Impact Pits Research Articles

Numerical Analysis of Cavitation Erosion in 316L Steel with CrN PVD Coating.

The erosion process of a 4 μm monolayer CrN coating deposited on 316L stainless steel due to cavitation was investigated using finite element analysis (FEA). To estimate load parameters from cavitation pit geometry resulting from high impact velocity and high strain rate, the explicit dynamic solver was employed. Water microjet impacts at velocities of 100, 200 and 500 m/s were simulated to recreate different cavitation erosion intensities observed in the experiment. The resulting damage characteristics were compared to previous studies on uncoated 316L steel. The relationship between impact velocity and postimpact geometry was examined. Simulations revealed that only impact at 500 m/s can exceed the maximum yield stress of the substrate without penetrating the coating. Subsequent impacts on the same zone deepen the impact pit and penetrate the coating, leading to direct substrate degradation. The influence of impact velocity on the coating degradation process is discussed.

Variation in Granular Frictional Resistance Across Nine Orders of Magnitude in Shear Velocity

AbstractDetermining the shear‐velocity dependence of dry granular friction can provide insight into the controlling variables in a dry granular friction law. Some laboratories believe that the quality of this study is at the forefront of the discipline for the following reasons. Results suggest that granular friction is greatly affected by shear‐velocity (v), but shear experiments over the large range of naturally occurring shear‐velocities are lacking. Herein we examined the shear velocity dependence of dry friction for three granular materials, quartz sand, glass beads and fluorspar, across nine orders of magnitude of shear velocity (10−8–2 m/s). Within this range, granular friction exhibited four regimes, following a broad approximate “m” shape including two velocity‐strengthening and two velocity‐weakening regimes. We discuss the possible physical mechanisms of each regime. This shear velocity dependence appeared to be universal for all particle types, shapes, sizes, and for all normal stresses over the tested range. We also found that ultra‐high frequency vibration as grain surfaces were scoured by micro‐chips were formed by spalling at high shear velocities, creating ∼20 μm diameter impact pits on particle surfaces. This study provides laboratory laws of a friction‐velocity (μ‐v) model for granular materials.

Failure analysis and numerical simulation of the regulating valve with particle erosion and cavitation erosion in the black-water treatment system

The black-water regulating valve is very easy to be damaged due to the erosion of the key components, such as valve spool and valve seat. This work presents the failure analysis of the spool and seat of regulating valve in the black-water treatment system. Scanning electron microscopy and X-ray energy-dispersive spectrometer were used to detect the morphology and chemical compositions of failure valve samples. The computational fluid dynamics method was also adopted to simulate the medium flow characteristics in black-water regulating valve. The results show that most erosion areas of the valve occur at the spool-seat throttle zone. The erosion profile is mainly manifested in plastic deformation pits, cutting abrasions, furrows, pinhole pits and impact pits. The particles and cavitation bubbles move toward the throttle zone driven by black-water medium, causing particles impact and bubbles collapse. The particle flow velocity in the throttle zone of the valve is between 50 and 175 m/s, while the maximum velocity can reach 175 m/s. The valve suffered severe particle erosion and cavitation erosion under the particle impact and bubble collapse, finally resulting in its failure.

Experimental and numerical study on projectile impact damage of EBC-SiC/SiC

The ingested particles or debris will cause high-speed & low-energy impact to the hot end components of aeroengine. Few literature focus on the projectile impact of SiC/SiC with Environmental Barrier Coating(EBC). The impact of 2 mm projectile was specially studied for Si/Yb2Si2O7/Yb2SiO5-SiC/SiC. Gas gun system was used to conduct impact testing at the speed of 3 m/s∼353m/s. The optical microscope, Scanning Electronic Microscope(SEM), micro CT were used to observe the impact and tension after impact(TAI) damage. For TAI, Digital Image Correlation (DIC) was used to conduct the full-field strain detection around the impact point. Meanwhile, the Smoothed Particle Hydrodynamics (SPH) methodology was programmed in C++ and developed to simulate SiC/SiC impact problem by introducing modified Hashin-Rotem criteria, extending interface method to 3D and adding GPU accelerated algorithm. The results indicate that threshold velocities of EBC huge peeling and SiC/SiC penetration are different, TAI residual strength also has extinct threshold at the velocity of 246 m/s with 37.1% declining extent, and the impact pit depth of SPH simulation is in good agreement with the experiment.

