Key Engineering Materials Vol. 827

Abstract: The prediction of a crack initiation and propagation occurring on the microstructural level of heterogeneous materials can be a very demanding problem. According to the results of recent investigations, the emerging phase field approach to fracture has a strong potential in modelling the complex crack behaviour in a simple manner. In this study, recently developed phase field staggered solution scheme with the residual norm stopping criterion has been employed for the fracture analysis of heterogeneous microstructure exhibiting complex crack phenomena. The microstructural geometries based on the metallographic images of the nodular cast iron and the material properties of an academic brittle material have been used in numerical simulations where the graphite nodules have been considered as porosities. Two commonly used energy decomposition models, the spectral decomposition and the spherical-deviatoric split, and their effects on the results of the phase field modelling are investigated. Numerical results show that the proposed algorithm recovers the complicated crack path driven by the complex microstructural topology.

Abstract: Transportation sector is required to reduce CO₂ emissions as environmental problems are becoming more serious. Carbon fibre reinforced thermoplastic (CFRTP) are expected to be applied to the structural parts of automobiles and aircrafts because of their superior mechanical properties such as high specific strength, high specific stiffness and high recyclability. One of the problems in using CFRTP for the structural parts is heat resistance, and it is necessary to clarify the mechanical properties under their service environmental temperature. The tensile strength of CFRTP at high temperatures decreases with temperature rise. The fibre matrix interfacial shear strength is reported to be improved by grafting of carbon nanotubes (CNTs) on the surface of carbon fibre. In this study, in order to clarify the effects of temperature on the fibre matrix interfacial shear strength of CNTs grafted carbon fibre reinforced PPS resin, single fibre pull-out test was conducted. While the interfacial shear strength of CNT grafted-CF/PPS is higher than that of As-received-CF/PPS at 25 °C, no significant difference was found in the interfacial shear strength of As-received-CF/PPS and CNT grafted-CF/PPS at 80 °C.

Abstract: The application of Glass Fibre Reinforced Thermoplastics (GFRTP) is expected to reduce the weight of automobiles. In order to use GFRTP for automotive parts, it is essential to apply Computer Aided Engineering (CAE) technology. Until now, prepreg sheets with thermosetting resin matrix are assumed to be used for materials in simulation software. When FRTP is applied for materials in simulation software, it is required to grasp the characteristics of FRTP under moulding temperature. In our previous study, a system capable of evaluating the tensile properties of FRTP laminates at moulding temperatures had been developed and their tensile properties had been evaluated. Bending stiffness under moulding temperature is also required for simulation software. While bending stiffness can be determined using Young's modulus for isotropic materials, thermoplastic prepregs have large anisotropy, especially at moulding temperature. In this study, a system that enables self-weight deflection test of thermoplastic resin laminate under moulding temperature was developed and self-weight deflection characteristics of plain weave GFRTP were evaluated. The analysed results in which the bending stiffness under the moulding temperature of GFRTP was taken into account, gave the most suitable results to the experimental results.

Abstract: Reinforced Concrete (RC) Beam undamaged and damaged were investigated by free vibration to obtain a variation of frequency values at different degree of damage. Experimental tests were carried out on RC beams in scale and in real scale. The damage of RC beams in real scale was obtained by cracking under static bending tests, while in the case of beam in scale is obtained by notches on the concrete cover with different width. In general, the effects on the dynamic response of diffused damages and of concentrated damages on a section of beam have been experimentally analyzed. The envelope of frequency response functions (FRFs) obtained by dynamic experimental tests was elaborated and the changes of natural frequency values were then correlated to the damage degree of RC beams. The experimental data have been discussed and analyzed by comparison with theoretical results.