DAMAGE MECHANISM ANALYSIS OF 2D 1×1 BRAIDED COMPOSITES UNDER UNIDIRECTIONAL TENSION

Coupling with the periodical displacement boundary condition,a representative volume element(RVE) model is established to simulate the progressive damage behavior of 2D1×1 braided composites under unidirectional tension by using the nonlinear finite element method.Tsai-Wu failure criterion with various damage modes and Mises criterion are considered for predicting damage initiation and progression of yarns and matrix.The anisotropic damage model for yarns and the isotropic damage model for matrix are used to simulate the microscopic damage propagation of 2D1×1braided composites.Murakami′s damage tensor is adopted to characterize each damage mode.In the simulation process,the damage mechanisms are revealed and the tensile strength of 2D1×1braided composites is predicted from the calculated average stress-average strain curve.Numerical results show good agreement with experimental data,thus the proposed simulation method is verified for damage mechanism analysis of 2D braided composites.

Influence of solution treatment on microstructure and properties of in-situ Mg_2Si/AZ91D composites

The influence of solution treatment on the microstructure and properties of Mg2Si/AZ91D composites fabricated from Mg-SiO2 system via in-situ processing method was investigated.The results show that coarse Chinese script shape Mg2Si phases can be formed by adding SiO2 into AZ91D magnesium alloy with Si content up to 1.5% of the alloy melt.During solution treatment,the morphology and distribution of the coarse Chinese script shape Mg2Si phases are modified.Meanwhile,the β-Mg17Al12 phase is dissolved into the magnesium matrix.With increasing holding time,the coarse Mg2Si phases tend to dissolve,break and spheroidize.After solution treatment at 420 ℃ for 16 h,Mg2Si phases become the finest and relatively well-distributed phase.The tensile strength and elongation are increased by 14.9% and 38.9%,respectively.It is believed that the Mg2Si phases continuously dissolve and break,and finally the spheroidized Mg2Si particles are obtained due to the interface tension of Mg2Si/Mg interface.

Trap analysis of composite 2D-3D channel in AlGaN/GaN/graded-AlGaN:Si/GaN:C multi-heterostructure at different temperatures

The graded AlGaN:Si back barrier can form the majority of three-dimensional electron gases(3DEGs)at the GaN/graded AlGaN:Si heterostructure and create a composite two-dimensional(2D)-three-dimensional(3D)channel in AlGaN/GaN/graded-AlGaN:Si/GaN:C heterostructure(DH:Si/C).Frequency-dependent capacitances and conductance are measured to investigate the characteristics of the multi-temperature trap states of in DH:Si/C and AlGaN/GaN/GaN:C heterostructure(SH:C).There are fast,medium,and slow trap states in DH:Si/C,while only medium trap states exist in SH:C.The time constant/trap density for medium trap state in SH:C heterostructure are(11μs-17.7μs)/(1.1×10^13 cm^-2·eV^-1-3.9×10^13 cm^-2·eV^-1)and(8.7μs-14.1μs)/(0.7×10^13 cm^-2·eV^-1-1.9×10^13 cm^-2·eV^-1)at 300 K and 500 K respectively.The time constant/trap density for fast,medium,and slow trap states in DH:Si/C heterostructure are(4.2μs-7.7μs)/(1.5×10^13 cm^-2·eV^-1-3.2×10^13 cm^-2·eV^-1),(6.8μs-11.8μs)/(0.8×10^13 cm^-2·eV^-1-2.8×10^13 cm^-2·eV^-1),(30.1μs-151μs)/(7.5×10^12 cm^-2·eV^-1-7.8×10^12 cm^-2·eV^-1)at 300 K and(3.5μs-6.5μs)/(0.9×10^13 cm^-2·eV^-1-1.8×10^13 cm^-2·eV^-1),(4.9μs-9.4μs)/(0.6×10^13 cm^-2·eV^-1-1.7×10^13 cm^-2·eV^-1),(20.6μs-61.9μs)/(3.2×10^12 cm^-2·eV^-1-3.5×10^12 cm^-2·eV^-1)at 500 K,respectively.The DH:Si/C structure can effectively reduce the density of medium trap states compared with SH:C structure.

