Fracture Failure Analysis Research Articles

Solution to ‘Mystery Fracture Surface and Failure Analysis’

Solution to ‘Mystery Fracture Surface and Failure Analysis’

Analysis Analysis and Suggestions on Device Clamp Screw Fracture of 110kV Transmission Line

Fracture failure analysis on device clamp screws of one 110kV transmission line has been carried out based on results of macro-observation, pre-tightening test, mechanical property examination, chemical composition analysis, microstructure observation, SEM observation and EDAX analysis. It is concluded that the main reason of the screw fracture lies in misuse material and improper heat processing which led to material degradation. Suggestions are put forward finally.

Torque Converter Turboshaft Fracture Failure Analysis and Improvement

Torque converter turboshaft is a hydraulic mechanical transmission devices of key components. In a new-mounted hydraulic mechanical transmission, super heavy laden vehicle during the test, the torque converter turboshaft fracture occurs when the vehicle traveling to 13 00 km, resulting in transmission power interruption, chassis parking problems. To achieve accurate positioning of the torque converter turboshaft fracture failure reasons, this paper analyzes the means of optical microscope and scanning electron microscopy, carried out on the fracture failure analysis, then using classical and finite element method to calculate the turboshaft intensity of the strength, and proposed optimization improvement program based on the cause of failure.

Fracture failure analysis and strength criterion for PTFE-coated woven fabrics

This paper presents the research on fracture failure analysis and failure criterion for PTFE-coated woven fabrics. First, groups of on-axial and off-axial tensile tests are carried out, and the corresponding failure mechanisms are analyzed. Then, the samples with initial defects are tested and the fracture toughness is discussed. Finally, several current strength criteria are compared to predict the failure strength of PTFE-coated woven fabrics and a new strength criterion is proposed. Results show the material failure strength depends on the stress ratio and off-axial angle of sample. The ratio of principal stress decides the material strength, and the angle between the principal stress and yarn orientation decides the failure mode. The predictions of current strength criteria agree well with most of the experiment data, except for the samples of small off-axial angles. The disagreements could be attributed to the unbalanced woven structure due primarily to the crimp interchange in the weaving and coating processes. The new strength criterion can make a good prediction of the failure strength of PTFE-coated woven fabrics.

Study on Fracture Morphologies of Nickel Based P/M Superalloy

Fracture morphology analysis is an important way to understand material fracture process, find the reason of fracture and improve its performance. Nickel based powder metallurgy (P/M) superalloy is an important material which is widely used in the modern aeronautic and astronautic industry. In order to determine the fracture characteristic morpholgies and mechanisms of the P/M superalloy fractured at different conditions, the fracture surfaces of the high temperature low cycle fatigue,high cycle fatigue, high-low cycle complex fatigue, tension and creep specimens from the P/M superalloy were studied by scanning electron microscopy and stereo-microscopy. The mechanisms and influencing factors of high temperature fatigue crack initiation and propagation were emphatically analyzed, and creep and tension fracture mechanisms of the P/M superalloy were also discussed. The application of the fracture surface analysis for the fracture failure analysis of the P/M superalloy turbine disk were introduced finally.

Fracture Failure Mechanism Analysis of LP Second Stage Blades of a Gas Turbine

To systematically study the root cause of the fracture failure on a gas turbine LP(low pressure) second stage blade, the damage impression, fractography, material composition and metallurgical structure of the fractured section were studied. Vibration characteristic calcultaion analysis to the blade was performed under considering the working condition and structure characteristic. The analysis results revealed that the LP second stage Blade fracture is high cycled fracture (HCF), and mainly caused by furrowed manufacturing defects close to the fatigue source. Preventive measures were presented accordingly. The studied work is valuable for being a reference to fracture failure analysis and structure design for gas compressor blades.

