International Journal of Materials and Product Technology (27 papers in press)
Research on Simulation Experiment of the Corn Seed Precision Metering Device Based on Pro/E
by Hui Yan, Duo Long, Ping Yu
Abstract: In this paper, a new type of corn precision seed metering device------ combination inner-cell corn seed precision metering device and two kinds of corn are concerned, considerable research on metering device modeling method of the complex structure of mechanical parts and discrete element method by pro/e software is conducted. Through the identification and reading of boundary information, the binding of motion and material property, and data storage, the 3D discrete element analytical model from 3D Pro/ENGINEER physical model is realized. Furthermore, simulation analysis on the working process of precision seed metering device is conducted on the working platform integrated by CAE software, so that, the results acquired by experiments of seed metering device can be analyzed contrastively for optimization design of corn precision seed metering device.
Keywords: Precision Seed Metering Device; Pro/ENGINEER; Discrete Element Method; Corn Seed; Simulation Experiment.
Synthesis, characterisation and qualification of high performance phenolic/carbon random-fibre oriented ablative thermal protection composite for re-entry applications
by L. Mohan Kumar, P. Chakravarthy, E.N. Anandapadmanabhan
Abstract: Ablatives are an elite class of fibre-reinforced polymer composites which find wide applications in re-entry space vehicles, solid rocket motor nozzles, liquid engine throats, control thrusters, etc. They are synthesised from a high temperature-resistant fibre likes carbon or Silica and a high char-yielding polymeric resin like phenolics. This paper describes a novel method to synthesise near net shape carbon phenolic ablative composite for re-entry applications through consolidating prepreg of 15 mm x 15 mm in a pre-designed mould. Subsequently, the random fibre-oriented composite laminates were subjected to various characterisation techniques and mechanical testing to qualify the same for re-entry missions. Thermal performance was evaluated under simulated re-entry conditions in a plasma wind tunnel. Property comparison and validation of performance in subscale tests are also discussed for random fibre-oriented composite and the layered laminate composite made through stacking plies one over the other. It was observed that the random fibre-oriented carbon phenolics composite possessed superior properties and exhibited better performance the layered laminate composite for re-entry and other space mission applications.
Keywords: ablative composites; carbon phenolic; random-fibre; erosion.
Research on optimization design using material substitution and its products
by Li Liu, Wenyou Jia, Dezhang Xu, Renjun Li
Abstract: In the era of globalization, cost competitiveness has been paid more and more attention. In different mechanical products, the material is one of the key factors of cost. The optimization design using material substitution is one of the important methods to enhance cost competitiveness. First of all, the designers chose the appropriate material according to the material characteristics. Then, they optimized the structure and evaluated its mechanical reliability. The material substitution was divided into semi-design and re-design. The experiments were implemented on the motor pulley and the brake system of washing machine. The results demonstrate the effectiveness of our research methods.
Keywords: Cost competitiveness; Material characteristics; Structure; Mechanical reliability.
Synthesis and Evaluation of Mechanical of AA 6063/MgO +Flyash(Al2 O3 ) Hybrid Surface
Composite by Friction Stir Processing
by Sabitha Jannet, R. RAJA
Abstract: Aluminum metal matrix composites are being studied extensively due to its versatility and wide applications in automobile, aircraft and marine sectors. Surface modification is a domain which will improve the surface properties for various applications. Here an attempt is made to fabricate AA6063/Al2O3+flyash hybrid surface composite by friction stir processing. Three different weight percentage of hybrid reinforcement was used. The process parameters used were 1200 rpm, 20 mm/min traverse speed and 10 KN axial load. Two passes were done to obtain better particle distribution. Cooling time was not allowed before the second pass. The mechanical properties were evaluated. There was 9.75 % increase in the Ultimate tensile strength for 12 % reinforcement with a 21.79% decrease in the elongation. The micro hardness results showed an increase in hardness for 12 % reinforcement.The SEM images obtained revealed the distribution of the reinforced particle in the matrix. It also reveals the formation of hybrid particles.
Keywords: Ultimate Tensile Strength;Elongation;Microhardness;SEM analysis.
