Residual Grain Research Articles

Modelling of Conventional and Severe Shot Peening Influence on Properties of High Carbon Steel via Artificial Neural Network

Shot peening (SP), as one of the severe plastic deformation (SPD) methods is employed for surface modification of the engineering components by improving the metallurgical and mechanical properties. Furthermore artificial neural network (ANN) has been widely used in different science and engineering problems for predicting and optimizing in the last decade. In the present study, effects of conventional shot peening (CSP) and severe shot peening (SSP) on properties of AISI 1060 high carbon steel were modelled and compared via ANN. In order to networks training, the back propagation (BP) error algorithm is developed and data of experimental test results are employed. Experimental data illustrates that SSP has superior influence than CSP to improve the properties. Different networks with different structures are trained with try and error process and the one which had the best performance is selected for modeling. Testing of the ANN is carried out using experimental data which they were not used during networks training. Distance from the surface (depth), SP intensity and coverage are regarded as inputs and microhardness, residual stress and grain size are gathered as outputs of the networks. Comparison of predicted and experimental values indicates that the networks are tuned finely and adjusted carefully; therefore, they have good agreement.

The Effect of Residual Stress and Fine Crystal Grain at the surface on Fatigue Strength of Rubbing Specimen with the cemented carbide tip

The Effect of Residual Stress and Fine Crystal Grain at the surface on Fatigue Strength of Rubbing Specimen with the cemented carbide tip

Scratch behavior of boron nitride nanotube/boron nitride nanoplatelet hybrid reinforced ZrB2-SiC composites

Spherical instrumented scratch behavior of ZrB2-SiC composites with and without hybrid boron nitride nanotubes (BNNTs) and boron nitride nanoplatelets (BNNPs) was investigated in this research. Typical brittle fracture such as microcracks both in and beyond the residual groove and grain dislodgement was observed in ZrB2-SiC composite, while hybrid BN nanofiller reinforced ZrB2-SiC composite exhibited predominantly ductile deformation. The peculiar three-dimensional hybrid structure in which BNNPs retain their high specific surface area and de-bundled BNNTs extend as tentacles contributes to the improved tolerance to brittle damage. Additionally, easier grain sliding due to BN hybrid nanofillers located at grain boundaries and these BN hybrid nanofillers attached on the scratch surface would provide significant self-lubricating effect to reduce lateral force during scratch and to alleviate contact damage.

Technology of thermal welding with ultrasonic weld joint treatment as applied to NPP formworks

Increasing the strength, reliability and durability of welded structures is an important problem in welding engineering. A significant influence is exerted by residual stresses. Uneven heating of the product during welding causes its uneven temperature deformation. The product material solidity prevents the free temperature deformation of its individual parts, resulting in the formation of stresses and plastic deformation of some parts of the joint metal during welding, and after cooling, welding stresses and deformations remain in the product.The paper describes an innovative technology of thermal welding with ultrasonic weld joint treatment as applied to aluminum sliding formworks used in NPP construction. Ultrasonic treatment in the process of welding greatly increases the strength of formwork weld joints by reducing their residual stresses, grain size and degassing. The structure and properties of aluminum welds become identical to the base metal. Thermal welding with ultrasonic weld joint treatment will improve the reliability of welded joints and increase their time in service. The paper presents the results of theoretical and experimental studies of ultrasonic effects on the welded joints and heat-affected zone.

Influence of laser peening on the hydrogen embrittlement resistance of 316L stainless steel

The effects of laser peening (LP) on the surface micro-structure and hydrogen embrittlement behavior of 316L stainless steel specimens were investigated. 316L stainless steel samples were treated by LP first, and then hydrogen charged electrochemically in 0.5mol/L dilute sulfuric acid solution in the presence of 1.25g/L sodium phosphate. Surface residual stress and microhardness of the specimens were recorded before and after hydrogen charging, while the surface microstructures of the specimens were also observed by means of optical microscope (OM) and scanning electron microscope (SEM). Furthermore, a slow rate tensile test was conducted by an electronic universal testing machine to study the toughness loss during the hydrogen charging process. The results showed that the LPed areas were less influenced by hydrogen atoms than the base metal. Also, susceptibility to hydrogen embrittlement was decreased after LP, and the strengthening mechanism of LP on hydrogen embrittlement resistance was subsequently revealed and analyzed on the basis of compressive residual stress, grain refinement and dislocation changes.

