Strip Yield Research Articles

Short Fatigue-Crack Growth from Crack-like Defects under Completely Reversed Loading Predicted Based on Cyclic R-Curve.

Understanding short fatigue-crack propagation behavior is inevitable in the defect-tolerant design of structures. Short cracks propagate differently from long cracks, and the amount of crack closure plays a key role in the propagation behavior of short cracks. In the present paper, the buildup of fatigue-crack closure due to plasticity with crack extension from crack-like defects is simulated with a modified strip yield model, which leaves plastic stretch in the wake of the advancing crack. Crack-like defects are assumed to be closure-free and do not close even under compression. The effect of the size of crack-like defects on the growth and arrest of short cracks was systematically investigated and the cyclic R-curve derived. The cyclic R-curve determined under constant amplitude loading of multiple specimens is confirmed to be independent of the initial defect length. Load-shedding and ΔK-constant loading tests are employed to extend the cyclic R-curve beyond the fatigue limit determined under constant amplitude loading. The initiation stage of cracks is taken into account in R-curves when applied to smooth specimens.

Study of the Milkability of the Mediterranean Italian Buffalo and the Tunisian Maghrebi Camel According to Parity and Lactation Stage.

While considered as hard milkers, both buffaloes and camels are milked with equipment destined for dairy cows based on external morphological similarities with this species. This work aimed to study similarities and differences in milkability traits between Mediterranean buffaloes and Maghrebi she-camels and to evaluate the effect of parity and lactation stage. A total of 422 milk flow curves recorded with an electronic milkmeter (Lactocorder®) for both species were accessed. Milking characteristics including milk yield per milking, peak milk flow, average milk flow, duration of the main milking phase, duration of total milking, duration of various phases of milk flow, lag time and time to milk ejection, stripping yield, overmilking time and incidence of bimodal milk flow curves were evaluated for both species. Results showed that the values of milk yield per milking, duration of the main milking phase and duration of total milking were higher in buffaloes (3.98 ± 0.10 kg; 4.07 ± 0.11 min; 9.89 ± 0.21 min, respectively) compared to camels (3.51 ± 0.08 kg; 3.05 ± 0.09 min; 3.76 ± 0.09 min, respectively). However, camels had significantly higher peak and average milk flow (2.45 ± 0.07 kg/min and 1.16 ± 0.03 kg/min, respectively). Camels took significantly less time for milk ejection to occur. Only 15.49% of recorded curves were bimodal in buffaloes while 34.93% of bimodal curves were recorded for camels. Overmilking was significantly higher in buffaloes (3.64 ± 0.21 min vs. 0.29 ± 0.02 min). Parity and lactation stage had a significant effect on most studied milking traits suggesting the need for some particular practices with primiparous animals and animals at different levels of lactation for both species.

A modified strip yield model to predict warm prestressing effects in turbine steel

A modified strip yield model to predict warm prestressing effects in turbine steel

Constraint definition at a crack tip for the strip yield model

Constraint definition at a crack tip for the strip yield model

Reaction engineering of continuous crystallization of β-ammonium tetramolybdate in concentric structure reactor and its application

Abstract β-ammonium tetramolybdate [β-(NH4)2Mo4O13] is an important product of molybdenum metallurgy because of its uniform crystal structure and excellent thermal stability. The yield of molybdenum strip produced with β-(NH4)2Mo4O13 as raw material and various processing properties have been significantly improved. However, the crystallization process of β-(NH4)2Mo4O13 is very complex, including neutralization, polymerization, nucleation, and crystal growth stages, resulting in a variety of polymerization morphology. In this work, a concentric structure reactor was used to segment these stages with directional regulation of each stage. Residence time distribution (RTD) was used to evaluate the simulation of flow field characteristics in the concentric structure reactor. Determination of the influence of inlet-outlet positions, size and position of paddle, and baffle setting on the fluid behavior in a single tank suggested measures to improve the abnormal flow condition and reduce the dead zone volume fraction. In the concentric structure reactor, the dead zone volume fraction was only 2.36% when the clapboards were arranged alternately in an up-down design, using an inlet flow rate of 100 mL/min. β-(NH4)2Mo4O13 was prepared continuously by adding aqueous ammonia and product slurry for crystallization in the concentric structure reactor.

