Carbon fiber-reinforced polymer (CFRP) easily realizes the integrated manufacturing of components with high specific strength and stiffness, and it has become the preferred material in the aerospace ...field. Grinding is the key approach to realize precision parts and matching the positioning surface for assembly and precision. Hygroscopicity limits the application of flood lubrication in CFRP grinding, and dry grinding leads to large force, surface deterioration, and wheel clogging. To solve the above technical bottleneck, this study explored the grindability and frictional behavior of CNT biological lubricant MQL through grinding experiments and friction-wear tests. Results showed that the CNT biological lubricant reduced the friction coefficient by 53.47% compared with dry condition, showing optimal and durable antifriction characteristics. The new lubrication was beneficial to suppressing the removal of multifiber block debris, tensile fracture, and tensile-shear fracture, with the advantages of tribological properties and material removal behavior, the tangential and normal grinding force, and the specific grinding energy were reduced by 40.41%, 31.46%, and 55.78%, respectively, compared with dry grinding. The proposed method reduced surface roughness and obtained the optimal surface morphology by preventing burrs, fiber pull-out, and resin smearing, and wheel clogging was prevented by temperature reduction and lubricating oil film formation. S
and S
of the CNT biological lubricant were reduced by 8.4% and 7.9%, respectively, compared with dry grinding. This study provides a practical basis for further application of CNT biological lubricant in CFRP grinding.
Since the last decades, solar energy has been used worldwide to overcome foreign dependency on crude oil and to control the pollution due to a limited source of non-renewable energy. Evacuated tube ...solar collectors are the most suitable solar technology for producing useful heat in both low and medium temperature levels. Evacuated tube solar collector is capable of working in hot, mild, cloudy or cold climates where flat plate collector is not an option. The objective of this review paper is the detailed investigation of evacuated tube solar collectors having heat pipe and direct flow are reviewed. All the design parameters which influence the collector performance are investigated and discussed in this work. More specifically, the tracking system, the collector design, the mass flow rate, the optical design and the kind of the working fluid are the main studied parameters. Moreover, this work focuses on the latest developments and advances, providing a review of experimental and numerical studies reported. Lastly, this work presents the future ideas that can be carried out to improve the performance of evacuated tube solar collectors.
Due to the stringent requirements of carbon emissions, traditional cutting using a large amount of mineral-based metal cutting fluid for lubrication no longer fulfilled the rigorous requirements of ...policies and standards. Nanofluid minimum quantity lubrication has been proven to be a new process to achieve clean manufacturing. However, due to adhesive contact friction, lubricant droplets cannot effectively penetrate the tool and workpiece interface during continuous turning. Changing the microstructure of the rake face of the tool, such as the micro-texture, may provide a geometric channel for the diffusion of the lubricant. However, the effects of micro-texture geometry and arrangement on the film formation and tribological properties of droplets have not been revealed yet. The spreading behavior of minimum quantity lubrication atomized microdroplet on the textured surface was calculated by hydrodynamic modeling. It was proven that the microchannel can effectively store the lubricating medium atomized by compressed air pneumatics. Furthermore, a comparative experiment was conducted on the influence of the texture arrangement on the cutting performance through the turning experiment. Results show that the microgrooves in the direction perpendicular to the main cutting edge obtained the lowest cutting force. The feed force, radial force, and tangential force were reduced by 13.46%, 16.23%, and 6.34%, respectively. Meanwhile, the texture arranged parallel to the cutting edge and crosswise increased the cutting force. The arrangement of the texture perpendicular to the main cutting edge direction obtained the optimal workpiece surface, the smallest chip curling radius, and the smoothest chip surface. Under the optimized texture arrangement, the anti-wear and anti-friction properties of nanofluids in the cutting area are enhanced.
Sustainable Development Goals were established by the United Nations General Assembly to ensure that everyone has access to clean, affordable, and sustainable energy. Third-generation biodiesel ...derived from algae sources can be a feasible option in tackling climate change caused by fossil fuels as it has no impact on the human food supply chain. In this paper, the combustion and emission characteristics of Azolla Pinnata oil biodiesel-diesel blends are investigated. The multi-objective response surface methodology (MORSM) with Box–Behnken design is employed to decrease the number of trials to conserve finite resources in terms of human labor, time, and cost. MORSM was used in this study to investigate the interaction, model prediction, and optimization of the operating parameters of algae biodiesel-powered diesel engines to obtain the best performance with the least emission. For engine output prediction, a prognostic model is developed. Engine operating parameters are optimized using the desirability technique, with the best efficiency and lowest emission as the criteria. The results show Theil’s uncertainty for the model’s predictive capability (Theil’s U2) to be between 0.0449 and 0.1804. The Nash–Sutcliffe efficiency is validated to be excellent between 0.965 and 0.9988, whilst the mean absolute percentage deviation is less than 4.4%. The optimized engine operating conditions achieved are 81.2% of engine load, 17.5 of compression ratio, and 10% of biodiesel blending ratio. The proposed MORSM-based technique’s dependability and robustness validate the experimental methods.
