Showing papers on "Fracture toughness published in 2017"
01 Jun 2017-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the tensile, fracture, and fatigue crack growth properties of 316L stainless steel (SS) produced using the selective laser melting (SLM) technique were evaluated and compared with those of conventionally manufactured (CM) austenitic SSs.
Abstract: The tensile, fracture, and fatigue crack growth properties of 316L stainless steel (SS) produced using the selective laser melting (SLM) technique were evaluated and compared with those of conventionally manufactured (CM) austenitic SSs. For SLM, both single melt (SM) and checker board (CB) laser scanning strategies were employed, so as to examine the effect of scanning strategy on the mechanical properties. The experimental results show that the SLM alloys' yield strength is significantly higher than that of CM 316L SS, a result of the substantial refinement in the microstructure. In contrast, only a marginal improvement in the ultimate tensile strength and a marked reduction ductility, which are a result of the loss of work hardening ability, are attributed to the absence of stress induced martensitic transformation common in CM austenitic SSs. In spite of these, the fracture toughness, which ranges between 63 and 87 MPa m 0.5 , of the SLM alloys is good, which is a result of the mesostructure induced crack tortuousity. The SLM process was found to marginally reduce the threshold stress intensity factor range for fatigue crack growth initiation and enhance the Paris exponent within the steady state crack growth regime. Both tensile and toughness properties were found to be anisotropic in nature. SLM with CB scanning strategy improves both these properties. All these observations on the mechanical properties are rationalized by recourse to micro- and meso-structures seen these alloys.
414 citations
TL;DR: In this paper, the development history and applications of Al-Li alloys over the last few years are reviewed, and the main issue of anisotropic behavior of all the alloys is discussed.
360 citations
TL;DR: In this article, the authors presented a methodology for stochastic modeling of the fracture in polymer/particle nanocomposites, which is based on six uncertain parameters: the volume fraction and the diameter of the nanoparticles, Young's modulus and the maximum allowable principal stress of the epoxy matrix, the interphase zone thickness and its Youngs modulus.
Abstract: The fracture energy is a substantial material property that measures the ability of materials to resist crack growth. The reinforcement of the epoxy polymers by nanosize fillers improves significantly their toughness. The fracture mechanism of the produced polymeric nanocomposites is influenced by different parameters. This paper presents a methodology for stochastic modelling of the fracture in polymer/particle nanocomposites. For this purpose, we generated a 2D finite element model containing an epoxy matrix and rigid nanoparticles surrounded by an interphase zone. The crack propagation was modelled by the phantom node method. The stochastic model is based on six uncertain parameters: the volume fraction and the diameter of the nanoparticles, Young’s modulus and the maximum allowable principal stress of the epoxy matrix, the interphase zone thickness and its Young’s modulus. Considering the uncertainties in input parameters, a polynomial chaos expansion surrogate model is constructed followed by a sensitivity analysis. The variance in the fracture energy was mostly influenced by the maximum allowable principal stress and Young’s modulus of the epoxy matrix.
336 citations
TL;DR: In this article, the authors contribute to an improved understanding of the factors influencing the mechanical properties of laser powder bed and electron beam melted TiAl6V4, and determine tensile tests, fracture toughness tests, fatigue crack growth measurements for different r-ratios as well as high cycle fatigue properties were determined for different surface roughness and heat treatments.
271 citations
TL;DR: It is shown here that when steel microstructures are hierarchical and laminated, similar to the substructure of bone, superior crack resistance can be realized and the exceptional properties enabled by this strategy provide guidance for all fatigue-resistant alloy design efforts.
Abstract: Fatigue failures create enormous risks for all engineered structures, as well as for human lives, motivating large safety factors in design and, thus, inefficient use of resources. Inspired by the excellent fracture toughness of bone, we explored the fatigue resistance in metastability-assisted multiphase steels. We show here that when steel microstructures are hierarchical and laminated, similar to the substructure of bone, superior crack resistance can be realized. Our results reveal that tuning the interface structure, distribution, and phase stability to simultaneously activate multiple micromechanisms that resist crack propagation is key for the observed leap in mechanical response. The exceptional properties enabled by this strategy provide guidance for all fatigue-resistant alloy design efforts.
270 citations
TL;DR: In this paper, a phase field approach is employed to model fracture in the matrix and the interphase zone of the polymeric nanocomposites (PNCs) while the stiff clay platelets are considered as linear elastic material.
