Actual Strain Research Articles

Analysis of a model for surfactant transport around afoam meniscus.

A model developed by Bussonnière & Cantat [1] is considered for film-to-film surfactant transport around a meniscus within a foam, with the transport rate dependent upon film-to-film tension difference. The model is applied to the case of a five-film device, in which motors are used to compress two peripheral films on one side of a central film and to stretch another two peripheral films on the central film’s other side. Moreover, it is considered that large amounts of compression or stretch are imposed on peripheral films, and also that compression or stretch might be imposed at high velocities (relative to a characteristic velocity associated with physico-chemical properties of the foam films themselves). The actual strain that results on elements within each film might differ from the imposed strain, with the instantaneous film length coupled to the actual strain determining the amount of surfactant currently on each film (and hence also the amount of surfactant that has transferred either from or onto films). Quite distinct surfactant transport behaviour is predicted for the stretched film compared with the compressed one. In particular, when a film is stretched sufficiently at high enough velocity, surfactant flux onto it is predicted to become extremely ‘plastic’, increasing significantly.

Usage of EB-CFRP for Improved Flexural Capacity of Unbonded Post-Tensioned Concrete Members Exposed to Partially Damaged Strands

The study presents the performance of flexural strengthening of concrete members exposed to partially unbonded prestressing with a particular emphasis on the amount (0, 14.2, and 28.5%) of cut strands-symmetrical and asymmetrical damage. In addition to examining the influence of cut strands on the remaining capacity of post-tensioned unbonded members and the effectiveness of carbon fiber reinforced polymer laminates restoration, The investigated results on rectangular members subjected to a four-point static bending load based on the composition of the laminate affected the stress of the CFRP, the failure mode, and flexural strength and deflection are covered in this study. The experimental results revealed that the usage of CFRP laminates has a considerable impact on strand strain. In addition to that, the flexural stiffness of strengthened members becomes increasingly significant within the serviceability phases as the damaged strand ratios increase. The EB-CFRP laminates increased the flexural capacity by approximately 13%, which corresponds to strand damage of 14.28% and about 9.5% for 28.57% of strand damage, which represents one of the unique findings in this field. Additionally, semi-empirical equations for forecasting the actual strain of unbonded tendons were presented. The suggested equations are simple to solve and produce precise results. Doi: 10.28991/CEJ-2022-08-06-014 Full Text: PDF

Effect of volume fraction and unit cell size on manufacturability and compressive behaviors of Ni-Ti triply periodic minimal surface lattices

Ni-Ti shape memory alloys with triply periodic minimal surface (TPMS) lattice structures have aroused increasing interests due to their great application potential in bone tissue engineering. In this study, the effect of volume fraction and unit cell size on the manufacturability, compressive mechanical properties, and shape memory behaviors after compression of Ni-Ti Gyroid TPMS lattice structures, which were fabricated by laser powder bed fusion ( L -PBF), were systematically investigated. A mathematical model was established to analyze the geometric influence factors on manufacturing fidelity of Ni-Ti Gyroid TPMS lattice structures fabricated by L -PBF. It was revealed that the manufacturing fidelity decreased as the volume fraction and unit cell size decreased due to the aggravation of powder adhesion caused by the increase of specific surface area and overhanging rate of struts. Three power-law equations based on the Gibson-Ashby models were established to describe the dependences of compressive modulus, nominal yield strength, and ultimate strength of Ni-Ti Gyroid TPMS lattice structures fabricated by L -PBF on the volume fraction and unit cell size. All the above mechanical properties showed positive dependences on the volume fraction but negative dependences on the unit cell size. Both the volume fraction and unit cell size had little influence on the martensitic transformation temperatures as well as the total shape recovery ratio of Ni-Ti Gyroid TPMS lattice structures prepared by L -PBF. All the as-built Ni-Ti lattices exhibited high total shape recovery ratios of above 96.5% after 8% compressive deformation at room temperature (RT). But noteworthily, as the volume fraction increased, the pseudoelastic response (i.e., the recovered strain during unloading) rapidly decreased, followingly the recovered strain during heating increased. This was ascribed to the enhanced stability of stress-induced martensite at RT caused by the increased actual strain of local struts at the same overall compressive deformation in the Ni-Ti lattices with higher volume fractions. In contrast, the Ni-Ti lattices with different unit cell sizes exhibited similar strain distribution and consequently similar deformation recovery behaviors. • Manufacturing fidelity decreases as volume fraction and unit cell size decrease. • Mechanical properties show positive dependences on volume fraction. • Mechanical properties exhibit negative dependences on unit cell size. • Both volume fraction and unit cell size hardly affect the total recovered strain. • Superelastic response decreases as volume fraction increases.

