Primary Failure Mode Research Articles

Mechanical behavior of Dou-Gong brackets in Chinese traditional timber structures: An experimental study

This study investigated the mechanical behaviour of Dou-Gong brackets with different structural forms, including Jixinzao and Touxinzao. Scaled Dou-Gong models were designed and fabricated at a 1:3.4 geometrical ratio. Vertical load tests were conducted to determine the failure modes, load-displacement response, stiffness degradation, and deformation capacity of the Dou-Gong models. Under vertical load, the primary failure modes of the Dou-Gong models were observed at the Lu-Dou, Nidao-Gong, and Hua-Gong component. The specimens demonstrated excellent load-bearing capacity and high deformation resistance. The Jixinzao Dou-Gong model exhibited a 15.0% higher ultimate load-carrying capacity than the Touxinzao Dou-Gong due to the presence of transverse arches. The number of transverse arches in the Dou-Gong models positively correlated with the compression stiffness, while their presence had a negligible effect on stiffness degradation rates. The Touxinzao Dou-Gong model exhibited superior ductility, characterized by a ductility coefficient 8.57% higher than that of the Jixinzao Dou-Gong model. Although the regular layering of the Dou-Gong models was disrupted by Ang component, the models remained stable in both the vertical and horizontal directions. The bi-linear model can effectively simulate the deformation behaviour of the Dou-Gong model under vertical load.

Automated measurements of interscrew angles in vertebral body tethering patients with deep learning

BACKGROUND CONTEXTVertebral body tethering is the most popular nonfusion treatment for adolescent idiopathic scoliosis. The effect of the tether cord on the spine can be segmentally assessed by comparing the angle between two adjacent screws (interscrew angle) over time. Tether breakage has historically been assessed radiographically by a change in adjacent interscrew angle by greater than 5° between two sets of imaging. A threshold for growth modulation has not yet been established in the literature. These angle measurements are time consuming and prone to interobserver variability. PURPOSEThe purpose of this study was to develop an automated deep learning algorithm for measuring the interscrew angle following VBT surgery. STUDY DESIGN/SETTINGSingle institution analysis of medical images. PATIENT SAMPLEWe analyzed 229 standing or bending AP or PA radiographs from 100 patients who had undergone VBT at our institution. OUTCOME MEASURESPhysiologic Measures: An image processing algorithm was used to measure interscrew angles. METHODSA total of 229 standing or bending AP or PA radiographs from 100 VBT patients with vertebral body tethers were identified. Vertebral body screws were segmented by hand for all images and interscrew angles measured manually for 60 of the included images. A U-Net deep learning model was developed to automatically segment the vertebral body screws. Screw label maps were used to develop and tune an image processing algorithm which measures interscrew angles. Finally, the completed model and algorithm pipeline was tested on a 30-image test set. Dice score and absolute error were used to measure performance. RESULTSInter- and Intra-rater reliability for manual angle measurements were assessed with ICC and were both 0.99. The segmentation model Dice score against manually segmented ground truth across the 30-image test set was 0.96. The average interscrew angle absolute error between the algorithm and manually measured ground truth was 0.66° and ranged from 0° to 2.67° in non-overlapping screws (N=206). The primary modes of failure for the model were overlapping screws on a right thoracic/left lumbar construct with two screws in one vertebra and overexposed images. An algorithm step which determines whether an overlapping screw was present correctly identified all overlapping screws, with no false positives. CONCLUSIONWe developed and validated an algorithm which measures interscrew angles for radiographs of vertebral body tether patients with an accuracy of within 1° for the majority of interscrew angles. The algorithm can process five images per second on a standard computer, leading to substantial time savings. This algorithm may be used for rapid processing of large radiographic databases of tether patients and could enable more rigorous definitions of growth modulation and cord breakage to be established.

