Fracture Failure Analysis Research Articles

Fracture Failure Analysis of the Energy Storage Spring of the Circuit Breaker in the 110kV Substation

Through a macro inspection, chemical composition analysis, hardness inspection, graphite carbon inspection and energy spectrum analysis, the reason for the break of the energy storage spring of the circuit breaker in a 110kV substation are analyzed. The results show that poor manufacturing technology and anti-corrosion technology of the spring are the main reason for its fracture. Corresponding control measures are put forward to avoid similar failures from happening again.

Fracture Failure Analysis of the Connecting Bolt of Circuit Breaker in 500kV Converter Station

Through a macroscopic inspection, a stereomicroscopic inspection, a material analysis, a hardness inspection, a metallographic analysis, scanning electron microscope and energy spectrum analysis, the reasons for the breakage of the connecting bolts of the circuit breaker in a 500kV converter station are studied. The results show that the bolt fracture is caused by the combined effect of a hydrogen embrittlement and a high-stress low-cycle fatigue. The corresponding recommended measures are proposed to improve the reliability of the bolts and ensure the safe operation of the circuit breaker.

Fracture failure analysis on drive shaft component of diesel locomotive

Failure analysis is a systematic method of investigation to find the cause of the failure mechanism of a component or equipment. This research describes the fracture analysis of driveshaft components in a diesel locomotive. The drive shaft which is a connecting component around the compressor in the locomotive engine has failed. The methods used in this study include literature studies, visual observations, data collection, material characteristics through chemical composition tests, hardness tests, tensile tests, microstructure observations, fractographic observation, data processing, and analysis of test results. Based on the results of chemical composition testing and mechanical testing shows that the drive shaft is classified as plain carbon steel, specifically AISI 1025 steel. Visual observations and microstructure observations show that the driveshaft failure occurred at the connection part, which is the connection around the welded region. From the fractography results show a visible pattern of deformation plastic that showing the fracture occurred since the connection cannot bear the load given.

Fracture failure analysis of metal materials by visual inspection and destructive testing

A methodology is presented to perform fault analysis in metal materials that have failed due to fracture. The proposed method was applied to the study of a fracture presented in the jaw supporting the test pieces in a universal machine used for mechanical tests on materials. The analysis was structured in two stages, initially a visual inspection of the failed element, followed by a series of destructive tests to identify the characteristics of the material and the occurrence of the failure. Visual inspection identified the morphology of the material in the fault zone with gloss and with a characteristic cleavage fracture shape corresponding to a fragile and brittle material. With arc and spark spectrometry the composition of the material was identified, Metallography showed the formation of martensite typical of medium-carbon steels subjected to thermal hardening and scanning electron microscopy identified the precipitation of carbides at the grain boundary, as well as the presence of gaps and other metallic and non-metallic inclusions in the microstructure. The proposed methodology allowed to characterize the fault and propose an appropriate solution by identifying possible hidden faults solving the root of the problem.

4D microstructural characterization of corrosion and corrosion-fatigue in a Ti–6Al–4V / AA 7075-T651 joint in saltwater environment

Dissimilar alloy couples are susceptible to environmentally assisted damage owing to the presence of crevices and potential difference between the constituent alloys. In this study, x-ray computed tomography has been employed to non-destructively study the corrosion behavior of a dissimilar alloy fastener-plate couple (AA7075-T651/Ti–6Al–4V) in a 3.5 wt% NaCl environment. Following this, the specimen was subjected to corrosion fatigue and post fracture failure analysis was performed. The precise locations of corrosion pitting damage in the specimen were studied with respect to corrosion time. Microstructural factors that contribute to crack initiation were identified using a correlative microscopy-based approach and are discussed.

Fracture failure analysis and research on solid expandable tubular with joint thread

Fracture failure occurred in solid expandable tubular with thread joint during bulging experiment. The mechanical properties and microstructure of fracture shell were investigated by scanning electron microscopy and tensile test. Tensile tests show that the plastic deformation capacity and strength of box thread joint material (AISI 316L) are better than that of pin thread joint material (SAE 1020). Dimples and cleavage facets can be observed in the fracture surface. The finite element analysis shows that the threaded joints carry great compressive stress in the axial and annular directions during the solid expandable tubular bulging. The irregular deformation of the threaded joints during bulging leads to stress concentration at the thread root. There is a great risk of cracking in the case of insufficient strength thread material, and finally leads to the fracture of the joint thread.