Fatigue evaluation on the effect of impact pits with various impact conditions by a CDM‐based approach

AbstractThis work aims to quantitatively evaluate the influence of the impact velocity, location, and angle of a spherical foreign object on fatigue lives. A continuum damage mechanics (CDM)–based fatigue approach is proposed to evaluate the fatigue behavior. The experiments on a cast AlSi7Mg1 aluminum alloy with a low‐velocity impact pit are used to validate the proposed fatigue model. The comparison between the predicted lives with the experimental data indicates an excellent agreement. Based on the proposed model, the effects of various impact velocities, locations, and angles are investigated. It is found that the velocities have negligible influence on the fatigue life in low‐velocity impact cases once the pit depth is the same. The most dangerous impact location for 90° normal impact cases is inferred to be a distance away from the boundary surface. The 45° transverse impact close to the boundary is different from other studied oblique impacts and has a longer life than the corresponding normal impact. This study uses a feasible method to predict the effects of different impact conditions and provides useful guidance for engineering applications.

Effect of ultrasonic impact treatment on welding residual stress and fatigue resistance of doubly-welded rib-to-deck joints in OSD

Innovative doubly-welded rib-to-deck joints (DRJ) have been developed to enhance the fatigue life of orthotropic steel decks (OSD) used in steel bridges. However, the welding process and welding residual stress (WRS) distribution of DRJ are more complicated than those of conventional single-side welded rib-to-deck joints. To release WRS and improve the fatigue resistance of DRJ, ultrasonic impact treatment (UIT) and fatigue tests were performed in this study. The effect of the UIT process on the WRS distribution and fatigue resistance of the DRJ was investigated. Furthermore, the welding processes of the DRJ and UIT were simulated using the finite element method and validated against the relevant measurements. Subsequently, they were used to investigate the effect of the UIT process on the WRS distribution and represent the mechanism of fatigue failure of the DRJ. Compared with the as-welded specimens without UIT, the fatigue strength of the DRJ increased by more than 60%, and the UIT process altered the dominant fatigue failure mode of the DRJ. The fatigue crack, caused by a UIT-induced fold defect, tends to initiate at the bottom of the impact pit. Owing to the UIT process, the adverse tensile WRS in the weld toe is eliminated, and beneficial compressive residual stress is introduced, leading to an improvement in the fatigue strength of the DRJ.

Effects of Different Materials on Residual Stress Fields of Blade Damaged by Foreign Objects.

Foreign object damage (FOD) is a common mode of failure in high-speed rotating machinery, such as aircraft engines. Therefore, research on FOD is crucial for ensuring blade integrity. FOD induces residual stress on the surface and within the blade, impacting its fatigue strength and service life. Therefore, this paper utilizes material parameters determined by existing experiments, based on the Johnson-Cook (J-C) constitutive model, to numerically simulate impact damage inflicted on specimens, compare and analyze the residual stress distribution of impact pits, and investigate the influence law of foreign object characteristics on blade residual stress. TC4 titanium alloy, 2A12 aluminum alloy, and Q235 steel were selected as foreign objects, and dynamic numerical simulations of the blade impact process were performed to explore the effects of different types of metal foreign objects. This study analyzes the influence of different materials and foreign objects on the residual stress generated by blade impact through numerical simulation, examining the distribution of residual stress in different directions. The findings indicate that the generated residual stress increases with the density of the materials. Additionally, the geometry of the impact notch is also influenced by the density difference between the impact material and the blade. The distribution of the residual stress field reveals that the maximum residual tensile stress in the blade is related to the density ratio, and the residual tensile stress in the axial and circumferential direction is relatively large. It is important to note that a significant residual tensile stress has a detrimental effect on the fatigue strength.

