Crack Tip Opening Displacement Research Articles

Mode Mixity in the Fracture Toughness Evaluation of Heat-Affected-Zone Material Using SEN(T) Experiment

Abstract Single-edge-notch-tension, SEN(T), specimens have been found to provide a good similitude for surface cracks in pipes, where a surface-cracked structure has lower constraint condition than single-edge notch bend, SEN(B) (bend-bars), and compact-tension, C(T) specimens. This lower constraint condition gives higher upper-shelf toughness values, and also a lower brittle-to-ductile transition temperature. Additionally, the SEN(T) specimen eliminates concern of material anisotropy since the crack growth direction in the SEN(T) specimen is the same as in a surface-cracked pipe. While the existing recommended and industrial practices for SEN(T) have been developed based on assumption of homogenous or monomaterial across the crack, their applicability for the evaluation of fracture toughness of the heat-affected zone (HAZ) were evaluated in this investigation. When conducting experiments on SEN(T) specimens with a prescribed notch/crack in the HAZ, the asymmetric deformation around the crack causes the occurrence of a combination of Mode-I (crack opening) and mode-II (crack in-plane shearing) behavior. The extent of this mode mixity is dependent on the relative difference between the material properties of the adjacent girth weld and pipe base metals, as well as the amount of crack growth in the experiment. This mode mixity affects the measurement of the crack-tip-opening-displacement (CTOD) and evaluation of fracture mechanics parameter, J. The CTOD-R curve depicts the change in toughness with crack growth, in a manner similar to the J–R curve methodology. Observations also show a mismatch in the length of the crack growth that is measured on the fracture surface, attributable to the material deformation differences across the two adjacent materials (weld and base metals). This paper discusses the experimental observations of Mode I and Mode II behavior seen in experiments conducted on SEN(T) specimens with a notch/crack in the HAZ and as the crack propagates through the weld/HAZ thickness. The paper addresses the issues related to and the changes needed to account for such behavior toward the development of recommended practices or standards for SEN(T) experiments of weld/HAZ. The effects of mode mixity in HAZ SEN(T) experiments is critical to the development of crack growth resistance, CTOD-R and J–R curves employed in engineering critical assessment (ECA) of pipelines.

Approximation of the mechanical characteristics of pipe base metal in the underwater offshore gas pipeline “Nord Stream-2”

The article describes methodological foundations for calculating the mechanical properties of the base metal of pipes: impact work, resistance to corrosion cracking under pressure, crack tip opening displacement at operating temperatures according to the known properties of table parameters “on the left” to unknown parameters “on the right”. The calculated values provide an assess of the system stability during the design and construction of extended offshore underwater pipelines, including a necessary reduction in the safety margin, taking into account hydraulic friction losses during gas pumping.

Fracture properties of the gold mine tailings-based geopolymer under mode I loading condition through semi-circular bend tests with digital image correlation

Sustainably reusing mine tailings and reducing the economic costs of storing them is an ongoing concern in the geomechanics field. This paper discusses the process of utilizing MTs in the manufacture of geopolymer through alkaline activation. Since geopolymer is subjected to various external and internal loading conditions that could result in failures and fractures, understanding the fracture behaviors of MTs-based geopolymer is critically important for its use and application. The fracture behaviors of geopolymer remain largely unexplored. The study presented in this paper addressed this knowledge gap by evaluating the mode I fracture tests that are commonly used in the rock mechanics field for adoption to test geopolymer by using three-point bending instrument and considering various influential parameters, such as notch depths. The geopolymer specimens in this study were cast into cylindrical molds by mixing different mine tailings with a 10 M NaOH solution at a water/tailings ratio of 22% and then cured with a slightly elevated temperature of 72 ± 2℃, for seven days. Thereafter, the cylindrical specimens were cut into semi-circular specimens and a series of semi-circular bending tests were performed. The mode I fracture toughness, KIC, of the geopolymer were estimated and the sensitivity of the notch depth was evaluated based on linear elastic fracture mechanics for the specimens with current sizes. Also, the strain behaviors of the semi-circular specimens were investigated through digital image correlation mapping. The mode I fracture behaviors were studied and the force-displacement behaviors of the semi-circular bending specimens with regard to the notch depths were compared and interpreted. Further, the strain properties of the semi-circular bending specimen were evaluated with respect to different load levels and the fracture process zone and crack tip opening displacement of the geopolymer then were measured by digital image correlation analyses.