Alkanolamine intercalation assisted liquid phase exfoliation of titanium carbide MXene nanosheets for highly efficient photocatalytic CO2 reduction

Two-dimensional titanium carbide (Ti3C2Tx) MXene nanosheets have been widely concerned due to its abundant surface functional groups, high conductivity, excellent photoelectrochemical properties and thermal conductivity. Nevertheless, it is still a challenge for the mass production of high-quality Ti3C2Tx MXene nanosheets. Herein, the bulk Ti3C2Tx MXene powders were stripped into monolayer or few layer nanosheets in propylene carbonate through liquid-phase exfoliation strategy assisted via alkanolamine as intercalators. It is shown that the stripping yield is up to 59.3 %, which is the recorded value for the delamination of Ti3C2Tx MXene nanosheets from bulk Ti3C2Tx MXene powder, and 62.2 % of nanosheets are monolayer. The ability of hydrogen bond donor and molecular size of alkanolamine have important effects on the yield. Moreover, Ti3C2Tx MXene nanosheets have been employed as catalysts in the photocatalytic CO2 reduction. The yield of CO is 149.7 μmol g-1h−1, which is about five times that of bulk Ti3C2Tx MXene powder. This work paves the way for the mass production of MXene nanosheets with high activity photocatalysis.

Analyzing the accumulative roll bonding deformation zone behavior by FEM, upper bound, and experimental methods

Kinematically admissible velocity field assumption is a significant step in analyzing metal forming processes by the upper bound method (UBM). While the rotational triangular velocity field is the most compatible one in simple rolling, there is no evidence for prevailing of this velocity field in accumulative roll bonding (ARB). Accordingly, in this article, the geometry of the prevailing velocity field at the deformation zone of simple rolling (SR), and twice-rolled ARB samples were investigated through two distinct methods including experimental tests, and finite element simulation (FEM). It was proved that: 1) rotational triangle velocity field is quietly detectable in SR and ARB samples, 2) at the strip contact surfaces of ARB samples, the surface discontinuities affect the geometry of velocity field, and 3) the number of appeared rotational triangles at the deformation zone can be related to the initial roll diameter/initial sheet thickness ratio (D0/H0 while ignoring roller flattening). These results were used to propose an angular velocity field containing a discontinuity at the ARB strip interfaces. In the next step, the effects of three independent parameters including strip/rollers friction, the angular velocity of rollers, and strip's yield strength on the geometry of the prevailing velocity field were evaluated for both SR and ARB at two different D0/H0 and thickness reductions.

Effect of test temperature on tensile behavior of Fe-6.5wt.%Si alloy as-cast strip

The non-oriented Fe-6.5wt.%Si alloy as-cast strip is prepared by the top side-pouring twin-roll casting (TSTRC) process and the solidification structure of the as-cast strip is a uniform fine equiaxed grain structure. This paper studied the mechanical properties, fracture morphology, ordered phase morphology, and types of Fe-6.5wt.%Si alloy as-cast strips at different temperatures. The results show that the yield and tensile strength of the as-cast strip decreased gradually with the increase of tensile temperature, and the elongation after fracture increased gradually. The temperature rise prevented the formation of cleavage cracks, and the temperature rise is an effective method to improve the plasticity of Fe-6.5wt.%Si alloys. Concurrently, the ambient temperature is the main factor determining the tensile mechanical properties of Fe-6.5wt.%Si alloy at medium temperature. When the stretching temperature exceeds 500 °C, the Fe-6.5wt.%Si alloy has apparent plastic deformation ability. The Fe-6.5wt.%Si alloy exhibits excellent elongation when the stretching temperature is 700 °C. The serration fluctuations that appear on the 400 °C stretch curve should be attributed to the Portevin-Le Chatelier (PLC) effect caused by the reordering of the antiphase domains and the deformation-induced disorder. The Fe-6.5wt.%Si alloy as-cast strip is directly subjected to warm-rolling without the hot-rolling. When the warm-rolling is performed at the temperature of 700 °C, there are almost no cracks at the edge of the plate, the edge cracks are effectively controlled, and the surface quality of the warm-rolled sheet is fine. The obtained 700 °C warm-rolled sheets were cold-rolled at room temperature, and after recrystallization annealing, the sample had good comprehensive magnetic properties. Suppose the TSTRC-warm rolling-cold rolling-annealing process prepares the Fe-6.5wt.%Si alloy cold-rolled sheet. In that case, the production efficiency will be significantly improved, the process flow will be shortened, and the goal of energy-saving and emission reduction will be achieved.

