Elastic-plastic Fracture Toughness Parameters Research Articles

Fracture characteristics of plain and steel fibre reinforced rubberized concrete

This study investigates the effect of recycled crumb rubber aggregates on the fracture characteristics of both plain concrete (PC) and steel fibre concrete (SFC) as a potential solution of the problem of discarded tires and due to the capacity of rubber aggregates to absorb high fracture energy. The variables considered in the experimental work are the concrete type (i.e., plain and steel fibre concrete) and the crumb rubber aggregate content as replacement ratios (i.e., 5%, 10%, 15%, 20%, and 25%) by volume of sand. The steel fibre used is a hooked-end fibre with an aspect ratio of 80 and a diameter of 0.75mm with a constant volume of 0.5%. The mechanical properties, fracture energy, stress intensity factor, critical strain energy release rate, elasticplastic fracture toughness parameter, and characteristic length of plain and steel fibre reinforced rubberized concrete are considered herein. Results show enhanced fracture characteristics induced by the crumb rubber inclusion in plain concrete. Further enhancement was observed by combination of steel fibre and crumb rubber aggregate in concrete. In addition to promote healthy environment using recycling waste tires.

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.

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.

Evaluation of quasistatic fracture toughness of a modified 9Cr-1Mo (P91) steel

For a modified 9Cr-1Mo (P91) grade steel in the normalised and tempered (NT) condition and also after accelerated thermal ageing (2900 h at 923 K), the elastic–plastic fracture toughness parameter J for 0.2 mm crack extension, J 0.2, has been determined at 653 and 803 K, and compared with J 0.2 of the NT material at 300 K. It is concluded that this thermal ageing does not significantly influence the toughness at 653 and 803 K. Also testing temperature has a marginal effect on J 0.2 at 300 and 653 K. At 803 K, however, creep effects become so prominent that a basic premise for J-controlled crack growth, namely rate-independent plasticity, is seriously violated, giving rise to anomalously high values of J 0.2.

Microstructural and Fractographic Characterization of a Thermally Embrittled Nuclear Grade Steel: Part I - Annealing

A nuclear reactor pressure vessel steel was submitted to different annealing heat treatments aimed at simulating neutron irradiation damage. The obtained microstructures were mechanically tested with subsequent metallographic and fractographic characterization. The relevant microstructural and fractographic aspects were employed in the interpretation of the mechanical behavior of the microstructures in both quasi-static (J-R curve) and dynamic (Charpy impact) loading regimes. A well defined relationship was determined between the elastic-plastic fracture toughness parameter J-integral and the Charpy impact energy for very most of the microstructures.

Microstructural and Fractographic Characterization of a Thermally Embrittled Nuclear Grade Steel: Part II - Quenching and Tempering

A nuclear reactor pressure vessel steel was submitted to different quenching and tempering heat treatments aimed at simulating neutron irradiation damage. The obtained microstructures were mechanically tested and submitted to metallographic and fractographic survey. The relevant microstructural and fractographic aspects were employed in the interpretation of the mechanical performance of the thermally embrittled microstructures. A well defined correlation was determined between the elastic-plastic fracture toughness parameter J-integral and the Charpy impact energy, which was achieved for some of the Q&T microstructures.

Nondestructive determination of tensile properties and fracture toughness of cold worked A36 steel

Tensile and fracture properties of ASTM grade A36 steel have been studied using nondestructive Stress–Strain Microprobe™ system (SSM), which is developed on the basis of automated ball indentation (ABI) technique. Tests have been carried out on as-received, and cold worked (4, 8 and 12%) materials at several temperatures in the range −150°C–+200°C at a constant strain rate. Tensile properties determined from ABI tests agreed well with the results from conventional tensile tests. The elastic–plastic fracture toughness parameter K JC was estimated from the ABI data. As expected, cold working resulted in increase in strength, decrease in fracture toughness and increase in ductile to brittle transition temperature. ABI is a reliable nondestructive technique for determining tensile and fracture properties of materials and has potential applications in the nuclear industry particularly to determine toughness degradation due to aging in service.

Cryogenic fracture toughness and temperature rise of thick section weldments in forged JJ1 type austenitic stainless steel plate

Summary JJ1 type austenitic stainless steel is emerging as the preferred structural material for nuclear fusion reactor superconducting magnet casings designed to operate at the temperature of liquid helium (4 K). To evaluate the cryogenic fracture toughness and temperature rise of tungsten inert gas (TIG) welds in 200 mm thick forged JJ1 type austenitic stainless steel plate for the next generation of nuclear fusion reactor superconducting magnets, clastic-plastic fracture toughness (J1C) tests were conducted with 1T compact tension specimens at 4 K. The tests were conducted to ASTM E813–87 standard specifications for determination of J1C by the unloading compliance technique to monitor crack growth. Au/0.07%Fe-chromel thermocouples were used to measure the temperature rise near the crack tip. The effects of the specimen sampling position and nitrogen content on J1C are examined. Specimens were examined by scanning electron microscopy (SEM) after fracture testing. The effect of the inclusion content on the elastic-plastic fracture toughness parameters (JQ, J1C) as determined by optical microscopy and energy dispersive X-ray spectrometry (EDX) is also discussed.