Temporal changes in stored-product insect populations associated with boot, pit, and load-out areas of grain elevators and feed mills

Commercial grain elevator and feed mill facilities can quickly become infested with stored-product insect pests, compromising the protection of the stored raw and processed cereal products. Elevators and feed mills were sampled monthly for adult stored-product insects in grain residues from the boot-pit areas and in bulk load-out samples from 2009 to 2010. The grain samples collected from the boot, pit, and load-out areas consisted of corn, soybeans, or a mixture of the two grains. Low insect densities were found in the boot-pit area during the cool winter months. Insect numbers increased in the spring and peaked during the warm summer months, prior to declining in the fall following a pattern of higher insect densities during higher ambient temperatures. The rice weevil, Sitophilus oryzae (L.), was the most prevalent species collected in all of the sampled grain residues, representing 69.2 and 35.8% of total insects collected in feed mills and elevators, respectively, during 2009 and was also commonly collected in 2010. Other commonly collected insect species included, the red flour beetle, Tribolium castaneum (Herbst); rusty grain beetle, Cryptolestes ferrugineus (Stephens); and sawtoothed grain beetle, Oryzaephilus surinamensis (Linnaeus). Our results showed that failing to clean out boot residual grain and a lack of sanitation of the pit area resulted in high numbers of insects that were transferred through the elevator leg to other locations within a facility. We conclude that the lack of sanitation at elevator and feed mill facilities allowed high numbers of insects to develop.

A physical-based constitutive model for surface integrity prediction in machining of OFHC copper

Due to the rising interest in predicting machined surface integrity and sustainability, various models for metal cutting simulation have been developed. However, their accuracy depends deeply on the physical description of the machining process. This study aims to develop an orthogonal cutting model for surface integrity prediction, which includes a physical-based constitutive model of Oxygen Free High Conductivity (OFHC) copper. This constitutive model incorporates the effects of the state of stress and microstructure on the work material behavior, as well as a dislocation density-based model for surface integrity prediction. The coefficients of the constitutive model were identified through a hybrid experimental/numerical approach, consisting in mechanical tests, numerical simulations and an optimization-based algorithm. The orthogonal cutting model was simulated by FEM, using ALE formulation, and was validated by comparing predicted and measured results, including residual stresses, dislocation density and grain size. The model is then used to analyze the influence of the cutting parameters and cutting geometry on surface integrity, and its results are compared to those obtained by the Johnson-Cook model.

High Strength and Wear Resistance of Tantalum by Ultrasonic Nanocrystalline Surface Modification Technique at High Temperatures

Enhancing the strength of materials is of great concern in that the failures such as wear, corrosion and fatigue occur on the surface. A tantalum (Ta), which is a refractory metal, was subjected to severe plastic deformation induced by ultrasonic nanocrystalline surface modification (UNSM) technique at room- and high-temperatures of 200°C and 800°C. The mechanical properties and wear resistance of Ta before and after UNSM treatment were characterized by X-ray diffraction (XRD), hardness tester, and ball-on-disk tribometer, respectively. The UNSM treatment at 800°C led to the intensity reduction and broadening, and the diffraction peaks were shifted to lower angles, which means the presence of compressive residual stress and grain size refinement. The hardness of the UNSM-treated sample at room temperature was higher than that of the untreated one, and it was further increased with increasing the UNSM treatment temperature. In addition, the effect of UNSM treatment at high-temperature on wear resistance was significant than that of the UNSM treatment at room-temperature. We demonstrate the possibility of further increasing the mechanical properties and wear resistance of Ta by UNSM treatment at high-temperatures in comparison with the untreated and UNSM-treatment at room temperature, which would be beneficial for applications of Ta.

Microstructural Evolution during Friction Stir Spot Welding of AZ31 and Its Effect on the Corrosion Resistance of the Joint

