Gotowa bibliografia na temat „FractureToughness”

This research studied the mechanical properties of orange and pomegranate shells powdersreinforced unsaturated polyester with different weight fractions %Wf. The compositespecimens were prepared by hand lay-up technique and sectioned according to (ASTM)for tensile, impact, bending and compression tests to obtain modulus of elasticity, ultimatetensile strength, elongation percentage, compression strength, impact energy and fracturetoughness of the composite specimens. The results showed that the composite specimensreinforced with pomegranate shells powder give high mechanical properties compared withcomposites specimens reinforced with orange shells powder.

Nanostructured Ti5Si3–TiC–Ti3SiC2 and Ti5Si3–TiC composites were in situfabricated through the spark plasma sintering (SPS) technique using Ti and SiC powders as reactants. It was found that the composites could be prepared in arelatively short time (6 min at 1260 °C) above 98% theoretical density. The phase constituents and microstructures of the samples were analyzed by x-ray diffractionand observed by scanning electron microscopy. Transmission electron microscopywas used for detailed microstructural analysis. The results showed that the reaction products mainly consisted of Ti5Si3 and TiC phases or Ti5Si3, TiC and Ti3SiC2phases, depending on the molar ratio of reactants (Ti to SiC). The composites exhibited fine microstructure; TiC grain size was less than 200 nm. Fracturetoughness at room temperature was also measured by indentation tests.

Pipelines are one of the most convenient and effectiveways of transporting petrol over a long distance. The environmentapplies, beyond extremely high external pressures, lowtemperatures and intensive corrosive process, the occurrence ofdefects on the pipe body, which compromises the structuralintegrity of pipelines leading to catastrophic failures. The mainmodifications concern the mechanical resistance, toughness at lowtemperatures weld ability and resistance to embrittlement relatedto hydrogen. Among mechanical characteristics, the fracturetoughness is very important for pipeline steels in design and safeassessment. Aiming to enhance the reliability and operation ofcomplex pipelines system, a study based on the mechanics of theelastoplastic fracture in order to determine better prediction of thefatigue life. The materials tested here are API 5L X42 and X52micro alloyed steels, as well as to evidence the toughness resistanceof these materials. Results indicated that both X42 and X52 steelbehave in a similar way and in all cases a slight increase of thetransition temperature was found. The characteristic toughnessvalue shows an evident loss in mechanical performances ifcompared to the uncharged one.

As the demand for fossil fuels increases, pipelines are constructed in inhospitable areas. Underthese conditions, not only the strength but also the deformability of the pipelines becomes crucial. A strainbased design (SBD) procedure needs to be established. Traditional stress based approaches to evaluatedefect tolerance lead to conservative predictions. There is a need to accurately define the fracturetoughness of the pipeline steel and assess the criticality of weld defects under strain based conditions. Thispaper focuses on the implementation of the unloading compliance method to determine stable crackgrowth. The standardized test procedure described in ASTM E1820 is applied. This method is a handy toolto obtain the J-resistance curves which can forecast ductile failure in pipeline girth welds. Preliminaryexperiments have been performed on Single Edge Notch Bend (SENB) specimens of plain pipe metal.Using the implemented procedure, it was possible to obtain a good fit between calculated and measuredcrack size. The most important result is the smoothness of the calculated crack growth and the rathermonotonic increase of crack size. Since testing on SENB is well known to provide conservativemeasurements, Single Edge Notch Tension (SENT) specimens will be evaluated in future work

In this study, nano-composite of polymeric materials, prepared from unsaturated polyesterresin (UP). Two groups of nanocomposites were prepared by Hand Lay-up method. The firstgroup consists from (UP) reinforced by hybrid nanoparticles consisting of a mixture ofzirconium oxide and yttrium oxide (30 mol%Y2O3- ZrO2) with particles size (83.98nm). Thesecond group consists of (UP) reinforced by zirconia nanoparticles (ZrO2) with particle size(47.23nm). The effect of volume fraction (0.5%, 1%, 1.5%, 2%, 2.5%, 3%) of thenanoparticles additives on some mechanical properties of composites materials was studiedalso. The results shown that the values of the flexural modulus, impact strength and fracturetoughness increased, as the volume fraction ratio of the nanoparticle increased for bothgroups of nanocomposites, while flexural strength values decreased with the increased thevolume fraction ratio of the nanoparticles for both groups of nanocomposites also. As wellas, the unsaturated polyester resins reinforced by hybrid nanoparticles has higher mechanicalproperties as compared with their counterparts of composites reinforced by zirconiananoparticles only. The morphological formation of the fracture surface showed a closeinterconnection between all components of the prepared polymeric compositions. Thisreinforce a good compatibility between unsaturated polyester resins and reinforcementnanoparticles, which enhancement the mechanical properties.

