Key Engineering Materials Vols. 577-578

Abstract: In this study, effect of crystallinity on mechanical properties of carbon fiber reinforced thermoplastics (CFRTP) was investigated. Polypropylene (PP) and maleic anhydride modified polypropylene (MAPP) were used as matrix. The crystallinity of PP was controlled by using heat treatment after hot press molding of CFRTP. The range of crystallinity of PP and MAPP were from 26% to 40%. Flexural tests and izod impact tests of CFRTP were conducted based on Japanese Industrial Standard (JIS) K 7074 and JIS K 7110, respectively. As a result, flexural property and izod impact value of CFRTP using PP increased with an increase of crystallinity. However, flexural property and izod impact value of CFRTP using MAPP almost did not change with an increase of crystallinity.

Abstract: This paper deals with the mechanical behavior of bamboo fiber-reinforced biodegradable composites (green composites). A starch-based, dispersion type biodegradable resin was used as matrix polymer, and this matrix was reinforced by long bamboo fibers which were extracted by a steam-explosion method. The experimental results showed that the developed green composites possessed the flexural and tensile strength of 263 MPa and 270 MPa, respectively. The mechanical properties of the green composites were evaluated as a function of fiber content. It is found that the observed tensile strength was slightly lower than that of estimated values from the rule of the mixture. This discrepancy might be related to the misorientation of the bamboo fiber in the composites and to that the final fracture of composites is also governed by the presence of weak bamboo fiber.

Abstract: Composite materials which main constituent part is a metal are called Metal Matrix Composites (MMCs). The other compounds may be metals too, ceramics or even organics. They are well known for their excellent thermo-physical and mechanical properties. Reinforcement is used to improve different properties of the main material, such as wear resistance, hardness, fatigue resistance, friction coefficient, thermal conductivity and others. As a result, during the last years, MMCs have found a lot of application in automobile industry for the production of brakes and parts of engines and in aerospace industry for the production of structural components, as well as in electrical and electronic industry and in many other applications. MMCs can be produced by many ways, such as, powder blending and consolidation, foil diffusion bonding, electroplating, spray deposition, stir-casting and others. In this research stir-casting was used as processing technique for the production of Aluminum matrix composites reinforced by ceramic particles and iron. The morphologies of the produced composite materials were examined using optical and SEM microscopy. The compositions of their micro structural features were determined by EDX spectroscopy. The phases formed were determined by XRD techniques. In the tribological tests, under dry wear conditions, the as-produced composites materials showed significant increased resistance to wear compared to pure Al metal.

Abstract: Effect of plant oil on the fatigue strength of a squeeze cast Al-Si-Mg alloy was investigated. Crack growth rate was higher in plant oil than in air, inducing a decrease in fatigue strength. The reason included is explained from the viewpoint of high water absorbency of plant oils, on basis of hydrogen enhanced localized plasticity.

Abstract: An ellipsoidal void model for simulating ductile fracture behavior was proposed by the author [K. Komori: Mech. Mater., Vol. 60 (2013), p. 36]. The nominal fracture strain calculated from this model is slightly larger than that calculated from the finite-element void cell when the initial void volume fraction is specified. To decrease the difference, an assumption must be made that the deformation gradient of the void does not coincide with that of the matrix. This study proposes a simple relationship between the two deformation gradients that produces agreement between the nominal fracture strain calculated using the ellipsoidal void model and that using the finite-element void cell.

Abstract: The effects of microalloying on the fracture toughness of 0.2%C1.5%Si1.5%Mn 0.05%Nb (mass%) transformation-induced plasticity-aided steel with a lath-martensite structure matrix were investigated. When 0.002% B or 1.0% Cr was added to the base steel, the steel achieved a fracture toughness that was as high as that of 18%Ni maraging steel. Based on our results, the high fracture toughness was essentially caused by (i) a matrix with a softened lath-martensite structure, low carbide content and low carbon concentration; (ii) the effective plastic relaxation of localized stress concentration by the strain-induced transformation of metastable retained austenite of about 3 vol% in the martensite-austenite constituent or phase.

Abstract: The paper is focuses on one of probabilistic methods which can be used for failure analysis and reliability assessment of steel structures which are subject to cyclic loads and exposed to fatigue. A particular attention is paid to creation and propagation of fatigue cracks from edges and surface. On the basis of the reliability assessment, a system of inspections is proposed for structural details which tend to be sensitive to fatigue damage. A new probabilistic method which is still under development - Direct Optimized Probabilistic Calculation (DOProC) was used for this probabilistic task. This method is the basis of the FCProbCalc code.

Abstract: The technology of flywheel energy storage is already widely used in motorcar, electric power systems, spaceflight and martial fields. Decreasing the weight, increasing rotating speed and strength of the flywheel rotor and improving the energy storage efficiency of the flywheel are always attention-getting. In this paper, the flywheel energy storage wrapped with composite material by interference fit to hub is designed and finite element analysis is done to obtain the stress distribution of it before being produced. The maximum and variety of stress are studied and the influence of composite material wrapped on flywheel rotating at a high speed is discussed. Then the action of composite material preload to the flywheel is thought about. The results of this analysis can prepare a valuable guide for flywheel energy storage at design and manufacture stage.

Abstract: In engineering composite materials, earthquake engineering and modern municipal construction, it can be found that there are shallow-buried cavity or inclusion structure near surface. When structure is impacted by dynamic load, scattering field will be produced because of the cavity or the inclusion, and it could cause dynamic stress concentration at the edge of the cavity or inclusion. In this paper, Green's Function is studied, which is the solution of displacement field for elastic semi-space with multiple shallow-buried cavities and inclusions while bearing anti-plane harmonic line source force at any point. In the complex plane, considering the symmetry of SH-wave scattering, the displacement field aroused by the anti-plane harmonic line source force and the scattering displacement field impacted by multiple cylindrical cavities and inclusions are constructed. Through applying the method of multi-polar coordinate system, the equations with unknown coefficients can be obtained by using the stress or displacement condition of the cylindrical cavities and inclusions in the radial direction. According to orthogonality condition for trigonometric function, these equations can be reduced to a series of algebraic equations. By solving these algebraic equations the value of the unknown coefficients can be obtained. So the total wave displacement field could be got. By using the expressions, an example is provided to show the effect of the change of relative location of the cylindrical cavities, inclusions and the location of the line source force.

Abstract: A set of mixed-mode I/II fracture tests was carried out on a polyurethane material. Using a single edge notched bend (SENB) type specimen, containing straight and respectively inclined U notches, the full range from pure mode I to dominant mode II was achieved. Two different fracture criteria were employed for the prediction of the fracture conditions: the UMTS criterion and the averaged SED criterion. Using these two criteria a set of curves were derived in terms of the fracture load vs. notch radius. The agreement between the experimental results and those predicted based on these two criteria is discussed finally.