Damping properties of pre-stressed shape-memory polymer sandwich beam
by Tomohisa Kojima, Daigo Sato
Abstract: Recently, the development of damping materials has attracted attention to the field of vibration suppression. In this study, a pre-stressed composite sandwich beam was made using aluminium plates and polyurethane-based shape-memory polymer (SMP) with high damping capacity at temperatures near the glass transition point as the core material. A tensile test was carried out to obtain the yield stress of the SMP. A composite beam was fabricated by applying a tensile stress lower than the yield stress to the SMP. Then, viscoelasticity measurements were carried out. It was found that, by sandwiching the SMP with aluminium plates, it may be possible to guarantee a higher stiffness than the vibration isolating rubber in the whole temperature range by a factor of at least 100. Furthermore, the sandwich composite specimen may achieve a value equivalent to or better than the loss factor of the vibration isolating rubbers at a temperature near the glass transition point of the SMP. It was also implied that the loss factor of the sandwich composite beam could be improved by pre-applying tensile stresses to the SMP.
Keywords: functional materials; shape-memory polymer; composite structure; sandwich beam; damping; viscoelasticity; loss factor.
Nickel-based overlay materials: Recent developments, characteristic effects and applicability with plasma transferred arc welding
by Vivek Kalyankar, Sachin Wanare
Abstract: Plasma transferred arc welding (PTAW) is being used extensively to improve surface characteristics of materials. Apart from PTAW process parameters, the selection of appropriate overlay material is vital to obtain desired properties. Nickel-based overlay materials are gaining attraction of researchers and industrialists due to their excellent performance in numerous aggressive service conditions. However, there are wide variants of nickel-based overlay materials which need a thorough study to understand several investigation aspects. This article presents comprehensive survey on nickel-based overlay materials used in depositing functional coatings by PTAW. Recent developments on surface characteristics such as wear resistance, corrosion resistance, metallurgical bonding characteristics, oxidation resistance, microstructural characterizations, etc. are critically reviewed and summarized. This dedicated review on nickel-based overlay materials used for PTAW at one place would be ready information for subsequent authors to understand the associated problems and future aspects which may help them to decide their further research direction.
Keywords: Nickel-based overlay materials; Plasma transferred arc welding; Wear; Corrosion; Microstructural characterization.
Effect of Machining Parameters on Surface Roughness and White Layer during Magnetic Field Assisted Powder Mixed EDM of AA6061
by Arun Rouniyar, Pragya Shandilya
Abstract: Surface integrity aspects of components during machining being one of the challenges of todays manufacturing industry. Magnetic field assisted powder mixed electrical discharge machining (MFAPM-EDM) is hybrid process which integrate the assistance of magnetic field and powder mixed in dielectric in EDM process towards improving the machining performance and surface integrity aspects. In the present experimental work, machining of aluminium 6061 alloy was carried out with fabricated MFAPM-EDM Setup considering one variable at a time experimental design. Five machining parameters namely, discharge current, spark on duration, concentration of powder, spark off duration, and magnetic field were considered as input parameters. The effect of machining parameters has been studied on the responses such as surface roughness, thickness of white layer and surface morphology of machined surface. Elemental analysis has also been examined and discussed in this paper. Decrease in surface roughness and thickness of white layer was observed with decrease in discharge current, spark on duration, and increase in concentration of powder and magnetic field. However, with increase in spark off duration surface roughness tends to increase whereas thickness of white layer decreases. The surface micro-structural analysis performed using scanning electron microscope revealed the presence of fewer cracks, craters and re-solidified debris particles on the surface of machined workpiece.
Keywords: MFAPM-EDM; aluminium 6061 alloy; magnetic field; surface roughness; thickness of white layer; powder.
Multi-Objective Optimisation of Plastic Injection Moulding Process Using Mould Flow Analysis and Response Surface Methodology
by Mohammad Saleh Sheikh Mohammad Meiabadi, Mahmood Moradi, Afshin Kazerooni, Vincent Demers
Abstract: In the production of plastic components using injection moulding, concurrently maintaining a stable part weight and a high production rate remains a challenge. As a statistical tool, the response surface methodology was exploited in the present study to examine the effects of process parameters on part weight and production rate as responses of the production process. The objective was to optimise the process parameters in order to obtain weight stability at high rates of production. The study took advantage of a validated numerical simulation using MoldFlow Insight to generate the input data required in the statistical analysis (response surface method). The influence of process parameters such as mould temperature, melt temperature, packing time, and packing pressure was studied using an analysis of variance. Results indicated that the packing time has a consequential impact on both responses, where an increase in packing time resulted in high part stability, but a low production rate. The analysis of variance revealed that the part weight was more affected by the packing time and packing pressure, but not by the melt temperature and mould temperature. Real-scale injection test using the optimal parameters producing the best trade-off between the part weight and production rate was performed to validate the efficiency of the optimisation procedure proposed in this work. The part weight and production rate predicted by the response surface methodology were in good accordance with the experimental observations, with relative errors of less than 2.5%.
