Elastic-plastic Fracture Toughness Research Articles

Effect of neutron irradiation on the mechanical properties of weld overlay cladding for reactor pressure vessel

This study investigates the effects of high fluence neutron irradiation on the mechanical properties of two types of cladding materials fabricated using the submerged-arc welding and electroslag welding methods. The tensile tests, Charpy impact tests, and fracture toughness tests were conducted before and after the neutron irradiation with a fluence of 1×1024n/m2 at 290°C. With neutron irradiation, we could observe an increase in the yield strength and ultimate strength, and a decrease in the total elongation. All cladding materials exhibited ductile-to-brittle transition behavior during the Charpy impact tests. A reduction in the Charpy upper-shelf energy and an increase in the ductile-to-brittle transition temperature was observed with neutron irradiation. There was no obvious decrease in the elastic–plastic fracture toughness (JIc) of the cladding materials upon irradiation with high neutron fluence. The tearing modulus was found to decrease with neutron irradiation; the submerged-arc-welded cladding materials exhibited low JIc values at high temperatures.

Effect of Nitrogen Addition and Test Temperatures on Elastic-Plastic Fracture Toughness of SS 316 LN

In the present investigation J-R curves have been determined for SS 316 LN with nitrogen contents of 0.08, 0.14 and 0.22 wt% at 298, 653 and 823K. Elastic-plastic fracture toughness (J0.2) corresponding to 0.2mm crack extension, was determined from the J-R curves. For all test temperatures, J0.2 values were the highest for the steel with 0.14 wt% nitrogen.

Essential Work of Fracture Testing Method Applied to Medium Density Polyethylene

Thermoplastic polyethylene has been increasingly used in important structural applications, e.g., in the production of pipelines for water and natural gas distribution systems, leading to the growing interest in the characterization of the material's fracture toughness. By virtue of its high ductility at room temperature, elastic-plastic fracture toughness concepts are most convenient for this purpose. In this work, a systematic study about the suitability of Essential Work of Fracture (EWF) test protocol to a medium density polyethylene (MDPE) resin designed for water pipelines extrusion is carried out. The influence of test piece preparation and geometry, along with different pre-cracking methods are investigated and their effects on the obtained results are assessed. It has been concluded that EWF methodology is well applicable for the characterization of MDPE resin and the test parameters allow, for instance, the evaluation of process induced anisotropy effects in the sample and the ranking of in-service mechanical performance of different resin grades. It has also been shown that pre-cracking method, test coupon thickness and processing technology impact the obtained results within 5% statistical significance level and that ‘rougher’ pre-cracking methods affect negatively the test results by increasing data dispersion.

Investigation of strength mis-match effect on elastic plastic fracture parameters in laser beam welded aluminium alloy joints using the finite element method

In this study, elastic plastic fracture toughness parameters of laser-welded 6013 aluminium alloy are investigated. For this purpose, compact tension specimens used in the experimental study are modelled using the finite element software. In the analyses, crack tip opening displacement ( δ5) and J-integral values are determined and crack tip opening displacement, δ5 and J-integral resistance curves (R-curves) are generated. Crack tip opening displacement, δ5 resistance curves are compared with those obtained from the experimental work, and J-resistance curves are compared with those obtained from formulation. Effect of weld strength undermatching on crack tip opening displacement, δ5 and J-resistance curves is discussed. δph values obtained by the plastic hinge method are compared with the crack tip opening displacement, δ5 values. Fracture toughness parameters obtained from the finite element analysis showed a good agreement with those obtained from the experimental work and formulation. It is observed that the resistance curves obtained using the crack tip opening displacement, δ5 and J-integral characterize the resistance of the material against crack growth in a similar manner, and strength undermatching decreases the fracture resistance. The relationship between δph and crack tip opening displacement, δ5 is nonlinear, and as crack tip opening displacement increases, crack tip opening displacement, δ5 becomes larger than δph.

