Hierarchical microstructures spanning from micro-sized eutectic structure to nano-sized precipitates are promisingly engineered in lightweight Al alloys to improve the high-temperature creep ...resistance that is increasingly required for rapid industrial development. However, the intrinsically-brittle eutectic phase is ready to fracture upon applied loading, which, dramatically reducing room-temperature ductility and fracture toughness, greatly hampers practical applications of the creep-resistant Al alloys. Here, through the combination of Sc microalloying with sub-rapid solidification, we observe the ductilization of Al11Ce3 eutectic phase in cast heat-resistant Al-Ce-Sc alloys due to the formation of atomic-scale compositional complexity. High-concentration Sc atoms are frozen within the Al11Ce3 intermetallic phase by the sub-rapid solidification, which then assemble into unusual atomic-scale compositional dipoles with the Sc atoms enriched at one pole and the Al atoms at the opposite during subsequent heat treatment. The dispersed Sc-Al compositional dipoles induce local lattice distortions that stimulate dislocation activities, as temporally and spatially visualized by in-situ neutron diffraction tensile test and microstructural characterizations. The unexpected plastic deformation triggered in Al11Ce3 improves the deformation compatibility between the eutectic phases, enabling the sub-rapidly-solidified Al-Ce-Sc alloy to reach a room-temperature tensile elongation 3 times and fracture toughness over 8 times of its counterpart derived from traditional solidification. In addition, the sub-rapidly-solidified Al-Ce-Sc alloy exhibits an excellent creep resistance at 300 °C, achieving a tensile creep stress threshold of ∼ 70 MPa. These findings provide new perspectives on the design of ductile intermetallic phases and the development of creep-resistant Al alloys with application-level ductility.
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•The relative notch-root radius ρ/G is incorporated to model Kcn-KIC relation.•Normal distribution is introduced to consider the inevitable scatter in Kcn.•Kcn value approximates KIC ...when notch root radius is less than grain size (ρ<G).•The proposed model can determine KIC and ft values from seemingly scattered data.
Unlike fracture toughness, the notch fracture toughness of a ceramic is not a constant; rather, it increases with the notch-root radius ρ in a notched specimen. In this study, by analyzing the fracture measurements of eight different notched ceramics with an average grain size G of 3–40 μm, a simple model describing the relation between the notch fracture toughness and fracture toughness is proposed as a function of the relative notch-root radius ρ/G. The normal distribution is incorporated to consider the inevitable scatter in measurements where fracture mechanisms and errors are present. The results demonstrate that the model can effectively predict the quasi-brittle fracture variation trend for ceramics, including the upper and lower bounds, with 96% reliability, from a normal distribution; thus, it can address virtually all of the experimental data. We also determined that the notch fracture toughness approximates the fracture toughness if ρ ≤ G.
Biocomposites based on commercial polylactic acid (PLA) matrix reinforced with three different short natural fibers (coir, fique and sisal) at 1; 3, and 5 % wt, were obtained by compression molding. ...The idea of keeping additional processing steps as low as possible, thus reducing costs, prevailed. Then, no chemical treatment was performed on natural fibers. Overall performance of composites was evaluated by means of fracture tests along with FTIR and thermal characterization, SEM micrographs, and tensile tests. Results show that the incorporation of short sisal fibers increased more than 130 % the fracture toughness of composite materials, by inducing additional mechanisms of energy dissipation prior to crack growth. This improvement in behavior was observed even though there was no good adhesion between fibers and matrix. Sisal fibers’ composites exhibited the best fracture and mechanical properties compared to coir and fique composites, without a detriment in degradation behavior.
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•Biocomposites of PLA and low content of non-treated natural fibers were obtained.•Fracture toughness of PLA was increased up to 130 % by fibers.•Fibers induced additional mechanisms of energy dissipation prior to crack growth.•Sisal fibers' composites exhibited the best fracture and mechanical properties.•Composites properties are comparable with commonly used materials in food packaging.
Drawing inspiration from the intricacies of nacre structure, Ti2AlNb/Ti6Al4V layered metal composite was fabricated by vacuum hot pressing and achieved high fracture toughness. The fracture toughness ...of the composite registers at 48.5 MPa∙m1/2, surpassing the theoretical fracture toughness calculated based on the rule of mixture (ROM) and exhibiting 54 % improvement compared toTi2AlNb alloy. The introduction of a layered configuration imparts complex crack propagation pathways to the composite. The occurrences of crack deflection, crack bridging, crack passivation, and interface delamination serve to increase the resistance to crack propagation. Moreover, the plastic deformation of the ductile Ti6Al4V layer and the large plastic zone size of the crack tip can release the stress concentration and delay the fracture of the composite. This understanding not only advances our comprehension of the toughening mechanisms but also has practical implications for the application and development of layered Ti2AlNb alloys.
•The full displacement and strain fields are measured using DIC.•The history of dynamic stress intensity factor of rocks is determined.•The effect of loading rate on dynamic fracture properties is ...characterized.•Dependence of fracture propagation toughness on fracture velocity is obtained.
Loading rate is the main controlling factor in dynamic failure of rocks. In this paper, digital image correlation (DIC) combined with ultra-high speed photography is utilized to study the loading rate effect of a granitic rock – Laurentian granite using notched semi-circular bend (NSCB) method. The dynamic stress intensity factors and crack tip positions are determined from the displacement fields obtained using DIC. Fracture time, fracture toughness and crack growth velocity all exhibit loading rate dependence. The dependence of fracture propagation toughness on crack growth velocity is also obtained, which is in good agreement with that reported in the literature.
