Key Engineering Materials Vols. 334-335

Abstract: Al2O3-TiC composites were fabricated by hot-pressing Cobalt coated powders at low temperature through liquid phase sintering. Cobalt coating layers effectively hinder the growth of grain and harmful reaction between Al2O3 and TiC particles, which would improve the mechanical properties of Al2O3-TiC composites. The hardness decreases with the increase of Co content and the bending strength was enhanced to 782MPa owing to the grain refinement effect of Co phase. The fracture toughness, about 9.23 MPa.m1/2, was measured for the composites containing 3wt% Co sintered at 1550°C. SEM images of fracture surface show that the toughening effect should be attributed to the conversion of fracture mode caused by the Co phase.

Abstract: Elasticity solution is presented for simply-supported, orthotropic, piezoelectric cylindrical shell with finite length under local ring load in the middle of shell and electrostatic excitation. The highly coupled partial differential equations (p.d.e.) are reduced to ordinary differential equations(o.d.e.) with variable coefficients by means of trigonometric function expansion in longitudinal direction for displacement and external forces. The resulting ordinary differential equations are solved by Galerkin finite element method. Numerical examples are presented for [0/90/P] lamination with sensor and actuator for different thicknesses.

Abstract: In this article, the densely SrCo0.8Fe0.1Sn0.1O3-δ (SSCF) tubular membranes were prepared by the traditional extrusion method. The prototype oxygen separator was constructed by the resulting SSCF tubular membrane. The resulting oxygen product had purity over 99%. At 920oC, a tubular membrane with a wall thickness of 1.4mm, had the permeation rate of 2.4ml/min.cm2, which kept unchanged during 1000hrs operation.

Abstract: The properties of photoluminescence (PL) and electroluminescence (EL) of 5,10,15,20- tetra-p-tolyl-21H, 23H-porphine (TTP) doped poly[2-methoxy-5-(2’-ethylhexyloxy)-1,4- phenylenevinylene] (MEH-PPV) was studied in this paper. A multi-color emission from the corresponding light-emitting device was observed.

Abstract: The paper presents an effective damage detection method of complex composite structures. It can be carried out through the experimental modal analysis of the damaged structure. The method using the improved Cross Modal Strain Energy (CMSE) technique and Niche GA has many advantages compared with other damage detection methods. The CMSE method can use any modes of the structure and the modes don’t need to be normalized or consistent in scale. The Niche GA improves the efficiency of the calculation and enhances the capacity of identifying structural damage localization. The model is the composite material airfoil case. The numerical results show that the method proposed in this paper is successful for damage detection of complex structures.

Abstract: Thermal vibration characteristics of the composite thin-cylindrical shell embedded with shape memory alloy (SMA) fibers are investigated. The shape memory alloy material behavior is programmed in the form of an ABAQUS user subroutine code (UMAT), and this program is successfully verified by using the response of pseudoelasticity and the shape memory effect (SME) at various temperatures and stress levels. Based on the ABAQUS UMAT code, the natural frequency of the composite thin-cylindrical shell embedded with SMA wires under thermal load and mechanical load is calculated respectively. Then the effects of the SMA wire temperature and the content on the thermal vibration characteristics of the structure are discussed. Numerical simulation results show that the temperature and the volume content of the SMA wires increase the stiffness and buckling critical load of the structure.

Abstract: Sintered NdFeB permanent magnet is widely used in many applications because of its excellent magnet property. However the report of EDM research on NdFeB magnet is not available. This paper presents a detailed investigation of the material removal mechanisms of sintered NdFeB magnet through analysis of the machining debris and the surface SEM quality. It is included three types of machining mechanisms: melting and evaporating, thermal cracking, spalling or whole grain removal.

Abstract: The thin polymer composite bipolar plates (the thickness < 1.5 mm) for use in polymer electrolyte membrane fuel cells (PEMFCs) containing vinyl ester resin, graphite
powder, organoclay have been fabricated by bulk molding compound (BMC) process. Organoclay prepared by ionic exchange of montmorillonite (MMT) with three different Mw of diamine intercalating agents was used to reinforce the mechanical properties of the composite bipolar plates. Results indicate that the basal spacing and content of MMT varied with Mw of POP-diamines are critical in determining the resultant mechanical properties for bipolar plates. The flexural strength and the unnotched impact strength of the plate were ca. 38 % (from 30.21 MPa to 45.66 MPa) and ca. 30 % (from 58.11 J/m to 80.21 J/m) higher than the pristine graphite plate, respectively, as the basal spacing of MMT (2 phr) was increased from 1.71 to 5.43 nm. The limiting oxygen index (L.O.I.) and the UL-94 test revealed that the bipolar plate possesses excellent flame retardant with L.O.I. higher than 50 and UL-94-V0. In addition, the electrical conductivity of the bipolar plates with different MMT contents and basal spacing of MMT is higher than 100 S/cm.

Abstract: A novel organic–inorganic mesoporous silica functionalized with perfluoroalkylsulfonic acid groups analogous to that of Nafion® has been prepared. A condensation reaction between surface silanol groups of the mesoporous silicas and 1,2,2-trifluoro-2-hydroxy-1-trifluoromethylethane sulfonic acid Beta-sultone was conducted. High proton conducting sulfonated poly(ether ether ketone) (sPEEK)/ functionalized mesoporous silica composite membranes were prepared through homogeneous dispersive mixing and solvent casting method. In the study, proton conductivity (σ) of composite membrane is increased from 0.01 to 0.038 (S/cm) as the modified mesoporous silica content is increased from 0 to 5 wt. %. It is found that the ion exchange capacity (IEC) is increased from 1.54 to 1.70 (meq/g) as the modified mesoporous silica content is increased from 0 to 5 wt. %. From morphology investigation, it is found that incorporation of modified mesoporous silica by rotary vacuum evaporation enables the preparation of homogeneous membranes. The membranes present a good adhesion between inorganic domains which could be used for fuel cell applications.

Abstract: In this paper, fiber Bragg grating (FBG) sensor and piezoelectric (PZT) actuator are used to develop a hybrid system for the evaluation of delamination in glass fiber-reinforced epoxy (GF/EP) composite laminates. The surface-bonded PZT actuator generates ultrasonic Lamb wave in the composite laminates, while the FBG sensor, which is embedded in the composite laminates, captures the Lamb wave signal. Wavelet analysis is introduced to extract signal spectrographic characteristics in the time-scale domain appropriately. Since the propagation characteristics of Lamb wave is altered by the existence of damage in the composite laminates, delamination information can be obtained from the received signal. With the assistance of a signal generation and an acquisition system, this methodology enables active sensing and non-destructive evaluation of delamination in the composite laminates. Experiments have been carried out with GF/EP composite beams to examine the feasibility of the proposed detection technique. The acquired and processed Lamb wave signals corresponding to different delamination sizes are compared.