Showing papers on "Fracture toughness published in 2012"
TL;DR: In this article, a technical review of fracture toughness testing, evaluation and standardization for metallic materials in terms of the linear elastic fracture mechanics as well as the elastic-plastic fracture mechanics is given.
594 citations
TL;DR: In this article, the authors report enhancements of 28-111% in mode I fracture toughness and up to 1580% in uniaxial tensile fatigue life through the addition of small amounts (≤1 wt %) of graphene oxide to an epoxy system.
Abstract: Epoxy systems have proven popular having important applications in aerospace and wind energy, but fracture and fatigue resistance of this polymer remain less than desired. Graphene oxide, a form of atomically thin carbon, possessing impressive multifunctional properties and an ideal interface for interacting with polymer matrices, has emerged as a viable reinforcement candidate. In this work, we report enhancements of 28–111% in mode I fracture toughness and up to 1580% in uniaxial tensile fatigue life through the addition of small amounts (≤1 wt %) of graphene oxide to an epoxy system. Graphene oxide was uniquely synthesized by unraveling and splaying open helical-ribbon carbon nanofibers. The resulting oxygenated basal planes and edges of the graphene oxide sheets were observed to promote onset of the cross-linking reaction and led to an increase in total heat of reaction effecting slightly higher glass transition temperatures of the cured composites. Measured improvements were also detected in quasi-st...
434 citations
TL;DR: In this paper, a new ductile fracture criterion is proposed to model fracture behavior of sheet metals for nucleation, growth and shear coalescence of voids during plastic deformation.
388 citations
TL;DR: In this paper, the effect of silica nanoparticles and particle size on glass transition temperature (T g ), coefficient of thermal expansion (CTE), Young's modulus (E ), yield stress ( σ ), fracture energy (G IC ), and fracture toughness (K IC ), were investigated.
254 citations
TL;DR: In this article, the authors established a universal, accurate and efficient fracture criterion for ductile metals based on a phenomenological fracture criterion using the magnitude of stress vector and the first invariant of stress tensor, which was compared to, and shown better than, the maximum shear stress fracture criterion proposed by Stoughton and Yoon, J 2 fracture criterion and Xue-Wierzbicki fracture criterion.
245 citations
TL;DR: In this paper, a recent development in fracture toughness measurement which involves the application of macrotension to a substrate in order to induce microtension in a patterned thin film is discussed.
235 citations
TL;DR: In this paper, a study on graphene platelet/zirconia-toughened alumina (GPL/ZTA) composites was carried out to evaluate the potential of the new structural materials.
Abstract: A study on graphene platelet/zirconia-toughened alumina (GPL/ZTA) composites was carried out to evaluate the potential of the new structural materials GPL–ZrO2–Al2O3 powders were obtained by ball milling of graphene platelets and alumina powders using yttria stabilized ZrO2 balls Samples were sintered at different temperatures using spark plasma sintering Fracture toughness was determined by the single-edge notched beam method The results show that the GPLs are uniformly distributed in the ceramic matrix and have survived high temperature sintering processes Several sintering experiments were carried out It is found that at 1550 °C, GPL/ZTA composites were obtained with nearly full density, maximum hardness and fracture toughness A 40% increase in fracture toughness in the ZTA composite has been achieved by adding graphene platelets The toughening mechanisms, such as pull out, bridging and crack deflection, were observed and are discussed
230 citations
TL;DR: In this article, the effect of water absorption on the mechanical and physical properties of reinforced cellulose fiber reinforced epoxy composites was investigated and the results showed that flexural strength, flexural modulus, fracture toughness and impact strength increased as the fibre content increased.
226 citations
TL;DR: In this paper, an uncoupled non-associated fracture model is proposed which makes use of a stress state dependent weighting function and an anisotropic plastic strain measure, which is obtained from applying the von Mises equivalent plastic strain definition after the linear transformation of the plastic strain tensor.
222 citations
TL;DR: In this article, a microstructure-based fracture mechanics model is presented to investigate the toughening effect due to the crack-bridging mechanism of platelets, and some guidelines for the biomimetic design of novel materials are proposed based on their theoretical analysis.
