Fracture Failure Analysis Research Articles

The fracture and perforation failure analysis of downhole tubes

：The downhole tubes were fractured and perforated after 5 years of shut-in due to high water cuts. This study employs a comprehensive array of analytical techniques to investigate the mechanisms behind fractures and perforations. Utilizing non-destructive testing (NDT), direct reading spectrometer, tensile strength testing machine, impact testing machine, optical microscope (OM), macroscopic fracture morphology observation, scanning electron microscope (SEM) and energy spectrum analysis (EDS), and sulfide stress corrosion cracking (SSCC) was studied. The reason for the fracture of the tubing is that under the condition of low pH value, high hydrogen sulfide environment, the tubing is fractured due to stress concentration caused by cracks in the outer thread relief groove. The perforation of the inner tube wall was caused by gradual wall thickness reduction under the influence of H2S, CO2, and Cl−, resulting in fouling and eventual perforation. To prevent tube corrosion during long-term shut-in, it is recommended to inject crude oil or diesel into the well.

Fracture failure analysis of plastic fiber based on thermodynamic strength theory and experiment

In order to analyze the mechanical behavior of plastic fiber bundle, a theoretical model considering elastic and plastic behavior of single fiber is established. Based on uniaxial tensile tests of polythene single fiber, elastoplastic mechanical properties, such as elastic modulus and plastic modulus, are obtained. Moreover, distributions of yield strength and breaking strength of single fiber are determined. The stress–strain curve of polythene fiber bundle is predicted by theoretical model. The correctness of this theoretical model is verified by uniaxial tensile test of polythene fiber bundle. All experimental data points are within the range predicted by theoretical model. Some key parameters which regulate mechanical behavior of single fiber are investigated theoretically. Results show that Weibull parameters of yield strength and breaking strength of single fiber have great effect on mechanical performance of fiber bundle. The concentration of distribution area of breaking strength can improve the overall fracture strength of fiber bundle. Results and conclusions in this investigation can extend and perfect fiber bundle model in terms of plastic behavior.

Fracture failure analysis of traction transformer oil pump flange

A flange fracture occurred during the installation of a traction transformer oil pump. The causes of the flange fracture were analyzed using physical, chemical, and finite element methods. The fracture surface shows expanded edges and a linear fracture source, indicating an overload fracture. No significant defects such as pinholes, looseness, or cracks were found in the internal structure, which contains elongated Si phases. The Si, Ti, and Zn content in the failure part does not meet standard specifications. The hardness of the failure part is HBW107.8, meeting standards, but the elongation at break is at the lower limit, suggesting higher material brittleness. Finite element analysis revealed a maximum tensile stress of 241.5 MPa on the flange, close to the yield strength, indicating a small safety margin. The flange fracture is related to high material brittleness and potential assembly anomalies. To prevent similar incidents, strict control of raw material quality, regular inspection of mechanical properties, and finite element analysis for structural optimization are necessary.

Fracture failure analysis of heavy-haul train couplers using convolutional neural network along with multilayer perceptron

Abstract Metal couplers are susceptible to unpredictable failure and fracture under long-term high-load conditions in heavy-haul railway transportation. The current mainstream manual inspection method has the disadvantages of high subjectivity and high a priori knowledge requirements, thus not meeting the rapid analysis requirements of production companies. Therefore, in this study, an automated failure analysis method is proposed for heavy-haul coupler fractures. First, a novel image segmentation method (PermuteNet) combining a visual multilayer perceptron and a convolutional neural network is designed to segment different failure patterns of fracture surfaces. The proposed method uses two newly proposed modules—permute attention module and context attention module—to improve the network’s ability to perceive weakly differentiated objects, thereby improving the recognition ability of the model for different failure patterns. In addition, a deep supervisory function is adopted to accelerate the convergence speed of the network. Finally, the proposed image segmentation method is deployed on a computer in conjunction with a developed client application to implement a single-click detection function for coupler fracture pattern analysis. Experiments are performed using the heavy-haul coupler fracture dataset established using on-site data; the proposed segmentation method achieves a mean intersection over union of 77.8%, which is considerably higher than that of other existing methods. By using the client software, the single-click detection function of the fracture area is realized. Thus, the proposed method provides a more convenient and accurate fracture identification solution for factory inspectors and has broad application prospects.

