Push-pull Tests Research Articles

Analytical study on hybrid thrust foil bearing, structural characterization and measurement of static performance

This work presents a novel hybrid foil thrust bearing (HFTB) with an outer diameter of 154 mm, along with simulation and test results. The HFTB incorporates a high-pressure air/gas injection to the taper portion of the thrust foil bearing, boosting the hydrodynamic effect on the main bearing surface and hydrostatic load capacity at zero speed. The bearing has high load capacity, low power loss, and no friction/wear during startup and shutdown. Firstly, push-pull tests were conducted on a double-acting HFTB configuration to evaluate the nonlinear structural stiffness of the bump foil structure. The measured nonlinear stiffness model was adopted to predict the overall bearing performance under various speeds and loads. The simulation uses an advanced model which predicts the 2D plate top foil deflection with physical bump locations mapped from the actual hardware. The simulation confirms that the hybrid operation significantly increases the load capacity compared to hydrodynamic bearing due to the boost effect of hydrostatic pressure in the main film. Tests were conducted at 10krpm, 15krpm, and 20krpm to measure load capacity, power loss, and average film thickness. At 20krpm, a maximum axial load of 1711 N was achieved before bearing failure. Ultimately, the novel HFTB shows excellent static performance with potential for use in Organic Rankine Cycle (ORC) generators and other large oil-free turbomachines.

Sustaining Irrigation Supplies through Immobilization of Groundwater Arsenic In Situ.

Geogenic arsenic (As) in groundwater is widespread, affecting drinking water and irrigation supplies globally, with food security and safety concerns on the rise. Here, we present push-pull tests that demonstrate field-scale As immobilization through the injection of small amounts of ferrous iron (Fe) and nitrate, two readily available agricultural fertilizers. Such injections into an aquifer with As-rich (200 ± 52 μg/L) reducing groundwater led to the formation of a regenerable As reactive filter in situ, producing 15 m3 of groundwater meeting the irrigation water quality standard of 50 μg/L. Concurrently, sediment magnetic properties were markedly enhanced around the well screen, pointing to neo-formed magnetite-like minerals. A reactive transport modeling approach was used to quantitatively evaluate the experimental observations and assess potential strategies for larger-scale implementation. The modeling results demonstrate that As removal was primarily achieved by adsorption onto neo-formed minerals and that an increased adsorption site density coincides with the finer-grained textures of the target aquifer. Up-scaled model simulations with 80-fold more Fe-nitrate reactants suggest that enough As-safe water can be produced to irrigate 1000 m2 of arid land for one season of water-intense rice cultivation at a low cost without causing undue contamination in surface soils that threatens agricultural sustainability.

Cyclic behavior of rubber-coated stud-UHPC shear connectors exposed to reversed cyclic loadings

Steel-ultra-high performance concrete (UHPC) composite structures that could maximize the benefits of two materials have gained ground in bridge structures for accelerating construction speed and reducing self-weight. However, the shear stiffness of ordinary stud connectors (OSCs) in UHPC might exceed the actual demand, leading to the insufficient deformation capacity of OSCs. Therefore, the flexible rubber-coated stud connectors (FRSCs) were developed to replace the OSCs for improving the ductility of shear connectors. The shear performance of FRSCs in UHPC subjected to reversed cyclic loadings has been not understood, which limits its application in the practical construction. The cyclic behavior of FRSCs was examined through modified push-pull test specimens, and the static loading tests were carried out to determine the characteristic slip capacity and shear strength. Numerical models were established to reveal the damage process and failure mechanism of FRSCs and employed to conduct detailed parametric studies. The results demonstrated the FRSCs exhibited high ductility and large energy absorption capacity than OSCs and possessed sufficient shear bearing capacity, indicating their potential application in steel-UHPC composite systems. Increasing the height and thickness of rubber sleeve could enhance the slip capacity of FRSCs under monotonic loadings, while having no effect on the cyclic ductility. Finally, an empirical equation was developed to accurately predict the FRSC shear strength.