Failure Analysis for Girth Weld of Gathering Pipelines

Through failure generalization, fracture feature analysis and material performance test, a comprehensively analysis was made on the fracture failure analysis for girth weld of gathering pipelines containing H2S gas. The results showed that the fracture failure might be mainly due to sulfide stress cracking in the girth weld. The crack originated from the fusion line on the inner surface of girth weld and extended along the girth weld to outside closed to bends. The sulfide stress cracking of the girth weld was caused by the intersection of multiple factors. The service condition was located in SSC 3 zone and the SSC risk of girth weld was high. The girth weld itself was not been stress-relieved, and its ability to resist SSC was poor. Due to low wall thickness, welding defects, welding stress and additional load, the actual stress of weld was higher.

Fracture Failure Analysis of the Blowout Preventer Ram in an Oilfield

This paper gives a thorough investigation on the fracture failure of the blowout preventer (BOP) ram. Through appearance inspection, magnetic powder inspection, physicochemical inspection, metallographic inspection and scanning electron microscope (SEM), the main fracture reason of the BOP ram is that there was some original cracks in the BOP ram before fracture, during the service process the bop ram is subjected to impact load, therefore brittle fracture occurs due to the high brittleness of the gate material (which is caused by large internal structure) and low anti-crack propagation ability. Key words: Blowout preventer (BOP) ram; Fatigue break; Brittle fracture; Failure analysis

Combined numerical and experimental estimation of the fracture toughness and failure analysis of single lap shear test for dissimilar welds

The single lap shear test is widely used to measure the strength of dissimilar welds even though such a test brings limited understanding of the intrinsic weld toughness. The present study proposes a numerical finite element (FE) analysis and experimental characterization of dissimilar joints presenting various microstructures (thickness of the intermetallic layer (IML) and hardness profile). For this purpose, Friction Melt Bonding (FMB) and Friction Stir Welding (FSW) were used to join aluminum AA6061 and Dual Phase steel (DP980). The FE simulations allowed calculating the evolution of the J-integral near this notch tip. It shows that crack initiation depends significantly on the plastic properties of the welded metallic alloys around the notch tip and the width of the welded zone, which both are significantly different for FSW and FMB processes. Nevertheless, a similar weld fracture toughness JC of approximately 1 kJ.m−2 is estimated from the analysis for both FMB and FSW. This is three orders of magnitude higher than the fracture toughness of the intermetallic layer, revealing that the plastic dissipation in the Al and steel plates around the crack tip has a major effect on the weld toughness.

Fracture failure analysis and finite element assessment of bridge detection vehicle

Microstructures and mechanical properties of the fractured bridge detection vehicle are investigated by scanning electron microscopy, and tensile tests in this paper. The finite element analysis shows that the maximum stress which is close to the material yield limit is near the fracture position. When the frame platform of the bridge detection vehicle bears a large combined load, it will cause the crack to propagate from inside to outside gradually, and finally, lead to the fracture of the weld of the frame platform. Microstructures show that there are a lot of gas holes in the weld and a long unwelded zone with the exception of ferrite and pearlite. Moreover, the layout of the accident vehicle frame platform is unreasonable, and the design and layout of the weld seam make the flange and frame platform weld unable to provide enough bearing capacity, thus leaving potential security risks for the accident.

