Wenfeng Hao

Effect of impact damage on the curved beam interlaminar strength of carbon/epoxy laminates

Abstract The bending interlaminar strength and bending interlaminar strength after impact of carbon/epoxy-laminated curved beams were studied experimentally using four-point bending test and low velocity impact. First, the post- impact damage of the laminated curved beams with different radii was analyzed based on ultrasonic C-scan images. Then, the effect of impact damage on both the interlaminar strength and the maximum interlaminar radial stresses of the laminated curved beams were investigated. Finally, the full-field displacement distributions of the laminated curved beams were obtained using digital speckle correlation method. Four-point bending experimental results play a significant role for interlaminar strength in evaluating the laminated curved beams with and without impact damage.

Displacement field denoising for high-temperature digital image correlation using principal component analysis

ABSTRACT Principal component analysis (PCA) was extended to minimize the noise effect in digital image correlation (DIC) measurement under a high-temperature atmosphere environment. First, the principle of PCA was introduced, and the singular vectors and singular values for each component of the displacement fields from DIC were obtained. Then, the simulated high-temperature speckle images were developed to investigate the influences of noise on the DIC method under a high-temperature environment. Finally, the displacement fields of several special conditions were extracted from the simulated speckle images and experimental images; the effects of noise on the PCA were also analyzed.

Study of matrix crack-tilted fiber bundle interaction using caustics and finite element method

In this work, the interaction between the matrix crack and a tilted fiber bundle was investigated via caustics and the finite element method (FEM). First, the caustic patterns at the crack tip with different distances from the tilted fiber were obtained and the stress intensity factors were extracted from the geometry of the caustic patterns. Subsequently, the shielding effect of the fiber bundle in front of the crack tip was analyzed. Furthermore, the interaction between the matrix crack and the broken fiber bundle was discussed. Finally, a finite element simulation was carried out using ABAQUS to verify the experimental results. The results demonstrate that the stress intensity factors extracted from caustic experiments are in excellent agreement with the data calculated by FEM.

Characterizing thermo-mechanical behavior of superalloy using the eigenfunction virtual fields method

EVFM was extended to characterize thermo-mechanical behavior of superalloy.Virtual fields were constructed using the eigenvectors of augmented strain matrix.Effect of mesh size and noise on the identification results was analyzed. An innovative procedure for characterizing thermo-mechanical behavior of superalloy using the Eigenfunction Virtual Fields Method (EVFM) was proposed. First, the principle of EVFM for thermo-mechanical constants identification was developed based on the principal components analysis. Then, the strain fields were extracted from finite element (FE) simulation of a superalloy plate with a circular hole under uniaxial tension and uniform temperature increment. In addition, the virtual fields were constructed using the eigenvectors of augmented strain matrix. Finally, the thermo-mechanical constants were inversed from the strain fields, and the effect of mesh size and noise on the inversion results was analyzed. The results show that the thermo-mechanical constants of superalloy inversed from EVFM using these eigenvectors as virtual fields are in excellent agreement with the true values.

Dynamic caustics in unidirectional fiber-reinforced composites with mode I cracks: Experiment and numerical simulation

ABSTRACT The stress singularities of a dynamic crack tip in orthotropic composites were studied through caustics. The parametric equations of the caustic and its initial curve surrounding the dynamic crack tip were derived through the elastic dynamic crack solutions of orthotropic composites and the basic principle of reflective caustics. Theoretical caustics and initial curves for three kinds of orthotropic composites were simulated, and the effects of crack velocity on the caustics and initial curves were analyzed. In comparison with numerical results, the dynamic caustic experiment was performed for dynamic cracks along the material axes in unidirectional, fiber-reinforced composites under drop-hammer, three-point-bend loading.