Unloading Process Research Articles

Unloading Model of Elastic-Plastic Half-Space Contacted by an Elastic Spherical Indenter.

A new unloading contact model of an elastic-perfectly plastic half-space indented by an elastic spherical indenter is presented analytically. The recovered deformation of the elastic indenter and the indented half-space has been found to be dependent on the elastic modulus ratio after fully unloading. The recovered deformation of the indented half-space can be calculated based on the deformation of the purely elastic indenter. The unloading process is assumed to be entirely elastic, and then the relationship of contact force and indentation can be determined based on the solved recovered deformation and conforms to Hertzian-type. The model can accurately predict the residual indentation and residual curvature radius after fully unloading. Numerical simulations are performed to demonstrate the assumptions and the unloading model. The proposed unloading model can cover a wide range of indentations and material properties and is compared with existing unloading models. The cyclic behavior including loading and unloading can be predicted by combining the proposed unloading law with the existing contact loading model. The combined model can be employed for low-velocity impact and nanoindentation tests and the comparison results are in good agreement.

Potato spindle tuber viroid (PSTVd) loop 27 mutants promote cell-to-cell movement and phloem unloading of the wild type: Insights into RNA-based viroid interactions

Variations in infection progression with concurrent or prior infections by different viruses, viroids, or their strains are evident, but detailed investigations into viroid variant interactions are lacking. We studied potato spindle tuber viroid intermediate strain (PSTVd-I) to explore variant interactions. Two mutants, U177A/A182U (AU, replication- and trafficking-competent) and U178G/U179G (GG, replication-competent but trafficking-defective) on loop 27 increased cell-to-cell movement of wild-type (WT) PSTVd without affecting replication. In mixed infection assays, both mutants accelerated WT phloem unloading, while only AU promoted it in separate leaf assays, suggesting that enhancement of WT infection is not due to systemic signals. The mutants likely enhance WT infection due to their loop-specific functions, as evidenced by the lack of impact on WT infection seen with the distantly located G347U (UU) mutant. This study provides the first comprehensive analysis of viroid variant interactions, highlighting the prolonged phloem unloading process as a significant barrier to systemic spread.

RISK ASSESSMENT OF BAGGED FERTILIZER UNLOADING ACTIVITY AT TUKS PUSRI BANYUWANGI BRANCH

The port is one of the distribution centers for goods in which there are loading and unloading activities. Loading and unloading activities sometimes involve loading and unloading personnel and heavy equipment which raises the potential for hazards that can cause work accidents and damage to goods. The purpose of this research is to conduct a risk assessment using the HIRARC (Hazard Identification, Risk Assessment and Risk Control) method on bagged fertilizer unloading work in the TUKS PUSRI Banyuwangi Branch Port area. The stages of bagged fertilizer unloading work activities include the unloading activity process, which consists of five work stages: opening the ship's hatch, workers (stevedores) entering the hatch, stevedoring, cargodoring, and delivery. The results stated that from a total of 5 work stages, 26 sources of hazards were identified with 6 sources of low risk level hazards at 23%, 7 sources of moderate risk level hazards at 27%, 6 sources of high risk level hazards at 23%, and 7 sources of very high risk level hazards (extreme) at 27%. Control measures that can be implemented are conducting briefings on OHS (Occupational Health and Safety) before starting work activities, supervision of compliance with the use of complete personal protective equipment and also the need for sanctions for workers who do not comply with the rules for using personal protective equipment.

Construction and analysis of a mechanical model for viscoelasticity and plasticity in potato

AbstractThe aim of this paper is to develop a precise collision model of potatoes falling onto a separation sieve to assess their damage characteristics. A viscoelastic‐plastic mechanics model is created by integrating the collision process with the potato soil separation device. Test factors include fall height, potato mass, fall direction, and varieties. Potato deformation and damage volume serve as evaluation indices in single‐factor tests to explore their relationships with these factors. The model analyzes the collision loading and unloading process, studying relationships between parameters and test factors, examining the potato collision damage mechanism. Predictive equations for potato damage volume based on fall height, potato mass, and plasticity ratio λp are derived: V1 = 1606λp–537, V2 = 4751λp–2087, and V3 = 12617λp–5303. This study provides a theoretical foundation for analyzing potato collision damage and offers technical references for optimizing potato harvesting machinery.Practical applicationsDamage resulting from the mechanical harvesting process significantly impacts the quality and economic worth of the tubers. Currently, research on constructing a mechanical model of potatoes, treating them as viscoelastic plastic bodies, and integrating the collision process with potato soil separation devices is limited. Thus, the objective of this paper is to investigate the correlation between various test factors and potato damage via drop tests, and to establish a viscoelastic–plastic mechanical model. Additionally, the study further explored the correlation between model parameters and tuber damage, resulting in the establishment of a mathematical model for predicting the extent of damage. This study provides a theoretical basis for an in‐depth analysis of the collision damage mechanism of potato, and a technical reference for the design and optimization of potato harvesting machinery.

Evolution of the damage precursor based on the felicity effect in shale

Damage precursors during hydraulic fracturing in shale gas reservoirs may be better understood if the deformation, failure, and acoustic emission (AE) characteristics under cyclic loading are known. Therefore, the purpose of this paper is to investigate the quantitative damage based on the Felicity effect under constant stress lower limit uniaxial cyclic loading-unloading rates (0.5, 1.0, 1.5, 2.0, and 2.5 kN/s). Variations in the b-value and the spatiotemporal evolution of cumulative AE were also used to observe how shale fractures formed. The findings reveal that during the unloading stage, there are many cumulative AE events when the stress level is low (≤1.50 kN/s) but that this number drops significantly when the stress level increases above (>2.0 kN/s). The AE amplitude, AE counts, and cumulative AE energy of each cycle in a loading-unloading test show an increasing trend, but the rate increases in the last cycle. During the whole process of loading and unloading, the Kaiser effects were present in the 3rd cycle at stress levels (≤1.5 kN/s). Still, the Felicity effect appeared in the 2nd and 1st cycles during 2.0 and 2.5 kN/s cyclic loading. The Kaiser effect occurs in the linear elastic stage, while the Felicity effect occurs in the crack initiation and crack damage stage. Furthermore, the Felicity ratio (FR) variations during shale deformation and failure can be divided into four phases: (Phase I = 1.01 ≥ FR > 0.89), (Phase II = 0.89 ≥ FR > 0.48), (Phase III = 0.48 ≥ FR > 0.23), and (Phase IV = FR ≤ 0.23). The b-value is relatively higher under the loading rate below (≤1.50 kN/s), indicating an increase in the number of small AE events. In contrast, the fact that the b-value is relatively smaller under the loading rate above (>2.0 kN/s) indicates that, the number of large AE events increases the number of cracks and fractures. These findings provide important design references for damaged precursors during hydraulic fracturing in shale gas reservoirs.

Damage characteristics of rock induced by unloading in hole under true triaxial boundary stresses: Experimental study

In order to study the effect of unloading of underground rock excavation on the stability of surrounding rock, the true triaxial compression (TTC) and coupled true triaxial compression and in-hole loading-unloading tests (TTC-HU) were conducted on hollow cubic rock (100mm × 100mm × 100mm). The experimental results indicate that the compressive strengths of the specimens increase as confining pressure increases in the equal biaxial stressand increase with increasing intermediate principal stresses in the unequal biaxial stress. At low confining pressure (σ < 30 MPa), the internal stress at unloading damage in the hole of hollow cubic specimen increases with the increase of the three-directional boundary stresses. At high confining pressure (σ ⩾ 30 MPa), the specimen will not be damaged during the entire unloading process in the hole. The damage mode of the specimen is dominated by tensile damage. The shape of the holes in the specimens did not significant change, and hole wall of specimen have layered destruction along the circumference in low confining pressure. In high confining pressure, the hole area of the specimen undergoes significant deformation damage, forming a V-groove along the direction of the minimum principal stress, and the wall of the hole is completely peeled off. This study can reasonably predict the actual engineering damage patterns and guide the optimization of surrounding rock support.

A novel unloading strategy for solar sails using reflectivity control device

For near-Earth spacecraft, many environmental forces are utilized to unload reaction wheels. However, effects like magnetic force or atmospheric friction hardly exist in deep-space environments where solar sails operate. Thus, this paper proposes an unloading method that uses reflectivity control devices to generate Solar Radiation Pressure (SRP) torque to conduct the unloading process of solar sails operating in deep space. Firstly, the basic principles of the Reflectivity Control Device (RCD), satellite kinetic model, and Pulse Width Pulse Frequency (PWPF) modulator are given. Secondly, based on the torque envelope obtained by traversing all switch combinations of RCD, a novel strategy using a PWPF modulator is specially designed to achieve efficient unloading. In the end, we carry out numerical simulations and analyze the influence of different parameters, through which the validity of the proposed torque resolution scheme is demonstrated.

Study on the Failure Process and Acoustic Emission Characteristics of Freeze–Thawed Sandstone under Cyclic Loading and Unloading

In order to investigate freeze–thawed red sandstone failure processes under cyclic loading and unloading conditions, real-time acoustic emission (AE) and scanning electron microscopy (SEM) techniques were used to reveal the fracture process of the saturated red sandstone after cyclic loading and unloading tests using uniaxial compression. The results show that the stress–strain curves of the freeze–thawed sandstones show signs of hysteresis and exhibit a two-stage evolution of “sparse → dense”. In the cyclic loading and unloading process, the modulus of elasticity in the loading process is always larger than that in the unloading process, while the Poisson’s ratio is the opposite, and the radial irreversible strain and cumulative irreversible strain are larger than those in the axial direction. As the number of freeze–thaw cycles increases, the rock specimens need more cycles of loading and unloading to make the crack volume compressive strain Δεcv+ reach the maximum value and tend to stabilize, while the crack volume extensional strain Δεcv− tends to decrease gradually. This study also shows that the growth phase of the cyclic loading and unloading process has more ringing counts and a shorter duration, while the slow degradation phase has more ringing counts with loading and less with unloading. In addition, the F-T cycle gradually changes the internal microcracks of the red sandstone from shear damage, which is dominated by shear cracks, to tensile damage, which is dominated by tensile cracks. This study’s findings contribute to our knowledge of the mechanical characteristics and sandstone’s degradation process following F-T treatment, and also serve as a guide for engineering stability analyses conducted in the presence of multiphysical field coupling.

Experimental study on response and precursor of pressure stimulated currents of combined coal-rock under cycling stress

The coal-rock combination body is prone to rock burst and surface subsidence under loading, and adopting effective monitoring methods are valuable. In this paper, cyclic loading and unloading (CLU) tests were conducted to investigate the response and precursor of pressure stimulated currents (PSCs) in coal-rock combination samples. The results indicate that the PSCs of the coal-rock combination samples have good response characteristics to stress. Furthermore, the PSCs between the two components are significantly larger and more stable than those of the coal body, which can clearly reflect the failure under a progressive failure mechanism and are related to the difference in the resistivities and microstructures of the components. During the CLU tests, the PSCs of each cycle are well fitted by the Gaussian distribution and have a memory effect. During the loading or unloading process of each cycle, the variation in PSCs with stress conforms to the power function relationship with exponent k. As the cycle number increases, the rates of increase in PSC under stress are gradually weakened, and the indexes of PSCs including exponent k increase or decrease sharply first and then remain stable or even decrease, which is due to the loading history. The stable state of these indexes with obvious inflection points in later cycles of CLU tests can be considered a precursor of coal-rock failure. The PSC flow direction between the two components is exactly opposite to that in the coal body. The results provide new ideas for the monitoring and prediction of coal-rock combination body failure, which is helpful for the prevention of geological disasters in mines.