In recent years, the corrosion resistance of friction stir spot welds made in magnesium alloys has been the focus of many research projects. Previous reports documented the cathodic behavior of the stir zone (SZ) with respect to the base material, causing increased localized corrosion in the region adjacent to the weld, which is known as the thermo-mechanically affected zone (TMAZ).1,2 While the electrochemical interaction between the SZ and the base metal have been thoroughly studied, the cause for the ennoblement of the weld nugget remains largely unknown. Various studies suggested that the microstructural evolution occurring during the welding process was responsible for the increased corrosion resistance of the stir zone, but the specific contribution from each microstructural feature has not been examined. The present study examines the effect of several microstructural features that are altered during the welding process, ultimately determining their individual contribution to the overall effect on the corrosion characteristics of the joint. Specifically, this investigation examines the effect of (i) residual stress, (ii) grain size and orientation, and (iii) second phase precipitation on the corrosion behavior of FSSW in magnesium alloys. The effect of microstructural variation on the corrosion resistance properties of the stir zone has been evaluated through characterization and electrochemical testing. The corrosion potential and current of the stir zone were determined using microcapillary polarization in 0.1M NaClO4, a localized electrochemical technique developed in previous work.2 Changes in grain size and orientation were monitored through electron back scattered diffraction (EBSD). The effect of residual stress was examined through a series of stress relieving heat treatments. Finally, the effect of second phase particles was investigated by electron microscopy (EM) and nuclear magnetic resonance (NMR). The effect of friction stir spot welding on the microstructure and electrochemical properties of AZ31 is summarized in table I. Each microstructural change was found to have a unique effect on the electrochemical properties of the stir zone region. The relatively small changes in grain size and residual stress induced by the welding operation have been shown to have negligible effects on the corrosion behaviour of the weld nugget.3 Investigation of the grain orientation revealed weaker basal texture in the stir zone than in the base metal. As a result, changes in grain orientation were found to be responsible for the reduction in the corrosion potential and current of the stir zone. Changes in the size and presence of second phase precipitates (Mg-Al and Al-Mn intermetallics) were determined to be the most dominant factor determining the electrochemical properties of the stir zone. Dissolution of these intermetallics eliminated the harmful microgalvanic cells formed between the particles and the surrounding matrix, as well as increased the overall aluminum content in the α-Mg matrix. Ongoing work is focused on producing a model that correlates the welding parameters to the microstructural features present in the SZ region and its subsequent electrochemical properties.

Dolomitization by penesaline sea water in Early Cambrian Longwangmiao Formation, central Sichuan Basin, China

The Lower Cambrian Longwangmiao Formation shoal dolostone reservoir in Sichuan Basin is currently an exploration and research highlight in China. Reservoir rocks mainly consist of crystalline dolomite with residual grain texture, and dolarenite of which the arene is mainly composed of muddy to micritic dolomite with some crystalline grain directionally aligned. The trace element indicates that the dolomites of Longwangmiao Formation may be related to the high salinity of sea water. The oxygen isotope values of crystalline dolomite and dolarenite are both similar to that of the Early Cambrian marine dolomites, and the carbon isotope values of every kind of dolomites are completely overlapped with that of the seawater in Early Cambrian, indicating the dolomitization fluid is originated from the Early Cambrian sea water. The restricted marine biological communities and a small amount of gypsum pseudonodule seen in muddy to micritic dolomite indicate that the sea water in Early Cambrian was restricted and evaporated. However, the general lack of massive evaporite mineral and gypsum karst breccia indicates that the salinity of sea water during dolomitization was lower than the value of gypsum's precipitation. The Longwangmiao Formation consists of several high-frequency sedimentary cycles, indicating frequent sea level changes. This study indicates that massive dolomitiza-tion may also occur in underwater palaeohigh in carbonate platform through the reflux of penesaline sea water driven by a combination of high- and low-frequency sea-level changes. This kind of dolomiti-zation can explain the generation of massive dolomites in the absence of evaporite precipitation, and further indicates that replacement dolomites can be produced by sea water with a wide range of salinity (normal, penesaline to hypersaline).

Effect of high energy shot peening on the microstructure and mechanical properties of Mg/Ti joints

The effects of high energy shot peening (HESP) on the microstructures and mechanical properties of tungsten inert gas (TIG) welded-brazed Mg/Ti joints were investigated, in terms of surface characteristics, residual stress variation, grain size, dislocation density and tensile strength of the resulting joints. The results show that HESP under an optimized Almen intensity of 0.16 mm N resulted in the surface defects elimination, high compressive residual stress, fine-grain strengthening and strain strengthening of Mg/Ti joint. All these factors contributed to the significant improvement in mechanical properties of the joints, leading to a notable enhancement (24.5%) in tensile strength of the Mg/Ti joint to 241 MPa over the joints without HESP treatment (193.5 MPa). However, further increment in Almen intensity to 0.24 mm N resulted in severe internal cracks within the joint, which deteriorated the mechanical properties of Mg/Ti joints.

