Showing papers in "Journal of Failure Analysis and Prevention in 2016"

Failure Analysis and Mechanical Characterization of 3D Printed ABS With Respect to Layer Thickness and Orientation

Abstract: In contrast to conventional subtractive manufacturing methods which involve removing material to reach the desired shape, additive manufacturing is the technology of making objects directly from a computer-aided design model by adding a layer of material at a time. In this study, a comprehensive effort was undertaken to represent the strength of a 3D printed object as a function of layer thickness by investigating the correlation between the mechanical properties of parts manufactured out of acrylonitrile butadiene styrene (ABS) using fused deposition modeling and layer thickness and orientation. Furthermore, a case study on a typical support frame is done to generalize the findings of the extensive experimental work done on tensile samples. Finally, fractography was performed on tensile samples via a scanning digital microscope to determine the effects of layer thickness on failure modes. Statistical analyses proved that layer thickness and raster orientation have significant effect on the mechanical properties. Tensile test results showed that samples printed with 0.2 mm layer thickness exhibit higher elastic modulus and ultimate strength compared with 0.4 mm layer thickness. These results have direct influence on decision making and future use of 3D printing and functional load bearing parts.

Failure Analysis and Anisotropy Evaluation of 3D-Printed Tensile Test Specimens of Different Geometries and Print Raster Patterns

Abstract: Anisotropic mechanical properties related to build orientation is a characteristic of parts fabricated with 3D printing technologies. In the development of new materials for 3D printing processes, understanding the effects of 3D printer build orientation and raster pattern on physical property and failure mode differences is extremely important. While there is currently no standard for the evaluation of build orientation-based mechanical performance, such analysis has typically been achieved through the fabrication and scrutiny of tensile and other test coupons which were printed in different build orientations. In some cases, printing specimens in the ZXY (or vertical) build orientation can be difficult due to the capability of a given 3D printer platform. There are also multiple tensile test specimen geometries specified in the ASTM D638 standard for the tensile testing of polymer materials and understanding which specimen geometry works best for 3D printing is not currently well understood. The work presented here explores the effect of tensile test specimen geometry on the anisotropy of mechanical properties related to the build orientation of tensile test specimens. The test coupons were fabricated using a material extrusion 3D printing platform based on fused deposition modeling technology using a grade of acrylonitrile butadiene styrene not typically used in 3D printing in order to simulate the testing of a new material. The effects of raster pattern and the geometric dependence of mechanical property anisotropy were explored, and validation of the use of “faux vertical” specimens in lieu of ZXY-printed specimens was demonstrated. Finally, scanning electron microscopy was used to perform fractography on the various versions of the printed tensile test specimens in order to determine the effect of raster pattern on failure mode.

A Comparative Study of Various Methods of Bearing Faults Diagnosis Using the Case Western Reserve University Data

Abstract: Bearing is probably one of the most critical components of rotating machinery. They are employed to guide and support the shafts in rotating machinery. Therefore, any fault in the bearings can lead to losses on the level of production and equipments as well as potentially unsafe. For these reasons, the bearing fault diagnosis has received considerable attention from the research and engineering communities in recent years. The purpose of this study is to review the vibration analysis techniques and to explore their capabilities, advantages, and disadvantage in monitoring rolling element bearings.

Application of EIS and SECM Studies for Investigation of Anticorrosion Properties of Epoxy Coatings containing ZrO 2 Nanoparticles on Mild Steel in 3.5% NaCl Solution

Abstract: The effect of corrosion protection performance of epoxy coatings containing zirconium oxide (ZrO2) nanoparticles on carbon steel was analyzed using scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). Localized measurements such as oxygen consumption and iron dissolution were observed using SECM in 3.5% NaCl in the epoxy coated sample. Line profile and topographic image analysis were measured by applying −0.70 and +0.60 V as the tip potential for the cathodic and anodic reactions, respectively. The tip current at −0.70 V for the epoxy coated sample with ZrO2 nanoparticles decreased rapidly, which is due to cathodic reduction of dissolved oxygen. The EIS measurements were conducted in 3.5% NaCl after wet and dry cyclic corrosion test. The film resistance (R f) and charge transfer resistance (R ct) values were increased by the addition of ZrO2 nanoparticles in the epoxy coating. SEM/EDX analysis showed that oxides of Zr were enriched in corrosion products at a scratched area of the coated steel after corrosion testing. Focused ion beam-transmission electron microscope analysis confirmed the presence of the nanoscale oxide layers of Zr in the rust of the steel, which had a beneficial effect on the corrosion resistance of coated steel by forming protective corrosion products in the wet/dry cyclic test.

