Effect Of Notch Depth Research Articles

The Effect of Notch Depth on the Absorbed Energy of High-Toughness Steels in the DWTT

Abstract Because of the larger specimen dimensions and more significant ligament for crack growth, the drop-weight tear test (DWTT) has become more widely used than other impact tests. On the other hand, very little information is available from DWTT experiments on weld metal (WM). In the present study, in addition to the standard chevron notch (CN) DWTT specimen with a notch depth (ND) of 5.1 mm, API X65 specimens with 10- and 15-mm ND were tested on the WM and also the base metal (BM). Fracture energies versus the ND were plotted, based on which tests can be performed successfully with lower-capacity DWTT machines to predict the absorbed energy for each ND, by specimens with increased ND and reduced absorbed energy. The standard requires thickness reduction for specimens thicker than 19 mm. With the method proposed in the present study, high-grade specimens can be tested with their original thickness. In the DWTT, regardless of specimen materials (BM or WM), about 44 % of the absorbed energy is spent on crack initiation, and 56 % is spent on crack growth. In all specimens, the BM absorbed energy was more than that of the WM. Therefore, this study proposes that the API standard, which does not include DWTT on the WM, should require performing DWTT on WM specimens. Hence, the results of the current study can form the basis for further studies that can initiate the development of new standards on the WM.

Semi-empirical formulas on notch stress field and SIF of orthotropic V-shaped thin plate with initial crack under tensile-bending loads

For orthotropic materials, the solution of notch stress field and stress intensity factor (SIF) is not only related to crack opening angle, crack depth, notch length, geometric parameters, but also obviously influenced by material characteristics and constitutive relation. On the basis of isotropic notch stress field and SIF theoretical formula, a series of multi-parameter models of orthotropic materials were constructed and fitted. The effects of notch depth, crack length, the ratio of notch depth to plate width, opening angle and mechanical properties of composite materials on geometric correction coefficient YI are systematically analyzed. On this basis, a semi-empirical formula of YI is put forward by combining stress field analysis and multi-parameter fitting. The semi-empirical formula is further verified with finite element method, traditional formula and various composite materials. The numerical results show that the simple formula proposed in this paper has higher prediction accuracy. Finally, the proposed formula is extended to the solution of notch stress field and geometric correction coefficient for V-notch-cracked plate under bending load, tension-bending complex loads.

Effect of the notch depth on fracture behavior of TC4 titanium alloy sheets

To evaluate the low-stress brittle fracture of TC4 titanium alloy sheet structures, the effect of notch depth (d) on the fracture behavior of the 1.8 mm thick TC4 titanium alloy sheets was investigated combied with tensile tests and digital image correlation method. The results show that the ductile–brittle transition (DBT) occurs with increasing notch depths. Ductile fracture occurs for the notched samples with d = 0.5–1.5 mm, and a uniform plastic deformation stage is observed in the load–displacement (P-L) curves, and there are stretch zone and the stable crack propagation zone in the fracture surfaces. Brittle fracture occurs for the notched samples with d = 3.0–5.0 mm, and there is only the linear elastic stage in the P-L curves, and no stretch zone in the fracture surfaces. The samples at the middle notch depths (d = 2.0–2.5 mm) are in the transition from ductile to brittle fracture, and there exists the elastoplastic deformation stage in the P-L curves, and the stretch zone and stable crack propagation zone are both decreased. The analysis of notch fracture parameters shows that fracture of notched samples is controlled by the stress concentration and the stress field intensity of an imaginary crack with the same notch depth. The effect of crack gradually increases with increasing d, which results in increased brittle fracture tendency. Moreover, the fracture energy γf can characterize the DBT of notched TC4 titanium alloy sheets, and the γf is proportional tothe ratio of critical plastic zone size to d (rpc/d). Finally, the rpc/d is proposed to characterize the DBT of the notched TC4 titanium alloy sheets, and the criterion of the DBT for the notched TC4 titanium alloy sheets is obtained.

