Unloading Process Research Articles

Research on springback compensation for multi-point forming of corrosion-resistant aluminum alloy hyperbolic component

Springback is the reverse elastic deformation produced by the unloading process, which is a common phenomenon in the sheet metal stamping and forming process and affects the final forming accuracy of the part. Aiming at the problem of springback error in the multi-point forming process of hyperbolic component for ships, the springback phenomenon of hyperbolic component was studied by combining theoretical analysis, numerical simulation and forming test. The mechanical property parameters and stress-strain curves were obtained by tensile tests using a new corrosion-resistant aluminum alloy as the sheet material. The springback compensation method is introduced, the springback compensation formula based on surface curvature is derived, and the compensated mold surface is further corrected and fitted using the cubic B-sample method. The multi-point punch tooling was generated and modeled by the multi-point 3D modeling software MPFCAD and finite element software to simulate the multi-point forming and unloading springback process of the hyperbolic member. Multi-point forming tests were conducted on a multi-point forming press for corrosion-resistant aluminum alloy hyperbolic component, and the formed parts were checked for accuracy and error analysis by 3D scanning and GOM Inspect software. The results show that the springback compensation method used in this paper can effectively reduce the springback error in the multi-point forming process of corrosion-resistant aluminum alloy hyperbolic component, and the effect is very good.

The Effect of Different Freeze-Thaw Cycles on Mortar Gas Permeability and Pore Structure

Two different freeze-thaw cycles (FTC) are considered in this study to assess the related impact on gas permeability and micro-pore structure of a mortar. These are the water-freezing/water-thawing (WF-WT) and the air-freezing/air-thawing (AF-AT) cycles. The problem is addressed experimentally through an advanced nuclear magnetic resonance (NMR) technique able to provide meaningful information on the relationships among gas permeability, pore structure, mechanical properties, and the number of cycles. It is shown that the mortar gas permeability increases with the number of FTCs, the increase factor being 20 and 12.83 after 40 cycles for the WF-WT and AF-AT, respectively. The results also confirm that gas permeability hysteresis phenomena occur during the confining pressure loading and unloading process.

Collaborative Optimization Control of Torque Unloading and Loading for a Dual-Motor Coupling Drive System

Taking a dual-motor planetary two-gear transmission drive system as the research object, this paper analyzes the factors influencing gear shift process and major performance indexes. The study focuses on the influence of torque unloading and loading process on vehicle impact during gear shift stage. In view of the collaborative operation of main motor, auxiliary motor and gear shift actuator of transmission, the author proposed a control method and strategy process featuring multiple collaborative gear-shift torque. Then, a simulation platform was built for the vehicle and power system to simulate and compare torque unloading and torque recovery under specified acceleration condition. Compared with non-collaborative torque control, the vehicle impact under multiple collaborative control was reduced by 60% in torque unloading stage and 80% in torque recovery stage. Further, the prototype was developed for transmission control unit and power system and tested on the vehicle. The test results further demonstrated that multiple collaborative gear-shift torque control could effectively reduce the vehicle impact during unloading and loading, with gear shift time shortened and gear shift comfort improved.

Research of the crop seed unloading process from the treatment chamber of a rotary seed treater

Purpose. Enhancing the productivity of the process of layer-by-layer application of protective agents on the seeds of agricultural crops through the justification of the shape of the unloading window of the seed treatment chamber of rotary batch treaters. Methods. The research uses an analytical and experimental methods using Microsoft Office software environments. Results. The analytical dependence of the ratio of the width of the live cross-section of the seed flow to the width of the unloading window on the central angle of the window girth and the experimental dependence of the seed unloading time from the processing chamber on the mass of its portion and the rotor rotation frequency were obtained. Conclusions. The ratio of the width of the live section of the flow of processed seeds to the width of the unloading window increases proportionally with the increase in the central angle of the window. The throughput of an unloading window with a larger window width is greater than the throughput of an unloading window with a smaller window width for the same area. The time of discharge of processed seeds depends on both the mass of its portion and the frequency of rotation of the rotor. At the same time, the seed unloading time from the processing chamber increases with the increase in the weight of its portion and at a rotor speed of 250 rpm is 4.3 s for a seed portion weight of 3.5 kg and 6.9 s for 14 kg portion weight. The time of seed discharge from the processing chamber decreases with an increase in the rotor rotation frequency, and for 10.5 kg seed portion weight, it is 5.4 s at a rotor rotation frequency of 150 rpm and 4 s at a rotor rotation frequency of 250 rpm. Keywords: seeds, treatment chamber, seed treater, layer treatment, protective preparations, unloading.