Fracture failure analysis of baseplates in a fluidic amplifier made of WC-11Co cemented carbide

A fluidic amplifier is a crucial automatic control component in a liquid jet hammer used to drill hard formations in the oil industry. This study aims to determine the true causes of the fracture failure of baseplates in a fluidic amplifier made of WC-11Co cemented carbide in a very short period of time. Computational fluid dynamics (CFD), theoretical estimation, and finite element analysis (FEA) were employed to analyze the effect of static and dynamic loads on the strength of the baseplates. Fractographic, metallographic, and processing defect analyses were also carried out. The FEA results showed that the static and dynamic loads caused stress concentrations at the actual fracture locations, and the effect of working loads on material strength was allowable and safe. Fracture surfaces exhibited typical characteristics of a brittle fracture. The metallographic analysis revealed that a specific amount of brittle eta-phase (?-phase) was present in the material. The microstructure of the processing cutting zone was inspected and the results revealed that some voids, pores, and microcracks were formed on the processing surface. The manufacturing and processing defects resulted in low stress fracture failure of the baseplates.

Fracture failure analysis of AISI 304L stainless steel shaft

Fracture failure analysis of an agitator shaft in a large vessel is investigated in the present work. This analysis methodology focused on fracture surface examination and finite element method (FEM) simulation using Abaqus software for stress analysis. The results show that the steel shaft failed due to inadequate fillet radius size and more importantly marking defects originated during machining on the shaft. In addition, after visual investigation of the fracture surface, it is concluded that fracture occurred due to torsional–bending fatigue during operation.

Failure Analysis of an Abutment Fracture on Single Implant Restoration

This study evaluated the mechanism of an abutment fracture by means of a case-based finite element (FE) stress analysis. A patient presented with a complaint of fracture of an implant-retained single posterior restoration that had been in place for 6 years. The retrieved restoration was examined on the original working cast and subjected to microscopic observation for fracture surface analysis. A case-based FE analysis was conducted to detect the location and magnitude of stress concentration in the implant structures. The fracture occurred at the concave neck of the abutment, with an evidence of fatigue fracture on the titanium surface. Ratchet marks were shown at the distal lingual edge, indicating that the crack proceeded from distolingual to mesial direction. The highest maximum tensile stress at the distolingual concave neck of the abutment was shown when the load was directed on the internal and external surfaces of the mesial buccal cusp. It is suggested that an offset loading because of the cantilever structure caused a high tensile stress on the distolingual edge, resulting in the fatigue fracture of the abutment.

Fracture failure analysis of automotive accelerator pedal arms with polymer matrix composite material

The booming automotive industry is undoubtedly not independent of the extensive applications of composite materials, especially the polymer matrix composite materials, aiming to optimize the price versus performance ratios. Actually, considering safety and reliability are the prior concerns of vehicles, evaluation of the ‘performances’ must never be stopped, from both laboratories and actual services. In this paper, fracture failure incidents of the automotive accelerator pedal arms with matrix of long glass fiber reinforced polypropylene were systematically investigated. Based on the analysis results of matrix materials inspection and fractograph observation, root causes of the failure were identified, and the countermeasures were proposed from the manufacturing point of view. Achievements of this study would provide an actual and vivid example to understand how the processing of polymer matrix composite materials affects the microstructures, the properties and the performances, and would consequently help to prevent similar failures on automotive parts with such materials.

Corrosion Failure Analysis of 35CrMo Bolt in Wet Hydrogen Sulfide Environment

Failure analysis of fracture of 35CrMo bolt was investigated. It was analyzed by means of morphology and microstructure analysis, chemical composition analysis, hydrogen content analysis, scanning electron microscope (SEM) micro-morphology of fracture surface, electronic differential system (EDS) corrosion products analysis. The results showed that the cause of fracture of 35CrMo bolt was stress corrosion cracking. Working stress of the bolt，H2S in surroundings and the high hardness of the bolt combined caused cracking of the bolt. Suitable heat treatment for the 35CrMo bolt is suggested.

