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.
Compared with the traditional phenomenological method, the multiscale simulation has significant advantages. This paper presents a methodology and computational homogenization framework to predict ...the macroscale behavior of woven composites based on fiber and matrix in microscale. The major challenge conducting multiscale analysis is the huge computational cost. To improve the efficiency, one of the reduced order models, which is called the data-driven self-consistent clustering analysis (SCA), is introduced and the multiscale framework is proposed by integrating two SCA solvers from different scales. The macroscale performance of 4-H satin weave carbon/carbon composites is investigated using the proposed framework. In order to reconstruct a real microstructure representative volume element (RVE), both microscale and mesoscale architectures are observed using scanning electron microscopy (SEM) and optical microscopy, and statistical geometry features are obtained. In addition, the SCA method is also verified by comparing the results with the finite element method (FEM). The uniaxial tension process is simulated using the multiscale approach, and strain/stress fields in both mesoscale and microscale can be captured simultaneously. Moreover, the uniaxial tensile experiments are also carried out to validate this framework, which shows high efficiency and great accuracy.
In this paper, a modified double-notched specimen (MDNS) is proposed to investigate shear strength of carbon/carbon composites at ultra-high temperatures. The effects of surplus notch length on ...distribution of shear stress in the gauge area are studied using finite element method. Both standard Iosipescu method and the MDNS method are used to test shear strength of 3D needled, 3D woven, and 4D woven C/C composites at room temperature. The results are in good agreement with each other. Uniform shear strain is observed using digital image correlation (DIC) technology to confirm the proposed method. Additionally, the shear strength of these three types C/C composites are measured at 2000 °C, 2400 °C, and 2800 °C using the designed testing system. The temperature field at 2000 °C is measured using a thermal imaging system to demonstrate uniform distribution of temperature. The failure mechanisms at ultra-high temperatures are also characterized via optical microscopy.
C/SiC composites exhibit nonlinearity and dispersions in macroscopic constitutive behaviors, and both characteristics are dependent on external load. Previously, only uncertainties in elastic modulus ...have been considered, and this is not sufficient. In this paper, a characterization method for uncertainty in material behavior of a C/SiC composite is established by introducing parameter uncertainties into the constitutive model. Two types of uncertainties related to material constants and functions of the constitutive model are considered and quantified with experimental data. Tolerance-interval and optimized kernel-density methods are employed to tackle sparse data condition. The method is validated against two categories of experiments: coupon tests and tension experiments for hat-shaped components. Monte-Carlo simulation and the sparse polynomial chaos expansion method are employed to propagate the uncertainties into strain responses. The predicted uncertainties of the strains agree well with the experimental results obtained, indicating the effectiveness of the method. The method could be employed easily in uncertainty quantification of structural responses, and further, could facilitate model calibration, reliability design, and other applications for which material uncertainties are significant factors.
•A collaborative multiscale phase-field model for trans-scale fracture propagation is developed.•Information exchange between fracture modes and each of nonlinear stress–strain relationship at the ...microscopic scale and strain levels at the macroscopic scale is achieved using the proposed bridging model.•For the first time, real-time coupling between macro- and microfracture evolution and the macro-stress–strain relationship of needled carbon/carbon composites is revealed.
Owing to their inherent multiscale characteristics, cracks in fiber-reinforced composites initiate and propagate normally at the microscale level during loading, spanning spatial scales up to the macroscopic fracture failure of the material. Motivated by this phenomenon, this study proposes a collaborative multiscale phase-field (CMPF) approach to model the trans-scale fracture propagation of fiber-reinforced composites. The CMPF model includes a region-based phase-field model for characterizing matrix cracking, fiber breaking, and interface debonding at the microscale; a two-modes phase-field model for characterizing the axial and transverse fracture modes at the macroscale; and a bridging model for exchanging information (fracture modes, nonlinear stress–strain relationship, and strain levels) between the macro- and micro-models. Specifically, the real-time attenuation mechanical properties of the composite caused by crack propagation are first obtained at the microscopic scale and then transferred to the macroscopic two-modes phase-field model to map the trans-scale fracture propagation. The CMPF model is implemented within a finite-element package for numerical calculations and then applied to analyze the tensile-fracture behavior of needled carbon/carbon composites, which is a typical type of fiber-reinforced composite. The calculated results show that the transverse fracture mode nucleates successively within the needled region and then in a 90° nonwoven cloth layer, whereas the axial fracture mode arises within a 0° nonwoven cloth layer. The source of the transverse fracture is matrix cracking and that of the axial fracture is fiber breaking at the microscopic scale. In addition, the fracture properties and overlap of the needled region significantly affect the propagation paths of cracks, thus changing the strength and toughness of the composite. This CMPF model offers a promising approach for modeling and understanding the trans-scale fracture mechanisms of fiber-reinforced composites.
Carbon/carbon (C/C) composites impress with their excellent high-temperature mechanical properties. In this paper, in order to simulate the complex service conditions of aerocraft thermal protection ...systems, an experimental platform for simultaneous ablation and tension was designed. The mechanical and ablation properties of the C/C composites were tested under an oxyacetylene flame at heat flux of 2185 kW/m2. Meanwhile, the mechanism of mutual influence of ablation and tensile loading was revealed by microstructural characterisation. By comparing the tension-only and ablation-only conditions, the results show that the strength of the C/C composites under ablation conditions decreased by 52.0%, which was associated with the crack propagation and porosity increase caused by flame. The tensile loading increased the linear and mass ablation rates by 21.8% and 82.9%, respectively, which was due to the interfacial damage caused by tensile stresses provides more channels for flame to enter the material interior, thus accelerating oxidative ablation.
Carbon/Carbon (C/C) composites are expected to serve as structural materials over 2800 ℃. Experiments under ultra-high temperatures (UHT) are critical and demanding. In this paper, we established the ...UHT compressive experiment technique using simultaneous Joule heating and compressive loading fixtures. The specimen was designed and validated to achieve uniform temperature and strain at the gauge section. Compressive strengths and failure behaviors of three-directional (3D) needled, 3D woven, and four-directional (4D) woven C/C composites under UHT up to 3100 ℃ were investigated. The failure modes and mechanism of strength differences were illustrated through mesoscopic surface morphologies. Results showed that the dog-bone-shaped specimen avoided crushing at loading ends and exhibited failure at gauge sections. Temperatures with peak compressive strengths for 3D and 4D woven C/C composites were determined. Differences between the C/C composites were related to heat treatment temperatures. The sublimation phenomenon was observed for 4D woven C/C composites over 3000 ℃, degrading the compressive strengths by over 50%.
The ZAO （ZnO：Al） thin films were prepared by DC reactive magnetron sputtering technique. The relationship between the process parameters and the organizational structure, optical and electrical ...properties was studied, Through optimizing the process parameters, an optimal preparation parameter can be obtained. Using the optimal parameters to prepare the ZAO thin films, the resistivity of the ZAO film is as low as 4.5×10^-4 Ω. cm and the average transmissivity in the visible region is around 80%, the optical and electrical properties meet the application requirements.
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