Keywords: Plastic injection moulding; Numerical simulation; Moldflow; Analysis of variance; Part weight; Production rate.
Distinguishing Process-Impact of Down milling and Up milling in Machining Aluminum Thin Wall
by GOPINATH Lakshmanaperumalsamy, Jerome S, Balamurugan Gopalsamy
Abstract: The study aims to understand the deformation mechanics that occurs during down and up milling of aluminium thin wall fabrication. With cutting forces as inputs, material properties were defined by the CoffinManson relation and the SmithWatsonTopper model. Hysteresis was found in the process of machining aluminium thin walls. Furthermore, the pattern of cutter loads differentiated the up and down milling through hysteresis. The finite element method was followed using ANSYS v14.5 software in the fatigue workbench to analyze the aspect. Down milling introduced both deflection and deformation. Conversely, up milling did not exhibit deflection. However, the Bauschinger effect and distinct fracture surfaces were diagnosed during up milling. By exploring the nature of hysteresis and fracture surfaces, the selection of down and up milling was made.
Keywords: Thin wall milling; Hysteresis; Deformation; Up milling; Down milling; Bauschinger effect.
Investigations on Performance Characteristics of Hybrid Peripheral Surface Grinding on Al/Al2O3p/B4Cp Hybrid Metal Matrix Composite
by Ram Singar Yadav, Vinod Yadava
Abstract: In the present work, an attempt has been made to investigate the performance characteristics of Electrical Discharge Diamond Peripheral Surface Grinding (EDDPSG) on one of challenging Hybrid Metal Matrix Composites (HMMCs) namely Al/Al2O3p/B4Cp using self-developed experimental setup. EDDPSG is one of innovative configurations of Electrical Discharge Diamond Grinding (EDDG) process suitably used for machining flat surfaces made of the materials having poor machinability. Performance parameters are Material Removal Rate (MRR) and Surface Roughness (Ra) which were experimentally studied under influence of different process parameters. Gap current, on-time, off-time, abrasive grit number, speed of wheel, and table speed are the process parameters considered for experimentation. EDDPSG has shown its promising potential capability of removing non-conductive ceramic reinforcements (Al2O3) of Al/Al2O3p/B4Cp HMMC together with very soft and ductile matrix material producing higher MRR and surface finish. Gap current is the most influential performance affecting process parameter and significantly affects MRR and Ra by 361% and 61% respectively. A very thin re-solidified layers and small streaks on machined surface were observed during analysis of surface texture and presence of re-solidified layers on machined surface using Scanning Electron Microscopy which demonstrate the potential applicability and suitability of the peripheral surface grinding mode of EDDG for machining of such complex and hybrid composite materials.
Keywords: hybrid metal matrix composite; electrical discharge diamond grinding; MRR; Ra.
Multi-criteria decision making approaches for aircraft material selection problem
by Aslı Çalış Boyacı, Mehmet Çağrı Tüzemen
Abstract: This paper is related to the use of multi-criteria decision-making (MCDM) tools for assisting material selection for aircraft parts. In this direction, decision models including analytic hierarchy process (AHP), complex proportional assessment (COPRAS), technique for order preference by similarity to ideal solution (TOPSIS), and Borda count methods were used to select the best materials for aircraft wings and nose. AHP was used to determine the criteria weights. According to the criteria weights, the rankings were obtained using AHP, COPRAS, and TOPSIS methods. Then, the final integrated rankings were obtained by Borda count method. Finally, the rankings obtained by AHP, COPRAS, and TOPSIS methods were compared to the final integrated rankings using Spearmans rank correlation coefficient.
Keywords: aircraft; material selection; analytic hierarchy process; AHP; complex proportional assessment; COPRAS; technique for order preference by similarity to ideal solution; TOPSIS; Borda count method.
