Impact Of Erosion Research Articles

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.

The role of hardening and roughening during the incubation period in water droplet impingement erosion of Ti–6Al–4V

The present work investigates the role of surface hardening and roughening on the damage accumulation during the incubation period in water droplet erosion (WDE). Water droplet erosion tests were carried out on Ti–6Al–4V alloy at an impact velocity of 250 m/s. The evolution of hardness and surface roughness during the incubation period were evaluated using microhardness tester and Confocal Laser Scanning Microscope (CLSM). Scanning Electron Microscopy (SEM) was conducted on the impact area at several intervals during the incubation period. Finite Element (FE) simulations were performed to obtain the impact stresses on both smooth and rough surfaces. It was found that the solid surface plastically deforms by the action of the initial impingements, and as a result, hardness and surface roughness increase progressively until the end of the incubation period. The cyclic increase in hardness results in gradual improvement in the erosion strength, making the surface more resistant to the subsequent droplet impacts. However, the finite element results revealed that the dynamic surface roughening process results in higher impact stresses for the same impact pressure due to geometrical stress concentration. It is concluded that the increase in impact stresses resulting from surface roughening negates the improvement in the erosion resistance due to hardening. Hence, cyclic hardening and roughening are crucial parameters in the damage accumulation process during the incubation period.

Numerical Investigation on Impact Erosion of Aeolian Sand Saltation in Gobi

Sand drift erosion is common on aeolian landforms, particularly in the Gobi desert where sand drift is often quite strong. Sand drift erosion can lead to many types of hazards, including severe crop loss, structural damage to buildings or infrastructure, and abrasion of soil or clay components that contribute to the production of fine particulate matter. This article combines the Gobi sand flow model with the solid particles erosion model to simulate the sand drift erosion process in a variety of Gobi environments. The results show that the impact erosion of saltation particles is highly dependent on both the friction velocity and the gravel coverage. Saltation erosion amount increases with the increment of friction velocity and the gravel coverage. The vertical profile of saltating erosion rate displays a clear stratification pattern composed of a linear increasing layer, a damage layer, and a monotonic decreasing layer. The maximum value of the saltation erosion rate increases as the friction velocity increases and their curve shows a power-law relationship. The damage height caused by saltation erosion is primarily concentrated in the height range of 0.03 m to 0.15 m, and it increases approximately linearly with friction velocity.

Spatial distribution of soil erosion and its impacts on soil productivity in Songnen typical black soil region

Soil erosion is an important reason for land degradation. The black soil region of Northeast China is the main grain production base in China, however, the black soil productivity in this region is at risk and unsustainable now because there was few soil conservation measures in nearly 100 years of cultivation. To assess the impact of erosion on land productivity, both 210 sampling points for 137Cs measurement and 112 sampling points for soil profile features were laid out on cultivated land of Songnen typical black soil region in combination with the 2010 China land use map. The current soil erosion/deposition rate and land productivity index PI were calculated over the study area, and then the PI values were predicted erosion by 20, 50, 100, and 200 years without soil and water conservation measures based on the current erosion rate and soil profile characteristics. The results showed that the average soil erosion rate of cultivated land in the study area was 705.8 t/(km2⋅a), and 77.0% of the cultivated land had soil erosion rate larger than the soil loss tolerance of 200 t/(km2⋅a). Spatially, the soil erosion rate in the northern region was greater than that in the southern region significantly, which was mainly affected by slope steepness. The relationship between soil erosion rate (SL) and slope steepness (θ) in degree was established according to the results of 137Cs measured at 210 sample points: SL = 556.4∗θ or SL = 0.464∗θ in mm/a (given soil bulk density is 1200 kg/m3). The current mean value of PI for cultivated land was 0.59, decreasing significantly from north to south, which was mainly influenced by organic matter content. The predicted PI values decreased significantly with the increase of erosion years in the northern area. This is related to the topography of rolling and hills in the northern area with a greater soil loss rate, leading to a rapid decrease of organic matter content and the increase of sand content in the topsoil in the future. The spatial distributions of the current soil erosion rates and predicted PI values after years of erosion for cultivated land would be helpful for soil conservation policy-making.