Simplified Elastoplastic Fatigue Correction Factor Analysis Approach Based on Minimum Conservative Margin

ASME and RCC-M codes specify an elastoplastic fatigue analysis technique: a simplified elastoplastic fatigue analysis method based on linear elastic analysis. In this method, the elastic strain range is multiplied by the elastoplastic correction factor (Ke) to envelope the actual plastic strain range for fatigue evaluation. The ASME or RCC-M provide the Ke parameters of typical materials, such as austenitic stainless steel and low alloy steel. However, how can the parameters of the material not included in the codes be determined? Based on the existing material Z2CND18.12 (nitrogen control) in the codes and taking into account various sensitive factors, the minimum conservative margin of Ke for this material is calculated, and then the parameters of nonstandard materials are determined iteratively based on the conservative margin. The sensitive factors include the different structure model, load types, the loading control mode, temperature value and the material constitutive model. Based this approach, the Ke parameters of TA16 are determined and verified by the transient with drastic change in temperature and pressure. The results of the case show that the simplified elastoplastic fatigue analysis can envelope the results of cyclic plastic fatigue analysis. The minimum margin approach established in this paper can reasonably determine the Ke value of materials beyond the ASME and RCC-M codes.

Application of copper as a pulse shaper in SHPB tests on brittle materials- experimental study, constitutive parameters identification, and numerical simulations

Generally, optimum dimensions of a pulse shaper (PS) in SHPB tests on brittle materials like rock are chosen by performing numerous experiments with different sizes of PS. The dimensions that give the best force equilibrium and constant strain rate loading in the specimen are selected. Experimental efforts can be saved if the constitutive behavior of the PS can be simulated numerically. In the current work, the behavior of pure copper is investigated at various strain rates (up to ∼4000 /s) and temperatures (till 250 °C) in as-received and annealed conditions. The mechanical behavior of copper is assessed in terms of strain hardening rate, strain rate sensitivity, and temperature sensitivity. It is found that the strain hardening rate in annealed samples is almost twice that of as-received ones. A strain rate increase strengthens copper while a temperature rise weakens it. Fractographs of quasi-static samples tested at various temperatures indicate that all samples undergo ductile failure. The experimental data is used to derive constitutive parameters of the Johnson-Cook (JC) model using a multi-objective optimization method. It is concluded that the modified JC model fits better than the original form, as substantiated by higher R2 and lower AARE (average absolute relative error) values. The derived parameters are successfully applied to model the dynamic behavior of the copper PS in SHPB tests on Kota sandstone samples. It is observed that the experimental and numerical incident pulses are qualitatively similar, and the Russell comprehensive error is well within 0.15 for all the cases. It is concluded that investigating copper behavior till ∼4000 /s yields sufficiently accurate results to predict PS behavior during SHPB tests, although the actual strain rates experienced by the pulse shapers are higher. A sensitivity and probabilistic analysis are carried out to understand the effect of parameters variations on the incident rise time.

Formulation of Irradiation Assisted Stress Corrosion Crack Growth Rates for Neutron-Irradiated Stainless Steels under Hydrogen Water Chemistry Conditions of Boiling Water Reactors

ABSTRACT This study developed a formula for the calculation of crack growth rates (CGRs) of irradiated austenitic stainless steels (SSs) under hydrogen water chemistry (HWC) conditions of boiling water reactors. First, the input parameters for the Hashimoto–Koshiishi model, which is a mechanistic crack growth model of stress corrosion cracking (SCC), were optimised for SSs irradiated up to 11 dpa. Electrochemical corrosion potential (ECP) of those SSs during crack growth tests nearly equalled −200 mVSHE. Second, a simplified formulation was developed to reproduce the model calculations of SSs. Calculated CGRs agreed well with experimental CGRs of various types of SSs, which were irradiated up to 13 dpa and tested at ECPs from −550 mVSHE to −200 mVSHE, when the experimental CGRs were less than the values for NWC conditions. On the other hand, there were some data in which experimental CGRs were much higher than calculated CGRs. By analysis of the experimental conditions of the data, the possible influencing factor for the discrepancy between the calculated and experimental CGRs was found to be the -validity. If the -validity criterion was not satisfied, the strain distribution used in the model calculation was not adequate for the actual strain distribution.

Modeling of confined circular RC columns using artificial neural network and finite element method

A Finite Element (FE) and an Artificial Neural Network (ANN) model were developed to investigate the effect of different parameters, such as the space between stirrups and the diameter of longitudinal steel, on the behavior of circular Reinforced-Concrete (RC) columns confined with fiber reinforced polymer (FRP) sheets using the actual hoop rupture strain of the FRP. The FE model was accomplished using the FE software ABAQUS 6.13 which incorporates the nonlinear behavior of concrete material, the bilinear stress–strain curve of steel, and the linear elastic behavior of FRP. It was found that there is a good agreement between the FE model (FEM) results and the experiments. The ANNs were trained and tested on an experimental database from the literature. The database contains the experimental ultimate FRP strain, and the ultimate load results of 92 FRP confined circular RC columns. The ANN results agreed well with the FEM results. The neural network results were carried out to develop empirical equations to predict the effective rupture FRP strain and the ultimate load for circular confined RC columns with R2 of 0.912 and 0.932, respectively. The proposed equations estimate the ultimate strain from experimental works of the FRP with a small error up to 20%. In addition, the predicted results from the proposed equations exhibited good accuracy compared with previous guidelines and experimental and FE results from the literature, and it can be easily used in engineering designs as well.

Evaluation of environmental and physiological indicators in lactating dairy cows exposed to heat stress.

This study aimed to better understand environmental heat stress and physiological heat strain indicators in lactating dairy cows. Sixteen heat stress indicators were derived using microenvironmental parameters that were measured at the surrounding of cows and at usual fixed locations in the barn by using handheld and fixed subarea sensors, respectively. Twenty high-producing Holstein-Friesian dairy cows (> 30.0kg/day) from an intensive dairy farm were chosen to measure respiration rate (RR), vaginal temperature (VT), and body surface temperature of forehead (FT), eye (ET), and muzzle (MT). Our results show that microenvironments measured by the handheld sensor were slightly warmer and drier than those measured by the fixed subarea sensor; however, their derived heat stress indicators correlated equally well with physiological indicators. Interestingly, ambient temperature (Ta) had the highest correlations with physiological indicators and the best classification performance in recognizing actual heat strain state. Using segmented mixed models, the determined Ta thresholds for maximum FT, mean FT, RR, maximum ET, mean ET, VT, mean MT, and maximum MT were 24.1°C, 24.2°C, 24.4°C, 24.6°C, 24.6°C, 25.3°C, 25.4°C, and 25.4°C, respectively. Thus, we concluded that the fixed subarea sensor is a reliable tool for measuring cows' microenvironments; Ta is an appropriate heat stress indicator; FT, RR, and ET are good early heat strain indicators. The results of this study could be helpful for dairy practitioners in a similar intensive setting to detect and respond to heat strain with more appropriate indicators.

Re-evaluation of shear contribution of CFRP and GFRP sheets in concrete beams post-tensioned with unbonded tendons

Contemporary design guidelines for the shear resistance of post-tensioned concrete (PC) beams retrofitted with fibre reinforced polymer (FRP) sheets are developed from the results of reinforced concrete (RC) beams. The accuracy of these guidelines for calculating the shear resistance of PC beams wrapped with FRP sheets is still questionable due to the difference in the shear behaviour of RC vs PC beams. The effects of the essential factors (e.g. tendon profile and anchorage system) on the shear resistance of PC beams have not been sufficiently studied, particularly for unbonded post-tensioned concrete (UPC) beams. This study presents an experimental investigation on the shear behaviour of UPC T-beams and the shear contribution of CFRP/GFRP sheets. The experiment consisted of 26 large-scale UPC T-beams with various factors including the tendon profile (harped or straight), concrete strength, FRP anchors, CFRP vs GFRP sheets, and various wrapping configurations. The experimental results showed that CFRP/GFRP sheets increased the shear resistance of UPC beams by 4–26%, which was much lower than that in RC beams. In comparison with the UPC beams with straight tendons, those with harped tendons exhibited a reduction in the shear contribution of CFRP/GFRP sheets (approximately 40%) and showed a more ductile failure mode with an improvement of the beam deformation (up to 2.3 times). FRP anchorage systems significantly enhanced the FRP shear contribution and energy absorption increased by 88% and 42% regarding those without anchors, respectively. Besides, it was observed from the test data that the widely-used method to determine the experimental shear contribution of FRP sheets in PC beams based on the difference between the shear resistance of strengthened and unstrengthened beams was inappropriate because it failed to consider the interactions between FPR sheets and other shear components, i.e. concrete and stirrups. Meanwhile, the experimental shear contribution of FRP sheets is recommended to be determined from the actual strain data of the FRP sheets across the main shear crack.

Fatigue Crack Propagation Estimation Based on Direct Strain Measurement during a Full-Scale Fatigue Test.

Military aircraft are subjected to variable loads, which are the main cause of initiation and propagation of cracks in the most stressed locations of the airframe. The aim of a Full-Scale Fatigue Test (FSFT) is to represent actual load conditions in such a way that the results obtained are a good representation of the actual loads and may be used as data that give insight into the development of real fatigue damage in critical locations. The FSFT load spectrum is a generalized depiction of the expected service loads and is designed to give an overall good representation of loads exerted on the airframe’s structural elements during operation. Moreover, the discrete method of load application on the structure (exerting loads with hydraulic actuators rather than pressure fields or inertia loads expected in actual operation) may cause some local effects, which may not be present in operation. The proposed usage of direct strain data from the test include such local effects. Moreover, operational loads may vary between individual aircraft, therefore it is crucial to understand the whole process of fatigue crack onset and development in order to determine safe inspection intervals and thereby mitigate risk. This paper presents crack propagation calculations regarding the development of a crack in a critical location of the PZL-130 “Orlik” TC-II aircraft, discovered during FSFT. The discussed crack was found already developed, hence the information about nucleation and initial propagation of the crack was not available. Therefore, there was a need to recreate the whole propagation process by means of numerical estimations using the FSFT results like location of the crack and total life for model validation. Moreover, in order to gather real load data for calculations a dedicated stain gage was installed on the damaged load path to monitor the actual remote strain in the element during the FSFT. This allowed for the definition of load sequence exerted on the damaged element directly during the test rather than estimating it from the general load conditions of the wing. The calculations allowed for the estimation of crack propagation curves from initiation to critical crack length causing fatal damage. The obtained curves allowed to visualize the crack behavior due to applied load and furthermore define initial and recurring inspection intervals for the entire fleet during operation, which allowed to define which cracks could be found before they reach critical size in order to carry out mitigation actions like repair or replacement of the damaged part. The authors present the methodology for load spectrum development based on direct strain measurements and furthermore crack propagation curves estimation, validated with the actual FSFT results, which allowed to propose nondestructive inspection intervals for future operation.

A Novel Feature Identification Method of Pipeline In-Line Inspected Bending Strain Based on Optimized Deep Belief Network Model

Both long-distance oil and gas pipelines often pass through areas with unstable geological conditions or natural disasters. As a result, they are prone to bending, displacement, and deformation due to the action of an external environmental loading, which poses a threat to the safe operation of pipelines. The in-line inspection method that is based on the implementation of high-precision inertial measurement units (IMU) has become the main means of pipeline bending stress-strain detection technique. However, to address the problems of the inconsistent identification, low identification efficiency, and high misjudgment rate during the application of the traditional manual identification methods, a feature identification approach for the in-line inspected pipeline bending strain based on the employment of an optimized deep belief network (DBN) model is proposed in this work. In addition, our model can automatically learn features from the pipeline bending strain signals and complete classification and identification. On top of that, after the network model was trained and tested by using the actual pipeline bending strain inspection data, the extracted results showed that the model after the implementation of the training process could accurately identify and classify various pipeline features, with an identification accuracy and efficiency of 97.8% and 0.02 min/km, respectively. The high efficiency, elevated accuracy, and strong robustness of our method can effectively improve the in-line inspection procedure of pipelines during the enforcement of a bending strain load.

Experimental Assessment and Numerical Modeling of the Bond-Slip Correlation for Steel Rebars in r.c. Members.

Refined non-linear static or dynamic analyses are increasingly used to assess the behavior of new and existing reinforced concrete structures. To perform these analyses, an adequate knowledge of the force–displacement, bending moment–curvature, and bending moment–rotation curves of relevant parts of structural members is needed, and modeling the bond–slip correlation for steel rebars becomes fundamental. The paper presents the results of an experimental campaign on r.c. specimens under tension, aiming, differently from previous studies, to better reproduce the bond–slip relationship accounting for the local confinement and anchorage conditions of real structural members. Resorting to an original numerical procedure allowing us to predict the relative displacement between steel reinforcement and the surrounding concrete in a reinforced concrete element, once assigned the stress in the naked steel bar and the bond–slip law, the experimental results are compared with the numerical outcomes obtained by adopting codified bond–slip laws. The comparison highlights that experimental values of sliding are well below those that are commonly given in existing bond slip laws, such as that adopted by the CEB-FIP Model Code. A new bond–slip model, which is able to satisfactorily predict actual strain fields and slips along the investigated r.c. elements, is thus proposed with the final aim of extending its implementation into non-linear analyses of r.c. structures.

A Novel Information Fusion Method of RFID Strain Sensor Based on Microstrip Notch Circuit

According to the current development situation, the application of chipless RFID sensors in structural health monitoring has the disadvantages of difficult detection, poor effect, and single design function, limiting the further development of this technology. Therefore, a new type of RFID strain sensor that realizes the compact structure and separated function of miniaturized chipless RFID coded tags is proposed. The integrated disc monopole antennas make wireless measurement possible. Through single-parameter strain simulation analysis, six characteristic parameters with good linearity are determined. The time sequences data enhancement algorithm and the background noise data enhancement algorithm are used to expand the training data set. Then the BP neural network is utilized for data fusion, and the training error finally converges to 0.0005. A comparison experiment between wired and wireless is designed, and the wireless experiment is optimized through the wired experimentation. The results of wireless measurement experiments show that combined with multi-parameter information fusion technology, the average error between the proposed sensor and the actual strain is 6.04%, and the minimum error is 0.25%. The multi-parameter fusion monitoring method of the strain sensor corrects the error of single-parameter measurement, and its accuracy and robustness are improved.

Optical characterization of strain sensing cables for Brillouin optical time domain analysis

Two innovative optical fiber cable layouts designed to improve strain measurement accuracy for Brillouin Optical Time Domain Analysis (BOTDA) sensors through improved strain transfer efficiency are presented and discussed. Swept Wavelength Interferometry (SWI) is used to experimentally evaluate their performance alongside analytical models and numerical simulation through Finite Element Method (FEM). The results show good agreement between the different methods and show that the second sensing cable design presents good features to minimize the mismatch between measured and actual strain. Finally, the strain response of both strain and temperature sensing cables of this design are evaluated, showing that their difference in response is reliable enough to allow temperature compensation.