Estimation of elastic–plastic fracture toughness by numerical simulation based on a stress-based criterion for ductile crack initiation

When estimating fracture strength of cracked components, it is important to know the fracture toughness of the material. However, in many cases, it is difficult to get the fracture toughness of in-service components. In this study, the elastic–plastic fracture toughness was obtained using numerical simulation. A stress based-criterion was adopted for determining onset of a ductile crack at the notch root, and the fracture toughness was derived as the J-integral value when a ductile crack was initiated. A detailed stress–strain curve was used in the simulation in order to obtain the precise stress near the notch root of the test specimens. Carbon steel specimens with a machined notch were subjected to fracture toughness tests. The radius of the machined notch root was changed and the fracture toughness was found to increase with the notch root radius. The simulation reasonably predicted the change in fracture toughness due to notch root radius, and the fracture toughness of the fatigue notched (sharp notch) specimen was determined by extrapolating the notch root radius dependency. The stress-based criterion obtained using notched bar specimens was shown to be valid for predicting ductile crack initiation at the notch root. It was concluded that, if the stress-based criterion could be identified, the fracture toughness could be obtained by the simulation.

An Experimental-Numerical Hybrid Method to Determine Dynamic Elastic-Plastic Fracture Toughness

The dynamic fracture behavior of 7075-T6 aluminum alloy was studied by finite element method to simulate a cracked three-point bending specimen loaded by stress wave loading. In order to determine the elastic-plastic dynamic fracture toughness using quasi-static fracture mechanics theory, the nominal load measured by Hopkinson pressure bar loaded fracture testing system was input into a finite element program to calculate the loading point displacement, and then this displacement was employed to obtain the load-displacement field in the vicinity of the crack tip without the inertia effect, the variation of J-integral as a function of time was established using the load-displacement parameters determined by finite element analysis. The critical J-integral corresponding to crack initiation time detected by a small strain gauge mounted on the three-point bending fracture specimen is determined as an elastic-plastic dynamic fracture toughness (JId). The comparison between the equivalent dynamic fracture toughness(KId) given by the aforementioned procedures and the value measured in previous studies was made to verify the validation of the proposed procedure.

Structural health monitoring of wind towers: residual fatigue life estimation

In a recent paper (Benedetti et al 2011 Smart Mater. Struct. 20 055009), the authors investigated the possibility of detecting cracks in critical sites of onshore wind towers using a radial arrangement of strain sensors around the tower periphery in the vicinity of the base welded joint. Specifically, the strain difference between adjacent strain sensors is used as a damage indicator. The number of sensors to be installed is determined by the minimum crack size to be detected, which in turn depends on the expected extreme wind conditions and programmed inspection/repair schedule. In this companion paper, we address these issues by investigating possible strategies for residual fatigue life assessment and management of onshore wind towers once the crack has been detected. For this purpose, fracture mechanics tests are carried out using welded samples to quantify the resistance to fatigue crack growth as well as the elastic–plastic fracture toughness of the welded joint at the tower base. These material strength characteristics are used to estimate (i) the critical crack size for structural integrity on the basis of fracture toughness tests, elastoplastic finite element analyses and loading spectra under extreme wind conditions, (ii) the residual life before structural collapse, applying a frequency-domain method to typical in-service wind actions and wind directionality.

Crack growth resistance of MAG butt-welded joints of S355JR construction steel

Fatigue crack growth resistance and elastic–plastic fracture toughness were measured on MAG (Metal Active Gas) butt-welded joints made of S355JR construction steel. For this purpose, C(T) specimens were extracted from virgin and welded 15mm thick rolled plates. Tests were conducted on the base material (BM), the heat affected zone (HAZ) and weld metal (WM). The analyses showed that compressive residual stresses due to welding increased the fatigue crack growth resistance of WM and HAZ owing to crack closure effects. The WM displayed the lowest elastic–plastic fracture toughness with respect to HAZ and BM. The highest value was exhibited by the HAZ because stable tearing crack extension is forced along an unfavourable crack path. Therefore, particular care must be taken in evaluating the crack path in welded joints in order to correctly estimate their resistance to crack advance.

Effect of Displacement Velocity on Elastic Plastic Fracture Toughness of SM490B Carbon Steel Plate in 0.7 MPa Hydrogen Gas

Effect of Displacement Velocity on Elastic Plastic Fracture Toughness of SM490B Carbon Steel Plate in 0.7 MPa Hydrogen Gas

Numerical evaluation of geometric independent stretch zone width value for assessing valid JSZW

To obtain geometry independent SZWc based evaluation of initiation fracture toughness (JSZW) value, there is a need to know the variation of SZWc with geometry. The present work attempts to predict this variation using the newly developed energy based numerical evaluation method of SZW prediction. The minimum thickness fracture specimen criteria available in the literature are also evaluated for determining the geometry independent JSZW value. To measure valid elastic–plastic fracture toughness value, the present study also showed the possibility of further improving the minimum thickness criterion of fracture specimen.

