1,721,078 research outputs found
Fracture behavior under torsion of notched round bars made of gray cast iron
No full textThe purpose of this paper is twofold and therefore it has been divided in two parts. In the first part, experimental results of 25 gray cast iron notched specimens tested under torsion loading are provided. V-notch (with an opening angle of 120°) geometry is considered with root radii ranging from 0.1 to 2.0. mm. Plots of torque loads versus twist angles are recorded for all notch root radii tested. Such results can help in evaluating numerical and theoretical models for fracture of notched components under mode III loading. The second part of the paper deals with an analysis of the experimental results by using the Strain Energy Density criterion. Because of the mode III loading conditions, a non-conventional application of such criterion is carried out, showing a good agreement between the experimental results and the theoretical fracture assessments and it is used to justify the link between nominal and local fracture approaches
Fracture assessment of U-notches under mixed mode loading: two procedures based on the 'equivalent local mode I' concept
No full textTwo fracture criteria are proposed and applied to blunt-notched components made of brittle materials loaded under mixed mode; the former is based on the averaged strain energy density over a given control volume, the latter on the cohesive crack zone model. In both instances use of the equivalent local mode I hypothesis is made. Only two material properties are needed: the ultimate tensile strength and the fracture toughness. Numerical predictions of rupture loads from the two criteria are compared with experimental measurements from more than 160 static tests with notched beams. The samples are made of PMMA and tested at -60 degrees C to assure a bulk behaviour almost linear elastic up to rupture. Notch root radii range from 0.2 to 4.0 mm and load mixicity varies from pure mode I to a prevailing mode II. The good agreement between theory and experimental results adds further confidence to the proposed fracture criteria
Fracture of U-notched specimens under mixed mode: Experimental results and numerical predictions
No full textThe first part of the paper gives an account of 153 fracture tests on blunted notched specimens (with notches of root radius ranging from 0.3 to 4.0 mm), loaded under mixed mode (ranging from almost pure mode I to mode II, and beyond). Maximum loads and initial crack angles were measured as a function of notch root radius and loading mixity. Such results can help in evaluating numerical models of the fracture of notched components. The second part of the paper deals with the suitability of the cohesive crack concept for predicting fracture loads under mixed mode. Use of local mode I was considered for numerical computations. Comparison of experimental results with numerical predictions was significantly accurate. Diagrams of fracture loci for notched components loaded under mixed mode are discussed
Fracture behaviour of notched round bars made of PMMA subjected to torsion at -60°C
No full textThis paper presents seventy new experimental results from PMMA notched specimens tested under torsion at -60 °C. The notch root radius ranges from 0.025 to 7.0. mm. At this temperature the non-linear effects previously observed on specimens of the same material tested at room temperature strongly reduce. The averaged value of the strain energy density over a control volume is used to assess the critical loads to failure. The radius of the control volume and the critical strain energy density are evaluated a priori by using in combination the mode III critical stress intensity factor from cracked-like specimens and the critical stress to failure detected from semicircular notches with a large notch root radius. © 2013 Elsevier Ltd
Effect of Silane coupling agent on mechanical performance of glass fibre
No full textMechanical performance of commercially manufactured unsized and γ-APS sized boron-free E-glass fibres has been characterised using single fibre tensile test. Both apparent fibre modulus and fibre strength were found to strongly depend on fibre gauge length. The average strength of sized fibres was found 40%-80% higher than unsized fibres at different gauge lengths. Weibull analysis suggested that the failure mode of unsized fibres could be described by unimodal Weibull distribution, whereas the strength distribution of sized fibres appeared to be controlled by two exclusive types of flaw population, type A and B. Comparison of the Weibull plots between unsized and sized fibres revealed that the strength of unsized fibres was likely to be dominated by type A flaws existing on the bare glass surface and type B flaws may be related to the defects on the glass surface coated with silane. This was partially supported by the observation of fractured cross-sectional area using SEM. It was, therefore, proposed that the strength difference between unsized and sized glass fibres may be more reasonably interpreted from the surface protection standpoint as opposed to the flaw healing effect. The results obtained from this work showed that silane coupling agent plays a critical role in the strength retention of commercially manufactured E-glass fibres and the silane effect on the fibre strength is also affected by the change in gauge length of the sample
Fracture assessment of U-notches under mixed mode loading: Two procedures based on the 'equivalent local mode I' concept