Probabilistic Fault Diagnosis of Safety Instrumented Systems based on Fault Tree Analysis and Bayesian Network

Abstract: Safety instrumented systems (SISs) are used in the oil and gas industry to detect the onset of hazardous events and/or to mitigate their consequences to humans, assets, and environment. A relevant problem concerning these systems is failure diagnosis. Diagnostic procedures are then required to determine the most probable source of undetected dangerous failures that prevent the system to perform its function. This paper presents a probabilistic fault diagnosis approach of SIS. This is a hybrid approach based on fault tree analysis (FTA) and Bayesian network (BN). Indeed, the minimal cut sets as the potential sources of SIS failure were generated via qualitative analysis of FTA, while diagnosis importance factor of components was calculated by converting the standard FTA in an equivalent BN. The final objective is using diagnosis data to generate a diagnosis map that will be useful to guide repair actions. A diagnosis aid system is developed and implemented under SWI-Prolog tool to facilitate testing and diagnosing of SIS.

Corrosion of Aluminum Alloy Metal Matrix Composites in Neutral Chloride Solutions

Abstract: The electrochemical behavior of UNS A0332.00S, UNS A0332.20S, UNS A0359.00S, and UNS A0359.20S aluminum alloys were studied in NaCl media through weight loss, potentiodynamic, and cyclic polarization techniques. UNS A0332.20S and UNS A0359.20S were reinforced with SiC, 20% by volume while the other two samples were not reinforced. Scanning electron microscopy and energy dispersive spectroscopy were used to analyze the role of intermetallic phases in both the corroded and non-corroded aluminum alloy samples. Results showed that unreinforced alloys have lower corrosion rates compared to the reinforced alloys. Pits on the reinforced alloys were significantly more numerous, shallower, and widespread than on the monolithic alloys. Al/SiC interface particles and intermetallic phases were observed to form at the mouth of the pits especially in alloys reinforced with SiC particles which might have contributed significantly to the weakening of regions where localized corrosion occurs. The result shows that intermetallic phases may directly influence the corrosion behavior of the aluminum alloys.

Evaluation of the Corrosion Protection Performance of Epoxy-Coated High Manganese Steel by SECM and EIS Techniques

Abstract: The corrosion protection performances of epoxy-coated Mn steel and carbon steel were evaluated by electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) analysis. EIS was performed on coated Mn steel with a scratch in a 0.1 M NaCl solution after a wet/dry cyclic corrosion test. The charge transfer resistance (R ct) and film resistance (R f) of the coated Mn steel displayed a higher value than the coated carbon steel. The increase in the charge transfer resistance and film resistance of the coated steel is due to the presence Mn in steel. SECM was conducted to estimate the corrosion protection performance of the epoxy-coated Mn steel immersed in a 0.1 M NaCl solution. It was found that dissolution of Fe2+ was suppressed at the scratch on the coated Mn steel due to the higher resistance for anodic dissolution of the substrate. SEM/EDX analysis showed that Mn was enriched in corrosion products at a scratched area of the coated steel after corrosion testing. FIB-TEM analysis confirmed the presence of the nanoscale oxide layer of Mn in the rust of the steel, which had a beneficial effect on the corrosion resistance of the coated steel by forming protective corrosion products in the wet/dry cyclic test.

