Key Engineering Materials Vols. 297-300

Abstract: The strength characteristics as well as local deformation behaviors of honeycomb sandwich composite (HSC) structures under three-point bending loads were investigated in consideration of various failure modes such as skin layer yielding, interface-delamination as well as shear deformation and local buckling in the core layer. Various types of aluminum honeycomb core and skin layer were used for this study. Their finite-element simulation was performed to analyze stresses and deformation behaviors of honeycomb sandwich plates. The results were very comparable to the experimental ones. Consequently, thicker skin layer, smaller cell size of honeycomb core and less delamiantion had dominant effects on the improvement in strength and deformation behaviors of honeycomb sandwich plates.

Abstract: The applicability of GLARE is restricted due to the frequent delamination of different materials at interlaminar. The previous researches showed that the major parameter to control the delamination of GLARE was a crack (a). On the other hand, it was also shown that a delamination width (b) could strongly effect on the delamination behavior. Therefore, the aim of this research is to define the delamination behavior using the above correlation. In conclusions, it was shown that the delamination aspect ratio (b/a) was slowly decreased and the delamination area rate (ADR) was increased as the normalized crack size (a/W) was increased. The effect of the delamination shape was strong at the beginning of the cyclic loading but it was gradually diminished.

Abstract: In order to estimate distribution of mechanical properties and fracture toughness in ceramic-metal functionally graded materials (FGMs), mechanical properties and fracture behavior have been investigated on non-graded ceramics-metal composites which correspond to each region of FGMs. The materials are fabricated by powder metallurgy using partially stabilized zirconia (PSZ) and stainless steel (SUS 304). Vickers hardness, Young’s modulus and bending fracture strength were examined on smooth specimens. The Vickers hardness of the composites continuously decreases with an increase in a volume fraction of SUS 304 metal phase, while the Young’s modulus and fracture strength exhibit low values in the composites with balanced composition of each phase. This suggests that the interfacial strength between the ceramic and metal phases is very low. Fracture toughness tests are conducted by three-point-bending on rectangular specimens with a sharp edgenotch. In contrast with the Young’s modulus and fracture strength, the fracture toughness obtained for the composites increases with an increase in a volume fraction of SUS 304 metal phase. The fracture toughness of the composites is slightly lower than that obtained previously by stable crack growth in a PSZ-SUS 304 FGM. The difference in fracture toughness between the composites and FGM seems to be attributed to the residual stress created during fabrication of the FGM.

Abstract: In this paper, a new micromechanical method, the Weighted Residual Self-consistent Scheme (WRSCS), is developed for the prediction of the effective thermal conductivity of particulate composites with arbitrary configurations. The method is based on the concept of the traditional Self-consistent Scheme (SCS). For some special configurations of inclusions, such as spherical or ellipsoidal, the effective conductivity of the composite can be solved without much difficulty using SCS. But for the composite with inclusion of arbitrary geometry, such as polygon or other irregular configurations, it is difficult to get an analytic solution. In the WRSCS, the arbitrary inclusion configuration is modeled by applying collocation points at interface. Based on SCS micromechanical model, the local fields inside the inclusion can be evaluated by using the solution of a single inclusion in an infinite matrix and inclusion interaction is taken into account through the yet unknown average equivalent medium. The solution for calculating the potential field inside the inclusion is obtained by means of Weighted Residual Method (WRM). Using the WRSCS, the effective thermal conductivities for composites with different inclusion’s geometry are calculated. For the case of spherical inclusion, the results from the WRSCS show good agreements with the one from traditional SCS [7, 8]. Examining results corresponding to different inclusion’s geometry, it shows that the effective thermal conductivity depends not only on the volume fractions and the properties of components, but also on the inclusion’s configuration.

Abstract: In recent years, the use of natural fibers as reinforcements in polymer composites to replace synthetic fibers like glass is presently receiving increasing attention. Because of their increasing use combined with high demand, the cost of thermosetting resin has increased rapidly over the past decades. However the widely used synthetic fillers such as glass fiber are very expensive compared to natural fibers. Natural fiber-reinforced thermosetting composites are more economized to produce than the original thermosetting. Moreover the use of natural fiber in thermosetting composites is highly beneficial, because the use of natural fibers will be increased. In this study, a bamboo fiber-reinforced thermoplastic composite that made the RTM was evaluated to mechanical properties.

Abstract: This paper introduces the concept of remotely-driven smart actuator utilized by electro-active paper (EAPap). The feature of remotely-driven smart actuator offers unique performance and application capabilities and exploit many of these unique capabilities. Since the microwave-driven actuator does not require carry-on-battery, ultra-lightweight, and distributed micro size actuators can be made. A dipole rectifying antenna (rectenna) array receives the microwave and converts it into a DC power. Recently, cellulose based paper has been came across as an lectroactive paper (EAPap) material so as to be used as artificial muscles for biomimetic insects. Since the power requirement of EAPap is less than the safety limit of microwave power in air, the EAPap actuators can be driven by wireless microwave power. This idea is useful for specific applications that require multifunctional capabilities such as smart skin, ultra-lightweight space structures, micro robots, flapping wing for insect-like flying objects and smart wall paper as well. Current research status along with its issues is addressed including a hybrid actuator of EAPap and conducting polymers that will enhance the performance of the actuator.

Abstract: In this paper, the effects of chamfering conditions on the surface roughness of ZrO2 ferrule applied to an optical fiber connector were investigated. The mesh number of the diamond wheel, the grinding speed of the spindle, the feed rate, and the initial cutting depth during grinding chamfer were regarded as the main parameters that have an effect on the surface roughness. Among these parameters, optimal combinations for chamfering conditions were obtained by using the Taguchi method. In addition, analytic values for maximum surface roughness (Rmax) estimated by the theoretical equations which were derived from the formative model of surface roughness on the grinding chamfer were compared with those of the experiments.

Abstract: Mechanical behavior of CFRP (Carbon Fiber Reinforced Polymer) containing Ni-Ti shape memory alloy (SMA) is investigated by experimental methods. Tensile and bending fracture tests were conducted to examine the strength of the composite for various volume fractions of the SMA. Charpy impact test was used to study the toughness of the SMA/CFRP hybrid composite. Finite element analysis was carried out for interface failure in bending test.

Abstract: Fatigue crack propagation tests are conducted on magnesium alloy, cruciform specimens under biaxial and uniaxial loadings by using the biaxial fatigue tester which was developed by the authors. We investigate the effect of microstructures of specimens on fatigue crack growth resistance under biaxial stresses. From electron-microscope observations of a fatigue fracture and microstructure observations, it becomes clear that the mechanical properties of a magnesium-alloy, AZ31B, are greatly influenced by the diameter of crystal grains. We find that static tensile strength falls by heat-treating in the high temperature region where the diameter of crystal grains of an X-Y plane becomes large. We also find that the crack progress velocity under equal biaxial stresses gets faster by heat-treating in the high temperature region where the diameter of crystal grain of a Z-X plane becomes large.