Amount and variation of strip yields collected by a defined hand-milking method after machine milking of Holstein dairy cows

Hand-milking methods to assess the completeness of milking in dairy cows need to be reliable as well as quick to apply in order to avoid delays in group milking parlours. A previous study comparing different methods demonstrated that a defined milking handgrip with a strip frequency of 1 Hz was most suitable to assess the completeness of milk-out in dairy cows. In a first step, the present study aimed to investigate how much milk can be hand-milked by the defined handgrip, strip frequency and within a time limit of 15 s per quarter. In a second step, the question was how many udder quarters of a cow needed to be hand-milked for a reliable prediction of the amount of rest milk in the udder. The experiment comprised 28 German-Holstein cows of one herd. The cows were hand-milked after cluster detachment by an experienced milker using the defined milking handgrip. All four quarters per cow were hand-milked during nine consecutive milking sessions. The strip yield per quarter per 15 s hand-milking (SY15) was collected in four different containers and weighed with a digital scale. Afterwards, the remaining milk of all four quarters was collected and weighed in a fifth container with a maximum volume equivalent to a net weight of 540 g milk. The analysis showed that neither the position of the quarter nor the chronological order, in which hand-milking was carried out, had an influence on SY15. The amount of rest milk in the udder could be estimated best by hand-milking all four quarters.

A novel lithium phosphate production method by stripping of lithium from the lithium enolate in kerosene using orthophosphoric acid

A novel orthophosphoric acid stripping (OpaS) system has been developed for the stripping and crystallization of lithium from the synergistically produced organolithium compound consisting of lithium enolate in kerosene. In order to determine regression models and optimum conditions, a D-optimal experimental plan was constituted. Reduced quadratic, cubic and quartic models were selected for lithium and non‑lithium metal stripping responses. Accordingly, the linear terms of A and B (A: Organic/aqueous phase ratio [O/A], B: [H3PO4]) were determined as a major factor for all lithium responses while the only two-factor interaction (2FI) of AB was determined for all responses. In optimization, the non‑lithium responses were minimized while the lithium responses were maximized. The O/A was determined as 8.2 when the upper limit of 1.0 M was targeted for [H3PO4]. The optimum validated lithium stripping yield and mass fraction of lithium crystallized were predicted as 94.1% and 0.77, respectively. Based on the lithium strip McCabe Thiele diagram, two theoretical stages are required with a 1.0 M H3PO4 strip solution at an O/A ratio of 8.2. At the validated optimum equilibrium pH (pH[eq]) of 7.44, the Li3PO4 crystals of 92.2% purity of were obtained. As a result, the OpaS system has been proven to be a novel method for stripping and crystallization of lithium as Li3PO4 from the lithium enolate organic system without any requirement of thermal and extra chemical processes.

Strip yield model for multiple straight cracks with coalesced yield zones: A theoretical study

The paper presents a complicated case of coalescence of yield zones between two internal cracks out of four collinear straight cracks weakened an infinite isotropic plate. Two solutions are presented for the case of opening and closing of multiple cracks under general yielding conditions. Using these two solutions and the principle of superposition, we found the analytical expressions for load-bearing capacity of the plate using complex variable method. A numerical study has been carried out to investigate the behavior of yield zone length concerning remotely applied stresses at the boundary of the plate and the impact of two outer cracks on the propagation of inner cracks due to coalesced yield zones. Results obtained are reported graphically.

Synthesis of new carbazole derivative extractants and study on extraction of perrhenate/pertechnetate

It is very necessary to remove radioactive TcO4− from nuclear waste because TcO4− is harmful to the environment and public health due to the extremely high mobility and long-term radioactivity. In this paper, four carbazole derivative extractants L1-L4 were synthesized, and their extraction behavior for ReO4− (as an analog of radioactive TcO4−) was preliminarily studied in the chloroform-HNO3 system. Compared with L1-L3, L4 showed excellent extractability toward ReO4−, and DRe is more than 100 at pH = 2 when the initial concentration of L4 is 50 mmol/L, with the high selectivity for ReO4− over other competition anions due to the pre-organized cavity of L4 matching the size of ReO4−. L4 also showed the high SFRe(VII)/U(VI)(5000). And more, ReO4− could be easily and efficiently stripped from the loaded organic phase by Na2CO3 solution with about 100% of the stripping yield. The mechanism was further studied by NMR, HRMS, and theoretical calculation, and the results found that the process of ReO4− extracted by L4 conformed to the anion-exchange extraction model, and the extraction compound is [H2L2+·ReO4−][NO3−]. Finally, the distribution ratio (4–33) of TcO4− by L4 is better than ReO4− (1–5). This research provides a new idea for the design of extractants for efficient separation of TcO4−.

