The LOX Tank Pressurization Module (LTPM) is a critical subsystem of the cryogenic stage, responsible for maintaining the required pressure in the tank. During a module-level cold-flow test conducted, an abnormal flow sound was detected near a TIG-welded joint, indicating a potential leakage. Subsequent leak localization using a snoop solution confirmed the presence of a leak at the interface between the AISI 304L stainless steel plumbing tube (Ø8 mm × 1 mm wall thickness) and the ICSS-1218-321 isolation valve adaptor. Visual examination revealed circumferential cracks in the tube adjacent to the TIG weld toe region. Prior this test, the plumbing assembly had successfully completed hydraulic proof pressure testing, pneumatic proof pressure testing, and module-level vibration qualification. To determine the origin of cracking, establish the failure mechanism, and identify the root cause, a comprehensive metallurgical investigation was carried out. The investigation revealed the presence of multiple microcracks at the weld toe region and fatigue striations on the fracture surfaces, indicating progressive fatigue crack propagation. Comparison with a sound reference weld showed a wider heat-affected zone and coarser grain structure in the leaked joint, suggesting relatively higher welding heat input. The failure was attributed to fatigue crack initiation at the weld toe due to local stress concentration associated with weld geometry and weld-related discontinuities, followed by progressive crack growth under cyclic mechanical and thermal loading, ultimately resulting in through-wall leakage during cryogenic cold-flow testing.
Scanning acoustic microscopy (SAM) is a critical nondestructive technique for detecting buried defects in semiconductor devices [1]. However, interpreting the complex acoustic data requires expert knowledge, especially as microelectronic structures grow increasingly intricate. This study presents a novel, unsupervised approach for defect detection in SAM data using an autoencoder neural network trained exclusively on intact reference samples. The method exploits reconstruction error as an indicator of signal anomalies, identifying potential defects without prior knowledge of their characteristics or the need for defective training samples. The resulting similarity parameter facilitates intuitive visualization of outlier regions through overlay on high-resolution SAM images. Furthermore, by analyzing the spatial and temporal deviation of the reconstructed signals, the method enables localization of the signal interval from which the deviation originates. This provides a rough estimation of the defect depth, adding an additional layer of interpretability to the detected anomalies. This enhances defect detection sensitivity and operator support, making SAM more accessible for less experienced users and highly promising for automation in production environments. While the method effectively highlights signal deviations, it may also flag non-defect-related anomalies such as sample tilting. Nonetheless, it significantly advances automated and operator-independent semiconductor failure analysis by enabling reliable detection of structural anomalies through learned representations of intact signal patterns.
This study explores the applicability of digital image correlation (DIC) techniques for measuring non-uniform residual stresses using the incremental hole drilling method. Specifically, it examines the residual stresses induced by a deep rolling treatment on 7075-T6 aluminum specimens, characterized by strong depth gradients. The aim is to assess the potential of replacing traditional strain gauge rosettes with DIC systems. After the deep rolling treatment, residual stresses were measured using the classic hole drilling method with a strain gauge rosette according to ASTM E837, providing a reference for the DIC measurements. The specimens and camera were mounted on a CNC machine, which allowed precise repositioning of both elements at each drilling step. Experimental results show that DIC measurements allow for the calculation of residual stresses with good accuracy. While their precision is lower than traditional strain gauge measurements, full-field DIC techniques partially compensate for this disadvantage by measuring the entire deformation field around the hole. This approach offers statistically advantageous data redundancy and captures displacements in areas immediately surrounding the hole, which are more sensitive to residual stresses. Considering the time and cost savings by avoiding the use of strain gauge rosettes, DIC techniques offer a valid alternative for determining residual stresses with the hole drilling method. The key factor for their application lies in the ease of repositioning both the camera and the drill at each depth increment.
