1,720,996 research outputs found
Processing of brass open-cell foam by silica-gel beads replication
No full textCellular metals can be produced by several routes, including molten metal infiltration of a leachable bed of solid particles, also known as space holder. The space holder is usually a mineral salt (i.e. NaCl) with relatively low melting point, but this is a limitation for processing high melting point metals and alloys.
This work introduces the use of amorphous SiO2 (silica-gel) particles as space holder and wet solutions of hydrofluoric acid (HF) as solvent for Cu-based open-cell foams production. Commercial grade CW614N brass (solidification interval: 880–895 °C)was successfully foamed through the proposed route, resulting in open-cell foams having relative density ≈0.30 and almost spherical cell morphology. Because of the high chemical stability of SiO2 particles no interaction with the metallic system during liquid infiltration has been found. On the other hand, due to the corrosion resistance of that alloy to HF attack there has been no evidence of damage on the treated alloy
Effect of build orientation on fracture and tensile behavior of A357 Al alloy processed by Selective Laser Melting
Get PDFFracture toughness evaluation of unidirectional fibre metal laminates using traditional CTOD (δ) and Schwalbe (δ5) methodologies.
No full textFibre metal laminates (FMLs) were developed for the aeronautical industry, which requires thin sheets with high resistance to fatigue crack growth, high damage tolerance and high specific strength. Considering all these requirements, FMLs are an advantageous choice when compared to metal alloys currently used. In order to employ FMLs in aircraft structures, designers must have a deep knowledge of a wide set of properties including fracture toughness. The aim of this work was to evaluate the available methodologies for critical CTOD measurement of unidirectional FMLs. To achieve this, tests were performed to obtain traditional (BSI/ASTM) and Schwalbe's CTODs by using experimental procedures especially adapted to these laminates. Results achieved point out that there are differences between both CTOD parameters, that Schwalbe method proved more appropriate, and also that the standard plastic-hinge model does not work properly in FMLs
CTOD-R curves of the metal-clad interface of API X52 pipes cladded with an Inconel 625 alloy by welding overlay
No full textCrack-tip opening displacement resistance curves (CTOD-R) of the substrate/cladding interface of an API 5 L X52 steel pipe internally coated with Inconel 625 applied by TIG (GTAW) welding were experimentally evaluated. A small pipe section with 168 mm of outer diameter and 22.5 mm of thickness was internally coated with a 15 mm thick layer of Inconel 625 corrosion resistant alloy. Tension test specimens were obtained from both substrate and cladding, as well as compact tension test specimens (C(T)) for the evaluation of CTOD-R curves. The fracture testing specimens were notched at the interface in RL orientation. In addition to fracture and tensile testing, microstructural characterization was conducted at the interface using optical microscopy (OM) and scanning electron microscopy (SEM). Qualitative chemical composition scanning and microhardness determination were also performed. The results indicated high fracture toughness for the substrate/cladding interface and the absence of low toughness regions at the interface of the tested samples
Residual strength of unidirectional fibre-metal laminates based on JC toughness of C(T) and SE(B) specimens: Comparison with M(T) test results
No full textFibre-metal laminates (FMLs) are structural composites designed with the aim of producing very low fatigue crack-propagation rate, damage-tolerant and high-strength materials, if compared to aeronautical Al alloys. Their application in aeronautical structures demands a deep knowledge of a wide set of mechanical properties and technological values, including both fracture toughness and residual strength. The residual strength of FMLs have been traditionally determined by using wide centre-cracked tension panels M(T). The use of this geometry requires large quantities of material and heavy laboratory facilities. In this work, fracture toughness (JC) of some unidirectional FMLs laminates was measured using a recently proposed methodology for critical fracture toughness evaluation on compact tension C(T) and single-edge bend SE(B) specimens. Additionally, residual strength values of wider M(T) specimens with different widths (W from 150 to 200 mm) and several crack to width ratios (2a/W) were experimentally obtained. Some experimental residual strength values of M(T) specimens (W from 150 to 400 mm and different 2a/W ratios) of Arall were also obtained from the bibliography. Based on JC results from C(T) and SE(B) specimens, and either using or not using crack-tip plasticity corrections, the residual strengths of the M(T) specimens were predicted and compared to the experimental ones. The results showed good agreement, especially when crack-tip plasticity corrections were applied
Experimental techniques for fracture instability toughness determination of unidirectional fibre metal laminates.