Organic-2D composite material-based RRAM with high reliability for mimicking synaptic behavior

The field of artificial intelligence and neural computing has been rapidly expanding due to the imple-mentation of resistive random-access memory(RRAM)based artificial synaptic.However,the low flexibility of conventional RRAM materials hinders their ability to mimic synaptic behavior accurately.To overcome such limitation,organic-2D composites with high mechanical properties are proposed as the active layer of RRAM.Moreover,we enhance the reliability of the device by ZrO_(2)insertion layer,resulting in stable synaptic performance.The Ag/PVA:h-BN/ZrO_(2)/ITO devices show stable bipolar resistive switching behavior with an ON/OFF ratio of over 5×10^(2),a~2400 cycles endurance and a long retention time(>6×10^(3)s),which are essential for the development of high-performance RRAMs.We also study the possible synaptic mechanism and dynamic plasticity of the memory device,observing the transition from short-term potentiation(STP)to long-term potentiation(LTP)under the effect of continuous voltage pulses.Moreover,the device exhibits both long-term depression(LTD)and paired-pulse facili-tation(PPF)properties,which have significant implications for the design of organic-2D composite material RRAMs that aim to mimic biological synapses,representing promising avenues for the devel-opment of advanced neuromorphic computing systems.

Modified micro-mechanics based multiscale model for progressive failure prediction of 2D twill woven composites

To consider fiber random distribution at the microscale for the multiscale model based on the micro-mechanics failure(MMF)theory,clustering method is used for the extraction of amplification factors.As the clustering method is a kind of unsupervised machine learning method,the elements with similar mechanical behavior under external loading can be included in a cluster automatically at the microscale.With this modification,the fiber random distribution model can be used for multiscale damage analysis in the framework of MMF theory.To validate the modified multiscale analysis method,progressive damage analysis of a kind of 2D twill woven composites is conducted based on different microscale models.The stress values for microscale models with fiber hexagonal and random distribution patterns are compared first.Much higher stress concentration is generated in the fiber random distribution model due to the smaller inter-fiber distance especially under longitudinal shear loading.The obtained cluster distribution results exhibit the characters of the stress distribution in the two microscale models.Thereafter,tensile and compressive responses of the 2D twill woven composite are predicted with the modified multiscale analysis method and accuracy of the method is verified through comparison with published experimental results.From the simulation results,it can be found that the matrix damage initiation from the model based on the fiber random distribution model is premature compared with that from the model based on the fiber hexagonal distribution model.Besides,under tensile loading,the damage all initiates from the fill tows and propagates to the wrap tows.However,under compressive loading,the matrix damage initiates from the wrap tows in the model based on the fiber random distribution model.

Bolt Design of Ceramic Matrix Composite and Superalloy Bolted Joint Based on Damage Failure Load

Ceramic matrix composite(CMC)and superalloy bolted joints are commonly used high temperature connection structures in aerospace and aeronautical fields.In this paper,a finite element model coupled with progressive damage analysis of 2D C/SiC composites and superalloy bolted joint was implemented to simulate the uniaxial tensile loading process by using the ABAQUS finite element software.The parametric effects of raised head bolt on stress distribution,tensile performance,and damage process were studied for the CMC⁃superalloy bolted joint structures.The results showed that the final failure load increased first to the maximum value,and then decreased with the rise of bolt diameter,bolt head diameter,and bolt head thickness,respectively.When the three parameters were 5.0 mm,9.5 mm,and 2.8 mm for the current studied bolt configuration,the joint structure gave the maximum load bearing capacity for the considered parameter ranges.It was also found that around 42%potential improvement in load bearing capacity could be achieved by very small adjustments in bolt parameters of the joints.

Effects of in-situ ZrB_2 particle on grain refinement of ZrB_2/AZ91D magnesium matrix composite

In-situ ZrB2/AZ91D magnesium matrix composite was successfully synthesized with AI/K2ZrF6＋NH4BF4 by means of Direct Melt Reaction. The fabricated ZrB2/AZ91D magnesium matrix composite through direct melt mixing method was investigated. Results from X-ray diffraction （XRD） and energy dispersive X-ray spectroscopy （EDS） confirmed the existence of ZrB2 particles in the AZ91D alloy, and most ZrB2 particles were in the size range of just several microns, some even to 100 nm. The cast specimens were studied through corrosion testing and heat treatment. The average grain size of AZ91D decreased markedly from about 250 pm to 50 IJm. In addition, the shape and size of the ,β-MglTAI12 phase as well as the morphologies of primary a-Mg in the magnesium matrix composite were greatly changed. The network structure of the β-MglTAI12 phase was broken into small blocks and the size of a-Mg decreased significantly.

