Fracture Toughness Test Methods Research Articles

Comparative analysis of fracture toughness test methods for ceramics and crystals at room and lower temperatures

Flexural and indentation tests to estimate the fracture toughness of ceramics and crystals were compared. It was demonstrated that different methods can give reliable estimates in tests of homogeneous ceramics and quite ambiguous in tests of nonhomogeneous materials. Zirconia ceramics partially stabilized with magnesia were shown to exhibit a low-temperature inelastic-elastic transition in the temperature range of their fracture toughness variations.

3D finite element analyses of a new fracture toughness testing method for tubular structures

Abstract A new fracture toughness testing is analysed by a three-dimensional elastoplastic finite element method. This technique is used mainly on thin-walled tubing structures. It can generate relatively stable crack propagation even for brittle materials. From the load-displacement curve, it is possible to deduce the fracture toughness by using the proposed formulation. The influence of relevant parameters such as material properties, specimen geometry, friction effects etc. has been evaluated. The stability of results is also critically evaluated by numberical simulations.

Fracture toughness testing methods for paper materials

Fracture toughness testing methods for paper materials

Alternative Method of RTNDT Determination for Some Reactor Vessel Weld Metals Validated by Fracture Toughness Data

Abstract The fracture toughness curves used for nuclear power plant operation pressure-temperature limits and for pressurized thermal shock evaluations are dependent on the reference temperature for nil-ductility transition (RTNDT). The original method to determine the RTNDT was formulated more than 20 yr ago when Section III of the ASME Code was adopted. At that time, there were insufficient data to judge whether some of the weld metals used in reactor vessel fabrication were unsuitable for this procedure. Presently, this causes a compliance problem for some weld metals used in nuclear reactor vessels, whereas there is no technical problem in meeting required safety margins. The RTNDT is a parameter to index degrees of irradiation embrittlement to adjust the Code reference fracture toughness curves to represent the actual degraded fracture toughness at a given fluence of a reactor vessel beltline region. When there is a problem determining RTNDT value for unirradiated material where Charpy transition temperature is the dominating criterion, an alternative RTNDT based solely on a drop-weight test was investigated for some of the weld metals. Using a new test method for fracture toughness in the transition range (ASTM, 1993), a fracture toughness curve was directly generated from a set of compact tension test data and used for validating the nil-ductility temperature (TNDT) from drop-weight test data as the sole mean for determining initial RTNDT value.

THE BLUNTING LINE IN ELASTIC‐PLASTIC FRACTURE

AbstractThe blunting line evaluation procedure used in the ESIS standard fracture toughness test method “Procedure for Determining the Fracture Behaviour of Materials” is re‐evaluated to see if a simpler format can be developed. An equation based on the ultimate tensile strength was found to represent the blunting line in a simple manner. This equation is in error at most ±5% from the analytical representation and is as accurate as the graphical procedure used to determine the blunting line. It is recommended that this equation be used for fracture toughness test standards which use the ESIS blunting line. A comparison of the ESIS blunting line and the ASTM blunting line is made using someJ‐Rcurve data generated with an elastic unloading compliance test procedure. These data do not favor one line over the other. Microscopic evaluation of the blunting line reported in the literature using the stretch zone width measured on the fracture surface suggests that the ESIS blunting line better represents the physical blunting process.

Influence of morphology on the fracture toughness of isotactic polypropylene

AbstractAn adaptation of the fracture toughness test method, the J‐integral technique, is described within the general framework of polymer fracture behavior. It is shown that there is a strong interaction between different morphological parameters in the way they affect the fracture behavior of isotactic polypropylene (iPP). The fracture toughness decreases with increasing crystallinity at a fixed spherulite size. The fracture toughness also decreases slightly with increasing spherulite size at a constant crystallinity, but this may not be a pure spherulite size effect. The use of a nucleating agent results in a very fine spherulitic structure but facilitates crack growth and reduces the material toughness beyond the crack initiation stage. This suggests that the material behavior is dictated by the increase in crystallization temperature caused by the presence of the nucleating agent and not by the change in spherulite size. © 1995 John Wiley & Sons, Inc.

Prestandardization study on mode II interlaminar fracture toughness test for cfrp in japan

Prestandardization study on mode II interlaminar fracture toughness test for cfrp in japan

Assessment of mixed-mode fracture toughness testing methods for rock

Assessment of mixed-mode fracture toughness testing methods for rock

Crack‐Growth Resistance of in Situ‐Toughened Silicon Nitride

The fracture toughness of a commercial, hot‐pressed, in situ‐toughened silicon nitride with an elongated grain structure is determined by four different testing methods. The fracture toughness is found to be 5.76 ± 0.27, 8.48 ± 0.50, 10.16 ± 0.66, and 10.68 ± 0.39 Mpa.m1/2, respectively, by indentation crack size measurement, indentation strength, single‐edge‐precracked‐beam, and chevron‐notched‐beam methods. The discrepancy in fracture toughness between the testing methods is related to R‐curve behavior, as measured using the indentation strength technique. These results indicate that there is no unique fracture toughness value and that a fracture toughness testing method with appropriate qualifiers is needed for rising R‐curve materials. Therefore, care should be taken in interpreting and utilizing fracture toughness values evaluated from different testing methods if a material exhibits a rising R‐curve. Complete characterization of the R‐curve may be a prerequisite.

