Yanan Yuan

Computational analysis of fatigue behavior of 3D 4-directional braided composites based on unit cell approach

The unit cell of 3D 4-directional braided composites were built up using ABAQUS.The fatigue behavior of the 3D 4-directional braided composites was analyzed.Effect of braiding angles and fiber volume fraction of on fatigue behavior was analyzed. The fatigue behavior of 3D 4-directional braided composites was investigated based on the unit cell approach. First, the unit cell models of 3D 4-directional braided composites with different braiding angles and fiber volume fraction were built up using ABAQUS. Then, the fatigue behavior of the 3D 4-directional braided composites was analyzed, and the effect of fatigue loading direction on the fatigue damage evolution and fatigue life was studied. Finally, the effect of braiding angles and fiber volume fraction of the unit cell on the fatigue behavior of 3D 4-directional braided composites was analyzed. These results will play an important role for evaluating the fatigue behavior of 3D 4-directional braided composites in engineering.

Study on the effect of inclusion shape on crack-inclusion interaction using digital gradient sensing method

The effect of inclusion shape on the mode I stress intensity factor of the matrix crack interaction with a rigid inclusion was studied experimentally using digital gradient sensing (DGS) method. First, the noncontact optical measurement system of DGS was built up, and the specimens with different shapes of inclusion ahead of matrix crack were performed using transparent epoxy resin. Then, the angular deflection contour at the crack tip with different shapes of inclusions was obtained, and the stress intensity factors were extracted from the stress gradient filed based on least square fitting. Finally, a numerical simulation was conducted on the same problem using ABAQUS, and the stress intensity factors computed from FEM were compared with the experimental results. The results show that the stress intensity factors extracted from the stress gradient filed are agreed well with the numerical and theoretical results.

Photoelastic Investigation of Interaction Between Matrix Crack and Different Shapes of Inclusions

The interaction between different shapes of inclusions and the mode I matrix crack was studied experimentally using the photoelasticity method. First, the stress intensity factor (SIF) at the matrix crack tip in the neighborhood of the inclusions was derived based on transformation toughening theory and the Eshelby equivalent inclusion method. Then, photoelastic experiments were conducted using specimens with different shapes of inclusions, and the typical isochromatic fringe patterns around the crack tip near the inclusions were obtained. Finally, a numerical simulation was conducted for the same problem using ABAQUS, and the stress intensity factors computed from the finite-element method were compared with the experimental results. The results show that the stress intensity factors extracted from isochromatic fringe patterns agree well with the numerical and theoretical results.

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.

Experimental study on the matrix crack-fiber interaction using photoelasticity method

The stress field of the matrix crack perpendicular to fiber bundles was studied by the method of photoelasticity. First, the stress intensity factor at the matrix crack tip in the neighbor of the fiber bundles are derived based on transformation toughening theory and Eshelby equivalent inclusion method. Then, a photoelastic experiment was conducted using a specimen with a fiber bundle in the center as an inclusion, and the typical isochromatic fringe pattern around the crack tip near the fiber bundle was obtained. Finally a numerical simulation was carried out based on the plane stress assumption, and the stress intensity factor measured using photoelasticity was compared with the numerical and theoretical results. These results will play an important role for evaluating the mechanism of crack-fiber interaction in fiber reinforced composites.

Stress field at V-notch tip in polymer materials using digital gradient sensing

ABSTRACT The digital gradient sensing (DGS) technique was used to study the stress field at the V-notch tip of polymer materials. First, DGS governing equations at the V-notch tip were deduced using the elastic singular stress fields. Then, theoretical angular deflections of light rays at the V-notch tip were simulated, and the effect of notch angle on the angular deflections was analyzed. Finally, the DGS experiments were conducted, and the angular deflection contours were obtained. The results show that the stress intensity factors at the V-notches extracted from the angular deflections agree well with the results calculated from the finite element method.

Comparison of the Fatigue Crack Propagation Behavior of Two Different Forms of PMMA Using Two-Stage Zone Model

AbstractThe fatigue crack propagation behavior of two different forms of PMMA was studied using two-stage zone model. First, the fatigue crack length and fatigue crack propagation velocities of different specimens were obtained experimentally. Then the effect of material forms and specimen types on the fatigue crack propagation velocities was analyzed. Finally, the data scatter of da/dN-ΔK curves in different forms and different types of specimens was analyzed. The results show that the expressions of fatigue crack propagation velocities of middle crack tension (MT) specimens and compact tension (CT) specimens in the same form PMMA are similar. And the scatter of MT specimens is larger than CT specimens in two forms of PMMA.