Pola Keterkaitan Perubahan Distribusi Kepadatan Vegetasi dengan Penggunaan Lahan DAS Pesisir, Case Study : DAS Garang

<p><em>The diversity and density of vegetation is key in managing sedimentation throughout the watershed, especially in the central and downstream regions. Measures of vegetation diversity and density that can be used are the Normalized Difference Vegetation Index (NDVI) which is a measure of vegetation greenness (chlorophyll levels), Normalized Difference Water Index (NDVI) to measure vegetation wetness levels, and soil adjusted vegetation index (SAVI) for low canopy vegetation cover. For watersheds that stretch long to downstream or coastal areas, the measure of land diversity needs to be supplemented by using the Normalized Difference Built-Up Index (NDBI) indicator that is useful for land use planning. Information on this vegetation index can be obtained by processing a satellite imagery map. The benefits of processing vegetation indexes in watershed management are becoming increasingly important in the era of climate change, especially with regard to efforts to harmonization of relationships between environmental elements that include the diversity of the interests of the resident population. That's why this research was done in order to find the link between natural factors including the impacts of climate change and humans. The test began by looking for changes in the NDVI, NDWI, SAVI, and NDBI indexes from the last 5 years with the Global Indicator Spatial Association (GISA) analysis using Moran's I Global Index, followedby looking for the association with the pattern of population change and the percentage of the area of the settlement. The results showed a link between moran's I Global index change pattern of population change and the spread of residential developments. The tendency of the distribution of this settlement area is an important point in analyzing the influence of its dispersal patterns in a watershed so that the continued impact of potential erosion and sedimentation triggered will be the main consideration in watershed management.</em></p>

ВЛИЯНИЕ ЭРОЗИОННО-РУСЛОВЫХ СИСТЕМ НА ИНФРАСТРУКТУРУ НАСЕЛЕННЫХ ПУНКТОВ ЕВРОПЕЙСКОЙ ЧАСТИ РОССИИ

The infrastructure of any settlement, whether it is a village or an urban agglomeration, ensures the functioning of the systems that serve the needs of the population. Regardless of the age of the settlement, its size and layout, the system of engineering communications depends on the features of the relief and erosion-channel processes in this area. To identify the impact of gully erosion and riverbed processes on the functioning of infrastructure, the southern megaslope of the Russian Plain was selected. There is a high degree of erosive dissection and activity of riverbed processes. Satellite images and cartographic material were used to assess the impact of erosion-channel processes. For the basins of the Volga, Oka, Don, and Dnieper rivers (within the territory of the Russian Federation), a map of the impact of erosion-channel processes on the infrastructure of settlements has been compiled. The basis for drawing up the map was a physical and geographical map of Russia on a scale of 1:8,000,000 and a map of the hazardousness of channel processes on the rivers of Russia. The resulting map shows 120 settlements: 84 – in the Volga River basin, 13 – in the Don River basin, and 24 – in the Dnieper River basin (within the Russian Federation). According to the developed methodology, each settlement was assigned a score of the impact of erosion and riverbed processes on the infrastructure. The most common are small values of such impact: 1 point – 45%, 2 points – 29.5%, 3 points – 23%, 4 points – 2.5% (only 3 settlements). The lowest (1–2 points) impact on the infrastructure corresponds to the territories within the lowlands and relicts of glacial relief. Settlements on the Central Russian and Volga Uplands are more dependent on gully erosion (3–5 points) and show a weak dependence on riverbed processes. The research results indicate an ambiguous impact of erosion and riverbed processes on the infrastructure of the settlements. Large and big cities are less dependent on erosion and riverbed processes, in contrast to small and medium-sized ones.

Landscape Architecture for Reducing the Impact of Coastal Flooding and Erosion

Landscape Architecture for Reducing the Impact of Coastal Flooding and Erosion

Analysis of the livelihood and health of internally displaced persons due to riverbank erosion in Bangladesh