Sustainable integration of industrial waste requires a rigorous understanding of long-term failure mechanisms in flexible pavement. This study characterizes the failure behavior of bituminous mastics modified with stone dust (SD), marble dust (MD), and dimension limestone dust (DLD) at 8–12
A 3A21 aluminum alloy strain clamp from a cold-region transmission line exhibited localized radial bulging and axial cracking in its uncrimped region. The failure was investigated using field examination, water-ingress-path verification, accelerated freeze–thaw reproduction, mechanical assessment, regional tensile testing, fractography, SEM–EDS, and TEM. Water was found to enter the uncrimped cavity through interstrand gaps at the conductor-entry end. After 27 days of accelerated freeze–thaw cycling, the laboratory specimen reproduced the principal field-failure features. Its maximum outer diameter increased from 60.3 to 85.05 mm, and an axial surface crack formed in the region of maximum bulging. The mean residual tensile strength and elongation decreased from approximately 162 MPa and 21.7
Generic gaskets used in demountable property flood resilience (PFR) barriers may degrade under repeated compression and hydrostatic loading. This study examines compression set in closed-cell EPDM foam and compares five profiles with 0, 10, 15 and 20
API 5CT L80 carbon-steel production tubing perforated after approximately three years of service in a high-temperature, CO2-rich gas-condensate well in the Ratana field, Pakistan. Multiple through-wall holes were found in the upper section of the string at about 456 ft (139 m). Materials testing confirmed the tubing was of the intended API 5CT L80 grade and temper. The inner surface exhibited deep spiral grooves containing pits and mesa-attack morphology, with the through-wall holes located within these grooves; the outer surface was unattacked. Vernier measurements indicated 15–20
A transmission shaft made of 42CrMo steel, serving as a critical component in a centrifugal pump within a power plant, experienced a catastrophic fracture after approximately one year of service. To determine the root cause of this premature failure and prevent future incidents, a comprehensive investigation was conducted using visual inspection, chemical analysis, mechanical testing, optical microscopy, and scanning electron microscopy (SEM). The fracture occurred at the transition zone between the upper conical section and the middle shaft section. The fracture surface exhibited typical multi-source fatigue characteristics. The investigation revealed a severe deviation in the chemical composition, particularly the absence of molybdenum, indicating material non-conformance. Consequently, the inadequate hardenability led to an improper microstructure (pearlite and ferrite at the core) and substandard mechanical properties. Furthermore, a sharp transition fillet (R1.5 mm) coupled with an adjacent pinhole created a severe localized stress concentration. Poor machining quality at the fillet left tool marks that acted as pre-existing micro-notches. The synergistic effect of material deficiency, improper heat treatment, geometrical stress concentration, and surface defects led to the premature fatigue fracture under normal operating cyclic loads. Quantitative stress analysis indicates that the combined stress concentration factor at the fillet-pinhole region exceeded 4.5, rendering crack initiation inevitable even with proper material. This case highlights the critical importance of integrating material verification, geometric design optimization, and manufacturing quality control for safety-critical rotating components.
Slag pot wheels are vital components for transporting molten slag in steel plants. The wheel shafts are subjected to severe cyclic loading/bending and impact loads. Under such conditions, appropriate material selection and heat treatment are critical for ensuring service reliability. In steel melting shop (SMS), premature failure of slag pot wheel shafts occurred after two months of operation (approximately 500 heats) typically it is around run for 10–12 years (around more than 1 lakh heat). Failure analysis revealed that the shafts were manufactured from EN8/S45C-HQ-HT steel with a ferrite–pearlite microstructure, but were not supplied in the specified quenched and tempered (Q T) condition, which could have been assessed through a portable hardness test. To investigate the effect of Q T, tensile and impact specimens were extracted from the shaft, heat-treated with different cycle, and tested for both mechanical and magnetic properties. A clear correlation was established between magnetic response and tempering behavior, enabling nondestructive evaluation of the heat treatment condition and mechanical properties. The findings demonstrate that magnetic property measurements provide a reliable tool for detecting improper heat treatment and preventing premature shaft failures in service.
The contact state of the sealing interface in flared tube fittings directly affects the reliability of tube connections, yet stable ultrasonic characterization of its evolution during loading remains challenging. This study proposes a shape-residual method based on the overall waveform mismatch of target echoes generated by local oblique-incidence guided waves. The method aims to characterize the relative evolution of the sealing-surface contact state during loading of flared tube fittings. Dispersion analysis, experimental group-velocity verification, and finite element simulation indicate that local oblique-incidence excitation generates a target wave packet dominated by flexural modal components in the flared tube. This wave packet exhibits good identifiability and continuity within the selected characteristic time window, making it suitable for subsequent state characterization. A reference-template-based shape-residual feature is then constructed using an early-load echo as the reference, so that the overall morphological deviation of the current echo from the early reference state can be quantified. Equivalent axial loading experiments show that the target echo becomes identifiable after the sealing interface enters a stable compressive contact state. As the axial load increases, the echo undergoes coupled changes in arrival time, amplitude, and local waveform profile. Across multiple independent repeated loading tests, the shape residual ε_init exhibits a consistent overall increasing trend and captures the stage-dependent transition of interface evolution from rapid adjustment to gradual stabilization. Compared with normalized energy attenuation and peak amplitude attenuation, the proposed shape residual shows better trend consistency, repeatability, and load-range discrimination capability. These results demonstrate that the method can convert the evolution of the sealing interface state during loading into a quantifiable process parameter, providing a relative characterization approach for ultrasonic testing and state evaluation of flared connection structures.