Effect of notch depth on creep rupture behaviour of 304HCu austenitic stainless steel

ABSTRACT Multiaxial creep behaviour of 304HCu austenitic stainless steel was studied at 973 K, 200 MPa by varying depth of U-notches from 1.67 to 3 mm, keeping the root radius of 1.25 mm on cylindrical specimen. Rupture life increased with notch depth and showed a peak value for 2.5 mm depth followed by rapid decrease, indicating the tendency towards notch weakening instead of strengthening. Creep rupture ductility decreased progressively with notch depth, resulting predominantly ductile dimple for shallow depth of notch and creep cavitation induced brittle fracture for deeper notch. Finite element analysis of stress and strain distributions across the notch along with SEM fractography and Electron Backscatter Diffraction (EBSD) studies was carried out to assess the effect of notch depth on creep rupture life. Creep strain concentration through Kernel Average Misorientation (KAM) map also supported the above views of creep strain accumulation which influence creep rupture life of notched specimens.

Effects of Notch Depth and Direction on Stability of Local Sharp-Notched Circular Tubes Subjected to Cyclic Bending

Cyclic bending of tubes leads to progressive ovalization of the tube cross-section, and persistent cycling causes catastrophic buckling of the tube. This paper presents the response and stability of SUS304 stainless steel tubes with local sharp-notched depths of 0.2, 0.4, 0.6, 0.8, and 1.0[Formula: see text]mm and notch directions of 0[Formula: see text], 30[Formula: see text], 60[Formula: see text], and 90[Formula: see text] under cyclic bending. The experimental results reveal that the moment–curvature relationship first exhibits cyclic hardening and then a steady loop after a few cycles. Because the notches are small and localized, notch depth and direction show minimal influence on the moment–curvature relationship. In contrast, the ovalization–curvature relationship demonstrates an increasing and ratcheting pattern along with the bending cycle, whereas notch depth and direction show a strong influence on this relationship. Finite-element analysis via ANSYS is used to simulate the moment–curvature and ovalization–curvature relationships, and an empirical model is proposed to simulate the relationship between the controlled curvature and number of cycles required to ignite buckling. The experimental and analytical data agree well with each other.

Effect of notch depth on fracture toughness of zirconia ceramics tested by SEVNB method

Ultra sharp V-notches with different depth to width ratio (a/w) were prefabricated on test bars by diamond wheel and femtosecond laser to measure the fracture toughness of 1.5Y/3Ca/6.5Al/1.5Si-PSZ, 2.5Y-TZP, 3Y-TZP and 8Y-FSZ ceramics by single-edge V-notched beam (SEVNB) method. For comparison, the fracture toughness of Al2O3 ceramics was also determined. Based on the analyses of SEM and XRD, the different microstructures and phase transformability led the plateau fracture toughness values of the investigated samples to vary from 1.6 to 9.4 MPa m1/2. The relationship between the a/w value and the plateau fracture toughness has been established.

Effect of notch depth on the mechanical behavior of Cu50Zr50 metallic glasses revealed by molecular dynamics simulations

Metallic glasses (MGs) with various geometrical notches have been one of the most attractive research topics because of their interesting mechanical behavior. In this work, molecular dynamics simulations were employed to examine the effect of internal notch depth on the mechanical behavior of Cu50Zr50 MGs. It is shown that both the strength and the deformation mode are sensitive to the notch depth, and in particular to the inter-void ligament distance. With increasing the notch depth, the notch intensification gets enhanced, while the deformation mode is seen to change from shear banding dominated to mixed mode and then to necking governed. Detailed stress distribution analysis reveals that the notch intensification and the deformation mode transition result from the stress state change induced by the presence of notches. The critical effective shear stress corresponding to local/atomic yielding in the MGs is identified to be around 1.9 GPa. In addition, the intrinsic size confinement effect also influences the deformation process. The findings are expected to provide useful guidance for materials design and investigation of yielding in MGs based on atomistic simulations.