Reoxidation of Reduced Peat Organic Matter by Dissolved Oxygen: Combined Laboratory Column‐Breakthrough Experiments and In‐Field Push‐Pull Tests

AbstractElectron transfer to peat particulate organic matter (POM) as terminal electron acceptor (TEA) in anaerobic respiration has been hypothesized to lower methane emissions from peatlands by competitively suppressing methanogenesis and/or allowing for anaerobic oxidation of methane. We herein provide evidence for two critical aspects of this hypothesis: (a) peat POM is present in a reduced state in situ in the anoxic peat subsurface, and (b) reduced POM at the oxic‐anoxic interface in peat soils can be oxidized by dissolved oxygen (DO), restoring its TEA capacity. We reacted reduced POM from three ombrotrophic bogs in Sweden with DO in soil‐packed column‐breakthrough experiments (CBEs), mimicking oxidation reactions at the oxic‐anoxic interface. Breakthrough of DO was substantially retarded relative to the inert tracer bromide, consistent with DO reduction by POM. Control experiments confirmed abiotic DO reduction and excluded DO consumption through aerobic respiration. Modeling DO breakthrough revealed fast and slowly reacting POM moieties with reaction times spanning minutes to days. Complementary push‐pull tests (PPTs) in the anoxic subsurface of one bog confirmed results from laboratory CBEs: lower recoveries of injected DO compared with bromide supported DO reduction by reduced POM. Rates of reduction of injected DO decreased with increasing number of injections, consistent with continuous oxidation of reduced POM. Electron‐donating capacities of POM to DO in CBEs and PPTs were comparable at 40–130 μmol e−/g dry POM. Our results substantiate that POM is a regenerable TEA at oxic‐anoxic interfaces in peat soils and, thereby, may substantially lower CH4 emissions from peatlands.

Performance evaluation of a HMA pavement longitudinal joint containing a void reducing asphalt membrane (VRAM)

Longitudinal joint cracking in Hot Mix Asphalt (HMA) pavements is a major issue that occurs because high density (low air voids) is not easily achieved during construction as compared to the mat away from the joints. High air voids allow water infiltration, which results in moisture-induced damage to the pavement and reduced pavement service life. The use of a Void Reducing Asphalt Membrane (VRAM) has been recommended and used at longitudinal joints of asphalt pavements as a preventative treatment to achieve good performance and increase density/reduce air void content at the longitudinal joint. The Void Reducing Asphalt Membrane material is sprayed on top of a tack coat at the longitudinal joint, 9 inches on each side of the joint below the Hot Mix Asphalt surface overlay, and is expected to migrate upward into the Hot Mix Asphalt overlay, filling 50%–70% of the air voids. This study evaluated and compared the performance of longitudinal joints constructed with Void Reducing Asphalt Membrane to that of a joint without Void Reducing Asphalt Membrane (control). Field cores were collected from 1) a section containing Void Reducing Asphalt Membrane and 2) a section without Void Reducing Asphalt Membrane that was paved for this research. Falling head permeability was carried out to determine the permeability coefficient of the specimen. Disk Compact Tension (DCT) and Semi-Circular Bend (SCB) tests were used to evaluate the cracking performance at low temperatures. A push-pull test was used to evaluate the improvement in adhesion between the top and bottom Hot Mix Asphalt layers at the intermediate temperature. The VRAM-containing samples show high values of fracture energy (Gf) and surface and joint bond energies as compared to the control sections. High surface and joint bond energies indicate that longitudinal cracking at the joints will be delayed as more energy is required to initiate cracks. Additionally, the VRAM-containing samples have a lower permeability coefficient compared to the control section. This indicates that the Void Reducing Asphalt Membrane reduces the possibility of water infiltration. The elastomeric polymer in the Void Reducing Asphalt Membrane increases the cohesion in the mixture, which increases the resistance to deformation and improves the bond strength of the joint Additionally, the Void Reducing Asphalt Membrane enhances the elasticity of the binder, thus increasing the cracking resistance of the joint.

A modified and rapid method for the single-well push-pull (SWPP) test using SF6, Kr, and uranine tracers