Three-Dimensional Surface Crack Growth of Maraging Steel Spherical Pressure Shell

This study focused on the three-dimensional surface crack growth of a spherical pressure shell. Eight maraging steel 18Ni (250) samples were fabricated and tested, and the fatigue crack growth rate curves were obtained. Considering the influence of plastic closure effect and sample thickness on crack growth, the fitting formula of fatigue crack growth only related to materials was obtained. Based on the three-dimensional crack closure theory and the strip yield model, a three-dimensional surface crack growth model of spherical pressure shell was established. By using a self-written program and FRANC3D, the three-dimensional surface crack growth simulations of the spherical shell were completed. The influence of the initial shape ratio and initial depth of the crack on the crack growth and the fatigue life of the spherical shell was analyzed.

Development and optimization of a bioelectrochemical system for ammonium recovery from wastewater as fertilizer

Bioelectrochemical systems (BES) have emerged as a potential technology for nitrogen removal and recovery from wastewaters with low energy consumption. In this work, a double chamber, flat plate BES reactor was connected to an air stripping system to recover ammonium from wastewater. The BES system was first operated under different electrochemical conditions working with synthetic wastewater. Applying an external voltage of +0.2 V and an air flow rate (for N stripping) of 150 mL min −1 proved to be the best scenario for ammonium recovery, in which 15.8 ± 1.6 g N–NH 4 + ·m −2 ·d −1 (vs. membrane surface area) were removed from wastewater (corresponding to 75.1 ± 3.8% of its original content) and 9.6 ± 1.9 g N–NH 4 + ·m −2 ·d −1 (vs. membrane surface area) were recovered (45.3 ± 7.5%) at a current density of 2.5 ± 0.2 A m −2 (vs. membrane surface area). The power consumption of the process (without considering aeration) was of 1.6 kWh per kg of removed nitrogen, which was lower than similar experiences reported in literature, making the proposed system quite appealing. Ammonia stripping yield was limited by catholyte pH and temperature, which were optimized along the experiment. Finally, tests with real blackwater as anolyte showed that the studied wastewater was not suitable for ammonium recovery in BES due to its low organic and nitrogen content. However, more concentrated blackwaters should also be tested to confirm this observation. Urine might also represent a valuable feedstock for ammonium bioelectrochemical recovery. • The proposed system allows nitrogen recovery as fertilizer at low energy consumption. • System performance is optimal under MEC operation as cations migration increases. • Tested BW is not suitable for recovery BES as it contained low organic content. • Stripping is a limiting step in recovery process, causing for not all removed nitrogen to be recovered. • Na + is the main cation competing with NH 4 + for charge transport across the CEM.

Fracture Toughness Analysis of Aluminum (Al) Foil and Its Adhesion with Low-Density Polyethylene (LPDE) in the Packing Industry

Liquid food packages consist of various polymers films, which are bonded together with Aluminum foil (Al-foil) using adhesion or by direct heat. The main aim of this research was to define important material properties such as fracture toughness and some FE-simulation material model parameters such as damage initiation, damage evolution, and the adhesion between Al-foil and low-density polyethylene (LDPE) film. This investigation is based on both physical experiments and FE simulations in ABAQUS with and without initial cracks of different lengths for comparison purposes. The final FE model in ABAQUS was used to compare the numerical input parameters in an extensive study with the ambition to investigate the materials’ parameters in cases with or without adhesion between laminates. Finally, the relation between the theoretical and experimental results for Al-foil using linear elastic fracture mechanics and modified strip yield model were shown, and the fracture toughness was calculated for two different thicknesses of Al-foil.

Recovery of germanium and indium from leaching solution of germanium dross using solvent extraction with TOA, TBP and D2EHPA

Germanium and indium are considered by many economies as critical raw materials. Therefore, investigation on possible methods of selective extraction of these elements from natural sources is getting increasing attention. The paper presents the results of solvent extraction tests of real sulphate solution obtained by leaching of dross and containing 5.15 g/dm3 Ge, 1.52 g/dm3 In and 5.81 g/dm3 Zn. In the first stage initial solution was doped with tartaric acid (citric and ascorbic acid were also tested) and germanium was extracted with trioctylamine(TOA)-tributyl phosphate (TBP) system. It was found that addition of complexing agent was necessary to achieve germanium extraction with TOA. Then, germanium was stripped with sodium hydroxide solution. Germanium extraction yield was >99%, while its stripping yield was 66–69%. Moreover, indium and zinc extraction yields were < 1%, therefore the operation was very selective. Additionally, it was found that stripping may be performed only if NaOH concentration was in the range between 10 and 20%. The reason was precipitation of germanium from aqueous phase at low NaOH (<10%) concentrations and formation of third phase and emulsion at higher NaOH levels (>20%). In the second stage, indium was recovered from the raffinate obtained after germanium extraction. Di-(2-ethylhexyl) phosphoric acid (DEHPA/D2EHPA) was used as an extractant and hydrochloric acid as a strippant. Indium extraction and stripping yields were > 98%, while zinc extraction yield was <1% allowing selective separation of In form Zn. It was found that solvent extraction using investigated system (3-stage germanium extraction, 3-stage germanium stripping, 2-stage indium extraction and 2-stage indium stripping) may be applied for selective recovery of germanium and indium.