251 citations
TL;DR: In this article, the microstructure and room temperature mechanical properties of a 18Ni (300) grade maraging steel (MS) fabricated using the selective laser melting (SLM) technique were studied, in both before-and after-aging conditions.
184 citations
183 citations
TL;DR: In this paper, the CNTs are functionalized by attaching melamine to improve the dispersibility in epoxy matrix and to enhance the interfacial bonding between CNT and matrix, and a significant increase of fracture toughness was observed for 2wt% M-CNT/Epoxy nanocomposite.
Abstract: Carbon nanotubes (CNTs) are considered as high potential filler material to improve the mechanical properties of epoxy nanocomposites. The CNTs are functionalized by attaching melamine to improve the dispersibility in epoxy matrix and to enhance the interfacial bonding between CNTs and matrix. The tensile tests and single edge notch bending (SENB) tests were performed for CNT/Epoxy and M-CNT/Epoxy nanocomposites at various weight fraction of functionalized CNTs. The M-CNT/Epoxy nanocomposites with addition of 2wt% functionalized CNTs exhibited enhancements of Young's modulus by 64% and ultimate tensile strength by 22%. Furthermore, a significant increase of fracture toughness by 95% was observed for 2wt% M-CNT/Epoxy nanocomposite. The homogeneity of CNTs in epoxy matrix has been analyzed and related to the improvement of modulus and strength. The phenomena of crack propagation has been investigated and related to the improvement of fracture toughness.
180 citations
TL;DR: In this article, a novel formulation combining the phase field approach for modeling brittle fracture in the bulk and a cohesive zone model for pre-existing adhesive interfaces is proposed to investigate the competition between crack penetration and deflection at an interface.
178 citations
TL;DR: In this paper, the role of location-specific defect distribution and microstructure variation on fracture resistance of Ti-6Al-4V produced via different generation of Arcam machines (e.g. A2, A2X) is reported, along with the effects of subsequent hot isostatic pressing (HIP) treatments.
TL;DR: In this paper, a ductile fracture model is proposed to describe shear fracture of sheet metals from shear to balanced biaxial tension via uniaaxial and plane strain tension.
TL;DR: In this paper, the authors examined the fatigue-crack propagation behavior of the Cantor alloy CrMnFeCoNi under cyclic fatigue loading and found that the fracture surfaces and crack paths indicate a transition from predominantly transgranular crack propagation at room temperature to intergranular-dominated failure at lower temperature.
TL;DR: In this paper, a vacuum filtration method was used to fabricate sandwiched carbon nanotubes/polysulfone nanofiber (CNTs/PSF) paper as an interleaf to improve the interlaminar fracture toughness of carbon fiber/epoxy composite laminates.
TL;DR: In this article, a hybrid filler composed of nanodiamond (ND) nanoclusters-decorated graphene oxide (GO) was fabricated and incorporated in an epoxy matrix using a facile thermoregulatory liquid-liquid extraction method.
Abstract: Novel hybrid fillers composed of nanodiamond (ND) nanocluster-decorated graphene oxide (GO) were fabricated and incorporated in an epoxy matrix using a facile thermoregulatory liquid-liquid extraction method. X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analyses confirmed a chemical bonding between the (3-aminopropyl)triethoxysilane-functionalized ND and (3-glycidyloxypropyl)trimethoxysilane-functionalized GO. The morphology of the hybrid filler (GN) was characterized by field-emission transmission electron microscopy. ND nanoclusters with an average diameter of 50–100 nm were uniformly grown on the GO surface. The hybrid filler provided significant enhancement of mechanical properties, such as flexural strength, flexural modulus, and fracture toughness. In particular, the epoxy composite containing 0.1 wt% of GN hybrid exhibited a stronger mechanical behavior compared to that containing 0.2 wt% of GO. As the GN loading increased, the thermal stability, the integral procedural decomposition temperature, and the activation energy increased as well. The toughening mechanism was illustrated by a microcrack theory based on the microscopic analysis of the fracture surfaces. The presence of ND nanoclusters not only hindered the aggregation of the GO sheets, but also played a crack pinning role in the polymer-matrix composites, which could significantly enhance its fracture toughness.
TL;DR: In this paper, the effects of roller compacted concrete (RCC) characteristics on their fracture behavior in both pure mode I and II are experimentally investigated, and the fracture toughness results revealed concrete mix specifications had a noticeable impact on the cracking initiation of RCC and the effect of substituting of waste materials with natural aggregates was found to be negative, although their behavior was still comparable to those obtained for control mixes.