Validity of small-scale yielding regime in notched-cracked geometries

This paper proposes a procedure based on crack tip opening displacement (CTOD) to define the boundary of the small-scale yielding (SSY) regime. Numerical modelling was applied to notched samples with different notch radii, under both plane stress and plane strain conditions, with and without crack flank contact. Results indicate that an increase in notch radius promotes the validity of SSY. The increase in crack length promotes a progressive decrease of SSY's validaty, particularly in notched specimens. Most of the situations studied fall outside the SSY regime, which reinforces the importance of verifying the applicability of LEFM to fatigue crack growth rate calculations.

Examining layer height effects on the flexural and fracture response of plain and fiber-reinforced 3D-printed beams

A significant amount of work has focused on the development of concrete mixtures for digital manufacturing (3D printing), and their rheological and mechanical properties. However, for extrusion-based layered manufacturing, it is also important to select the appropriate printing parameters that have the potential to impact the performance of 3D printed elements. Among the many such parameters, this paper places emphasis on layer height, which has a direct bearing on rheology requirements, print quality, overall printing time, and interlayer bonding. Specifically, this paper examines the effects of layer height (5, 10, and 15 mm layer heights corresponding to 25, 50, and 75% of the nozzle diameter, which is 20 mm) on the flexural strength and fracture properties of 3D printed beams. Flexural and fracture properties indicate that smaller layer heights are beneficial for unreinforced and fiber-reinforced 3D printed mortars, even though this results in greater number of interfaces and longer printing times. A small amount of steel fiber reinforcement is shown to be useful in eliminating the negative effects of weak interfaces on the measured bulk properties, with average flexural strengths higher by 30–40% and fracture toughness and crack tip opening displacement higher by almost 30% as compared to plain mixtures. Strain energy release rates, digital image correlation, and optical images/micrographs are used to explain crack propagation in layered 3D printed mortars under unnotched four-point, and notched three-point bending.

Investigation of Correlation Between Fracture Toughness and Charpy Impact Energy of Cryogenic Steel Welds.

The high manganese steel was developed to improve the fracture toughness and safety at cryogenic temperatures, the austenite structure was formed by increasing the manganese (Mn) content. The developed weld high manganese steel was alloyed with austenite stabilizing elements (e.g., C, Mn, and Ni) for cryogenic toughness and fluxes contained less than 10% of acidic slag formers such as rutile (TiO₂) and silica (SiO₂). This paper describes the work carried out to enhance the fracture toughness of Mn contents in an economical way by means of increase of manganese up to 23% instead of using nickel (Ni) which has unique element to improve fracture toughness especially at cryogenic steel. The new cryogenic steels should be carefully evaluated in terms of safety for application in real structures including LNG ships. In this study, the fracture toughness performance was evaluated for recently developed cryogenic steels (high-Mn steels), especially the crack tip opening displacement (CTOD) parameter was evaluated using the prediction formula proposed by conventional equation. The CTOD value was investigated the effect of microstructure and mechanical properties of Fe-C-Mn and Fe-C-Mn-Ni high manganese steel, it was revealed that the e-martesnsite phase formed in high manganese steel of 0.2C-20Mn and 0.4C-20Mn as a result of a low stability of austenite upon strain-induced phase transformation.

SAE 4340 Fracture Toughness Evaluation Following Wang’s Formulation for Spiral Notch Torsion Test Specimens

Abstract The fracture toughness parameter (fracture toughness in plane strain-state [KIC], fracture toughness near the onset of crack growth, or crack tip open displacement) is essential information for understanding fracture behavior in mechanical and structural components. To determine this property, several methods have been developed; these require specimens with sufficient thickness to ensure a plane-strain condition at the crack front, which depending on materials mechanical properties, may lead to the need of large amounts of material. To overcome this problem, the spiral notch torsion test (SNTT) was proposed by Wang in 2000, and over these years, methodologies for testing many different materials have been presented, as well as the elastic compliance equations for assessing crack size (essential for introducing the fatigue precrack), also presented in 2012. Although the SNTT presented advantages and potentialities, its application is still quite restricted, and information on its use is limited. Implementation of the SNTT is a challenge, mainly because of the inexistence of a specific standard, thus producing ambiguities when dealing with the application of the test, methodology, and limitations because the SNTT implementation is principally based on previously published theoretical and experimental studies. The study presented herein aims at organizing already existing information based on work conducted by Wang while presenting in detail a test chart and the necessary techniques for obtaining a fracture toughness parameter, in mode I loading and in the domain of a plane strain-state. Determining KIC using the SNTT was performed on a quenched and tempered AISI 4340 steel (45 HRC) in air at room temperature. The obtained results proved the great potential of SNTT methodology for KIC determination. The KIC values obtained by the SNTT methodology exhibited a maximum error of 3.5 % and were statistically equal to those provided by the conventional method compact tension (C(T)) that follows ASTM E399-20, Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness KIC of Metallic Materials. The fracture surfaces observed in SNTT and C(T) specimens showed similar fractographies and mechanisms.