Consideration of the influences of the driving direction within the calculation of the pitting load-carrying capacity of bevel and hypoid gears

Pitting is, besides scuffing, tooth flank fracture and the phenomenon micropitting, one of the primary failure modes of the flank load-carrying capacity of bevel and hypoid gears. The international standard ISO 10300-2:2014 is widely used for the estimation of the flank load-carrying capacity of bevel and hypoid gears based on operational data and the macrogeometry of the gear set. The calculated safety factors against pitting often show similar values for pinion and wheel. Due to similar safety factors against pitting, the gear is expected to fail as often as the pinion. However, investigations in the field do not confirm this. Initial experimental investigations show an influence of the driven and driving part of the gear set. Within this paper, the phenomenon regarding the driven and driving part of the gear set will be discussed for the first time and the influence parameter will be clarified. Because of the potential for recuperation in electrified agricultural tractors, railroad trains, hybrid and electrical vehicles, this topic is of great importance. In this context an actual calculation approach based on the standard calculation method of the ISO 10300-2:2014 will be presented and verified with test results.

Effect of orientation deviation on random vibration fatigue behavior of nickel based single crystal superalloy

Vibration fatigue refers to the failure of a structure that is repeatedly subjected to loads causing resonance. The vibration fatigue performance of DD6 single crystal superalloy, an anisotropic material, is significantly affected by its various crystal orientations. This study investigates the impact of different vibration signal intensities and orientation deviation angles on the vibration fatigue behavior of DD6 single crystal superalloy. The fracture surface of the specimen that failed due to vibration fatigue was examined using scanning electron microscopy. The findings reveal that the primary failure mode for vibration fatigue of DD6 single crystal superalloy is the dislocation motion on the {111} plane with the greatest resolved shear stress in the octahedral slip system. Moreover, various methods, including time domain and frequency domain methods, were employed to predict the random vibration fatigue life of DD6 single crystal superalloy with different orientation deviation angles. Finally, a New Model was established to consider the vibration signal intensity and crystal orientation deviation angle, which improved the sensitivity of the frequency domain method to the crystal orientation deviation angle under different vibration signal intensities. Compared to other methods, the New Model is more suitable for predicting the random vibration fatigue life of DD6 single crystal superalloy with different orientation deviation angles.

Digital Twin for Diagnosis of Belt Looseness in HVAC Systems using multi-body dynamics simulation

Most heating, ventilation, and air conditioning (HVAC) systems operate using a belt pulley system that provides high efficiency at a low cost. To monitor the health of the HVAC system, it is essential to detect looseness, which is one of the primary failure modes of belt-pulley systems. The main feature used to identify looseness is belt slip, which can be computed using the ratio of angular velocity and diameter between the drive pulley and driven pulley. However, accurately diagnosing the condition of the HVAC system based on the slip distribution calculated by measuring the rotational speed can be based on empirical criteria. To overcome this problem, this paper proposes constructing a digital twin model for accurate diagnosis of belt loosening in HVAC systems. The proposed approach involves performing multi-body dynamics (MBD) based time-domain analysis considering uncertainty. To validate the proposed model, belt looseness is applied to the HVAC system, and the slip distribution is calculated and compared with the results computed by the digital twin model. Through this comparison, it was demonstrated that the proposed model can be utilized to diagnose belt looseness in the HVAC system.

Investigating the Mechanism of Continuous–Discrete Coupled Destabilization of Roadway-Surrounding Rocks in Weakly Cemented Strata under Varying Levels of Moisture Content

This study examines frequent disasters, including large-scale deformation and collapse, caused by underground mining in weakly cemented strata in Western China. The weakly cemented rock’s unique characteristics, including low strength and easy disintegration, demonstrate a different damage pattern than that traditionally seen in the central and eastern regions. Using Fast Lagrangian Analysis of Continua-Particle Flow Code (FLAC2D-PFC2D) coupling, we model the strata, focusing on the 3-1 coal seam roadway at Hongqinghe mine. This study investigates the damage–rupture–destabilization progression in the peripheral rock under varying levels of moisture content. Our findings indicate that a water content of ω = 5.5% is the threshold for roadway damage, and moisture content <5.5% yields minimal rock deformation. However, moisture content >5.5% abruptly increases cracks and shifts the rock’s force chain, causing significant deformation and affecting the ceiling the most. Moreover, higher levels of moisture content weaken the anchor solid’s performance, with two primary failure modes: anchor interface slippage (comprising five stages: elasticity, elasticity–shear hardening, elasticity–shear hardening–decohesion, shear hardening–decohesion, and decohesion) and shear damage. These insights are vital for improving numerical simulations of underground mining, obtaining a more accurate understanding of mineral pressure disasters in weakly cemented strata mining regions in Western China, and developing a solid foundation for the better control of such strata.