RESEARCH ON NONLINEAR VARIATION OF ELASTIC WAVE VELOCITY DISPERSION CHARACTERISTIC IN LIMESTONE DYNAMIC FRACTURE PROCESS

The elastic wave propagating in rock has velocity dispersion characteristic that holds an imperative significance in rock engineering. This paper aims at study elastic wave velocity dispersion characteristic in limestone dynamic fracture process. For this purpose, the experiment of elastic wave propagates in the limestone when cyclic loading and unloading process is conducted, and elastic wave velocity dispersion characteristic is analyzed. Based on multifractal theory and Raiga model, the influence of fracture degree on velocity dispersion characteristic is discussed qualitatively and quantitatively with evolution characteristic of the AE event. The research results indicate that there is velocity dispersion characteristic when elastic wave propagates in the limestone sample, which presents positive correlation between velocity and frequency. The variation of wave velocity dispersion characteristic is consistent with that of AE activities and both of them show a nonlinear increase trend with an increase of loading. The reason for velocity dispersion characteristic is that the retarding effect of microcracks on elastic wave velocity with different frequencies is different, and the effect is enhanced with the microcrack scale increasing. According to the variation of multifractal parameter [Formula: see text] of the AE event energy series, the limestone sample under loading experiences a transformation process from small-scale microcrack to large-scale microcrack and small-scale microcrack dominance to multi-scale microcrack coexistence, and this complex transformation process results in nonlinear variation of velocity dispersion characteristic. Further, the multifractal parameter [Formula: see text] is introduced into Raiga model to establish the velocity dispersion quantitative model. The model can describe well elastic wave velocity dispersion characteristic, and indicates quantitatively that there is an obvious nonlinear positive correlation between the dispersion characteristic and the fracture degree. The research results have important theoretical and practical significance for understanding elastic wave velocity dispersion characteristic in limestone dynamic fracture process. It can provide important support for characterizing rock fracture process using elastic wave velocity dispersion characteristic.

Full-Scale investigation on inclined ballastless cant track using concrete slab panel at high temperature setting

The topography condition in the mountainous region has limited the construction of high-speed railways. Therefore, the proposed research aims to develop a new cant track model which is designed at a maximum inclination of 180 mm to simulate the curved sections on these highland areas. This construction methodology incorporates the advantages of the strong stress-bearing property of concrete slab panels and the robust stress distribution ability of the asphalt concrete trackbed. The installment of concrete slab and optimized asphalt concrete mixture were also used to counter the negative impact of the high temperature during summer in South Korea on the asphalt concrete layer. In this research, the performance of the cant track system was analyzed by using the Rail Load System built by the Korea Railroad Institute. There are two featured loading stages including the static load and cyclic load. The static load was designed in the loading and unloading process between 0 and 210kN with an amplitude of 30kN. Concerning the dynamic behavior on the testbed section, 3 million cyclic train loads were applied at a frequency of 7 Hz to simulate the train speed of 350 km/h. The thermal air blow system was installed surrounding the cant track to keep the temperature at the core asphalt concrete at a constant value. Overall, the full-scale testbed results confirm the positive applicability of the cant track since stress can be homogenously distributed along the track substructure. Moreover, the rail plastic displacement and tensile strain of asphalt concrete roadbed were noticeably reduced compared to the conventional long sleeper ballastless track.