Study on the Influence of Adjacent Double Deep Foundation Pit Excavation Sequence on Existing Tunnel Deformation Based on HSS Constitutive Model

With the increase in the number of buildings along the subway, the impact of building construction on the adjacent subway tunnels has gradually come to the forefront and become an important problem to be solved in the engineering field. In particular, the excavation and unloading process of deep foundation pits will trigger an additional deformation of the subway structure, which may pose a serious threat to the safety and stability of subway tunnels. This article is based on a foundation pit project in the sub-center of Beijing, focusing on the form of a connected double foundation pit. Using the HSS constitutive model for soil materials, this study simulates the deformation response of adjacent existing subway tunnels under three excavation sequences: sequential excavation, simultaneous excavation, and the comprehensive excavation of the connected double foundation pits. The study shows that, from the point of view of the total displacement of the whole construction process, the impact of a synchronized excavation of double pits on the existing tunnel line is relatively large in the process, and the impact of sequential excavation is relatively small in the construction cycle. The result of the similarity of the excavation sequence is the similarity of the impact trend. The volume of excavated earth determines the value of displacement change for each excavation scenario in each working condition and is also responsible for the convergence of changes. The trend of total tunnel displacement is more consistent with that of vertical displacement, which is dominated by vertical displacement, with horizontal displacement having a relatively small influence. The maximum value of the total tunnel displacement occurs at the side of the tunnel near the excavation area, and the direction is inclined to the excavation area. The application of supporting structures, especially the center plate and the bottom plate, can suppress the vertical deformation of the tunnel bulge.

A framework to efficiently simulate the cyclic variation of the residual stresses induced by chip formation in machining of Ti-6Al-4 V alloy

Residual stresses is a key part of surface integrity, having a strong influence on the functional performance and lifespan of components. Advances in modeling of machining-induced residual stresses are fundamental to achieve more accurate predictions. Due to the low computational efficiency and the lack of consideration of the whole residual stress formation process, a framework to simulate the residual stress in the machining of Ti-6Al-4 V titanium alloy using CEL (Coupled Eulerian and Lagrangian) and Lagrangian approaches is proposed. A model of the cutting and workpiece unloading processes is simulated using CEL approach and explicit time integration scheme. Then, a model of the cooling process of the workpiece is developed in order to calculate the residual stresses. To improve computation efficiency and to reduce the effects of cumulative errors, this model is simulated using Lagrangian approach and implicit time integration scheme. Data transfer between these two models is performed by combining a strategy of data transfer and mesh rebuilding. The cutting force and residual stress are obtained by simulation with average errors of 18% and 21%, respectively. The predicted and measured thicknesses of the layer are reasonable well predicted. The computational time of proposed approach can be greatly reduced from 81 h to 5.3 h by comparison with traditional one. This framework was then used to investigate the cyclic variation of the residual stress along the cutting direction, which is due to the cyclic nature of the chip formation process.

A closed-form Timoshenko beam element with multiple localized singularities for nonlinear material behavior using the strong discontinuity approach

The development of a novel closed-form beam element for nonlinear material behavior in structures is described, which is formulated according to Timoshenko beam theory and the embedded strong discontinuity approach. Multiple strong transverse and rotation discontinuities are considered to model several dissipative mechanisms due to localized singularities in the shear strain and curvature fields. Issues of dependence on numerical techniques, as occurs in displacement- and forced-based beam elements with the finite element method, are overcome since the formulated element is derived from a pure mathematical treatment. Theoretical principles are stemming from a Lagrangian variational model, from which singularities are naturally derived. The proposed formulation is solved by the conventional methods of calculus of variations, resulting in the boundary value problem. Then, closed-form expressions for any boundary conditions are obtained. By particularizing closed-form expressions for a basic system, a symmetric closed-form flexibility matrix is obtained. This matrix naturally leads to a symmetric closed-form stiffness matrix for any type of loading and unloading process, in which the nodeless degrees of freedom of the multiple embedded strong discontinuities are naturally condensed. Since Gauss integration methods are not used, the multiple localized singularities are not influenced by predefined positions of the integration points. However, the accuracy depends on the chosen number of singularities and their positions. Then, the proposed element is mesh independent when sufficient discontinuities are considered, which does not imply an increase in the degrees of freedom. Softening discontinuities are modeled at arbitrary positions in a single element, which overcomes the drawbacks of other embedded beam theories where more than one element is necessary to identify failure since strong discontinuities are generally located at the midpoint of the beam element. The obtained closed-form stiffness matrix is not always positive definite for strain-softening problems. Nevertheless, there are no major convergence issues as it is a symmetric matrix that does not require a constraint equation, so even the complex snap-back behavior in structures is adequately modeled. The capability of the formulated beam element for nonlinear material behavior in structures is validated with representative examples.

