Key Engineering Materials Vol. 627

Abstract: This work analyses the effects of hydrogen-assisted rolling-contact fatigue on bearings of wind turbines. To this end, the well-known ball-on-rod test to evaluate the resistance to rolling-contact fatigue was simulated by the finite element method for obtaining the stress-strain state undergone by the bearings considering their in-service conditions. Results of this paper allow a simple estimation of the hydrogen amount in potential damage zones of the specimen.

Abstract: The objectives in this paper are the followings: evaluate the seismic performance of the three buildings and compare the elastic and inelastic seismic responses of the buildings, calculated with the records CCH-NS (Chilean earthquake 2010) and SCT-EW (Mexican earthquake 1985) of the cases of strengths elastic and inelastic with nominal strength and over-strength of each model. The building 1 is a real case of a concrete wall building that collapsed during the Chilean earthquake of February 27, 2010. The building 2 was analyzed and designed with the Chilean Norm “Seismic Design of Buildings” (NCH-433) and “Reinforced Concrete–Design and Calculus Requirements” (NCH-430). The analyses and design of the building 3 was realized with the Mexican Norms “Complementary Technical Norms for seismic design” (NTC-Seismic), “Complementary Technical Norms for Design and Construction of Concrete Structures” (NTC-Concrete) of the “Code of Constructions for the Federal District” (RCDF-04). The elastic and inelastic seismic responses of each building were calculated with the step by step dynamic method. Should be avoided that the fundamental period of vibration of the structures match with the dominant period of the ground (T_s). In the design of concrete structural walls is very important classified the walls according to its slenderness in order to recognize the behavior that will govern the wall, and with it determine the detailed of the steel reinforcement that could provide the best behavior when the wall be submitted to an important earthquake.

Abstract: The aim of this paper is to estimate a value of the critical applied force for a crack initiation from the sharp V-notch tip. The classical approach of the linear elastic fracture mechanics (LELM) was generalized, because the stress singularity exponent differs from 0.5 in studied case. The value of the stress singularity exponent depends on the V-notch opening angle. The finite element method was used for a determination of stress distribution in the vicinity of the sharp V-notch tip and for the estimation of the generalized stress intensity factor depending on the V-notch opening angle. Critical value of generalized stress intensity factor was obtained by using stability criterion based on the tangential stress component averaged over a critical distance d from the V-notch tip. Calculated values of the critical applied force were compared with experimental data taken from the literature.

Abstract: To solve the problem of large environmental burden caused by disposal of FRP (Fiber Reinforced Plastics), Poly Lactic Acid (PLA), which is plant-derived and biodegradable, has received a lot of attention as an environmentally friendly material for the matrix of FRP. However, since the decomposition rate is very slow as compared with other biodegradable resins, it is difficult to make a processing of a large amount of PLA in the natural environment. Therefore, a method to accelerate decomposition rate of PLA by blending hydrolysis accelerator to PLA has been developed. In this study, composite material, in which PLA is blended with hydrolysis accelerator and reinforced with glass fibers, was molded using high speed compression molding process, and its tensile strength and the effect of heat treatment and tensile strength on the crystallinity was clarified. In consequence, regardless of the existence of hydrolysis accelerator, crystallinity of glass fiber reinforced PLA composites was improved by the annealing process. Tensile strength of glass fiber reinforced PLA decreased by the annealing process. For glass fiber reinforced PLA which was blended with hydrolysis accelerator, however, annealing process did not affect their tensile strength.

Abstract: To use Carbon Fiber Reinforced Thermoplastics (CFRTP) for automobile applications, mechanical properties of CFRTP under actual operating temperatures are needed to be clarified. When focusing on heat resistance of CFRTP, to use Polyphenylenesulfide (PPS) for the matrix is desirable. However, the effect of high temperature on mechanical properties of CFRTP using PPS has not been clarified yet. In this study, single fiber pull-out tests of CF/PPS model composites under high temperature were conducted to reveal the fiber/matrix interfacial properties.

Abstract: Matrices for carbon fiber reinforced thermoplastics are appropriate to use comparatively cheaper resins such as polyamide. However polyamide 6 is highly hygroscopic and the mechanical properties of materials are reported to be degraded by water absorption. Polyoxamide (PX) has been developed as polyamide resins with low hygroscopicity. In this study, the effect of hot water environment on the tensile fracture properties of carbon fiber/polyoxamide composites has been clarified.

Abstract: This paper was aimed to evaluate temperature characteristics on housing made of aluminum alloy, and in lubricant oil of gearbox installed at independent wheel drive while the vehicle was running under various running mode (speed, climate condition). Based on the measured temperatures, operational stability of the gearbox was discussed in this paper.

Abstract: Size effect for tension specimen in creep condition is not very well recognised phenomenon. The Weibull’s works on influence of nonhomogeneity of material properties on its strength suggest that such effect should take place also for creep. The most of authors regard that the stress redistribution occurring during creep considerably reduces size effect. To examine it the author performed a series of experiments for thin tin alloy wires creeping in room temperature as well as some numerical simulations. The results confirmed the existence of size effect for time to failure. The numerical analysis was made for time of first macroscopic damage occurrence t₁ and for time of cross-section failure t₂. Both these parameters show the influence of specimen size according to size effect law, but the dependence of parameter t₁ was more pronounced.

Abstract: The joining of the galvanized sheet is normally difficult to be done with classical methods, requiring special attention to the specific problems involved during the welding process. This paper presents the development of the joint technology by Cold Metal Transfer (CMT) of galvanized steel sheet using as filler material a CuSi wire electrode. The salt fog corrosion test was made to certify anticorrosive protection of the galvanized sheet metal joints. This test revealed a minimal deterioration of the galvanized zinc coating during welding and also confirms that using adequate technology galvanized steel can be weld without affected anticorrosive protection of the zinc layer.Experimental researches include optimization of the welding technology using CMT concept; technical skill development solutions of the joints; elaboration and implementation of laboratory advanced technology; experimentation and demonstration of technology functionality by obtaining of braze welded joints corrosion resistant.

Abstract: The aim of the present research is to investigate the fatigue behaviour of friction stir (FS) welded tubular joints in aluminium alloy subjected to torsional fatigue loading. To manufacture the samples which were tested, an MTS I-STIR process development system was equipped with a retracting tool specifically designed for these tubular welds. Al 6082-T6 FS welded samples were tested under cyclic torsion with a nominal shear stress ratio equal to-1 and 0. The test data show that, strictly speaking, the presence of non-zero mean shear stresses has a detrimental effect on the overall torsional fatigue strength of the FS welded joints. However, the reanalysis discussed in the present paper suggests that, from a statistical point of view, any detrimental effect is small. This means that fatigue assessment under torsional fatigue loading of these FS welded tubular connections can be performed with little loss of accuracy by neglecting the presence of non-zero mean shear stresses.