Analisis kekuatan struktur ramp door haluan pada kapal Ferry Ro-Ro 1500 GT dengan variasi beban menggunakan Finite Element Method

Ramp Door is a door to put a vehicle into a Ro-Ro ship or any other type of ship that transports vehicles. The use of Ramp Door is needed to facilitate the process of unloading and loading vehicles from the crossing dock to the ship and vice versa. This study aims to analyze the strength of Ramp Door structure with load variations from various types of vehicles in order to compress the maximum stress results and safety factors. The method used is the FEM method with the help of an element-based application up to. The results of the study obtained the maximum stress value of Ramp Door Bow with MPV vehicle type at an even load is 43.26 MPa. In this type of SUV vehicle, the maximum stress with an even load is 50.37 MPa. In sedan vehicle type the maximum stress with an even load is 37.61 MPa. in commerial vehicle type the maximum stress with an even load is 45.70 MPa. In this type of small truck vehicle, the maximum stress with an even load is 81.53 MPa. In large truck vehicles the maximum stress with an even load is 302.48 MPa. In this type of vehicle, the maximum stress bus with an even load is 178.08 MPa. For the largest safety factor value is a type of Commercial vehicle with a value of 8.91. While the smallest safety factor value is the type of Big Truck vehicle with a safety factor value of 1.01.

Maintenance of Cera Tanks and Bucket Elevators to Streamline the Unloading Process on Cement Carrier MV. Oceanic Success

Cement is one of the most important building materials in the world of construction today. So that the demand for cement can be used as a benchmark in the implementation of development in a country. Cement ship unloading equipment is very influential on the availability of cement supply both in Indonesia and the world. Damage to the unloading equipment on the cement carrier ship, especially the Cera Tank and Bucket Elevator, has an impact on the delay in the loading and unloading process at the port. So that maintenance is very important in order to avoid the delay in loading and unloading. This research was conducted in MV. Oceanic Success for 12 months. The aim is to find out things that must be considered in terms of maintenance of cement carrier ship unloading equipment. This research method uses a qualitative descriptive method with data analysis techniques, namely Root Cause Analysis with the help of the 5 Why Analysis Method tool. The results of this study indicate that the Cera Tank and Bucket Elevator unloading tools are lacking in terms of maintenance. Thus causing delays in the unloading process on the MV ship. Oceanic Success.

A risk factor tracing method for LNG receiving terminals based on GAT and a bidirectional LSTM network

LNG terminals are important transfer stations for LNG storage, processing, and outbound transmission which involve intensive manual operation and safety management activities. Traditional safety evaluation methods can provide "cause-effect" information when investigating the traceability of incorrect manual operation. However, manual analysis and summarizing risk factor causality is time-consuming and labor-intensive, and there are inaccuracy problems. Usually, HAZOP meetings require safety, electrical, mechanical, instrumentation and other engineers to brainstorm and summarize the risk factors of LNG receiving terminals. This process is laborious and time-consuming, and there is no guarantee that the person will be able to record it completely every time. In this paper, a graph attention network (GAT) and bidirectional Long and Short-Term Memory Network (LSTM) deep integrated learning model is proposed. The model can automatically extract risk factor causal relationships. After starting with a risk factor text, the number type features and syntactic dependency graph features of the input text are fused to enhance the causal relationship traceability of incorrect personnel operation. Taking the unloading and storage processes as examples, in terms of the effect of automatic extraction risk factors, the integrated algorithm model improves the extraction accuracy by up to 7.1% compared with a single algorithm. In addition, the correct extraction rate of different cause-effect relationships increases by 21.57%, while the integrated algorithm considers sentence matching, improves the granularity of cause-effect information based on the traditional method, expands the root cause of risk factors, and the traceability results are consistent with on-site accident event results. At the same time, it is more conducive to accurately managing incorrect manual operations. In the model training sample size sensitivity analysis, the algorithm has a superior correct causal label extraction rate for different sample sizes when the number of hidden layer stacking layers is K= 2, which solves the problem of model adaptation for the text volume of LNG terminal risk factors.