In the present study, a single-well push-pull (SWPP) test was conducted with multi-component tracers, including inert gas (SF6 and Kr) and uranine (conservative), to understand the volatile/semi-volatile component transport characteristics in the groundwater system. In an SWPP test, it is essential to obtain an initial breakthrough curve (BTC) of the inert gas concentration at the beginning of the pulling stage to analyze the hydraulic properties of the groundwater system. As a result of the SWPP test using a proposed method in this study, physicochemical parameters of the groundwater and BTC of gas tracers and uranine were acquired simultaneously and successfully. In addition, on-site measurements of uranine, pCO2, and water quality data, such as electrical conductivity (EC), temperature, pH, and dissolved oxygen, were undertaken. Modification of an existing pCO2 measuring system allowed the gas samples to be collected, transported, and analyzed for inert gas components within a few hours. As a result, reliable and interpretable data with a recovery ratio of 26%, 85%, and 95% for SF6, Kr, and uranine, respectively, were obtained. The differences in the recovery ratio were utilized to identify the environmental system, whether it contains gas inside the isolated system (closed) or not (open), and to understand plume behavior characteristics in the experimental zone. By applying a two-dimensional advection-dispersion model to the acquired tracer test data and comparing the observed and computed tracer concentrations, helpful information was obtained on the hydraulic and transport characteristics of the targeted zone. This method can be extended to the design of dissolved CO2 transport monitoring of an aquifer above a CCS site.

Reservoir characterization by push-pull tests employing kinetic interface sensitive tracers - a pore-scale study for understanding large-scale processes

The kinetic interface-sensitive (KIS) tracer experiment is a newly developed method to quantify the fluid-fluid interfacial area (FIFA) during drainage processes. The concentration breakthrough curves, obtained by measuring reaction product concentration in brine/water samples after breakthrough, are interpreted with a specialized numerical model to determine the FIFA. However, this method has its own limitations since the volume of the usable water sample (after breakthrough), based on which the analysis takes place, is often insufficient. This happens because this volume strongly depends on the aquifer material, i.e. sand type and system parameters. An alternative is to employ KIS tracers in a “push-pull” experimental set-up, i.e. primary drainage is followed by a consequent main imbibition process, with the flow direction being reversed. This study applies a pore-scale numerical model to study the KIS tracer reactive transport during a push-pull experiment in a 2D porous medium. The advective-dispersive-reactive transport during both primary drainage and main imbibition processes is discussed. The concentration breakthrough curves show a non-linear descending trend with time, until reaching a constant concentration at the steady state. By analyzing the spatial concentration distribution and the concentration breakthrough curve, the macro-scale KIS tracer reactive transport model can be interpreted for the push-pull process. Finally, the new method is applied in a column experiment, where the determined specific interfacial area is found to be close to literature data.

Degradation of seven pesticides and two metabolites before and during aquifer storage transfer and recovery operation

Degradation of 7 common pesticides (bentazon, boscalid, chloridazon, fluopyram, flutolanil, imidacloprid, and methoxyfenozide) and 2 metabolites of chloridazon (desphenyl-chloridazon, and methyl-desphenyl-chloridazon) was studied in an anoxic and brackish sandy aquifer before and during Aquifer Storage Transfer and Recovery (ASTR) operation. Fresh tile drainage water was injected and stored for later re-use as irrigation water. We hypothesized that electron acceptors (O2, NO3), dissolved organic carbon (∼24.7 mg/L), nutrients (NO3: ∼14.1 mg/L, NH4: ∼0.13 mg/L, PO4: ∼5.2 mg/L), and biodegrading bacteria in tile drainage water could stimulate degradation of the pesticides and metabolites (ranging between 0.013 and 10.8 μg/L) introduced in the aquifer. Pesticide degradation was studied at 6 depths in the aquifer using push-pull tests lasting ±18 days before the onset of ASTR operation. Degradation was too limited to quantify and/or could not be assessed because of the potential occurrence of pesticide retardation. Utilizing push-pull tests to obtain degradation constants should only be considered in future studies for non-retarding pesticides with relative low half-lives (here <20 days). During ASTR operation, pesticide degradation was studied at the same depths during 3 storage periods equally spread over 1.5 years of ASTR operation. Overall, trends of degradation were observed, although with relatively high half-lives of at least 53 days. Microbial adaptation of the aquifer and/or bioaugmentation by the injected biodegrading bacteria did not result in enhanced degradation during consecutive storage periods. Operational monitoring data over longer periods and distances yielded half-lives of at least 141 days. The slow degradation mostly agrees with previous studies. The injected tile drainage water composition did therefore not notably stimulate pesticide degradation. The relatively persistent behavior of the studied pesticides/metabolites implies that ASTR abstracted water will have generally high pesticide concentrations, and non-abstracted water may form a contamination risk for the surrounding native brackish groundwater.