Anti-plane fracture analysis of 1D hexagonal piezoelectric quasicrystals with the effects of damage due to materials degradation

Most fracture mechanics analysis is based on the assumptions of prefabricated crack and ideal undamaged body. In practical, a cracked structure contains microstructural defects so that the material damage is considered to exist in the body rather than an ideal defect-free body. In this paper, it is the first time to take the material damage into account to the constitutive equation of quasicrystals, and the anti-plane fracture analysis of the one-dimensional hexagonal piezoelectric quasicrystals is carried out to obtain the more actual solutions. The continuum damage mechanics theory is used to define the damage variable and evolution law of the micro-voids’ growth in the quasicrystals. Semi-qualitative analysis of damage effects on the stress intensity factors are conducted, in which the stress intensity factors and J-integral are solved by using the boundary element method. In a case study, the fields of stress and displacement along the crack or distributed on the plate are obtained. The comparisons between the presented numerical results and the analytical results have good agreement, which verifies the accuracy of the presented solutions. The numerical results suggest that fracture failure analysis for quasicrystals engineering applications should consider the effective (actual) stress intensity factors calculated by the effective stress instead of nominal stress intensity factors.

Fracture failure analysis on swivel nut of 30CrMnSiA steel in aircraft

In this work, the cracks of HB4-49-14CdD swivel nut in aircraft were found and analyzed by macroscopic observation, morphology testing and metallographic examination. In order to figure out the cause of cracks, manufacturing and assembling process were investigated, and finite element method was used to simulate the tightening process. The results showed that overload tightening torque lead to the fracture and failure of swivel nut.

Fracture failure analysis in compression spring of a wagon torpedo

This work aimed to identify and evaluate the reasons that led to a compression spring to fail. The compression spring was operating in a wagon torpedo, a vehicle that transported pig iron in a liquid state from the blast furnace to the steel mill. For this purpose, optical microscopy (OM), scanning electron microscopy (SEM), quantitative chemical analysis by combustion and x-ray fluorescence, Vickers microhardness test (HV), Rockwell superficial hardness with N scale (HRN), and residual stress analysis by x-ray diffraction were used. The industrial quenching, tempering heat treatment, and shot peening process, were also redone for the spring under analysis, all in order to simulate the treatments that were supposedly done on the original spring. It can be concluded that the process that led to spring fracture was a mechanism of fatigue failure that originated from a defect in the spring surface. Although residual stresses on the spring surface were expected to prevent fatigue failures from surface defects, the hardness in this region of the material was lower than specified due to a decarburizing process.

Fracture failure analysis of conductive arm spring of isolation switch in 500kV substation

Through macro inspection, chemical composition analysis, hardness inspection, graphite carbon inspection, metallographic inspection, the causes of spring fracture on conductive arm of isolation switch in a 500kV substation were analyzed. The results show that poor manufacturing technology and anti-corrosion technology of the spring are the main reason for its fracture. Corresponding control measures are put forward to avoid similar failures from happening again.

Failure analysis of an offshore drilling casing under harsh working conditions

An N80 casing in a certain oil well was broken. After the casing was pulled out, many cracks, sand holes, and corrosion and rust marks were observed in the casing fracture. To test the cause of the fracture, failure simulation using ANSYS software was carried out. Metallographic analysis test, chemical composition analysis test, and conventional mechanical performance test of the casing body were designed, and finally the failure analysis of the casing fracture was completed. The results revealed several large-scale oxide metallurgical inclusions in the casing near the upper end of the wellhead, which reduced the strength of the casing material and caused the casing to crack at the maximum stress position. In addition to harsh service environment, the casing was subjected to strong stress, which exceeded the strength limit of the casing and eventually caused the casing to break. The casing material met the standard requirements at all parts except the fracture areas. A calculation method is proposed for the ocean current and wind force; the method has high accuracy and can be used for analyzing similar offshore conditions. To prevent accidents, it is recommended to strictly control the heat treatment process of the casing material, optimize its microstructure, test its performance before deployment, and establish a real-time analysis system. Timely adjustments should be made to the operating schedule when operating in harsh environments.

Fracture failure analysis of pressure gauge bolt on fuel gas system of offshore platform

Gas turbine generator unit is the most important equipment on the offshore platform, the reliability of pressure gauge on its fuel gas system affects the operation of the entire platform equipment. In this paper, an abnormal fracture failure of pressure gauge bolt on fuel gas system of offshore platform was investigated. Series experiments of visual examination, chemical analysis, fractography analysis, metallographic analysis, and hardness analysis were conducted on the pressure gauge bolts. Thereafter, the failure mechanism of the pressure gauge bolt was discussed based on the experimental results and bolt service environment. It was concluded that the bolt was fractured due to the stress corrosion cracking, and the poor corrosion resistance of bolt materials is the main cause. Finally, countermeasures were proposed to address similar problems.

