Key Engineering Materials Vols. 334-335

Abstract: Based on our previous model on piezoelectric fibre pullout, the effects of electric input and piezoelectric parameters on the fatigue degradation on piezoelectric fibre bridging force are discussed. Numerical results indicate that an electric field can promote or impede the degradation, depending on its direction. It is also shown that piezoelectric parameters play important roles on the degradation. Also, comparisons between the effects of electric load and piezoelectric parameters on fatigue degradation of pullout force and those on pullout force obtained in previous work are carried out.

Abstract: This study deals with the development of PEEK (polyetheretherketone) and PTFE (polytetrafluoroethylene) based composites, optimized for low friction and low wear performance under extreme environments. It is demonstrated that the incorporation of a harder polymer component into PTFE (such as PEEK particles), a short fiber reinforcement (e.g. carbon fibers CF), and internal lubricants (e.g. PTFE particles), helps to reduce the friction and to improve the wear resistance over a very wide temperature range.

Abstract: Spherical indentation of superelastic shape memory alloys (SMAs) has been theoretically analyzed. Two characteristic points on the superelastic indentation curve have been discovered. The bifurcation force corresponding to the bifurcation point relies on the forward transformation stress and the return force corresponding to the return point relies on the reverse transformation stress. Based on these theoretical relationships, an approach to determine the transformation stresses of superelastic SMAs has been proposed. To improve the accuracy of the measurement, a slope method to locate the two characteristic points from the slope curves is further suggested. Additionally, the spherical indentation hardness was also analyzed.

Abstract: The wear resistance of epoxy-based nanocomposites reinforced with octadecylamine-modified clay was studied. Two testing methods, including the ball-on-disc abrasion test and the nanoscratch test, were used to measure the macro- and micro-wear behaviors. The ball-on-disc abrasion test suggests that the short- and long-term wear behaviors of neat epoxy and 5wt% nanoclay composites were similar, although the wear resistance as measured by the volume of material removed was greater for the clay nanocomposite than for the neat epoxy. The incorporation of nanoclay into the epoxy showed little effect on the coefficient of friction.

Abstract: Epoxy ecocomposites reinforced with recycled paper (rP) and nano-kaolinite (nK) have been synthesized. The effect of seawater soaking on the flexural and impact properties have been characterized. This new but cost-effective approach has been developed to improve the physical and mechanical properties of polymeric materials without adversely affecting their processing characteristics. The micromechanisms of toughening and failure processes are discussed.

Abstract: This work investigated the post buckling strength and failure behavior of advanced grid stiffened structures (AGS) under thermal-mechanical load using a finite element method. Based on the first order shear deformation theory (FSDT), Von Karman non-linear deformation assumption, and a progressive failure criterion, the buckling, large deformation，local failure modes in the AGS were studied. The thermal effect was also analyzed. By some numerical examples, the failure characteristics of the AGS were discussed.

Abstract: Results on the effect of water absorption on the mechanical and dielectric properties of nano-size spherical alumina (Al2O3) filled epoxy are presented in this paper. The results from tensile tests indicate that incorporation of the Al2O3 nanoparticles into the epoxy can improve the stiffness of the matrix. DMA results show that the stiffness improvement is more pronounced at the rubbery region of the matrix. The alumina nanoparticles can increase the dielectric constant of the epoxy resin due to the increase in the total interfacial area. Upon water absorption, the mechanical properties of the alumina/epoxy nanocomposites decrease evidently, because of the damages induced by water on the epoxy resin. However, the ductility of epoxy can be improved by the water absorption process. In addition, the dielectric constant of the alumina/epoxy nanocomposites increased greatly after water absorption treatment.

Abstract: To better understand the responses of ultrananocrystalline diamond (UNCD) under extreme working conditions, a numerical study is performed to investigate the size, loading rate and thermal effects on the material properties of UNCD films. A combined kinetic Monte Carlo (KMC) and molecular dynamics (MD) method is first applied to simulate the growth of polycrystalline UNCD films. The responses of the resulting UNCD films with various grain sizes are then investigated by applying displacement–controlled tensile loading with different rates and temperatures in the MD simulations. The preliminary results presented in this paper provide a better understanding of the combined size, rate and thermal effects on the material properties of UNCD.

Abstract: Statistical methods were employed to study the structure characteristics of sisal fibers. Two types of fiber surface treatment methods, namely chemical bonding and oxidization were used to improve the interfacial bonding properties of sisal fiber reinforced HDPE (sisal/HDPE) composites. Interfacial properties were evaluated by single fiber pull out test. The interfacial shear strength (IFSS) was calculated and analyzed by the statistical parameters. The results were compared with those obtained by traditional ways. A novel method which could more accurately evaluate the interfacial properties between natural fiber and polymeric matrices was proposed.