Comparison of fracture toughness measuring methods applied on silicon nitride ceramics

Different fracture toughness testing methods on unreinforced and with Si 3 N 4 whiskers reinforced silicon nitride ceramics were compared. The results revealed that in the reinforced ceramics the K IC rises with the increasing of the crack size, which indicates a rising R-curve behaviour in this system. Using IF testing method equations given by Niihara and by Shetty proved to have the nearest values to these achieved using SENB in both investigated systems

鉄鋼材料の破壊靭性 （ＩＩ） 破壊靭性試験方法

鉄鋼材料の破壊靭性 （ＩＩ） 破壊靭性試験方法

Comparison of fracture toughness testing methods applied to Si3N4 + Si3N4-whisker system

The different methods of fracture toughness measurement in the Si3N4 + Si3N4-whisker system are compared. The Si3N4 + beat-Si3N4 whisker system with 20 wt pct of whiskers is studied. The system was prepared by hot pressing at 1800 C and 32 MPa. The developed indentation crack profile for the system under consideration is found to be of the Palmquist type in the whole range of the indentation load from 49 to 294 N. Fracture toughness values measured by single-edge notch beam (SENB), indentation strength, and MIS are in the interval from 6.5 Mpa sq rt m to 7.5 MPa sq rt m if, in the MIS method, the crack profile at the moment of catastrophic failure is taken into account. Higher fraction toughness values with the rising crack size achieved in bending tests on the samples with 'traction-cracks' suggest a rising R-curve behavior of the Si3N4 + 20 pct Si3N4 whisker system. 24 refs.

QUANTIFYING POP‐IN SEVERITY IN FRACTURE TOUGHNESS TESTS

AbstractThis paper describes the rationale and details of a conservative pop‐in assessment procedure that has been included in some new ASTM and BSI fracture toughness test methods. The procedure may be used for either graphical or numerical assessments of pop‐in.

Novel rock fracture toughness testing method: Cracked-Chevron-Notched Brazilian Disc method : Chen Jun Fang Proc 6th International Congress International Association of Engineering Geology, Amsterdam, 6–10 August 1990V1, P389–392. Publ Rotterdam: A A Balkema, 1990

Novel rock fracture toughness testing method: Cracked-Chevron-Notched Brazilian Disc method : Chen Jun Fang Proc 6th International Congress International Association of Engineering Geology, Amsterdam, 6–10 August 1990V1, P389–392. Publ Rotterdam: A A Balkema, 1990

Effect of cooling configuration on thermal shock fracture toughness of SiC

Abstract Experiments were carried out to establish a test method for thermal shock fracture toughness and to generate the experimental data for silicon carbide. A 20mm wide, 50 mm long, and 6 mm thick specimen having an edge crack in the central section was heated up to a given temperature and quenched in such a way that the crack mouth side of the specimen was sunk to a depth of 1 mm from the water surface. The thermal shock fracture toughness of SiC was greater than the fracture toughness obtained using a three-point bending specimen at the corresponding temperature. This was well explained from the fact that the normal stress component parallel to the crack line is greater than the perpendicular stress component near the crack tip in the thermal shock specimen. Time histories of the stress intensity factors for various values of a/W and two cooling methods were analysed by using the finite element method and appropriate conditions were determined.

Stress intensity factor extraction using moiré interferometry based on a two-parameter displacement eigenfunction: Validity criteria and comparison with ASTM E-399 K IC plane strain test methods

Abstract Validity criteria are presented for use of moire interferometry as a means to obtain near tip crack data combined with the use of a truncated two parameter, displacement based, KIC eigenfunction extraction method. Comparison is made with standard ASTM plane strain fracture toughness test methods for a three point bend specimen of 15V-3Cr titanium. Agreement between the experimental and ASTM plane strain KIC is found even though surface data were used. Quantitative explanations of this agreement are postulated, based on extreme near tip data extraction, the theoretical three-dimensional free surface crack tip eigenvalue for a relatively low Poisson ratio material and a direct measurement of this eigenvalue based on measured displacement.

Fracture toughness of acrylic bone cements

Clinical experience has shown that fracture of PMMA-based bone cements is a significant factor in the failure of orthopaedic joint replacements. Earlier studies of the fracture toughness properties of bone cement have been limited to relatively large test specimens — ASTM standard test methods require the use of specimens with dimensions considerably larger that those associated with bone cement in clinical use. In this study, a miniature short-rod specimen was used to measure the fracture toughness (K IC) or two bone cements (Simplex-P and Zimmer LVC). The dimension of our mini specimens approaches the cross-section of bone cements as usedin vivo. The short-rod elastic-plastic fracture toughness test method introduced by Barker was utilized to ascertain the effect of specimen preparation and ageing in distilled water on fracture toughness. Our study indicated that slow hand-mixed specimens possess comparable fracture toughness to centrifuged specimens. After ageing in water, however, centrifuged and slow hand-mixed specimens are more fracture resistant than specimens prepared by mixing the cement quickly. An optimum void content for the bone cements studied was suggested by the experimental results; for Simplex-P bone cement it appeared to be less than 1.6% whereas it was between 1.6 and 3.6% for Zimmer LVC cement. