Applied Mechanics and Materials Vols. 249-250

Abstract: The tensile response of three-dimensional angle-interlock woven composite (3DAWC) under quasi-static loading was investigated in experimental and finite element model (FEM) analysis. The FEM analysis was based on micro-structure at yarn level and connected with commercial FEM software ABAQUS/Explicit (ver. 6.10) to calculate the tensile property under quasi-static loading. The experimental and FEM stress-strain results were compared. Good agreement proved that the FEM method based on micro-structure was reasonable and effective and could be used to design 3-D woven structural composite.

Abstract: The TPGDA drop was suspended in the atmosphere under acoustic levitation and induced by photoinitiation for polymer preparation at the first attempt. The kinetics of TPGDA photopolymerization induced by the UV light under containerless condition was studied. Compared to the normal condition, the average initial polymerization rate of TPGDA under acoustic levitation is relatively lower, while the final conversion is higher. Relative to oxygen inhibition, container effect plays a more significant role on the conversion in this polymerization system.

Abstract: We propose a mathematical model of large elastoplastic deformations with rheological features. As an example of applying the model relations, we present a solution of the boundary-value problem on collapsing process of microdefect continuity in elastic-creep-plastic materials under uniform pressure. In the case of a single micropore we obtained quantitative estimates of this process. The fields of stress and the residual deformation are computed.

Abstract: This paper presents a spectral element model for the laminated composite beams with a surface-bonded PZT layer. The spectral element model represented by exact dynamic stiffness matrix is derived in the frequency-domain by using the frequency-dependent dynamic shape functions which are formulated from the free wave solutions satisfying the governing differential equations transformed into the frequency-domain by using the DFT theory. The performance of the present spectral element model is then evaluated by comparing its solutions with those obtained by using the conventional finite element model

Abstract: In this paper, UV curable waterborne polyurethane emulsions were prepared by fractional step method using toluene diisocyanate (TDI), polyethylene glycol (PEG, MW=1000), α,α-dimethylol propionic acid (DMPA), 2-hydroxyethyl methacrylate (HEMA) as raw material, and UV-WPUs were modified with epoxy resin. The effect of different content of epoxy resin on the viscosity, the water resistance, and other properties was investigated. The synthesized polyurethane structure was confirmed by the Fourier transform infrared spectroscopy (FTIR). The FTIR analysis identified that the target product was expected epoxy modified waterborne UV polyurethane. And with –COOH content increasing, the emulsion viscosity of the WPU increased and the water absorption of the films increased; with epoxy content increasing, the viscosity of the WPU emulsion increased and the water resistance of the films was improved.

Abstract: Structural Health Monitoring (SHM) for composite materials is becoming a primary task due to their extended use in safety critical applications. Different methods, based on the use of piezoelectric transducers as well as of fiber optics, has been successfully proposed to detect and monitor damage in composite structural components with particular attention focused on delamination cracks.In the present paper a Structural Health Monitoring model, based on the use of piezoelectric sensors, already proposed by the authors for isotropic damaged components, is extended to delaminated composite structures. The dynamic behavior of the host damaged structure and the bonded piezoelectric sensors is modeled by means of a boundary element approach based on the Dual Reciprocity BEM. The sensitivity of the piezoelectric sensors has been studied by varying the delamination length characterizing the skin/stiffener debonding phenomenon of composite structures undergoing dynamic loads.

Abstract: This paper experimentally investigates the damage detection of filament-wound (FW) thick-wall composite cylinder using ultrasonic waves. The multi-layered cylinder has a 20 mm-thick steel liner with an inner radius of 421 mm, an 11 mm-thick layer of unidirectional carbon fiber reinforced composite that is wound on the steel liner, and a 2.15 mm-thick layer of coating over the composites. Damages are pre-manufactured in different wall depths of the cylinder. The main damages to be detected include the defects in the composite layer, the interface debonding between the composite layer and the steel liner, and the change of thickness of the steel liner due to corrosion. To interrogate above mentioned damages, the longitudinal waves are excited using an ultrasonic transducer in pulse-echo mode along the radial direction of the cylinder. The continuous wavelet transform (CWT) is used to analyze the reflected-ultrasonic signals in order to obtain the Time-of-Flight (ToF) and the amplitude ratio of different interfaces. Based on the ToF and amplitude ratios, the location and size of the damages are identified and the thickness of the steel liner is determined. Experimental results show that the ultrasonic pulse-echo technique combined with the CWT is feasible in damage detection of multi-layered filament-wound composite cylinder especially when a coating layer exists.

Abstract: Using compression test on a thermo-mechanical simulator/dilatometer, hot deformation behavior of steel AISI 4340 was studied in the temperature range of 850-1150°C and strain rate range of 0.01-10 s-1. The resulted true stress-strain curves exhibited a peak stress at low strain values, after which the flow stresses decreased monotonically until higher strains, representing the dynamic flow softening. The stress level decreased with increasing deformation temperature and decreasing strain rate. The material flow behavior at elevated temperatures was described using a Zener-Hollomon parameter with an exponent-type equation. Additionally, the model was modified by compensating strain rate parameter. The stress-strain responses for the investigated steel predicted by the proposed model agreed well with the experimental results. It was confirmed that the modified constitutive equations provided a more accurate prediction of the flow stress under hot working conditions for steel AISI 4340.

Abstract: Similar welds composed of 5083 were produced by friction stir welding. In the solution of 0.2 M NaHSO₃ and 0.6 M NaCl, the electrochemical corrosion behaviors of the friction stir welds (FSW) and 5083 were comparatively investigated by static weight loss experiments and potentiodynamic polarization curve tests at the ambient temperature. The results indicated that the average corrosion rate of the weld was less than that of 5083. Then, sodium molybdate was added to the corrosive solution and its effect on the corrosion behaviors of the weld and parent metal was comparatively assessed. The inhibition efficiency (IE) for the weld was beyond that for 5083 base materials, sodium molybdate may be thought of as an effective inhibitor.

Abstract: By applying the shear damage criteria, facture occurrence for roll forming of U Section parts of TRIP 600 steel is analyzed with nonlinear finite element. In accordance with the maximum value of steel sheet of plastic strains for the fracture initiation and with the application of the element deletion technology of the ductile fracture, the calculation of the damage evolution parameters of the material fracture is successfully set up. By applying the explicit dynamic solution method, the fracture finite element analysis of TRIP600U type section roll forming is realized, and the relationship among the stress, strain, energy density as well as damage evolution and material fracture is obtained.