The uncertainty surrounding the fracture behaviour of CMT-WAAM deposited steel, in terms of crack tip condition (J and CTOD) needed to cause crack tip extension, has made this manufacturing technique ...unpopular to date. Fracture toughness parameters are crucial in the structural integrity assessment of components and structures in various industries for assessing the suitability of a manufacturing process and material. In the offshore wind industry, the EN-GJS-400-18-LT ductile cast grade for the mainframe and hub has lower fracture toughness resistance for its high strength grade. Its high weight level affects the Eigen frequency of the tower and imposes high installation cost incurred from heavy lifting equipment usage. Poor fracture toughness is currently a challenge for wind turbine manufacturers in the quest for a cleaner and cheaper energy in the form of offshore wind. In this study, CMT-WAAM is used in depositing steel components with an oscillatory and single pass deposition strategy. The effects of microstructural variation, as a result of layer by layer deposition and the layer band spacing, on the fracture resistance in the build and welding direction was shown here. The fracture mechanics and failure mode of the WAAM deposited parts were investigated. The microstructural variation, again as a result of the layer by layer deposition and the layer band spacing, are the key parameters that control the fracture toughness of WAAM steel. Anisotropic behaviour in the Jq values was observed between both fracture orientations. The constructive transformation mechanism of the WAAM oscillatory process made way for intragranular nucleation of acicular ferrite on the Ti containing inclusion, thereby improving the toughness of the ER70S-6 deposit with a unique microstructure and Jq value of 640kJ/m2 .
Anisotropic dependence of fracture resistance of cold metal transfer wire + arc additive manufactured (CMT-WAAM) structural steel components of high strength low alloy (HSLA) steel. Display omitted
Hf6Ta2O17 ceramics are successfully prepared by solid state reaction and pressureless sintering. The mechanical properties and the calcium-magnesium-alumino-silicate (CMAS) corrosion behavior of ...Hf6Ta2O17 ceramics are studied. The hardness, elastic modulus and fracture toughness of Hf6Ta2O17 ceramics are 18.45 GPa, 273.42 GPa and 2.6–3.1 MPa m1/2, respectively. As the Hf6Ta2O17 ceramics are attacked by CMAS, the reaction layer and dense layer are formed on the ceramic surface, which prevents the further infiltration of molten CMAS. HfSiO4 and Ca2Hf7O16 are confirmed as the main reaction products of Hf6Ta2O17 and CMAS. Hf6Ta2O17 ceramics exhibit better CMAS corrosion resistance than 8 wt% yttria stabilized zirconia (8YSZ) ceramics, which is attributed to the dense structure formed by corrosion products (hafnium tantalum oxide and Ca2Hf7O16) and lower theoretical optical basicity (OB) value. Furthermore, Hf6Ta2O17/YSZ double ceramic top coat thermal barrier coatings (TBCs) are successfully prepared by plasma spraying, and the thermal cycling performance is investigated. Hf6Ta2O17/YSZ double-layers TBCs has good thermal cycling performance as 8YSZ single-layer TBCs.
In this work more than 2500 published experimental data on hardness and indentation fracture toughness of cemented carbides during the last 40 years have been collected. The significant number of ...samples displays the influence of microstructure, chemical composition, and processing on the hardness - toughness relationship of cemented carbides. Selected two-dimensional plots are presented and discussed as an example of visualization of the available experimental information. This collected record can serve as an initial reference set for the cemented carbide community using all available shared knowledge organized in one well-structured database.
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•2500 published experimental data on hardness and indentation fracture toughness of cemented carbides•Shared knowledge of cemented carbides during last 40 years organized in structured database•Microstructure, chemical composition and processing influence on the Hv-KIC of cemented carbides•Selected two-dimensional Hv-KIC plots for visualization of the available experimental information
•Small-sized specimen techniques were developed and applied to determine fracture critical properties representative for actual products produced by Electron Beam Melting.•Three material conditions ...were prepared, characterized microstructurally and evaluated mechanically: as-deposited, stress relieved, and HIP-ed.•Local mechanical properties are assessed with the use of miniaturized compact tension (MCT) fracture toughness specimens and miniaturized tensile tests (MTT)•The results are complemented by microstructural and fractographic analyses and are discussed in the light of literature values.
Rapidly developing additive technologies for metallic parts production have led to the development of a wide range of methods supporting this field, including mechanical properties characterization. Components produced by AM processes are built spot to spot and layer by layer and that leads to varying local heat absorption and distribution, resulting in varying local properties depending on the shape complexity and build parameters. Different properties in different directions and at various component locations can be expected.
Since AM parts are often sub-scale and/or with topological complexity, mechanical characterization with the use of standard specimens is not typically possible and small-sized specimen techniques have to be developed and applied. In the current paper, three AM produced parts made of Ti-6Al-4V by Electron Beam Powder Bed Fusion (EB-PBF) technology have been investigated. Three material conditions are reported here: as-deposited, stress relieved and HIP-ed. Local mechanical properties are assessed with the use of miniaturized compact tension (MCT) fracture toughness specimens and miniaturized tensile tests (MTT). The results are complemented by microstructural and fractographic analysis and are discussed in the light of literature values.
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