Influence of gamma-irradiation sterilization and temperature on the fracture toughness of ultra-high-molecular-weight polyethylene

Surface damage of the tibial plateau components of knee prostheses made from medical grade ultra-high-molecular-weight polyethylene (UHMW-PE) has been attributed to delamination wear caused by a fatigue fracture mechanism. It has been proposed that factors such as component design and method of sterilization contribute to such failure mechanisms. Understanding the fracture behaviour of UHMWPE is therefore critical in optimizing the in vivo life-span of total joint components. The elastic-plastic fracture toughness parameter J was consequently determined for a commercial UHMW-PE at ambient and body temperatures, before and after γ-irradiation sterilization in air at a minimum dose of 25kGy. Both ductile stability theory and experimental data suggest that cracks propagate in a stable manner, although stability is affected by the sterilization process. Sterilization with γ-irradiation results in a loss in fracture toughness JIc of 50% and a decrease in tearing modulus (Tm) of 30%. This dramatic reduction could result in a 50% decrease in the residual strength of the components, maximum permissible crack size under service loading and service life (assuming flaws such as fusion defects exist). The time required for a crack to grow from its original size to the maximum permissible size could be decreased by 30%, resulting in earlier failure. In terms of the design of joint replacement components the critical factor to envisage is the design stress level, which should be halved to account for the irradiation process. A scanning electron microscope study reveals that the material fails in layers parallel to the fracture surface.

Fracture mechanics behavior of a NiFe superalloy sheath for superconducting fusion magnets. Part 2. magnet life analysis model

From previous results of fatigue crack growth and fracture toughness measurements for a NiFe base superalloy, a primary candidate for the International Thermonuclear Experimental Reactor (ITER) central solenoid (CS) conduit, we derive an improved magnet life analysis model from the framework of Newman and Raju. For the superalloy conduit with an initial semielliptical surface crack in its thickness direction, the model predicts the evolution of crack aspect ratio for a wide range of initial crack geometries under pure tension and bending fatigue. The prediction of final fracture due to fatigue crack growth using the linear elastic fracture mechanics approach is shown to be underconservative. An alternative model based on Newman's elastic-plastic fracture toughness parameter is derived for the base metal with nearly semicircular cracks. The improved life analysis model taking into account the fatigue and fracture behavior is applied to the ITER CS magnet and the results are compared with these from earlier models. Accounting for the crack shape evolution leads to significantly longer life compared to assuming a constant aspect ratio. For the superalloy base metal we find that the expected fatigue life of Engineering Design Activity (EDA) design of the CS magnet is about eight times the design requirement. Even the Conceptual Design Activity (CDA) design with a free-standing CS meets the life requirement when analyzed by the improved model.

Recrystallization-etch approach to study the plastic energy absorbtion at crack initiation and extension of pressure-vessel steel A533B-1

To evaluate the elastic-plastic fracture toughness parameter of nuclear pressure-vessel steel A533B-1, a newly developed technique (the recrystallization-etch technique) for plastic strain measurement was applied to different sizes of compact tension specimens with a crack length/specimen width of 0.6–0.5 that were tested to generate resistance curves for stable crack extensions. By means of the recrystallization-etch technique, the plastic energy dissipation or work done within an intense strain region at the crack tip during crack initiation and extension was measured experimentally. Furthermore, the thickness effects on this crack tip energy dissipation rate were examined in comparison with other fracture-parameter J integrals. Thickness effects on critical energy dissipation and energy dissipation rate during crack extension were obtained and the energy dissipation rate dWp/da in the mid-section shows a constant value irrespective of specimen geometry and size, which can be used as a fracture parameter or crack resistance property.

Evaluation of dynamic crack initiation and growth toughness by computer aided charpy impact testing system

The validity of the newly developed CAI system ( C omputer A ided I nstrumented Charpy Impact Testing System ) for the evaluation of the dynamic elastic-fracture toughness parameters, i.e. the dynamic crack initiation toughness ( K Id , J Id ) and growth toughness ( J R curve, tearing modulus: T mat ) was investigated in various materials such as steel, aluminum alloy, titanium alloy, cast iron and so on. The dynamic elastic-plastic fracture toughness parameters ( J Id and T mat ) values in various materials could be easily obtained from the single load-deflection curve of the precracked specimen using the CAI system. The introduction of the side grooves was found to be effective to obtain the valid J Id value using the standard size Charpy specimen. In addition, the strain rate dependency of the specimen compliance ( C 3 ), and the effect of the specimen size on J d value and impact velocity on the geometry of the load-deflection curve were studied.