TL;DR: In this article, an in situ quantitative tensile testing platform is developed to enable the uniform in-plane loading of a freestanding membrane of 2D materials inside a scanning electron microscope.
Abstract: An in situ quantitative tensile testing platform is developed to enable the uniform in-plane loading of a freestanding membrane of 2D materials inside a scanning electron microscope. The in situ tensile testing reveals the brittle fracture of large-area MoSe2 crystals and measures their fracture strength for the first time.
TL;DR: In this article, the fracture toughness of acrylonitrile butadiene styrene (ABS) was analyzed in three orthogonal orientations to analyze how fracture toughness varied with mesostructure.
Abstract: Fused deposition modeling (FDM) has been gaining industrial interest due to its potential to simplify and lower the cost of complex manufacturing. To better understand the mechanical response of these materials—due to potential integration of FDM parts into structural components—compact tension samples of acrylonitrile butadiene styrene (ABS) were printed in three orthogonal orientations to analyze how the fracture toughness varied with mesostructure. Furthermore, in each of these orientations the raster pattern was either an alternating +45/−45° or a 0/90° pattern. When the alignment of extruded filament layers changed from parallel to perpendicular with respect to the crack plane, a 54% increase in fracture toughness was observed. However, the raster pattern only had a significant effect in one of the print orientations; the fracture toughness decreased by 11% when a 0/90° pattern was used in place of a +45/−45° pattern in layers oriented perpendicularly to the crack plane. The orientation of individual tracks of deposited material with respect to the crack tip appeared to have the most pronounced role in altering the fracture toughness of FDM ABS. This research provides useful information and insight to future designers determining how processing affects the crack stability of these new materials used for space hardware
TL;DR: In this paper, an experimental and numerical study on fracture behavior of bamboo fiber reinforced epoxy composites is presented, where the authors used single fiber tensile test and microscopic inspection of fiber surface through SEM (Scanning Electron Microscopy).
Abstract: In this work, experimental and numerical study on fracture behaviour of bamboo fiber reinforced epoxy composites is presented. Optimum NaOH concentration for treatment of bamboo fibers was determined through single fiber tensile test and microscopic inspection of fiber surface through SEM (Scanning Electron Microscopy). The results demonstrated that 6% NaOH treated fibers showed maximum ultimate tensile strength of 234 MPa. Single fiber fragmentation test results showed that interfacial adhesion is improved by treating fibers with 6% NaOH. Bamboo fiber reinforced epoxy composite was fabricated using 6% NaOH treated bamboo fibers of length 10 mm, 20 mm and 25 mm with random distribution in epoxy matrix. Mode-I plane strain fracture toughness (K IC ) of bamboo fiber reinforced epoxy composites was investigated based on Linear Elastic Fracture Mechanics (LEFM) approach as per ASTM D5045 . Results showed that composites having 25 mm length of fibers had the largest K IC value of 2.67 MPa.m 1/2 , whereas composites with 10 mm fiber length showed lowest value of fracture toughness K IC of 1.61 MPa.m 1/2 . SEM results revealed that fiber breakage, matrix cracking, fiber matrix debonding and fiber pull out are major causes of failure of composite. Simulation/modelling of crack propagation in CT (Compact Tension) specimen by using FEA software ABAQUS ® showed similar results as experimental values.
TL;DR: In this paper, the microstructural evolution of additively manufactured Inconel 625 during a post-build stress-relief anneal of 1-hour at 1143 K (870 K) is investigated.
Abstract: The microstructural evolution of laser powder-bed additively manufactured Inconel 625 during a post-build stress-relief anneal of 1 hour at 1143 K (870 °C) is investigated. It is found that this industry-recommended heat treatment promotes the formation of a significant fraction of the orthorhombic D0a Ni3Nb δ-phase. This phase is known to have a deleterious influence on fracture toughness, ductility, and other mechanical properties in conventional, wrought Inconel 625; and is generally considered detrimental to materials’ performance in service. The δ-phase platelets are found to precipitate within the inter-dendritic regions of the as-built solidification microstructure. These regions are enriched in solute elements, particularly Nb and Mo, due to the micro-segregation that occurs during solidification. The precipitation of δ-phase at 1073 K (800 °C) is found to require up to 4 hours. This indicates a potential alternative stress-relief processing window that mitigates δ-phase formation in this alloy. Ultimately, a homogenization heat treatment is recommended for additively manufactured Inconel 625 because the increased susceptibility to δ-phase precipitation increases the possibility for significant degradation of materials' properties in service.
TL;DR: In this paper, the effect of layer orientation on the fracture properties of poly(acrylonitrile-butadienestyrene) (ABS) materials fabricated through the fused filament fabrication (FFF) process was explored.
TL;DR: In this article, the effects of various strain rates on the fracture toughness as well as the energy-release rate of gas shales were investigated using three-point bending method was applied using notched semicircular bending shale specimens that were prepared as per the international standards.
TL;DR: In this paper, the effects of both natural and synthetic fibers on enhancing the performance of the tested WMA mixtures was more pronounced for dominantly pure mode I loading case compared to the control mixture.
TL;DR: In this article, the authors proposed fracture-based forming limit criteria for anisotropic materials in sheet metal forming to predict the sudden fracture in complicated forming processes, where the Lou-Huh ductile fracture criterion was modified using the Hill's 48 yield function instead of the von Mises isotropic yield function to account of the influence of anisotropy on the equivalent plastic strain at the onset of fracture.
TL;DR: In this paper, the tensile performance of a one-part strain hardening geopolymer composite (SHGC) reinforced by ultra-high-molecular-weight polyethylene (PE) fibers was investigated.
TL;DR: In this paper, the fracture toughness of a Ti-6Al-4V alloy octet-lattice truss structure manufactured using a "snap-fit" method was investigated.
Abstract: The only engineering materials with both high strength and toughness, and with densities less than 1000 kg m−3, are natural materials (woods) and some plastics. Cellular structures such as the octet lattice, when made from periodic arrangements of strong, low-density metallic trusses, are known to have high specific strengths and elastic moduli. However, much less is known of their resistance to fracture. Here we investigate the fracture toughness of a Ti-6Al-4V alloy octet-lattice truss structure manufactured using a ‘snap-fit’ method. The samples had densities between 360 and 855 kg m−3 (relative densities of 8–19%) and free truss lengths between 4 and 15 mm. Their fracture resistance was determined using the J-integral compliance method applied to single-edge notched bend specimens. The toughness is shown to increase linearly with the relative density and with the square root of the cell size, while the strength was confirmed to scale only with relative density and the strength of the solid. A moderate increase in resistance with crack length (an R-curve effect) was seen for the higher relative density and larger cell size samples. With a fracture toughness between 2 and 14 MPa m1/2 and a compressive strength between 20 and 70 MPa, these structures offer a new lightweight engineering material solution for use at temperatures up to 450 °C.
TL;DR: In this article, the macroscopic mechanical properties of granite collected from the Fujian Province, China were measured using uniaxial compression and three-point bending after the granite was exposed to high temperatures.
TL;DR: In this paper, an ambient temperature cured "one-part" strain hardening geopolymer composite (SHGC) was developed as a "dry mix" using a small amount of solid activator and eliminating the necessity for heat curing.
TL;DR: In this paper, the length of fracture process zones (FPZs) in the NSCB and CCNSCB tests with representative specimen geometries were theoretically estimated using the maximum normal stress criterion, and their effects on these fracture toughness tests were evaluated according to the effective crack model.
TL;DR: In this article, up to centimeter-thick nacre-mimetic clay/polymer nanocomposites are produced by the lamination of self-assembled films.
Abstract: Nacre inspires researchers by combining stiffness with toughness by its unique microstructure of aligned aragonite platelets. This brick-and-mortar structure of reinforcing platelets separated with thin organic matrix has been replicated in numerous mimics that can be divided into two categories: microcomposites with aligned metal oxide microplatelets in polymer matrix, and nanocomposites with self-assembled nanoplatelets—usually clay or graphene oxide—and polymer. While microcomposites have shown exceptional fracture toughness, current fabrication methods have limited nacre-mimetic nanocomposites to thin films where fracture properties remained unexplored. Yet, fracture resistance is the defining property of nacre, therefore centrally important in any mimic. Furthermore, to make use of these properties in applications, bulk materials are required. Here, up to centimeter-thick nacre-mimetic clay/polymer nanocomposites are produced by the lamination of self-assembled films. The aligned clay nanoplatelets are separated by poly(vinyl alcohol) matrix, with 106–107 nanoplatelets on top of each other in the bulk plates. Fracture testing shows crack deflection and a fracture toughness of 3.4 MPa m1/2, not far from nacre. Flexural tests show high stiffness (25 GPa) and strength (220 MPa) that, despite the hydrophilic constituents, are not substantially affected by exposure to humidity.