Degradation of swollen NR/EPDM filled with Graphene Nanoplatelets in different types of service oils for engine mounting
by Khairu Ilwani Karim, Noraiham Mohamad
Abstract: Rubber engine mounts are prone to chemical and environmental degradation due to the high-temperature exposure to various factors during service. Graphene derivative has been known as a promising material with outstanding physical, mechanical, electrical, and thermal properties hence serve as an excellent filler in elastomer composites. This study focuses on the degradation of swollen NR/EPDM blend and NR/EPDM filled with graphene nanoplatelets in different automotive service liquids and later subjected to tensile testing. The blends and nanocomposites were melt compounded using an internal mixer and fabricated by using a hot press. They were then swollen in gear, brake, and engine oils for 6 and 27 days. The change in mass, length and tensile properties are measured to determine the degradation effect. Swollen blends and nanocomposites experienced severe dimension changes and dropped in tensile properties. The results were in good agreement with morphological, structural, thermal, and compositional analyses.
Keywords: natural rubber; ethylene propylene diene monomer; graphene nanoplatelets; swelling properties; tensile properties.
Influence of weight ratio of conductive additive to binder in an electrode on the capacity of Li-ion battery
by CHEOL KIM, Jung-hoon Lee
Abstract: Changes in the charge and discharge capacity of a lithium ion battery are investigated by way of varying the % weight composition ratios of conductive additive to polymeric binder in an electrode of a lithium ion battery. The cathode is made of active material (LiMn2O4), binder (PVDF), and conductive additive (carbon black). In order to study the influence of inactive material composition on a battery performance experimentally, the weight percentage of active material in a cathode is fixed at 85 % and five different ratios of PVDF/carbon black are assessed by varying conductive additive from 1.5 wt % to 13.5 wt % and binder from 13.5 wt % to 1.5 wt % while fabricating lithium ion batteries. For the study of particles cohesive behaviors between inactive materials in the electrode, various SEM images are taken and analyzed for 5 different compositions of carbon black and PVDF. As a result, the improved battery performance is observed at the ratios of 7.5 10.5 wt % carbon black and 7.5 4.5 wt % PVDF.
Keywords: binder material; conductive additive; electrode composition; inactive material; lithium ion battery.
Plastic behaviour of SUS304 stainless steel tubes under intermittent uniaxial tensile loading
by Lianfa Yang, Daofu Tang, Yulin He
Abstract: The plastic behaviour of SUS304 stainless steel tubes was investigated at room temperature via conventional single-round and intermittent uniaxial tensile testing (UTT), and the Hollomon model was adopted to describe the true stressstrain relationship under uniaxial tensile loading. The observed effects of the strain rate and unloading gap on tensile properties and the resulting stressstrain curves were interpreted in terms of microstructural transformation. The results indicate that the flow stress obtained by intermittent UTT was higher than that obtained by conventional single-round UTT, and the ultimate tensile strength (UTS) and tensile elongation decreased with an increase in the unloading gap. In addition, the yield strength increased with increasing strain rate, while the UTS and tensile elongation decreased. Further, both the strength coefficient and strain-hardening exponent used in the Hollomon model decreased with increasing unloading gap and strain rate.
Keywords: SUS304; stainless steel tube; uniaxial tensile test; strain rate; unloading gap; tensile properties; plastic behaviour.
Experimental and finite element analyses for residual stress prediction of welded SAE-1018 steel joints
by Mukhul Venkatesh Babu, Ajith Ramesh, Saravanamurugan Sundaram
Abstract: Welded joints are a critical part of any structural component, and the stresses induced can cause a major problem in structural integrity. The presented work discusses the development of a numerical model using finite element techniques to determine the residual stress of an SAE-1018 welded joint. A 3D thermo-mechanical coupled model for shielded metal arc welding is developed to predict the tensile and compressive residual stresses. Further, a uniaxial tension test is also modelled to predict the weld joint strength, and the numerical results are validated with the experiments. ASTM E8 standards are used to perform the tensile test.
Keywords: shielded metal arc welding; SMAW; weld joint; FEM; damage; residual stress; failure strength; SAE-1018 steel; ASTM E8.
Influence of superimposition of high frequency current to CC-GTAW and PC-GTAW welding producing superior characteristics of weld joints of SDSS
by Rajeev Kumar, Somnath Chattopadhyaya, B.P. Agarwal, Sanjeev Kumar, K. Devakumaran
Abstract: The joints are made with UNS32750 super duplex stainless steel plate. The joints are also made by superimposing high frequency current to these welding techniques namely CC-GTAW, constant current gas tungsten arc welding with superimposed high frequency current (CC-GTAWHF), pulse current gas tungsten arc welding (PC-GTAW) and pulse current gas tungsten arc welding with superimposed high frequency current (PC-GTAWHF) respectively. The thermal characteristics and its effects are further correlated to corrosion resistance. The correlation between thermal characteristics and pitting corrosion resistance in all weld joints was established using weight loss method and potentiodynamic polarisation experiment. The effective thermal impact and consequently corrosion rate has been found minimum in PC-GTAWHF. EDS shows that there is reduction in Ni and increase in Mo content in the weld metal which have also an effect on corrosion of weld.