Experimental and Numerical Investigation on Specimen Geometry Effect on the CTOD Value For VL-E36 Shipbuilding Steel

Abstract There are special cases in the marine industry, where additional material tests, such as the fracture toughness test, must be performed. Additional fracture toughness tests, such as CTOD (Crack Tip Opening Displacement), are typically performed on three-point bend specimens. The dimension that defines all the specimen dimensions is the thickness of the material to be tested. It is recommended by classification societies (e.g. DNVGL) to test specimens that are twice as high as the material thickness. The width determines the length and, therefore, the weight of the specimen which, for a 100 mm plate is over 140 kg. Current ASTM E1820, BS7448-1 and ISO 12135 testing standards also allow for proportions other than those recommended. This results in a much smaller test piece. Reducing the specimen size allows the testing machine to achieve lower forces than a specimen with a width to thickness ratio of two. This paper presents the effect of changing the specimen geometry on CTOD test results. Research was performed for specimens with a height to thickness ratio of one and two. Abaqus software was used for numerical calculations. The numerical results were, at selected points, verified experimentally.

Elastic-Plastic Analytical Solution for SEMI’s Horizontal Brace with a Circumferential Through Crack under Tension and Bending

The elastic-plastic behavior of semi-submersible’s horizontal brace with a circumferential through crack which lies at its boundary was studied. Both tension and bending were considered to investigate the closed-form analytical solution. The results indicate that the tensile plastic zone and crack tip opening displacement (CTOD) on the cracked section increase sharply after a smoothly increment when loads became larger. The cracked horizontal brace with a greater initial circumferential through crack has a larger tensile plastic zone and earlier compressive plastic zone appearance on the cracked section. Compared with the load of tension, the bending load has larger effect on the plastic zones of the cracked section and CTOD of the crack. Introduction Since the first semi-submersible platform (SEMI) named as “Ocean Driller” which was designed for drilling wells in the ocean, the SEMIs have gained popularity in the recent decades with ongoing development in oil and natural gas exploration in deepwater. Because of the high risk of environment pollution and casualties of operators which a destruction accident of SEMI might bring, making sure the structure is safe during its service life has become the most important task of SEMI designers and operators. Although the safety design standards for SEMI structures are quite strict, cracks inescapably are initiated during their service life. According to the destruction accidents happened before, Moan (2009) and Zaron et al. (2015) found that the cracks often occur at the horizontal braces which function as the supporting structures in SEMIs and bear complex loads. The presence of such cracks at critical locations can compromise the safety of the braces and then can cause serious disaster eventually. Because of the initial fracture of a horizontal brace, e.g., the accident of Alexander Kielland platform, the loads were transferred to the other braces and led them break because of the overload (see Colin et al. [2014]).

Application of Failure Assessment Diagram (FAD) for Steel Welded Connection Based on BS7910 and DNV-RP-108

The failure assessment diagram (FAD) method has been widely accepted to evaluate the extent to which cracks may affect structural safety. The usage of this FAD method has been validated and included in [1]-[3]. The structure under investigation, described in four fully welded T-joint (BCC5) specimens, where these welded joints are a source of stress concentration and defects from which fatigue cracks can grow. The four specimens were modeled under different displacement loading using a finite element analysis program Ansys and SolidWorks software. In this work, the application of a FAD (Lr, Kr) using maximum stress, cumulative stress ranges, and the last half-cycle stress range was investigated. The results are showing that all the points were lying outside the FAD curve except for the BCC5D specimen point was inside FAD when using maximum stress.
 Conclusions made that the cumulative stress gives Lr and Kr are extremely large and hence predict failure too early. With the Crack Tip Opening Displacement (CTOD) of the test specimen assumed to be about 1mm rather than 0.1mm it was found that, if a FAD is to be used to indicate failure, then both Lr and Kr should be based on the maximum stress. It appears that the FAD methodology does help to predict the final failure (which is the usual application in such cases). This represents more effectively the structural behavior and would be more easily used by designers.

