Increase In Cycle Time Research Articles

Salt-freeze resistance and life prediction of geopolymer recycled concrete mixed with rice husk ash and modified rubber particles

Rice husk ash (RHA) and Span-40 modified waste rubber particles (WRP) were mixed into geopolymer recycled concrete (GRC) to improve its frost resistance in normal and chlorine environment. The freeze-thaw and static loading test results show that GRC has the best freeze-resistance when 5 %RHA and 10 %WRP are added. The strength loss rate of GRC after 200 freeze-thaw cycles in normal environment and chlorine salt environment is 8.3 % and 8.8 % lower than that of GRC without RHA and modified WRP, respectively. Based on the test results, the material damage model and strength loss model of GRC doped with RHA and modified WRP were established. The failure probability and service life of GRC were predicted. The results showed that the failure probability of GRC mixed with 5 %RHA and 10 %WRP was reduced by more than 10 % compared with that of GRC mixed with no RHA and modified WRP at 200 freeze-thaw cycles under normal environment and chlorine salt environment, and the failure probability decreased with the increase of cycle times. The life prediction results showed that the service life of GRC mixed with 5 %RHA and 10 %WRP increased by 17.9 % and 21.6 %, respectively, compared with that of GRC mixed with no RHA and modified WRP under the freeze-thaw cycle of normal environment and chlorine salt environment.

Study on the Dispersion Characteristics of Coal Complex Resistivity under the Effect of Liquid Nitrogen Cyclic Freeze-Thaw and Evaluation of Permeability Enhancement.

The effect of liquid nitrogen freeze-thaw fracturing on coal seams can be potentially evaluated by the complex resistivity method. The real part (Reρ) and the imaginary part (Imρ) of the complex resistivity and permeability of coal were determined under different cycle times and in different bedding directions. The reason for permeability enhancement was discussed, and the dispersion mechanism of complex resistivity during cyclic freeze-thaw fracturing was analyzed. The results indicated that (1) the complex resistivity parameters have a good response to the cycle times; Reρ, |Imρ|, and the dispersion degree (α) are positively correlated with cycle time; the fully polarized frequency (f p) of Reρ, the characteristic frequency (f c) of Imρ, and variation are negatively correlated with cycle time. (2) The difference in complex resistivity parameters between the vertical bedding direction and the parallel bedding direction is significant, and the difference in electrical properties of the bedding structure continuously decreases with the increase in cycle time. (3) Under the effect of liquid nitrogen cyclic freeze-thaw, a complex network of fractures in coal is formed, the anisotropic characteristics of coal are weakened, and effective conductive channels are damaged. The peak frost heave force decreases exponentially with the increase in cycle time, and the difference in bedding electrical properties gradually disappears. (4) Comparing the inversion degree of measured data with three conductive models, ρ0 and τ are selected as the optimum parameters for evaluating the effect of liquid nitrogen cyclic freeze-thaw. A logarithmic permeability evaluation model is constructed based on ρ0 and τ. This work provides a new perspective based on electrical detection for evaluating the permeability enhancement of coal during liquid nitrogen cyclic freeze-thaw.

Study on the microstructure and strength characteristics of marine soft soil under wet-dry cycle condition

For marine soft soil under the periodic wave loading, the pore water content in soil suffering dry-wet cycle for a long time, which affects its microstructure and macroscopic mechanical strength, resulting in insufficient bearing capacity and excessive deformation of soft soil. To reveal the microstructural characteristics and strength attenuation law of marine soft soil under dry-wet cycle condition, electron microscopy scanning and direct shear tests under different times of dry-wet cycles were carried out, and the mathematical equations of pore structure and strength parameters were established based on fractal theory. The research results showed that: (1) The pore structure changed considerably after the first dry-wet cycle, and then changed gently with the increase of dry-wet cycle times, which was reflected by the fractal dimension D value decreases to a constant value gradually. (2) The shear strength of the soil diminishes with an increase in the number of dry-wet cycle times, and the maximum attenuation occurs after the first dry-wet cycle. (3) The relationship between cohesion (c), internal friction angle (φ), and fractal dimension (D) is exponential, with the curve shapes being concave and convex, respectively.