Abstract: Studying the structure–property relation of biological materials can not only provide insight into the physical mechanisms underlying their superior properties and functions but also benefit the design and fabrication of advanced biomimetic materials. In this paper, we present a microstructure-based fracture mechanics model to investigate the toughening effect due to the crack-bridging mechanism of platelets. Our theoretical analysis demonstrates the crucial contribution of this mechanism to the high toughness of nacre. It is found that the fracture toughness of nacre exhibits distinct dependence on the sizes of platelets, and the optimized ranges for the thickness and length of platelets required to achieve higher fracture toughness are given. In addition, the effects of such factors as the mechanical properties of the organic phase (or interfaces), the effective elastic modulus of nacre, and the stacking pattern of platelets are also examined. Finally, some guidelines for the biomimetic design of novel materials are proposed based on our theoretical analysis.
211 citations
TL;DR: In this paper, the authors used various graphene platelets with the aim of improving the fracture toughness of Si3N4 composites, with the highest value of 9.92 MPa/m 0.5.
TL;DR: A comprehensive review of techniques for the experimental characterisation of the fracture toughness associated with the translaminar (fibre-breaking) failure modes of continuously reinforced laminated composites is presented in this article.
TL;DR: In this article, a new model based on finite fracture mechanics is proposed to predict the open-hole tensile strength of composite laminates and failure is predicted when both stress-based and energy-based criteria are satisfied.
Abstract: A new model based on finite fracture mechanics is proposed to predict the open-hole tensile strength of composite laminates. Failure is predicted when both stress-based and energy-based criteria are satisfied. The material properties required by the model are the ply elastic properties, and the laminate unnotched strength and fracture toughness. No empirical adjusting parameters are required. Using experimental data obtained in quasi-isotropic carbon–epoxy laminates it is concluded that the model predictions are very accurate, resulting in improvements over the traditional strength prediction methods. It also is shown that the proposed finite fracture mechanics model can be used to predict the brittleness of different combinations of materials and geometries.
01 Jan 2012
TL;DR: In this paper, the physical and mechanical properties of pure copper and copper alloys with the focus on precipitation-hardened CuCrZr and dispersion-strengthened CuAl25 alloys are reviewed.
Abstract: High strength, high conductivity copper alloys are prime candidates for high heat flux applications in fusion energy systems. This chapter reviews the physical and mechanical properties of pure copper and copper alloys with the focus on precipitation-hardened CuCrZr and dispersion-strengthened CuAl25 alloys. The effect of neutron irradiation on copper and copper alloys is reviewed in terms of radiation effects on physical properties and mechanical properties (tensile properties, fracture toughness, fatigue and creep-fatigue), irradiation creep and void swelling. The effect of irradiation on the microstructure of copper and copper alloys and dislocation channeling is also presented. Joining techniques for copper alloys in fusion plasma facing components are briefly discussed.
TL;DR: In this paper, the authors used micrometer-sized notched cantilevers to investigate the possibility of determining fracture mechanical parameters for the semi-brittle material tungsten.
Abstract: Fracture experiments using micrometer-sized notched cantilevers were conducted to investigate the possibility of determining fracture mechanical parameters for the semi-brittle material tungsten. The experiments were also used to improve the understanding of semi-brittle fracture processes for which single crystalline tungsten serves as a model material. Due to the large plastic zone in relation to the micrometer sample size, linear elastic fracture mechanics is inapplicable and elastic-plastic fracture mechanics has to be applied. Conditional fracture toughness values J Q were calculated from corrected force vs. displacement diagrams. Crack growth was accessible by direct observation of in-situ experiments as well as with the help of unloading compliances. As a further tool, fracture toughness can be determined via crack tip opening displacement. The micro samples behave more ductile and exhibit higher fracture toughness values compared to macro-sized single crystals and fail by stable crack propagation.
TL;DR: In this article, the influence of the addition of graphene platelets on microstructure development and fracture toughness of Si 3 N 4 + GPLs composites was investigated, and the main toughening mechanisms originated from the presence of GPL platelets.
Abstract: Silicon nitride + 1 wt% graphene platelet composites were prepared using various graphene platelets (GPLs) as filler. The influence of the addition of GPLs on the microstructure development and on the fracture toughness of Si 3 N 4 + GPLs composites was investigated. The GPLs with thickness from 5 nm to 50 nm are relatively homogeneously distributed in the matrix of all composites, however overlapping/bundle formation of GPLs was found, containing 2–4 platelets as well. The single GPLs and overlapped GPLs are located at the boundaries of Si 3 N 4 , and hinder the grain growth and change the shape of the grains. The fracture toughness was significantly higher for all composites in comparison to the monolithic Si 3 N 4 with the highest value of 9.9 MPa m 0.5 for the composite containing the GPLs with smallest dimension. The main toughening mechanisms originated from the presence of graphene platelets, and responsible for the increase in the fracture toughness values are crack deflection, crack branching and crack bridging.
