Setting critical nutrient values for ditches using the eutrophication model PCDitch

The influence of slow crack growth on the initiation of radial cracks at the lower surfaces of ceramic layers bonded to polymeric substrates is studied, with particular relevance to biomechanical systems, e.g., dental crowns and hip replacement prostheses. Critical loads are measured as a function of loading rate (dynamic fatigue) for model bilayers fabricated by epoxy-bonding selected clinical ceramics to polycarbonate bases. Radial crack initiation is observed in situ by viewing from below the transparent base during loading. Declines in the critical loads with diminishing load rate are consistent with slow crack growth of intrinsic flaws prior to radial crack pop in. A simple fracture mechanics relation incorporating a crack velocity function is used to analyze the data. Extrapolation beyond the data range enables long-lifetime (10 yr) estimates of sustainable loads. The procedure provides a basis for ranking ceramic types, and in particular for eliminating vulnerable candidate materials, for use in biomechanical systems. While slow crack growth is an important factor in failure, other mechanisms could operate in concert and even dominate under severe testing conditions, especially under cyclic loading.

The paper presents the results of combined experimental, analytical, and computational studies of contact-induced deformation and cracking in dental multilayers. These include studies of individual layers and composite structures that consist of tri-layers of glass bonded to ceramic-filled polymer foundation with an acrylate-based join material. Loading-rate-dependent Young's moduli of the join and foundation materials were obtained from monotonic compression tests. Critical loads were also determined for the tri-layers from Hertzian contact tests at different loading rates. The fracture onset (sub-surface radial cracking) was detected using an in situ telescope. The measured rate-dependent Young's moduli were then incorporated into a finite element model that was used to predict the rate-dependent critical loads in the tri-layer system. Finally, the paper shows that the observed loading rate-dependence of the critical load (for radial cracking) is due to the combined effects of slow crack growth in glass and rate-dependent Young's moduli in the join and foundation layers.

Water quality of agricultural coastal plain watersheds

The surface scratch resistance, damage evolution and damage detection during microscratching of pure AlN and AlN with an Al2O3 oxide layer (∼0.1 μm) were investigated. The microscratch experiments were performed in a progressive load-ramped mode where the load was linearly increased from 0 to 3 N as the scratch progressed with a loading rate of 0.2 N/min. The experiments resulted to two different failure mechanisms; Ductile scratching and fracture dominated scratching. In the case of pure AlN, inconsistent different kinds of damages were found to initiate at low critical load measured as 0.30 N. This critical load was also found to decrease with increasing the surface roughness, material density and grain size of AlN. In the case of pure AlN with an Al2O3 oxide layer, the critical load for crack initiation was measured as 0.45 N, higher than pure AlN. This critical load was found to generate uniform discontinuous chipping. The distance between these defects decreased and the failure mode gradually transformed to continuous chipping as the scratch progressed. The surface modification of AlN with the use of an Al2O3 oxide layer was found to improve the tribological properties of AlN.

Nitrogen deposition and exceedance of critical loads for nutrient nitrogen in Irish grasslands