Bangladesh is particularly vulnerable to natural calamities such as flooding, cyclones, droughts, and severe riverbank erosion as a deltaic country. Riverbank erosion brings about terrible consequences such as loss of land, human displacement, social isolation, and physical and mental well-being problems. The study used a mixed-method research approach and a multi-method data collection procedure to analyse the impact of riverbank erosion on livelihood and health. Households of Internally Displaced Persons (IDPs) due to riverbank erosion in Bangladesh's Lakshmipur district were surveyed using a structured questionnaire and an unstructured interview schedule to collect quantitative and qualitative data. Thematic content analysis, and descriptive statistics were applied to identify how riverbank erosion is inextricably linked to the IDPs' socio-economic conditions and well-being vulnerability. The findings show that riverbank erosion is responsible for the IDPs' livelihood uncertainty and substantial health concerns. Uncertainty about livelihood gives rise to socio-economic instability, poverty, diseases, and medical expenses. On top of that, the displaced people faced several difficulties, including no land ownership, living in substandard housing, no access to power, use of unhygienic toilets, social isolation, and anxiety. The research also finds inadequate government or non-governmental master plans for IDPs to overcome miserable conditions. The study results will help policymakers in Bangladesh and elsewhere to better understand the needs of vulnerable riverine communities and to design and implement policies and programmes to improve those communities' capacity to withstand shocks and recover quickly.

Количественная оценка эрозионных потерь почвы на различных участках распахиваемого склона (бассейн Верхней Oки)

The paper presents the results of detailed erosional study of soil loss observed during the post-Chernobyl period. Radiocaesium method was applied in the experimental area located in Oryol district of the Oryol region (Upper Oka basin). The humidification conditions analysis was conducted for recent decades (2021–2022), an increase in the groundwater supply of rivers and lakes was observed. It was found that intense April precipitation has a strong erosional impact onto the soil cover, despite the decrease in the volume of meltwater in recent years. The analysis of temperature conditions confirmed the warming of the winter season in the last decade and in 2022, erosional potential of meltwater has almost halved. Intense precipitation in September and October of 2021, a warm winter and intense rains in April 2022 caused intensive soil washing in spring. The inter-aggregate adhesion is disrupted in the soil after freezing and consequent thawing, so the intense spring precipitation forms a soil washout. Soil runoff in the studied area is carried out by a complex system of furrows and erosional ravines. The article describes the main approaches applied to develop a semi-empirical methodology for erosional soil loss estimation, and the equations obtained on its basis for six zones of studied area differing in the structure of the surface. The methodology is based upon the in-situ data collected by authors in 2014–2017. The dependences of caesium-137 specific activity on morphometric variables (namely catchment area and profile curvature) are estimated. The reference value of caesium-137 specific activity was establish reducing the results of layer-by-layer in-depth measurements within three block elevations on the watershed. The equations used for the calculation of soil runoff amount were applied to produce a grid map of the soil runoff intensity for the sloping surface of the southern exposure. Estimation of the soil runoff (provided under the conditions of 25 cm arable layer depth and 1110 g/m³ soil material density) shows that in the studied area of gray forest heavy loam soils, the soil runoff value varies from 5 t/ha/year to more than 20 t/ha/year. The proposed methodology can be refined by enlarging the (spatial) scale of research.

Non-destructive technique for erosion and corrosion monitoring system

Erosion and corrosion of pipeline occurs over time and this data should be given the same care as other data in oil and gas industry. Moreover, most notification systems available send an alert only when the issue is at a late stage. Therefore, the aim of this study is to create a monitoring system that would help in minimizing the impact of erosion and corrosion of pipeline related issues. There are three objectives includes: data separation, online and offline database storage and an email notification system. This study also emphasizes the importance of incorporating a database for evaluation of oil and gas pipeline’s wall thickness data in terms of its health status. As the data obtained is essential, a web application is created to store the data whenever internet is available. Otherwise, it will be stored in a temporary offline database known as MYSQL Workbench, and the data is automatically uploaded once the internet is available. A notification system via internet is developed to notify the executives regarding unhealthy pipeline status. A healthy pipeline wall thickness is between 4.3mm and 4.5mm. Thus, data with lower than 4.3mm is noted as eroded while data greater than 4.5mm is recorded as corroded. The monitoring system designed for online and offline data storage along with email notification performed accordingly. Therefore, the developed system fulfils the objectives and help in mitigating erosion and corrosion of pipelines related issues at an earlier stage in saving lives, maintenance fees and the environment.

