Materials Science Forum Vols. 475-479

Abstract: The photo-oxidation stability is crucial for the materials that are exposed to outdoor application. For polyethylene, it has been investigated thoroughly and the auto-oxidation mechanism has been widely accepted. Nevertheless, the photo-oxidation of polyethylene composites, the most widely used materials, has not attracted enough attention yet. It is well known that the mechanical properties of composites are of great difference to that of matrix polymers, due to the introduction of the fillers and the different interfacial interactions between the matrices and the fillers. Also the oxidation behavior of composites have interesting characteristics owing to the various fillers and interfacial interactions, which always depend on the coupling agents. In the present work, the natural photo-oxidation of high-density polyethylene composites was studied. The results showed that the coupling agent had the most important but different influence on the oxidation stability of the composites, according to the different fillers.

Abstract: The cure kinetics of middle temperature curing 3234 epoxy resin was investigated under both isothermal and dynamic curing conditions by Differential Scanning Calorimetry (DSC) technique. The kinetic equations for isothermal and dynamic curing were established respectively by analyzing experimental data obtained from DSC . By following the temperature procedure of the standard cure cycle of the resin system, the validity of the cure kinetic equations was verified by means of determining the residual heat of reaction of samples from different stages of the cure cycle. Results showed that the cure kinetics under both isothermal and dynamic conditions could be described by the autocatalytic kinetic model. Predictions by the kinetic equation for dynamic curing agreed well with the experimental results.

Abstract: In this paper, the dynamic behaviors of several kinds of high strength fibers, including Kevlar, UHMPE, glass fibers, carbon fibers etc., are investigated experimentally, with a Split Hopkinson Tension Bar（SHTB）. The effect of strain rate on the modulus, strength, failure strain and failure characteristics of fibers, under impact loading, is analyzed with the relative stress vs. strain curves. At the same time, the mechanism about the rate dependence of mechanical behaviors of various fibers is discussed based on the understanding on the microstructures and deformation models of materials. Some comments are also presented on the decentralization of experimental results, and a new method called traveling wave method is presented to increase the experimental accuracy. Research results obtained in this paper will benefit to understand the energy absorption and to build up the constitutive law of protective materials reinforced by high strength fibers.

Abstract: In order to get rid of health hazard of asbestos fiber, a new kind of non-asbestos fiber reinforce composite by beater-addition process, which is used for sealing and gasket, has been developed to replace traditional asbestos gasket materials. The mechanical properties of the new composite were tested, and the performance between it and asbestos sheet paper were contrasted. Results show that the density, cross direction tensile strength, machine direction tensile strength and ignition loss at temperature of 300°C of the new composite are 1.19g/cm3, 2.62MPa, 3.15MPa and 15.61% respectively, while the performances of asbestos paper produced under the same condition are 1.26g/cm3, 2.87MPa, 3.24MPa and 12.03% respectively. Excellent performance, low cost and simple manufacture process of the new composite make it is possible to substitute traditional asbestos paper and apply widely.

Abstract: Being subjected to the bending load, the structure of plate often has the high demand of bending rigidity. Fiber reinforced composites are used in an increasing number of structural applications, this due to their higher specific strength and specific stiffness compared to homogenous structural materials. For the orthotropic carbon fiber reinforced plastics (CFRP) plate with multiple holes, the application of the classical stress-strain analysis is very difficult because of the anisotropism and the effect of the holes. Therefore, the finite element method (FEM) is used to investigate the effect of a plate with multiple holes on the bending rigidity. The bending rigidity in the situation that stiffeners are fixed firmly to the plate is much higher than they are separated. The computation results are consistent to the experiment results. Based on the computation, a FEM model to optimize the bending rigidity of this kind of laminate circular plate with multiple holes is established. The placement of holes, the form and number of stiffeners are optimized in this paper. The computation results show if the number of stiffeners change to 6 and are matched with holes the bending rigidity will be increased remarkably and the weight of plate is reduced simultaneously. The computation results are consistent to the experiment results. The resolution of this study provides a reference for the design of this kind of laminate circular plate with multiple holes.

Abstract: Carbon nanotube is seen to be an excellent reinforcement candidate to produce multifunctional composites with improved mechanical, thermal and electrical properties. Strong interfacial bonding and homogenous dispersion are necessary conditions to obtain effective load transfer for mechanical enhancement. This paper addresses the processing of polymer composites reinforced by functionalized single wall carbon nanotubes. FTIR, SEM/EDX and DMA analysis are presented. The results demonstrated that the chemical functionalization of nanotubes helps to improve both dispersion and interaction in polymer matrix. Mechanical property improvement for the epoxy polymer composites has been shown with a small amount of carbon nanotube addition.

Abstract: It had been impossible to inspect the Eddy Current (EC) since the Fiber Reinforced Composite Materials (FRCM) had the low electric conductivity of resin layer. However, it has been successful for our previous research to inspect the defect using the EC. In the case of loading to FRCM, the researches of relationship between the failure behavior and the variation of EC signals have not been carried out. Therefore, this research focused on the comparison and the evaluation of the EC signals according to the variation of the defect depth using the unloading and the radial-loading FRCM tube. We obtained results are as follow. Firstly, The EC signals similar to that of the unloading specimens could be obtained from the loading specimen of 80% defect. Secondly, Regardless of the unloading and the loading specimens, the defect of 100% and 80% depths had the similar phase angles and Lissajous figures. Finally, it was guessed that the length of micro-cracks distributed at the whole specimens under the loading was less than 60% of the specimen thickness.

Abstract: This paper intends to present two-dimensional elasticity solutions for static problem of thick laminated composite beams using a hybrid method of state-space-based differential quadrature. The technique of differential quadrature is employed to reduce the partial differential state equations into the ordinary differential ones at all arbitrary sampling points for each individual laminate. General solution to the assembled state equation is then obtained according to the matrix theory. Taking account of the continuity conditions at the interfaces of all the adjacent lamina, a relationship between state variables at the top and bottom surfaces of the beam is established through a global transfer matrix. After incorporating the boundary conditions at these two surfaces, an eigenvalue equation for static problem is then derived. Numerical examples are presented, through which the accuracy and convergence characteristics of the present method are investigated. It is shown that the present method is of excellent efficiency for laminated composite thick beams subjected to arbitrary end supporting conditions.

Abstract: Although tribological tests on polymers are traditionally performed on small-scale pin-on-disc or bloc-on-ring configurations, present sliding tests under high load provide more accurate de-sign data. For wear tests on large samples edge effects, stress concentrations and the moveability of wear debris into the contact zone are simulated close to practice. It is illustrated that friction is gene-rally lower compared to small-scale tests, while overload and deformation occur more frequently.