Effect Of Notch Root Radius Research Articles

Notch effect in tension-tension fatigue of short glass fibre reinforced polyphenylene sulfide composites

An experimental investigation of the fatigue behaviour of plain and notched specimens made of 40 % wt. short glass fibre-reinforced PolyPhenylene sulfide is presented. To this end, plain and V-notched specimens (with notch root radius ranging from 0.2 mm to 10 mm) were produced by injection moulding, and the final geometries were obtained by means of two different technological processes (i.e., directly after the injection moulding process and by machining them from injected plates). To investigate the effect of notch root radius and fibre orientation, tension–tension fatigue tests were carried out in load control mode, and the experimental results were reanalysed in terms of net stress amplitude defining the traditional stress-life curves. During the fatigue tests, the damage evolution was monitored using a travelling microscope to define the number of cycles spent for fatigue crack nucleation. Furthermore, the fracture surfaces were observed at the microscopic level to investigate the damage mechanisms and the actual fibre orientation was evaluated by computed tomography analysis. Then, by employing coupled finite element analysis of the injection moulding process and the structural behaviour, four different approaches available in the open literature were used to correlate the geometrical and/or manufacturing process effects in the fatigue strength of the considered material.

Modeling the effect of temperature and notch root radius on fracture toughness

In this work, a physics-based analytical model without any fitting parameters for fracture toughness depending on temperature was proposed. The quantitative relationship between fracture toughness, melting point, Young’s modulus, Poisson’s ratio, and temperature was established. Furthermore, the effect of notch root radius on fracture toughness was investigated, and then we developed a simple theoretical model to characterize the combined effect of temperature and notch root radius on the fracture toughness. Satisfactory agreement between the available experimental measurements and our model predictions was achieved. This study not only advances our in-depth understanding of the quantitative relationship between the temperature and fracture toughness but also provides a powerful and convenient tool to predict the temperature-dependent fracture toughness at different notch root radius.

A geometry and temperature dependent regression model for statistical analysis of fracture toughness in notched specimens

In this work, a novel methodology for fracture characterization of metallic notched components including the effect of notch root radius and temperature is proposed based on the brittle-to-ductile transition curve. To this aim, two different regression models are derived, either by considering temperature as an influencing variable or combined with the notch radius effect. In the former case, the compatibility condition between the statistical distributions of the fracture toughness for a given temperature and of the temperature for a given fracture toughness is applied. This allows the Kc-T field to be analytically defined proving that both distributions are interrelated and cannot be arbitrarily defined. The second regression model is based on the Theory of the critical distances by converting the experimental data at different notch radii to a reference value. In this way the so-called notch or apparent fracture toughness is calculated in a probabilistic manner for any combination of notch radii and temperature. The proposed methodology is applied to the results of a large experimental campaign on a S355J2 steel involving different temperatures and notch root radii conditions confirming its utility and suitability.

Fracture loads for blunt notches under mode I loading

In the present study, fracture load evaluation technique for blunt notches under mode I loading is investigated using the mean stress based line criterion. Considering the effect of notch root radius ρ, a new fracture evaluation method, applicable not only for the V-shaped notches but also for other notches such as shallow notches, is developed, For a large notch root radius ρ (i.e. ρ>ρ|Cri-1), the notch fracture can be evaluated by a simple rule that the fracture occurs when the maximum stress σmax reaches the material ultimate tensile strength σC. If ρ is large adequately such that ρ|Cri-1>ρ>ρ|Cri-2, the notch fracture is evaluated as the fracture problem of a circle hole in an infinite plate. Here, ρ|Cri-1 and ρ|Cri-2 are the critical values for ρ to satisfy the σmax-alone condition and the ρ-alone condition, respectively. Moreover, as long as the V-notch condition is fulfilled by the notch geometry, the notch fracture under mode I loading can be treated as the fracture problem of V-shaped notches and evaluated by the generalized notch stress intensity factorKIV,R or the maximum stress at the notch root σmax. Whether the σmax-alone condition, the ρ-alone condition or the V-notch condition is fulfilled is mainly determined by the ratio of the characteristic length d0m to the geometric size of notched specimen.