Static and Fatigue Behavior Investigation of Artificial Notched Steel Reinforcement.

Pitting corrosion is one of the most common forms of localized corrosion. Corrosion pit results in a stress concentration and fatigue cracks usually initiate and propagate from these corrosion pits. Aging structures may fracture when the fatigue crack reaches a critical size. This paper experimentally simulates the effects of pitting morphologies on the static and fatigue behavior of steel bars. Four artificial notch shapes are considered: radial ellipse, axial ellipse, triangle and length-variable triangle. Each shape notch includes six sizes to simulate a variety of pitting corrosion morphologies. The stress-strain curves of steel bars with different notch shape and depth are obtained based on static tensile testing, and the stress concentration coefficients for various conditions are determined. It was determined that the triangular notch has the highest stress concentration coefficient, followed by length-variable triangle, radial ellipse and axial ellipse shaped notches. Subsequently, the effects of notch depth and notch aspect ratios on the fatigue life under three stress levels are investigated by fatigue testing, and the equations for stress range-fatigue life-notch depth are obtained. Several conclusions are drawn based on the proposed study. The established relationships provide an experimental reference for evaluating the fatigue life of concrete bridges.

Universal size effect of concrete specimens and effect of notch depth

The universal size effect law of concrete is a law that describes the dependence of nominal strength of specimens or structure on both its size and the crack (or notch) length, over the entire of interest, and exhibits the correct small and large size asymptotic properties as required. The main difficulty has been the transition of crack length from 0, in which case the size effect mode is Type 1, to deep cracks (or notches), in which case the size effect mode is Type 2 and fundamentally different from Type 1. The current study is based on recently obtained comprehensive fracture test data from three-point bending beams tested under identical conditions. In this test, the experimental program consisted of 80 three-point bend beams with 4 different depths 40, 93, 215 and 500mm, corresponding to a size range of 1:12.5. Five different relative notch lengths, a/D = 0, 0.02, 0.075, 0.15, 0.30 were cut into the beams. A total of 20 different geometries (family of beams) were tested. The present paper will use these data to analyze the effects of size, crack length. This paper presents a studying to improve the existing universal size effect law, named by Bazant, using the experimentally obtained beam strengths for various different specimen sizes and all notch depths. The updated universal size effect law is shown to fit the comprehensive data quite well.

Effect of notch depth on fracture toughness of Y-TZP and determination of its actual value

Femtosecond lasers were used to cut ultra-sharp V-notches (ρ<0.5µm) on the yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP). The actual fracture toughness of Y-TZP ceramics is 4.4MPa/m1/2 measured by SEVNB method. As comparison, the fracture toughness values of Y-TZP samples with different U-groove width were measured by SENB method. The fracture toughness value with U-groove width of 200µm is 13.1MPa/m1/2, which is about 3 times than the value with ultra-sharp V-notch. In addition, fracture toughness values of the Y-TZP ceramics with different notch depth were studied. To obtain the actual fracture toughness of Y-TZP ceramics with ultra-sharp V-notch, the ratio of notch depth to sample height (a/W) should be controlled in 0.25–0.6.

Effect of notch depth and radius on the critical fracture load of bainitic functionally graded steels under mixed mode I + II loading

Functionally graded steels are produced from austenitic stainless steel and carbon steel by controlling the chemical distribution of chromium, nickel and carbon atoms at the remelting stage through electroslag remelting process. In the present paper, the strain-energy density criterion is employed to assess the critical load of rounded V-notched components made of functionally graded bainitic steel. A crack arrester configuration under mixed mode loading is considered. The flow (yield/ultimate) strength and fracture toughness are assumed to vary exponentially along the notch depth direction while the Young’s modulus and the Poisson’s ratio are assumed to be constant. The control volume, which is a reminiscent of Neuber’s elementary structural volume, depends on the ultimate tensile strength σut and the fracture toughness K IC in the case of brittle or quasi-brittle materials subjected to static loadings. Since, σut and K IC are not constant along the notch depth, the control volume which can be obtained numerically as a function of the variation of these material properties through the specimen width. Different values of the notch root radius (from 0.2 to 2.0 mm) and notch depth (from 5 to 7 mm) are considered. The assessed critical fracture loads are in sound agreement with the experimental results.