Keywords: constant current gas tungsten arc welding; CC-GTAW; pulse current gas tungsten arc welding; PC-GTAW; current gas tungsten arc welding with superimposed high frequency current; CC-GTAWHF; pulse current gas tungsten arc welding with superimposed high frequency current; PC-GTAWHF; pitting corrosion resistance; gas tungsten arc welding; GTAW.
RF sputtered hexagonal boron nitride film-based printed circuit board for high voltage and high-power electronic applications
by K.R. Remesh Kumar, K. Shreekrishna Kumar
Abstract: The power electronic devices use big heat sinks for the removal of heat from the components. These heat sinks are bulk in size. Therefore, the strategy is to remove the heat sink from the PCB and instead use the PCB itself as a heat sink. For making heat conductive PCBs, copper is selected as the base layer. Since copper is electrically conductive, hexagonal boron nitride (h-BN) is layered over it. The quality of h-BN thin film made using RF sputtering is analysed using XRD graph, TEM and SEM images. The voltage-current analysis of h-BN layer is done for finding its suitability for high voltage and high-power applications. A DC voltage regulator is created in normal PCB with heat sink, flexible PCB and our h-BN-based PCB and compared. Based on results of these experiments, it is clear that the proposed h-BN-based PCB is useful for power electronic applications.
Keywords: thermally conductive PCB; RF sputtering; hexagonal boron nitride; h-BN; h-BN thin film; thin film PCB.
Statistical and experimental evaluation of multi-performance in turning of AISI D6 using Grey relational analysis
by Latif Ozler, Gul Tosun, Nihat Parlak, Nihat Tosun
Abstract: In this study, the impact of machining variables and the relationship among the performance outputs (surface quality and tool life) and process variables were investigated using Grey relational analysis (GRA) in finish turning of AISI D6 tool steel with the CBN insert. The experiments were done under different cutting speeds, cutting depths and feed rates. Hardening heat treatment was applied to the workpiece used in experiments, and the hardness is 62 HRC after the heat treatment. The most important and best suitable process variables were found by the GRA and Taguchi experimental design method. According to the obtained results, the life of the cutting tool shortened with the increasing cutting depth, feed rate and cutting speed, and the increment in feed rate and cutting depth resulted in a deterioration of the surface quality of work material. The tool wears increased with a rise in all cutting parameters, while the surface quality only increased with raising the cutting speed. During the turning of AISI D6 steel, it was verified that CBN cutters were not the appropriate choice for high cutting speed and feed rate.
Keywords: turning; AISI D6; tool wear; tool life; surface roughness; Grey relational analysis; GRA.
Multi-objective optimisation for indentation rate, nugget diameter and tensile load in resistance spot welding using Taguchi-based grey relational analysis
by Celalettin Yuce
Abstract: In this study, a multi-objective optimisation method based on grey relational analysis with weighted responses is conducted to optimise the RSW parameters of electrode force, welding current, and welding time. Three objectives, such as indentation rate, nugget diameter, and tensile load, are simultaneously optimised. In order to assign the optimum level for each parameter individually, the Taguchi technique was applied. ANOVA results showed that the most influential parameters on indentation rate, nugget diameter, and tensile load are welding current, welding time, and welding current, respectively. In the grey relational analysis, the grey relational grades were obtained using weighted responses. The weight factors for the indentation rate, nugget diameter, and tensile load are 33.24%, 35.67%, and 31.1%, respectively. The optimum parameter combination was obtained as 2,500 N, 9 kA, and 0.5 s. Under these parameter combinations, indentation rate, nugget diameter, and tensile load were 26.2%, 8.34 mm, and 20.04 kN, respectively.
Keywords: grey relational analysis; GRA; resistance spot welding; RSW; multi-objective optimisation; weighted factors.