Effect of notch parameters on the critical effective T-stress in elastic brittle fracture

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 Teff has been estimated as the average value of the T-stress distribution in the region ahead of the notch tip at the effective distance Xeff. 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.

Effect of notch root radius on tensile behaviour of 316L(N) stainless steel

Type 316L(N) stainless steel (SS) is used as the major structural material for high temperature components of sodium cooled fast reactors. The influence of notch root radius on the tensile behaviour of 316L(N) SS under multi-axial stress state was investigated. Double U-notches with five different kinds of notch geometry were incorporated symmetrically into the tensile testing specimens by changing the notch root radius while keeping the gross diameter, net diameter and notch depth as the same for all the notches. The notch root radius was varied as 0·25, 0·5, 1·25, 2·5 and 5 mm. Tensile tests were carried out on the notched specimens at room temperature (298 K) and at 923 K at a constant strain rate of 3×10−3 s−1. The tensile strength and yield strength of notched specimen of 316L(N) SS increased with decrease in notch radius at both the temperatures and the notch severity was less pronounced at high temperature. The fractured notch surface was analysed using scanning electron microscope and unfractured notch was sliced along the axis and observed under optical microscope. Finite element analysis was performed on the models of notched specimens with various notch root radii. These results showed that Von Mises equivalent stress which was derived from triaxial stresses decreased with decrease in notch radius. The shift of location of peak values of maximum principal stress and hydrostatic stress towards the axis of the specimen, leading to formation of cracks, occurred at a lower nominal stress when the notch radius was increased.

Effect of Notch Root Radius on the Apparent Fracture Toughness in CNT and Carbon Fiber Reinforced, Epoxy-Matrix Hybrid Composite

Significantly improved fracture resistance (in terms of fracture toughness) can be imparted to monolithic materials by adopting composite design methodology based on fiber and nano particulate reinforcement technology. The present work describes the fracture behaviour of one such reinforced material; in this case, carbon fiber (Cf)- and carbon nanotube (CNT)- reinforced epoxy composite. The Cf and CNT reinforced, epoxy-matrix hybrid composite in longitudinal and transverse orientations with varied finite notch root radii (in the range of 120–750 μm) are subjected to mode-I (tensile) fracture. The fracture toughness/resistance (KQ) of the material is then evaluated and analyzed by investigating the influence of varying notch root radii in longitudinal and transverse orientations. Such an analysis has revealed that the present unidirectional epoxy hybrid composite exhibits a critical notch root radius of 270 μm in longitudinal and 390 μm in transverse orientation.

A combined experimental–numerical investigation of fracture of polycrystalline cubic boron nitride

Numerical modelling of a series of experimental Single Edge V-Notched Beam tests was carried out for a number of grades of polycrystalline cubic boron nitride using the finite volume method (FV) and cohesive zone model approach. The effect of notch root radius observed experimentally was reproduced numerically via a unique CZM for each material examined. It was also found that the shape of the cohesive zone model can be significant, especially when the material has a relatively high fracture energy. It was also demonstrated that the experimentally observed drop in fracture toughness with increase in test rate was not explainable in terms of the system dynamics. It was found that in order to predict the experimental fracture loads for a range of loading rates, it was necessary to modify the CZM in such a way as to preserve the micro-structural length scale information of the material embedded within the CZM.

Effect of notch root radius on fracture toughness of polycrystalline cubic boron nitride

The fracture toughness of five grades of polycrystalline cubic boron nitride (PCBN) has been determined using Single Edge V-Notched Beam specimens. Both coarse and fine grade materials were considered, containing CBN grain sizes of between 1 μm and 22 μm. The influence of notch root radius on the measured fracture toughness was examined. The notch root radius was found to have a major effect for materials with smaller CBN grain sizes while only a small effect was noted for the material with large CBN grain sizes. A simple analytical model was developed to explain the effect of the notch root radius on the fracture toughness and was found to agree well with experiment for all the materials tested. It was shown that the effect of notch root radius is directly linked to the size of the CBN grain. It is proposed that this effect results from the interaction between the microstructure and the stress field around the notch tip.

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It has been recognized that the threshold stress intensity factor range ΔK_<th> of a short crack is lower than that of a long crack. This behavior is unsafe in mechanical design if only ΔK_<th> of long crack is considered. Therefore many researchers have studied short crack behavior using plane fatigue test specimen. These studies provided quantitative understanding of the short crack behavior in relation to crack closure. However, for a short crack at notch root, the behavior has not been clarified yet. In this study, crack propagation tests using various kinds of notched specimens with a short pre-crack were done to consider the effect of notch root radius and stress ratios on the crack propagation behavior of the short crack at notch root. The crack closure was different depending on the stress ratio as well as notch root radius. This resulted difference in the ΔK_<th> of the short crack. When high stress ratio was applied, since there was no crack closure the ΔK_<th> was relatively low regardless of notch root radius. The effect of notch root radius on the ΔK_<th> of the short crack at notch root was significant when the stress ratio was low. The change in ΔK_<th> with the decrease in notch root radius could be understood by development of crack closure.

Notch Radius and Specimen Size Effects on Fracture Toughness of Low Alloy Steel

The present work is amid to investigate the effect of notch root radius ρ and specimen size (thickness B and ligament b) on the apparent fracture toughness KI,app. Series of fracture tests on non standard compact tension CT specimen of AISI 4340 low alloy steel with different values of notch root radius (ρ=0.08 mm-3 mm) and ligament size/crack length to the specimen width ratio (a/W=0.1-0.9) have been conducted to measure the apparent fracture toughness KI,app. The experimental results show that KI,app depends on ρ and specimen size (B and b). There is a critical notch root radius ρc under which the apparent fracture toughness becomes independent of the notch radius ρ. Two empirical models have been proposed to transfer the data among specimens of different notch radii and predict the experimental values of KI,app considering the effect of ρ value. Also, Two models have been developed to transfer the data among specimens with different sizes and predict KI,app considering the effect of specimen thickness B, specimen ligament band the combined effect of B and b values. The combined effec –based model is developed by modifying the E 1921 standard equation (that is usually used to predict the thickness effect only). The models predictions are in good agreement with the present work experimental results and results reported in the literature.

Application of FIB technique to introduction of a notch into a carbon fiber for direct measurement of fracture toughness

For the direct measurement of the fracture toughness of the carbon fiber, a new technique was proposed and examined its applicability. At first, machining condition of the notch was examined. The notch was introduced using focused ion beam (FIB). The ion beam can be electronically scanned to introduce a sharp notch on the carbon fiber. Notches with various notch width and length were introduced by changing beam and scanning conditions. Tensile tests on notched carbon fibers were carried out following the test method for carbon fiber monofilaments. Fractured specimens were successfully corrected without secondary damage using protection films. SEM observations revealed that a crack propagated from a notch-tip, and notch size was able to be determined successfully. Effect of notch root radius was also examined to investigate the validity of the fracture toughness obtained by this method.

Dynamic fracture toughness of a near alpha titanium alloy Timetal 834

Abstract The dynamic fracture toughness of Timetal 834 alloy under impact loading was evaluated using fatigue pre-cracked specimens and compared with the fracture toughness under static loading condition evaluated in an earlier study. It was found that the dynamic fracture toughness under impact loading was higher than the fracture toughness value under static loading conditions. This behaviour was attributed to the effect of strain rate on strain hardening exponent and yield strength. The effect of notch root radius on dynamic fracture toughness of this alloy was also studied. It was found that there exists a critical notch radius ( ρ 0 ) of ∼150 μm below which the dynamic fracture toughness was independent of notch root radius. Above ρ 0 , the dynamic fracture toughness increased linearly with square root of notch root radius.

Fracture of metallic glasses at notches: Effects of notch-root radius and the ratio of the elastic shear modulus to the bulk modulus on toughness

The Anand–Su theory for large elastic–plastic deformations of metallic glasses is modified to account for the strongly nonlinear and eventually softening dilatational volumetric elastic response of these materials. Using this theory, we have conducted finite-element simulations of fracture initiation at notch tips in a representative metallic glass under Mode-I, plane-strain, small-scale-yielding conditions. We show that our theory predicts three important experimentally observed phenomena: (a) fracture initiates ahead of the notch root, where the mean normal stress reaches a maximum value; (b) the fracture toughness increases linearly with the square-root of the notch-tip radius; and (c) the fracture toughness decreases as the ratio of the elastic shear modulus to the bulk modulus increases.

