Temperature Loading Conditions Research Articles

Exergy analysis of hybrid air-conditioning systems with different evaporative-cooling condensers under hot-humid climates

Evaporative cooling (EC) technology can effectively improve the energy efficiency of the mechanical vapor compression (MVC) system by enhancing the heat exchange capacity of its condenser. However, the current evaporative-cooling condenser system is usually only equipped with a single-stage evaporative cooler as the precooling unit, and these designs are mainly suitable for hot-dry conditions. In this study, three hybrid air-conditioning systems with different two-stage evaporative-cooling condenser configurations were proposed, one is single-condenser type and the other two are dual-condenser type, which are used to improve the exergy performance and adaptability of the evaporative condenser system under hot-humid climates. Then, the all systems were modeled via the distributed parametric method and analyzed comparatively based on the exergy method. A suitable exergy reference temperature at air saturation was discussed. Finally, the effect of four key parameters (ambient temperature and relative humidity, outdoor airflow rate and room heat load) was studied. The results showed that under the high temperature, relative humidity or room heat load conditions, the hybrid systems have a low exergy efficiency ratio (EXR) and high exergy efficiency (ηx,OEC). Among them, the newly countercurrent dual-condenser configuration (MVC-TSEC(C)) exhibits the best exergy performance under most hot-humid conditions. Compared to the conventional MVC system, the EXR and ηx,OEC of MVC-TSEC(C) increased by at most 35.0 % and 78.2 %, respectively. Moreover, its components like compressor, condenser and expansion valve have the maximum reduction rates of exergy destruction of 43.5 %, 17.2 % and 55.3 %, respectively.

Wear behaviour analysis of thermo-mechanically processed AA7075 and AA7075/SiC/Graphite composite

The current work focuses on investigating the tribological performance of AA7075 alloy and AA7075 hybrid composite with SiC and graphite reinforcements of 2 and 0.5 wt percentages, respectively. The alloy and hybrid composite are fabricated through stir casting and thermo-mechanically processed through hot rolling routes. Dry sliding wear characterization has been carried out using a pin-on-disc wear testing setup for alloy and composite under various processing conditions using experiments designed according to Taguchi's L9 orthogonal array. The technique for order preference by similarity to ideal solution (TOPSIS) method has been adopted to achieve a single multi-response index (MRI) considering the minimization of multiple objective functions for specific wear rate (SWR) and coefficient of friction (COF). The analysis of variance (ANOVA) results of the MRI indicated that sample processing condition and load were the most significant parameters. The wear mechanism at different experimental conditions was studied using Scanning electron microscope (SEM) micrographs, energy dispersive spectroscopy analysis and 3D surface profile of wear track. The AA7075 composites are found to be comparatively good in all experimental conditions compared to the base alloy due to load-bearing SiC particles and solid lubricant graphite as reinforcing elements. The mechanically mixed layer (MML) formation in hybrid composites helped achieve good tribological properties. The AA7075 alloy and hybrid composites cross rolled at 350 °C yielded better results than other samples. The wear mechanism was abrasive and adhesive at low temperature and low load conditions in both alloy and hybrid composites. Whereas, at higher temperatures and high loads oxidative wear mechanism with delamination was prevalent. The transition of SWR from mild to severe value occurs at 250 °C in all experimental cases. The specific wear rate was improved by 85.64 % between worst and best conditions, i.e., annealed alloy and cross rolled composite.

Investigation on memory package crack and prevention under temperature cycling test

Memory package with multiple die stacking in one package faced package crack issue during package level temperature cycling test (TCT) and the failure cycle cannot meet reliability requirement. Failure analysis showed epoxy molding compound (EMC) cracking located at the center area of package surface. Finite element modeling and simulation was conducted to study package stress and failure mechanism under cyclic temperature loading condition. Simulation results showed that the center of package surface is subjected to higher stress and stress variation during stringent TCT test due to high and tight die stacking structure. Several parametric studies were conducted to further understand failure mechanism and provide solution for crack prevention. Design guideline was proposed to eliminate or reduce package crack risk for multi-chip package (MCP) in memory chip package.