Special Issue on: ISCEG 2020 Recent Advances of Construction and Building Materials
Experimental studies of the interfacial shear mechanical behaviour of geosynthetics-soil
by Guangqing Yang, Zheng Zuo, Linying Xu, Zhijie Wang, He Wang
Abstract: At present, limited researches had been performed on comparison of shear mechanical behaviour between geogrid or geocell and soil. In current research, direct shear tests (DST) were performed on the geogrid and geocell to investigate the impact of the friction characteristics and differences of the geogrid and geocell. Results showed that the geogrid and geocell can improve interfacial shear strength characteristics. The reinforcement effect of the geocell was better than that of geogrid, especially under higher vertical stress. The performance of geocell with 260 mm in distance of junctions was better than that of the 440 mm. The performance of geocell with 150 mm in strip height was better than that of the 100 mm. Additionally, in current studies, the contribution of geocell height to the soil strength was greater than the junction distance. The experimental results may provide an idea for application of geocell reinforced mass structures.
Keywords: direct shear test; DST; geogrid; geocell; height of geocell strip; distance of junction.
Optimization of Mix Proportions for the Cemented Sand and Gravel in Cold Region
by Guo Lixia, Guo Yuhang, Zhong Ling, Zhang Guozhi
Abstract: Cemented sand and gravel (CSG) is recognised as having poor quality due to its high porosity. An experimental study was carried out on the mix proportion design of CSG, taking into account the strength and frost resistance requirements of CSG dams in frozen areas .The main factors affecting the compressive strength and frost resistance of CSG were determined by orthogonal experiments. The influencing factors are water/binder ratio, fly ash, cement consumption, admixture and sand ratio, every factor sets up two cases, and the orthogonal table L8 (24) is adopted. There is a positive correlation between compressive strength and frost resistance, as the test results show. An optimal function about compressive strength and frost resistance to improve the quality of CSG in cold region was proposed, in which, weight was determined by OWA operator and entropy weight method to eliminate the influence of extreme values in the subjective evaluation. With the application of the function, significant factors influencing the desired performance of CSG are sand ratio, cement consumption, water/binder ratio and content of fly ash, while the optimum mix proportion is water/ binder ratio of 1.0, ratio of sand of 0.2, while 60 kg/m3 and 40 kg/m3 for the contents of fly ash and cement. The results can provide a theoretical basis for application and design of CSG dam in cold region.
Keywords: Cemented sand and gravel; Ordered Weighted Average operator;Orthogonal experiment; Optimization; Compressive Strength;Frost resistance.
Influence of fiber type on unconfined compressive strength of fiber-reinforced cemented soil under freeze-thaw cycling
by Lina Xu, Lei Niu
Abstract: In order to study the influence of the fiber type on the unconfined compressive strength of fiber-reinforced cemented soil under the freeze-thaw cycling, several experiments on freeze-thaw cycling and unconfined compressive strength were carried out, using fiber-reinforced cemented soil as the object. Specifically, basalt fiber and glass fiber with the content of 0.5% respectively by weight of soil, and the lengths of 3 mm, 6 mm, and 20 mm respectively were added to the cemented soil, which was cured for 28 d. The result shows that the unconfined compressive strength of these samples increased at first stage and then decreased as the length of fiber increased. Fiber in the cemented soil mitigated its strength loss under the freeze-thaw cycling. During the experiments, the glass fiber-reinforced cemented soil had a smaller strength loss, a higher peak strength and a smaller failure strain than the basalt fiber-reinforced cemented soil. Those findings can provide reference for the selection of reinforcing fibers for cemented soil under the freeze-thaw cycling.
Keywords: basalt fiber; glass fiber; freeze-thaw cycling; cemented soil; unconfined compressive strength.
A Causal Time-varying Analysis Method for Assessing Impacts of Cracks on Service States of Concrete Dams
by Bo Xu, Aimin Gong, Shuyan Fu, Bin Ou
Abstract: The impact of cracks on the service state of concrete dams is an important topic. At present, there is relatively little research on the method of analyzing the impacts of cracks on the service state of concrete dams based on effect variables in dam safety monitoring. This study proposes a causal time-varying (CTV) analysis method to assess the effect of cracks on the service state of concrete dams through analysis of the impacts of cracks on effect variables, such as the deformation, stress, and strain of the dam. Specifically, the CTV characteristics of changes in the effect variables were first analyzed considering both the causal action mechanisms between the contributing factors and effect variables, and the time-varying characteristics of the causal effect; then, the cracks were regarded as an contributing factor on the effect variables of concrete dams. On this basis, a CTV analysis model was established, which consisted of an analytical model of impact degrees and an analytical model of impact sensitivity of cracks on effect variables. Accordingly, the CTV analysis method for impacts of cracks on service states of concrete dams was built. The method was applied to a study case of a concrete gravity-arc dam, which proved the method reasonable and feasible. This research is expected to provide a reference for prevention and control of cracks in concrete dams.