Development of self-sensing engineered cementitious composite sensors for monitoring flexural performance of reinforced concrete beam

In this paper, self-sensing engineered cementitious composite (ECC) was prepared and post-processed to obtain self-sensing ECC sensors. The sensor piezoresistive effect was modified considering the constraint of concrete. Then the sensor was embedded in the reinforced concrete beam to analyze the sensing performances under different conditions. The results show that the modified piezoresistive effect formulas were obtained by introducing correction coefficients, the formulas can describe the relationship between strain and impedance well. Sensors embedded in concrete beams cannot affect the bending performance and the development of cracks. The sensor can be used to monitor the strain in the compression under loading and unloading process of the beam and its sensing performance has good linearity, repeatability and accuracy. In the tension, when cracking, the sensors maintain the monitoring ability, but the accuracy needs to be improved. The gauge factor of the sensor applied in the beam is above 130.

Auroral Characteristics Related to AU&amp;AL Indices

AbstractAuroral images of the N2 Lyman‐Birge‐Hopfield emissions from Polar Ultraviolet Imager (UVI) for 1.5 years are used to investigate the auroral characteristics related to the AU and AL indices that represent the directly driven and unloading processes in the solar wind‐magnetosphere‐ionosphere coupling, respectively. Findings include: (a) Growing AL mainly relates to the nightside aurora and tends to keep the general auroral morphology. (b) As AU increases, the aurora brightens and expands more globally, especially in the midnight to postmidnight sector. (c) The regional auroral power (AP), equatorward boundary, poleward boundary, and peak intensity change quasi‐linearly with intensifying AU and AL. (d) The rates of change depend on the MLT and AU/AL levels. The same dataset has been used to construct the empirical Feature Tracking of Auroral Precipitation (FTA) model which specifies the global energy flux and mean energy determined by the AE index (FTA‐AE). As an extension of FTA‐AE, the relationships of the auroral emission with the AU&amp;AL indices were derived to construct the FTA‐AU&amp;AL model which specifies a more consistent aurora during different magnetospheric driving modes compared to FTA‐AE. Comparisons of AP from the Defense Meteorological Satellite Program Special Sensor Ultraviolet Spectrographic Imagers (SSUSI) measurements and empirical auroral models show that the FTA‐AE and ‐AU&amp;AL models predicted larger AP than the Fuller‐Rowell and Evans (1987) model and the OVATION‐prime model did. As the activity level increased, all four models tended to underestimate the AP but the FTA APs increased relatively faster and were therefore more consistent with the data.

A Raw Material Truck’s Queue System Optimization

We present a field study investigating the impact of raw material supply chain optimization within PT Mekabox International, a producer of high-quality brown papers utilizing recycled sources. To ensure consistent productivity, maintaining supplier interest is crucial due to limited raw material availability. Our findings reveal that expediting unloading processes significantly improves supplier satisfaction beyond pricing alone. Through quantitative analysis using a multi-channel single-phase queuing model, we demonstrate that adding one additional unloading team reduces truck waiting times from 33 to 17 minutes. These improvements enhance operational efficiency, foster stronger relationships with suppliers, and ultimately contribute to sustainable growth in the brown paper industry.&#x0D; Highlight :&#x0D; &#x0D; Optimizing the raw material supply chain for brown paper production can be achieved by expediting unloading processes, which improves supplier satisfaction.&#x0D; Quantitative analysis using a queuing model shows that adding one more unloading team can reduce truck waiting times from 33 to 17 minutes.&#x0D; These improvements lead to better operational efficiency, stronger relationships with suppliers, and contribute to sustainable growth in the brown paper industry.&#x0D; &#x0D; Keywords: brown paper, raw material, supplier satisfaction, unloading, queuing model

Abnormal superelastic cyclic behavior and stress-induced martensitic transformation mechanism of NiTi alloy with R phase