Failure analysis and finite element simulation of deformation and fracture of an exploded CNG fuel tank

This paper reports the analysis and simulation of the catastrophic failure of a compressed natural gas (CNG) fuel tank. The initial analyses of the deformation and cracking patterns, along with the observed fractographic features, were indicative of an internal gaseous combustion. Accordingly, a set of transient-dynamic elasto-plastic finite element (FE) analyses was carried out to simulate the structural response of the tank to a special type of combustion-induced dynamic pressure. The FE model was composed of 3D brick elements equipped with interface cohesive elements for crack growth analysis. Excellent agreements were found between the final simulation results and the observed deformation and fracture patterns. The simulation results clearly revealed that the observed failure characteristics, like the overall asymmetric deformation and fracture patterns, initiation and partial growth of parallel cracks at the same section, multiple cracking at the neck, and the self-similar growth of the main axial crack were all caused by traveling of a deflagration-induced sonic pressure wave from the neck towards the bottom of the tank. Finally, a comparison was made between the characteristics of deflagration-induced and detonation-induced deformation and fracture behaviors of closed-end cylinders.

Dynamic Analysis of Motorcycle Engine Rod Bending and Fracture Failure

Taking Motorcycle Engine as the research object, force analysis of the single cylinder engine connecting rod bending and fracture by engine linkage dynamic model. By calculating the connecting rod compression, combustion chamber total pressure, reciprocating movement of the inertia force and from the rod bend parameters to compare the models currently on the market four types in the working state suffered total stress and strength margin safety factor, found that the safety factor of four models in general partial link is small, especially 152QMI engine connecting rod end connecting rod in the hole near easier to bend and break. This study provide a scientific basis for the engine connecting rod design, the quality of correction and failure analysis.

AE Regularity of Coal Failure Shear Deformation Localization under Triaxial Dynamical Loading

Based on MTS-815.02 servo-controlled rock mechanics and acoustic emission (AE) integrated test system, the strength, shear deformation localization and damage AE-energy-rate characteristics process of coal specimen from Weihuliang Coal Mine under tri-axial loading were analyzed. A new model of Weibull distribution on the AE higher energy-rate emergence interval under tri-axial loading had been established, the total probability of coal sample localization failure in an interval is proposed. Then, the forecasting analysis of the coal fracture failure can be studied. The results indicate that the Weibull distribution of the AE higher energy-rate emergence were similar to the experimental results that measured. It is very important to the identification and ration prediction of coal failure in the mining.

Fracture load and failure analysis of zirconia single crowns veneered withpressed and layered ceramics after chewing simulation

This study determined the fracture load of zirconia crowns veneered with four overpressed and four layered ceramics after chewing simulation. The veneered zirconia crowns were cemented and subjected to chewing cycling. Subsequently, the specimens were loaded at an angle of 45° in a Universal Testing Machine to determine the fracture load. One-way ANOVA, followed by a post-hoc Scheffé test, t-test and Weibull statistic were performed. Overpressed crowns showed significantly lower fracture load (543-577 N) compared to layered ones (805-1067 N). No statistical difference was found between the fracture loads within the overpressed group. Within the layered groups, LV (1067 N) presented significantly higher results compared to LC (805 N). The mean values of all other groups were not significantly different. Single zirconia crowns veneered with overpressed ceramics exhibited lower fracture load than those of the layered ones after chewing simulation.

Fracture Failure Analysis of Ductile Cast Iron Crankshaft in a Vehicle Engine

The engine crankshaft of a vehicle suddenly fractured, as the vehicle was running normally on a highway. The engine crankshaft was made from ductile cast iron. The failure cause was analyzed by chemical and metallographic examination, evaluation of mechanical properties, determination of depth of the quenched layer, measurement of distance between the quenched layer and the web, observation on the fracture surface as well as value determination of the fillet radius. The results showed that the failure mechanism of the crankshaft was fatigue fracture resulting from co-effect of bending and twisting, and the crack originated from the subsurface shrinkage in the unquenched layer of the crankshaft journal. Several aspects of the crankshaft were not up to the technical standards, such as distance between the quenched layer and the web, chemical composition, hardness and microstructure of the quenched layer, yield strength, and impact toughness.