Molybdenum strip test experiments and simulations at various temperatures to determine friction coefficients

The aim of the presented study was to perform the strip test of 0.5 mm thick molybdenum strip specimens by various simulated drawbead heights from 2 mm up to 6 mm and various temperatures from 20 °C up to 320 °C to obtain friction coefficients between the molybdenum strip and steel cylinders built-in the developed test device simulating the drawbead. The friction coefficients between the dry and lubricated molybdenum strip and the steel cylinders simulating the drawbeads were obtained by changing its value in the bilinear friction model and matching the holder drawing force and the drawbead restraint force curves achieved during the tests and the simulations. The increasing temperature of molybdenum strip led to reduced holder drawing force and drawbead restraint force and increased friction coefficient because of the decrease of molybdenum strip yield strength and the increase of surface contact between molybdenum sheet and the testing tool at elevated temperature.

Stripping of Fe (III) from D2EHPA Using Sulphuric Acid, Hydrochloric Acid, and Reductive Stripping in Vacuum (Dept.M)

Whereas, Fe (III) is easily extracted using di (2-ethylhexyl) phosphoric acid (D2EHPA), it is hard to strip it from the organic phase. It is well known that Fe (II) is readily stripped from( D2EHPA), so a reduction of ferric to ferrous iron could be away to solve this problem. In this work, the conventional way of stripping using acidic solutions such as H2SO. and HCl has been studied. Fe (III) stripping was found to increase with increasing acid concentration. The optimum acid concentration required is 10 N and S N for H2SO, and HCT, respectively. Also, reductive stripping in vacuum has been studied by using SHG zinc powder as a reducing agent. The optimisation of operating conditions, such as degree of vacuum, acid concentration and quantity of added zinc, has been made. The experiments showed that a stripping yield greater than 90% in only one stage can be achieved, depending on A/O ratio, at 60 kPa of pressure. Iron reduction and stripping live been done simultaneously.

Stress intensity factors and plastic zones of stiffened panels with multiple collinear cracks

Stiffened panel with multiple site cracks has been a great concern in the aviation industry and academia. In this paper, an analytical method for solving the stress intensity factor and strip yield model with coalesced plastic zone is developed based on the superposition principle, displacement compatibility and weight function method. It is then applied to obtain the stress intensity factors and plastic zone sizes for stiffened panels with two and three collinear cracks. The determined stress intensity factors and plastic zone sizes are compared with those from finite element analysis and existing literature. The present method is demonstrated to be accurate and efficient in calculating the stress intensity factor and plastic zone size for residual strength and fatigue crack growth prediction of stiffened panel with multiple site cracks.

Surface fatigue crack growth under variable amplitude loading

Plasticity-induced fatigue crack closure plays an important role in fatigue crack growth. Under fatigue loading with variable amplitude, however, the influence of fatigue crack closure along the crack front in three-dimensional cracked bodies is difficult to analyze. Here we develop a three-dimensional strip yield model to calculate crack opening stresses of surface fatigue cracks under variable amplitude loading. An equivalent thickness concept is incorporated to quantify the thickness effect for points on the surface crack front with a series of straight-through cracks. Using this equivalent thickness based strip yield model and fatigue crack growth rate curves obtained with standard through the thickness cracked specimen under constant amplitude loading, fatigue growth of surface cracks under variable amplitude loading are able to be predicted. We used this method to calculate fatigue crack growth of five semi-elliptical surface cracks and found that the ratios of the predicted life to the experimental life ranged from 0.86 to 1.01. The average value of the results was 0.93 and the standard deviation was 0.055. Good agreements are found between the predicted and experimental life for semi-elliptical surface cracks under variable amplitude loading. This method paves an avenue for fatigue crack growth life prediction of practical structures using materials properties obtained in laboratory according to material test standards.