Synergistic Effects of Layered Double Hydroxide and MoS2 on the Performance of Lubricants

In this study, layered double hydroxide (LDH) and molybdenum disulfide (MoS2) were used as additives to prepare lubricants. The morphology and particle distribution of the LDH and MoS2 were characterized using a scanning electron microscope and a laser particle size analyzer, respectively. Thermogravimetric analysis was used to compare the performance of the lubricants at high temperature. The extreme pressure and wear resistance performance of the lubricants were tested using a four-ball machine and a fretting-wear machine. Then, the lubricants were applied in a bolt fastener. The loosening torque and surface wear condition at high temperature were compared. By adding LDH and MoS2 to the lubricants, the extreme pressure and wear resistance performance and anti-seize performance at high temperature were improved significantly. The LDH showed better anti-seize performance than the MoS2 because of its strong and stable structure at high temperature. The MoS2 showed better anti-wear performance under a high load because of its soft layered structure. The MoS2 with a larger particle size showed better extreme pressure performance under a high load. The LDH and MoS2 played a synergistic effect under the conditions of high temperature and high load.

Joint identification method for thermal–mechanical coupling loads

The crucial role in evaluating structural fatigue life, implementing health monitoring, and optimizing lightweight and reliable design is played by load identification technology. With the development of the aviation industry towards high-speed aircraft, the challenges under high temperature and high load conditions have been intensified. Unfortunately, in environments characterized by the coexistence of force and heat, difficulties are faced by existing load identification methods in achieving key decoupling and accurate identification of force and temperature fields. To address this gap, the Joint Identification Method (JIM), a new method that integrates force and thermal strain patterns, is introduced in this article. This method has been developed through in-depth research on “joint physical fields” and “joint basis functions.” Multiple physical fields for load identification are systematically decomposed by our method, each field is theoretically deduced, and they are seamlessly reassembled using the same structural spatial field. Through the method, mechanical strain and thermal strain are separated in high-precision temperature field reconstruction, and a basis function method for identifying the full field load distribution under a few measurement points is obtained. To verify the accuracy of our proposed Joint Identification Method (JIM), five experiments were designed, and the results consistently demonstrated the superiority of our method in accuracy (with an error always below 5%), efficiency (avoiding a large number of redundant calculations in traditional Duhamel methods), and reliability in static and dynamic load static heat identification. In the end, accurate, efficient, and reliable identification of the structural strain field, structural load field, and temperature field were achieved by our method.

A novel metamaterial with instantaneously sign-switchable coefficient of thermal expansion and Poisson's ratio

Most materials expand when heated and contract when cooled. In contrast, negative thermal expansion materials exhibit the opposite behavior. In this paper, we present a metamaterial that expands both when heated and cooled. The unit cell configuration is crafted by embedding two isosceles triangular structures composed of high thermal expansion materials within a re-entrant hexagonal honeycomb framework. Initially, the bases of the two isosceles triangles are in contact. The metamaterial exhibits two deformation states under different external loads. Analytical formulas for the equivalent parameters were derived based on classical beam theory within the regime of small deformation. Finite element simulations were conducted to validate the accuracy of these analytical formulas. The influence of geometric parameters on the metamaterial is discussed in detail. The results demonstrate that the metamaterial can exhibit excellent multi-functional properties within a small range of deformation, including instantaneous sign-variable coefficients of thermal expansion and Poisson's ratios, along with significantly distinct tensile and compressive stiffnesses. This metamaterial consistently exhibits expansive characteristics regardless of variations in ambient temperature. Additionally, the material always expands laterally regardless of the sign of uniaxial loads. Based on these properties, the metamaterial can be applied to fasteners in the aerospace industry that require permanent locking, ensuring stability in various temperature and mechanical load conditions.