Formability Prediction of Laser-Welded Stainless Steel AISI 304 and AISI 430

The effect of laser welding on the mechanical properties and the prediction of formability for austenitic stainless steel AISI 304 and ferritic steel AISI 430 when welded by a YLS-5000 fiber laser, were studied in the paper. The microstructure of the welded joint was analyzed using light microscopy. The mechanical properties were determined by static tensile testing. The forming limit diagrams were produced from notched samples at R5, R17, and R25 mm. The hardness values of the welded joint and the base material were determined using the Vickers method. Samples made of AISI 430 showed that the formability suffered due to laser welding. Longitudinal coarse ferrite grains were observed in the microstructure of the AISI 430 weld metal. The coarse-grained structure of the welded joint and the continuous interface along the centerline caused the failure of the AISI 430 laser-welded samples at significantly lower actual stress and strain values than were required to break the base material. No significant changes in the formability were observed in the AISI 304 samples after laser welding. The growth of dendrites was observed in the microstructure of the AISI 304 welded joint in a direction towards the centerline of the welded joint. A comparison of the experimentally determined FLD0 values and the values calculated from predictive equations showed that a better agreement was achieved for uniform elongation than for the strain hardening exponent. The manufacturability and economic efficiency of selected parts of an exhaust system by hydromechanical drawing were evaluated on the basis of the process capability index Cpk.

Fatigue Behavior of Smart Composites with Distributed Fiber Optic Sensors for Offshore Applications

Continuous inspection of critical zones is essential to monitor the state of strain within offshore wind blades, thus, enabling appropriate actions to be taken when needed to avoid heavy maintenance. Wind-turbine blades contain various substructures made of composites, sandwich panel, and bond-joined parts that need reliable Structural Health Monitoring (SHM) techniques. Embedded, distributed Fiber-Optic Sensors (FOS) are one of the most promising techniques that are commonly used for large-scale smart composite structures. They are chosen as monitoring systems for their small size, being noise-free, and low electrical risk characteristics. In recent works, we have shown that embedded FOSs can be positioned linearly and/or in whatever position with the scope of providing pieces of information about actual strain in specific locations. However, linear positioning of distributed FOS fails to provide all strain parameters, whereas sinusoidal sensor positioning has been shown to overcome this issue. This method can provide multiparameter strains over the whole area when the sensor is embedded. Nevertheless, and beyond what a sensor can offer as valuable information, the fact remains that it is a “flaw” from the perspective of mechanics and materials. In this article and through some mechanical tests on smart composites, evidence was given that the presence of embedded FOS influences the mechanical behavior of smart composites, whether for quasi-static or fatigue tests, under 3-point bending. Some issues directly related to the fiber-architecture have to be solved.

Laws Governing Free and Actual Drying Shrinkage of 50 mm Thick Mongolian Scotch Pine Timber

The relationships between free shrinkage and actual shrinkage of different layers in Mongolian Scotch pine (Pinus sylvestris var. mongolica Litv.) were explored to provide basic data for the further study of drying shrinkage properties. The free shrinkage coefficients at different temperatures and the actual shrinkage strain of each layer were examined under conventional drying. The results showed high precision of free drying shrinkage of corresponding layers of thin small test strips in each layer of sawn timber. The free shrinkage increased linearly as moisture content declined. At the same temperature, the free shrinkage coefficient reached the largest values for the first layer (above 0.267%), while the smallest values were recorded for the ninth layer (below 0.249%). Except for the ninth layer, the free shrinkage coefficients in width directions of other representative layers decreased as temperature increased. At constant temperature, the difference in free shrinkage coefficient of test materials in the length direction of sawn timber was small for the first layer, but slightly larger and changed irregularly in the fifth and ninth layer direction. At the end of conventional drying, the plastic deformation of each layer in the early stage of drying showed a reducing trend or even reversal due to the effects of reverse stress and later damp heat. In sum, these findings look promising for future optimization of wood drying process.