The special mechanical properties of cemented carbide with high strength and hardness will cause complex stress due to excessive force and heat in the process of precision manufacturing, which will ...affect precision retention and endurance limit. Given the health and environmental threat of conventional flood cooling and the harsh processing environment of dry grinding, minimum quantity lubrication (MQL) has become an irreplaceable method to machining cemented carbide. However, the addition of nanoparticles changes the force and heat during grinding, which makes the influence on the residual stress of cemented carbide complicated. Therefore, based on the single abrasive grinding force model, the effective abrasive particle number was obtained by simulating the distribution of abrasive particles on the grinding wheel surface, and the mechanical stress model was established, which was loaded onto the workpiece in iterative attenuation mode. The thermal stress model was established based on the temperature field model. The final residual stress prediction model was obtained by determining whether the grinding process yields results and carrying out stress loading and stress relaxation. Experimental verification of the model was carried out under four different grinding conditions of YG8. The minimum friction coefficient of 0.385 was obtained under nanofluid minimum quantity lubrication (NMQL). In the precision analysis of the model, the minimum error value was 5.9% in the direction perpendicular to the feed direction of the workpiece in the dry grinding condition, which proved that the residual stress model had certain reliability.
The cutting fluid is significant in any metal cutting operation, for cooling the cutting tool and the surface of the workpiece, by lubricating the tool-workpiece interface and removing chips from the ...cutting zone. Recently, many researchers have been focusing on minimum quantity lubrication (MQL) among the numerous methods existing on the application of the coolant as it reduces the usage of coolant by spurting a mixture of compressed air and cutting fluid in an improved way instead of flood cooling. The MQL method has been demonstrated to be appropriate as it fulfills the necessities of ‘green’ machining. In the current study, firstly, various lubrication methods were introduced which are used in machining processes, and then, basic machining processes used in manufacturing industries such as grinding, milling, turning, and drilling have been discussed. The comprehensive review of various nanofluids (NFs) used as lubricants by different researchers for machining process is presented. Furthermore, some cases of utilizing NFs in machining operations have been reported briefly in a table. Based on the studies, it can be concluded that utilizing NFs as coolant and lubricant lead to lower tool temperature, tool wear, higher surface quality, and less environmental dangers. However, the high cost of nanoparticles, need for devices, clustering, and sediment are still challenges for the NF applications in metalworking operations. At last, the article identifies the opportunities for using NFs as lubricants in the future. It should be stated that this work offers a clear guideline for utilizing MQL and MQL-nanofluid approaches in machining processes. This guideline shows the physical, tribological, and heat transfer mechanisms associated with employing such cooling/lubrication approaches and their effects on different machining quality characteristics such as tool wear, surface integrity, and cutting forces.
In this study industrial grade Multi-walled carbon nanotubes (MWCNTs) nanoparticles dispersed in distilled water (DW) are investigated to evaluate its impact on the thermal behavior of linear Fresnel ...solar reflector technology. The stability and thermophysical properties of the MWCNTs/DW nanofluids are obtained experimentally. Stable nanofluids that showed higher thermal conductivity compared to DW were obtained. Thermal conductivity (TC) of the nanofluids increased by 3%, 6% and 7% for the volume fractions of 0.05%, 0.1% and 0.3% at 25 °C, respectively. TC also increased with the increase in temperature (i.e. 11% for 0.3% volume fraction at 70 °C). A one-dimensional model is developed to evaluate the transient behavior of the nanofluid within the linear solar reflector. Matlab code based on the finite difference method is developed to solve the energy balance equations at the different components of the studied solar collector. The numerical model is then validated with experimental results, where a maximum experimental thermal efficiency of 29.205% at 14:00 is achieved. MWCNTs/DW nanofluid with 0.3% volume fraction has the highest thermal efficiency of 33.81% and the highest PEC value as well as the lowest entropy generation.