Failure analysis of the brittle fracture of a thick-walled 20 steel pipe in an ammonia synthesis unit

In this paper, the analysis of a brittle fracture explosion accident of a thick-walled 20 steel pipe, which connects the outlet of an ammonia separator and the inlet of a cold exchanger in an ammonia synthesis unit of a chemical fertilizer plant, is presented in detail. The causes and mechanism of the material degradation are investigated by analyzing chemical compositions (especially the elements of nitrogen, hydrogen), testing mechanical properties, observing microstructures and defects, and strain aging sensitivity, and analyzing annealing behavior of the pipe. Furthermore, the mechanism of crack initiation and propagation are analyzed carefully through macro- and micro-crack observations by means of Optical Microscopy (OM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The research results not only support the conclusions given by the accident survey group, but also clarify the uncertainty in the report of the survey at that time. The further research makes it clear that the decrease of material toughness due to strain aging embrittlement (SAB), and the crack initiation and propagation is caused by SAB and its lowering effect on the threshold value of hydrogen-induced cracking (HIC). The research work described in the paper has a significant meaning to recognize or eliminate SAB occurred in quite ductile plain carbon steels very commonly used in industry, such as 20 steel in China.

Fracture mechanisms and failure analysis of carbon fibre/toughened epoxy composites subjected to compressive loading

Abstract This study investigates the failure mechanisms of unidirectional (UD) HTS40/977-2 toughened resin composites subjected to longitudinal compressive loading. A possible sequence of failure initiation and propagation was proposed based on SEM and optical microscopy observations of failed specimens. The micrographs revealed that the misaligned fibres failed in two points upon reaching maximum micro-bending deformation and two planes of fracture were created to form a kink band. Therefore, fibre microbuckling and fibre kinking models were implemented to predict the compressive strength of UD HTS40/977-2 composite laminate. The analysis identified several parameters that were responsible for the microbuckling and kinking failure mechanisms. The effects of these parameters on the compressive strength of the UD HTS40/977-2 composite systems were discussed. The predicted compressive strength using a newly developed combined modes model showed a very good agreement to the measured value.

Applicability of Applied Stress Estimation Method Based on the Micro Hardness of Fatigue Fracture Surface of Stainless Steel without Striations

In the failure analysis of fatigue fracture, the estimation of applied stress by examining the fatigue fracture surface is important in order to investigate the cause of failure. A fractographic method using striations has been established. Striations, however, can be observed only when a crack propagated at relatively high rate. In the case of failure after a long period of operation under low stress condition, striations are rarely observed. The estimation of applied stress is almost impossible in such a case. Therefore, an estimation method which can be applied in the low stress intensity region where striations are not observed is desirable. In this study, the applicability of micro hardness measured directly on the fatigue fracture surface as a parameter for the stress estimation was examined. The hardness of fatigue fracture surface was correlated with the stress intensity factor range. In addition, as an approach to service load, the relationship between the hardness of fatigue fracture surface and K value was investigated using repeated two-step stress.

Study on the Parameters Applicable to the Stress Estimation of Fatigue Fracture Surface without Striations

In the failure analysis of fatigue fracture, the estimation of applied stress by examining the fatigue fracture surface is important in order to investigate the cause of accident. A fractographic method using striations has been established. Striations, however, can be observed only when a crack propagated at relatively high rate. In the case of fracture accident after a long period of operation under low stress condition, striations are rarely observed on the fracture surface. The estimation of applied stress is almost impossible in such a case. Therefore, an estimation method which can be applied in the low stress intensity region without striations is desirable. In this study, the high frequency current impedance method and the hardness measurement method were investigated as candidates aiming the application to failure analysis. The former uses the electrical impedance of fatigue fracture surface. A positive relationship was found between the electrical impedance and stress intensity factor range. The latter uses micro hardness which was measured directly on the fatigue fracture surface. The hardness of fatigue fracture surface was correlated with the stress intensity factor range. These parameters might be used as parameters in the estimation of applied stress by examining the fatigue fracture surface without striations formed in low stress intensity region.