Risk Assessment of Import Cold Chain Logistics Based on Entropy Weight Matter Element Extension Model: A Case Study of Shanghai, China

The development of world trade and fresh-keeping technology has led to the rapid development of international cold chain logistics. However, the novel coronavirus epidemic continues to spread around the world at the present stage, which challenges disease transmission control and safety supervision of international cold chain logistics. Constructing an Import Cold Chain Logistics Safety Supervision System (ICCL-SSS) is helpful for detecting and controlling disease import risk. This paper constructs an evaluation index system of ICCL safety that comprehensively considers the potential risk factors of three ICCL processes: the logistics process in port, the customs clearance process, and the logistics process from port to door. The risk level of ICCL-SSS is evaluated by combining the Extension Decision-making Model and the Entropy Weight Method. The case study of Shanghai, China, the world's largest city of ICCL, shows that the overall risk level of ICCL-SSS in Shanghai is at a moderate level. However, the processes of loading and unloading, inspection and quarantine, disinfection and sterilization, and cargo storage are at high risk specifically. The construction and risk assessment of ICCL-SSS can provide theoretical support and practical guidance for improving the safety supervision ability of ICCL regulation in the post-epidemic era, and helps the local government to scientifically formulate ICCL safety administration policies and accelerate the development of world cold chain trade.

Research on the Effects of Two-Sided Ground Surcharge/Unloading on Existing Shield Tunnels

For the effect of two-sided sudden surcharge/unloading on existing shield tunnels, an indoor dimensional reduction model test was conducted at a scale of 1:15.5, measuring the ground settlement, lateral convergence of the shield tunnel, and additional surrounding pressure after changing the location and soil quality of surcharge/unloading, and an analysis was carried out. The results showed that the location of the maximum transverse convergence value of the existing shield tunnel is related to the position of the surcharge; when surcharging on both sides of the tunnel, as the position of the left surcharge’s offset increases from 0.2 m to 0.6 m, the transverse convergence value of the tunnel first increases and then becomes smaller; the ground settlement value of each measurement point in the unloading process also increases and then becomes smaller. The settlement value of each measurement point first increases and then decreases, and the alleviation effect of unloading on ground settlement is not obvious; after surcharge on one side of the tunnel, if the other side continues to surcharge, it will lead to a continued increase in the surrounding pressure. Unloading can effectively reduce the additional surrounding pressure of the tunnel, but the additional surrounding pressure cannot be immediately and completely eliminated; compared with dry sand, the maximum value of lateral convergence of the tunnel in wet sand is significantly decreased, and the peak value of ground settlement on both sides is not significant; when both sides are surcharged to 172 kg, the additional soil pressure of the tunnel’s subsoil shows three peaks, one of which occurs at measurement point 4 at the bottom of the tunnel, which may be due to the occurrence of stress concentration at the location.

An Abnormal Psychology Study Using Stressors and Symptoms for a Hypothetical Individual with Borderline Personality Disorder and a Comparison with the Physio-Pathology Study Using Lifestyle Details and Glucoses from an Individual with Type 2 Diabetes by Applying the Concepts from Viscoelastic and Viscoplastic Glucose Theory (VGT #12) Based on GH-Method: Math-Physical Medicine (No. 591)

