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Damage Mechanisms (damage + mechanism)
Selected AbstractsSensing of Damage Mechanisms in Fiber-Reinforced Composites under Cyclic Loading using Carbon NanotubesADVANCED FUNCTIONAL MATERIALS, Issue 1 2009Limin Gao Abstract The expanded use of advanced fiber-reinforced composites in structural applications has brought attention to the need to monitor the health of these structures. It has been established that adding carbon nanotubes to fiber-reinforced composites is a promising way to detect the formation of microscale damage. Because carbon nanotubes are three orders of magnitude smaller than traditional advanced fibers, it is possible for nanotubes to form an electrically conductive network in the polymer matrix surrounding the fibers. In this work, multi-walled carbon nanotubes are dispersed into epoxy and infused into a glass-fiber preform to form a network of in situ sensors. The resistance of the cross-ply composite is measured in real-time during incremental cyclic tensile loading tests to evaluate the damage evolution and failure mechanisms in the composite. Edge replication is conducted to evaluate the crack density after each cycle, and optical microscopy is utilized to study the crack mode and growth. The evolution of damage can be clearly identified through the damaged resistance parameter. Through analyzing the damaged resistance response curves with measurements of transverse crack density and strain, the transition between different failure modes can be identified. It is demonstrated that the integration of an electrically conducting network of carbon nanotubes in a glass fiber composite adds unique damage-sensing functionality that can be utilized to track the nature and extent of microstructural damage in fiber composites. [source] Thermal Cycling Damage Mechanisms of C/SiC Composites in Displacement Constraint and Oxidizing AtmosphereJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2006Hui Mei A constraint stress of 62.5 MPa is created on a three-dimensional C/SiC composite specimen whose both ends are fixed when temperature is cycled between 900° and 1200°C. The cyclic stress results in a maximum damage strain of 0.06% within 50 cycles owing to coating and matrix cracking, fiber debonding, sliding, and breaking in the composite. This constrained specimen elongation also leads to a final compressive stress of 14 MPa on the composite through a decrease in the baseline constraint stress. Wet oxygen atmosphere at a high cyclic temperature, concomitant with stresses, can aggravate the damage situation by alternate oxidation between internal and external fibers in composites. [source] Evaluation of Damage Evolution in Ceramic-Matrix Composites Using Thermoelastic Stress AnalysisJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2000Thomas J. Mackin Thermoelastic stress analysis (TSA) has been used to monitor damage evolution in several composite systems. The method is used to measure full-field hydrostatic stress maps across the entire visible surface of a sample, to quantify the stress redistribution that is caused by damage and to image the existing damage state in composites. Stress maps and damage images are constructed by measuring the thermoelastic and dissipational thermal signatures during cyclic loading. To explore the general utility of the method, test samples of several ceramic-matrix and cement-matrix composites have been fabricated and tested according to a prescribed damage schedule. The model materials have been chosen to illustrate the effect of each of three damage mechanisms: a single crack that is bridged by fibers, multiple matrix cracking, and shear bands. It is shown that the TSA method can be used to quantify the effect of damage and identify the operative damage mechanism. Each mechanism is identified by a characteristic thermal signature, and each is shown to be effective at redistributing stress and diffusing stress concentrations. The proposed experimental method presents a new way to measure the current damage state of a composite material. [source] An In Vitro Investigation of Pulmonary Alveolar Macrophage Cytotoxicity Introduced by Fibrous and Grainy Mineral DustsACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 4 2006DONG Faqin Abstract, In order to study the damage mechanism of mineral dusts on the pulmonary alveolar macrophage (AM), the changes in their death ratio, malandialdthyde (MDA) content and activities of lactate dehydrogenase (LDH) and superoxide dismutase (SOD) were measured, and the technique of cell culture in vitro was used to investigate the cytotoxicity of six mineral dusts (twelve crystal habits) from twelve mineral deposits. The results show that wollastonite and clinoptilolite have no AM cytotoxicity, while other fibrous and grainy mineral dusts damage pulmonary AM in various degrees. The cytotoxicity of fibrous mineral dusts was greater than that of the grainy ones, and the cytotoxicity of dusts was positively correlated with the active OH content in dusts, but not necessarily so with its SiO2 content. The high pH values produced by dust was unfavorable for the survival of cells and the dusts with low bio-resistance were safe for cells. The content of variable valence elements in dusts might influence their cytotoxicity and the surface charge of dusts was not a stable factor for their toxicity. It is demonstrated that the shape of mineral dusts was one of the factors affecting cytotoxicity, and that the cytotoxicity of mineral dusts depends mainly on their properties. [source] In Situ Damage Detection With Acoustic Emission Analysis During Cyclic Loading of Wire Reinforced EN AW-6082,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Kay André Weidenmann In the field of lightweight construction, hybrid structures such as reinforced metal matrix composites are highly qualified materials. The direct composite extrusion process allows for continuous manufacturing of wire reinforced aluminum matrix profiles. The aim is to increase the stiffness and specific strength in a way that the composite material shows better mechanical properties than the single matrix material. To determine and locate damage evolution during cyclic loading of spring steel reinforced EN AW-6082 matrix the acoustic emission analysis is used. Furthermore it allows for getting more information about the damage mechanisms during fatigue of the matrix and the final failure of the reinforcing element. The current work also includes the determination of damage evolution using strain measuring methods. [source] Study of Fatigue Damage Micromechanisms in a Duplex Stainless Steel by Complementary Analysis TechniquesADVANCED ENGINEERING MATERIALS, Issue 9 2009Ahmed El Bartali The low-cycle fatigue (LCF) damage micromechanisms are studied in a duplex