21,376 research outputs found
Fatigue life prediction of bolted joints using fatigue modulus
No full textThe fatigue life prediction of SUS304 stainless steel with bolted joints has been investigated using fatigue modulus concept proposed by Hwang & Han. In this paper, modified fatigue life prediction equation (MFLPE) is derived by fatigue modulus degradation model, which is a exponential function of fatigue modulus, fatigue cycle and load transfer level in order to consider the relaxation of stress concentration due to fasteners. Tests have been performed using various load transfer levels to verify the derived prediction equation. The experimental results show that fatigue modulus can be used as a parameter to represent fatigue damage and the geometry parameters affect the constants in the fatigue life prediction equation.X111sciescopu
Fatigue life modeling of short fiber reinforced metal matrix composites using mechanical and acoustic emission responses
No full textThe cyclic fatigue behavior of short fiber reinforced metal matrix composites was studied. Three fatigue life prediction models were developed by monitoring the resultant maximum strain and counts of acoustic emission during cyclic fatigue. Their increasing trends with the number of fatigue cycles were studied using the assumption that they can be expressed as a power-law function of the fatigue cycle number. Post-fatigue static tension tests were conducted to examine the degradation of the damaged materials. The acoustic emission count accumulated during tension testing decreased as the applied fatigue cycles increased; this change was also used to formulate life prediction models. All the new models show a better agreement to experimental data than do the existing equations.X1111sciescopu
Damage and failure monitoring of fiber-metal laminates using optical fiber sensors
No full textOptical fiber vibrations sensors(OFVS) and extrinsic Fabry-Perot interferometer(EFPI) were used in damage monitoring of fiber-metal laminates(FML). The OFVS and EFPI were applied in order to detect and evaluate the strain, damage and failure of FML. Indentation tests were performed with the measurement of optical signal and acoustic emission(A-E). Robust signal processing methods based on time-frequency analysis were proposed to monitor damage signals of the structure with removing the influence of environmental and sensor noise. The signals of the OFVS due to damages were quantitatively evaluated by wavelet transform(WT). Relative position and condition between the specimen and indenter were able to estimate by observing the fiber-optic interference fringes of EFPI. It was found that damage information of comparable in quality to acoustic emission data could be obtained from the OFVS signals. The OFVS proved to be effective for monitoring the damage process of the material studied here.X111sciescopu
Mechanical properties and solid lubricant wear behavior of Al/Al2O3/C hybrid metal matrix composites fabricated by squeeze casting method
No full textIn this study, mechanical properties and wear behavior of Al/Al2O3/C hybrid metal matrix composites fabricated by squeeze casting method was characterized. The effects of volume fraction of carbon fiber on mechanical properties of hybrid composites was investigated. Tensile strength of Al/Al2O3/C composites was decreased by increasing the addition of carbon fiber. The carbon fiber additions were seen to be less effective in strength than when only alumina fibers were incorporated, because carbon fibers in hybrid systems are difficult to wet by molten aluminum alloys and react with a matrix alloy to form brittle aluminum carbide (Al4C3). Ductility was considerably reduced by increasing the incorporation of carbon fiber. Wear behavior of Al/Al2O3/C composites was characterized by the dry spindle wear test under various sliding speeds. The wear resistance of Al/Al2O3/C composites was remarkably improved over Al/Al2O3 composites by adding carbon fibers to Al/Al2O3/C composites. Specifically, at the intermediate sliding speed the wear resistance of Al/Al2O3/C composites containing 8 vol.% carbon fiber was found to be better than that of the rest of the carbon hybrid composites, but amounts of carbon volume fraction were of little effect on wear resistance at high sliding speed of 3.62 m/sec. From fractographic studies, damaged sections in wear surfaces of hybrid composites at intermediate sliding speed were seldom observed due to the formation of solid lubrication film. The solid lubrication film which was formed as a result of adding carbon fibers improved the wear resistance of carbon hybrid composites because this film reduced the high friction force between MMCs and counter material. Wear model of Al/Al2O3/C composites was also suggested by the examination of worn surfaces.X1120sciescopu
Effect of volume fraction of carbon fibers on wear behavior of Al/Al2O3/C hybrid metal matrix composites
No full textWear behavior of Al/Al2O3/C hybrid metal matrix composites fabricated by squeeze casting method was characterized. The effects of volume fraction of carbon fiber on wear behavior of hybrid composites was investigated. Wear behavior of Al/Al2O3/C composites was characterized by the dry spindle wear test under various sliding speeds. The wear resistance of Al/Al2O3/C composites was remarkably improved over Al/Al2O3 composites by adding carbon fibers to Al/Al2O3/C composites. Specifically, at the intermediate sliding speed the wear resistance of Al/Al2O3 composites containing 8 vol.% carbon fiber was found to be better than that of the rest of the carbon hybrid composites. From fractographic studies, damaged sections in wear surfaces of hybrid composites at intermediate sliding speed were not observed due to the formation of solid lubrication film. The solid lubrication film which was formed as a result of adding carbon fibers improved the wear resistance of carbon hybrid composites because this film reduced the high friction force between MMCs and counter material. © 1998 Elsevier Science Ltd. All rights reserved.X1141Nsciescopu