Effect of Notch Depth on the Adhesively Bonded Steel Butt-Joint under Charpy Impact Test

The effect of the notch depth on the impact properties of the adhesively bonded steel butt joint under the Charpy impact test is studied using both the finite element method (FEM) and experimental method. The results obtained from numerical simulation showed that the value of the peak stressSeqvincreased first and then decreased evidently when the notch depth increased from 2 mm to 8 mm. Comparing the results with that from Izod impact test, it is found that the response time retarded about 0.02 ms and the peak value of the stressSeqvdecreased evidently under the Charpy impact test. The results from the experiments showed that the effect of notch depth on the impact energy absorbed by unit area of joint is as same as that from the Izod impact test.

Stochastic Fracture Simulations of Concrete Beams with Shallow Notches

We present a numerical study on virtual concrete beams with shallow midspan notches loaded in three-point bending. We document how spatial randomness of material parameters allows a crack to initiate outside the shallow notch. The interacting effects of notch depth and fluctuation rate of material parameters are shown. We use a discrete meso-level model to simulate material behavior. An approach that introduces material spatial randomness into the discrete mechanical model for concrete fracture through an autocorrelated random field is briefly presented.

Effect of Notch Depth on the Butt-Joint under Izod Impact Test with Material Properties and Mechanics Analysis

The effect of the notch depth on the impact toughness of the adhesively bonded steel butt joint under Izod impact test is studied using both the finite element method and experimental method. The results obtained from numerical simulation showed that the response time with the peak stress Seqv occurred becomes little longer when the notch depth increased from 2 mm to 8 mm. And a negative longitudinal stress occurred when there is an 8 mm depth notch which might be beneficial to subject impact load. The results from the experiments showed that the effect of notch depth is evidently on the Izod impact properties. The impact energy absorbed by unit area of joint is increased as the notch depth increase

Finite element analysis and experimental studies on fracture splitting processing by Nd: YAG laser ablation

Laser fracture splitting technology significantly improves the processing quality and efficiency of engine crankcase main bearing block. In order to research the splitting mechanism of ductile iron material fracture notch cauterized by Nd: YAG Laser, the FEAmodel of fracture splitting processing of engine crankcase main bearing block has been developed successfully. The splitting parameters of ductile iron material (QT500-7) main bearing block is analyzed. The numerical simulation results indicate that: among all the key parameters affecting the quality of fracture splitting, the effect of notch depth on fracture splitting load is more obvious than that of the notch opening angle and radius. The value of splitting load decreases rapidly with the increasing notch depth, while the splitting load increases with the increasing notch angle and radius. The optimum value of the notch depth, angle, and radius should be respectively at 0.5 mm, 60 o, and 0.2 mm. The results have been proved by experiments. The optimum parameters obtained from the ABAQUS simulation and experiments provide a numerical reference for significantly reducing the splitting load and optimizing the fracture splitting process, help to achieve the rapid development of engine block process and promote the green manufacture of automobile industry.

J-integral evaluation of austenitic–martensitic functionally graded steel in plates weakened by U-notches

In this paper, a numerical method for J -integral evaluation of plates weakened by U-notches for brittle or quasi-brittle functionally graded steel (FGS) has been proposed. The material contains austenite phase in addition to martensite layer produced by electroslag remelting (ESR). The Young’s modulus and the Poisson’s ratio have been assumed to be constant, while other mechanical properties vary exponentially along the specimen width. The effect of notch depth on the J -integral and the critical fracture load has been studied. A comparison of the J -integral between functionally graded and homogeneous steels was made, where the notch tip in the functionally graded steel is situated in a layer with same mechanical properties as the homogeneous steel.