Static and Dynamic Sealing Performance Analysis of Rubber D-Ring Based on FEM

Abstract: In order to study the performance of the dynamic seal and static seal of D-ring, the FEM models of D-ring and O-ring were built, and the process of reciprocating seal of the D-ring was simulated. In addition, the effects of pre-compression, medium pressure, friction coefficient, and rubber hardness on sealing performance were discussed. The friction coefficients between rubber sealing ring and steel part, under different lubrication conditions, were measured through the experiment. The results show that, in static seal, the maximum contact stress of the D-ring increases with the increasing of pre-compression, friction coefficient, medium pressure, and rubber hardness. Besides, O-ring can be well replaced by D-ring in static seal. Since it can avoid distortion and twisting effectively in reciprocating dynamic seal and prolong its working life, D-ring has a better sealing performance in reciprocating seal than O-ring. As the friction coefficient grows, the amplitude of the maximum contact stress fluctuation increases as well as the fluctuation of the cross-section deformation which has a bad influence on sealing performance and fatigue life of the D-ring.

Investigation of Mesh Sensitivity Influence to Determine Crack Characteristic by Finite Element Methods

Abstract: In this research, an extended finite element model has been investigated. Investigation of opening and closure stress always has been one of the difficult parameters to analysis of results; therefore, the utilization of finite element methods would be a good and logical alternative for this purpose. In addition, linear elastic fracture criteria are used for validation of numerical results from the simulation. In this work, a detailed analysis of the influence of different parameters in the results of a specific specimen with a semi-elliptical tooling groove in terms of closure and opening stress is presented, and the impact of optimum element size in fracture characteristic in various load cycles has been discussed.

Mechanical Response of a Buried Pipeline to Explosion Loading

Abstract: In order to study the stress-strain response of a buried pipeline with internal pressure under the ground explosive, a numerical calculation model of the buried pipeline with internal pressure was established. The dynamic process of the buried pipeline was simulated after the explosion on the ground. Effects of internal pressure, magnitude of TNT, wall thickness, and buried depth on the stress-strain of pipeline were studied. The results showed that the region of high stress and plastic strain presented to the upper pipeline and extended toward axial direction, and then extended toward circumferential direction under the ground explosion. With the increasing of internal pressure, the high-stress zone fades away, the plastic strain zone and deformation of pipeline decrease. The stress and deformation of buried pipeline increase with the magnitude of TNT increases, but they decrease with the increasing of buried depth and wall thickness. Those results can provide theoretical basis and reference for pipe laying of oil-gas pipeline, safety evaluation, and maintenance, etc.

Managing Cold Temperature and Brittle Fracture Hazards in Pressure Vessels

Abstract: Brittle fractures of pressure vessels can be both catastrophic and costly. The intent of this article is to provide guidance in avoiding such failures by identifying some of the causes for cold embrittlement hazards and brittle fracture in pressure vessels. Selected examples will help illustrate the main factors that contribute to brittle fracture, through identifying brittle fracture features, and demonstrating the importance of coordination of materials and potential operating condition. This article also discusses how to assess existing equipment pressure vessels subject to cold conditions and brittle fracture concerns using the guidelines of API 579-1/ASME FFS-1, Part 3.

Erosion-Corrosion of Low-Carbon Steel in the Absence and Presence of Slurry in Saline Water: Kinetic and Mathematical Views

Abstract: The purpose of this work is to study the combined effect of corrosion-erosion of mild steel in 3.5% NaCl solution as a function of flow rate, angle, sand concentration, and exposure time. Weight loss technique is used to obtain the corrosion-erosion data. The present work is focused on determining the optimum mathematical equation and operating conditions in order to achieve good prediction properties. Three mathematical-kinetics equations were suggested. A computer-aided program was used for developing these models. Results show that the polynomial mathematical equation was able to accurately predict the measured data with high correlation coefficients.

Failure Analysis of AISI 321 Austenitic Stainless Steel Water Piping in a Power Plant

Abstract: The objective of this work was to analyze a reported pitting damage mechanism in water piping of a power plant. The investigated material was a longitudinal-seam welded pipe which was made of AISI 321 austenitic stainless steel. Pitting occurred on the internal surfaces of the pipe and adjacent to the girth welds. Optical emission spectrometry, metallography, and electrochemical testing were the techniques employed to analyze the failure. The investigation showed that the flowing water contained chloride ions in which AISI 321 austenitic stainless steel is not immune against pitting corrosion. In addition, the polarization data showed the susceptibility of the material to pitting corrosion in the service conditions. Furthermore, the result of double loop electrochemical potentiokinetic reactivation tests showed that the material was sensitized during welding. It was found that the damage was due to pitting corrosion in chloride-containing water. Thus, it was recommended to replace the pipe with material having higher pitting resistance equivalent number to be more resistant against pitting corrosion.

