Throughout the composite structure’s lifespan,it is subject to a range of environmental factors,including loads,vibrations,and conditions involving heat and humidity.These factors have the potential to compromise the...Throughout the composite structure’s lifespan,it is subject to a range of environmental factors,including loads,vibrations,and conditions involving heat and humidity.These factors have the potential to compromise the integrity of the structure.The estimation of the fatigue life of composite materials is imperative for ensuring the structural integrity of these materials.In this study,a methodology is proposed for predicting the fatigue life of composites that integrates ultrasonic guided waves and machine learning modeling.The method first screens the ultrasonic guided wave signal features that are significantly affected by fatigue damage.Subsequently,a covariance analysis is conducted to reduce the redundancy of the feature matrix.Furthermore,one-hot encoding is employed to incorporate boundary conditions as features,and the resulting data undergoes preprocessing to form a sample library.A composite fatigue life prediction model has been developed,employing the aforementioned sample library as the input source and utilizing remaining life as the output metric.The model synthesizes the strengths of convolutional neural networks(CNNs)and bidirectional long short-term memory networks(BiLSTMs)while leveraging Bayesian optimization(BO)to enhance the optimization of hyperparameters.The experimental results demonstrate that the proposed BO-CNN-BiLSTM model exhibits superior performance in terms of prediction accuracy and reliability in the damage regression task when compared to both the BiLSTM and CNN-BiLSTM models.展开更多
This work was dedicated to performing surface oxidation and coating treatments on carbon fibers （CF） and investigating the changes of fiber surface properties after these treatments, including surface composition, r...This work was dedicated to performing surface oxidation and coating treatments on carbon fibers （CF） and investigating the changes of fiber surface properties after these treatments, including surface composition, relative volume of functional groups, and surface topography with X-ray photoelectron spectroscopy （XPS） and atom force microscopy （AFM） technology. The results show that, after oxidation treatments, interfacial properties between CF and non-polar polyarylacetylene （PAA） resin are remarkably modified by removing weak surface layers and increasing fiber surface roughness. Coating treatment by high char phenolic resin solution after oxidation makes interface of CF/PAA composites to be upgraded and the interfacial properties further bettered.展开更多
In order to explore the effect of artificial accelerated aging temperature on the performance of carbon fiber/epoxy resin composites,we used artificial seawater as the aging medium,designed the aging environment of se...In order to explore the effect of artificial accelerated aging temperature on the performance of carbon fiber/epoxy resin composites,we used artificial seawater as the aging medium,designed the aging environment of seawater at different temperatures under normal pressure,and studied the aging behavior of carbon fiber/epoxy composites.The infrared spectroscopy results show that,with the increase of aging temperature,the degree of hydrolysis of the composite is greater.At the same time,after 250 days of aging of artificial seawater at regular temperature,40 and 60 ℃,the moisture absorption rates of composite materials were 0.45%,0.63%,and 1.05%,and the retention rates of interlaminar shear strength were 91%,78%,and 62%,respectively.It is shown that the temperature of the aging environment has a significant impact on the hygroscopic behavior and mechanical properties of the composite,that is,the higher the temperature,the faster the moisture absorption of the composite,and the faster the decay of the mechanical properties of the composite.展开更多
Maxacalcitol,the 22-oxa-derivative of 1a,25-dihydroxyvitamin D3,has been used as an antihyperparathyroidism and antipsoriatic drug.In this paper,an alternative synthetic route has been developed using commercially ava...Maxacalcitol,the 22-oxa-derivative of 1a,25-dihydroxyvitamin D3,has been used as an antihyperparathyroidism and antipsoriatic drug.In this paper,an alternative synthetic route has been developed using commercially available vitamin D2as the starting material.In addition,as a key intermediate,the asymmetric synthesis of 20（S）-alcohol 14 with the chiral auxiliary（R-CBS） was described for the first time.This new synthetic route afforded Maxacalcitol with improved overall yield（13.9%） in eleven steps.展开更多