Application of Failure Assessment Diagram (FAD) for Steel Welded Connection Based on BS7910 and DNV-RP-108

The failure assessment diagram (FAD) method has been widely accepted to evaluate the extent to which cracks may affect structural safety. The usage of this FAD method has been validated and included in [1]-[3]. The structure under investigation, described in four fully welded T-joint (BCC5) specimens, where these welded joints are a source of stress concentration and defects from which fatigue cracks can grow. The four specimens were modeled under different displacement loading using a finite element analysis program Ansys and SolidWorks software. In this work, the application of a FAD (Lr, Kr) using maximum stress, cumulative stress ranges, and the last half-cycle stress range was investigated. The results are showing that all the points were lying outside the FAD curve except for the BCC5D specimen point was inside FAD when using maximum stress.
 Conclusions made that the cumulative stress gives Lr and Kr are extremely large and hence predict failure too early. With the Crack Tip Opening Displacement (CTOD) of the test specimen assumed to be about 1mm rather than 0.1mm it was found that, if a FAD is to be used to indicate failure, then both Lr and Kr should be based on the maximum stress. It appears that the FAD methodology does help to predict the final failure (which is the usual application in such cases). This represents more effectively the structural behavior and would be more easily used by designers.

Flexural Tensile Strength of Concrete with Synthetic Fibers.

Fiber reinforcement is currently most often used in floors, railway sleepers, prefabricated structural elements such as slabs, beams and tanks, and in small architecture elements. Designing elements or structures made of fiber-reinforced concrete requires knowledge of its basic mechanical parameters. In the case of concretes with metallic fibers, the literature can find many tests and standard guidelines regarding compressive, flexural, tensile strength and fracture energy. The properties of concretes with non-metallic fibers are slightly less recognized, especially concretes with new types of polymer fibers. Additionally, the lack of standardized methods of testing concrete with polymer fibers make their application much more difficult. In the article, the possibility of using the EN 14651 standard to assess the flexural tensile strength of concrete with the addition of 2.0 and 3.0 kg/m3 of synthetic fibers with different geometry and form was presented. There was a 5.5–13.5% increase in the flexural tensile strength depending on the mixture type. Moreover, in the case of fiber-reinforced concretes, the ductility was enhanced and the samples were characterized by significant residual flexural tensile strengths. Additionally, from the workability tests it was concluded that after the incorporation of fibers, the consistency class decreased by one, two or three. Nevertheless, the compressive strengths of concrete with and without fibers were very similar to each other, and varied from 58.05 to 61.31 MPa. Moreover, it was concluded that results obtained from three-point bending tests significantly differed from empirical formulas for the calculation of the flexural tensile strength of fiber-reinforced concretes with dispersed steel fibers present in the literature. As a result, the new formula determined by the authors was proposed for concrete with polymer fibers with a nominal fiber content ≤1.0% and slenderness of up to 200. It must be mentioned that the formula gave a very good agreement with studies presented in different literature positions. In addition, an attempt was made to evaluate the strengths of tested mixes in accordance with the Model Code 2010. However, it occurred that the proposed fiber-reinforced concrete mixtures would not be able to replace traditional reinforcement in a form of steel bars. Furthermore, in uniaxial tensile tests, it was not possible to determine the σ–w graphs, and received results for maximum tensile strength did not show the clear influence of fibers incorporation on concrete. Then, the fracture energy enhancement (from about 16 to 22 times) and dependencies: crack mouth opening displacement–deflection; crack mouth opening displacement–crack tip opening displacement; and crack tip opening displacement–deflection were analyzed. Finally, the results from flexural tensile tests were compared with measurements of the surface displacement field obtained through the Digital Image Correlation technique. It was concluded that this technique can be successfully used to determine the crack mouth and crack tip opening displacements with very high accuracy.