Failure Investigation of Boiler Water Wall Tubes of a Thermal Power Station

Abstract: Failure investigation was carried out on boiler water wall tubes of a thermal power plant through visual inspection, chemical analysis, and metallurgical analysis. Failure was in the form of thin/micro cracks along the length of the tubes which were located at the girth welding joint of tubes. Experimental results revealed that the cracking was from inward to outward of the tube thickness. Discontinuities/cavities were observed in the welded region which might have occurred due to lack of fusion of base metal and the weld metal. Cracks were initiated from the sharp corner/crack tip of the cavities/discontinuities present at the welded region under the action of hoop/thermal stress existed during the operation. Nature of the crack propagation indicates the case of typical hydrogen-induced cracking. Moreover, the presence of the cavities/discontinuities reduced the cross-sectional area of tubes resulting increased stress intensity. Increased stress beyond the flow stress of the material assisted by hydrogen-induced effect resulted the cracking of the tubes. In order to mitigate the problem, proper welding of tubes joints should be carried out followed by proper inspection after weld. Secondly, hydrogen dissolution during welding should be prevented and treatment for its removal after welding should be carried out.

Rolling Bearing Degradation State Identification Based on LCD Relative Spectral Entropy

Abstract: In the interest of obtaining an effective bearing degradation feature from complex, nonlinear, and nonstationary vibration signals, a new analytical methodology based on local characteristic-scale decomposition (LCD) and relative entropy theory is proposed. On the one hand, LCD is a new and relatively excellent time-frequency analysis method to analyze practical vibration signals polluted by noise. On the other hand, relative entropy theory is a good way to characterize different degradation states by calculating the probability distribution difference between the degradation signals and the normal signal. Combining the above two theories, two new degradation features named LRNE and LRQE are extracted to indicate the bearing degradation trend from normal state to even failure state. The noise resistance ability and extensive applicability of both the features are verified by simulation signal. For further analysis of experimental vibration signals, the two features have a satisfying performance to characterize different bearing degradation states. With the help of gray relational analysis and fuzzy C-means clustering, the proposed two characteristics can identify different bearing degradation states of inner ring fault mode with high accuracy. In the end, the two features are applied to doing bearing failure analysis with the full-life bearing data. The results show that the LRNE and LRQE are sensitive to bearing degradation trend in the whole life of bearing.

The Vibration Characteristics Analysis of Pipeline Under the Action of Gas Pressure Pulsation Coupling

Abstract: In order to research the pipeline vibration and prevent the fatigue failure of pipeline, the calculation model and methods for vibration characteristics analysis of pipeline under the action of the gas pressure pulsation and pipeline coupling are presented in this paper. According to the pipeline structure, the pipeline model with different pipe diameters is established. Based on the model and combined with the structure parameters of pipeline, the calculation methods of gas column natural frequency, gas pressure pulsation, and exciting force are built. By these ways, the relationships between the gas column natural frequency and orders, the gas pressure pulsation and orders, and the exciting force and aspect ratio are acquired. Besides, the variable relationships of vibration displacement and velocity of pipeline can be obtained. Comparing the calculated results with the field test values, the calculated results are in agreement with the test values, and the correctness of the calculation model and method is verified. The results show that taking the pressure pulsating and pipe coupling effect account into the vibration analysis of different pipe diameters, which can truly reflect the vibration characteristics of pipeline and possess important reference value for preventing fatigue failure and reducing the vibration of the pipeline.

Finite Element Modeling of Magnetic Flux Leakage from Metal Loss Defects in Steel Pipeline

Abstract: Magnetic flux leakage is a nondestructive method for inspection of steel pipelines carrying petroleum products, and is most widely used technique. The inspection tool used for this purpose is called instrumented pipeline inspection gauge (IPIG) which moves with the pressure of fluid inside the pipeline. In this paper, a three-dimensional finite element modeling and static simulation of the magnetic circuit of a magnetic flux leakage-based IPIG has been carried out. A FEM-based MagNet software has been used. Rectangular defects of different dimensions on a plate have been modeled, and the magnetic flux leakage response from each of these defects has been studied. Appropriate properties and boundary conditions have been imposed in the simulation. The dependency of some of the characteristic defect dimensions and the leakage flux signal has been studied. In addition, the effect of sensor liftoff on the leakage flux values for specific defect geometry has been studied and understood. Furthermore, the effect of defect orientation on the internal or external surface as against the sensor positioning has also been studied. A comparison of the FEM-simulated flux values with that of experimental leakage flux values has been made.