Rapid prediction of compression after impact properties of composite structures: An equivalent strategy for impact damage

Combined with the results of finite element simulation and experimental ultrasonic C-scan, a phenomenological-based equivalent impact damage finite element model was proposed and established to rapidly predict the damage evolution and buckling deformation of composite structures in compression after impact. An image recognition technology was adopted to divide the impact damage of composite laminates and stiffened panels into different regions, and a damage equivalent was conducted based on the measured impact damage size and morphology. Additionally, the material stiffness and strength parameters in different damage equivalent regions were reduced appropriately by different degrees. The impact pit deformation was equivalent to the element node offset in the corresponding area of the model, and the interface delamination and debonding were equivalent to the voids without elements. The equivalent impact damage model was applied to evaluate the buckling behavior and compressive strength after impact for laminates and stiffened panels using ABAQUS software. Moreover, a three-dimensional damage model considering the interaction of interlaminar delamination damage and interlaminar matrix and fiber damage was introduced to characterize the damage initiation, evolution, and extension behaviors of different damage modes. The comparative analysis indicated that the buckling and failure modes and compression after the impact strength simulated using the equivalent model were identical to the experimental results and had high correlation. This confirmed the accuracy, effectiveness, and applicability of the established equivalent impact damage model in predicting the compression buckling as well as residual strength and fracture modes for composite laminate and stiffened panel with simultaneous multi-zone impact damage.

Study on the impact erosion wear resistance and damage evolution of TiN films under different impact cycles

Depositing TiN coating is an effective way to improve the erosion resistance of titanium alloy. However, few studies have been carried out to analyze the damage process of TiN coated specimens. In this study, a TiN coating was prepared on the Ti6Al4V by employing a filtered cathodic vacuum arc. The erosion performance and damage evolution of TiN coating were investigated, accompanied by varying the impact cycles from 500 to 10,000. The change of peak impact force and energy absorption rate with increasing impact numbers were analyzed. A white-light interferometer was used to characterize the 3D surface topographies of the damaged surface. Scanning electron microscopy and energy dispersive spectrometer were used to observe the state of the eroded surface. The results show that the sand is embedded in the substrate with the increase of impact numbers. With decreasing the number of impacts, the energy absorption rate of the TiN coating increased rapidly, while the peak impact force decreases rapidly. The formation of impact pits, plow grooves, micro-cutting, brittle spalling, and cracks can be regarded as the wear mechanisms of the samples under sand erosion.

Microtextures on quartz grains in the Estuary sediments of Gurupura River, Dakshina Kannada district, Karnataka State, West coast, India.

The present study focuses on the surface textures of the quartz grains derived from the granitic rocks in a fluvial regime on the west coast of India. The surface microtextures formed during transport due to their stable physical and chemical properties. The surface textures include information about source rock types, transporting force, sedimentary environment and evolution history of the sediment. For this purpose, eight samples were collected and investigated from the Gurupura River estuary of Dakshina Kannada District of Karnataka state west coast in India. The quartz grains show distinct surface textures with unique mechanical, chemical and morphological features. The mechanical features such as conchoidal fractures with arcuate steps indicate that the sand grains were derived from crystalline source rock (i.e., granite) and transported in a high-energy condition. The silica globule, overgrowth, and precipitation marks on the grain surfaces suggest action of chemical processes in a saturated silica environment, which is evident in the upper reaches of the Gurupura River. Surface textures of the quartz grains along the lower reaches of the Gurupura River display an array of mechanical features like a conchoidal fracture, V-shaped marks and impact pits, indicating the impact of mechanical processes. The overall pattern of the surface textures present on the quartz grains suggests moderate to high energy conditions in the Gurupura River.

Coupled CEL-FDEM modeling of rock failure induced by high-pressure water jet

The coupled Euler-Lagrange (CEL) method and finite-discrete element method (FDEM) are adopted to simulate the rock fracture process induced by high-pressure water jet and to solve the problems of highly nonlinear, fluid-solid coupling and large deformation. The water is characterized by the CEL model, and water can flow freely in the Euler mesh, which can better simulate the actual shape of water jets. The rock is integrated into the FEDM model, which is produced by embedding zero-thickness cohesive elements. The traction-separation criterion of the cohesive element is used to simulate the rock damage. In the simulation process of rock fracture by the water jet, infinite elements are used to realize the non-reflection boundary conditions, simulate real working conditions, and improve the calculation reliability. Furthermore, the VUSDFLD user subroutine is used to delete the elements outside the box and reduce the impact of the fallen rock debris on simulation speed, thus improving calculation efficiency. The formation process of rock impact pits and slits, as well as the velocity and distribution of water jets, are studied by comparing the simulation and experiments of water jet fixed-point impact and moving cutting. Subsequently, the fracture mechanism of rock under the water jet is revealed, presenting new possibilities for studies into rock fractures by high-pressure water jet.

A new aspect of post-depositional alterations of lithic artefacts: the case of Medzhibozh Lower Palaeolithic assemblages

Flint artefacts have been identified in the materials of the Lower Palaeolithic sites of Medzhibozh, which have experienced the effects of post-depositional alterations (PDA). We suggest a particular combination of anthropogenic and natural effects on lithic artefacts. In the vicinity of Medzhibozh in the Khmelnytskyi region in the West of Ukraine, several multilayered stratified Lower Palaeolithic sites are currently known. Artefacts and accompanying fauna have been identified in subaerial buried soils, initial hydromorphic soils, and alluvial deposits. The ages of the artefact-bearing sediments are preliminarily estimated to be between 1.2 and 0.4 Ma. The lithic assemblages of all horizons contain technologically and typologically archaic artefacts, the industry being referred to as Mode 1. Various types of rock were used as raw materials, including locally occurring flints in the form of pebbles and flattened nodules. Flint products from many assemblages are characterized by rounding and sheen due to their extended exposure to water-permeable horizons. Most of the flint artefacts belonging to a particular assemblage are of a similar type of preservation. The assemblages also contain artefacts with surfaces of different states of preservation, suggesting that they are of different ages. These could either be products of reutilisation or natural alterations. However, more recent surfaces tend to be isolated and do not form a removals system. Moreover, most of the individual PDA pieces show a technological and morphological consistency of differently preserved surfaces, indicating that a force initiating detachment was applied simultaneously. We, therefore, consider artefacts showing a variate state of scar preservation to be PDA products. We assume we are dealing with a new aspect of post-depositional alterations of lithic artefacts. Natural alteration had subjected artefacts, which received internal damage to the structure earlier when processed by man. The bipolar-on-anvil technique was actively used at Medzhibozh. Many artefacts show signs of multiple attempts of knapping, accompanied by a change in the position of the segmenting item. Such signs are impact pits, visible cracks, and Herzian cones disturbing the rock's texture. We believe that the internal cracks that appeared in the area of the not detached spall contribute to the accelerated natural alteration of the item in this area and, ultimately, to the detachment of the flake. The probability of spalling depends on the intensity of the internal distress, the structure of the rock, the climatic conditions, and the post-depositional environment. The most responsible factor for the effect of the “time-delayed spalling” seems to be repeated cycles of temperature changes. A comprehensive study of post-depositional modifications of lithic artefacts is essential in studies of Lower Palaeolithic sites, particularly the technological Mode 1 (Oldowan). This is due to the highly heterogeneous raw materials used, the bipolar-on-anvil knapping technique, and a long period of post-discard behaviour of artefacts. Key words: Lower Palaeolithic, Medzhibozh, stone artefacts, post-depositional alterations, time-delayed spalling, taphonomy.

Study on Key Parameters for Jet Impacting Pulverized Coal Deposited in Coal-Bed Methane Wells

Cleaning out the pulverized coal deposited at the bottom of a coalbed methane (CBM) well is key to achieving continuous CBM drainage and prolonging the workover period. In this study, Fluent is used in conjunction with the standard k-ε model and the Eulerian-Eulerian model to simulate and analyse jet erosion of deposited pulverized coal particles. The depth and width of the stable erosion pit that is formed by jet-impacting deposited pulverized coal under different conditions are determined and provide a theoretical basis for the cleanout of pulverized coal in the bottom of a CBM well. In this paper, the three parameters of the jet target distance, nozzle diameter and nozzle outlet flow velocity are selected to perform an orthogonal simulation. The change trends in the depth and width of the scouring pit with time are determined. The results show that jet impacting of deposited pulverized coal can be categorised into four stages, periods of rapid growth, stability, jet swing and dynamic stability. A sensitivity analysis shows that the nozzle outlet flow velocity has the strongest influence on the depth of the scouring pit among the selected parameters. The depth of the jet impact pit can reach the maximum depth at t = 3 s, while the width of the impact pit can reach the maximum after t = 7 s. This can provide key design parameters for CBM well pulverized coal impacting operation. It is of great significance for capacity damage control during CBM well workover operation.

