A notch root radius to attain minimum fracture loads in plates weakened by U-notches under mode I loading (original) (raw)
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In this paper, the mean value of strain energy density criterion has been used to predict the critical fracture load in specimens with U-shaped notch under bending loads. An equation for calculation of averaged strain energy density in this zone has been presented. Bending loads under mode I have been considered. Two cases have been studied: 1) the control volume only includes the semicircular arc of the notch root, and 2) the control volume includes rectilinear edge of the notch. The effect of notch root radius and notch depth on the mean value of strain energy density has been studied in two cases above and the critical fracture load rate has been predicted. Finite Element Analysis has been carried out for verification. The studies show that the critical fracture load increases and then decreases by increasing the notch root radius. Also, this parameter decreases exponentially by increasing the notch depth.
Influence of notch parameters on fracture behavior of notched component
2014
In the present study, the influence of variation of notch parameters on the notch stress intensity factor KI is studied using CT- specimen made from steel construction. A semi-elliptical notch has been modeled and investigated and is applied to finite elements model. The specimen is subjected to a uniform uniaxial tensile loading at its two ends under perfect elastic-plastic behavior. The volumetric method and the Irwin models are compared using a finite elements method for determined the effective distance, effective stress and relative gradient stress which represent the elements fundamentals of volumetric method. Changing made to notch parameters affect the results of stress intensity factor and the outcomes obtained shows that the increase in size of minor axis reduces the amplitude of elastic-plastic stresses and effective stresses. In lengthy notches, the Irwin model remains constant with very little disturbance of outcomes.
Effect of notch parameters on the critical effective T-stress in elastic brittle fracture
Journal of Adhesion Science and Technology, 2016
The present work is aimed to investigate the effect of notch root radius ρ and angle of specimen on the critical effective T-stress. A notched plate made of molybdenum alloy TZM is considered and subjected to a tensile loading. In brittle materials, the tools derived from linear elastic fracture mechanics are applicable and the analysis was made according to a local approach defined by the volumetric method. Different values of notch root radius (ρ = 0.5, 1, 1.5, 2 mm) and angle (= 0°, 15°, 30° and 45°) have been selected to conduct an analysis of the critical effective T-stress and the distribution of T-stress at the notch tip in brittle fracture. The effective T-stress T eff has been estimated as the average value of the T-stress distribution in the region ahead of the notch tip at the effective distance X eff. The obtained results showed that the variation of radius affects strongly the critical effective T-stress, while the variation of angle gives a very small change in values of critical effective T-stress.
Fracture assessment of U-notches under three point bending by means of local energy density
Materials & Design, 2010
The main purpose of the paper is twofold. First, to provide a new set of experimental results on fracture of U-notched samples, made of two different materials; second, to apply a fracture criterion based on the strain energy density (SED) averaged over a control volume to assess the fracture load of blunt-notched components under three point bending. Two different materials are considered in the tests: a composite material (Al-15%SiC) tested at room temperature and a steel with a ferritic-pearlitic structure tested at À40°C. All samples are weakened by U-notches characterized by different values of notch root radius and notch depth. The theoretical loads to failure as determined according to the SED criterion are compared with the experimental data from more than 40 static tests and with a SED-based scatter band recently reported in the literature for a number of materials exhibiting a brittle behaviour under static loads.
Crack onset at a v-notch. Influence of the notch tip radius
International Journal of Fracture, 2000
A criterion to predict crack onset at a sharp notch in homogeneous brittle materials has been presented in a previous paper of one of the authors. It is reviewed and improved herein. It fulfils both the energy and the strength criteria and takes an Irwin-like form involving the generalized intensity factor of the singularity governing the elastic behaviour in the vicinity of a notch tip. The prediction agrees fairly well with the experiments although it slightly underestimates the experimental measures. A cause of this discrepancy can be that a small notch tip radius blunts the sharp corner. It is analysed in this paper by means of matched asymptotics involving 2 small parameters: a micro-crack increment length and the notch tip radius. A correction is brought to the initial prediction and a better agreement is obtained with experiments on PMMA notched specimens. Experiments performed on a stiffer material (Alumina/Zirconia) show that it is less sensitive to small notch tip radii. A remaining small discrepancy between experiments and predictions can be due to some non linear behaviour of the materials near the notch tip. In addition, without new developments, the method allows to determine the stress intensity factor at the tip of a short crack emanating from a sharp or a rounded v-notch.
