Papers by Keyword: Fragmentation Test

Abstract: Among the different test methods to characterize the fibre/matrix interfacial shear strength, the fragmentation test is one of the most simple in terms of experimental setup and the amount of data that can be extracted from one single test. In this work, the fragmentation test method was implemented to assess the interface shear strength obtained for a single steel filament embedded in an unsaturated polyester resin.. The fragment lengths were discriminated and processed using the Kolmogorov-Smirnov and Chi-square fitting test methods showing that the fragment lengths correspond to the extreme statistical distributions. In addition, a very high shear strength (67MPa) of the steel/polyester interface was estimated using the Kelly and Tyson criteria considering the critical fragment length.

Abstract: ZnO thin films were deposited on polyimide foil substrates using cathodic vacuum arc deposition technique. X-ray diffraction was used to investigate the influence of bias voltage on the structure of ZnO thin films. The results show that all the samples have (002) preferred orientation. The internal stress of the films is compressive stress which increases with the bias voltage. Fragmentation test shows that the intrinsic interfacial shear strength of ZnO thin film without bias voltage is slightly lower than the shear yield strength of polyimide substrate; the intrinsic interfacial shear strength of ZnO thin film increases with the bias voltage from -50V to -200V, which indicates that bias voltage is beneficial to the enhancement of the adhesion between ZnO films and polyimide substrates. Further increase of the bias voltage to -300V leads to surface damage of the polyimide substrates.

Abstract: Application of coating fragmentation test for determination of coating properties is considered. A probabilistic model of coating fragmentation under uniaxial tensile loading is applied for coating and interface property identification of thin brittle coating/polymer substrate system. A finite element model is developed to simulate the process of buckle formation in coating strips during fragmentation test. The measured buckle geometry parameters and buckle density evolution as a function of the applied strain is used to estimate the interface toughness.

Abstract: An energy-based analysis has been developed to evaluate interfacial adhesion between fiber and matrix in a single fiber composite over the years. However, the value of the energy-based parameter, e.g. an energy release rate, depends on a stress distribution predicted by a model employed. In the case of carbon fiber-reinforced plastics (CFRP), laser Raman spectroscopy (LRS) is significantly effective to validate the stress distribution predicted. The fragmentation tests with a model of carbon fiber-reinforced epoxy composite are performed, and LRS is used to detect a distribution of the fiber axial strain. An elasto-plastic shear-lag analysis methodology is employed, and a stress distribution is predicted under various approximations of s-s curve of the matrix resin and compared with the experimental results. Our recent energy-balance method, including an energy dissipation induced by plastic deformation around an interfacial debonding tip, is used to calculate an energy release rate to initiate an interfacial debonding (interfacial energy). An effect of the difference between the approximations on the value of the interfacial energy is discussed.

Abstract: A shear-lag model is developed to predict the stress distributions in and around an isolated fiber in a single-fiber polymer matrix composite (PMC) subjected to uniaxial tensile loading and unloading along the fiber direction. The matrix is assumed to be an elasto-plastic material that deforms according to J2 flow theory. The stress distributions are obtained numerically and compared with a different shear-lag model that employs total strain theory as a constitutive equation of the matrix material. An effect of the difference between the models on the derived stress state is discussed.

Abstract: Phase-stepping photoelasticity has been used to study the fragmentation of an E-glass fibre in epoxy resin and examine quantitatively the effect of a transverse matrix crack on the stress transfer at an interphase. Unsized glass fibre was coated by plasma polymerisation with a crosslinked conformal film of 90% acrylic acid and 10% 1,7-octadiene. The micro-mechanical response at the fibre-matrix interphase and in the adjacent matrix has been described in detail using contour maps of fringe order. From these, the interfacial shear stress profiles at fibre-break have been calculated.

Abstract: The single fiber fragmentation test has been continuously used to determine the interfacial shear strength. However, the results of the tests were still suspected by some researchers. To evaluate the reliability of the fragmentation test, the stress singularity near the interface end of fragmentation is investigated. According to the local failure modes near the interface end of a fiber fragment, there are three cases of the interface end conditions to be considered for the fragmentation tests: (A) fiber breaks only, without matrix cracking and de-bonding, (B) fiber breaks and matrix cracks, without interface de-bonding, (C) fiber breaks and interface de-bonds, with or without matrix cracking. After the singularity analysis of stress field near the interface end was depicted, it is obvious, that the interfacial shear strength given by the fragmentation test is not proper, because of that a stress singularity exists near the interface end.

Abstract: The effect of interfiber distance on the interfacial properties in two dimensional multi-Eglass fiber/epoxy resin composites has been investigated using fragmentation test. In additions, the effect of the fiber surface treatment on the interfacial properties has been studied. We found that the interfacial shear strength decreased with the decreasing of the interfiber distance at the range of under 50µm and the extent of the decreasing was more serious as the increasing of the number of adjacent fiber. This is probably that the interface between the fiber and the resin was damaged by the adjacent fiber breaks and the damage increased with closing the interfiber spacing and the number of adjacent fiber. We can guess from this interfacial shear strength in real composites is much smaller than that of multi-fiber fragmentation sample with touched fiber. It was seen that the interfacial shear strengths saturated when the interfiber distance was over 50µm, the ones were saturated regardless of fiber surface treatment and the ones were in close agreement with those of the single fiber fragmentation test. Finally, the interfacial shear strength evaluated using two dimensional fragmentation tests are shown as real values in-site regardless of fiber surface treatment, interfiber distance and existing of matrix cracks.