Simulation and Experimental Research of PDC Bit Cutting Rock

Abstract: In order to achieve efficiently the optimal design and evaluation of PDC (polycrystalline diamond compact) bit, a finite element model for PDC bit cutting rock was established, forecasting the torque and the drilling pressure distribution trends of the cutting teeth on the bit. Through the PDC bit drilling rock, our experimental model validates the reasonableness and effectiveness of finite element simulation. It further demonstrates that the results of the changing trend of experiment and finite element simulation are very close and verify the accuracy and feasibility of the simulation model. The finite element model for single wing PDC cutting rock was established. This paper analyzes the distribution trends of the cutter torque and drilling pressure on bit under the conditions of the different penetration rates and rotational speeds. The “attack” of the cutting teeth is also analyzed. The results show that the torque of the cutting teeth is increased with the increasing penetration rate with the other conditions being the same. Under the same penetration rate and rotating speed, the drilling pressure of the cutting teeth tends to increase first with the increasing distance from the center axis of the drill bit, and then decrease. The cutting force of each tooth increases with the increasing penetration rate, and near the shoulder, it reaches the maximum, even though the cutting force is less affected by the rotating speed.

Failure of Low-Pressure Turbine Blades in Military Turbofan Engines: Causes and Remedies

Abstract: Failure of low-pressure (LP) turbine rotor blades in low bypass military turbofan engines is a great concern for designers, manufactures, repair and overhaul agencies, operators, and airworthiness authorities. The present paper analyzes the LP turbine blade failure cases to determine its root cause. Forensic and metallurgical investigations are carried out on the failed blades. In most cases, the failure was originated from the leading edge and had propagated toward the trailing edge. Intergranular features and high oxidation on the fractured surface have been found as the cause of fatigue failure. Operation at elevated temperatures for considerable time was found responsible for these fatigue failures. Malfunction of fuel system, failure in control sensors, and nonuniformity in atomizer characteristics were the root cause of high temperature in turbine leading to the failure of blades. The paper also presents various remedial measures to address the blade failures from manufacturing and operational points of view.

Failure and Fracture Analysis of Bolt Assembled on the Fan Used in the Internal Combustion Engine

Abstract: Three connecting bolts fractured, which were assembled on the fan used in the internal combustion engine. Detailed fractographic study and metallurgical analysis were focused on the fractured bolts. Fractographic and metallurgical studies indicate that the fracture surface and the microstructure of three bolts exhibit similar features. The fatigue fracture is the main failure mechanism of the bolts. Appearance of the micro-cracks in the thread tip of the fractured bolts makes the stress at the thread regions increase intensively so that the fatigue cracks initiated from the thread regions. Due to the presence of dynamic load, the bolts were never properly tightened during installation which should be responsible for the formation of the cracks.

A New Signal Processing and Feature Extraction Approach for Bearing Fault Diagnosis using AE Sensors

Abstract: In this paper, a new signal processing and feature extraction approach for bearing fault diagnosis using acoustic emission (AE) sensors is presented. The presented approach uses time-frequency manifold analysis to extract time-frequency manifold features from AE signals. It reconstructs a manifold by embedding AE signals into a high-dimensional phase space. The tangent direction of the neighborhood for each point is then used to approximate its local geometry. The variation of the manifolds representing different condition states of the bearing can be revealed by performing multiway principal component analysis. AE signals acquired from a bearing test rig are used to validate the presented approach. The test results have shown that the presented approach can interpret different bearing conditions and is effective for bearing fault diagnosis.

