Key Engineering Materials Vols. 334-335

Abstract: Sensor data are the basis for health assessment of complex structural systems. Careful selection and logical layout of sensors is critical to enable the high reliability of system health assessment. This paper presents a methodology how to use a minimum number of sensors, and what locations of them should be placed, so that the voltage signals received from the sensor can be used to detect both presence and extent of damage. In this study, an optimization procedure is developed using Genetic Algorithm (GA) to determine the location of piezoelectric sensor for damage detection in a composite wingbox. A new damage index using all differences in voltage signals decomposed by wavelet transform is proposed. Results show that the proposed method is available at determining number and location of sensors for structural damage detection using piezoelectric patch sensors.

Abstract: The quality of the interfaces in multilayer composites is a critical issue in the reliability testing of the composite product during the manufacturing process and in-service. Weak interfaces have often gone undetected and may become potentially defective at a later stage. One example is the interface between mold compound and silicon (MC/Si) in IC packaging. There is a desire to study the interface quality quantitatively, so the potential defective area can be evaluated and identified early. In this paper, a nondestructive evaluation methodology is proposed to measure the available strength of the interface by using ultrasonic reflection coefficients. It is known that interface degradation can be either due to poor manufacturing process and stress loading. Characterization of the interface quality of the MC/Si interface is first conducted by measuring longitudinal ultrasonic wave reflections from the interface samples fabricated under varying conditioning processes that simulate the degradation. A combined test that measures the reflection coefficient of the interface under stress load has also been conducted to quantify the effect of the load. Finally, it is shown that the overall effect on the reflection coefficient and available strength of the interface is derived and can be used as a quantitative indicator.

Abstract: Continuous carbon fiber-reinforced silicon carbide (Cf/SiC) composite was fabricated by hot-pressing, via liquid phase sintering. Sintering conditions strongly affect the densification process, and therefore dominate the mechanical properties and fracture behavior. The composites under the lower sintering temperature behaves less densified matrix and it demonstrates a relatively weak fiber/matrix bonding allowing the longer fibers pull-out. Increasing sintering temperature could accelerate the densified matrix and make fiber/matrix bonding stronger. In this case, the shorter fibers pull-out was predominant fracture behavior and it could improve mechanical properties.

Abstract: Relaxor-based lead-lanthanum-zirconate-titanate (PLZT) thick films were prepared on Ti substrates by a simplified hydrothermal method, in which the precursors were heated to 150 oC with durations from 8 to 32h. The mixture of oxides was used as the staring materials. The smooth PLZT films with a single perovskite structure were obtained through the synthesis route. Structural and morphological studies were carried out on hydrothermally synthesized films. The influences of the mineralizer concentration on the structural, morphological, and physical characteristics of the particles are studied. Phase characterization and crystal orientation of the PLZT thick films were investigated by x-ray diffraction analysis (XRD). The dielectric constant and dielectric loss of the PLZT thick films were measured. In the frequency range from 1000 to 100 MHz, the dielectric constant and the dielectric loss were very steady.

Abstract: The fabrication processing, dielectric properties and thermal properties of polymer-matrix composites containing AlN particles (10μm) for electronic substrates and microelectronic packaging applications were investigated. The epoxy resin (E-51) is used as the matrix, and the dispersion of the AlN in the composites is varied form 0 vol% to 40 vol%. The microstructures of the polymer-matrix composites are observed through scanning electron microscopy (SEM). With increasing the AlN content, thermal conducting of composites is improved, while the composites still keep the relatively low dielectric constant and dielectric loss. According to the dielectric properties dependence on frequencies (1kHz-10MHz) of the composites, the Cole-Cole plot is analyzed. The dipole relaxation in the composite is induced, and it is suggested that the air layer exit between the epoxy resin and the AlN particles.

Abstract: Microstructure and mechanical properties of 20% Al-Cu-Cr/Al composites synthesized by hot-pressing technique after annealing, quenching and aging was studied by means of X-ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and uniaxial compressive test. Microstructure of Al-Cu-Cr particles in the composites after hot-pressing is mainly consist of icosahedral quasicrystals and which transformed into decagonal quasicrystals after annealing. Microstructure of matrix in the composites after hot-pressing, annealing, quenching and aging is pure Al, Al + Al2Cu, supersaturated solid solution Al and Al + Al-Cu transition phases respectively. Hardness, fracture strength and the Young’s modulus of the composites are improved by age-hardening.

Abstract: Silica nanoparticles and silica/titania hybrid nanocomposites were synthesized by sol-gel processes, and padded on cotton fabric. The sizes of these particles ranged from tens to hundreds of nanometers. The morphologies of nanoparticles and hybrid nanocomposites were characterized by high magnification field-emission scanning electron microscope (FESEM). The UV-blocking properties of untreated and treated fabrics with silica/titania nanocomposites were studied and discussed.

Abstract: In recent years, chitosan/inorganic composites have attracted increasing attention due to its fascinating properties and potential applications in biodegradable materials, drug release, electrochemical sensor, packaging materials and so on. Chitosan/inorganic composites are expected to be as an effective way to overcome shortcomings of slow flocculating speed of chitosan particles, not good enough to meet those wide range of applications in wasterwater treatment. In this study, novel chitosan/clay/PAC (polyaluminium chloride) composite was prepared, and it was used in treating effluent from dying and finishing process. One set of orthogonal experiments were conducted to optimize the experimental condition, and the results showed that removal of waste dye is affected by the dosage of chitosan, PAC, clay, pH and treatment time. The experiments results indicated that the effluent from dying and finishing process treated by the prepared composites became obviously fade, and its COD (chemical oxygen demand) decreased from original 1398.2mg/L to 197.6mg/L, the removing rate reached 85.9%.