The majority of this article focuses on stressors and symptoms of a hypothetical patient with borderline personality disorder (BPD) during the period from Y2010 to Y2022. The example cited is a purely hypothetical patient with BPD conditions. The author has accumulated knowledge on abnormal psychology since 2002 and augmented it from his established five psychotherapy centers to care for approximately 200 abused women and abandoned children from 2006 to 2010. Due to confidentiality, he cannot reveal any of their identities, but their general stories or commonly observed behaviors have been included in the hypothetical BPD case. Psychology is an empirical science and, at times, it is easier to describe in words stressors (root causes), symptoms, behaviors, reactions, and/or treatments; however, it is more difficult to describe them in numbers, a quantitative manner, even though most psychological research works are based on statistics only, but not based on any branches of natural science. The author self-studied, observed, and managed abnormal psychology therapy for 9-years, from 2002 to 2010. He has read approximately 100 textbooks and 500+ clinical reports during that period. Based on his findings, he tried to develop some “scientific” formula-based equations with a quantitation and precision approach to study and research abnormal psychology. Here, the word “scientific” means observing physical phenomena, applying physics principles, deriving mathematical equations, building engineering modeling, and utilizing computer and artificial intelligence tools - not applying statistics tools alone. Since 2010, it has been difficult to collect and utilize data from patients with Personality Disorder (PD) without breaching professional ethics and patient confidentiality. The author has given up his original idea of using the developed math-physical medicine research approach (MPM) for the psychology field. In the summer of 2010, when his health conditions became life-threatening due to severe type 2 diabetes (T2D) complications, he launched his GH-Method: math-Physical medicine (MPM) research approach on metabolism, endocrinology, and food nutrition to save his own life. To date, he has written and published nearly 600 medical papers using the MPM method. This particular paper is one of his few attempts to apply his developed MPM methodology to the abnormal psychology field of BPD. The author hopes to continue his psychological research by using more of the MPM approach. He appreciates the invaluable inputs, comments, criticisms, and suggestions from his colleagues regarding the area of abnormal psychology. In summary, although this article mainly focused on a psychological case study with hypothetical data from any BPD patient, it was also complemented with a physio-pathological case study with the collected data of an actual T2D patient. When the author displays the two case results together using a space diagram (SD) of stress (causes) versus strain (symptoms), these two case results have demonstrated an observed viscoplastic behavior, e.g. time-dependency, nonconvergence between the initial period data and ending period data, and hysteresis loops (energy loss through loading and unloading process). By using descriptive psychology language, it can illustrate the viscoplastic BPD behavior that their stressors and symptoms are changing from time to time which does not have the same pattern at the initial and ending states of a selected period. Furthermore, this up-and-down orloading-and-unloading cycle creates a loss of energy for the BPD patient, while coping with this disorder.

An Analytical Model for Hysteretic Pressure-Sensitive Permeability of Nanoporous Media

Hysteretic pressure-sensitive permeability of nanohybrids composed of substantial nanopores is critical to characterizing fluid flow through nanoporous media. Due to the nanoscale effect (gas slippage), complex and heterogeneous pore structures of nanoporous media, the essential controls on permeability hysteresis of nanohybrids are not determined. In this study, a hysteretic pressure sensitive permeability model for nitrogen flow through dry nanoporous media is proposed. The derived model takes into account the nanoscale effect and pore deformation due to effective stress. The model is validated by comparing it with the experimental data. The results show that the calculated permeability and porosity are consistent with the measured results with the maximum relative error of 6.08% and 0.5%, respectively. Moreover, the hysteretic pressure-sensitive permeability of nanohybrids is related to effective stress, gas slippage, pore microstructure parameters, grain quadrilateral angle, and the loss rate of grain quadrilateral angle. The nanoscale effect is crucial to the permeability of nanoporous media. In addition, as impacted by the comprehensive impact of multiple relevant influential parameters, permeability during the pressure unloading process is not a monotonous function but presents complicated shapes. The proposed model can explain, quantify, and predict the permeability hysteresis effect of nanoporous media reasonably well.

Understand anisotropy dependence of damage evolution and material removal during nanoscratch of MgF2 single crystals

To understand the anisotropy dependence of the damage evolution and material removal during the machining process of MgF2 single crystals, nanoscratch tests of MgF2 single crystals with different crystal planes and directions were systematically performed, and surface morphologies of the scratched grooves under different conditions were analyzed. The experimental results indicated that anisotropy considerably affected the damage evolution in the machining process of MgF2 single crystals. A stress field model induced by the scratch was developed by considering the anisotropy, which indicated that during the loading process, median cracks induced by the tensile stress initiated and propagated at the front of the indenter. Lateral cracks induced by tensile stress initiated and propagated on the subsurface during the unloading process. In addition, surface radial cracks induced by the tensile stress were easily generated during the unloading process. The stress change led to the deflection of the propagation direction of lateral cracks. Therefore, the lateral cracks propagated to the workpiece surface, resulting in brittle removal in the form of chunk chips. The plastic deformation parameter indicated that the more the slip systems were activated, the more easily the plastic deformation occurred. The cleavage fracture parameter indicated that the cracks propagated along the activated cleavage planes, and the brittle chunk removal was owing to the subsurface cleavage cracks propagating to the crystal surface. Under the same processing parameters, the scratch of the (001) crystal plane along the [100] crystal-orientation was found to be the most conducive to achieving plastic machining of MgF2 single crystals. The theoretical results agreed well with the experimental results, which will not only enhance the understanding of the anisotropy dependence of the damage evolution and removal process during the machining of MgF2 crystals, but also provide a theoretical foundation for achieving the high-efficiency and low-damage processing of anisotropic single crystals.