Partial Load: A Key Factor Resulting in the Failure of Gear in the Wind Turbine Gearbox

Abstract: Gearbox is a critical component in the wind turbine system which can transfer wind energy into wind power to replace some fossil energy in order to reduce the environmental pollution. A 1.5-MW wind turbine gearbox failed after about 5 years of service; however, the design life of the gearbox is 20 years. In this paper, the failure mechanism of the gearbox was investigated based on standard failure analysis procedures and finite element (FE) simulation. The failure of gear could be attributed to fatigue fracture, because typical macroscopic features—beach marks and ratcheting marks—could be observed on the fracture surface. Furthermore, contact fatigue caused the formation of pits on the failed working tooth flank, even brought some microcracks. It should be emphasized that fatigue pitting mainly concentrated at the left end of the failed gear. Based on the physical, chemical analysis, and FE simulation, the failure of gear should be essentially ascribed to abnormal load rather than the material defects. Finally, based on the failure characteristics, partial load should be responsible for the failure of the gear in the wind turbine gearbox.

Characterization of Damage Induced by Impacting Objects in Udimet-500 Alloy

Abstract: Foreign object damage (FOD) is one of the common mechanisms in turbine blade failures which reduces high cycle fatigue life and contributes significantly to premature failure. Therefore, this study experimentally simulated FOD on the first stage blade of a gas turbine. Foreign objects with two parameters of object nose shape (spherical, conical, and flat) and impact angle (90° and 45° relative to the blade surface) were impacted on the surface of flat specimens of Udimet-500 at a temperature of 733°C with velocity of 300 m/s (same as working condition of blades). In order to evaluate the impact site morphologies, induced craters were first studied by scanning electron microscopy (SEM). Then samples were sectioned symmetrically, and by using image analysis tool software, the depth of each crater was measured. Finally, based on the results, it was found that maximum and minimum stress concentration factors and induced microcracks, respectively, are regarding to flat projectiles with impact angel of 45° and spherical at impact angle of 90°.

Flow Motion and Dust Tracking Software for PIV and Dust PTV

Abstract: Dust resuspension and mobilization in case of loss of vacuum accidents and loss of coolant accidents is an important safety issue for Tokamaks. The Quantum Electronics and Plasma Physics Research Group of the University of Rome Tor Vergata has produced an experimental facility, STARDUST-Upgrade, able to replicate these accidents and to obtain fluid dynamic characterization and dust mobilization information in order to validate CFD models. The authors decided to implement two non-intrusive optical methods, particle image velocimetry (PIV) and shadowgraph technique. Two software programs have been developed to compute numerical values from PIV and Shadowgraph frames, namely Flow Motion and Dust Tracking Software. Flow Motion Software has the capability to extract flow velocity field analyzing consecutive frames. Dust Tracking Software follows the path of single objects (i.e., dust particles) tracing their velocity, direction, and position over time. Two experiments have been realized for each software program in order to validate them: cigarette smoke and burning paper plume have been used for flow motion software, while tungsten dust and flour mobilization have been used for dust tracking software.

A Study to Establish Correlation Between Intercolumnar Cracks in Slabs and Off-Center Defects in Hot-Rolled Products

Abstract: Delamination and cracking related to segregations are mostly observed at the centerline of hot-rolled products. The delamination is related to heavy concentration of manganese sulfide inclusions originating from centerline segregation in slabs. In multiple cases, similar delamination or cracking is observed at locations away from the mid thickness plane of hot-rolled products during forming operations at customer end. This leads to rejection of materials. Metallographic investigation reveals segregation line with plenty of manganese sulfide stringers at the off-center location similar to observations in cases of centerline defects. Centerline segregation is a well-understood phenomenon, but the presence of off-center segregation line in hot-rolled products has not been systematically studied before. Several literatures report intercolumnar cracks in slabs to be filled with segregations. Also, they occur away from the centerline of continuously cast slabs. A laboratory-based experimental study was conducted using a slab suspected by S-printing to contain intercolumnar cracks. The aim of this study was to evaluate the effect of intercolumnar cracks on internal quality of rolled products. This paper reports the finding of this study that established a strong correlation between intercolumnar cracks in slabs and off-center cracking in hot-rolled products.