No full textThe aim of this work is to propose procedures for the measurement of the fracture toughness of fibre metal laminates (FMLs) reinforced with unidirectional fibres of aramid or glass. Experimental techniques for fracture toughness evaluation by using Compact (C(T)) and Single-Edge Bend (SE(B)) specimens obeying ASTM standards are introduced. Procedures from the standard for thick metallic materials were modified in order to overcome problems, which can arise when testing FMLs - that is, specimen buckling, indentations and crack growth in planes other than the plane of the fatigue precrack or notch. The methodology proposed was experimentally tested leading to satisfactory results
Fatigue crack propagation in API 5L X-70 pipeline steel longitudinal welded joints under constant and variable amplitudes
No full textFatigue crack propagation (FCP) under constant and variable amplitude loading in base metal (BM), weld metal (WM) and heat affected zone (HAZ) of longitudinal welded joints of an API X-70 pipeline steel was investigated. Constant amplitude loading tests were performed at R = 0.1 and 0.5, whereas for variable amplitude testing single peak tensile overloads (OLs) alternating between 75 and 100% of maximum load were applied at 2.5 mm intervals in crack growth. Results of SE(B) specimens tested under constant and variable amplitude loading revealed that BM, WM and HAZ regions subjected to R = 0.5 and low ÎK-values presented the highest crack growth rates. At higher ÎK values FCP rates in all the studied regions were similar and the R effect on FCP rate was no more observed. Crack growth retardation due to OLs was observed at the three studied regions, showing a decrease on the FCP delay with a decreasing on ÎK. © 2010 Blackwell Publishing Ltd
Critical fracture toughness, JC and δ5C, of unidirectional fibre-metal laminates.
No full textFibre-metal laminates (FMLs) are structural composites designed aiming to produce a damage-tolerant and high strength material. Their main characteristic is their very low fatigue crack propagation rates when compared to traditional aeronautical Al alloys. Their application in aeronautical structures demands a deep knowledge of a wide set of mechanical properties and technological values, including both fracture toughness and residual strength. The objectives of the present work were to present critical toughness values (JC and δ5C) of unidirectional FMLs obtained following a recently proposed methodology and to use them for critical crack length and residual strength predictions. Residual strengths of middle centre-cracked panels of Arall® 2 and 3 were predicted and compared to experimental values from the literature. The results showed that all FMLs evaluated presented higher fracture toughness and crack tolerance than their constituent alloys and that the measured fracture toughness was useful for an accurate prediction of residual strength in centre-cracked plates of Arall
Experimental determination of crack growth resistance curves of high-strength steel using thin clamped SENT specimens
No full textMartensitic stainless steels (MSS) are known for their high mechanical strength and moderate corrosion resistance across various environments. However, their martensitic structure imposes limitations on fracture toughness. By employing heat treatments like quenching and partitioning, it becomes feasible to augment the presence of residual austenite in the material. This microstructural change enables the material to better absorb energy during fracture, thereby increasing its fracture toughness. The development of high-strength steels with good fracture toughness could influence the project and design of structural components, potentially resulting in reduced structural thickness. Experimental determination of crack growth resistance curves and fracture toughness for thin high-strength steels is challenging because most standardized methodologies were developed for thicker samples. The American Society for Testing and Materials has published a standard test method for the determination of resistance to stable crack extension under low-constraint conditions (ASTM E2472) in terms of critical crack-tip-opening angle (CTOA, ψc) and/or critical opening displacement at the original crack tip (δ5), involving the use of thin compact tension C(T) and middle-tension M(T) specimens. However, this method requires specific instrumentation, relatively large specimens, and additional experimental devices such as anti-buckling guides. In this context, this paper evaluates the applicability of the elastic unloading compliance technique for determining crack growth resistance curves in terms of J-integral of MSS using relatively small, non-standard thin clamped SENT specimens with thickness of 1 mm. The proposed methodology, based on a combination of BS 8571 standard and the compliance, stress intensity factor, and ηpl factor solutions from the literature, has proven to be suitable for evaluating toughness in thin clamped SENT specimens and could be useful for assessing fracture toughness in high-strength steels of small thickness
Comparison of J-R curves and JC values of C(T) and M(T) specimens of bidirectional GLARE 3 5/4 0.3 fiber-metal laminates
No full textThe experimental evaluation and comparison of J-R curves from compact tension C(T) and middle-crack tension M(T) specimens of commercial GLARE 3 5/4 0.3 fiber-metal laminates was done. Fracture tests were performed on 50 mm wide C(T) specimens with crack to width ratio a/W = 0.5, and 230 mm wide M(T) specimens having two different crack to width ratios, 2a/W = 0.25 and 0.35. For C(T) specimens J-R curves were evaluated based on the ASTM E1820 standard methodology, whereas for M(T) specimens the ASTM E561 standard methodology was applied. In both cases crack length was measured through unloading compliance. The results indicate that unloading compliance is applicable to bidirectional GLARE laminates in both geometries, estimating the stable crack growth during the tests with reasonable accuracy. The results also showed good agreement between J-R curves from both geometries, as well as similar J values at the beginning of stable crack growth. The experimental J-R curves were slightly higher for M(T) specimens, which were many times larger than C(T) ones
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