Effect of notch root radius on fracture toughness of Ti–18Al–8Nb alloy

The effect of notch root radius on the mode I fracture toughness of Ti–18Al–8Nb alloy in beta solution treated and water quenched condition was investigated. The apparent fracture toughness KIA was found to be independent of the notch root radius below a critical notch root radius ρ0 and subsequently increase linearly with the square root of notch root radius ρ1/2 beyond ρ0. The critical notch root radius in this alloy was found to be ∼50 μm. The results were explained on the basis of strain controlled fracture model.

An elastoplastic phase-field model for the evolution of hydride precipitation in zirconium. Part II: Specimen with flaws

An elastoplastic phase-field model, described in Part I, was applied to bulk materials containing flaws such as sharp cracks and blunt notches. An additional set of long range order parameters, namely, stress-free strains for flaws, was introduced. The nucleation and growth of hydrides near a void or a crack were simulated by the proposed elastoplastic phase-field model. The effects of notch root radius, hydrogen concentration in solid solution, yield stress of the matrix and the level of externally applied stress on hydride morphology around flaws were studied. It is demonstrated that parameters such as the distribution of the tensile stress component perpendicular to the hydride platelet normal may be closely monitored during hydride growth near a flaw with or without externally applied stresses. Combined with a fracture criterion and real experimental data, the model is capable of predicting the rate and morphology of hydride precipitation, and crack initiation near flaws.

Investigation of blunting line and evaluation of fracture toughness under mixed mode I/III loading in commercially pure titanium

The blunting line and fracture toughness in commercially pure titanium under mode I and mixed mode I/III loading was studied. A modified compact tension geometry was used for determining the blunting line as well as mixed mode I/III fracture toughness. The results showed that the constraint factor m in the blunting line equation under mode I loading was 1.84. Also, there was no effect of notch root radius on the slope of the blunting line. The blunting line slope under mixed mode I/III loading was found to be lower than that under mode I loading and agreed with empirical correlations. The fracture toughness under mode I loading was found to be higher for specimens with larger notch root radius. However, notch root independent fracture toughness could be obtained from blunt notch specimen tests using stretch zone width measurements. The fracture toughness was found to decrease with increasing mode III loading.

Effects of Notch Root Radius on Fracture Toughness of Gypsum and Polymer Gypsum Composite

Effects of Notch Root Radius on Fracture Toughness of Gypsum and Polymer Gypsum Composite

An investigation into the location of crack initiation sites in alumina, polycarbonate and mild steel

The effects of notch root radius on fracture toughness and crack initiation sites have been investigated in this paper using three different classes of materials. Data on alumina which represent ceramics, mild steel from the metals ffeily and polycarbonate representing plastics were obtained and analysed. The locations of crack initiation sites have been pinpointed by scanning electron microscopy. These identified sites more or less are located within the critical process zone or the theoretical plastic zone. The critical process zone size (Dc ) or the theoretical plastic zone size (RYF ) are independent of the notch root radius unlike the plain‐strain fracture toughness of notched specimens [KIC (ρ)]. The authors emphasize why the parameters Dc and RYF are useful for a quantitative evaluation of the reliability of structural materials.

Effects of notch root radius on crack initiation and growth toughnesses of a cross-ply Ti [sbnd]6Al [sbnd]4V/SiC composite

Effects of notch root radius on the crack initiation and growth toughnesses of a cross-ply [90°/0°] 2s Ti 6Al 4V/SiC f composite have been studied. The initiation toughness was found to be independent of the notch root radius, below a critical value of ϱ ≈ 50 μm. Beyond this value, the initiation toughness increases linearly with the notch root radius. In contrast, the crack growth toughness was found to be more or less independent of the initial notch root radius. The results are rationalized on the basis of the mechanism of fracture as well as the strain concentrations ahead of the notch.