Yuuyaraq today, Yuuyaraq tomorrow: modeling erosion threats to Yup’ik traditional land use areas

ABSTRACT The following article illustrates the impact of contemporary coastline change on Yup’ik subsistence practices known collectively as Yuuyaraq. We draw from an extensive archive (n = 490) of historic maps, aerial photographs, and surveying reports collected and digitized over the course of on-site visits to Quinhagak, AK from 2018-2021. In addition, our research team conducted numerous recorded (n = 7) and unrecorded (n = 42) interviews with community members about recent environmental changes near Quinhagak to study the impact of coastal erosion. Our aim is to demonstrate how archival maps can provide high quality, mobile-friendly visualizations so that Yupik researchers and community members can study the impact of climate change in the Yukon-Kuskokwim (Y-K) Delta.

Distribution of soil physical and hydraulic properties between erosion and deposition topographies in five small catchments from north to south on the Loess Plateau of China

Soil erosion, the most widespread form of soil degradation worldwide, has been acknowledged to cause onsite soil physical deterioration. However, the off-site impact of erosion on the soil physical and hydraulic properties of deposited sediments remains unclear, especially at catchment or larger scales. Here, we measured soil physical and hydraulic properties in erosion topography (hillslopes) and deposition topography (check dams) at 0–2 m depth in five eroding catchments across China's Loess Plateau. Results indicated that the deposition zone exhibited a higher clay content (+13%) at the southern sites with a finer texture and a higher erosion modulus, while the same zone exhibited a higher sand content (+25%) at the northern sites with a coarser texture and a higher extreme rainfall erosivity. The deposition zone exhibited a higher bulk density (+9%) and a lower saturated hydraulic conductivity (-13%), field capacity (−9%), and porosity (-5%) than those of the erosion zone, which was strengthened by a higher mean annual precipitation. Soil macroaggregate proportion and mean weight diameter of aggregates were significantly lower in the deposition zone (14.36% and 0.69 mm, respectively) than those in the erosion zone (15.71% and 0.75 mm, respectively), and the differences were larger at sites with higher rainfall erosivity levels and in surface 20 cm soils. However, sediment reaggregation occurred due to the accumulation of binding agents such as clay and organic carbon at sites with lower rainfall erosivity levels. The spatial heterogeneities of sediment physical and hydraulic properties were greater than or similar to those of soils in the erosion zone. Results of our study highlight the dependence of variations in soil physical and hydraulic properties driven by erosion and deposition on erosion factors, which contributes to a better understanding of the hydrology cycle and carbon stability in erosion and deposition topographies.

Ultrasonic coupled abrasive jet polishing (UC-AJP) of glass-based micro-channel for micro-fluidic chip

The efficiency of abrasive jet polishing (AJP) is relatively low for glass-based micro-channels, and an ultrasonic coupled AJP (UC-AJP) approach was thus proposed. The fluid mechanic model of the UC-AJP was established to reveal the ultrasonic enhancement law and the optimal design parameters. The calculation results indicated that ultrasonic vibration could help significantly improve the turbulent kinetic energy and impact erosion that had an important role in jet stability and polishing efficiency. High-speed photograph and polishing experiments with different amplitudes were then performed to explore the performance of the proposed UC-AJP method. It was found that for glass-based micro-channel UC-AJP produced a smoother surface and higher polishing efficiency than AJP. There is an optimal amplitude range in the UC-AJP process, which can maximize the polishing efficiency for the micro-channel. Such improvements were ascribed to the synergistic effect of the pulse and cavitation as a result of the formation of pulsed abrasive jet.

The soil microbiome unveils strong imprints of artificial erosion after 27 years

Soil erosion is a severe and widespread form of land degradation worldwide, and is being exacerbated by effects of climate change, such as increased storm frequency and intensity. It is important to study the impact of soil erosion on the soil microbiome because soil microbes are crucial drivers of many important soil biological processes in agriculture. In 2016 and 2017, we sampled a simulated soil erosion field trial established in 1990 to investigate the effects of different depths of topsoil removal and restorative soil amendments on soil pH, microbial biomass carbon (MBC) and the activities of enzymes that mediate C, nitrogen (N), phosphorus (P), and sulfur (S) cycling, plus the diversity and composition of soil prokaryotic (bacteria and archaea) and fungal communities. The one-time (1990) treatments consisted of a split-plot combination of three depths of topsoil removal (0, 10, and 20 cm) as main plots, and three restorative soil amendments (check, topsoil, and cattle manure) as subplots. Soil pH was higher in the eroded treatments than the noneroded treatment, but the opposite was observed for MBC and the activities of β-glucosidase (C cycling) and N-acetyl-β-glucosinidase (C and N cycling). The restorative amendments did not affect soil pH, MBC, or enzyme activities. The relative abundances of the archaea Thaumarchaeota was higher in noneroded treatments than in eroded treatments, but the reverse was observed for the bacteria Chloroflexi, Gemmatimonadetes, Planctomycetes, and Verrucomicrobia. For fungi, the relative abundance of Basidiomycota was lower in eroded treatments than in the noneroded treatment, but the opposite was true for Mortierellomycota. The β-diversity analyses also showed different prokaryotic and fungal community structures between eroded and noneroded treatments, but the restorative amendment effects were less distinct. Therefore, soil erosion and excavation can have lasting imprints on the soil microbiome, particularly negative imprints on total microbial biomass and its C and N cycling potential, while imprints of restorative measures such as manure or topsoil amendment were not as strong. A single desurfacing event has effects that last for decades, and our efforts to reverse them are largely ineffective when applied only once.