オーステナイトステンレス鋼（ＳＵＳ３１６ＬＮ）の極低温破壊靭性に及ぼす試験片寸法効果

This investigation has been carried out to determine the influence of specimen size and side groove depth on elastic-plastic fracture toughness parameters. Elastic-plastic fracture toughness JIC and tearing modulus Tmat were evaluated by the unloading compliance method which was described in ASTM E813-81 standards. Compact tension specimens were prepared from SUS316LN and the test were conducted at cryogenic temperature 4.2K. It is understood that JIC and Tmat are independent of specimen size when the specimen satisfies ASTM standard size requirements. JIC and Tmat decrease with the increase of side groove depth for 0-12.5% of original thickness, and they are independent of side groove depth when the depth is 12.5-37.5%. These results suggest that a 0.5CT small specimen with 25% side grooves can provide proper JIC and Tmat values independent of specimen size and side groove depth.

Effect of size on elastic-plastic fracture toughness for SUS316LN at cryogenic temperature.

This investigation has been carried out to determine the influence of specimen size and side groove on elastic-plastic fracture toughness parameters. Elastic-plastic fracture toughness JIC and tearing modulus Tmat were evaluated by the unloading compliance method which describes ASTM E813-81 standards. A compact tension specimen was prepared from SUS316LN and the test was conducted at cryogenic temperature 4.2K. It is understood that JIC and Tmat were independent of specimen size when the specimen satisfied ASTM standard size requirements. JIC and Tmat decrease with the increase of side groove for 0-12.5%, and they are independent of the side groove when the side groove is 12.5-37.5%. These results suggest that a 0.5 CT small specimen with a 25% side groove can provide a proper JIC and Tmat independent of specimen size and side groove.

On the accuracy of measurement of dynamic elastic-plastic fracture toughness parameters by the instrumented charpy test

It had been developed in a previous study [ Engng Fracture Mech. 24, 773–782 (1986)] that dynamic elastic-plastic fracture toughness parameters J d and T mat could be evaluated from the instrumented Charpy impact test. However, to popularize this method, strict measuring methods and judging standards on the validity of obtained values must be established. One old and important problem to be clarified is a relationship between an instrumented energy ( E t ) obtained from the area under a load-deflection curve and a dial reading energy ( E r ) calculated from the potential energy of the hammer. The purpose of this study is, therefore, to solve this problem first, and moreover to clarify the dynamic phenomena accompanying the measurement of the load-deflection curve. It is concluded that the energy condition necessary for the test without changing the load-deflection relationship is E 0 (applied energy) ≧ 3 E (total absorbed energy). This is the necessary condition to evaluate meaningful values of J d and the tearing modulus ( T mat ). Moreover, it is shown how the vibrational wave superimposes the load-deflection curve, analyzing the vibrational mode shape of the hammer.

Effect of Size on Elastic-Plastic Fracture Toughness Parameters

Abstract An investigation has been carried out to determine the influence of thickness and width on the elastic-plastic fracture toughness parameters: J value obtained from area under load/displacement curve JR, tearing modulus, and stress intensity factor corrected for plasticity KR. Compact tension specimens prepared from aircraft quality American Iran and Steel Institute (AISI) 4340 (Unified Numbering System [UNS] G43400) steel heat treated to a yield strength of 1000 MPa were used. All specimens satisfied the ASTM Test for JIc, a measure of Fracture Toughness (E 813) standard size requirements. This investigation demonstrates that when the specimens satisfy all ASTM standard size requirements, ductile fracture toughness JIc is independent of size. JIc values were found to vary a maximum of ±16% of mean value even in the present of some shear lips. Conversely, the tearing modulus was found to decrease as specimen thickness increased. A one to one relationship was found to exist between JR and JK, where JR is the J value calculated from the area under the load/displacement curve and JK is the J value computed from KR using the linear elastic fracture mechanics (LEFM) relationship.

Determination of Crack Tip Energy Dissipation and Elastic-Plastic Fracture Toughness Parameter with Ductile Crack Extension

Abstract In order to evaluate the elastic-plastic fracture toughness parameter of nuclear pressure vessel steel, SA533B-C1 1 (Unified Numbering System [UNS] K12539), near and beyond general yielding, a newly developed technique for large plastic strain measurement, that is, the recrystallziation-etch technique, was applied to compact tension and three-point bend specimens with a crack length/specimen width of 0.6 that were tested to draw resistance curves for stable crack extension. Based on the results reported previously that the equivalent plastic strain distribution around the blunted crack tip could be measured by means of the recrystallization-etch technique, the plastic energy dissipation or work done within an intense strain region at the crack tip accompanying ductile crack extension was measured experimentally. Furthermore, the size and loading condition effects on this crack tip energy dissipation rate were examined in comparison with other candidate parameters for crack extension criteria in the presence of large scale plasticity. The size of the intense strain region could be regarded as equal to the process zone size where the fracture is taking place. Formation and extension characteristics of this zone were discussed from a view point of elastic-plastic fracture toughness parameters including the relationships with existing fracture toughness parameters such as crack opening displacement and J integral.