Analysis of damage characteristics and energy evolution of salt rock under triaxial cyclic loading and unloading

The gas injection, water-soluble excavation, and gas recovery process in the gas storage salt cavern can be regarded as the loading and unloading process of the surrounding rock stress. By conducting triaxial loading and unloading tests on salt rock samples, several findings are presented: 1) The failure formed in the rock sample is a shear failure mode when confining pressure is below 15 MPa, and after confining pressure exceeds 15 MPa, it is bulging in the middle part of sample. The scientific strain is proved to be more suitable for describing the deformation of salt rock sample than the engineering strain. 2) During the unloading-reloading process, the produced stress difference is small at the beginning of unloading, while the rock undergoes more stress loss in the post-peak stage than that in other stages. 3) When the strain increases to reach a specific value, the dissipative energy difference increases with higher confining pressure. 4) Higher confining pressure improves the initial damage degree to the sample. But under different confining pressures, the damage variable has a similar evolution trend, which reaches a steady growth stage with the loading/unloading cycles gradually.

Analysis of the labor consumption and duration of the assembly processes of structural coating plates blocks using the crane method

The labor intensity of the construction process is determined by the methods of technical standardization of processes by the methods of time tracking. On the basis of these observations, regulations are developed in the form of GN or other collections of norms of labor costs. Labor intensity is measured in person–hours, and the rate of labor costs is derived from the rate of time, taking into account the number of performers. Variants of consolidation and installation of structural plates of the covering are not typical. The main processes necessary for the duration and labor–intensiveness of the structural slabs of the coating by the free method have been analyzed. A potential development has been identified that will ensure a reduction in the labor–intensiveness of the assembly process and provide cyclical assembly work. The consolidation process is optionally performed on the assembly stand, which belongs to the assembly equipment equipment. To install the stand, a site is specially prepared in the form of a horizontally planned surface of the earth with a layer of compacted crushed stone. Cells made of wooden sleepers are placed on the crushed stone, which are set according to vertical planning marks with the help of geodetic devices. Then a collection stand is installed on the sleeping cells. Structurally, the stand consists of several parts. That is why the manufacturability of the installation of the structural plates of the covering was improved by means of constructive and technological solutions. First, the columns are mounted (columns with a height of 12 m were used for the analysis), so it is not possible to carry out consolidation in the area of the columns. The stands are placed next to each other in the working area of the crane. All calculations were performed in tabular form according to the formula. The installation process of 12 m high columns includes the sub–processes of unloading and disassembly, installation and fastening. The components of these processes are actions (operations). According to the methodology, a schedule of the processes of consolidation and installation of blocks of structural slabs with preliminary installation of columns according to the corresponding calculations was built.

Fish Losses of Euthynnus affinis Products at The Fish Landing Base Karangsong Indramayu, West Java

Euthynnus affinis is one of the most loved fish by the community. Fulfillment of the demand for tuna from the process of catching until it is landed for sale has the potential to experience a decrease in yield. The purpose of this study was to determine handling techniques, determine quality, and determine yield losses in tuna catches at the Karangsong Indramayu Fish Landing Base (PPI) West Java. The research was conducted by directly observing the handling process, observing the cold chain of tuna from unloading to loading, conducting organoleptic quality testing, ALT, TVB and calculating fish losses by referring to the Load Tracking (LT) method. The calculation of yield loss is carried out in three types, namely: physical loss, quality loss, and financial loss. The flow of the tuna handling process observed is the unloading process to the loading process. The value of the organoleptic quality test on tuna caught was 8, the ALT test value of the lowest average value was 16,000 col/g and the highest value was 35,000 col/g. The lowest average TVB test value was 9.96 mgN/100 g and the highest was 11.19 mgN/100 g. Euthynnus affinis from unloading to loading experienced physical, quality and financial losses of: 1.07%; 0.84%; and 2.05%.