Residual Stress, Defects and Grain Morphology of Ti-6Al-4V Alloy Produced by Ultrasonic Impact Treatment Assisted Selective Laser Melting

For large-scale selective laser melting (SLM) additive manufacturing technology, three main problems severely restrict its development and application, namely the residual stress, defects, and columnar grains with anisotropy. To overcome these problems, a new method is proposed by combining SLM with ultrasonic impact treatment (UIT) technique. This study explores the feasibility of UIT assisted SLM, as well as the effect of UIT on the residual stress, defects and β grains of Ti-6Al-4V alloy sample. The results indicate that after the application of UIT during SLM, residual stress can be largely reduced and defects can be hammered flat and even eliminated. Meanwhile, the epitaxial growth of columnar grains is prevented, and fine equiaxed grains are formed due to plastic deformation and recrystallization.

Microstructure, local mechanical properties and stress corrosion cracking susceptibility of an SA508-52M-316LN safe-end dissimilar metal weld joint by GTAW

The microstructure, local mechanical properties and local stress corrosion cracking susceptibility of an SA508-52M-316LN domestic dissimilar metal welded safe-end joint used for AP1000 nuclear power plant prepared by automatic gas tungsten arc welding was studied in this work by optical microscopy, scanning electron microscopy (with electron back scattering diffraction and an energy dispersive X-ray spectroscopy system), micro-hardness testing, local mechanical tensile testing and local slow strain rate tests. The micro-hardness, local mechanical properties and stress corrosion cracking susceptibility across this dissimilar metal weld joint vary because of the complex microstructure across the fusion area and the dramatic chemical composition change across the fusion lines. Briefly, Type I boundaries and Type II boundaries exist in 52Mb near the SA508-52Mb interface, a microstructure transition was found in SA508 heat affected zone, the residual strain and grain boundary character distribution changes as a function of the distance from the fusion boundary in 316LN heat affected zone, micro-hardness distribution and local mechanical properties along the DMWJ are heterogeneous, and 52Mw-316LN interface has the highest SCC susceptibility in this DMWJ while 316LN base metal has the lowest one.

Effect of grain size and residual stress on the corrosion resistance of friction stir spot welded AZ31B joints

Localized corrosion at the weld periphery of AZ31B friction stir spot welds has been associated with the formation of a galvanic cell between the stir zone material and the adjacent base metal. However, this explanation did not take into account the effects of residual stress and grain growth in material adjacent to the stir zone region. In this study, the influence of microstructural changes on the electrochemical characteristics of FSSW joints is investigated using a combination of microcapillary polarization, stress relief heat‐treatment and micro‐hardness testing. It is confirmed that residual stress has no significant effect on the corrosion resistance properties of completed joints. Also, based on a detailed examination of the electrochemical characteristics of materials in the stir zone, TMAZ and HAZ regions, grain growth had negligible influence on the corrosion resistance properties.

Summary of Auger-Related Entanglement Incidents Occurring Inside Agricultural Confined Spaces.

Entanglements in energized equipment, including augers found in agricultural workplaces, have historically been a significant cause of traumatic injury. Incidents involving augers located inside agricultural confined spaces (primarily grain storage structures and forage silos), although relatively rare events, are a widely recognized problem due to the relative severity of the resulting injuries and the complexities of victim extrication. However, this problem is neither well documented nor elucidated in the research literature, other than anecdotal observations relating to medical treatment of auger-related injuries and citations for non-compliance with federal and state workplace safety regulations. A review of nearly 1,650 cases documented in the Purdue Agricultural Confined Spaces Incident Database from 1964 to 2013 identified 167 incidents involving entanglement in an energized auger that occurred while the victim was working inside an agricultural confined space. These incidents primarily included in-floor unloading augers, sweep augers, stirring augers, and auger components found on silo unloaders. Cases involving portable tube augers used to handle grain outside grain storage structures were not included. Based on analysis of the data, approximately 98% of known victims were male, with the 21-45 age group reporting the largest number of incidents. Nearly one-third (32.3%) of incidents were fatal, and lower limb amputation was the most frequently reported injury type. (It is believed that non-fatal incidents are grossly under-reported in the data set due to a lack of comprehensive reporting requirements, especially for most farms, feedlots, and seed processing operations, which are generally exempt from compliance with OSHA machine guarding, confined-space, and grain-handling standards.) The type of auger identified most frequently as the agent of injury was the exposed in-floor auger (48), which frequently resulted in amputation of one or more lower limbs when the victim stepped into an unguarded opening or well in the floor of the confined space. The primary reason identified as to why workers were exposed to energized augers in the cases documented was to assist in the removal of residual or out-of-condition grain. The large number of cases involving augers on top-unloading silo unloaders (36) was not anticipated. Silo unloaders also accounted for the largest number of documented fatalities (15). This analysis is the first known attempt to provide a better understanding of the frequency, severity, and causative factors of these incidents. Those key causative factors were found to be: (1) lack of or inadequate guarding, (2) unintentional energizing of components due to a lack of lockout/tagout training and provisions, and (3) exposure of untrained or inexperienced workers to energized and unguarded components during procedures to remove residual grain or other agricultural crops from storage structures. It is hoped that the results and recommendations presented will raise awareness of the hazards related to using energized equipment in confined spaces as well as contribute to development of new evidenced-based educational resources, engineering safety standards, and workplace safety regulations.