Stock Levels and Repair Sourcing in a Periodic Review Exchangeable Item Repair System

Background: Exchangeable item repair systems are inventory systems. A nonfunctional item is exchanged for a functional item and returns to the system after being repaired. In our periodic review setting, repair is performed either in-house or outsourced. When repair is in-house, a repaired item is returned to stock regardless of the repair status of the other items in its order. In contrast, with outsourced repair, the entire order must be repaired for it to return to stock. Methods: We develop formulas for the window fill rate (probability for a customer to be served within a given time window) to measure the system’s performance and compute it for each repair model. The cost of outsourcing is the difference between the number of spares needed to maintain a target performance level when repair is internal and when it is outsourced. Results and Conclusions: In our numerical example, we show that the window fill rate in both models is S-shaped in the number of spares and show how the graph shifts to the right when customer tolerance decreases and order cycle time increases. Further, we show that the cost of outsourcing is increasing with customer tolerance and with the target performance level.

Experimental study on the impact of effective stress and cyclic loading on permeability of methane hydrate clayey sediments

Permeability evolution directly determine gas production and its efficiency of gas hydrates in the South China Sea. Due to existence of submarine overlying rocks and change of soil internal mechanics during the hydrate exploitation, permeability evolution is significantly affected. Therefore, in this paper, influence of effective stress on the porosity and permeability of sediment with different hydrate saturation was studied, and functional relationship between them was revealed. Effect of cyclic loading and unloading stress on the permeability recovery and damage degree was also discussed. The results show that when hydrate saturation increases, the relation of permeability and effective stress are power function rules, while porosity and effective stress are exponential function rules in clayey sediments. An empirical prediction equation for gas permeability of clay sediments with effective stress was presented, which takes into account hydrate saturation and porosity. In addition, during cyclic loading experiments, the results showed a linear increase in permeability during unloading. The permeability recovery rate and permeability damage rate are completely opposite with change of hydrate saturation. Permeability damage rate of kaolin is different from that of other two kinds of sediment. With the increase of cycle times, the proportion of plastic deformation of sediment decreases gradually.

Study on the influence of injection pressure and frequency on the deformation and damage law of the surrounding rock in the old cavity of salt mine

AbstractThe long‐term cyclic gas injection and production mode of the gas storage will lead to accelerated deformation of the surrounding rock of the old cavity, and even the instability and failure of the cavity. Considering the geological conditions and cavity measurement data of the old cavity of the horizontal butted‐well in China, the deformation and failure characteristics of the long‐term cyclic injection‐production process of the surrounding rock of the old cavity under different internal pressure difference and injection‐production frequency are studied. The long‐term stability of the gas storage is predicted by six indexes: the deformation of surrounding rock, dilatancy safety factor, volume shrinkage rate, plastic zone volume, equivalent strain, and no tensile stress. The results show that with the increase of operation duration and cycle times, the deformation, volume shrinkage rate, and plastic zone volume of the surrounding rock gradually increase after the old cavity is reconstructed into the gas storage and the difference of results under different UGS and CAES gradually expands. The stability of the surrounding rock of the old cavity under the cycle action of CAES will be lower. The number of cycles has a limited impact on the stability of the surrounding rock of the old cavity, while the operation duration and injection‐production pressure are the main determinants of the stability of the surrounding rock of the old cavity. If the old cavity of the salt mine is reconstructed into CAES, the parameters such as the number of cycles, the operation duration, and the injection‐production pressure still need to be considered comprehensively. The research results can provide reference value for the reasonable design of the gas storage pressure range of the old cavity and the safety and stability evaluation of the surrounding rock.