High temperature tribological response of Fe-2Cu-0.8C-CaF2 self-lubricating composites at high speeds

In this work, Fe-2Cu-0.8C-CaF2 self-lubricating composites with calcium fluoride solid lubricant (3 □ 12 wt.%) were examined for their friction and wear at 5 and 10 m/s, at 500 °C. Addition of CaF2 decreased density and hardness of composites. During sliding, materials gained weight due to oxidation. Compared to the base matrix (Fe-2Cu-0.8C), composites showed lower weight gain and lower coefficient of friction. Increase in porosity with CaF2 content increased oxidation resulting in higher weight gain and increased friction due to wear debris abrasion. Increase in speed reduced weight gain due to higher material loss. Adhesion was the dominant wear mechanism in base matrix; delamination and wear debris abrasion in composites. Temperature rise at sliding surfaces was theoretically estimated. Increase in speed increased temperature, which reduced friction due to softening and shearing of solid lubricant. Composite with 3 wt.% CaF2 showed least surface damage and 6 wt.% showed lowest coefficient of friction, i.e., lower by 16% and 10% at 5, 10 m/s than base matrix. Tribological response of the composites to a broad range of applied parameters, viz. speed, load and temperature taken from earlier works and present work is briefly summarized. The study suggests the dominant role of CaF2 content and the wear debris in altering the tribological response. Further, the stability of the developed composites at high temperature and high load conditions was also established. The study suggests that the developed composites could serve high-load and high-temperature applications for heavy machinery such as bearings, shafts and gears.

A simple phenomenological model for recovery behaviors of amorphous thermoset‐based shape memory polymers via a time‐varying viscosity

AbstractShape memory polymers are a typical class of smart materials with wide potential applications. Mathematically modeling their thermomechanical behaviors with both simplicity and accuracy is challenging. In this work, a time‐varying viscosity model was introduced to investigate amorphous thermoset‐based shape memory polymers, with a special focus on recovery behaviors. This model employs only a varying viscosity to describe both the mechanism of strain storage and release during the shape memory cycle and the modulus‐temperature trend, along with a phenomenological description for the structural transition. Furthermore, the model effectively captures the effect of temperature rates and load conditions on recovery behaviors by tracking the evolution of parameter τ. This parameter shares the same dimension as time and serves as a phenomenological indicator of the chain mobility. Moreover, the parameter τ exhibits similar values among diverse materials at a specific characteristic temperature, providing a simple way to estimate the extent of recovery.Highlights Introduced a simple phenomenological model to reproduce recovery behaviors and depict the modulus‐temperature trend. Both simulation and prediction results exhibit good agreement with tests. Effects of heating rates and load conditions can be traced by the model. The key model parameter τ possesses engineering and physical significance.

Experimental study on the thermal performance of a liquid-cooled heat sink integrating heat pipes for dual CPU servers

The increasing power consumption of server CPUs poses a challenge for data center cooling. In this work, a liquid-cooled heat pipe heat sink (LHPHS) with compactly arranged heat pipes is designed and fabricated for CPU cooling in dual CPU servers. Water is selected as the working fluid in the heat pipes. Experiments are conducted to explore the heat dissipation potential of LHPHS under high inlet coolant temperature and high heat load conditions, and to investigate the operational stability of LHPHS under the conditions of uneven heat generation between two CPUs. Furthermore, a one-dimensional thermal resistance network and numerical model of the LHPHS are established to quantitatively analyze the thermal resistance distribution of LHPHS and the variation of thermal resistance with coolant flow rate. The results show that, firstly, the LHPHS operates stably under high inlet coolant temperature and high heat load conditions, meeting the heat dissipation requirements of up to 37.5 W/cm2 with a coolant flow rate of 1 L/min and inlet coolant temperature of 35℃. Secondly, the LHPHS exhibits excellent performance in controlling temperature difference between CPUs and even when there is discrepant heat generation between them. Thirdly, the LHPHS performs a low thermal resistance, measuring 0.044 ℃/W at a coolant flow rate of 0.5 L/min, and this resistance further decreases as the flow rate increases. Additionally, it is observed that the thermal resistance of the liquid-cooled plate decreases with the increasing flow rate, and heat transfer within the heat pipes becomes a critical aspect under high coolant flow rates. Therefore, reducing the thermal resistance of the heat pipe is crucial for the thermal performance improvement of the LHPHS.