The twisters for composed of anisotropic material were designed and manufactured.And two kinds of directional-composites were made:one was fiber direction vertical with frictional interface and another was parallel wi...The twisters for composed of anisotropic material were designed and manufactured.And two kinds of directional-composites were made:one was fiber direction vertical with frictional interface and another was parallel with frictional interface and moving direction.By varying the proportions of epoxy resin and fiber and arranging the orientations of fiber,the composites anisotropy along longitudinal and circumferential were got.Using density measurement,the mass fraction of resin and fiber were calculated.According to composite meso-scopic mechanics,the elasticity constants of composite were analyzed and calculated.The composite different thicknesses were sliced,and attach to the rotor,then the load characteristics,no-load speed,stop load of ultrasonic motor(USM)were test.The output properties of USM with 0.6 mm thickness composite were superior.The effect of friction material on ultrasonic motor was analyzed.Elastic modulus,thickness and micro-morphology of material are main factors which affect characteristics of ultrasonic motor.展开更多
The polycarbosilane(PCS)precursor for SiC with high molecular weight and medium molecular weight distribution was synthesized from polydimethylsilane at normal pressure.The chemical formula,the number average molecula...The polycarbosilane(PCS)precursor for SiC with high molecular weight and medium molecular weight distribution was synthesized from polydimethylsilane at normal pressure.The chemical formula,the number average molecular weight,and the polydispersivity index of the synthesized PCS are SiC_(1.94)H_(5.01)O_(0.028),1135,and 1.66,respectively,which can be attributed to the higher reaction temperature used for polymerization.The polymer to ceramic conversion of PCS was completed at 900℃with a ceramic yield of 85%.The crystallization started at 1100℃,and at 1200℃,well resolved peaks ofβ-SiC were formed with small amount ofα-cristobalite.The X-ray diffraction(XRD)and transmission electron microscopy(TEM)studies indicated the presence of nanocrystallineβ-SiC.展开更多
The synthesis of polycrystalline aluminum oxynitride （AlON） powders was investigated by the carbothermal reduction and ni- tridation （CRN） of amorphous precursor obtained by wet chemical processing. Co-precipitati...The synthesis of polycrystalline aluminum oxynitride （AlON） powders was investigated by the carbothermal reduction and ni- tridation （CRN） of amorphous precursor obtained by wet chemical processing. Co-precipitation processing was employed to achieve amorphous precursor from AI（NO3）3 solution dispersed by nanosized carbon particles, which was composed of AI（OH）3 and C particles homogeneously. The effects of the content of carbon black, pH value, and calcination temperature on formation of A1ON phase were investigated by means of XRD, SEM and TEM, respectively. It was found that single phase AION powder could be synthesized when the resultant precursors were calcined at 1750℃ for 2 hours under flowing N2. Un- der optimal additional content of C （5.6wt%）, the resultant A1ON powders exhibited the primary particle size of about 1-3 μm with a specific surface area of 3.2 m2/g, which were superior to that of carbothermal reduction of immediate mixture of γ-A1203/C powders.展开更多
基金funded by the Key Technologies R&D Program of CNBM(2023SJYL01)Postgraduate Research&Practice Innovation Program of Jiangsu Province(SJCX24_1356).
文摘Throughout the composite structure’s lifespan,it is subject to a range of environmental factors,including loads,vibrations,and conditions involving heat and humidity.These factors have the potential to compromise the integrity of the structure.The estimation of the fatigue life of composite materials is imperative for ensuring the structural integrity of these materials.In this study,a methodology is proposed for predicting the fatigue life of composites that integrates ultrasonic guided waves and machine learning modeling.The method first screens the ultrasonic guided wave signal features that are significantly affected by fatigue damage.Subsequently,a covariance analysis is conducted to reduce the redundancy of the feature matrix.Furthermore,one-hot encoding is employed to incorporate boundary conditions as features,and the resulting data undergoes preprocessing to form a sample library.A composite fatigue life prediction model has been developed,employing the aforementioned sample library as the input source and utilizing remaining life as the output metric.The model synthesizes the strengths of convolutional neural networks(CNNs)and bidirectional long short-term memory networks(BiLSTMs)while leveraging Bayesian optimization(BO)to enhance the optimization of hyperparameters.The experimental results demonstrate that the proposed BO-CNN-BiLSTM model exhibits superior performance in terms of prediction accuracy and reliability in the damage regression task when compared to both the BiLSTM and CNN-BiLSTM models.