This work explores the convergence of additive manufacturing (AM) technologies and investigates the survivability of printed circuit structures (PCSes) in extreme environments that sustain high-impact shock loads. The substrates of the PCSes were manufactured by additive friction stir deposition (AFSD), a solid-state metal AM process. The as-deposited (AD) condition of AFSD processed AA6061 was machined, anodized, and subjected to circuit printing to create a functional PCS. Split-Hopkinson pressure bar configurations were used to shock load PCS specimens in triplicate and characterize the compressive strength of the AA6061 AD material at high strain rates, which was compared to its quasi-static behavior. Cyclic shock loads of 35 kg, an acceleration load higher than expected in near-field applications, were implemented to uncover failure mechanisms and demonstrate instances of circuit survivability in PCS specimens. Results showed that AD AA6061 substrate material exhibited no failure throughout cyclic shock loads and demonstrated increased compressive strength at dynamic strain rates of 2000 s−1 compared to its quasi-static comparison at 0.001 s−1. The trace material exhibited various failure mechanisms such as hardware ejection and trace cracking, flaking, and peeling. However, there were instances where circuit traces maintained continuity within a 20
Present work systematically describes a long-term overheating failure of boiler re-heater tubes as the root cause of failure. Investigation was carried out through visual inspection, chemical composition analysis, and mechanical properties like YS and UTS evaluation, examination of microstructure, fractography/surface analysis by SEM-EDS and XRD analysis to derive the root cause of failure. Based on the various experimental results, it was concluded that the failure of the tube was because of accelerated growth of iron oxide scale and its cracking followed by spalling and creep of tube metal. Substantially thick iron oxide scale formation occurred from the inner surface as well as outer side surface of the tubes toward the hot side of the tube. Accelerated oxidation of base metal reduced the effective thickness of the tube resulting premature failure by over stress. Accelerated oxidation occurred because of overheating to an extended period. The adjacent undamaged tube also showed similar and progressive characteristic features of degradation as that of the failed tube.
This study addresses the insufficient torsional strength and fatigue life of conventional API NC50 threaded connections under extreme downhole conditions in deep and ultra-deep wells. Through three-dimensional finite element modeling validated against API standards, an orthogonal optimization scheme was applied to key geometric parameters—including pitch, taper, secondary shoulder clearance, secondary shoulder slope, and the thread height of the first and last engaged threads—resulting in the development of a novel variable-height-thread design, referred to herein as VHT516. The optimized structure incorporates a double shoulder and a refined thread profile to mitigate stress concentration in critical engagement zones. Comparative simulations demonstrate that the VHT516 connection exhibits a 62.5
During underbalanced drilling operations, the packing element is subjected to sustained high wellbore pressure, making it highly susceptible to failure modes such as tension-compression fatigue cracking and material spallation. Initially, uniaxial tensile tests were conducted on specimens fabricated from the rubber material of the rotating control head (RCH) packing element to fit and obtain the parameters for the material’s constitutive model. Subsequently, a mechanical analysis of the RCH packing element was performed for different stages of the tripping process. Finite element models were established for both a conventional packing element and a new design incorporating reinforcing ribs. The simulation results from both models were extracted and analyzed. A comparative assessment of the sealing performance and fatigue performance was conducted based on three key aspects: the distribution and magnitude of von Mises stress, the contact stress at the sealing interface along with the effective sealing width, and the deformation behavior of the elements. During tripping-in when sealing the drill pipe, the Mises stress concentration at the critical failure-prone location in the reinforced packing element decreased by 45.285