Optimizing the subcritical water valorization of insect (Hermetia illucens l.) farming waste for biodiesel production

To counter the proliferation of secondary waste streams generated on insect (black soldier fly) farms, the present study integrated green water technology and acid-catalyzed transesterification as a basis to assess further value extraction potentials. By valorizing the waste streams, a process was developed to promote the circular economy paradigm. In this regard, wastes generated from a local insect farm were initially subjected to subcritical water extraction (SWE) for lipid recovery. The SWE process was optimized such that an enhanced lipid yield of 13.31 wt% was obtained at temperature, time, and solid loading conditions of 236.8 °C, 10 min of extraction, and 1 g/ 100 mL respectively. The lipids recovered were then subjected to an acid-catalyzed transesterification reaction for the production of a fatty acid methyl ester (FAME) mixture. A preliminary economic assessment of the process was also undertaken. The results showed that the wastes had the potential to be economically employed in the production of biodiesel that satisfied fuel property standards. In addition, the potential of employing the side streams as an animal feed was also highlighted due to the determined dominance of oligopeptides, which are known for their favorable bioactive properties. The results indicated that insect farming waste is a promising renewable source for high-quality biodiesel and animal feed production through the environmentally friendly biorefinery.

Damage identification in concrete under impact loading at varying temperatures using voltage strain relations technique: an experimental and numerical study

Impact-loaded concrete structures cause severe and rapid damage, resulting in significant property and human life loss. As the temperature rises, the damage caused by impact loading becomes increasingly severe. Concrete structures need structural health monitoring (SHM) to avoid this damage and loss. In this study, the voltage strain relation technique was used to identify the damaged state of concrete under impact loads at various temperature conditions experimentally and numerically. For this purpose, an experimental study was performed on concrete cube specimens in which different piezo configurations (surface bonded, non-bonded, and jacketed) were installed to acquire the voltage data. Before applying an impact load to the top surface of the concrete specimen, it was preheated at 50 °C, 100 °C, and 150 °C to provide the temperature effect, and then a free-falling iron ball was dropped from 3 m heights on the top of the specimens. Furthermore, finite element analysis has been carried out to validate the experimental results with analytical results. The experimental results show that the voltage strain relation technique is well capable of detecting the damage in concrete under the temperature and impact loading conditions. The maximum absolute voltage value (Vp) of 17.11 V was recorded for the jacketed sensors under an impact height of 3 m at 100 °C. All the piezo sensor configurations are capable of finding the damage. Jacketed sensors are more efficient in the health assessment of concrete in terms of voltage strain relations. In terms of strain values, the analytical results are in good agreement with the experimental results.

Improving properties of h-BN/GH4169 self-lubricating composites prepared using nickel coated h-BN powders

ABSTRACT The service conditions of high temperature and heavy load of aero-engine require high-temperature self-lubricating composites with high strength, low wear and long life. Hence, the high-level objective of this study is to regulate the interface between the substrate and hexagonal boron nitride (h-BN) lubricant in GH4169 nickel-based high-temperature self-lubricating composites to improve the interfacial bonding strength and the overall performance. Electroless plating method was adopted to coat nickel on h-BN, and the dense high-temperature self-lubricating composites were fabricated through hot-pressing sintering. The effects of nickel coating on h-BN on the microstructure, mechanical properties and high-temperature tribological behaviors of composites were analyzed in detail, and the lubrication mechanism was also elucidated. The results illustrate the Ni@h-BN/GH4169 composites with addition of chemically modified lubricant particles have excellent mechanical properties and lubrication and wear reduction properties, compared to h-BN/GH4169 composites. This is mainly due to the introduction of nickel coating contributed to the distribution uniformity of h-BN in the matrix, and the wettability between h-BN and the substrate together with interfacial bonding strength were enhanced as well. This work provides an insight to overcome the challenges facing the technology when using GH4169 nickel-based self-lubricating composites in manufacturing of mechanical components in aerospace.