The effect of notch depth on J-integral and critical fracture load in plates made of functionally graded aluminum–silicone carbide composite with U-notches under bending

The present paper deals with the effect of notch depth on J-integral and critical fracture load in a plate made of functionally graded aluminum–silicone carbide composite (Al–SiC) with U-notch under bending. The weight fraction of SiC particles varies from 0% to 20% through the specimen width. Using three criteria namely mean stress (MS), point stress (PS), and averaged strain-energy density (ASED), the critical fracture load has been predicted and its variation with respect to the notch depth has been studied. A comparison of the J-integral between functionally graded and homogeneous Al–SiC composite were made, where the notch tip in the functionally graded material is situated in a layer with same mechanical properties as the homogeneous composite. The results indicated that in the case where the notch scene is toward brittleness increment the critical J-integral in functionally graded material (FGM) is larger than that of in homogeneous material with the same mechanical properties at the notch tip. Therefore, FGM is more convenient than homogeneous material against fracture.

Influence of notch on the elastic–plastic response of clamped beams subjected to low velocity impact

In the present paper, experimental and numerical results on deformation and failure of clamped mild steel beams with and without notches subjected to low velocity impact are reported. Three sets of mild steel beams are used in experiments: (i) Beams without notch (ii) beams with 3.0 mm wide rectangular notch and (iii) beams with 0.35 mm wide rectangular notch. The response of the beam is studied in terms of maximum permanent deflection and strain history during contact period. High-speed digital camera was used to capture the impact phenomena of beam specimens. The effect of notch depth, notch width and impact location on the beam response is studied. The presence of notch in beams increases the permanent deflections, and increases the chances of initial tearing failure at the notch location. It is observed from experiments that, the extent of notch influence on dynamic response depends on notch depth and location. In the notched beam, the crack started at the notch corner and extended upwards resulting in failure. The numerical simulations of the experimental impact tests were carried out using the commercial finite element software (ANSYS) and good agreement between numerical and experimental permanent deflection values was observed. The instantaneous distributions of curvature profiles of beam computed numerically are presented for both notched and unnotched beams.

Method to calculate stress intensity factor of V-notch in bi-materials

Based on Zak's stress function, the eigen-equation of stress singularity of bi-materials with a V-notch was obtained. A new definition of stress intensity factor for a perpendicular inter-facial V-notch of bi-material was put forward. The effects of shear modulus and Poisson's ratio of the matrix material and attaching material on eigen-values were analyzed. A generalized expression for calculating K I of the perpendicular V-notch of bi-materials was obtained by means of stress extrapolation. Effects of notch depth, notch angle and Poisson's ratio of materials on the singular stress field near the tip of the V-notch were analyzed systematically with numerical simulations. As an example, a finite plate with double edge notches under uniaxial uniform tension was calculated by the method presented and the influence of the notch angle and Poisson's ratio on the stress singularity near the tip of notch was obtained.

Molecular Dynamics Analysis for Deformation and Fracture Behavior of Copper Thin Films

Molecular dynamics simulation is conducted to investigate the effect of notch depth on the deformation and fracture behavior of a single crystal copper which is expected to a conductive material of micro-devices. In the stress – strain relationship, a normal stress increases with increasing applied strain. Then, the normal stress decreases rapidly. When the stress decreases, the dislocation emits from a notch root and the stacking fault is formed on the {111} plane, which is slip plane of the fcc crystalline structure. The maximum stress decreases with notch depth. The non-damaging defect size is quite small. The shear stress in the slip direction at dislocation emission is constant irrespective of the notch depth. The criterion of the dislocation emission is given by the critical value of the resolved shear stress in the sliding direction.