No full textTwo fracture criteria are proposed and applied to blunt-notched components made of brittle materials loaded under mixed mode; the former is based on the averaged strain energy density over a given control volume, the latter on the cohesive crack zone model. In both instances use of the equivalent local mode I hypothesis is made. Only two material properties are needed: the ultimate tensile strength and the fracture toughness. Numerical predictions of rupture loads from the two criteria are compared with experimental measurements from more than 160 static tests with notched beams. The samples are made of PMMA and tested at -60°C to assure a bulk behaviour almost linear elastic up to rupture. Notch root radii range from 0.2 to 4.0 mm and load mixicity varies from pure mode I to a prevailing mode II. The good agreement between theory and experimental results adds further confidence to the proposed fracture criteria. © Springer Science+Business Media B.V. 2008
Fracture of V-notched specimens under mixed mode (I plus II) loading in brittle materials
No full textThe purpose of this research is threefold. First, to provide experimental results of fracture loads for V-notched beams loaded under mixed mode. Second, to check the suitability of fracture criteria based on the cohesive zone model and strain energy density when applied to those samples. And, third, to suggest a very simple fracture criterion, based on the dominance of the local mode I, for notched samples (with different V-notch angles and notch root radii) loaded under mixed (I + II) mode. This proposal unifies predictions for the experimental results obtained under mode I and mixed mode loading. To this end, 36 fracture tests on V-notched beams were performed and reported: three V-notched angles were investigated (90A degrees, 60A degrees, 30A degrees, four different loadings (mixed modes I and II) were selected and three samples were tested for each configuration
Brittle failures from U- and V-notches in mode I and mixed, I plus II, mode: a synthesis based on the strain energy density averaged on finite-size volumes
No full textA large bulk of static test results carried out on notched specimens are presented in a unified way by using the mean value of the strain energy density (SED) over a given finite-size volume surrounding the highly stressed regions. In plane problems, when cracks or pointed V-notches are considered, the volume becomes a circle or a circular sector, respectively, with R(C) being the radius. R(C) depends on the fracture toughness of the material, the ultimate tensile strength and the Poisson's ratio. When the notch is blunt, the control area assumes a crescent shape and R(C) is its width as measured along the notch bisector.
About 900 experimental data, taken from recent literature, are involved in the local SED-based synthesis. They have been obtained from (a) U- and V-notched specimens made of different materials tested under mode I loading; (b) U- and V-notched specimens made of polymethyl-metacrylate (PMMA) and an acrylic resin, respectively, tested in mixed, I + II, mode; (c) U-notched specimens made of ceramics materials tested under mode I.
The local SED values are normalized to the critical SED values (as determined from unnotched specimens) and plotted as a function of the R/R(C) ratio. A scatter band is obtained whose mean value does not depend on R/R(C), whereas the ratio between the upper and the lower limits are found to be about equal to 1.6. The strong variability of the non-dimensional radius R/R(C) (ranging here from about zero to around 1000) makes stringent the check of the approach based on the mean value of the local SED on a material-dependent control volum
Local strain energy to assess the static failure of U-notches in plates under mixed mode loading
No full textThe averaged value of the strain energy density over a well-defined volume is used to predict the static strength of U-notched specimens under mixed-mode conditions due to combined bending and shear loads. The volume is centered in relation to the maximum principal stress present on the notch edge, by rigidly rotating the crescent-shaped volume already used in the literature to analyse U- and V-shaped notches subject to mode I loading. The volume size depends on the ultimate tensile strength sigma(u) and the fracture toughness K-IC of the material. In parallel, an experimental programme was performed. All specimens are made of polymethyl-metacrylate (PMMA), a material which,exhibits quasi-brittle behaviour at -60 degrees C. Good agreement is found between experimental data for the critical loads to failure and theoretical predictions based on the constancy of the mean strain energy density over the control volume
A synthesis of Polymethylmethacrylate data from U-notched specimens and V-notches with end holes by means of local energy
No full textIn this paper a volume criterion based on a simple scalar quantity, the mean value of the strain energy (SED), has been used to assess the static strength of notched components made of Polymethylmethacrylate (PMMA).The control volume is thought of as dependent on the linear elastic ultimate tensile strength and the fracture toughness in the case of brittle or quasi-brittle materials subjected to static loadings.The local-strain-energy based approach has been applied to two well-documented set of experimental data recently reported in the literature. Data refer to blunt U-notched specimens of commercial PMMA subjected to static loads and characterised by a large variability of notch tip radius (from 0.25. mm to 2.5. mm).Critical loads obtained experimentally have been compared with the theoretical ones, estimated by keeping constant the mean value of the strain energy in a well-defined small size volume.In addition, some new tests dealing with V-notched specimens with end holes have been carried out to investigate the effect of the notch opening angle and thirty new data have been summarised in terms of the SED. The new data have permitted to strengthen the validation aspects of the modelling. © 2013 Elsevier Ltd
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