•Interlaminar tensile (ILT) strengths and microscopic failure mechanisms of 3D needled C/C composites were studied at ultra-high temperatures (up to 2800 °C).•The V-shaped notched specimen ...compression method is effective for measurements of 3D needled C/C composites.•The ILT strengths of the 3D needled C/C composites were measured at 1200 °C, 1600 °C, 1800 °C, 2000 °C, 2400 °C, and 2800 °C.•The ILT strengths were primarily dependent on interfacial strength.
In this work, interlaminar tensile (ILT) strengths and microscopic failure mechanisms of 3D needled C/C composites were studied at ultra-high temperatures (up to 2800 °C). Experiments were conducted using the V-shaped notched specimen compression method. The measured ILT strengths compared favorably to results obtained via flatwise tension and diametral compression tests. In addition, the high-temperature transverse displacement field was measured using digital image correlation and the temperature field was measured using an infrared thermal imager. The transverse displacement and temperature fields were uniform in the gage section. The results confirm the effectiveness of this method for measurements of 3D needled C/C composites. The ILT strengths of the 3D needled C/C composites were measured at 1200 °C, 1600 °C, 1800 °C, 2000 °C, 2400 °C, and 2800 °C. The ILT strengths increased with the temperature up to 1600 °C, and then decreased in the 1600–2800 °C range. The failure mechanisms were investigated via optical microscopy. The needling fibers were pulled out, which indicates that the ILT strengths were primarily dependent on interfacial strength. It is intended that these results will provide some practical guidelines for ultra-high temperature engineering applications.
ZrB₂-based nanocomposites with and without carbon nanotubes (CNTs) as reinforcement were prepared at 1600 °C by spark plasma sintering. The effects of CNTs on the microstructure and mechanical ...properties of nano-ZrB₂ matrix composites were studied. The results indicated that adding CNTs can inhibit the abnormal grain growth of ZrB₂ grains and improve the fracture toughness of the composites. The toughness mechanisms were crack deflection, crack bridging, debonding, and pull-out of CNTs. The experimental results of the nanograined ZrB₂-CNTs composites were compared with those of the micro-grained ZrB₂-CNTs composites. Due to the small size and surface effects, the nanograined ZrB₂-CNTs composites exhibited stronger mechanical properties: the hardness, flexural strength and fracture toughness were 18.7 ± 0.2 GPa, 1016 ± 75 MPa, and 8.5 ± 0.4 MPa·m
, respectively.
Coronavirus disease 2019 (COVID-19) is sweeping the globe and has resulted in infections in millions of people. Patients with COVID-19 face a high fatality risk once symptoms worsen; therefore, early ...identification of severely ill patients can enable early intervention, prevent disease progression, and help reduce mortality. This study aims to develop an artificial intelligence-assisted tool using computed tomography (CT) imaging to predict disease severity and further estimate the risk of developing severe disease in patients suffering from COVID-19.
Initial CT images of 408 confirmed COVID-19 patients were retrospectively collected between January 1, 2020 and March 18, 2020 from hospitals in Honghu and Nanchang. The data of 303 patients in the People's Hospital of Honghu were assigned as the training data, and those of 105 patients in The First Affiliated Hospital of Nanchang University were assigned as the test dataset. A deep learning based-model using multiple instance learning and residual convolutional neural network (ResNet34) was developed and validated. The discrimination ability and prediction accuracy of the model were evaluated using the receiver operating characteristic curve and confusion matrix, respectively.
The deep learning-based model had an area under the curve (AUC) of 0.987 (95% confidence interval CI: 0.968-1.00) and an accuracy of 97.4% in the training set, whereas it had an AUC of 0.892 (0.828-0.955) and an accuracy of 81.9% in the test set. In the subgroup analysis of patients who had non-severe COVID-19 on admission, the model achieved AUCs of 0.955 (0.884-1.00) and 0.923 (0.864-0.983) and accuracies of 97.0 and 81.6% in the Honghu and Nanchang subgroups, respectively.
Our deep learning-based model can accurately predict disease severity as well as disease progression in COVID-19 patients using CT imaging, offering promise for guiding clinical treatment.
The accurate characterization of the surface microstructure of ultra-high temperature ceramics after thermal shocks is of great practical significance for evaluating their thermal resistance ...properties. In this paper, a fractal reconstruction method for the surface image of Ultra-high temperature ceramics after repeated thermal shocks is proposed. The nonlinearity and spatial distribution characteristics of the oxidized surfaces of ceramics were extracted. A fractal convolutional neural network model based on deep learning was established to realize automatic recognition of the classification of thermal shock cycles of ultra-high temperature ceramics, obtaining a recognition accuracy of 93.74%. It provides a novel quantitative method for evaluating the surface character of ultra-high temperature ceramics, which contributes to understanding the influence of oxidation after thermal shocks.
Ultra-high temperature ceramic (UHTC) composites are widely used in high-temperature environments in aerospace applications. They experience extremely complex environmental conditions during service, ...including thermal, mechanical and chemical loading. Therefore, it is critical to evaluate the mechanical properties of UHTCs subject to an environment with elevated temperature, mechanical stress and oxygen. In this paper, an experimental investigation of the uniaxial tensile properties of a ZrB
2
-SiC-graphite subject to an environment with a simultaneously elevated temperature, mechanical stress and oxygen is conducted based on a high-temperature mechanical testing system. To improve efficiency, an orthogonal experimental design is used. It is suggested that the temperature has the most important effect on the properties, and the oxidation time and stress have an almost equal effect. Finally, the fracture morphology is characterized using scanning electron microscopy (SEM), and the mechanism is investigated. It was concluded that the main fracture mode involved graphite flakes pulling out of the matrix and crystalline fracture, which indicates the presence of a weak interface in the composites.