Study on the VCRplus Back-Up Roll Contour of 1500 mm CVC Mill

The back-up rolls of hot strip mills wear considerably under the conditions of high temperature and heavy load, which affects the roll service period and the stability of strip profile control. Serious uneven wear, short service periods, and spalling problems occurred on conventional back-up rolls of upstream stand CVC mills in 1500 mm continuous hot rolling production lines. Through finite element simulations, the problems are determined to be caused by the configuration of a flat roll contour of the back-up roll and the CVC roll contour of the work roll, which leads to uneven contact pressure between the rolls. The wear distribution form is ‘anti-CVC’ shape, and there is peak contact pressure between the rolls on both sides of the roll body. In particular, the long-term negative shifting of CVC on site further increases the peak contact pressure between the rolls, resulting in uneven wear and spalling accident. Based on the design technology of VCR back-up roll contours with variable contact lengths, and considering the cooperation between the middle of the back-up roll and the CVC work roll contour, the roll contour of the back-up roll has been improved. The designed VCRplus roll contour was analyzed and evaluated by finite element simulation, including the distribution of contact pressure between rolls, the control effect of bending force, and the transverse stiffness of the roll gap. The simulation results show that the VCRplus roll contour can effectively improve the uneven distribution of contact pressure between the rolls, and effectively improve the control effect of bending force and the transverse stiffness of the roll gap. Industrial tests demonstrate that VCRplus back-up roll contours have the advantages of uniform back-up roll wear, enhanced self-sustaining of the roll contour, and further extension of the back-up roll service life. The roll contour has now stably been put into industrial production, and the rolling capacity during the back-up roll service period has been extended from 150,000,000 kg to 250,000,000 kg.

Temperature Field and Stress Analysis of the Heavy-Concrete Transfer-Purge Chamber of the Nuclear Power Plant.

A transfer-purge chamber (TPC) is a double-steel-plate, heavy-concrete, curved-surface composite structure composed of steel plates, heavy concrete, and shear connectors. It is an important facility in the external refueling system of a nuclear power plant (NPP), providing a safe and reliable biological shielding space for reactor refueling operations. Temperature load is one of the most important factors that must be considered in the design of NPP structures. The temperature loads experienced by the TPC during its life cycle include those encountered in both normal and abnormal operation, which are distinct. In this study, we investigated the steady state and transient-state temperature fields and stresses of a TPC structure under normal operation and after 48 h of abnormal operation, respectively, which were calculated using Abaqus finite element software and the directly coupled method. During normal operation, the temperature field of the structure shows relatively uniform changes, and the temperature gradient of the internal concrete in the direction of its thickness has a constant value of 0.245 °C/cm. At the junction between the transfer and purge sub-chambers of the TPC, under the influence of wall curvature and deformation constraints, the maximum tensile strain of heavy concrete is 8.84 × 10-3, the maximum compressive strain is 2.04 × 10-3, the peak stress of the steel plate is 98.305 MPa, and the peak stress of the stud is 306.725 MPa. After 48 h of abnormal operation, the temperatures of the inner surface of the heavy concrete of the wall, the inner steel plate of the wall, the outer surface of the heavy concrete of the wall, and the inner steel plate of the wall increased by 8.12, 8.11, 0.31, and 0.30 °C, respectively. The tensile strain of the heavy concrete of the wall increased significantly by 52.64%, and the compressive strain of the concrete increased by 67.33%, whereas the stresses of the studs and steel plates increased by only 1.57% and 6.79%, respectively. These results show that the change in the temperature field greatly influences the stress and strain on the TPC structure. As measures for mitigating the development of this unfavorable situation of temperature stress concentration, the temperature operating range should be rationally controlled or the junction structure between the transfer and purge sub-chambers of the TPC optimized accordingly. The results of our study can provide basic data for a dynamic analysis of the TPC under conditions of combined earthquake and temperature loads.