Smoothed Particle Hydrodynamics Modeling of Thermal Barrier Coating Removal Process Using Abrasive Water Jet Technique

Abstract In this work, a new smoothed particle hydrodynamics (SPH)-based model is developed to simulate the removal process of thermal barrier coatings (TBCs) using the abrasive water jet (AWJ) technique. The effects of water jet abrasive particle concentration, incident angle, and impacting time on the fracture behavior of the TBCs are investigated. The Johnson–Holmquist plasticity damage model (JH-2 model) is used for the TBC material, and abrasive particles are included in the water jet model. The results show that the simulated impact hole profiles are in good agreement with the experimental observation in the literature. Both the width and depth of the impact pit holes increase with impacting time. The deepest points in the pit hole shift gradually to the right when a 30-deg water jet incident angle is used because the water jet comes from the right side, which is more effective in removing the coatings on the right side. A higher concentration of abrasive particles increases both the width and depth, which is consistent with the experimental data. The depths of the impact pit holes increase with the water jet incident angle, while the width of the impact holes decreases with the increase in the water jet incident angle. The water jet incident angle dependence can be attributed to the vertical velocity components. The erosion rate increases with the incidence angle, which shows a good agreement with the analytical model. As the water jet incident angle increases, more vertical velocity component contributes to the kinetic energy which is responsible for the erosion process.

Laser Texturing for Superwetting Titanium Alloy and Investigation of Its Erosion Resistance

Erosion of materials is one of the major causes that lead to the malfunction of equipment and facilities, and surface texturing can be a solution for enhancement of erosion resistance. In this work, superwetting (superhydrophilic/superhydrophobic) titanium (Ti) alloy surface with periodic microstructure was prepared by a facile laser-based surface texturing approach which combines laser surface texturing and low-temperature annealing. The effect of laser-induced surface texture and wettability on the erosion resistance of the laser textured surface was studied. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to analyze the chemical surface microstructure and surface on the untreated and laser textured surfaces. The hardness and contact angle of the untreated surface, superhydrophilic surface and superhydrophobic surface were measured by microhardness tester and contact angle goniometer. Using an in-house built erosion experimental setup, the erosion resistance of the untreated surface, superhydrophilic surface and superhydrophobic surface was investigated. The experimental results demonstrate that micro-bumps are formed after laser surface texturing. In the meantime, the surface hardness for the laser textured surface with a step size of 150 μm is increased by 48% under the load of 1.961 N. Compared with the untreated surface, the erosion resistance is increased by 33.9%, 23.8% and 16.1%, respectively, for the superhydrophobic surface. The SEM results show that the untreated surface has large and deep impact pits, while the superhydrophobic surface only has small and shallow impact pits, indicating that the erosion process resulted in less damage to the substrate. The EDS results shows that superhydrophobicity plays a critical role in protecting the substrate from erosion. It is thus believed that the superhydrophobic surface has pronounced effects for improving the hardness and erosion resistance of Ti alloy.

Fatigue tests and damage model development on Al-Si-Mg aluminum alloys with low-velocity impact pit

An experimental-analytical investigation was conducted to study the fatigue properties of ZL114A aluminum alloy with low-velocity impact pit. The analysis of the fracture surfaces indicated that the cracks initiated at the position with tension residual stress rather than at the pit. Considering that the pit depth has a direct correlation with the magnitude of residual stresses, a new damage evolution equation involving a dimensionless parameter about pit depth was proposed to reflect the detrimental effect of pit. The proposed model was applied to the fatigue life prediction of specimens and hole plates with impact pit, and the result was within a twice-error band compared with the experimental data.