Denitrification kinetics during aquifer storage and recovery of drainage water from agricultural land

An aquifer storage transfer and recovery (ASTR) system was studied in which tile drainage water (TDW) was injected with relatively high NO3 (about 14 mg/L) concentrations originating from fertilizers. Here we present the evolution of denitrification kinetics at 6 different depths in the aquifer before, and during ASTR operation. First-order denitrification rate constants increased over time before and during the first days of ASTR operation, likely due to microbial adaptation of the native bacterial community and/or bioaugmentation of the aquifer by denitrifying bacteria present in injected TDW. Push-pull tests were performed in the native aquifer before ASTR operation. Obtained first-order denitrification rate constants were negligible (0.00–0.03 d−1) at the start, but increased to 0.17–0.83 d−1 after a lag-phase of about 6 days. During the first days of ASTR operation in autumn 2019, the arrival of injected TDW was studied at 2.5 m distance from the injection well. First-order denitrification rate constants increased again over time (maximum >1 d−1). Three storage periods without injection were monitored in winter 2019, fall 2020, and spring 2021 during ASTR operation. First-order rate constants ranged between 0.12 and 0.61 d−1. Denitrification coupled to pyrite oxidation occurred at all depths, but other oxidation processes were indicated as well. NO3 concentration trends resembled Monod kinetics but were fitted also to a first-order decay rate model to facilitate comparison. Rate constants during the storage periods were substantially lower than during injection, probably due to a reduction in the exchange rate between aquifer solid phases and injected water during the stagnant conditions. Denitrification rate constants deviated maximally a factor 5 over time and depth for all in-situ measurement approaches after the lag-phase. The combination of these in-situ approaches enabled to obtain more detailed insights in the evolution of denitrification kinetics during AS(T)R.

A Simplified Model for Numerical Investigation of Bump-Type Foil Bearings Based on Contact Nonlinearity

Abstract The paper introduces a simplified structural model for the numerical investigation of bump-type foil bearings. This analytical model is based on an efficient nonlinear contact procedure with consideration of friction, small deformations, and elasticity. The bump foil is modeled with a truss structure, while the top foil uses two-dimensional (2D) beam elements. In this present model, the normal and tangential contact forces between the bump foil and the bearing sleeve and between the foils are dealt with the penalty method. Even for a simple loading, the contact state might change between separation, stick, and slip. To avoid convergence problems caused by discontinuity, the regularized smooth friction model is used instead of the Coulomb friction model. In addition, due to contact problems that depend on time are accompanied by nonlinear evolution, the solution of the system equation using the incremental iterative method and the Newton–Raphson method is presented. The deflection of the top foil is added to the film controlled by the Reynolds equation (RE) to obtain the air pressure distribution. The theoretical predictions of the rotor push-pull tests agree well with results from the literature, which verifies the validity of the model. Using this present model, the quasi-static behaviors of the foil structure are mainly discussed, and parametric studies concerning environmental pressure and radial clearance are also conducted.

Single-well push-pull tests evaluating isobutane as a primary substrate for promoting in situ cometabolic biotransformation reactions.

A series of single-well push-pull tests (SWPPTs) were performed to investigate the efficacy of isobutane (2-methylpropane) as a primary substrate for in situ stimulation of microorganisms able to cometabolically transform common groundwater contaminants, such as chlorinated aliphatic hydrocarbons and 1,4-dioxane (1,4-D). In biostimulation tests, the disappearance of isobutane relative to a nonreactive bromide tracer indicated an isobutane-utilizing microbial community rapidly developed in the aquifer around the test well. SWPPTs were performed as natural drift tests with first-order rates of isobutane consumption ranging from 0.4 to 1.4day-1. Because groundwater contaminants were not present at the demonstration site, isobutene (2-methylpropene) was used as a nontoxic surrogate to demonstrate cometabolic activity in the subsurface after biostimulation. The transformation of isobutene to isobutene epoxide (2-methyl-1,2-epoxypropane) illustrates the epoxidation process previously shown for common groundwater contaminants after cometabolic transformation by alkane-utilizing bacteria. The rate and extent of isobutene consumption and the formation and transformation of isobutene epoxide were greater in the presence of isobutane, with no evidence of primary substrate inhibition. Modeled concentrations of isobutane-utilizing biomass in microcosms constructed with groundwater collected before and after each SWPPT offered additional evidence that the isobutane-utilizing microbial community was stimulated in the aquifer. Experiments in groundwater microcosms also demonstrated that the isobutane-utilizing bacteria stimulated in the subsurface could cometabolically transform a mixture of co-substrates including isobutene, 1,1-dichloroethene, cis-1,2-dichloroethene, and 1,4-D with the same co-substrate preferences as the bacterium Rhodococcus rhodochrous ATCC strain 21198 after growth on isobutane. This study demonstrated the effectiveness of isobutane as primary substrate for stimulating in situ cometabolic activity and the use of isobutene as surrogate to investigate in situ cometabolic reactions catalyzed by isobutane-stimulated bacteria.