This research used extensive field data collected during the 1990’s by a consortium of federal, state, local, and university personnel in agricultural areas in the Mississippi Delta region to evaluate runoff, soil erosion, and nutrient losses. Agricultural phosphorus export modelling was performed on Deep Hollow watershed (11.29 ha) using the Hydrological Simulation Program FORTRAN – HSPF to demonstrate the usefulness of the continuous processesbased model for a farm scale drainage area in the Mississippi Delta region. The main goal of this study was to evaluate the ability of HSPF to simulate storm, seasonal, and long-term runoff, sediment, and phosphorus export at the farm scale in Mississippi. The model was spatially divided into six hydrologic respond units based on similarity of land cover and soil characteristics. Rainfall and other climate time series were setup every 15-minutes and the model results were output at the same time step. Agricultural field operations (tillage, cultivation, harvest, fertilization) were incorporated into the HSPF model using the special actions module. Phosphorus simulations were accomplished using the AGCHEMPHOS module. Phosphorus adsorption and desorption were simulated by the Freundlich method. Model outputs: runoff, sediment load, dissolved & total phosphorus loads were evaluated against observed data from storm, seasonal, and long-term periods. Collected storm-event data at the drainage area outlet were available for runoff (69 events), suspended sediment load (40 events), and phosphorus loads (23 events) from 1997 to 1999. The model was calibrated using available data from 1998 to 1999 and validated using field data in 1999. All the parameter values used in this assessment were in the range provided by HSPF model developers or found in the literature. Simulated runoff values showed very good agreements to storm, monthly, and annual basis. In analyzing simulated sediment load export values, storm type steps yielded poor performance, but HSPF produced good seasonal and annual sediment load values. Simulated dissolved phosphorus (DP) loads were better at long-term time steps than storm-by-storm periods. HSPF total phosphorus (TP) loads were better at simulating long-term periods than storm-by-storm time steps. In conclusion, HSPF runoff algorithms are very robust at any time scales from storm to annual periods and sediment and phosphorus modules are very comprehensive for seasonal and annual time steps at the farm scale.

Plastic instabilities were observed to appear during dynamic ultramicrohardness testing of a solid solution Al–3.3 wt.% Mg alloy. The tests were carried out at room temperature with a Vickers hardness indenter in a computer-controlled dynamic ultramicrohardness testing machine. During the tests the applied load was increased from 0 to 2000 mN at constant loading rate. The instabilities appear as characteristic steps in the continuously recorded load-indentation depth curves. The physical basis for the occurrence of the instabilities is the interaction between moving dislocations and solute atoms, a phenomenon termed in the literature as serrated yielding, jerky flow, or Portevin-Le Châtelier effect. The instabilities start at a critical load, Fc, in the depth-load curve. Varying the loading rate, μ, by two orders of magnitude Fc was found to increase linearly with the loading rate.

PVD thin film based on chromium nitride was deposited on XC100 steel substrate with reactive radio frequency magnetron sputtering. Thin film was characterized in terms of both surface properties and adhesion behavior. The characterization of surface properties was based on the measurement of mechanical properties coupled with a preliminary microstructural study using SEM and AFM. Fatigue resistance was considered as an important surface properties and it was investigated using multi-cyclic nanoindentation test. Results indicated that chromium-based coatings have a smooth, dense and compact microstructure with a grain size of about 109 nm and a roughness of about 11 nm. CrSiN showed a high adhesion quality, critical loads were LC1 = 16 N, LC2 = 20 N and LC3 = 25 N. PVD coatings exhibited a hardness of about 30.52 GPa and Young’s modulus of about 338.32 GPa. Moreover, multi-cycle nanoindentation technique, with variation of loading mode (progressive and quasi-static) and loading rate (from 200 mN/mn, 400 mN/mn and to 600 mN/mn) was used to analyze superficial fatigue behavior and surface resistance. Whatever, the cyclic loading mode, an elasto-plastic behavior was observed and an appearance of hysteresis loops in the unloading-reloading curves witch was explained by a fatigue effect. In addition, a hardening phenomenon was found when the loading rate increase.KeywordsPVD coatingSurface propertiesAdhesionMulti-cycle nanoindentation

Kinematic analysis of plastic instabilities occurring in microhardness tests

ABSTRACT:Phosphorus loading from precipitation and more than a dozen tributaries of Big Beat Lake, Woman, was determined for the period from January to December 1978. Direct precipitation contributed 1120 kg·P·yr‐1 (0.096 g P·m‐2·yr‐1) while tributary runoff contributed 21,560 kg for a total P loading of 1.84 g P·m‐2 Rathbone creek, although accounting for only 4 percent of the hydro‐logic input to Big Bear Lake, contributed >27 percent of the annual phosphorus load. Phosphorus loading increased with increased impervious geology and increased development. Nitrogen loading exhibited similar loading patterns. Big Beat Lake is currently eutrophic and is likely to remain eutrophic. Calculations based on Vollenweider's critical phosphorus loading concept indicated that tributary P‐loading would have to be reduced by >95 percent to achieve mesotrophic conditions. The completion of Big Bear Dam created a “naturally” eutrophic re mix which dl require proper management to enhance its resource potential.