Acoustic emission as a tool of fatigue assessment
No full textA series of laboratory investigations concerned about fatigue assessment with acoustic emission method was presented. Fatigue aspects including cumulative fatigue damage, fatigue crack growth and creep-fatigue interaction were considered. As a basic approach, residual strength and acoustic emission characteristics of fatigue damaged materials were considered from the nominal stress-life (S-N) viewpoint. Acquired signal indicated that counts emission quantity can be a good measure of cumulated fatigue damage. In the fatigue crack growth approach, interrelationship between acoustic emission parameter and stress intensity factor was examined with different stress level and crack length. Experimental results were somewhat scattered since sensitive characteristics of acoustic emission method. However, their empirical relation indicated that counts rate correlated with fracture mechanics parameter. Finally, acoustic emission application was extended to the creep-fatigue interaction at elevated temperature. Emission response under each damage mode was compared and characterized. Based on these characteristics, creep-fatigue interaction was evaluated by use of acoustic emission parameter. Overall investigations concluded acoustic emission is very effective tool of fatigue assessment.X112sciescopu
Creep rupture life prediction of short fiber-reinforced metal matrix composites
No full textThe creep rupture life of an Al/Al2O3 composite and its creep behavior were studied. The metal matrix composite was produced by using a squeeze casting technique. High-temperature tensile tests and creep experiments were conducted on a 15 vol pet alumina fiber-reinforced AC2B Al alloy metal matrix composite (MMC). The high-temperature tensile strength of Al/Al2O3 composite is 14 pet higher than that of an AC2B Al alloy. The steady-state creep rate and the creep life were measured. The stress exponent in Norton's equation and the activation energy were computed. The stress exponents of the AC2B and Al/Al2O3 composites were found to be 4 and 12.3, respectively. The activation energy of the AC2B and Al/Al2O3 composites was found to be 242.74 and 465.35 kJ/mol, respectively. A new equation for predicting creep life was established, which was based on the conservation of the creep strain energy. The theoretical predictions were compared with those of the experiment results, and a good agreement was obtained. It was found that the creel, life is inversely proportional to the (n + 1)th power of the applied stress and strain failure energy of creep is conserved. The creep fracture surface, examined by scanning electron microscopy (SEM), showed that the MMC specimen failed in a brittle manner.open116sciescopu
Damage monitoring and impact detection using optical fiber vibration sensors
No full textIntensity-based optical fiber vibrations sensors (OFVSs) are used in damage monitoring of fiber-reinforced plastics, in vibration sensing, and location of impacts. OFVSs were constructed by placing two cleaved fiber ends in a capillary tube. This sensor is able to monitor structural vibrations. For vibration sensing, the optical fiber sensor was mounted on the carbon fiber reinforced composite beam, and its response was investigated for free and forced vibration. For locating impact points, four OFVSs were placed at chosen positions and the different arrival times of impact-generated vibration signals were recorded. The impact location can be determined from these time delays. Indentation and tensile tests were performed with the measurement of the optical signal and acoustic emission (AE). The OFVSs accurately detected both free and forced vibration signals. Accurate locations of impact were determined on an acrylate plate. It was found that damage information, comparable in quality to AE data, could be obtained from the OFVS signals.X1119sciescopu
Fabrication of graphite nanofibers reinforced metal matrix composites by powder metallurgy and their mechanical and physical characteristics
No full textAluminum metal matrix composites reinforced by graphite nanofibers (GNFs) are fabricated by conventional powder metallurgy methods, and their mechanical and physical characteristics are investigated. Mixing conditions are established by microhardness tests and microscopy observations. The GNF-Al composites are consolidated by hot isostatic pressing (HIP); a high density of composites can be achieved. From microhardness and compression tests, the optimal nanofiber content is determined. The physical properties of the GNF-Al composites are measured by thermal and electrical transport tests. The results indicate that the addition of nanofibers improves the thermal conductivity and the electrical resistivity, but the dimensional stability under high temperatures is not improved. This study may provide experimental information in the design and fabrication of functional metal matrix nanocomposites.X1111sciescopu
Finite element analysis of deep drawing and ironing process in the steel D & I canmaking
No full textThe bodymaking of D&I can consists of a deep drawing process, a redrawing process and a multi-stage wall ironing process. From the viewpoint of mechanics, it can be classified into a complicated high-speed forming process, including nonlinear and coupled thermal-mechanical contact problem. In this study, an ax isymmetric non-isothermal finite element analysis using the FEA code ABAQUS has been conducted to analyze the continuous steel D&I canmaking process from deep drawing to three stages of wail Ironing. information on punch load histories, stress/strain distributions and temperature increases are obtained from the analysis. To compare the results from the FE analysis, canmaking experiments utilizing a pilot canmaking line are also carried out. The material considered is a tinplate, a type of low carbon steel for the commercial production of steel D&I can.X114sciescopu
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