-机械性质。计算得出的残余应力值很大，且集中在钢管的内侧和外侧弯曲区域。利用有限元模型（FEM）确定了钢管弯曲后的应力分布，并证实弯曲后的残余应力、蒸汽压力和温度以及钢管点蚀共同导致了裂纹的形成和扩展。通过电子反向散射衍射（EBSD）分析，对过热钢管壁厚横截面上的局部机械应力分布进行了实验。获得的结果与米塞斯残余应力相关联。

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引用次数: 0