Pneumatic Control for Sustainable Compressed Air Systems: Multi-criteria Optimisation for Energy Efficient Production

Compressed air is widely utilised in manufacturing processes across all industries due to numerous advantages associated with its use. However, the energy efficiency of compressed air generation is often very low, making pneumatic systems one of the most expensive processes in a manufacturing facility. Additionally, compressed air leakages further artificially increase the demand and decrease their efficiency and productivity. This study focused on identifying the effects of pressure and flowrate regulation on the energy efficiency and productivity of a pneumatic automation system. By combining these two control strategies, a reduction in air consumption was achieved while also maintaining the system's cycle time in order to minimise productivity loss. The assessed system included various leaks of different sizes at different locations. When implementing pressure regulation, a reduction in air consumption of up to 22 per cent was achieved. As expected, this also resulted in an increase in cycle time of up to 19 per cent, which was then reduced to 7 per cent by regulating the system's flowrate at the end of use. Multi-criteria optimisation was subsequently employed to identify the optimal control parameters for a balanced effect on both air consumption and cycle time, affecting energy efficiency and productivity, respectively.

A user-friendly toolkit to select and design multi-purpose grippers for modular robotic systems

Robotic grasping is a billion-dollar industry with significant growth potential for the next decade. Unsurprisingly, technology providers and integrators are increasingly assisting in optimising production efficiency by implementing industrial robots and the necessary end-effectors into production lines. However, still too often in today’s robotic applications, dedicated grippers are designed to perform single tasks therewith adversely increasing cycle times and robot cell spaces due to constantly switching grippers from a tool magazine. In order to reduce handling costs and to cope with mass customisation, versatile grasping of various objects with multi-purpose grippers is key in evolving to modular assembly systems.Nowadays, thoughtful selection and design of robotic grippers is still mainly restricted to expert knowledge due its ad hoc and multi-objective nature. However, gripper selection and design should be tailored to the properties of the objects to be grasped, and the tasks to be executed. As a result, current solutions often end up being partly appropriate and/or over-dimensioned. The use of software tools to support this complex decision-making process is needed but limited so far.This paper presents a user-friendly toolkit that assists in selecting appropriate robotic grippers for grasping pre-specified ranges of objects. For this, a web API has been established for accessing the available gripper database and selection methodology. Additionally, this toolkit assists in designing multi-functional jaws for impactive grippers, and lay-outing individually positioned astrictive grippers. The underlying optimiser will try to find the most ideal grasping points on each object in accordance with quality metrics and constraints, and this for each of the selected grippers. To demonstrate the functionality of the presented toolkit, two case studies on impactive and astrictive gripper designs have been worked out involving 3D mechatronic and 2D sheet metal parts.

The Effect of Cycling Process Between −196 and 120 °C on Microstructure and Properties of Additively Manufactured 7050 Al Alloy

Wire arc additively manufactured (WAAM) aluminum alloys have been applied in the aerospace field. However, there was a lack of research on the stability of additive components under high‐ and low‐temperature cycling conditions in space. This study focuses on the evolution of microstructure, defects, and mechanical properties of WAAM 7050 aluminum alloy during high‐ and low‐temperature cycling from −196 to 120 °C. The number of cycles is 1, 2, 5, and 10, and one cycle time is 100 min. The results show that the number of η nanophases increase significantly after 5 cycles, and the η′ phases precipitate after 10 cycles. In defects, the porosity increases to 4 times of the as‐deposited state after 10 cycles, and the mean equivalent diameter of micropores is stabilized at 0.77 μm. In mechanical properties, the ultimate tensile strength decreases gradually with the increase of cycle times, and the hardness reaches the maximum of 143.2 HV after 5 cycles. The number of micropores increases after 10 cycles, and micropores have a weak effect on the failure mechanism. Cracks tend to sprout and expand along the eutectic phases and pores in the equiaxial grain zones, and equiaxial grain zones are the weak areas when they break.