3D printing of flexible strain sensor based on MWCNTs/flexible resin composite

The flexible strain sensor is an indispensable part in flexible integrated electronic systems and an important intermediate in external mechanical signal acquisition. The 3D printing technology provides a fast and cheap way to manufacture flexible strain sensors. In this paper, a MWCNTs/flexible resin composite for photocuring 3D printing was prepared using mechanical mixing method. The composite has a low percolation threshold (1.2% ωt). Based on the composite material, a flexible strain sensor with high performance was fabricated using digital light processing technology. The sensor has a GF of 8.98 under strain conditions ranging between 0% and 40% and a high elongation at break (48%). The sensor presents mechanical hysteresis under cyclic loading. With the increase of the strain amplitude, the mechanical hysteresis becomes more obvious. At the same time, the resistance response signal of the sensor shows double peaks during the unloading process, which is caused by the competition of disconnection and reconstruction of conductive network in the composite material. The test results show that the sensor has different response signals to different types of loads. Finally, its practicability is verified by applying it to balloon pressure detection.

Experimental Study on the Entropy Change Failure Precursors of Marble under Different Stress Paths

In this paper, the indoor loading and unloading tests and acoustic emission (AE) monitoring tests of marble under different stress paths are carried out. Based on the AE events in the process of rock failure, this paper introduces the concept of information entropy of Shannon, and defines a new cumulative state information entropy which can characterize the degree of disorder and accumulation of rock microcracks. This paper also offers a comparative analysis on the evolution law of rock entropy under different paths and different loading and unloading conditions. The results show that the newly defined cumulative state information entropy can well reflect the order change of the loading and unloading process system, and there are significant differences in entropy evolution under different stress paths, but the entropy generally evolves with the development of the system from “quasi-equilibrium” to “far away from equilibrium”. The higher the unloading level is, the greater the confining pressure is, the stronger the unloading disturbance is, and the entropy value drops sharply at the starting point of unloading. The faster the unloading rate is, the later the rock fracture instability is, and the later the entropy drop point of the system appears. The change rate of entropy value ∣ΔH∣ = 0.1 can be used as the precursory signal threshold of rock confining pressure unloading disturbance damage and peak rupture instability.

Fracture and damage properties of high-strength concrete under cyclic loading

To study the fracture and damage characteristics of high-strength concrete (HSC), three-point bending (TPB) tests were performed on single-edged notched beams under cyclic loading, and digital image correlation (DIC) technique was used to measure the surface deformation of the beams. First, the crack mouth opening displacement (CMOD) measured by the DIC was compared with that obtained by clip gauge to verify the reliability of the DIC technique in measuring the surface deformation of materials. Then, the relationships between the load and displacements were studied; Finally, the impact of loading history on the CMOD, crack length (Lc), stiffness (S), dissipated energy, fracture energy (GF), strain concentration zone (SCZ) and damage zone were investigated. The experimental results indicated that the bearing capacity, deformation performance and the GF of HSC were not affected by the loading and unloading process; under cyclic loading, as the dimensionless crack mouth opening at the unloading point (CMODduni) increases, the dimensionless residual crack mouth opening (CMODdri) gradually increases while the load degradation rate (φ) gradually decreases; in the ith cycle of the post-peak stage, the crack opening rate was greater than the crack growth rate when the beam was loaded to the peak point from the reloading point. To quantify the damage degree of the single-edged notched beam, damage index (D) was calculated, which is more suitable obtained from the damage zone-based method than that calculated from the P-CMOD curve.