Exploring mechanical and fracture properties in geopolymer concrete with ternary precursor waste materials through laboratory investigations and statistical analysis

The prevalent excessive utilization of cement concrete, characterized by energy-intensive processes and notable carbon dioxide emissions, necessitates a shift towards sustainable construction materials. This study addresses the environmental challenges posed by conventional cement concrete by investigating the potential of recycled precursor geopolymer concrete as an environmentally friendly alternative. The research delves into the mechanical and fracture characteristics of ternary blend geopolymer (TBG) concrete incorporating an industrial by-product, red mud (RM), through comprehensive laboratory testing and statistical analysis. The investigation focuses on assessing the impact of varying RM replacement levels (0 %, 8 %, 15 %, 23 %, and 30 %) on mechanical properties and fracture behaviour in both Mode I and Mode II, utilizing semi-circular bend (SCB) specimens for fracture tests. Statistical methodologies, including Weibull fracture failure probability modelling and analysis of variance (ANOVA), were employed to interpret the results derived from 180 SCB test specimens. Furthermore, microstructural analysis through FTIR, SEM, and EDX testing was conducted on the diverse mixes. The outcomes revealed that the incorporation of RM in geopolymer concrete consistently diminished the compressive strength and flexural strength of the geopolymer concrete as the incorporation levels increased. For instance, the compressive strength decreases from approximately 40 MPa in the RM-free sample to about 25 MPa in the sample with 30 % RM. However, statistical analysis revealed that up to 8 % RM inclusion does not significantly affect the compressive strength and, in some cases, may even slightly increase it, highlighting the subtle effect of RM dosage. Additionally, Weibull modelling revealed that the probability of failure for samples with 30 % RM is about five times higher than for samples without RM. The microstructural analysis also depicted that high RM content may lead to decreasing homogeneity and the formation of deep cracks, negatively impacting mechanical properties. Elevated Fe and Al concentrations with higher RM content suggest potential reactions forming stable geopolymer gels and the presence of minerals like katoite.

An Efficient FEniCS implementation for coupling lithium-ion battery charge/discharge processes with fatigue phase-field fracture

Accurately predicting the fatigue failure of lithium-ion battery electrode particles during charge–discharge cycles is essential for enhancing their structural reliability and lifespan. The fatigue failure of lithium-ion battery electrode particles during charge–discharge cycles poses a significant challenge in maintaining structural reliability and lifespan. To address this critical issue, this study presents a mathematical formulation for fatigue failure in lithium-ion batteries, utilizing the phase-field approach to fracture modeling. This approach, widely employed for fracture failure analysis, offers a comprehensive framework for capturing the complex interplay between mechanical deformation, chemical lithium concentration, and crack formation. Specifically, an additive decomposition of the strain tensor is employed to account for the swelling and shrinkage effects induced by lithium diffusion. Moreover, open-source code (https://github.com/noiiG) is provided, constituting a convenient platform for future developments, e.g., multi-field coupled problems. The developed chemo-mechanical model undergoes fatigue failure package is written in FEniCS as a popular free open-source computing platform for solving partial differential equations in which simplifies the implementation of parallel FEM simulations. Several numerical simulations with two different case studies corresponding to monotonic charge process and fatigue charge/discharge process are performed to demonstrate the correctness of our algorithmic developments.