Two-dimensional MOF Cu-BDC nanosheets/ILs@silica core-shell composites as mixed-mode stationary phase for high performance liquid chromatography

Here,silica microspheres were decorated with two-dimensional metal-organic frameworks(2 D MOFs)nanosheets and ionic liquids,and evaluated as the mixed-mode stationary phase for chromatographic separation.The ionic liquids were used to assist the synthesis of 2 D MOFs nanosheets,and also acted as adhesives among the nanosheets and silica.In contrast with the 2 D MOFs-based column without ionic liquids and commercial columns,the prepared column exhibited enhanced chromatographic separation performance for partially hydrophilic compounds such as alkaloids,sulfonamides and antibiotics,etc.In addition to excellent chromatographic repeatability and stability,it has also been verified that the composites could be easily and repeatedly prepared.The relative standard deviation of the retention time of the same type of analyte between the three batches of materials was ranging from 0.21%to 1.7%.In short,these results indicated that the synthesized composites were promising separation material for liquid chromatography,which made it possible to broaden the application of 2 D MOFs in the field of chromatography.

Real-time damage analysis of 2D C/SiC composite based on spectral characters of acoustic emission signals using pattern recognition

In this study,unsupervised and supervised pattern recognition were implemented in combination to achieve real-time health monitoring.Unsupervised recognition(k-means++)was used to label the spectral characteristics of acoustic emission(AE)signals after completing the tensile tests at ambient temperature.Using in-plane tensile at 800 and 1000°C as implementing examples,supervised recognition(K-nearest neighbor(KNN))was used to identify damage mode in real time.According to the damage identification results,four main tensile damage modes of 2D C/SiC composites were identified:matrix cracking(122.6–201 kHz),interfacial debonding(201–294.4 kHz),interfacial sliding(20.6–122.6 kHz)and fiber breaking(294.4–1000 kHz).Additionally,the damage evolution mechanisms for the 2D C/SiC composites were analyzed based on the characteristics of AE energy accumulation curve during the in-plane tensile loading at ambient and elevated temperature with oxidation.Meanwhile,the energy of various damage modes was accurately calculated by harmonic wavelet packet and the damage degree of modes could be analyzed.The identification results show that compared with previous studies,using the AE analysis method,the method has higher sensitivity and accuracy.

MoS_(2)core-shell nanoparticles prepared through liquid-phase ablation and light exfoliation of femtosecond laser for chemical sensing

Molybdenum disulfide(MoS_(2))-based nanostructures are highly desirable for applications such as chemical and biological sensing,photo/electrochemical catalysis,and energy storage due to their unique physical and chemical properties.In this work,MoS_(2)core-shell nanoparticles were first prepared through the liquid-phase processing of bulk MoS2by a femtosecond laser.The core of prepared nanoparticles was incompletely and weakly crystalline MoS_(2);the shell of prepared nanoparticles was highly crystalline MoS_(2),which wrapped around the core layer by layer.The femtosecond laser simultaneously achieved liquid-phase ablation and light exfoliation.The formation mechanism of the core-shell nanoparticles is to prepare the nanonuclei first by laser liquid-phase ablation and then the nanosheets by light exfoliation;the nanosheets will wrap the nanonuclei layer by layer through van der Waals forces to form core-shell nanoparticles.The MoS_(2)core-shell nanoparticles,because of Mo-S bond breakage and recombination,have high chemical activity for chemical catalysis.Afterward,the nanoparticles were used as a reducing agent to directly prepare three-dimensional(3D)Au-MoS_(2)micro/nanostructures,which were applied as surface-enhanced Raman spectroscopy(SERS)substrates to explore chemical sensing activity.The ultrahigh enhancement factor(1.06×10^(11)),ultralow detection limit(10-13M),and good SERS adaptability demonstrate highly sensitive SERS activity,great ability of ultralow concentration detection,and ability to detect diverse analytes,respectively.This work reveals the tremendous potential of 3D Au-MoS_(2)composite structures as excellent SERS substrates for chemical and biological sensing.