Effects of residual stress and grain boundary character on creep cracking in 2.25Cr-1.6W steel

Effect of residual stresses on creep behavior was investigated using designed compact tension specimens in 2.25Cr-1.6W steel before and after heat treatment. The heat treatment was carried out to obtain partial austenitization microstructure and to cause zigzag configuration of grain boundaries. Residual stresses were generated ahead of crack root by loading in compression beyond yield and then unloading. A three-dimensional finite element model was developed to predict the evolution of creep damage and residual stress within the specimens during creep time. The extent of creep crack has also been assessed through destructive examination, providing validation for the creep damage prediction model. Fractal analysis was applied to quantitative determinate the correlation between the grain boundary configuration and creep behavior.

Variations in surface residual compressive stress and magnetic induction intensity of 304 stainless steel

This study proposed micromagnetic nondestructive detection technology to detect the surface residual compressive stress of 304 stainless steel specimens after annealing treatment and loading. X-ray diffraction was used to determine the changes in residual compressive stress, microstrain, and grain size to aid in verification. Variations in surface residual compressive stress and magnetic induction intensity were analyzed. When residual compressive stress changed markedly, the change in magnetic induction intensity reflected the change in residual compressive stress. With the increase in residual compressive stress, the surface magnetic induction intensity and residual compressive stress of the specimen exhibited an approximate linear relationship, manifesting an increasing trend. Therefore, residual compressive stress was analyzed by detecting the changes in the surface magnetic induction intensity of specimens. Micromagnetic nondestructive detection allows the effective detection of the surface residual compressive stress of 304 stainless steel.

Tensile properties, residual stress distribution and grain arrangement as a function of sheet thickness of Mg–Al–Mn alloy subjected to two-sided and simultaneous LSP impacts

Two-sided and simultaneous laser shock peening impacts is considered as a novel surface treatment technology for the turbine blade and thin-walled component. In this paper, tensile properties of Mg–Al–Mn alloy specimens with different sheet thickness under two kinds of laser shock peening strategies were investigated, and an overlapping three-dimension axisymmetric numerical model was developed to analyze the effects of sheet thickness on residual stress distributions. Meanwhile, special attentions were paid to the in-depth microstructural evolution as a function of sheet thickness. Results showed that sheet thickness had an important influence on the tensile properties of Mg–Al–Mn alloy, and the generated residual stress distribution and grain arrangement were two important factors. The corresponding influence mechanism of sheet thickness on the tensile properties of Mg–Al–Mn alloy was also presented, and the optimal thickness of Mg–Al–Mn alloy sheet may be 4mm or more.

Effect of Residual Phase and Grain Size on Corrosion Resistance of SiC Ceramics in Mixed HF-HNO$lt;inf$gt;3$lt;/inf$gt; Acid Solution

Effect of residual phase and grain size the corrosion resistance of SiC ceramics in mixed HF-HNO3 acid so- lution was investigated. Three kinds of fabrication methods (SSiC-solid state sintered SiC, LPS SiC-liquid phase sin- tered SiC and RB SiC-reaction bonded SiC) were adopted to prepare SiC ceramics. Besides, the grain size in SiC ce- ramics was adjusted under different sinter temperatures. Compared to RB SiC and LPS SiC ceramics, SSiC ceramics showed a better corrosion resistance for the good corrosion resistance of residual graphite and 'island' structure of re- sidual phase in ceramics. The grain size of SiC ceramics sintered at temperature between 2100℃ and 2160℃ in- crease from 2 μm to 6 μm, and the absolute values of Y intercept, which reflect the corrosion of SSiC ceramics with none residual phase, are 9.22 μg/cm 2 (2100℃), 5.81 μg/cm 2 (2130℃) and 0.29 μg/cm 2 (2160℃), which demonstrate

激光喷丸IN718 镍基合金残余应力高温松弛及晶粒演变特征

激光喷丸IN718 镍基合金残余应力高温松弛及晶粒演变特征