Cyclic hardening/softening and deformation mechanisms of a twip steel under reversed loading

Push-pull tests at fixed plastic strain amplitude or fixed stress amplitude were run on a TWIP steel, and followed by TEM observations, to analyze its cyclic behavior in relation with the deformation mechanisms. The kinematic and isotropic components of the flow stress were measured throughout the whole cyclic hardening/softening stages, and their evolution with the cumulated plastic strain was compared to those measured in tension. The rise of the internal stress was found responsible for the initial cyclic hardening, but this stress reached at most 50% of the flow stress, as compared to nearly 70% in tension. Special constitutive equations were identified to capture these evolutions, as well as the transition from hardening to softening. Both components of the flow stress slightly decrease during the softening stage, whose origin is discussed, based on TEM observations at peak stress amplitude, or after softening. The present measurements and TEM observations, combined with those from a previous study of twinning/detwinning kinetics in push-pull on the same steel [29], suggest that under cyclic loading, mechanical twinning cannot be responsible for significant kinematic hardening of intragranular nature (or “dynamic Hall-Petch effect”), but rather contributes to a back stress of intergranular origin.

Centrifuge modeling of temperature effects on the pullout capacity of torpedo piles in soft clay

This study presents the results from centrifuge modeling experiments performed to understand the effects of temperature changes on the vertical pullout capacity of scale-model torpedo piles embedded in soft clay layers. The model torpedo pile is a pointed stainless-steel cylinder with fins at the top, installed by self-weight to the base of a clay layer using a stepper motor. An internal electrical resistance heater was used to control the pile temperature. The torpedo pile was first heated until the temperature and pore water pressure of the surrounding clay layer stabilized (drained conditions), after which the torpedo pile was cooled. Pullout tests performed on torpedo piles indicate that allowing drainage of excess pore water pressures induced by heating to different temperatures followed by cooling leads to an increase in axial pullout capacity with maximum temperature but does not affect the pullout stiffness. Push-pull T-bar penetration tests performed before and after pile heating indicate that an increase in undrained shear strength of the clay occurs near the torpedo pile, and post-test gravimetric water content measurements indicate a greater decrease in void ratio occurred in the soil layers heated to higher temperatures. The pullout capacity of the torpedo pile was found to follow a linear trend with maximum pile temperature change, but with a smaller slope than that observed for end-bearing energy piles tested in previous studies in the same clay.

Denitrification and DNRA in Urban Accidental Wetlands in Phoenix, Arizona.

Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) both require low oxygen and high organic carbon conditions common in wetland ecosystems. Denitrification permanently removes nitrogen from the ecosystem as a gas while DNRA recycles nitrogen within the ecosystem via production of ammonium. The relative prevalence of denitrification versus DNRA has implications for the fate of nitrate in ecosystems. Unplanned and unmanaged urban accidental wetlands in the Salt River channel near downtown Phoenix, Arizona, USA receive high nitrate relative to non-urban wetlands and have a high capacity for denitrification, but unknown capacity for DNRA. We conducted in-situ push-pull tests with isotopically labelled nitrate to measure denitrification and DNRA rates in three of the dominant vegetative patch types in these urban accidental wetlands. DNRA accounted for between 2 and 40% of nitrate reduction (DNRA plus denitrification) with the highest rates measured in patches of Ludwigia peploides compared to Typha spp. and non-vegetated patches. The wetland patches were similar with respect to dissolved organic carbon concentration but may have differed in carbon lability or strength of reducing conditions due to a combination of litter decomposition and oxygen supply via diffusion and aerenchyma. The ratio of DNRA to denitrification was negatively correlated with nitrate concentration, indicating that DNRA may become a more important pathway for nitrate attenuation at low nitrate concentration. Although DNRA was generally lower than denitrification, this pathway was an important component of nitrate attenuation within certain patches in these unmanaged urban accidental wetlands.