Determination of Elastic Plastic Fracture Toughness Parameters for a Compact Tension Specimen Using the Finite Element Method

Abstract In this study, elastic-plastic fracture toughness of an aluminum alloy is investigated. J-integral was calculated using the finite element software and formulation. Crack tip opening displacement (CTOD) is determined by using the plastic hinge model (δph) and direct measurement (δ5). J-Δ a and CTOD-Δ a resistance curves are constructed and compared with those obtained from formulation and those generated from test data, respectively. Good agreement has been obtained between the test results, the formulation and the results of the finite element analysis. The relationship between δph and δ5 is nonlinear and as CTOD increases δ5 becomes larger than δph. The relationship between J-integral and CTOD is found to be linear for both δph and δ5. It has been seen that the proportionality constant dn considerably depends on the method of calculation of CTOD.

Scatter band prediction for fracture toughness of specimens with prior load

This study investigates the warm pre-stress effects under Load–Unload–Cool–Fracture transient with deep-cracked single edge bend specimens of a high strength steel. In the experiment, it has been found that warm pre-stressing increases the apparent overall elastic–plastic fracture toughness KJc_total compared to those of as-received specimens. A simple prediction procedure for fracture toughness of specimens with warm pre-stressing is proposed based on critical plastic zone criterion using fracture parameter superposition rule. It is shown that the increase and the narrower scatter band of fracture toughness of specimens with prior load can be well evaluated within the framework of the Master Curve methodology.

SM490鋼の弾塑性破壊じん性に及ぼす塑性ひずみの影響（応力破壊基準による検討）

SM490鋼の弾塑性破壊じん性に及ぼす塑性ひずみの影響（応力破壊基準による検討）

Influence of microstructural inhomogeneities on the fracture toughness of modified 9Cr–1Mo steel at 298–823 K

Quasistatic fracture behaviour of two heats of modified 9Cr–1Mo steel for steam generator applications have been assessed at 298, 653 and 823 K. J– R curves were established and the elastic–plastic fracture toughness values at 0.2 mm crack extension ( J 0.2) were determined. The fracture mechanisms were entirely different for the two steels at 298 K, with brittle fracture controlled by cleavage crack initiation in one and ductile fracture in the other by void nucleation and growth. At 653 and 823 K, fracture in both materials was by ductile crack growth. The difference in behaviour between the two steels at 298 K was attributed to the differences in microstructure, distribution and density of inclusions as well as phosphorous contents.

Influence of ageing on the quasistatic fracture toughness of an SS 316(N) weld at ambient and elevated temperatures

The leak before break analysis of SS 316L(N) components of the prototype fast breeder reactor requires the elastic plastic fracture toughness parameter J for 0.2 mm crack extension, J 0.2, especially for the welds, at the operating temperatures. The J– R curves for the welds produced using the consumable developed by Indira Gandhi Centre for Atomic Research, were determined in the as-welded condition as well as after thermal ageing (923 K/4200 h) conditions at 298 K and 643 K, using unloading compliance method for 298 K and normalization method for 643 K. The aged material exhibited pop-in crack extensions of magnitudes that, according to ASTM E1820 standard, could be ignored for multi-specimen data analysis for determining J 0.2. Therefore, for this condition, J nom– Δ a curves were established using the multiple specimen method and also single specimen normalization method; for the latter, a modification earlier developed by the authors for accounting for small pop-in crack extensions was used. The value of J 0.2 from both methods showed excellent reproducibility. Ageing is seen to reduce the toughness of this material considerably at both the testing temperatures.

Cryogenic fracture behavior of metastable austenitic stainless steel in a high magnetic field

We study the effect of magnetic field on the fracture behavior of the metastable austenitic stainless steels at cryogenic temperatures. Elastic-plastic fracture toughness tests were performed on compact tension specimens in liquid helium at 4 K with and without a magnetic field, and the effect of magnetic field on the cryogenic fracture toughness was discussed. Quantitative phase analysis was also done by magnetic method, and the fracture surfaces were examined by scanning electron microscopy to correlate with the fracture properties.