Impact fracture failure analysis and mechanism study of a TBM disc cutter ring

The fracture of the disc cutting ring significantly impedes the efficiency of TBM. This phenomenon is particularly obvious in geological conditions with high impact loads, such as fracture zones and extremely hard rock areas. In these environments, the incidence of disc cutter ring fracture failure escalates dramatically. To explore the impact fracture failure causes and mechanisms of the disc cutter ring under high impact loads, and to guide the improvement of cutter ring manufacturing process, an in-depth analysis was conducted. The chemical composition, tensile strength, hardness, impact toughness, structure morphology and impact specimen fracture morphology of the cutter ring from a TBM project were measured and analyzed. The results show that the tensile strength point of the disc cutter ring coincides with the fracture point, demonstrating that the ring has an extremely strong brittleness. The impact toughness of the surface of the disc cutter ring is lower than that of the inside, and cracks are easy to start on the surface of the disc cutter ring. According to the microstructure analysis, there are coarse Al-rich inclusions precipitated between grains, accompanied by microcracks and microvoids, which reduce the mechanical properties of the disc cutter ring. Through the fracture morphology analysis, the type of the disc cutter ring impact fracture is a mixture of quasi-cleavage, cleavage and intergranular. When a very high impact load is applied, cracks first nucleate at hard points such as coarse carbides, Al-rich inclusions and voids, and then the main crack propagates in a tortuous manner parallel to the force direction.

Failure analysis of the suspender fracture in a railway self-anchored suspension bridge: Damage identification, fatigue mechanism and remaining life prediction

A suspender fracture accident was reported in a railway self-anchored suspension bridge, arousing intensive concern to fatigue issue in the suspender end connector area which is exposed to complex stress states and cyclic traffic loads. Some critical issues involving the fatigue mechanism, the damage identification, and the remaining life prediction were investigated on the basis of on-site and lab tests, numerical simulations, and theoretical analyses. It was found that the root of an ear-plate screw with threads becomes the fatigue-prone detail since action of stress concentration and the unexpected cyclic bending. Also, an effective crack identification scheme by the ultrasonic phased array inspection as well as a verified prediction method for remaining life were proposed. Short suspenders in the main span are significantly affected by the cyclic bending, resulting in the extremely lower fatigue life than that of a long or side-span suspender. Suggestions for a classified disposal plan are provided based on fatigue risk for individual suspender.

Fracture characteristics and failure analysis of underground caverns in Longyou Grottoes induced by humidity change

The stability of underground caverns in Longyou Grottoes is greatly influenced by humidity change since they are mainly composed of argillaceous siltstone, which is highly sensitive to moisture. In this work, a coupled humidity diffusion-fracture model based on the finite-discrete element method (FDEM) is employed to study the fracture characteristics and failure mechanism of underground caverns No.4 and 5 in Longyou Grottoes caused by humidity change. Firstly, the input parameters are calibrated with uniaxial compression tests on dry and saturated siltstone samples. Then, the crack patterns of a disk rock specimen under drying and wetting conditions are captured, which are compared with experimental results to validate the coupled model and calibrated parameters. Subsequently, numerical models of caverns No.4 and 5 in the Longyou Grottoes are established based on the actual geological conditions. The failure processes of the surrounding rock under moisture evaporation and absorption are simulated, and the stress evolution caused by humidity change is analyzed. Results indicate that the caverns primarily experience tensile failure under the evaporation condition with a distribution of tensile cracks perpendicular to the cavern boundary. However, shear failure occurs in the surrounding rock during moisture absorption, and the cracks gradually propagate into the deep rock with humidity diffusion. Additionally, several factors influencing cavern failure are discussed, and the number of cracks is quantified. Finally, it is found that the HDZ of the caverns is significantly reduced by applying a waterproof layer. The findings in this study have practical significance for predicting and improving the long-term stability of underground caverns in Longyou Grottoes under complex climatic conditions.

Fracture failure analysis of high-strength bolts in power plant steel structures

The high-strength bolts of a power plant steel structure fractured and failed in many places. To find the cause of the failure, this paper analyzed the failure reasons of fractured bolts through macroscopic inspection, chemical composition analysis, mechanical performance test, metallographic inspection, and fracture microscopic analysis. The results show that the main cause of bolt fracture is that improper heat treatment leads to a carburized layer on the surface of the bolt, which makes the surface of the bolt sensitive to hydrogen. At the same time, there is a certain amount of hydrogen in the material matrix, which leads to hydrogen accumulation and cracks in the bolt at the stress concentration. Eventually, the cracks propagate and lead to fracture failure.