TL;DR: In this paper, the effect of aggregate-free silica nanoparticles and phase-separated submicron rubber particles on the mechanical properties of modified epoxy resins was investigated.
TL;DR: In this article, the tensile and fracture behavior of as-cast and age-hardened aluminium (6063), silicon carbide particulate composites produced, using borax additive and a two-step stir casting method, was investigated.
TL;DR: In this paper, a new uncoupled anisotropic fracture criterion based on the magnitude of stress vector (MSV) was proposed to simulate the ductile fracture of Al2024-T351 alloy.
TL;DR: The semi-circular bend (SCB) specimen has been used for many other applications as mentioned in this paper, such as testing of in situ conditions such as elevated temperature, confining pressure and pore water pressure.
TL;DR: In this paper, an epoxy nanocomposites reinforced with recycled cellulose fibres (RCFs) and organoclay platelets (30B) was fabricated and investigated in terms of WAXS, TEM, mechanical properties and TGA.
Abstract: Epoxy nanocomposites reinforced with recycled cellulose fibres (RCFs) and organoclay platelets (30B) have been fabricated and investigated in terms of WAXS, TEM, mechanical properties and TGA. Results indicated that mechanical properties generally increased as a result of the addition of nanoclay into the epoxy matrix. The presence of RCF significantly enhanced flexural strength, fracture toughness, impact strength and impact toughness of the composites. However, the inclusion of 1 wt.% clay into RCF/epoxy composites considerably increased the impact strength and toughness. The presence of either nanoclay or RCF accelerated the thermal degradation of neat epoxy, but at high temperature, thermal stability was enhanced with increased char residue over neat resin. The failure micromechanisms and energy dissipative processes in these nanocomposites were discussed in terms of microstructural observations.
TL;DR: In this paper, in situ micro-cantilever tests were carried out to determine the anisotropic fracture toughness of NiAl single crystals using a focused ion beam, and the applicability of the small sample geometries for testing the fracture toughness is finally discussed in terms of size effects in the flow stress of the material due to dislocation nucleation and strain gradients at the crack tip.
TL;DR: In this paper, the mixed mode fracture toughness depends on the geometry and loading conditions such that for any similar mode mixture, the Brazilian disc (BD) test data were significantly greater than the SCB fracture toughness results.
Abstract: Mixed mode fracture experiments were conducted on Harsin marble using two disc-shape samples namely the Brazilian disc (BD) and the semi-circular bend (SCB) specimens. For each specimen, a complete fracture toughness envelope ranging from pure mode I to pure mode II was obtained. The experimental results indicate that the mixed mode fracture toughness depends on the geometry and loading conditions such that for any similar mode mixture, the BD test data were significantly greater than the SCB fracture toughness results. Therefore, the conventional fracture criteria which present a unique mixed mode fracture curve, fail to predict the test results. It is shown that a generalized criterion, which takes into account the effects of geometry and loading conditions, is able to provide individual fracture curves for theses specimens with very good estimates for the test results obtained from both BD and SCB specimens. The BD and SCB specimens can be suggested as appropriate specimens for obtaining typical upper bound and lower bound envelopes for mixed mode fracture toughness of rocks.
03 Oct 2012
TL;DR: In this article, the effect of microstructure on fracture toughness of pure tungsten, potassium doped tungststen, tengststen with 1wt% La2O3 and tengsten rhenium alloys were investigated by means of 3-point bending and double cantilever beam.
Abstract: Tungsten and tungsten alloys show the typical change in fracture behavior frombrittle at low temperatures to ductile at high temperatures. In order to improve theunderstanding of the effect of microstructure the fracture toughness of pure tungsten,potassium doped tungsten, tungsten with 1wt% La2O3 and tungsten rheniumalloys were investigated by means of 3-point bending -, double cantilever beam -and compact tension specimens. All these materials show the expected increase infracture toughness with increasing temperature. The experiments demonstrate thatthe grain size, texture, chemical composition, grain boundary segregation and dislocationdensity seem to have a large effect on fracture toughness below the DBTT.These influences can be seen in the fracture behavior and morphology, where twokinds of fracture occur: on one hand the transgranular and on the other hand the intergranularfracture. Therefor techniques like electron backscatter diffraction, augerelectron spectroscopy and x-ray line profile analysis were used to improve the understandingof the parameters influencing fracture toughness.
TL;DR: In this paper, the authors describe and analyze fracture toughness and crack propagation of selective laser molten (SLM) components made from Ti6Al4V powder particles, which is a relatively new material and improves the static and dynamic behavior of cracked SLM-Ti components.