Acoustic emission characteristics of rock salt under multi-stage cyclic loading

Rock salt is a common sedimentary rock found in the crust and is widely used for underground energy storage and waste disposal. This research conducted multi-stage cyclic loading on impure Huai'an rock salt while monitoring acoustic emissions (AE) in real-time. The results show that as the loading stress increases, the cumulative AE energy increases in a stepwise manner. The frequency distribution displays a band pattern of low, medium, and high frequencies. As the loading stress increases, the proportion of high-frequency signals decreases while that of low-frequency signals increases. The proportion of medium-frequency signals remains consistently the highest. The b-value initially decreases and then increases, with a sharp drop near the failure. Compared to the increased lower limit stress (ILLS), the constant lower limit stress (CLLS) causes higher cumulative AE energy and amplitude, and smaller b-values for the salt samples. These results indicate that the CLLS increases the size of cracks and damage in the salt samples. Based on the RA (risetime/ amplitude)-AF (average frequency) distribution, it is found that the primary mode of failure for rock salt under multi-stage cyclic loading is tensile cracking. Compared to the ILLS, the CLLS promotes the development of shear cracks. The AE test results of the rock salt provide an important basis for explaining the in-situ microseismic signals generated during the operation of salt cavern energy storage.

Analysis of Erosion Mechanism of Wear‐Resistant Layer in Large Blast Furnace Tuyere

The blast furnace tuyere is a crucial component for blast furnace production. The frequent damage of the copper tuyere impedes the smooth operation of the blast furnace. Welding a wear‐resistant layer on the tuyere can extend its service life, but it still falls short of the expectation in a large blast furnace. In this article, it is aimed to elucidate the erosion mechanism of the wear‐resistant layer. A scanning electron microscope, an energy dispersive spectrometer, and an optical microscope are employed to examine the morphology, composition, and metallographic structure of the samples obtained from a 5800 m3 blast furnace tuyere in China, as well as to calculate the frequency of daily slag crust shedding from cooling staves. The results indicate that the main cause of the erosion of the wear‐resistant layer is the shedding of slag crust due to the temperature fluctuation of the cooling staves. Finally, the erosion mechanism of the wear‐resistant layer is proposed. It is suggested that the formation and propagation of cracks caused by erosion of slag and hot metal are the primary failure mode of the wear‐resistant layer.

Evaluation of air oxidation and internal stresses induced by quenching of partially Cr-coated and uncoated optimized ZIRLO part I: Materials characterization

It is critical to develop technologies that minimize risk of nuclear reactor failure. Coated claddings present an opportunity to preserve fuel rod integrity in the case of a loss of coolant accident. In this work, the material evolution of quenched Optimized ZIRLO (OPZ) rings and Cr-coated OPZ rings is studied at temperatures up to 1000 °C, until full oxidation in air is uncovered through a variety of microstructural characterization techniques, including optical analysis and X-ray diffraction. A number of microstructural reorienting and complex, multi-stage oxidation mechanisms are found to play a role in the structural and material changes. At 1000 °C, the primary failure mode of uncoated ZIRLO is breakaway oxidation; however, the introduction of a single-sided Cr coating protects ZIRLO from oxygen penetration through the exterior surface. The material is seen to undergo several microstructural reorientations from 315° to 900°C while remaining in the α-Zr phase. At 900 °C, Cr-coated OPZ begins the α to β phase transition, and the chromium diffuses into the substrate layer. When both events are present, the Cr phase change can lead to the formation of a Cr-β-Zr eutectoid, and subsequent eutectic temperature at 1332 °C. For uncoated samples, a new phenomenon of iron-rich oxide (rust) development along the ring center in air at 1000 °C is unveiled and explained as an extension of spinodal decomposition. This study is Part I of a two-part series regarding the behavior of Cr-coated and uncoated OPZ at high temperatures. Part II investigates the internal stresses and other mechanical behaviors induced by metallic restructuring and oxide development.