stainless steel at room temperature using complementary analysis techniques. Surface damage is observed in real-time with an in-situ microscopic device during a low-cycle fatigue test. Slip systems activated in each grain in each phase are identified from SEM photographs and EBSD measurements. The surface relief appeared at the end of the test is measured with an interferometric profilometer. Displacement and strain fields on the microstructural scale are calculated using DIC technique from surface images taken during cycling. Observations were combined to analyse damage mechanisms from slip marking appearance to strain localisation and crack initiation. [source] Modeling of Environmental Degradation in Fatigue-Life Prediction of Near-, Titanium Alloy IMI 834 under Complex High-Temperature Loading Conditions,ADVANCED ENGINEERING MATERIALS, Issue 6 2003R.G. Teteruk The crack propagation model successfully applies to life-prediction of near-,-titanium alloy IMI 834 under complex high-temperature fatigue-loading conditions. The predictive capabilities of the model can be attributed to the close correlation of the model with the relevant damage mechanisms (among them environmental degradation under varying conditions) and micro-structural processes. The Figure shows an SEM image of a typical crack-initiation site for a test run at 400,°C. [source] Impact behavior of hybrid composite platesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010Metin Sayer Abstract This experimental study deals with the impact response of hybrid composite laminates. Two different hybrid composite laminates, aramid/glass and aramid/carbon, and two different stacking sequences, such as [0/0/90/90]A+ [90/90/0/0]G for AG1 and [0/90/±45]A+ [±45/90/0]G for AG2 and so on (see Table I), were chosen for impact testing. The impact energy was gradually increased until complete perforation took place, and an energy profiling method (EPM) was used to identify the perforation thresholds of composites. The damaged samples were visually inspected. The images of the several samples subjected to various impact energies were registered and used for comparison and identifying damage mechanisms. The perforation thresholds for [0/90/±45]s aramid/glass and aramid/carbon laminates were found to be approximately 5% higher than those for their counterparts with the [0/0/90/90]s stacking sequence. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Evaluation of Damage Evolution in Ceramic-Matrix Composites Using Thermoelastic Stress AnalysisJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2000Thomas J. Mackin Thermoelastic stress analysis (TSA) has been used to monitor damage evolution in several composite systems. The method is used to measure full-field hydrostatic stress maps across the entire visible surface of a sample, to quantify the stress redistribution that is caused by damage and to image the existing damage state in composites. Stress maps and damage images are constructed by measuring the thermoelastic and dissipational thermal signatures during cyclic loading. To explore the general utility of the method, test samples of several ceramic-matrix and cement-matrix composites have been fabricated and tested according to a prescribed damage schedule. The model materials have been chosen to illustrate the effect of each of three damage mechanisms: a single crack that is bridged by fibers, multiple matrix cracking, and shear bands. It is shown that the TSA method can be used to quantify the effect of damage and identify the operative damage mechanism. Each mechanism is identified by a characteristic thermal signature, and each is shown to be effective at redistributing stress and diffusing stress concentrations. The proposed experimental method presents a new way to measure the current damage state of a composite material. [source] Morphology and compression-after-impact strength relationship in interleaved toughened compositesPOLYMER COMPOSITES, Issue 1 2003B. J. Derkowski Morphology and compression after impact (CAI) strength relationships in interleaved toughened high performance composites are investigated using a quantitative two-dimensional image analysis approach. A group of six quasi-isotropic carbon fiber-epoxy composites with identical compositions, but having variations in CAI strengths, were analyzed to study how the interleaf particle size, particle size distribution, and location of particles in the interlaminar region affect the CAI strength values and the corresponding damage mechanisms. It is found that the CAI strength of interleaved-toughened composites is significantly affected by the size and size distribution of toughener particles in the interlaminar regions of the composite. In general, high CAI strength composites exhibit more uniform particle size distribution throughout the interlaminar regions. Whereas, for low CAI strength composites, the interleaf particles tend to cluster together and have varied size distribution. [source] Theoretical Studies of Damage to 3,-Uridine Monophosphate Induced by Electron AttachmentCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2008bo Zhang Ass. Abstract Low-energy electrons (LEE) are well known to induce nucleic acid damage. However, the damage mechanisms related to charge state and structural features remain to be explored in detail. In the present work, we have investigated the N1-glycosidic and C3,O(P) bond ruptures of 3,-UMP (UMP=uridine monophosphate) and the protonated form 3,-UMPH with ,1 and zero charge, respectively, based on hybrid density functional theory (DFT) B3,LYP together with the 6-31+G(d,p) basis set. The glycosidic bond breakage reactions of the 3,UMP and 3,UMPH electron adducts are exothermic in both cases, with barrier heights of 19,20,kcal,mol,1 upon inclusion of bulk solvation. The effects of the charge state on the phosphate group are marginal, but the C2,OH group destabilizes the transition structure of glycosidic bond rupture of 3,-UMPH in the gas phase by approximately 5.0,kcal,mol,1. This is in contrast with the C3,O(P) bond ruptures induced by LEE in which the charge state on the phosphate influences the barrier heights and reaction energies considerably. The barrier towards C3,O(P) bond dissociation in the 3,UMP electron adduct is higher in the gas phase than the one corresponding to glycosidic bond rupture and is dramatically influenced by the C2,OH group and bulk salvation, which decreases the barrier to 14.7,kcal,mol,1. For the C3,O(P) bond rupture of the 3,UMPH electron adduct, the reaction is exothermic and the barrier is even lower, 8.2,kcal,mol,1, which is in agreement with recent results for 3,-dTMPH and 5,-dTMPH (dTMPH=deoxythymidine monophosphate). Both the Mulliken atomic charges and unpaired-spin distribution play significant roles in the reactions. [source] | ||||||||||