Abstract: This paper describes and analyzes fracture toughness and crack propagation of selective laser molten (SLM) components made from Ti6Al4V powder particles The main goal of this research is to gain more insight in the fracture mechanisms of this relatively new material and to improve the static and dynamic behavior of cracked SLM-Ti components At first, the SLM process parameters are optimized until the relative material density equals 997% This is close to the relative density of vacuum arc remelted mill annealed standard oxygen titanium which is used as a reference for all experiments A distinctive difference in phase morphology and texture of the microstructure is noticed between the SLM and the reference titanium The fine acicular martensite phase of the SLM-Ti results in more brittle behavior and inferior fracture toughness On the other hand, the fine grained microstructure leads to a large number of grain boundaries acting as obstacle points for crack propagation Consequently, crack growth properties do not significantly differ between both Microstructural analysis of the crack growth and final failure areas on the fractured surfaces is performed to study the failure mechanisms in more detail
TL;DR: In this paper, the authors conducted a comprehensive set of fracture toughness tests on a suite of key rock types in air under different relative humidity and at constant temperature in order to investigate the influence of relative humidity on fracture toughness.
19 Sep 2012
TL;DR: In this article, the authors present a method for the preparation of single lap joint with flat adherends under Hydrostatic pressure and demonstrate the properties of these joints using the ELS test.
Abstract: MANUFACTURE OF QUALITY SPECIMENS Preparing Bulk Specimens by Hydrostatic Pressure Preparing Bulk Specimens by Injection Preparing Bulk Specimens by Pouring Preparing Lap Joints with Flat Adherends SimpleMethods for the Preparation of Single Lap Joints Specimens Preparing Thick Adherend Shear Test Specimens Modified Thick Adherend Shear Test Preparing Butt Joints Preparing Napkin Ring Specimens Preparing T Joint Specimens Preparing Flexible-to-Rigid Peel Specimens Preparing Specimens for Fracture Properties: Double Cantilever Beam and Tapered Double Cantilever Beam Preparing Bonded Wood Double Cantilever Beam (DCB) Specimens Modified Arcan Test QUASI-STATIC CONSTITUTIVE AND STRENGTH TESTS Quasi-Static Testing of Bulk Tensile Specimens Uniaxial and Bulk Compression Quasi-Static Testing of Bulk Compression on Flat Specimens Iosipescu (V-Notched Beam) Test Arcan (V-Notched Plate) Test Quasi-Static Testing of Butt Joints in Tension Shear Properties of Adhesives Measured by Napkin Rings and Solid Butt Joints in Torsion Quasi-Static Testing of Thick Adherend Shear Test Specimens Modified Thick Adherend Shear Test Quasi-Static Testing of Lap Joints Modified Arcan Test Pin-and-Collar Test Method QUASI-STATIC FRACTURE TESTS Measuring Bulk Fracture Toughness Quasi-Static Fracture Tests: Double Cantilever Beam and Tapered Double Cantilever Beam Testing End-Notched Flexure Mode II Fracture Characterization of Bonded Joints Using the ELS Test The Notched Torsion Test to Determine the Mode III Fracture Properties of Adhesives Other Mixed Mode Adhesive Fracture Test Specimens Compact Mixed Mode (CMM) Fracture Test Method Mixed Mode Bending (MMB) with a Reeder and Crews Fixture Mixed Mode Fracture Testing Fracture of Wood Double Cantilever Beam (DCB) Specimens The T-Peel Test Peel Testing at 180' The Floating Roller Peel Test Climbing Drum Peel Test The Analysis of Peel Tests HIGHER RATE AND IMPACT TESTS Dynamic Elastic Modulus The Pendulum Impact Test for Adhesives and Adhesive Joints Higher Rate and Impact Tests: Fracture at High Rates High-Strain-Rate Testing of Adhesive Specimens and Joints by Hopkinson Bar Technique Clamped Hopkinson Bar Testing of Adhesive Bonds under Peel and Shear Loads at Increased Velocities DURABILITY Measurement of the Diffusion Coefficient Tests with Moisture Durability Testing Using Open-Faced Specimens Tests with Temperature The Wedge Test Fatigue Mixed-Mode Fatigue Testing of Adhesive Joints Measurement of Time-Dependent Crack Growth Curvature Mismatch Fracture Test for Subcritical Debonding OTHER TEST METHODS Thermal Characterization Dynamic Mechanical Analysis with a Vibrating Beam Method Bimaterial Curvature Method for Residual Stress and Thermal Expansion Coefficient Determination The Pull-Off Test Shaft-Loaded Blister Test Tests under Hydrostatic Pressure INDEX
TL;DR: The lowest fracture toughness was reached in the GIC group, followed by the microfilled RBCs, resin-modified GIC, and flowable compomers, which do not differ significantly among each other as a material group, compared with the ormocer-based, packable, and micro-hybrid R BCs, which performed statistically similar.