Effect of Plastic Strain on Elastic-Plastic Fracture Toughness of SM490 Carbon Steel

Although the plastic strain induced in materials increases the mechanical strength, it may reduce the fracture toughness. The change in the fracture toughness is brought about by four factors; reduction in critical plastic strain due to pre-strain, localization of deformation, increase of material strength by work hardening, and change in material resistance for fracture. In this study, correlation between change in fracture toughness by pre-strain and the four factors was investigated. Firstly, the change in the tensile properties and fracture toughness were examined for pre-strained SM490 carbon steel. The specimens with blunt notch of 0.2 mm and 0.4 mm radius were used in addition to those with conventional fatigue pre-cracking. The degree of applied plastic strain was 5%, 10% and 20%. The fracture toughness was largest when the induced plastic strain was 5%, although it decreased in the cases for the plastic strain of 10% and 20%. Secondly, the stress and strain field near notch tip was evaluated by simulating the experiment using elastic-plastic finite element analyses. It was concluded that the change in fracture toughness was mainly brought about by the change in material resistance caused by the plastic strain. Under the plastic strain of 10% and 20%, the critical plastic strain for crack initiation decreased due to change in material resistance in addition to apparent reduction by pre-straining. The localized deformation and work hardening had minor effect on the change in fracture toughness.

균열선단 변위측정위치에 따른 STS 316L의 구속효과 A2거동

Abstract ： The magnitude of constraint effect A 2 values on the non-linear elastic plastic fracture toughness was experimentally estimated by using displa cement at various measuring positions near crack tip. Constraint effect A 2 value was dependent on specimen configuration and on the measured displacement near crack front. The crack tip opening displacement in the vicinity of the crack tip front should be estimated within plastic region when appropriately constraint effect was calculated. It was found that the magnitude of constrain effect |A 2 | is below 8.0 at the crack tip. But an appropriate location to measure the effective constraint effect s A 2 at the critical value of J that crack initiation is characterizable by is r = 2mm and θ = 90° away from original crack tip, and the constraint effect |A 2 | estimated is 5.3. Key words ：Constraint effects A 2 (구속효과 A 2 ), Near crack front(균열선단), Fracture toughness(파괴인성), Crack tip opening displacement(균열선단 개구변위), Crack propagation(균열진전)

Fracture-Toughness Analysis in Transition-Temperature Region of Three American Petroleum Institute X70 and X80 Pipeline Steels

The fracture toughness in the transition-temperature region of three American Petroleum Institute (API) X70 and X80 pipeline steels was analyzed in accordance with the American Society for Testing and Materials (ASTM) E1921-05 standard test method. The elastic-plastic cleavage fracture toughness (K Jc ) was determined by three-point bend tests, using precracked Charpy V-notch (PCVN) specimens; the measured K Jc values were then interpreted by the three-parameter Weibull distribution. The fracture-toughness test results indicated that the master curve and the 98 pct confidence curves explained the variation in the measured fracture toughness well. The reference temperatures obtained from the fracture-toughness test and index temperatures obtained from the Charpy impact test were lowest in the X70 steel rolled in the two-phase region, because this steel had smaller effective grains and the lowest volume fraction of hard phases. In this steel, few hard phases led to a higher resistance to cleavage crack initiation, and the smaller effective grain size led to a higher possibility of crack arrest, thereby resulting in the best overall fracture properties. Measured reference temperatures were then comparatively analyzed with the index temperatures obtained from the Charpy impact test, and the effects of microstructures on these temperatures were discussed.

OS0213 強磁場下におけるオーステナイト系ステンレス鋼の極低温弾塑性破壊特性評価(先端材料システムの力学とメゾスケールモデリング(2))

This paper studies the effect of magnetic field on the fracture behavior of the metastable austenitic stainless steels at cryogenic temperatures. Elastic-plastic fracture toughness tests were performed on compact tension (CT) specimens in liquid helium at 4 K with and without a magnetic field, and the effect of magnetic field on the cryogenic fracture toughness was discussed. Quantitative phase analysis was also done by magnetic method, and the fracture surfaces were examined by scanning electron microscopy (SEM) to correlate with the fracture properties.