Shearing behavior of suction caisson wall-sand interface throughout the suction caisson life-cycle

Suction caissons are widely used as foundations for offshore platforms and offshore wind turbines. The life-cycle of a suction caisson includes penetration, service and retrieval. The mechanical characteristics of the interface between sand and suction caisson wall are crucial for assessing the penetration behavior and bearing capacity of suction caissons. Interfacial shear tests under constant normal loading (CNL) and variable normal loading (VNL) conditions were conducted to investigate the shearing behavior of suction caisson wall-sand interface throughout the suction caisson life-cycle. Results show that the interfacial shear stress increases with an increase in normal stress and decreases with an increase in penetration rate throughout the life-cycle of the suction caisson. The value of vertical displacement of the interface decreases with an increase of cycle times during service and the sand particles’ movement, rotation and rolling were observed by visualization tests. Under the test conditions, the interface frictional coefficient ranges from 0.46 to 0.80 and the interface friction angle varies between 25.64° and 27.43° during retrieval. Both the interface friction angle and interface friction coefficient during the penetration stage are greater than those during the retrieval stage, indicating that retrieval stage is not an inverse process of penetration stage. In addition, the control groups were carried out to investigate the effect of penetration on service stage and the effect of service on retrieval stage. It was also found that the influence of the penetration stage on shear stress during service stage is mainly observed in the first two cycles. The influence of service stages on shear stress during retrieval stage is more obvious. After prolonged cycling during service stage, the strength of the interface would be reduced.

PERANCANGAN DAN MODIFIKASI MOLD INSERT UNTUK MENINGKATKAN KAPASITAS PRODUKSI LIGHT GUIDE

The use of plastic is often found in human life. Therefore, many manufacturing companies are competing to increase the production and quality of their plastic products. One way to increase production is to redesign a Mold base so that the Mold has a larger production capacity than before. The increase in product demand from consumers, which was initially 65,000 pcs/month to 95,000 pcs/month, is also the background for conducting this research. The purpose of this study is to redesign the soft tool using the old Mold base. The design uses Siemens UG NX 5 software. The Mold used is a two-plate Mold. The manufacture of the core cavity uses NAK 80 steel and plastic raw material in the form of Polycarbonate (PC). At the end of the study, a simulation was carried out using the Moldex 3D Flow Mold software to see the cycle time of the old and new Mold injection processes. From the results of this study, production capacity increased from 67,804 pcs/month to 118,536 pcs/month resulting in twice as many products as the old Mold design, with an increase in cycle time of 14.37% longer than the old Mold design also ensuring the quality of the product is maintained.

The electrochemical and tribocorrosion behavior of hybrid ceramic film-coated Ti alloys

In this study, anodic TiO2 ceramic coating was formed on titanium alloys produced by SLM by using the anodization method. After then, hybrid ceramic coatings are produced by combining a formation of ZrO2 nanostructures in the TiO2 coating with the SILAR technique. The microstructure, wettability, electrochemical properties, and tribocorrosion behavior of anodic TiO2 and hybrid ceramic coatings were also investigated. According to XRD results, two TiO2 peaks are observed in anodic TiO2 films. After the SILAR process, the tetragonal-ZrO2, and monoclinic-ZrO2 with TiO2 peaks were obtained in the hybrid ceramic coatings. Especially, while the intensity of the TiO2 peaks decreased, the intensity of the ZrO2 peaks increased with the increase in cycle time. The surface wettability experiments indicate that the HB-80 specimen exhibits superhydrophobic behavior, and it also has the highest contact angle value among all specimens. Corrosion tests in SBF solution confirmed that hybrid ceramic films importantly increased the anticorrosion performance of anodic TiO2 film, depending on the cycle times owing to filling the pores, and the best outcomes for corrosion resistance were obtained from the HB-80 specimen owing to its superhydrophobic properties. Moreover, the results of tribocorrosion tests revealed that all hybrid ceramic films displayed higher tribocorrosion resistance than anodic TiO2 ceramic film and uncoated Ti6Al4V substrate, and the best performance was seen from the HB-80 specimen due to its decreased porosity and the direct contact area between pin and surface.