Jet characteristics of a double-structure oxygen lance and its interaction with the molten pool in BOF steelmaking

An oxygen lance represents a commonly used piece of equipment in converter steelmaking. Its jet characteristics and the interaction of these jets with the molten pool will directly affect the smelting effect and blowing time. This work investigates the oxygen lance of a 260 t converter in a steel plant. Through numerical simulations and physical experiments, the influence of the operating pressure, ambient temperature, top-blowing flow, lance position, and other operating parameters on the jet flow characteristics of the oxygen lance is studied. Furthermore, the oxygen lance interaction with the molten pool is analyzed. The results show that the operating pressure has little effect on the fusion distance of the jet; however, its size determines the impact force of the jet on the molten pool. In addition, the high-temperature environment causes the density of the jet fluid to decrease, the jet attenuation speed to decrease, the jet fusion speed to increase, and the degree of fusion to attenuate. Furthermore, the spray volume of the furnace mouth continues to increase upon increasing the top-blowing flow; by contrast, the spray volume first increases and then decreases as the gun position increases. The maximum spray volume of the furnace mouth occurs at the 35-de gun position; the diameter of the impact pit varies with the gun position. As the top-blowing flow increases, the depth of the impact pit increases with the decrease in the gun position and the increase in the top-blowing flow. The mixing time gradually reduces with the increase in the top-blowing flow and the decrease in the gun position.

Numerical Investigation of Degradation of 316L Steel Caused by Cavitation.

The degradation process of 316L stainless steel caused by cavitation was investigated by means of finite element analysis. The damage characteristics of metal specimens subjected to the cavitation bubble collapse process were recreated by simulation with a micro-jet water hammer. The simulation results were compared with the cavitation pits created in the experimental tests. In the experiment, different inlet and outlet pressures in a test chamber with a system of barricade exciters differentiated the erosion process results. Hydrodynamic cavitation caused uneven distribution of the erosion over the specimens’ surface, which has been validated by roughness measurements, enabling localisation and identification of the shape and topography of the impact pits. The erosion rate of the steel specimens was high at the beginning of the test and decreased over time, indicating the phase transformation and/or the strain-hardening of the surface layer. A numerical simulation showed that the impact of the water micro-jet with a velocity of 100 m/s exceeds the tensile strength of 316L steel, and produces an impact pit. The subsequent micro-jet impact on the same zone deepens the pit depth only to a certain extent due to elastoplastic surface hardening. The correlation between post-impact pit geometry and impact velocity was investigated.

Late Pleistocene Fossil Record of Cuora amboinensis (Testudines: Geoemydidae) from the Wajak Site, East Java, Indonesia, and Its Paleozoogeographic and Archeozoological Implications

Abstract. A Late Pleistocene fossil represented by an incomplete right hypoplastron of Cuora amboinensis was recovered from the Wajak site (ca. 37 ka–29 ka: Late Pleistocene) in East Java, Indonesia. The fossil constitutes the first certain prehistoric record of this species from Java, which implies that the current conspecific population in this island is indigenous to the region rather than artificially introduced from the Southeast Asian continent in historic times. The specimen has four small distinct impact pits on the hypoplastron in dorsal view, which were possibly caused by a pointed stone artifact or a bone tool. The presence of such percussion marks suggests that this turtle was consumed by the Wajak people.

Numerical Simulation of Impact Behavior of Ceramic Coatings Using Smoothed Particle Hydrodynamics Method

Abstract In this work, the impact behavior of an alumina spherical particle on alumina coating is modeled using the smoothed particle hydrodynamics (SPH) method. The effects of impact angle (0 deg, 30 deg, and 60 deg) and velocity (100 m/s, 200 m/s, and 300 m/s) on the morphology changes of the impact pit and impacting particle, and their associated stress and energy are investigated. The results show that the combination of impact angle of 0 deg and velocity of 300 m/s produces the highest penetration depth and largest stress and deformation in the coating layer, while the combination of 100 m/s and 60 deg causes the minimum damage to the coating layer. This is because the penetration depth is determined by the vertical velocity component difference between the impacting particle and the coating layer, but irrelevant to the horizontal component. The total energy of the coating layer increases with the time, while the internal energy increases with the time after some peak values, which is due to energy transmission from the spherical particle to the coating layer and the stress shock waves. The energy transmission from impacting particle to coating layer increases with the increasing particle velocity and decreases with the increasing inclined angle. The simulated impact pit morphology is qualitatively similar to the experimental observation. This work demonstrates that the SPH method is useful to analyze the impact behavior of ceramic coatings.