Fracture failure analysis of freeze–thawed granite containing natural fracture under uniaxial multi-level cyclic loads

Rock mass containing natural fractures is susceptible to freeze-thaw (F-T) weathering in cold regions and could result in the instability of rock engineering and even serious geological hazards. Yet the F-T action on the change of fracture physical characteristics and the associated fracturing evolution of naturally fractured rock is poorly understood. In this work, multi-level compressive cyclic loading experiments were performed to investigate the fracture evolution of naturally fractured granite using real time acoustic emission monitoring and post-test CT scanning. The results show that the aperture change of natural fracture is related to the fracture openness and filling characteristics, the open-type fracture is sensitive to F-T treatment and its aperture increases faster than the close-type and fill-type fractures. In addition, the stress strain curve pattern is impacted by the initial natural fracture volume. The AE activities at fatigue loading stage are weaker than the stress-increasing stage. The proportion of low frequency AE signals increases with increasing natural fracture volume, and the shear-sliding along natural fracture results in the occurrence of low-frequency signals. Moreover, interactions between the natural fracture and stimulated new fracture are visualized using CT scanning and it is found that the initial natural fracture volume impacts the failure mode and fracture network pattern. The testing results are expected to improve the understanding of the influence of natural fractures on rock damage and deformation in cold regions.

Fracture failure analysis of transmission gear shaft in a bidirectional gear pump

A failure investigation has been conducted on a transmission gear shaft in a bidirectional gear pump. The fracture failure of studied gear shaft occurred in the running process test on the test bench after it ran about 60 h at the pressure of 21 MPa and the speed of 2000 r/min. A static strength check revealed the gear shaft was safe under normal working conditions. Detailed examinations on the fractured part of this gear shaft indicated that no no-metallic inclusions and other micro-structure defects existence could attribute to the failure of it. Further check on the fracture surface revealed typical tracks formed by fatigue crack propagation. The obvious machining tracks in the arc resulting in stress concentration and exacerbating the initiation and propagation of cracks in these areas.

Fracture failure analysis and research on thread joint of drive shaft shell of positive displacement motor

Microstructures and mechanical properties of the fractured shell are investigated by scanning electron microscopy and tensile tests in this paper. Tensile test shows that yield strength of the drive shaft shell are low. It can be seen that the fatigue arc lines with small spacing of striations in the fracture surface. It is found that there are deformation characteristics in the local dimple and the quasi cleavage characteristics of specimen. The finite element analysis shows that the stress on the first four teeth of the external thread will gradually increase greatly and the rupture risk will increase with the increase of the torque. When the torque reaches the upper limit, the maximum stress on the external thread is close to the material yield limit. In the torque test, the torque of the thread connection part exceeds the standard of torque value, resulting in too much preload on the thread connection part. When the drive shaft shell bears a large combined load in the wellbore, it will cause the crack propagates from inside to outside gradually, and finally lead to the fracture of the shell.

Complete Block Shear Fracture Failure Finite Element Analysis

The experimental and finite element (FE) analyses of the block shear fracture failure in the published literature are limited to the analysis of the fracture on the surface of the gusset plates and connected members without the analysis of the through-thickness fracture in block shear fracture failure. This paper presents the FE analysis of the complete block shear fracture failure covering the analyses of the block shear surface and through-thickness fracture failure. This study reveals the following: The block shear fracture initiation occurs at the tensile plane mid-thickness and not on the tensile plane surface reported in the published literature. The tension plane through-thickness fracture propagation involves mid-thickness-to-surface fracture propagation and not the surface-to-mid-thickness fracture propagation reported in the published literature. The pure shear fracture that is parallel to the tensile loading direction exhibits a surface-to-mid-thickness fracture sequence while the shear lip fracture that is inclined to the tensile loading direction exhibits a mid-thickness-to-surface fracture propagation. This paper thus identifies the accurate fracture initiation location and through-thickness fracture propagation sequence in block shear fracture essential for the accurate and complete analysis of the block shear fracture not hitherto presented in any published literature.