Performance of rice husk biocarrier on ammonia nitrogen removal in the MBBR treating aquaculture wastewater using biological attached growth process: Performance and kinetic study

This study investigates the feasibility of using rice husk (RH) as a cost-effective and environmentally friendly bio-carrier for immobilizing isolated microorganisms to treat synthetic recirculating aquaculture system (RAS) ‎wastewater. Two moving bed biofilm reactors (MBBR) inoculated with indigenous microorganisms were operated simultaneously for 391 days under various ‎cycle times and compared. The RH and Kaldnes-3 (K3) bio-carriers were placed in reactors R1 and R2, respectively.‎ The results indicated that at constant influent TAN, with increases in cycle ‎time from 6 to 24 h, TAN and COD ‎removal ‎efficiencies ‎increased in both bioreactors; but at an optimum cycle time of 6 h, the TAN and COD removal efficiencies were‎ ‎82 ± 1.5% ‎ ‎and‎ 77.9 ± 1.7%‎‎ for the R1 and, 89.9 ± 3.3%‎ ‎and ‎84 ± 1.2% ‎for the R2, respectively. Also, at a constant cycle time, ‎the performance of R2 was better ‎compared to R1 filled with RH. Microbial identification confirmed the presence of four dominant genera, including Arthrobacter, Bacillus, ‎Rhodococcus, and ‎Staphylococcus, which were heterotrophic nitrification bacteria (HNB). The TAN removal kinetics were investigated using a Modified Stover-Kincannon (MSK) model. In reactors R1 and R2, the biokinetic constants were determined to be Umax: 0.116 and 0.149 g/Lday, and KB: 0.158 and 0.182 g/Lday, respectively. The correlation coefficients (R2) of the MBBRs were higher than 0.97, indicating that the model adequately described the experimental data.

Abnormal variation of P-wave velocity of red sandstone after cyclical thermal shock in water

Hot dry rock (HDR) has great development potential because of its advantages of clean, environmental protection and renewable. The study of physical and mechanical properties of HDR is one of the important links in the process of geothermal energy development. Previous studies have mainly focused on the granite thermal reservoir but research on the sandstone thermal reservoir, especially the physical properties of sandstone after multiple thermal shocks, is scarce. Therefore, in this study, cyclic thermal shock experiments of sandstone at different temperatures are carried out, and the variation law of P-wave velocity of sandstone after heat treatment is revealed. It is found that the P-wave velocity of red sandstone decreases with the increase of temperature and cycle times, especially when the temperature is higher than 400 °C, the maximum change rate of wave velocity reaches 52.6%. It is particularly noteworthy that the P- wave velocity of sandstone increases abnormally at about 600 °C. And this article puts forward three hypotheses to explain the wave velocity anomaly. In addition, the nonlinear relationship model among P-wave velocity, temperature and number of cycles is established for the first time, and the correlation coefficient R2 is more than 0.9. This study serves as a reference for the development and utilization of the sandstone geothermal reservoir.

Rotationplasty outcomes assessed by gait analysis following resection of lower extremity bone neoplasms