New J-CTOD empirical correlations for p-SPT specimens

Three-dimensional Finite Element Analyses of pre-cracked small punch test (p-SPT) specimens are performed to evaluate plastic constraint factor (m). The m factor is useful to correlate the J-integral with the crack tip opening displacement (CTOD). The through-thickness square pre-cracked specimen is analyzed for this purpose. Parametric studies are carried out by varying the crack length, the material yield strength and the strain hardening coefficients. Based on the computed results, two new J-CTOD correlations are proposed. These are (a) a correlation as a function of the crack length (a/W) and the yield to tensile strength ratio (σYS/σUTS) and (b) another correlation as a function of the crack length (a/W), the yield to tensile strength ratio (σYS/σUTS) and the current applied loading expressed in terms of load-line-displacement/crack length (LLD/a). The second correlation is more versatile. However, it is applicable only for the present geometry. The predicting capabilities of the correlations are checked by comparing the calculated values with the computed results.

Microstructure and Mechanical Properties of Nb-API X70 Low Carbon Steel

The oil and gas production has grown steadily, and the care with its transportation grid needs to be maintained and expanded. The pipeline used in the transport of gas and oil by-product requires materials with high mechanical strength, toughness, and fatigue resistance. The chemical composition and distribution, amount, and morphology of the final microconstituents of the steel are of paramount importance once it will directly influence the mechanical properties. The fracture toughness is one of the most important mechanical properties for the suitability of the steel for pipeline usage, and is most of the literature with pipelines study does not present tests such as crack tip opening displacement (CTOD), with a steady and controlled crack growth behavior, to evaluate its fracture toughness. This study compares the fracture toughness of the API 5L X70 steel between two plates of steel with different Nb content, 0.06 and 0.09 Nb wt.% by CTOD tests. The mechanical response was correlated to the grain size and distribution. The CTOD parameter was used to assess the fracture toughness at 25 °C and − 60 °C. The microstructures and microconstituents of the two plates of steel were similar. The matrices were composed of ferrite, with bands of secondary products, including degenerated pearlite. Results showed a prone to the formation of a bimodal microstructure, coarse and fine grains, due to the addition of Nb. High-Nb steel presented better fracture toughness than normal-Nb steel at low-temperature.

Application of fracture energy for the assessment of frost degradation of high-strength concretes

Knowledge of fracture mechanics parameters can help for a more accurate assessment of frost degradation of high-strength concrete. High strength concretes, despite the tight structure, are characterized by increased brittleness. Cracks in the concrete structure are places of accumulation of significant stresses. Additional stresses resulting from cyclic freeze/thaw stimulate the material destruction processes. The basic strength parameters of concrete do not take into account structural defects of the material and do not give a complete description of susceptibility to damage caused by, e.g., frost degradation. This study aimed to determine the relationship between frost degradation of high-strength concretes and changes in the value of their fracture energy associated with the initiation of cracking after 150, 250, 350 and 450 freeze/thaw cycles. The research was carried out using 100 × 100 × 400 mm samples, with a pre-initiated 30 mm deep notch. The I load model under a three-point bending test was used, based on the procedure recommended by RILEM. Concrete with a compressive strength of 90 MPa with steel fibres and a mixture of steel and basalt fibers was tested. The obtained results allow for the evaluation of frost degradation using fracture energy GF and critical crack tip opening displacement CTODc.

Mechanism of Crack Initiation and Propagation of Re-Entrant Auxetic Honeycombs Under Thermal Shock

Abstract Thermal shock multiple cracking behaviors of re-entrant auxetic honeycombs with a negative Poisson’s ratio are investigated, and the crack initiation and propagation behavior are discussed. An effective macro continuum model is developed to detect the effects of cracking density and microstructures of auxetic honeycombs on the thermal stress and intensity. The microscale tensile stresses in the struts ahead of the crack as functions of the corresponding thermal stress intensity factor (SIF) at the macroscale are evaluated by employing a macro–micro model. Then, a lower-bound method is proposed to assess the critical thermal load of auxetic honeycombs by combining the macro-micro model and the macro continuum model. A significant increase in both transient thermal stress and intensity as the growing cell-wall angle is demonstrated. Results for the maximum thermal SIF as well as the maximum tensile stress in the middle of cracks are calculated as functions of crack density and length. With the identical SIF, the microscale tensile stresses ahead of the crack in honeycombs with smaller cell-wall angles are greater than that in mediums with larger angles due to the more significant crack tip opening displacement. Critical thermal load prediction reveals that the honeycombs with smaller cell-wall angles generally possess more excellent thermal shock resistance. Also, the varying failure modes of different auxetic honeycomb strips under specific thermal load are predicted. The corresponding mechanisms of crack initiation and propagation are revealed.