Abstract: The ability of a restorative material to withstand fracture is of crucial importance especially in stress-bearing area. Therefore, the study aims to analyse the fracture toughness of a large number of dental restorative materials categories. The fracture toughness (K
IC
) of 69 restorative materials belonging to ten materials categories—micro-hybrid, nanofilled, microfilled, packable, ormocer-based, and flowable resin-based composites (RBC), compomers and flowable compomers, as well as glass ionomer cements (GIC) and resin-modified GIC was measured by means of the single-edge notched-beam method after storing the samples (n = 8) for 24 h in distilled water. Data were analyzed with the one-way analysis of variance (ANOVA) followed by the Tukey’s test and partial eta-squared statistics (p < 0.05). Large variations between the tested materials within a material category were found. The lowest fracture toughness was reached in the GIC group, followed by the microfilled RBCs, resin-modified GIC, and flowable compomers, which do not differ significantly among each other as a material group. The ormocer-based, packable, and micro-hybrid RBCs performed statistically similar, reaching the highest fracture toughness values. Between the two categories of flowables—composites and compomers—no differences were measured. The correlation between K
IC
and filler volume (0.34) and respective filler weight (0.40) was low. K
IC
increased with the volume fraction of fillers until a critical value of 57%, following with a plateau, with constant values until ca. 65% volume fraction. Above this value, K
IC
decreased slightly. Due to the very large variability of the fracture toughness within a material type, the selection of a suitable restorative material should have not been done with respect to a specific material category, especially in stress-bearing areas, but by considering the individual measured material properties.
TL;DR: In this paper, double-cantilever-beam tests were applied to investigate the mode I interlaminar fracture toughness of carbon fibre/epoxy laminates, in which the epoxy matrices were incorporated with rubber and silica nano-particles, either singly or jointly.
Abstract: Double-cantilever-beam tests were applied to investigate the mode I interlaminar fracture toughness of carbon fibre/epoxy laminates, in which the epoxy matrices were incorporated with rubber and silica nano-particles, either singly or jointly. It is shown that the toughness is improved owing to the presence of these nano-particles although nano-rubber is more effective than nano-silica. Further, by keeping the total particle weight percentage constant in epoxies (e.g., at 8 and 12 wt.%) filled with equal amount of nano-silica and nano-rubber, the interlaminar toughness values of the hybrid laminates are always higher than those with nano-silica filled epoxies but lower than those with nano-rubber filled matrices. Scanning electron microscopy examination of the delaminated surfaces of composite laminates filled with nano-particles revealed that cavitation of nano-rubber particles/void growth and debonding of nano-silica from epoxy matrix are responsible for the improved interlaminar toughness observed. It is also shown that the bulk toughness of nano-particle filled epoxies cannot be fully transferred to the interlaminar toughness of composite laminates, being limited by the constraint effect imposed by the carbon fibres. Finally, the role of fibre-bridging on the delaminated crack and hence delamination toughness is discussed.
28 Feb 2012-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the most important room temperature mechanical properties of two-phase Ti-6Al-4V Alloy with ultrafine grained microstructure were studied in comparison with conventionally heat-strengthened condition of the alloy.
Abstract: The most important room temperature mechanical properties of two-phase Ti–6Al–4V alloy with ultrafine grained microstructure were studied in the present work. Bulk preforms of the alloy with ultrafine grained microstructure were produced by warm multiaxial forging. The final structure consisted of alpha and beta particles with size of 150–500 nm depending on deformation temperature. The mechanical properties of ultrafine grained material were carried out in comparison with conventionally heat-strengthened condition of the alloy. Room-temperature strength of the ultrafine grained material was found to be 16–33% higher than that of the heat-strengthened alloy. However, ductility-related properties including tensile elongation, impact toughness, fatigue crack growth resistance and fracture toughness noticeably decreased with decreasing grain size. The efforts to increase ductility the ultrafine grained alloy by annealing was restricted by rather intensive softening of the material. Considerable enhancement of ductility of the alloy with a bi-modal microstructure consisting of large primary alpha in UFG alpha/beta matrix was shown.