Concrete-to-concrete shear friction behavior under cyclic loading

The main objective of this paper was to study the concrete-to-concrete shear friction behavior under cyclic loading and different test rates. Eight dynamic push-pull tests were performed on concrete specimens with as-cast surface roughness type applying four different test rates. The test results include the hysteresis loops of the friction force-displacement relations. It is concluded that the dynamic coefficient of friction decreased with the increased test rate. This reduction in the dynamic coefficient of friction should be considered in the design of structural elements under cyclic or dynamic loading.

The effect of boundary conditions on the single-well push-pull test in a partially penetrated well

Boundary conditions of well screen are critical formodeling reactive transport around a partially penetrated well in a single-well push–pull (SWPP) test. Previous SWPP test models often assumed that water flux was uniformly distributed along the well screen of the partially penetrated well, named the uniformly distributed flux boundary condition (UFBC). To investigate the influence of such an assumption on reactive transport in the SWPP test, we develop a new finite-difference numerical model under a flow field with a finite hydraulic diffusivity in this study, considering the wellbore storage. The uniformly distributed head boundary condition (UHBC) is employed for both groundwater flow and reactive transport across the well screen. The dispersion coefficients are in a tensor form, depending on both horizontal and vertical flow components. The results show that the UFBC model may cause non-negligible errors when modeling reactive transport in the SWPP test with a partially penetrated well. Such errors are obvious at the early stage of the extraction phase, but become negligible at late stage of the extraction phase. The UHBC solution for reactive transport is smaller than the UFBC solution at the middle of the well screen, but greater than the UFBC solution at the top or bottom of the well screen. Using the SWPP test to investigate the reactive transport in subsurface, in addition to the breakthrough curves (BTCs), the information of the flow field (like well geometry information and the observed time-drawdown data) is necessary and could be used to calibrate the model. Field application demonstrates that the UHBC model performs better than the UFBC model when interpreting BTCs of the SWPP test in the extraction phase. The findings of this study can help for better understanding of reactive transport in the SWPP test.

Reactive transport modelling of push-pull tests: A versatile approach to quantify aquifer reactivity

Push-pull tests (PPTs) were evaluated with 1-D radially axisymmetric multi-component geochemical reactive transport modelling (RTM) to assess aquifer reactivity controlling groundwater quality. Nutrient fate and redox processes were investigated in an Aquifer Storage and Recovery (ASR) system, in which oxic tile drainage water (TDW; nitrate ~14 mg/L; phosphate ~17 mg/L) was stored in an anoxic aquifer for later re-use as irrigation water. During the PPTs, the ASR system did not operate. PPTs were performed in two monitoring wells (MW2, MW3), with 1 m well screens in contrasting geochemical formations at different depths. In these wells, 300 L TDW was injected, and consecutively 720 L was abstracted within 12 days, during which water quality changes were studied. The RTM simulated cation exchange, precipitation of Hydrous Ferric Oxides, Iron (III)-phosphate and Calcium-phosphate minerals, and surface complexation as equilibrium processes. Oxidation of Pyrite, soil organic matter, and dissolved ferrous iron were simulated with kinetic rate expressions. Oxygen (within 2 days) and nitrate (within 4–7 days) were fully reduced during the PPTs. The main reductants were ferrous iron (Monitoring Well (MW) 2: 2%, MW3: 13%), soil organic matter (MW2: 93%, MW3: 6%), and Pyrite (MW2: 5%, MW3: 81%). The intra aquifer differences in dominant reduction pathways are remarkable as higher reduction rates coincided with lower contents of soil organic matter and Pyrite, respectively. Phosphate was mostly re-abstracted (MW2: 73%, MW3: 64%) and partially immobilized due to precipitation of Iron-hydroxyphosphates (MW2: 4.6%, MW3: 35%), Hydroxyapatite (MW2: 23%, MW3: 0%), and to a lesser extent by surface complexation on various minerals (MW2-3: <1%). The PPT-RTM approach enables a better understanding of reaction networks controlling water quality changes, and the reaction kinetics. PPT-RTM is a promising tool in exploratory studies or regular monitoring of water quality aspects of subsurface water technologies.