Deformation of Si(100) in spherical contacts — Comparison of nano-fretting and nano-scratch tests with nano-indentation

SUMMARY. 1. The exchange of phosphorus between the epilimnetic (shallow zone) sediment and water column in Lough Ennell was investigated in laboratory experiments using five intact cores.2. Variations in water mixing, sediment suspension and aerobic–anaerobic oxygen status in the water column and its effects on sediment phosphorus release rates were determined.3. Experimental results indicated that phosphorus release is possible under both aerobic and anaerobic conditions. Aerobic release (0.025 mg P l−1 over 5 days) was possible up to the point when mass resuspension of sediment occurred. Anaerobic release for the same period and mixing conditions was 0.183 mg Pl−1.4. The release rate under aerobic conditions at 10°C equates to an internal areal loading of 0.134 g P m−2 yr−1, which is approximately 17% and 30% of the average total phosphorus and orthophosphate loadings respectively for the period 1974–79.5. The results clearly implicate aerobic inorganic phosphorus release from the epilimnetic sediments as a significant source of this nutrient to the overlying water column and is likely a major factor in the continuing eutrophic status in the lake.

Phosphorus loading and ecological impacts from agricultural tile drains in a west Michigan watershed

This paper presents a procedure for fatigue analysis where the dynamic response of the structure is analyzed through a spectral approach. The sea waves, which constitute the forcing function acting on the structure, are represented as energy spectra; the response is obtained in spectral terms and subsequently is interpreted according to probabilistic concepts. Introduction The critical loading conditions for design of an offshore platform are primarily dependent on water depth and prevailing meteorological conditions such as waves, currents, and winds. If dynamic amplification is not a major consideration, the static applied force of the largest single wave traditionally is used as the critical or design load condition for fixed offshore structures. In the corresponding fatigue analysis the sea surface is represented by a discrete set of waves characterized by period, amplitude, and percentage of occurrence. The expected fatigue life then is obtained by applying each wave to the structure and totaling the individual effects.Due to the dynamic amplification of wave-induced response, this approach is not adequate for deepwater structures, where fatigue may be a controlling factor in design. In this case, distribution of the frequencies of wave loadings is needed over a much larger range to give a more realistic description of the sea surface. In practice, this is accomplished by statistically modeling the sea-surface elevation. It has been shown that the time history of sea-surface elevation over a period of several hours (i.e., a sea state) can be represented as a stationary random process with Gaussian probability distribution and process with Gaussian probability distribution and narrow-band power spectrum. This work discusses a fatigue analysis procedure based on these considerations.The first three sections of this paper describe a fatigue analysis procedure in which the spectral density of member end stresses is obtained by a frequency domain solution using existing dynamic analysis and space-frame static analysis programs. The fourth section discusses narrow-band approximations for the stress-range distribution and their effect on fatigue analysis. The fifth section presents fatigue results for a caisson structure. The presents fatigue results for a caisson structure. The sixth section gives conclusions and observations. Fatigue Analysis Procedure The first step in this fatigue analysis technique involves a static analysis. The structural model uses a space-frame, full-geometry simulation of the jacket with three-dimensional beam elements. Every member of the structure contributing to the overall stiffness is modeled by one or more elements. Unit loads are applied at selected levels of the three-dimensional model, and the resulting deflections for each unit load are noted. For each preselected member, the stresses at the member ends also are computed and saved for use later in the analysis.Next, the wave-induced dynamic response is calculated using a modified version of the TOWER spectral analysis program developed by Penzien et al. JPT P. 1614

Assessment of phosphorus loading dynamics in a tropical reservoir with high seasonal water level changes