Keywords: causal time-varying analysis; concrete dam crack; effect variable; impact degree; sensitivity of impact; service state.
Evaluation of in-soil creep characteristics of HDPE geogrid using the time-stress superposition method
by Guangqing Yang, Qiaoyi Li, Zhijie Wang, He Wang
Abstract: The tensile creep characteristics of geogrids in-soil were studied by using a self-designed creep test device. To study the influence of normal stress on the tensile creep characteristics of geogrids, creep tests were carried out at three tensile stress levels. The restraint of normal stress can reduce the creep strain of a geogrid. The HDPE geogrids exhibited primary and secondary creep stages under restraint. According to the principle of time stress superposition, the creep strain time curves under three different tensile stress levels were moved along the logarithmic time axis to obtain the master strain curve at a given reference stress level. Based on the 500 hours creep test data, the principal curve was used to predict the creep characteristics up to 100 years by the time stress superposition principle.
Keywords: geogrid; tensile creep; in-soil; time stress superposition; master strain curve.
Special Issue on: Advances in Innovative Engineering Materials and Processes
Filling method of thin shell 3D printing material based on implicit surface
by Huijian Shu
Abstract: The traditional filling method of thin shell 3D printing material has poor capturing effect on missing features, low filling efficiency and poor economic benefit. Therefore, this paper proposes a thin shell 3D printing material filling method based on implicit surface. The 3D material filling process of implicit surface is designed, and the implicit surface is constructed to mark the image surface features of material defects; the two-phase segmentation is used to realise the mesh division of material defect image, and the thin shell 3D printing material filling algorithm is designed, and finally the material filling is realised by 3D printing technology. The experimental results show that the average accuracy of missing feature capture is 97.35%, the average length of filling path is 570.3 mm, and the average filling time is 3.65 min.
Keywords: 3D printing; implicit surface; two-phase segmentation; filling efficiency.
Analysis of rheological characteristics of cement mortar based on microstructure
by Huan Liu, Zhan-zhan Zheng, Quan-sheng Yang
Abstract: In order to solve the problems of low precision of rheological characterisation and large error of characteristic analysis existing in traditional analysis methods of rheological properties of cement mortar, a new method of rheological properties analysis of cement mortar based on microstructure is proposed in this paper. According to Bingham fluid, power law fluid and Carson fluid equation, the rheological characteristics of cement mortar are obtained. According to the microstructure of cement mortar, the evaluation model of rheological properties of cement mortar is constructed. The internal structure relationship of cement mortar is determined by grey correlation method, and the damage variables of cement mortar are obtained to complete the rheological properties analysis of cement mortar. The experimental results show that the highest accuracy of the proposed method is about 95%, and the error of rheological property analysis is always less than 2%.
Keywords: fine microstructure; cement mortar; rheological properties; Bingham fluid; power law fluid; damage variable.
Numerical simulation analysis of bearing capacity of reinforced concrete high-pressure members
by Tong Wu, Li Wang
Abstract: In order to solve the problem that the numerical simulation results of the bearing capacity of the reinforced concrete high pressure members are not accurate, the numerical simulation research of the bearing capacity of the reinforced concrete high pressure members is put forward. The additional stress of concrete members is calculated by elastic theory formula, and the longitudinal equilibrium differential value of concrete members is obtained. The additional stress of the compression member is calculated. In order to meet the requirements of calculation time and simulation precision, the reinforced concrete members are discretised by grid partitioned. The experimental results show that, compared with the traditional method of mean square root value of relative error is 0.10, accuracy was 98%, 99% of the reliability, effectively overcome the numerical simulation of high pressure bearing capacity of reinforced concrete members, the main tension stress measurement of fixed end concrete members to limit state, and the finite element simulation results closer to the experimental value, this improves the accuracy of the numerical simulation of high pressure bearing capacity of reinforced concrete member, ensure construction quality to a certain extent.
Keywords: reinforced concrete; high-pressure member; bearing capacity; numerical simulation.