Hydrogen embrittlement cracking constitutes a critical constraint on the service safety and lifetime of high-strength valve steel. This study investigated the hydrogen embrittlement behavior and micromechanism of 40Cr valve steel processed by induction heating quenching and tempering, using SEM, TEM, EBSD, EDS, residual stress measurement, and LAMMPS molecular dynamics simulation. Results show that hydrogen embrittlement cracks in 40Cr steel are characteristic of intergranular fracture, propagating from the surface inward to a depth of 200–500 μm. The crack path is controlled by Cr–Mo enriched M23C6 carbides, propagating along carbide boundaries or deflecting at carbides. High-density dislocation accumulation and severe lattice distortion occur at crack tips. Residual stress exhibits a sharp gradient: compressive stress (− 100 to − 300 MPa) dominates in crack-free zones, while a local tensile stress peak ( 80 MPa) appears at crack initiation sites, lowering the crack initiation threshold by approximately 54
Fatigue is the dominant failure mechanism in engineering components subjected to cyclic loading, particularly in heavy-duty automotive systems where structural reliability is critical. Understanding the fatigue behavior in components is essential for improving design and service performance. In this study, failure analysis was conducted on two drivetrain components, a drive shaft (Case I) and a gearwheel (Case II), extracted from a heavy-duty truck. Each case was investigated using macroscopic examination and fractographic analysis. The results showed that fatigue was the primary cause of failure. In Case I, fatigue behavior was expected because the rotating shaft experienced cyclic bending stresses during service loading. Crack initiation occurred at the shaft periphery under rotating-bending conditions and propagated progressively, accounting for most of the fracture surface. The final overload region was small ( 9
With the rapid development of hydrogen storage and transportation technologies, hydrogen blending in existing natural gas pipelines and the construction of dedicated hydrogen pipelines have become important approaches for large-scale hydrogen utilization. However, pipeline steels are susceptible to hydrogen embrittlement in high-pressure hydrogen environments, posing a serious threat to pipeline safety. In this study, X52 and X80 pipeline steels were selected to systematically evaluate the effects of hydrogen pressure, strain rate, hydrogen pre-charging time, and hydrogen-blended atmosphere on hydrogen embrittlement susceptibility. The influence of surface oxidation and nitrooxidation treatments on hydrogen embrittlement resistance was further investigated. Optical microscopy, scanning electron microscopy, X-ray diffraction, and microhardness testing were used to characterize the microstructure, phase composition, and hardness gradient of the surface-modified layers. High-pressure gaseous in-situ hydrogen slow strain rate tensile tests were conducted to evaluate mechanical properties in hydrogen environments, and fracture morphologies were analyzed to reveal the hydrogen embrittlement mechanisms. The results show that the hydrogen embrittlement susceptibility of X52 pipeline steel in a 6.3 MPa hydrogen environment varies non-monotonically with hydrogen pre-charging time, reaching a maximum after 24 h of pre-charging and decreasing significantly after 48 h. For X80 pipeline steel, hydrogen embrittlement susceptibility increases with hydrogen pressure, while hydrogen blending markedly reduces embrittlement due to the lower hydrogen partial pressure and competitive gas adsorption. Surface oxidation treatment forms a dense Fe2O4-dominated oxide layer on X52/X80 pipeline steels, effectively suppressing hydrogen ingress into the substrate and significantly reducing the hydrogen embrittlement index. The oxidation treatment decreases the hydrogen embrittlement index of X52 steel from 11.1
Mechanical seals are widely used in critical marine equipment, and their seal faces are susceptible to wear degradation under particle-containing seawater conditions. Accurate wear-state identification is essential for fault diagnosis and preventive maintenance. This study proposes a diagnostic framework combining the two-dimensional Higuchi fractal dimension (TDHFD) with a human memory optimization-based kernel extreme learning machine (HMO-KELM). The proposed TDHFD extends the length–scale principle of conventional Higuchi fractal dimension from one-dimensional signals to two-dimensional wear images by constructing a three-dimensional gray-level surface, multi-scale directional chains, and local curvature weights. This enables more effective characterization of subtle wear textures, including scratches, plowing marks, and local gray-level transitions. The HMO algorithm is introduced to optimize the key parameters of KELM, improving classification stability and generalization. The framework is validated using both noise-contaminated texture images and mechanical seal wear images obtained from accelerated degradation tests. Results show that TDHFD provides stronger noise resistance and better feature separability than conventional fractal descriptors. Combined with HMO-KELM, the proposed method achieves a classification accuracy of 90
