Papers by Author: Jian Yu Zhang

Abstract: Fatigue tests have been carried out to investigate the effects of mean-stress and phase-difference on the tension-torsion fatigue failure of 2A12-T4 aluminum alloy. The results show that for fully reversed tension-torsion loading, the fatigue life increases with the increase of phase angle, but the fatigue life decreases with the increase of phase angle, when mean-stress exists, both for shear mean-stress and normal mean-stress. Fracture appearance shows that the crack initiation is on the direction of maximum shear stress amplitude plane. Critical plane criteria based on the linear combination of the maximum shear stress amplitude and maximum normal stress are studied and further discussion on the drawbacks of this kind of criteria are performed.

Abstract: Low velocity impact tests were carried out on T300/QY8911 and CCF300/QY8911 composite laminates, which led to similar impacted damage characterized by dent depths on laminates. Compression/compression fatigue strength tests of the impacted laminates were further conducted. The comparison of the compression/compression fatigue performance between the two types of composite laminates with similar impacted damage shows the compression/compression fatigue behaviors of T300/QY8911 and CCF300/QY8911 are similar. It follows that the CCF300/QY8911 is an effectively alternative to the T300/QY8911 in damage tolerance behavior.

Abstract: Damage resistance behaviors of CCF300/5428 laminates under five levels of impact energies have been researched by using progressive damage method. The progressive damage models (PDM) are composed of 3D finite element models, Hashin-type failure criteria and Camanhos degradation rules. The impact procedure has been simulated by the progressive damage analysis with user defined subroutines which have been developed and embedded into the general finite element analysis package. The history curves of the contact force and the impact point displacement are plotted. The global damage at typical events for various impact energies is investigated.

Abstract: Fatigue properties of the newly-formed and served canopy PMMA, which was applied in a certain airplane, were studied by experimental method. In order to gain the fatigue strength in the designated life, experiments based on up and down method had been conducted. The S-N curves of the PMMA were acquired based on three-parameter exponential function. Fatigue properties of the canopy PMMA in the two different condition of service were discussed. The results of analysis showed that fatigue properties of the served PMMA did not decrease significantly compared to the newly-formed PMMA.

Abstract: Fatigue stiffness degradation behaviour of woven composite π joint subjected to tensile-tensile cycle loading is studied. Because of the complex structural configuration of woven composite π joints and a variety of failure modes, there exhibited four stiffness degradation modes in fatigue test. For example, stable slight reduction mode, abruptly decreasing mode, step decreasing mode and constant stiffness mode. Each stiffness degradation mode has a corresponding failure mode in fatigue test.

Abstract: Experiments have been conducted to investigate the crack growth characteristics of 7050-T7451 aluminium plate in L-S orientation. Two loading conditions are selected, i.e. constant amplitude and constant stress intensity factor range (ΔK). The effects of ΔK-levels and stress ratios (R) on crack splitting are studied. Test data shows that crack splitting could result in the reverse of crack growth rate trend with the increasing R ratio at high ΔK-level. The appearance of crack splitting depends on both ΔK and R.

Abstract: A series of low-velocity impact tests and residual compressive strength tests after impacts on CCF300/QY8911 composite materials were carried out to study the mechanism of compression failure of the laminates after low-velocity impact. The curves of impact energy verse dent depth and impact energy verse the damage area was obtained. And the residual compressive strength and stiffness after impact verse damage parameters were analyzed. The results showed that when the impact energy exceeded the inflection point, as the impact energy increased, the dent depth on the impacted surface of the laminates notably increased while the damage area of the internal layers merely increased slowly. If the impact energy was continued to increase, the expansion of the laminates' internal damage mainly consisted of fiber breaks. The main reason for the decrease in compressive performance of composite laminates was inside delamination between layers, while in the case in which impact energy exceeded the inflection point, there were no obvious changes in delamination damage area for different energy, so the residual compressive performance kept almost stable.

Abstract: A group of low-velocity impact tests on CCF300/QY8911 composite laminates were implemented by the low-velocity drop hammer test machine. The dent depth and the internal damage pattern with corresponding impact energy were studied, the internal delamination damage state of laminates after impact were observed through thermal layer exposing tests, and the mechanism of low-velocity impact delamination damage were discussed. The results indicated that there existed a significant inflection point in the curve of impact energy verse dent depth of CCF300/QY8911 composite material, which was also the transition point of different damage patterns. When the impact energy was smaller than the inflection energy, the damage pattern consisted mainly of matrix flaws and delamination damages, but when the impact exceeded the inflection energy, delamination damage hardly expanded while the expansion of damage was mainly fiber break.

Abstract: All composite π joints, which can minimize structure redundancy and pave the way for much reduced assembly time, have been developed as a great achievement of the integrated structure technique. To obtain knowledge about the mechanics behavior of composite π joints after cycle loadings, especially residual strength, cycle fatigue test and tensile test for the joints are conducted. From this study, some significative remarks can be made: the strength of composite π joint has reduced slightly by fatigue crack; the residual strength and the general rigidity of the joint exhibit large scatter; the filler zones and tip zones are those of potential weakness in the joints, and the sample in residual strength test has similar failure patterns with that in static tensile test.

Abstract: In order to research the static properties of FRP composite laminates with central hole, the numerical simulation and experimental method are used. The simulation is achieved by the finite element analysis tool with the progressive damage method. During the simulation, the Hashion failure criteria and the selective completed material degradation models are adopted. Proper specimens of FRP composite laminates with central hole are prepared and the static tests are carried out. The results indicate that progressive damage method can simulate the failure process of FRP laminates with central hole and the simulative results agree well with the experimental data.