Fatigue fracture failure analysis of guide valve based on welding defects

Fatigue fracture failure analysis of guide valve based on welding defects

Failure Analysis of Corrosion and Fracture of P110 Tubing in a Development Well

In this paper, a fractured and corroded tubing string was analyzed through macroscopic observation, chemical composition analysis, metallographic and mechanical test. The corrosion products were studied by SEM, EDS, and XRD method. The results showed that the corrosion of tubing in this well was caused by CO2 corrosion, the well contains CO2 medium and increasing water cut in the late stage of development were the main reasons of serious corrosion, the scaling on the tubing wall aggravated the corrosion. Finally, some suggestions were proposed for avoiding or slowdown this kind of corrosion failures.

Fracture failure of internal thread joint on back redressing stabilizer

Stabilizers have been one of the most critical components in the drilling string, due to their great function to prevent the unintentional sidetracking and vibrations in whole drilling assembly. In recent years, with the increasing of the well depth, the rising of the harsh service conditions have pose big challenges to the stabilizers. So it is very necessary to conduct systematic research on the failure mechanism of the stabilizer and carry out ideal failure prevention measures. In this article, the fracture failure analysis of an internal thread joint of the back redressing stabilizer was carried out, and the failure causes were investigated by nondestructive testing, mechanical property tests, chemical composition analysis, metallographic analysis and scanning electron microscope analysis. The results show that the mechanical tests and chemical composition analysis results all meet the requirements of the SY/T 5051-2016 standard, the fracture mode of the back redressing stabilizer is fatigue fracture, and the causes of the failure is mainly belong to the pit shape defects on the surface of internal thread and the quenching crack in the internal thread.

Fracture failure analysis of the main shaft of a large sewage treatment equipment

In view of the main shaft fracture failure accident occurred in the service process of a sewage treatment equipment, this paper carried out the fracture macro analysis, chemical composition analysis, material mechanical properties testing, metallographic structure analysis, fracture micro morphology analysis of the failure of the main shaft. The analysis results show that there are cold cracks in the weld and toe of the main shaft of the equipment, and the cracks expand under the action of rotating and bending alternating loads. The main shaft speed of the equipment is 3r/min, the load change frequency is very small, and the corrosive medium has sufficient time to play a role in the crack tip, fatigue cracks further propagated, leading to corrosion fatigue fracture of the main shaft. So in order to prevent this kind of failure, it is suggested to improve the welding process regulations for the equipment of the main shaft and rationally select welding materials.

Fracture failure analysis of 5 “drill collar double shoulder external thread in a well

This article analyzes a well using 5 “Based on the analysis of the chemical composition of the drill collar, mechanical property testing, metallographic structure analysis, fracture morphology and energy spectrum analysis, as well as the analysis of the stress, bending strength ratio, and double shoulder structure of the drill collar, combined with the deviation of the well section where the drill collar fracture occurred and the drilling pressure during drilling, it is clear that the main reason for the failure of the drill collar is that there is a large well deviation in the area and the drilling pressure is not properly reduced, resulting in The drill collar undergoes severe bending alternating stress and initiates fatigue cracks and propagates at the root of 1-2 threads at the large end of the external thread.

Fracture failure analysis of a lightning rod on a substation frame considering residual thermal stress

The collapse of a typical lightning rod on a 500-kV high-voltage substation frame in central China is investigated to identify the mechanism of fracture. Comprehensive analyses are performed on the fracture morphology, metallurgical structure, chemical composition and mechanical properties of the materials at the fracture site. A finite element (FE) model of a typical lightning rod structure with an intersecting joint weld is developed and verified using experimental results. Based on the FE results and wind tunnel tests, the fatigue life is estimated for the lightning rod structure at the accident site considering residual stress. The results indicate that the fracture failure of the typical lightning rod structure is mainly caused by wind-induced fatigue damage in the weld area of the intersecting joint of the rod base and the frame beam. The welding residual stress has a severe impact on the fatigue life of the structure. Regardless of the welding residual stress, the actual fatigue life of the typical lightning rod structure under a long-term wind load is lower than the design service life. Therefore, complete analysis of the structure under complex wind-induced dynamic effects is needed in engineering design. Additionally, attention should be given to the quality control of the welding, and measures should be adopted to reduce residual stresses during manufacturing and installation.