This paper presents a simple methodology to perform a high temperature coupled thermo-mechanical test using ultra-high temperature ceramic material specimens (UHTCs), which are equipped with chemical ...composition gratings sensors (CCGs). The methodology also considers the presence of coupled loading within the response provided by the CCG sensors. The theoretical strain of the UHTCs specimens calculated with this technique shows a maximum relative error of 2.15% between the analytical and experimental data. To further verify the validity of the results from the tests, a Finite Element (FE) model has been developed to simulate the temperature, stress and strain fields within the UHTC structure equipped with the CCG. The results show that the compressive stress exceeds the material strength at the bonding area, and this originates a failure by fracture of the supporting structure in the hot environment. The results related to the strain fields show that the relative error with the experimental data decrease with an increase of temperature. The relative error is less than 15% when the temperature is higher than 200 °C, and only 6.71% at 695 °C.
Carbon fiber-reinforced silicon carbide composites (C/SiC) are widely used in lightweight aerospace structures for thermal protection due to its excellent mechanical properties. The low interfacial ...shear strength of the composites decreases its performance and limits its application. To investigate the shearing performance of C/SiC composite, interlaminar shear and in-plane shear tests were conducted. Real-time X-ray micro-computed tomography (XCT) non-destructive testing technology is an effective method for damage analysis of composite materials. The damage mechanisms of 2D plain weave C/SiC composites prepared by chemical vapor infiltration process under interlaminar shear loading are investigated using the combination of XCT and acoustic emission detection system. The in-situ XCT results reveal the damage visualization mechanisms of the composites and the damage evolution process including matrix damage, interfacial debonding and fiber fracture. The failure mechanisms and morphology of the shear effect for 2D plain weave C/SiC were analysed.
Multiscale simulation of woven composites structure remains a challenge due to extremely expensive computational cost for solving the nonlinear woven Representative Volume Element (RVE). Recently, an ...effective and efficient Reduced Order modeling method, namely Self-consistent Clustering Analysis (SCA), is proposed to solve the RVE problem. In this work, the curse of computational cost in woven RVE problem is countered using the SCA, which maintains a considerable accuracy compared with the standard Finite Element Method (FEM). The Hill anisotropic yield surface is predicted efficiently using the woven SCA, which can accelerate the microstructure optimization and design of woven composites. Moreover, a two-scale FEM×SCA modeling framework is proposed for woven composites structure. Based on this framework, the complex behavior of the composite structures in macroscale can be predicted using microscale properties. Additionally, macroscale and mesoscale physical fields are captured simultaneously, which are hard, if not impossible, to observe using experimental methods. This will expedite the deformation mechanism investigation of composites. A numerical study is carried out for T-shaped hooking structures under cycle loading to illustrate these advantages.
•For a woven composite material, the novel RVE solution method SCA greatly reduces the solution cost.•Rapid macroscale anisotropic Hill yield surface generation through SCA.•Woven structural responses prediction based on yarn and matrix properties.•Macroscale and mesoscale (woven RVE) physical fields evolution captured simultaneously.
Fibre-reinforced resin matrix composites exhibit excellent resistance to ablation, thermal insulation and mechanical properties at high temperatures, making them widely used in aerospace engineering. ...Needle-punched reinforced carbon/phenolic composites are the most commonly used structural material for solid rocket engine nozzles. However, during the working process of the engine, the mechanical behaviour under ultra-high heating rates is difficult to characterise due to extreme loads. Therefore, in this study, specimens were carbonised before testing, and an electric heating testing machine was combined with an infrared thermal imager and digital image correlation system to characterise the mechanical behaviour of carbon/phenolic at ultra-high heating rates. The results indicate that at a heating rate of 200 °C/s, the compressive modulus increases linearly with temperature, reaching 63.1 GPa at 1400 °C. The maximum compressive strength is 61.9 MPa at 1400 °C, while the minimum is 27.4 MPa at 600 °C. Referring to the high-temperature damage constitutive model, a pyrolysis damage high-temperature strengthening constitutive model was constructed, accurately describing the in-plane compression mechanical behaviour of carbon/phenolic composites.
•Temperature difference does not exceed 20 °C at ultra-high heating rates.•Mechanical properties were tested by combining ohmic heating with DIC system.•A pyrolysis damage-high temperature strengthening model was constructed.•The model accurately describes the mechanical behaviour of carbon/phenolic.
•A successful preparation of continuous gradient ceramic–polymer gradient composite with a thickness of 40 mm.•Studied the oxyacetylene ablation properties and mechanism of continuous gradient ...ceramic–polymer composite.•Put forward a novel structure concept for the integrated design of thermal protection system.
In this study, the ablation mechanism and ablation properties of continuous gradient ceramic–polymer composites were studied in an oxyacetylene environment, with the ablation heat flow being 2.38 MW/m2. The samples were prepared through six impregnation–crosslinking–pyrolysis cycles using a three-dimensional seven-directional carbon fiber preform. There were no noticeable ablation pits on the surface of ablated samples. The polysilazane coating and amorphous SiCN ceramics provided good protection for the surface of gradient material. The continuous gradient structure provides a new solution to the problems of thermal mismatch and thermal short-circuit, which are caused by the performance difference between materials.
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