Weidong Wen

Finite Element Analysis of 2.5D Woven Composites, Part II: Damage Behavior Simulation and Strength Prediction

In the first part of the work, a new 2.5D woven composites finite element model (2.5D WCFEM) which took into consideration the impact of face structures and can accurately predict the main elastic performances has been established. In this part, the stress–strain behavior and the damage characteristic of this material under uniaxial tension are simulated using nonlinear progressive damage analysis based on damage mechanics. Meanwhile, experimental investigation and fracture analysis are conducted to evaluate the validity of the proposed method. Finally, the influence of woven parameters on the mechanical behavior is discussed. Compared with the test results, a good agreement between the computational and experimental results has been obtained. The progressive damage characteristic and main failure modes are also revealed.

Finite Element Analysis of 2.5D Woven Composites, Part I: Microstructure and 3D Finite Element Model

A new parameterized finite element model, called the Full-cell model, has been established based on the practical microstructure of 2.5D angle-interlock woven composites. This model considering the surface layer structure can predict the mechanical properties and estimate the structural performance such as the fiber volume fraction and inclination angle. According to introducing a set of periodic boundary condition, a reasonable overall stress field and periodic deformation are obtained. Furthermore, the model investigates the relationships among the woven parameters and elastic moduli, and shows the structural variation along with the corresponding woven parameters. Comparing the results calculated by FEM with the experiments, the veracity of calculation and reasonability based on the Full-cell model are confirmed. In the meantime, the predicted results based on the Full-cell model are more closed to the test results compared to those based on the Inner-cell model.

Reliability-Based Shape Optimization of Tenon/Mortise in Aero-engines with Contact

Based on the theory of reliability-based structural shape optimization, exact expressions of the sensibility using the stochastic finite element method for contact problems were derived in detail, and the basic steps of structural optimization were given. A coattail-type tenon/mortise of an aero-engine was optimized. In this model, the maximum equivalent stress of the nodes on the boundary of the tenon was the objective function; the width of tooths neck and the side surfaces slope angle of a tenon were design variables, with constraints of tension stress, extrusion stress and reliability index. The result showed that the distributions of the contact pressure between tenon and mortise, the equivalence stress and reliability index were more reasonable. It validates the correctness of the optimization model and the reliability-based structural shape optimization, and provides valuable references for structural design of the tenon/mortise.

Vibration Fatigue Probabilistic Life Prediction Model and Method for Blade

Vibration fatigue is one of the main failure modes of blade. The vibration fatigue life of blade is scattered caused by manufacture error, material property dispersion and external excitation randomness. A new vibration fatigue probabilistic life prediction model (VFPLPM) and a prediction method are proposed in this paper. Firstly, as one-dimensional volumetric method (ODVM) only considers the principle calculation direction, a three-dimensional space vector volumetric method (TSVVM) is proposed to improve fatigue life prediction accuracy for actual three-dimensional engineering structure. Secondly, based on the two volumetric methods (ODVM and TSVVM), the material C-P-S-N fatigue curve model (CFCM) and the maximum entropy quantile function model (MEQFM), VFPLPM is established to predict the vibration fatigue probabilistic life of blade. The VFPLPM is combined with maximum stress method (MSM), ODVM and TSVVM to estimate vibration fatigue probabilistic life of blade simulator by finite element simulation, and is verified by vibration fatigue test. The results show that all of the three methods can predict the vibration fatigue probabilistic life of blade simulator well. VFPLPM & TSVVM method has the highest computational accuracy for considering stress gradient effect not only in the principle calculation direction but also in other space vector directions.

The effect of voids on the quasi-static tensile properties of carbon fiber/polymer-laminated composites

Static longitudinal/transverse tensile tests for unidirectional carbon fiber/polymer (T300/924) laminates and laminates with lay-ups [ 0 / ± 45 / 0 / 90 ] s at various void levels were conducted, and degradations in stiffness/strength were observed with the presence of voids. The void levels were controlled by compression pressure during the compression molding process. The characterization of voids was achieved by digital microscopy image analysis; the density distributions of equivalent diameters and aspect ratios were analyzed with respect to compression pressure. For the purpose of quantifying the effect of voids on the static mechanical properties of composites, a stiffness prediction method based on the Mori-Tanaka method and void geometric statistical data have been used with the implementation of a finite element model of the representative volume element for unidirectional composites; the prediction results show good correlation with experimental data. Finally, a modified continuum damage model for laminated composites with the presence of voids was proposed, the model is capable of capturing the effect of voids; and gradual damage analysis for carbon fiber/polymer composite laminates at different void levels was conducted to evaluate the effect of voids on their tensile properties.

Study on low-velocity impact and residual strength at high temperatures of composite laminates

In this paper, low-velocity impact characteristics and residual tensile/compressive strength of composite laminates at high temperatures are experimentally and analytically investigated. Low-velocity impact tests at room temperature were performed using a drop-weight apparatus, and residual strength tests at high temperatures were performed using a hydraulic MTS machine. The experimental results show that both residual tensile and compressive strength decrease monotonically with the increase of impact energy, while the variation trend of residual tensile/compressive strength of composite laminates keeps the same with longitudinal tensile/compressive strength with the increase of temperature. In addition, a new stress-based delamination failure criterion was established, in which the delamination is considered to be controlled by the difference between through-thickness stresses of adjacent layers. Once delamination occurs, only the elements below the interface are marked with delamination, whereas the material properties of the elements on both sides of the interface are reduced simultaneously. In this way, delamination can be defined more precisely without cohesive elements, and a considerable reduction in CPU time can be achieved. Combined with extended Hashin failure criteria, an integrated finite element model was established to simulate low-velocity impact damage and to predict residual tensile and compressive strength of composite laminates. The numerical results show good agreements with experimental data.