An eutectic alloy in the LaB6‒VB2 system was obtained by the cold crucible method. The ratio of components in the initial powder mixture was 40:60 mol. %. In the structure of the alloy, two-phase eutectic regions are observed, which are a LaB6 matrix filled with cylindrical VB2 fibers up to 2 μm in diameter or extended VB2 crystals with a complex cross-section and an equivalent diameter of up to 10‒15 μm. The Vickers hardness and the fracturetoughness were determined, and the relationship between these characteristics and the load on the indenter, the direction of load application, and the type of eutectic structure was established. The maximum value of crack resistance (8,6 MPa·m1/2) and high hardness (20,0 GPa) were recorded for an alloy with a rod eutectic structure when a 2 N indenter load was applied parallel to the crystallographic axis c VB2. The greatest hardening effect both at a load of 2 N and 30 N, expressed in a combination of high hardness (20,5 GPa at 2 N and 20,0 GPa at 30 N) and crack resistance (6,5 MPa·m1/2 at 2 N and 4,9 MPa·m1/2 at 30 N) was demonstrated by an alloy with a coarse conglomerate eutectic structure. Ill. 4. Ref. 24. Tab. 1.

We provide a brief review of our recent studiesconcerning the effects of various mechanisms of plasticdeformation of nanocrystalline materials on their fracturetoughness. We consider both conventional deformationmechanisms, such as lattice dislocation slip, and the deformationmechanism pronounced mostly in nanocrystalline solids, such asgrain boundary (GB) sliding and migration. We demonstrate thatwith a decrease in grain size, the effect of conventional latticedislocation slip on fracture toughness enhancement significantlydecreases. At the same time, for nanocrystalline solids withsmallest grain size fracture toughness can be increased due to GBsliding and migration. This implies that a transition from latticedislocation-mediated toughening to GB-deformation-producedtoughening can occur at a critical grain size in nanocrystallinesolids.

Background: Water sorption is one of the concern regarding acrylic resin denture base materials since itmight affect the dimensional stability of the prosthesis, furthermore the absorbed water may dramaticallycompromise the physical and mechanical properties. Methods: Three different commercial denture basematerials (heat-curing acrylic resin) available in local markets were used (Vertex, Ivoclarw and Luxacryl)to evaluatewater sorption and the effect of dry andwet environment on the fracture toughness ofthese materi-als. Water sorption test was carried out according to international organization for standardization (ISO) Specification 1567-2000.The fracture toughnesswasdeterminedusing single edge notch bending test(SEN-B) according to ISO 13586:2000. Results: Water sorption in term of percentage was highest for Ivoclar (0.78%ofitsweight) andlowestforLuxacryl(0.68%ofitsweight). Statistical analysiswithtwo-wayAnalysis of Variance (ANOVA)test showed a significant difference between different acrylic material groups, and be-tweendifferentwater immersiontimes (p<0.0001). For fracture toughness,ithas been foundthatthe Ivoclar samples displayed the highest fracture toughness after 28 days of immersion in distilled water at room tem-perature.Statisticalanalysiswithtwo-wayANOVAtest showedasignificantdifference for fracturetoughness between different acrylic material groups (P<0.04).Conclusion: in general, fracture toughness of denture base materials was highly-changed after immersionin water.