•Small linear Fresnel reflector has been manufactured and experimentally tested.•The maximum experimental thermal efficiency of DW is equal to 29.205%.•Stability and thermophysical properties of the MWCNTs/DW nanofluids are obtained.•Thermal conductivity of the nanofluids increased with the increasing volume fractions.•Highest thermal efficiency of 33.81% was obtained for MWCNTs/DW nanofluid.
Aluminum alloy is the main structural material of aircraft, launch vehicle, spaceship, and space station and is processed by milling. However, tool wear and vibration are the bottlenecks in the ...milling process of aviation aluminum alloy. The machining accuracy and surface quality of aluminum alloy milling depend on the cutting parameters, material mechanical properties, machine tools, and other parameters. In particular, milling force is the crucial factor to determine material removal and workpiece surface integrity. However, establishing the prediction model of milling force is important and difficult because milling force is the result of multiparameter coupling of process system. The research progress of cutting force model is reviewed from three modeling methods: empirical model, finite element simulation, and instantaneous milling force model. The problems of cutting force modeling are also determined. In view of these problems, the future work direction is proposed in the following four aspects: (1) high-speed milling is adopted for the thin-walled structure of large aviation with large cutting depth, which easily produces high residual stress. The residual stress should be analyzed under this particular condition. (2) Multiple factors (e.g., eccentric swing milling parameters, lubrication conditions, tools, tool and workpiece deformation, and size effect) should be considered comprehensively when modeling instantaneous milling forces, especially for micro milling and complex surface machining. (3) The database of milling force model, including the corresponding workpiece materials, working condition, cutting tools (geometric figures and coatings), and other parameters, should be established. (4) The effect of chatter on the prediction accuracy of milling force cannot be ignored in thin-walled workpiece milling. (5) The cutting force of aviation aluminum alloy milling under the condition of minimum quantity lubrication (mql) and nanofluid mql should be predicted.
•Convolutional neural network application as a processor for thermography.•Combined CNN and Deep Forward neural network approach for quantification.•A full automatic demonstration of defect detection ...and depth quantification.•Detailed analysis of CNN training for thermography application.•New approach to process CFRP NDT thermograms.
Recent advancements in the field of Artificial Intelligence can support the post-processing of thermographic data, efficiently, especially for nonlinear or complex thermography scanning routines. This study proposes the implementation of an autonomous/intelligent post-processor that is capable of automatically detecting defects from given thermograms via a Convolutional Neural Networks (CNN) coding, in tandem with a Deep Feed Forward Neural Networks (DFF-NN) algorithm to estimate the defect depth as well. Thus, the proposed NN combination will process (detect and quantify) the defects from acquired thermograms in real-time, and without any human (inspector) intervention. The study shows that employing a pre-trained network, using a relatively small dataset of thermograms for training, can detect and quantify defects in thermographic sequences. In this paper, pre-trained networks with CIFAR-10 and ImageNet databases are used, and followed by a fine-tuning step of the later layers in the network; using a relatively small thermograms dataset. This text will also provide several in-depth studies to compare how transfer learning, state of the art object detection architectures, and the convolutional neural networks influence the performance of the trained post-processing system. The proposed post-processor applied to thermograms obtained from a pulsed-thermography setup testing a Carbon Fiber Reinforced Polymer (CFRP) sample with artificially created sub-surface defects validates the CNN approach.
Extreme pressure (EP) and antiwear (AW) additives are necessary for boundary lubrication. However, their mechanisms and physical and chemical properties remain unclear. EP and AW additives were ...reviewed to fill gaps in theoretical and industrial applications. Compounds containing chlorine, sulfur, and phosphorus elements were first used in boundary lubrication because of thermal reaction with metal to form film characteristics. First, the mechanisms of traditional EP and AW additives were analyzed, the physical and chemical properties were compared, and properties affecting factors were studied. Traditional EP and AW additives are not environmentally friendly, but nanoparticle EP and AW additives are excellent substitutes. The mechanisms of nanoparticle EP and AW additives were summarized. The influence of nanoparticle structure parameters, concentration, and media polarity on properties was studied. Second, the influence law of non-polar chain length on traditional EP and AW additives was revealed. The improvement interval of traditional EP and AW additives on the performance of the base fluid was determined. The structural advantage of low crystallinity onion-like and multilayer sheet-like low wrinkle effect of nanoparticles was explained. The particle size design principle attached to the surface roughness and size-dependent melting inhibition mechanism was established. The influence of concentration and media polarity on nanoparticle properties was obtained. Finally, the research of minimum amount matching database and mathematical selection model for traditional EP and AW additives and the molecular dynamics analysis of surface-modified nanoparticles and the development of green general-purpose additives based on molecular design are prospected.
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