AimsThe standard of surgical treatment for lower limb neoplasms had been characterized by highly interventional techniques, leading to severe kinetic impairment of the patients and incidences of phantom pain. Rotationplasty had arisen as a potent limb salvage treatment option for young cancer patients with lower limb bone tumours, but its impact on the gait through comparative studies still remains unclear several years after the introduction of the procedure. The aim of this study is to assess the effect of rotationplasty on gait parameters measured by gait analysis compared to healthy individuals.MethodsThe MEDLINE, Scopus, and Cochrane databases were systematically searched without time restriction until 10 January 2022 for eligible studies. Gait parameters measured by gait analysis were the outcomes of interest.ResultsThree studies were eligible for analyses. Compared to healthy individuals, rotationplasty significantly decreased gait velocity (-1.45 cm/sec; 95% confidence interval (CI) -1.98 to -0.93; p < 0.001), stride length (-1.20 cm; 95% CI -2.31 to -0.09; p < 0.001), cadence (-0.83 stride/min; 95% (CI -1.29 to -0.36; p < 0.001), and non-significantly increased cycle time (0.54 sec; 95% CI -0.42 to 1.51; p = 0.184).ConclusionRotationplasty is a valid option for the management of lower limb bone tumours in young cancer patients. Larger studies, with high patient accrual, refined surgical techniques, and well planned rehabilitation strategies, are required to further improve the reported outcomes of this procedure.Cite this article: Bone Jt Open 2023;4(11):817–824.

Increasing Rates of Human Papillomavirus Catch-Up Vaccination at a Sexual and Reproductive Health Clinic: A Quality Improvement Project.

Catch-up human papillomavirus (HPV) vaccination of adults aged 19 to 26 who were not vaccinated as children or adolescents may decrease rates of HPV-associated cancer. The purpose of this project was to increase uptake of catch-up HPV vaccination at a sexual and reproductive health clinic through the implementation of a multicomponent, systems-based intervention. Catch-up vaccination rates were recorded at an intervention health clinic and a comparison health clinic. A comparative, interrupted time series design was used to compare rates of catch-up vaccination pre- and postintervention. Electronic health record prompts, in-clinic education, and scheduling of a next visit at the current visit were implemented. Data were analyzed using descriptive statistics, t tests, and regression analysis. The proportion of all patients aged 19 to 26 who received an HPV vaccination rose at the intervention health clinic from 0.76% preintervention to 4.42% postintervention. At the intervention clinic there was a nonsignificant increase (4.47 minutes) in average daily patient cycle times between the pre- and postintervention periods (t(13) = 1.895, P = .075). Rates of catch-up HPV vaccination increased significantly following the multicomponent, systems-based intervention. Further iteration of the quality improvement process should examine the sustainability of the interventions and the effects of the intervention on vaccine series completion.

Inhibiting segregation enabled outstanding combination of mechanical and corrosion properties in precipitation-strengthened aluminum alloys

Segregation of solutes to grain boundary (GB) is the dominant restriction on enhancement of mechanical properties and corrosion resistance during aging in precipitation-strengthened aluminum alloys. Here, we innovatively introduce the cyclic deformation by the vibration during aging to eliminate the GB segregation, resulting in the formation of the narrow precipitate-free zone (PFZ) widths near the GB, as well as the fine and discontinuous grain boundary precipitations (GBPs). Compared with the traditional peak-aging, the 2014 aluminum alloy treated by thermal cooperative vibration aging (TCVA) exhibits a superb combination of impact toughness and corrosion resistance, and retains the strength and ductility. In addition, the atomic simulations show that TCVA generates numerous vacancies near the GB, but does not change the dislocation density with the increase of cycle time. These results indicate that the vacancy significantly promotes the nucleation and growth of precipitates in the vicinity of GB, resulting in the narrow PFZs and fine discontinuous GBPs. The present work provides the fundamental knowledge and method to inhibit the equilibrium segregation of solutes to GB during aging, and further realizes the precipitation-strengthened aluminum alloys with excellent mechanical and corrosion properties.