Les essais de ténacité permettent de mesurer les propriétés de résistance d'un matériau vis-à-vis de l'amorçage et de la propagation de fissure. La réalisation de ces essais nécessite l'utilisation d'éprouvettes suffisamment grandes afin de mesurer une propriété valide. Cependant, il existe de nombreux cas pour lesquels il n'est pas possible d'obtenir des éprouvettes de dimensions suffisantes. En combinant une approche expérimentale et la simulation, cette thèse vise à développer des méthodes de mesure de la ténacité d'un matériau ductile à l'aide de petites éprouvettes. Un acier 316L(N) a été retenu pour cette étude car il est largement utilisé dans l'industrie nucléaire. Afin d'évaluer la robustesse de la démarche, l'étude a été conduite sur l'alliage à l'état neuf et sur un état moins ductile vieilli à 750°C en 2000h.L'étude a été faite sur une large gamme d'éprouvettes non fissurées (lisses, axisymétriques entaillées, doublement entaillées (DENT), de déformation plane) et fissurées (CT) de géométries variables. Les éprouvettes fissurées ont été analysées en terme de courbe J-da et les éprouvettes non fissurées (DENT) en terme de travail essentiel de rupture. Cette large base d'essais, combinée avec des expertises fractographiques et des essais interrompus, a permis d'identifier la séquence d'endommagement et d'ajuster un modèle de comportement et d'endommagement couplé (type GTN). La confrontation entre expériences et simulations a permis de discuter l'effet de taille sur la mesure de J, les limites de validité des normes et la compétition entre rupture par déchirement ductile et instabilité pastique
Fracture toughness tests allow measuring a material's properties resisting crack initiation and propagation. They require the specimen size to be large enough to measure a valid value. However, there are numerous cases where obtaining specimens of adequate dimensions is impossible. By combining an experimental approach with simulations, this thesis aims to develop methods for measuring the toughness of a ductile material using small specimens. This study is carried out on 316L(N) stainless steel, which is widely used in the nuclear industry. To assess the robustness of the approach, the material was studied at its as-received state and at an aged state at 750°C for 2000 hours, which is less ductile.A broad range of uncracked specimens (smooth and notched tensile, double edge notched tensile (DENT), and flat-grooved) and cracked specimens (CT) with variable geometries was studied. The cracked specimens were analyzed in terms of J-da curve, and the uncracked specimens (DENT) in terms of essential work of fracture. These tests, combined with fractographic analysis and interrupted tests, allow identifying the damage sequence and adjusting a coupled plastic behavior and damage model (GTN type). The comparison between experiences and simulations facilitated discussions on the size effect on J measurement, the validity limits of standards, and the competition between rupture by ductile tearing and plastic instability

碩士
逢甲大學
紡織工程所
93
Nylon-6/Silicate particles composites were prepared on a twin-screw extruder with a particle content of 0–40 wt%. The injection-molding process prepared test samples of the composite material. The influence of particles surface treatment (with and without stearic acid) on the mechanical properties and fracture toughness were studied. The experiment included uniaxial tensile, three point bending, Izod impact tests and fracture toughness tests using single edge three point bending sample configuration. The results showed that the tensile and flexural modulus of Nylon-6 composites increased with the increase in filler ratio independent of filler surface treatment. The tensile and flexural strength of untreated particle filled Nylon-6 composites higher than stearic acid treated, whereas the impact strength and maximum elongation decreased with the increase in filler ratio even though low particle concentration of stearic acid coated talc and wollastonite showed some improvement of impact toughness. The resulting J-R curves have also been evaluated to obtain values of the initiation toughness, JIC, following the extrapolation and interpolation schemes prescribed by ASTM E813-81 and ASTM E813-87 test procedures, respectively about non-elastic of load-displacement curve. The values of JIC obtained from the power-law regression method are higher than those obtained from the linear regression method. Finally, the effects of interfacial interactions between the fillers and matrix on the mechanical properties were also evaluated with semi-empirical equations.

This manual will help you develop elastic-plastic fracture toughness data in accordance with the ASTM Test Method for J-Integral Characterization of Fracture Toughness (E 1737) and ASTM Test Method for Crack-Tip Opening Displacement (CTOD) FractureToughness Measurement (E 1290). 9 chapters provide guidance and instruction on equipment apparatus, test fixtures, transducers, test setup, test procedure, and data analysis. Through the use of test examples, example calculations, photographs of test apparatus and fracture samples, as well as expert advice and reference to papers in the literature describing various test techniques, MNL 27 gives you the next-best thing to hands-on training. The chapters are organized sequentially, just as you would proceed to develop a laboratory capability to accomplish these fracture mechanics tests: Overview of Elastic-Plastic • Analysis • Apparatus • Specimen Preparation • Basic Test Procedure • Advanced Test Procedure • Qualification of the Test Results • Future Developments in Elastic-Plastic Fracture Testing • Appendix A: Software Listings (includes the text of an interactive unloading compliance data acquisition program written in Microsoft QuickBASIC) • Appendix B: ASTM Fracture Test Standards. For mechanical and materials engineers; nuclear, civil, and aerospace structures engineers. Also for lab technicians and test mechanics.