Refill friction stir spot welding of thermoplastic composites: Case study on Carbon-fiber-reinforced polyphenylene sulfide

Refill Friction Stir Spot Welding (refill FSSW) is an innovative solid-state welding technique that has been successfully applied to various combinations of metallic materials. The objective of the present study is to investigate the feasibility of refill FSSW for polymer–polymer structures, with a specific emphasis on carbon-fiber-reinforced polyphenylene sulfide (CF-PPS). The influence of the key joining parameters, i.e. force, plunge depth, rotational speed, and tool diameter, has been analyzed in terms of the resulting joint microstructure, mechanical strength, and failure mechanisms. The lap shear tests revealed two primary failure modes: interfacial shear failure and nugget pull-out. Fracture surfaces exhibited broken fibers. The depth of the joint was found to play a crucial role in determining the failure mode, with interfacial shear failure resulting in higher lap shear strength. Thermal analyses conducted on the produced joints showed no evidence of thermal degradation, which aligns with the temperature measurements during the process, as they remained below the melting temperature of CF-PPS.

Experimental and numerical studies on shear behavior of prefabricated bridge deck slabs with compact UHPC wet joint

Ultra-high performance concrete (UHPC) as a joint material for precast bridge decks might reduce the width of the joint and improve its connection performance and durability. This study proposes a type of compact UHPC wet joint based on the mechanical properties of UHPC and the force characteristics of transverse joints in prefabricated bridge decks. The shear behavior of the novel joint was investigated through experimental study and numerical simulation. In addition, the shear properties of compact UHPC wet joints were compared with epoxy joints. The results indicated that the shear resistances of compact UHPC joints are comparable to those of epoxy joints. The failure process of the precast bridge deck with new joint might be divided into three stages: elastic stage, working stage with cracks, and yield stage. No interface cracks or reinforcement slippage was observed throughout the loading process, indicating that the UHPC joint and the epoxy joint exhibited adequate shear resistance. The ultimate load capacity and corresponding mid-span deflection of UHPC joint specimens were respectively increased by 8.6 % and 75.0 %, when compared with the epoxy joint specimens. Finite element analysis reveals that the transverse shear transfer range of the compact UHPC joints is within 57.1 %. Bending failure due to the yielding of the transverse reinforcement at the bottom of the precast bridge deck is the primary failure mode for both specimens. Moreover, the stresses applied to the deck system have good continuity at the joint.

Fatigue tests and fatigue-life prediction models for hybrid welded-bolted demountable shear connectors

Four push out tests were conducted to assess the structural performance of a welded demountable shear connector (WDSC) under high-cycle fatigue loading. The primary failure mode observed was stud fracture at the base. The presence of grout inside the tube significantly increased the WDSC's fatigue life by 5.4 times. The study also analysed stiffness degradation and relative slip evolution during fatigue cycles. Two finite element-based approaches were employed for fatigue life prediction: the critical plane method for fatigue crack initiation life and fracture mechanics for crack propagation life. Based on the experimental and numerical results, fatigue life prediction formulas (Wöhler curves) are proposed for WDSCs with and without grout to aid in predicting fatigue failure in fatigue-sensitive structural designs.

Modes of failure following locking plate fixation of the distal radius: a thematic analysis of 517 fractures.

Anterior locking plate fixation of the distal radius is a common procedure with reliable results. Failure of fixation is sometimes seen. The aim of the present study was to identify the reasons for failure. In total, 517 cases met the study inclusion criteria. Of them, 23 cases had failure of fixation (4.4%). Failure analysis generated qualitative data. Subsequent thematic analysis identified the primary mode of failure and contributing factors. Primary modes were identified as failure to support all key fracture fragments (n = 20), wrong choice of implant (n = 1), failure of union (n = 1) and poor bone quality (n = 1). Contributing factors were errors in plate positioning, fracture reduction, implant selection and screw configuration, as well as fracture pattern complexity and poor bone quality. Most failed fixations had a primary mode and two or three contributing factors. Overall anterior plating is reliable with a low rate of surgical failure. Knowledge of failure modes will aid operative planning and prevent failure.Level of evidence: V.