Investigations on the long-term skid resistance of epoxy asphalt mixture based on accelerated loading test

Under long-term vehicle loads and large attenuation degrees, asphalt pavements are expected to have reduced slip resistance that does not meet the code requirements, thus impacting driving safety. Epoxy asphalt mixture has been widely used in road construction throughout recent years. Accordingly, it is necessary to explore the long-term skid resistance of epoxy asphalt mixture. Therefore, based on the indoor accelerated loading testing methodology, this paper investigates the anti-skidding performance attenuation of epoxy asphalt and SBS-modified asphalt mixtures at room and high temperatures. The rule of skidding resistance of asphalt mixture with loading times is analyzed, and the feasibility of epoxy asphalt in improving the long-term skid resistance of asphalt pavement is also explored. In general, the study results have shown that the decay rates of British Pendulum Number (BPN), the mean texture depth (MTD), and mean profile depth (MPD) epoxy asphalt mixtures are lower than those of SBS-modified asphalt ones under normal and high temperature loading conditions. Moreover, the fractal dimension of the epoxy asphalt mixture is larger and decays more slowly, and its section texture can be preserved to a greater extent during the loading process. Besides, it is observed that epoxy asphalt mixtures have better long-term skid resistance and greater retention of section texture than the SBS-modified asphalt ones.

Plastic collapse analysis in multiaxially loaded defective pipe specimens at different temperatures

A comprehensive numerical investigation is carried out using a newly developed constitutive model to describe failure at low temperatures in multiaxially loaded cracked pipes made of 316L stainless steel. The kinetic phase transformation and the temperature-dependent fracture criterion are implemented to accurately capture the mechanical response at different temperature levels. Although experimental observations of these simulations were not available, their results were quite consistent with some already published results obtained on similar materials and loading conditions at room temperature. The results indicate that the existing multiaxial plastic collapse failure criterion, including shearing, still provides a fail-safe design margin for low temperature loading conditions, including internal pressure. Moreover, martensite kinetic phase transformation plays an important role, especially during straining at low temperatures.

Improvement of surface properties of alloy constructional steel with ultrasonic composite strengthening modification

The key components of the automatic gun are subjected to the severe working condition of high temperature, transient state and continuous strong impact load in the shooting process, the surface of which using the alloy constructional steel is prone to fatigue cracks and gradual expansion, resulting in the fracture of the key components and the fault of the automatic gun. To improve the lifespan of the automatic gun, ultrasonic composite strengthening modification treatment (UCSM) was employed to improve the surface properties of alloy constructional steel in the present work. The three aspects of surface roughness, surface hardness and friction-wear properties, in comparison with those of the traditional dry cutting and advanced ultrasonic-rolling surface modification (AURSM), were characterized. The results show that the surface roughness of the samples after the ultrasonic composite strengthening modification fluctuates by about 0.31 μm, and the surface hardness increases by about 23.5% when compared with the cutting hardness, and the friction-wear properties of the samples has been increased by more than 75%. Ultrasonic composite strengthening modification can increases the local residual compressive stress on the material surface, which endows the material with better surface properties.

Nonlinear Constitutive Model of High-Temperature Viscoelastic Deformation of Gussasphalt Concrete

To accurately evaluate the high-temperature stability of cast asphalt concrete, based on the traditional viscoelastic mechanical model, this paper innovatively improves the traditional viscoelastic mechanical model considering the conditions of temperature and dynamic load and deduces the viscoelastic constitutive model of high-temperature deformation performance of cast asphalt concrete, using a dynamic penetration test (DPT) to regress improved the Burgers model parameters and verify the model’s applicability and reliability. The results show that for the modified Burgers model parameters, E1, E2, A, and η2 decrease with increasing temperature, while parameter B increases with the increase of temperature. The high-temperature deformation of cast asphalt concrete is mainly related to η1, and η1 decreases, and deformation increases with the increase in temperature. With the increase in loading times, the dynamic penetration of cast asphalt concrete (AC) gradually increases, that is, when the greater the permanent deformation is. When the specimen is loaded 3000 times, the dynamic penetration value at 60°C is about 1.237 mm, and the dynamic penetration value at 50°C is about 0.819 mm. Under other loading times, the permanent deformation of the specimen at 60°C is much greater than that at 50°C. There is a good fit between the mechanical model derived from the viscoelastic theory and the measured test data, and the correlation coefficient is greater than 0.98, indicating that the model can accurately describe the permanent deformation law of GA under periodic semivector sinusoidal pulse load at high temperatures. The research results of this paper provide a solid theoretical basis for the promotion and application of cast asphalt concrete, and the method has wide applicability in practical engineering.