Optimization Analysis on the Effects of Slip Insert Design on Drill Pipe Damage

Abstract: New oil and gas reservoir discoveries in deep conditions have become common. Constructing wells in these deep environments has challenged the petroleum industry to develop new technologies for reaching extended depths while focusing on limitations of the pipes due to excessive damage from slips. This paper addresses a serious problem pertinent to the design of slip insert. Firstly, a series of numerical simulation models are established to analyze the effects of slip insert design on drill pipe damage under a pipe weight of 200 tons, where the drill pipe is 5 in. which is subjected to the American Petroleum Institute. Secondly, the models are conducted to find the optimized parameters of the slip insert by comparing the maximum stress of different combinations. Finally, laboratory experiment is carried out to verify the simulation results. For the drill pipe and slip system selected, an optimized slip insert with a front-rake angle of 75°, a back-rake angle of 30°, a chamfer of 0.2 mm, and a tooth height of 2 mm is obtained. This research provides a method for designing the slip insert.

Investigation of the Influence of Small Hole on the Fatigue Crack Growth Path

Abstract: The goal of this paper is to investigate the fatigue crack growth (FCG) path in 7075-T6 aluminum alloy affected by small hole. The codes ANSYS and FRANC3D are jointly used to compute the stress intensity factors and predict the FCG path. The predicted results show that the fatigue crack turns its growth direction toward the hole. The different locations and sizes of single hole have different influences on the FCG paths, while two symmetrically distributed holes have no effects on the FCG path. The predicted FCG paths are validated by the related FCG test results.

Mixed-Mode Crack Propagation in Cruciform Joint using Franc2D

Abstract: The focus of this research was on determining the cracking behavior when parameter such as the biaxiality ratio was varied. The crack propagation under mixed-mode loading was simulated by means of finite element method. The stress intensity factors have been calculated by the linear elastic fracture mechanics approach using fracture analysis code-2D (Franc2D). The crack growth under opening mode-I was considered because the crack growth occurs mainly along the direction where the mode-I stress component becomes the maximum. The numerical integration of Paris’ equation was carried out. The effect of normal and transverse applied load (σ x, and σ y, respectively) on crack propagation was presented. It was found that the fatigue crack growth was faster at a smaller biaxial stress ratio (λ), i.e., higher σ y on the horizontal crack plan. Moreover, fatigue strength values decrease as λ decreases. The results confirm the use of fracture mechanics approach in biaxial fracture.

Corrosion Resistance Studies of Austenitic Stainless Steel Grades in Molten Zinc-Aluminum Alloy Galvanizing Bath

Abstract: The corrosion inhibition performance and mechanical behavior of galvanized and heat-treated four newly developed austenitic stainless steel grades and type 316L austenitic stainless steel for application as sink rolls in galvanizing baths of 0.14–0.21 wt.% aluminum was investigated and compared through immersion corrosion test to determine the weight loss between 168 and 504 h, tensile test, and Charpy impact test. The delta ferrite content of the test samples was observed and estimated through optical microscopy, feritscope, and ONRL diagram. Scanning electron microscopy and energy dispersive spectroscopy were used to characterize the surface microstructure, morphology, and chemical composition of the galvanized coating of the steel samples. Result showed that only two of the newly developed stainless steel compositions were selected for use in fabrication of galvanizing hardware based on the comparisons of corrosion and mechanical performances of tested alloys.

Reliability Target Assessment Based on Integrated Factors Method (IFM): A Real Case Study of a Sintering Plant

Abstract: The success of a company depends on customer’s satisfaction: quality, price, and service. These three goals depend in particular on R.A.M.S. characteristics: reliability, availability, maintainability, and safety. In the last few years, in order to guarantee high standards of reliability and maintainability, new methodologies and techniques have been developed to estimate the R.A.M.S. targets. In particular, the reliability target represents both the starting and the ending point of R.A.M.S. analysis. The design of the reliability target of a system is a crucial aspect of reliability analysis, as it affects the performance of the system and components. This paper aims to develop a new approach called “IFM Target,” to define the reliability target for complex systems through the integrated factors method, to combine the advantages of usually used approaches, and to overcome some criticalities highlighted in a careful literature analysis. The proposed method has been applied on a sintering system. The results show the effectiveness of the proposed approach.