In this work, an abnormal phenomenon of the superelastic cycle in NiTi alloy with R phase is reported. The phase transformation of the 500°C-annealed-sample is B2-R-B19'. During the first superelastic cycle, the critical stress of stress-induced martensitic transformation (SIMT) is reduced to 305.5 MPa and the phase transition plateau is shortened. With the loading process, the transformation of R–B19′ and the elastic deformation of the B19′ occur. With the unloading process, martensite reversal transformation occurs and the high-density dislocation zone and residual martensite are formed. During the superelastic cycle, the R phase is consumed. The increase of irreversible residual martensite and crystal defects leads to the deterioration of superelasticity.

Temperature Control and Data Exchange in Food Supply Chains: Current Situation and the Applicability of a Digitalized System of Time–Temperature-Indicators to Optimize Temperature Monitoring in Different Cold Chains

The current situation of temperature monitoring in perishable food supply chains and the optimization of temperature control was studied by combining two approaches. First, a survey among German companies (production, processing, logistics, wholesale, retail) was conducted to analyze the current temperature monitoring and data management conditions as well as the use of novel monitoring systems, such as Time–Temperature-Indicators (TTIs). Second, the temperature conditions in three different supply chains (B2C for raw pork sausage, B2B for fish, B2C e-commerce for mixed products) were investigated to analyze the applicability of TTIs with an app-based read-out system to identify weak points and to optimize cold chain management under practical conditions. The results of the survey showed that mainly static conditions are tested along the supply chain. Thus, the actors rely mostly on visual inspection or best-before date labeling while TTIs are not widely used. Currently, temperature data are barely exchanged by stakeholders. In the B2C chain, mean temperatures on different pallet levels were comparable, also reflected by TTIs and the app-based read-out system, respectively. In the B2B chain, temperature interruptions during the unloading process were detected, revealing main challenges in perishable supply chains. Temperature monitoring by TTIs on a box level was possible by positioning the label close to the product. Results in the e-commerce sector showed heterogeneous conditions in different boxes depending on initial product temperatures and loading. TTIs and the app-based read-out system showed reliable results based on different temperature scenarios, when TTIs are positioned close to the most sensitive product.

Facile molybdenum and aluminum recovery from spent hydrogenation catalyst

Facile molybdenum and aluminum recovery from spent hydrogenation catalyst

Research on Intelligent Supervision System of Ore Pass

To prevent safety accidents caused by mining vehicles and personnel entering the operation area by mistakes, it is necessary to reduce the risk of the ore pass. However, the underground space of the mine is narrow, and factors such as dust and noise during the unloading process endanger the health of the personnel on duty in the ore pass. As such, the target detection technology based on deep learning is introduced into the underground monitoring system. The underground surveillance video samples are collected to establish a dataset for Yolov3 algorithm to identify minecarts. Through optimizing the Yolov3 model training process and algorithm, and using the dual-camera collaborative discrimination method, the influence of brightness on the recognition results when the loaders or trucks lights are turned on can be overcome. Four types of minecarts can be accurately identified from the underground surveillance video. On the basis of mining car recognition, an intelligent access control system for mine shafts based on Jetson Nano’s embedded development is developed. The on-site operation results show that the average accuracy of target vehicle recognition is within the range of 95%-100%. The system continuously recognizes the mine car 5 times from the detection program and sends the opening and closing command to complete a 90 ° rotation, which takes only 3 seconds，effectively meeting the needs of the mine for ore pass control.

A CRITICAL REVIEW ON FATIGUE ASSESSMENT APPROACH IN SHIP STRUCTURAL DETAILS

Review of the methods used in the fatigue analysis of structures has been widely used. The resulting fatigue is primarily the result of repeated loads acting on the structure both internally and externally. Internal loads are caused by the cargo loading and unloading process, while external loads are caused by sea waves. The interaction of the two loads affects the strength of the structure. In this paper, we will discuss materials, residual stresses and environmental factors that cause fatigue in structures. The focus of analysis in this critical review is on the structural details of the ship. In determining fatigue in detailed structures, it can occur in welded joints, section cuts and shape imperfections.