An exact method to incorporate ergonomic risks in Assembly Line Balancing Problems

Since ergonomic risks related to the tasks performed by each worker are generally neglected when solving the Simple Assembly Line Balancing Problem (SALBP) or partially treated in post-processing, this paper aims to incorporate ergonomic issues natively in the decision process (ErgoSALBP). For such a problem, we present a novel Mixed-Integer Linear Programming (MILP) model that linearizes and incorporates into the SALBP the Occupational Repetitive Action (OCRA). This well-known method gives ergonomic risk indicators for musculoskeletal disorders. A lexicographical approach to address the problem is proposed, where the minimum number of stations is obtained for SALBP and used as a starting point to solve a type-F ErgoSALBP (feasibility problem) focused on satisfying the maximum ergonomic risk workload. Once the exact solution is found, we establish an objective function to smooth the ergonomic risk distribution among stations. We tested a total of 2160 instances with up to 297 tasks. Our method was able to solve 94% of all instances optimally. The share of solutions found with only green stations (the ideal ergonomic condition) was 87%, surpassing the state of the art. For the instances where the model did not converge to a solution within the time limit, we present a procedure to assess the optimality gap. Furthermore, the model can be embedded as a building block for other assembly line configurations. Finally, the results provide trade-off insights for managers: the average OCRA for the line improves as the cycle time increases, which may positively impact workers’ satisfaction and product quality in the long run.

Influence of extrusion pressures on shape memory properties of carbon fiber/basalt fiber hybrid composites with graphene oxide fabricated by the vacuum infiltration hot pressing system

AbstractThis work investigated the extrusion pressure‐microstructure‐shape memory properties relationship of carbon fiber/basalt fiber hybrid composites with graphene oxide (GO‐CF/BF hybrid composites), and the associated mechanism was systematically discussed. GO‐CF/BF hybrid composites were fabricated by the vacuum infiltration hot pressing system (VIHPS). The critical infiltration pressure of the composite was calculated according to the dynamic infiltration model, and it was 0.09 MPa. The microstructure and shape memory properties were analyzed by scanning electron microscopy (SEM) and a shape memory testing system. The results showed that the shape fixation ratio first decreased and then increased, but the shape recovery ratio and the shape recovery force tended to initially increase and subsequently decrease with the increase in extrusion pressure. This was mainly determined by void defects. When the extrusion pressure was 0.5 MPa, the shape memory properties of the composite were excellent. Furthermore, with the increase in cycle times, GO‐CF/BF hybrid composites were damaged, and the shape memory properties all decreased. When the extrusion pressure was 0.7 MPa, fiber fracture and delamination appeared in composites, and the shape memory properties deteriorated significantly. However, when the extrusion pressure was 0.5 MPa, the fiber was fractured slightly, and the shape memory properties degenerated vaguely.

Morphological Features of Fractures Developed by Direct Shearing of Intact Granites after Water Cooling Cycles.

Rock fractures are considered as favorable objects for enhanced geothermal development. The fracture morphologies play an important role in enhanced geothermal development. Therefore, the study of fracture morphologies has a certain guiding significance for the geothermal reservoir. Water cooling and water cooling cycles can change the morphology of fracture surfaces formed by the shear failure of intact granites. To date, however, there is little work on the effect of water cooling and water cooling cycles on the morphology of fracture surfaces formed by direct shearing of intact granites. In this study, the direct shear tests of intact granites treated by water cooling cycles at different temperatures were conducted, and the variations in the laws of shear strength of intact granites and morphologies of fracture surfaces with temperature or cycle times were analyzed. Test results showed that the shear strength and shear stiffness of intact granites decreased nonlinearly with the increase of temperature or cycle times, but the height and apparent dip angle of asperities on the fracture surface increased with the increase of temperature or cycle times, and the overall uniformity of the fracture surface was improved. The height distribution frequency of asperities on fracture surfaces can be divided into four types: right-biased peak type, left-biased peak type, left-biased middle peak, and left-biased flat peak. The asperities on the fracture surface formed by the shearing of intact granites have asymmetric characteristics. The maximum apparent dip angle and average apparent dip angle in the reverse shear direction are larger than those in the shear direction, and the initial contact area ratio between the shear direction and reverse shear direction is in the range of fluctuation between 1.4 and 2.