Multiscale simulation of temperature- and pressure-dependent nonlinear dynamics of PMMA/CNT composite plates

Owing to the excellent mechanical properties, polymethyl methacrylate (PMMA)/carbon nanotube (CNT) composite has been increasingly adopted in the aerospace field, which is usually subjected to various temperature conditions and supersonic aerodynamic loads. Using a molecular dynamics (MD)-based multiscale simulation, the nonlinear forced vibration of PMMA/CNT composite plate is investigated under coupled temperature and aerodynamic load conditions. The longitudinal, transverse and shear moduli of PMMA/single-walled CNT (SWCNT) nanocomposite obtained from MD simulation at different temperature and pressure levels are substituted into the extended rule of mixtures to establish the constitutive equations of PMMA/CNT composite plate. Meanwhile, Poisson’s ratio and thermal expansion coefficient of nanocomposite are used in the constitutive equations. Based on the third-order shear deformation theory, von Karman nonlinear strain–displacement relation and Hamilton’s principle, the partial differential equation of composite plate is derived, which is reduced into a set of coupled ordinary differential equations by applying Galerkin method and is solved using the fourth-order Runge–Kutta method. The bifurcation diagrams, phase portraits, time histories and Poincare maps of composite plate are obtained under the complex loads including transverse harmonic excitation and aerodynamic pressure, which are applied to analyze the dynamic characteristics of system. This study reveals the nonlinear dynamic characteristics of PMMA/CNT composite plate, which contributes to the prediction of long-term performance of composite materials in aerospace field.

Wear Resistance Mechanism of Sub-Nano Cu3P Phase Enhanced the Cu-Pb-Sn Alloy

High Cu-Pb-Sn, as the material for bimetallic cylinder block, is widely used in the selection of wear-resistant parts due to its excellent wear reduction, thermal conductivity, fatigue resistance, and strong bearing capacity, such as bearings and bearing bushes, aerospace pump rotor, turbine and guide plate, etc. However, because its wear resistance is not enough to meet the harsh conditions of high temperature, high speed, and heavy load, the research on high wear resistance Cu-Pb-Sn materials has important theoretical significance and application value for the application of bimetallic materials. ZCuPb20Sn5 alloy was taken as the research object to analyze the influence mechanism of its different microstructure and mechanical properties on the friction and wear properties of alloy materials. Friction experiments under two conditions of oil lubrication and dry friction were carried out on the MMW-1A pin-on-disc friction and wear testing machine. The wear resistance and wear mechanism of ZCuPb20Sn5alloy under the action of Cu3P were discussed, and a high wear-resistant Cu-Pb-Sn alloy for bimetal cylinder block was prepared. The results show that with the increase of P content, both the friction coefficient and wear rate decrease, and the wear reduction of ZCuPb20Sn5 alloy increases. Under oil lubrication conditions, the friction coefficient decreases by 21.4% and the wear rate decreases by 85.5% compared with that without adding P. The friction-reducing and wear-resistant properties of ZCuPb20Sn5 alloy materials are increased. In dry friction and oil lubrication, the mass wear amount of ZCuPb20Sn5 alloy material decreases with the increase of P element addition, and the change rule of alloy wear amount is consistent under the two methods. In the process of friction and wear, adhesive wear occurs, and the wear amount of the alloy material increases. With the increase of P content, the lead particles are refined and evenly distributed, which promotes the formation of a uniform self-lubricating lead film during the friction process and reduces the degree of adhesive wear. The appearance of Cu3P reduces the contact area of the friction surface and weakens the adhesive wear, so the wear rate is reduced.