Quantification of wind turbine energy loss due to leading‐edge erosion through infrared‐camera imaging, numerical simulations, and assessment against SCADA and meteorological data

AbstractQuantification of the performance degradation on the annual energy production (AEP) of a wind farm due to leading‐edge (LE) erosion of wind turbine blades is important to design cost‐effective maintenance plans and timely blade retrofit. In this work, the effects of LE erosion on horizontal axis wind turbines are quantified using infrared (IR) thermographic imaging of turbine blades, as well as meteorological and SCADA data. The average AEP loss of turbines with LE erosion is estimated from SCADA and meteorological data to be between 3% and 8% of the expected power capture. The impact of LE erosion on the average power capture of the turbines is found to be higher at lower hub‐height wind speeds (peak around 50% of the turbine rated wind speed) and at lower turbulence intensity of the incoming wind associated with stable atmospheric conditions. The effect of LE erosion is investigated with IR thermography to identify the laminar to turbulent transition (LTT) position over the airfoils of the turbine blades. Reduction in the laminar flow region of about 85% and 87% on average in the suction and pressure sides, respectively, is observed for the airfoils of the investigated turbines with LE erosion. Using the observed LTT locations over the airfoils and the geometry of the blade, an average AEP loss of about 3.7% is calculated with blade element momentum simulations, which is found to be comparable with the magnitude of AEP loss estimated through the SCADA data.

Evaluation of Internal Stresses in Modified Near-Surface Layer of 20Kh13 Steel during Incubation Period of Water Droplet Impact Erosion

This study investigates the change in internal stresses of ion nitrided and Cr–CrC ion-plasma-coated 20Kh13 steel samples during the incubation period of the droplet impact erosion. To obtain internal stress values, a method based on measuring the deformation (curvature) of the sample along the surface profiles before and after its modification/coating, as well as during the subsequent droplet impact has been applied. The results suggest that the initial droplet impact on the uncoated, nitrided and coated material leads to a sharp increase in the initial internal stress values. The rate of increase in internal stress decreases with the surface damage development and accumulation. The proposed method of stress evaluation can be used in selecting a criterion for comparing the erosion resistance of a material and a method for modifying its surface.

12,000 years of landscape evolution in the southern White Mountains, New Hampshire, as recorded in Ossipee Lake sediments

AbstractContinuous records of sediment yield spanning from the late glacial through the Holocene to the present day provide an important opportunity to investigate landscape evolution over various timescales in response to a variety of natural and anthropogenic forcing mechanisms. This study investigates variations in sediment yield and landscape evolution in the 768 km2 watershed of Ossipee Lake, New Hampshire, USA. We pair subbottom sonar observations with analyses of lacustrine sediment cores to interpret a 12,000+ yr record of lake sedimentation in terms of changes in sediment yield and landscape evolution. Our results indicate high rates of sediment redistribution following deglaciation at ~14,500 to ~12,000 cal yr BP, followed by a period of gradually decreasing sediment yield until ~9000 cal yr BP, marking the termination of the most intense period of paraglacial landscape adjustment. From 9000 cal yr BP to 1850 CE, sediment yield is highly variable and reveals a slightly increasing trend that we attribute to a dominant hydroclimatic control on erosion driven by increasing effective precipitation in the region throughout the Holocene. Despite evidence for a highly dynamic landscape and an abundance of unconsolidated glacigenic surface deposits throughout the watershed, we interpret a modest erosional impact from anthropogenic land use.