Rapid evaluation of lateral-torsional buckling of European standard I-section cantilevers

Lateral-torsional buckling (LTB) is the primary failure mode for thin-walled steel members where the cantilever beams experience nonuniform twisting and buckling about their weak axes. Much research exists in the literature, and modern codes have presented simple formulations for calculating of elastic LTB load of simply-supported beams. However, there are limited numbers of treatments for predicting of elastic LTB load of cantilevers, most of which are numerical, because as different from the simply supported beams, the LTB failure mode of the thin-walled cantilevers is much more complicated. The present study aims to develop a simplified equation for calculating the elastic LTB of the cantilevers with the European standard I-section. First, an analytical model considering first-order bending distribution, load height level, and monosymmetry property of the section has been introduced. Then, a simplified formula for cantilevers has been introduced utilizing the analytical model and two dimensionless coefficients called the slenderness and the load case parameters. The presented analytical solutions were verified with the finite element analysis (FEA), and the effects of slenderness and loading positions on the LTB behavior of cantilevers with European standard I-section have been investigated. It is found analytical solutions are quite compatible with FEA, and the proposed equation could be safely used for calculating the elastic LTB of the cantilevers.

An Accelerated-Based Evaluation Method for Corrosion Lifetime of Materials Considering High-Temperature Oxidation Corrosion

In the realm of industrial automation, corrosion represents one of the primary modes of failure, especially in the case of armored thermocouples exposed to temperatures ranging between 1073.15–1373.15 K. In this context, the selection of metal materials that can withstand high-temperature oxidation and corrosion is of paramount importance. Typically, the corrosion resistance of a given metal material is assessed by measuring the “annual corrosion rate” or “corrosion depth”, which can provide an estimated life expectancy value. However, such an approach fails to account for the individual characteristics of the material, and thus does not conform to objective laws. Rather, the corrosion life of a batch of metallic materials should follow the Weibull distribution, or possibly a normal distribution, as per recent studies that have examined the high-temperature oxidation corrosion mechanism of machine or core components. This investigation effectively combines the standard approach for evaluating metal corrosion resistance in the field of materials with the method of assessing component life in the domain of reliability. Furthermore, we consider the individual differences among materials and provide the life distribution function of metals in corrosive environments and thereby refine the evaluation of metal corrosion resistance. This study ultimately establishes a thermocouple accelerated life evaluation model that enhances the accuracy and efficiency of life evaluations for related products.

Behavior of FRP grid-reinforced ultra-high performance concrete (UHPC) pipes under lateral compression

In this paper, ultra-high performance concrete (UHPC) pipes internally reinforced with fiber-reinforced polymer (FRP) grid (abbreviated as “FRP grid-UHPC pipe”) are proposed. The lateral load carrying performance of FRP grid-UHPC pipes was explored by testing 15 pipe specimens. The test variables included the presence and amount of FRP grid reinforcements, pipe thickness, as well as the presence of carbon FRP (CFRP) jacketing. Results showed that separation failure and flexural fracture were the primary failure modes for the pipes with and without FRP grid reinforcements, respectively. The typical load-vertical displacement curve of a FRP grid-UHPC pipe exhibited a two-stage ascending behavior. Without CFRP jacketing, the two ascending segments were linked by a load reduction, while the transition was smooth with CFRP jacketing. For the variables, it is found that the presence of FRP grid reinforcements could enhance the pipe initial cracking load by approximately 30%, while increasing the FRP grid layers could lead to a much steeper rising in the second ascending segment. Increasing pipe thickness and applying CFRP jacketing could increase the slopes of both initial and second ascending segments. Therefore, increasing pipe thickness (from 30 mm to 45 mm) and applying 1-ply CFRP jacketing could enhance the pipe ring stiffness by 422% and 115% respectively, which was more efficient that increasing the FRP grid layers.