Notch Fracture Mechanics Approaches in an Analysis of Notch-like Defects
Ecf19, 2013
The concept of notch fracture mechanics has been developed for describing the notch failure assessment diagram as well as the J-integral for U-and V-notches under Mode I loading and materials obeying a power hardening law. Effects of constraint were incorporated into the basic equations which describe the constraint-dependent fracture toughness and failure assessment diagrams for various structural elements with a crack/notch and various types of loading. It is shown that a crack can be considered as a special case of a notch. The load separation method has been employed to measure the notch fracture toughness c J , using non-standard specimens with notches. Structural integrity assessment of the components damaged by notch-like defects is discussed from viewpoint of the notch failure assessment diagram. Acceptable state of the damaged component with a notch-like defect is determined by introducing safety factors against fracture and plastic collapse in the fracture criterion describing the notch failure assessment diagram.
Metals, 2018
The main goal of this paper is the application of the Strain Energy Density (SED) criterion and the Theory of Critical Distances (TCD), both of them in combination with the Equivalent Material Concept (EMC), to predict the fracture loads of aluminum alloy Al7075-T651 Compact Tension (CT) specimens containing U-shaped notches. For this purpose, 45 fracture tests were performed combining two rolling orientations (transverse and longitudinal) and 6 notch radii, which cover from crack-type defects (0 mm) up to 2 mm-notch radius. Crack-type specimens are used to define the fracture properties of the material and the rest of the tests are used to check and compare the experimental fracture loads with the loads predicted using the different aforementioned criteria: SED, EMC-SED and EMC-TCD. The theoretical results of the fracture load predictions for the virtual brittle material obtained employing the EMC are in good agreement with the experimental results reported for real samples.
Notch strengthening or weakening governed by transition of shear failure to normal mode fracture
Scientific reports, 2015
It is generally observed that the existence of geometrical discontinuity like notches in materials will lead to strength weakening, as a resultant of local stress concentration. By comparing the influence of notches to the strength of three typical materials, aluminum alloys with intermediate tensile ductility, metallic glasses with no tensile ductility, and brittle ceramics, we observed strengthening in aluminum alloys and metallic glasses: Tensile strength of the net section in circumferentially notched cylinders increases with the constraint quantified by the ratio of notch depth over notch root radius; in contrast, the ceramic exhibit notch weakening. The strengthening in the former two is due to resultant deformation transition: Shear failure occurs in intact samples while samples with deep notches break in normal mode fracture. No such deformation transition was observed in the ceramic, and stress concentration leads to its notch weakening. The experimental results are confirm...
Analysis of stress and strain concentrations in notched members made of alloys D16 and 1460
Technical Sciences
EN The aim of the study was to present findings on the effect of the presence of a notch upon stress and strain concentrations in model members for aeronautical structures, made of selected aluminum alloys, i.e. D16 and 1460. Flat specimens with centrally positioned holes and side cuts, loaded with some bending moment of stress ratio R = 1, were tested. Specialized FEM software (MSC.Patran and MSC.Nastran) was applied to examine stress and strain distributions. The findings are presented in the form of σ[max] and ε[max] values as well as functions of the following factors: α σ, α ε, and αk, computed on the grounds of these values for both different distances from the bottom of the notch and assumed levels of load put on the specimens. Theoretical analysis was supplemented with experimental investigations into the microstructure of fatigue-fracture surfaces in the area of crack initiation and in that of fatigue of a propagating crack. PL Przedstawiono wyniki badań wpływu działania ka...
Influence of notch (TIP) radius on fatigue crack growth rate
JOURNAL …, 2006
The paper deals with the problem of fatigue crack propagation from notches in plates made of FeP04 steel and AA356-T6 aluminium alloy. The tests were performed under different stress ranges by keeping the nominal load ratio (R= 0. 1) constant. The specimens were ...