Exploring the Socioeconomic Impact of Riverbank Erosion in the Brahmaputra Valley of Assam, India: A Case Study of Two Districts

This paper explores the socioeconomic impact of riverbank erosion and measures the incidence and severity of poverty among the riverbank inhabitants of Assam, India. Primary data from two erosion effected districts of Assam have been collected using multistage random sampling technique. To measure the incidence of Poverty among the riverbank inhabitants, Head Count Ratio (HCR) method has been used. Severity of poverty is measured using Poverty Gap Index (PGI). The results reveal that the level of poverty and the severity of poverty are related with the degree of erosion. Similarly, the migration (both short-term and long-term) also related with the degree of erosion. It has also found that various types of socioeconomic issues arise due to riverbank erosion, such as loss of cropland and livestock, education and transportation problem, social displacement, etc. An important fact observed is that the problem of migration and poverty also exist in the non-eroded villages. For which, it cannot be say that migration issue arise only because of riverbank erosion. But, riverbank erosion pushes the other problems to more vulnerable situation which compels the affected people to take their decision. Therefore, riverbank erosion may be considered as a cause of migration and poverty in the study areas. In this context the paper recommends that with the erosion control measures, the policies such as resettlement, financial support and social safety nets should be implemented in the erosion affected areas to reduce poverty as well as to reduce outmigration.

Modelling of surface morphology and roughness in fluid jet polishing

Fluid jet polishing (FJP) has been extensively used in various kinds of fields such as precision molding, optical components, etc. However, previous works mainly focused on the material removal process on the macro-scale (e.g., tool influence function, surface generation) to improve the form accuracy, the understanding of surface morphology evolution of FJP on the micro-scale is still far from complete, which makes it difficult to predict the surface quality under certain polishing conditions. Time-consuming and high-cost trial and error are usually needed to obtain suitable polishing conditions for specific surface quality requirements. In this paper, a physical model was developed to predict the surface morphology and roughness after FJP, by combining the computational fluid dynamics (CFD) simulation and kinetic analysis of the abrasives. The single abrasive erosion process including indentation action, ploughing action, and cutting action was analyzed by kinetic analysis. Besides, the overlap of single abrasive erosion pits was modeled to simulate the surface morphology evolution in FJP and determine the surface roughness after polishing. Different parameters were considered in the model including jet pressure, jet angle, and abrasive size. A series of polishing experiments were conducted to validate this model and the effect of different polishing parameters on surface quality was elucidated by the impact velocity distribution and erosion morphologies. It is found that the simulation results agree well with the experimental results. This paper not only provides a deeper understanding of the microscale material removal in FJP, but also provides an effective method for the prediction of surface roughness in FJP.

Ultrastructure of the Dentin Pellicle and the Impact of Erosion

While the ultrastructure of the enamel pellicle and its erosion protective properties are well studied, the dentin pellicle is still neglected in dental research. Therefore, the ultrastructure and erosion protective properties of a pellicle formed on bovine dentin specimens were investigated in the present study. The dentin pellicle was formed in situ for 3, 30, 120, and 360 min at buccal or palatal oral sites of 3 subjects and analyzed by transmission electron microscopy. In order to clarify the impact of an erosive challenge to the ultrastructure of the pellicle and the underlying dentin, specimens were exposed to the oral cavity and eroded in vivo with 0.1% or 1% citric acid either immediately or after 30 min of pellicle formation. Specimens that were eroded without exposure to the oral cavity served as control. In another trial, specimens with a 30-min pellicle were exposed to the oral cavity for a further 60 min after the erosive challenge to investigate the effect of saliva on the impaired pellicle and dentin. Transmission electron micrographs reveal a globular and granular structured pellicle layer, which was thicker when the pellicle was formed buccally or with longer formation times. Erosion with citric acid reduced the thickness of the pellicle and interrupted its continuity. The dentin was also affected by erosion, which was represented by a lower electron density and formation of demineralized lacunae. These were infiltrated by a granular structured material when specimens were exposed to the oral cavity. After further intraoral exposure, the infiltration was more pronounced, indicating a significant impact of saliva on the demineralized dentin. A reformation of the dentin pellicle on the other hand did not occur. In conclusion, the dentin pellicle is neither acid-resistant nor able to effectively protect dentin from erosion.