文摘This work was dedicated to performing surface oxidation and coating treatments on carbon fibers （CF） and investigating the changes of fiber surface properties after these treatments, including surface composition, relative volume of functional groups, and surface topography with X-ray photoelectron spectroscopy （XPS） and atom force microscopy （AFM） technology. The results show that, after oxidation treatments, interfacial properties between CF and non-polar polyarylacetylene （PAA） resin are remarkably modified by removing weak surface layers and increasing fiber surface roughness. Coating treatment by high char phenolic resin solution after oxidation makes interface of CF/PAA composites to be upgraded and the interfacial properties further bettered.
文摘In order to explore the effect of artificial accelerated aging temperature on the performance of carbon fiber/epoxy resin composites,we used artificial seawater as the aging medium,designed the aging environment of seawater at different temperatures under normal pressure,and studied the aging behavior of carbon fiber/epoxy composites.The infrared spectroscopy results show that,with the increase of aging temperature,the degree of hydrolysis of the composite is greater.At the same time,after 250 days of aging of artificial seawater at regular temperature,40 and 60 ℃,the moisture absorption rates of composite materials were 0.45%,0.63%,and 1.05%,and the retention rates of interlaminar shear strength were 91%,78%,and 62%,respectively.It is shown that the temperature of the aging environment has a significant impact on the hygroscopic behavior and mechanical properties of the composite,that is,the higher the temperature,the faster the moisture absorption of the composite,and the faster the decay of the mechanical properties of the composite.
文摘Maxacalcitol,the 22-oxa-derivative of 1a,25-dihydroxyvitamin D3,has been used as an antihyperparathyroidism and antipsoriatic drug.In this paper,an alternative synthetic route has been developed using commercially available vitamin D2as the starting material.In addition,as a key intermediate,the asymmetric synthesis of 20（S）-alcohol 14 with the chiral auxiliary（R-CBS） was described for the first time.This new synthetic route afforded Maxacalcitol with improved overall yield（13.9%） in eleven steps.
文摘The twisters for composed of anisotropic material were designed and manufactured.And two kinds of directional-composites were made:one was fiber direction vertical with frictional interface and another was parallel with frictional interface and moving direction.By varying the proportions of epoxy resin and fiber and arranging the orientations of fiber,the composites anisotropy along longitudinal and circumferential were got.Using density measurement,the mass fraction of resin and fiber were calculated.According to composite meso-scopic mechanics,the elasticity constants of composite were analyzed and calculated.The composite different thicknesses were sliced,and attach to the rotor,then the load characteristics,no-load speed,stop load of ultrasonic motor(USM)were test.The output properties of USM with 0.6 mm thickness composite were superior.The effect of friction material on ultrasonic motor was analyzed.Elastic modulus,thickness and micro-morphology of material are main factors which affect characteristics of ultrasonic motor.
文摘The polycarbosilane(PCS)precursor for SiC with high molecular weight and medium molecular weight distribution was synthesized from polydimethylsilane at normal pressure.The chemical formula,the number average molecular weight,and the polydispersivity index of the synthesized PCS are SiC_(1.94)H_(5.01)O_(0.028),1135,and 1.66,respectively,which can be attributed to the higher reaction temperature used for polymerization.The polymer to ceramic conversion of PCS was completed at 900℃with a ceramic yield of 85%.The crystallization started at 1100℃,and at 1200℃,well resolved peaks ofβ-SiC were formed with small amount ofα-cristobalite.The X-ray diffraction(XRD)and transmission electron microscopy(TEM)studies indicated the presence of nanocrystallineβ-SiC.
文摘The synthesis of polycrystalline aluminum oxynitride （AlON） powders was investigated by the carbothermal reduction and ni- tridation （CRN） of amorphous precursor obtained by wet chemical processing. Co-precipitation processing was employed to achieve amorphous precursor from AI（NO3）3 solution dispersed by nanosized carbon particles, which was composed of AI（OH）3 and C particles homogeneously. The effects of the content of carbon black, pH value, and calcination temperature on formation of A1ON phase were investigated by means of XRD, SEM and TEM, respectively. It was found that single phase AION powder could be synthesized when the resultant precursors were calcined at 1750℃ for 2 hours under flowing N2. Un- der optimal additional content of C （5.6wt%）, the resultant A1ON powders exhibited the primary particle size of about 1-3 μm with a specific surface area of 3.2 m2/g, which were superior to that of carbothermal reduction of immediate mixture of γ-A1203/C powders.