The effects of the temperature in the testing system on the measurements of thermal rock strain with clip-on extensometers

The present work was aimed to identify and quantify the offsets biasing the thermal rock strain as measured with clip-on extensometers at a mechanical testing system (MTS) so as to increase the reliability of such measured strain. We conducted an experiment via cycling the temperature of a sample of aluminum alloy between ambient temperature and 90 °C under the hydrostatic confining pressure as maintained at 2 MPa. Thereby, the readouts of the extensometers appeared to be irreversible subsequent to the temperature cycle mimicking residual deformation in the sample. The numerically simulated temperature in the setup of the testing system was heterogeneous throughout such temperature cycling test showing an irreversible plug-in temperature in particular. These temperatures resulted in the apparent amplification of the circuit as constituted by the extensometer and the amplifiers as well as the relevant reading offset. Such induced offset biased the actual sample strain besides the expansion (contraction) in the metal parts of the extensometers yielding the apparent irreversible strain in the sample. We presented a workflow for quantifying the amplification- and the metal part-related offsets. The validity of the workflow was demonstrated via rectifying the strain in a rock sample that was monitored throughout a temperature cycle between 30 °C and 40 °C. Our present work would be referable for experimental researches on thermal rock strain with similar setup of measurement. The amplification- and the metal part-related offsets could be likewise estimated and excluded from the measurements conducted elsewhere before the strain in a tested sample could be obtained.

Effects of p-type conductive properties of triaxial strain-regulated ZnO (S, Se, Te) system

P-type ZnO materials are a difficult problem worldwide. The strain caused by doping, substrate and sample lattice constant mismatch, and thermal expansion coefficient mismatch is often ignored. First principle calculation is used to select the appropriate strain range and solve this problem. The effect equivalent to the actual strain is simulated to study the conductive properties and the mechanism of a doping system. Studies have shown that under unstrained conditions, the binding energies of undoped ZnO and all doped systems are negative, and the stability is relatively high. The formation energy of all doped systems increases, and their stability decreases with the increase in tensile strain or compressive strain. This study shows for the first time that when the compressive strain is −5%, the hole mobility of the same doping systems of Zn36SO35, Zn36SeO35, and Zn36TeO35 is relatively maximum. The difference between the hole concentration of the Zn36MO35 (M = S, Se, Te) systems is extremely small regardless of tensile strain or compressive strain. When the compressive strain is −5%, the hole conductivity of the Zn36SO35 system is the best. These findings can serve as guide in the experimental design and preparation of new p-type ZnO conductive functional materials.

Analysis of actual confinement provided by high‐strength steel spirals in reactive powder concrete of anchorage zones

AbstractThe local bearing strength and deformation capacity of the reactive powder concrete (RPC) specimens can be dramatically improved by arranging steel spirals. In effect, the actual stress level of spirals is closely correlated with the compression behavior of concrete loaded over limited area. However, limited work has been focused on the actual stress of steel spirals in RPC. To obtain the actual confinement provided by the high‐strength spirals in anchorage zones, 10 RPC specimens loaded over limited area were conducted. The load–spiral strain relationships and the deformation–spiral strain responses were discussed to investigate the lateral response of RPC. The high‐strength spirals failed to reach the yield strength at the peak load, and the actual strain of the spirals ranged from 1800 to 2500 με, while the residual strength of the high‐strength spirals could be fully utilized after the peak load. The actual stress of the spirals at the peak load decreased with the concrete compression strength, which increased the volumetric ratio of spirals. Furthermore, the actual stress predicting equation of spirals in RPC at the peak load was developed based on the results. Meanwhile the formula for calculating the bound value of the volumetric ratio of spirals was derived to determine whether the spirals yielded at the peak load. In view of the above analyses, a method for calculating the local bearing capacity considering the actual stress of the spirals was further developed.