Publications

Progressive failure prediction of woven fabric composites using a multi-scale approach

Lei Xu, YuanChen Huang, Chao Zhao and Sung Kyu Ha, International Journal of Damage Mechanics 2016

Keywords:

Woven textile composites
Weave pattern
Micromechanics
Progressive damage

Abstract

Finite element representative unit cell models are established for the study of progressive failure of woven fabrics: plain weave, twill weave, and satin weave. A multi-scale approach ranging from the meso-scale to micro-scale regime is used, providing the failure observation inside the constituents. The constituent stresses of the fiber and matrix in the warp and fill tows of the woven fabric unit cell are calculated using micromechanics. Correlations between meso-scale tow stresses and micro-scale constituent stresses are established by using stress amplification factors. After calculating micro-scale stresses, the micromechanics of failure damage model is employed to determine the progressive damage statuses in each constituent of woven fabric composites. For the matrix of tows, a volume-averaging homogenization method is utilized to eliminate damage localization by smearing local damages over the whole matrix region of the unit cell. Subsequently, the ultimate strength is predicted for woven composites with different tow architectures. The prediction results are compared with the experimental values, and good agreement is observed.

Ultimate strength prediction of braided textile composites using a multi-scale approach

Lei Xu, Cheng Zhu Jin and Sung Kyu Ha, Journal of Composite Materials 2014; 46(18): p. 2255-2270

Strength prediction of braided composites

Keywords:

Braided textile composites
Micromechanics
Progressive damage
Ultimate strength prediction

Abstract

In this paper, the strength of braided textile composites is predicted using a multi-scale approach bridging the mesoscale and microscale regimes. Mesoscale finite element (FE) models of representative unit cells (RUCs) of biaxial and triaxial braided composites are developed for predicting strength. The constituent stresses of tows inside the braided unit cell are calculated using micromechanics. Correlations between mesoscale stresses and microscale constituent stresses are established by using stress amplification factors (SAFs). After calculating microscale stresses, a micromechanics-based progressive damage model is employed to determine the damage statuses of braided composites. A volume-averaging homogenization method is utilized to eliminate damage localization in the matrix of tows, and a parametric study is performed to evaluate the effects of damage homogenization. Subsequently, the ultimate strength is predicted for braided composites in which the braiding angle ranges from 15° to 75°. The prediction results are compared with the experimental values, and good agreement is observed.

Effect of shallow-angled skins on the structural performance of the large-scale wind turbine blade

Sung Kyu Ha, Khazar Hayat, Lei Xu, Renewable Energy 71 (2014) 100-112

Keywords:

Cost of energy
Large-scale wind turbine blade
Shallow-angled skin

Abstract

Two shallow-angled symmetric and asymmetric skins, with off-axis fiber angles of less than 45, were proposed and employed to a 5 MW wind turbine blade. For the symmetric configuration, shallow-angled skins were applied to both the pressure and suction sides of the blade, while, for the asymmetric configuration, only the pressure side was implemented with a shallow-angled skin, keeping the conventional 45-degree-angled skin for the suction side. The blade tip deflection, modal frequencies, buckling stability, and failure index were computed for off-axis fiber angles of 45, 35, and 25. The use of shallow-angled skins improved blade bending stiffness and strength. The buckling resistance decreased for symmetric skins and remained unchanged for asymmetric skins; the former case was compensated for by increasing the core thickness. For both skin configurations, a reduction in the blade failure index of up to 18% and 38%, and mass reductions of up to 8% and 13% were demonstrated for the 35 and 25 shallow-angled skins, respectively.

Prediction of material properties of biaxial and triaxial braided textile composites

Lei Xu, Seong Jong Kim, Cheng-Huat Ong and Sung Kyu Ha, Journal of Composite Materials 2012; 46(18): p. 2255-2270

Keywords:

Braided textile composites
Meso unit cell
Micro unit cell
Biaxial and triaxial braids
Effective material property

Abstract

Biaxial and triaxial braided composites are modeled using finite element methods to predict effective material properties: for biaxial braids, diamond pattern (1/1), regular pattern (2/2), and Hercules pattern (3/3) are modeled, while for triaxial braids, a regular pattern (2/2) is modeled. A micromechanical approach is adopted to calculate material properties of the tows, which are critical compositions of braided composites. By applying periodical boundary conditions (PBC), four representative unit cells (RUC) in correspondence to the four types of braids are analyzed and compared. Subsequently, effective material properties are obtained with the braiding angle varying from 15° to 75° with an increment of 5°, from which the variation of the engineering constants with the braiding angle is studied. The prediction results are compared with the experimental values for two material systems, and good agreement is achieved.

Prediction of three-dimensional composite laminate response using micromechanics of failure

Yuanchen Huang, Lei Xu and Sung Kyu Ha, Journal of Composite Materials 2012; 46(19-20): p. 2431-2442

Keywords:

Micromechanics of failure
Nonlinear
Strength
Progressive damage
Three-dimensional loading

Abstract

A three-dimensional micromechanics of failure model was developed and applied in order to predict triaxial failure envelopes and stress–strain curves for 12 test cases in the Second World-Wide Failure Exercise (WWFE-II), which involves five continuous fiber–matrix laminates and multi-axial loadings, including those in through-thickness direction. The micromechanics of failure is based on micromechanical unit cell models, which characterize the microstructure of composites, and consists of independent constituent failure criteria and a progressive damage model for the matrix. Nonlinear ply behavior in the matrix-dominant directions was successfully simulated. Thermal stresses were also considered. Results of prediction were presented together with an explanation of the phenomena.