Fracture failure analysis of an offshore drilling centralizer

Abstract As an important device to control the drilling direction in the drilling process, centralizer plays an important role in slowing the deviation and improving the casing centering degree. This paper makes a detailed analysis on the fracture failure of centralizer after multiple repair welding. First, the macroscopic appearance of the port is observed by macroscopic inspection. Secondly, the physical and chemical performance analysis shows that all indicators meet the requirements of the indicators. Finally, through the microscopic morphology, energy dispersive spectrometer (EDS) and other means to analyze the port crack source, combined with a variety of tests to find the true cause of fracture failure centralizer. After inspection, it was found that the centralizer was fatigue fracture, and showed multi-source cracking characteristics. Therefore, strict control of centralizer especially after repair welding quality, strengthen the quality inspection of centralizer, to carry out the relevant thermal processing technology research, and further effectively prevent the occurrence of fracture failure.

Failure analysis and improvement of a 42CrMo crankshaft for a heavy-duty truck

The crankshaft of a heavy-duty truck engine fractured and failed. The failure occurred in the left crank web of the seventh main journal. To investigate the cause of the crankshaft fracture failure, macroscopic fracture and microscopic morphological analysis, chemical composition and mechanical properties testing, metallurgical examination and numerical simulation methods were used to analyse the failure of the fractured crankshafts and to propose improvement measures. The results show that the crack source was located at the junction of the threaded bottom hole column surface and taper surface, and the failure mechanism was high cycle fatigue fracture failure. The main reason for the failure was the stress concentration caused by the lack of an obvious transition fillet at the junction of the threaded bottom hole column surface and taper surface, with the maximum stress value of 486.9 MPa. In addition, the metallographic structure transformation of the surface layer of the bottom hole sidewall (maximum depth of about 22 μm) caused by the high machining temperature also had an important influence on the fracture. The proposed improvement scheme of increasing the transition fillet and using an internal cold machining tool was proposed, and the feasibility of the proposed scheme was verified by a fatigue bench test.

Time-Dependent Reliability Analysis of Fracture Failure of Corroded Cast Iron Water Pipes and Bayesian Updating for Lifetime Prediction

Affected by the underground soil environment, buried cast iron pipelines are subject to corrosion during their long-term service, resulting in damage accumulation to the pipe wall and the eventual fracture failure of pipes. This paper aims to propose a probabilistic method to quantitively assess the time-dependent reliability of fracture failure of corroded cast iron pipes. A Gamma-based corrosion process of the pipe wall is derived according to the reported corrosion models. The first-order reliability method and the Monte Carlo simulation are used to cross-validate and conduct the time-dependent reliability analysis based on the fracture failure criterion. Furthermore, uncertain physical parameters of the pipes are updated by the Bayesian Markov Chain Monte Carlo (MCMC) algorithm based on the regional historical data of failed pipes, and lifetime predictions of buried cast iron pipelines are then obtained. A worked example is provided to illustrate the application of the proposed method. It is found that the Gamma process can well simulate the corrosion process hence can be employed to calculate the probability of pipe fracture failure. Sensitivity analysis reveals that the pipe internal water pressure, the fracture toughness, and the geometry of corrosion pits are the most influential parameters to the probability of fracture failure. It is also found that the predicted lifetime of corroded cast iron pipes in the worked example decreases from 110 to 85 years after the Bayesian updating.

Fracture failure analysis and prevention of carbon fiber thin wall crossbar

The fracture failure of a crossbar occurred in a routine deployment test of a satellite ring antenna truss structure. In this study, the fracture cause of the carbon fiber thin wall crossbar was analyzed using body microscope observation, scanning electron microscope observation, metallographic analysis, hardness analysis, XRD analysis, and other methods. The analysis results show that the failure bar had interlaminar damage and local crack or breakage before this deployment test. This defect has further expanded and intensified in the multiple deployment tests of the circular antenna, resulting in the gradual decline of the local stiffness of the crossbar, and finally the buckling failure. By using the bottom plate reflection method to carry out non-destructive testing on the rod, it can effectively avoid false inspection and missing inspection of defects.