Method for measuring rice grain internal damage degree undergoing threshing force

During the threshing process of rice, the grains fall off the head of the rice ear due to the impact of the threshing bar. At the same time, the impact force of the threshing element causes a certain degree of damage to the grain. However, there are relatively few methods to analyze the internal damage of rice grains during the threshing process. In this study, the connection force between rice grains and stalks and the compressive bearing capacity of the grains were tested on a push-pull test machine, and then the critical impact force and velocity of rice grains during plastic deformation and brittle fracture were obtained by Hertz theory. On this basis, the quantitative evaluation model of grain internal damage was established through the extraction and calculation of the damaged area inside the grain, and the damage degrees inside the grain under different loading times and loading forces were analyzed. The results showed that the average threshing force required for rice grains is 1.57 N (variance is 0.0529), and the critical impact forces for plastic deformation and brittle fracture of the grains during threshing are 138.79 N and 145.77 N. Since the threshing force during the threshing process was 43.9-71.9 N, it could be known from the internal damage model that the grain is in the safe loading area. Under the same load, the vertical pressure causes the most damage, the lateral pressure takes second place, and the positive pressure was the least. The results of this study can provide a basis for the development of combine harvester and rice grains damage evaluation. Keywords: threshing process, internal damage of grain, threshing force of roller, plastic deformation, critical impact force DOI: 10.25165/j.ijabe.20211401.5750 Citation: Ren H, Tang Z, Li X Y, Li Y, Liu X, Zhang B, Li Y M. Method for measuring rice grain internal damage degree undergoing threshing force. Int J Agric & Biol Eng, 2021; 14(1): 63–73.

Method for measuring rice grain internal damage degree undergoing threshing force

During the threshing process of rice, the grains fall off the head of the rice ear due to the impact of the threshing bar. At the same time, the impact force of the threshing element causes a certain degree of damage to the grain. However, there are relatively few methods to analyze the internal damage of rice grains during the threshing process. In this study, the connection force between rice grains and stalks and the compressive bearing capacity of the grains were tested on a push-pull test machine, and then the critical impact force and velocity of rice grains during plastic deformation and brittle fracture were obtained by Hertz theory. On this basis, the quantitative evaluation model of grain internal damage was established through the extraction and calculation of the damaged area inside the grain, and the damage degrees inside the grain under different loading times and loading forces were analyzed. The results showed that the average threshing force required for rice grains is 1.57 N (variance is 0.0529), and the critical impact forces for plastic deformation and brittle fracture of the grains during threshing are 138.79 N and 145.77 N. Since the threshing force during the threshing process was 43.9-71.9 N, it could be known from the internal damage model that the grain is in the safe loading area. Under the same load, the vertical pressure causes the most damage, the lateral pressure takes second place, and the positive pressure was the least. The results of this study can provide a basis for the development of combine harvester and rice grains damage evaluation. Keywords: threshing process, internal damage of grain, threshing force of roller, plastic deformation, critical impact force DOI: 10.25165/j.ijabe.20211401.5750 Citation: Ren H, Tang Z, Li X Y, Li Y, Liu X, Zhang B, Li Y M. Method for measuring rice grain internal damage degree undergoing threshing force. Int J Agric & Biol Eng, 2021; 14(1): 63–73.

The SEM and TEM Analysis of IN718 Alloy after Fatigue Push-Pull Loading at 700°C

Specimens from Ni-Cr-Fe wrought superalloy INCONEL 718 were used for fatigue push-pull test at elevated temperature 700 °C. Fatigue loading was with the coefficient of cycle asymmetry R = -1. Temperature of fatigue test was chosen from two reasons; one is that limit operating temperature for this type of alloy is 650 – 700 °C due to precipitation of stable but incoherent orthorhombic Ni3Nb delta phase; the second reason for this temperature is fact that metastable body-centred tetragonal Ni3Nb gamma double prime phase starts to transform to delta phase and from that reason there is an expectation for mechanical properties decreasing due to increased volume of delta phase. For evaluation of fatigued specimens were Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) observation used. Also methods of quantitative metallography – coherent testing grids were used for evaluation of delta phase volume. Some references describe that higher volume of delta phase, mostly situated at grain boundaries, act as initiation sites for cracks and therefore decreasing mechanical properties. Employed SEM and TEM analysis confirm the increased volume of delta phase in specimens after fatigue loading but a negative influence on dynamic properties, such fatigue lifetime, for this alloy was not confirmed.