A closed-form fracture model to predict tensile strength and fracture toughness of alkali-activated slag and fly ash blended concrete made by sea sand and recycled coarse aggregate

A new type of concrete, namely alkali-activated slag and fly ash blended sea sand recycled aggregate concrete (AASRAC), is developed in this paper. By considering its future service under ocean environment, crack resistance of the new concrete should be emphasized and evaluated rationally. Similar to ordinary concrete, however, size effect would be inevitable in the determined tensile strength and fracture toughness based on traditional continuum mechanics. To address this issue, the intention of this paper is to propose an analytical fracture model to predict the tensile strength ft, fracture toughness KIC and energy GF by using tests on three-point-bending notched beams of AASRAC. The average aggregate size davg and two discrete numbers β and βw are introduced to represent the material heterogeneity and discontinuity, respectively. The critical effective crack propagation length and critical crack-tip opening displacement are quantified as the davg multiplied by β and βw, respectively, when the maximum applied load Fmax is reached. Closed-form solutions of the size-independent ft, KIC and GF are then obtained by using the experimentally measured Fmax based on boundary effect model. The means, and upper and lower bounds of the fracture parameters with 95% reliability are determined from the normal distribution analysis. Results show that the fracture parameters can be yielded with reasonable accuracy if β = 1.0 and βw = 1.0. The predicted ft, KIC and GF are higher as the slag-to-fly ash mass ratio increases in AASRAC. The predicted ft based on the proposed model is significantly larger than the traditional splitting tensile strength. The main failure mode of the tested AASRAC beam is that about 80% of the recycled coarse aggregates are fractured due to the improved interfacial micro-structures between the mortar and aggregates. The proposed model can give a rational design method for the new concrete.

Experimental study on fracture properties of concrete under cyclic loading using digital image correlation method

Three-point bending tests are performed on notched concrete beams under various cyclic loading regimes. Meanwhile, the digital image correlation (DIC) method is used to monitor the crack propagation. The fatigue fracture life decreases with the loading level increases for constant-amplitude cyclic loading. The residual crack mouth opening displacement (CMOD) accumulates and fracture stiffness degrades with the loading process. The size of fracture process zone (FPZ) can be determined based on the full displacement field monitored by DIC method. The length of FPZ increases linearly with the increasing of effective crack length before the crack tip opening displacement (CTOD) exceeds the critical value. When CTOD exceeds the critical value, a macroscopic crack formed in front of the initial crack tip. For cyclic envelope loading, the length of FPZ increases at beginning and then decreases with the increasing of effective crack length. For constant-amplitude loading, CTOD never reaches the critical value, and the macroscopic crack does not propagate forward. Finally, it is found that both the calculated effective crack lengths of concrete under constant-amplitude loading by two-parameter model (TPM) and DIC methods present three-stage feature, but the values calculated by TPM are smaller than those by DIC method.

Test Research on Toughness Evaluation of Long-span Bridge Welded Joint

Aiming at the inherent unavoidable defects of welded joints, a CTOD (Crack Tip Opening Displacement) test was carried out on the E43 steel weld specimen under the fatigue state. The research results provide experimental and calculation basis for the use of bridge steel. In this paper, a CTOD fatigue pre-crack test study was carried out on the welded joint of E43 steel.

Limitations of small-scale yielding for fatigue crack growth

The work described here has led to a simple criterion that defines the boundary of the small-scale yielding, SSY, regime to avoid invalid use of the LEFM parameter, ΔK, as the characterising parameter for fatigue crack growth rate. The approach proposed is based on the analysis of crack tip opening displacement, CTOD, and its separation into elastic and plastic components. SSY conditions are shown to dominate when the elastic component of CTOD is >75% of the total CTOD measured at a distance of 8 μm (the finite element mesh size) behind the crack tip, i.e., Δδe/Δδt > 75%. Large-scale yielding, LSY, conditions become dominant for relatively large values of plastic CTOD, Δδe/Δδt < 60%. An increase in crack length (and therefore of ΔK), a decrease in yield stress of the material and the existence of plane stress conditions all promote LSY. The results obtained from various loading and geometric conditions simulated in this work demonstrate that caution should be used in assuming that the use of ΔK is valid even for high strength alloys like Ti6Al4V. In this material, the boundary of the elastic regime was crossed and SSY conditions lost, for the longest crack lengths studied and in the case of overloads.