Ballistic performance of spherical fragments penetrating PCrNi3MoV target plates

PCrNi3MoV steel is a medium-carbon, low-alloy quenched and tempered steel that finds its applications in military gun barrels due to the high wear resistance and ablation resistance. To study the penetration and failure modes of PCrNi3MoV plates impacted by tungsten spheres, tungsten spheres of various diameters (5 mm, 8 mm, and 10 mm) were used to impact PCrNi3MoV steel plates with thicknesses of 6 mm, 9 mm, and 14 mm. The penetration performance of the spheres was analyzed for different velocities, and the ultimate penetration velocity of the plate was obtained. It was found that the primary failure modes of the PCrNi3MoV plate were compression pitting failure and shear failure. Using the dimensional analysis method, a relationship between the bulge height of the steel plate and the fragment velocity, an equation for the ultimate penetration velocity, and a relationship between the target penetration energy and the fragment velocity were obtained. Then, a projectile–target action index was proposed to describe the process of tungsten spheres with different velocities impacting target plates. The results suggested that under the same thickness of the target plate, a larger-diameter fragment required more kinetic energy to obtain the same ultimate penetration effect as a smaller-diameter fragment. The equations obtained through dimensional analysis predicted values that agreed well with experimental values, indicating that these equations can be applied to engineering applications.

Fatigue life assessment of GFRP composite laminate under axial and transverse fatigue loading

The strong cyclic nature of the loads that the structures are designed to support can lead to fatigue, which is one of the primary failure modes that can occur in the structures. Throughout their service lives, composite materials experience many kinds of fatigue loads. In this experiment, we look at how glass fiber-reinforced laminates with different stacking sequences react to axial and transverse loading. Hand lay-up method followed by the press molding technique was adapted for the fabrication of laminates. Experimental studies were carried out on universal testing machine to characterize GFRP laminate under both static and dynamic loading conditions. Tensile and flexural fatigue tests were performed according to ASTM D-3479 and ASTM D790-17 standards respectively on symmetric [(0/90) / (±45)2/ (0/90)] s and asymmetric glass fiber reinforced laminates (0/90) / (±45)2/ (0/90) // (±45) / (0/90)2/ (±45). Fatigue tests were conducted at stress ratio(R) = 0.1 and frequency = 3 Hz for tensile fatigue and 1 Hz for transverse fatigue at 90%, 70%, and 50% stress levels of their respective ultimate strength. Results were presented in terms of stress–strain, wohler curve, and hysteresis loops. Results of tensile and flexure fatigue tests showed that symmetric laminates have a better fatigue life.

Axial Compression Behaviour and Modelling of Pultruded Basalt-Fibre-Reinforced Polymer (BFRP) Tubes

Laminated fibre-reinforced polymer (FRP) tubes are increasingly used as compression members in large-span spatial structures due to their high bearing capacity, corrosion resistance, and superior stability compared to high-strength steel pipes. In this study, axial compression tests were conducted on slender BFRP tubes to evaluate their compression characteristics as compression members. The results indicated that BFRP tubes exhibited three distinct failure modes, namely local failure, critical failure, and buckling failure. Overall, buckling was identified as the primary mode of failure under compression. The stress–strain curves of BFRP tubes were characterized by three stages, including elastic, elastic-plastic, and plastic stages. To enable design-oriented approaches, two three-stage theoretical models for BFRP tubes were developed through experimental data analysis. The models predicted the stress–strain curves and the load-lateral deflection curves, taking into account the post-peak softening behaviour of the stress–strain curves. Comparisons between the test results and the predictions calculated using the proposed models indicated that they were in good agreement.

Experimental investigations into delamination behavior of curved composite laminates reinforced by a pre-hole z-pinning (PHZ) method

In this paper, an experimental study is conducted on the resistance of delamination in curved carbon fiber/epoxy composite laminates reinforced by z-pins. The curvature of the specimens is designed according to that of the aero-engine fan blade roots. A cost-effective pre-hole z-pinning (PHZ) technique is employed to mitigate initial in-plane damage, and the impact of z-pin volume fraction and diameter on interlaminar fracture toughness and bridging behavior is determined through double cantilever beam (DCB) testing. The mode-mixity of z-pin is determined, and the fracture toughness of curved specimens is calculated based on Timoshenko curved beam theory. The results indicate that the mode-mixity varies depending on the location of z-pins. Z-pins are subjected to a mix of crack opening and crack sliding loads during the tests. The primary failure mode of z-pins is pull-out, with a minor portion of the pins experiencing fracture. Specimens with 0.8 vol% z-pins exhibit a fracture toughness that is approximately 567% higher than that of unpinned specimens. The delamination resistance capacity of z-pins is dependent on the mixed-mode ratio, due to the transition in delamination resistance mechanism and failure behavior of the z-pins.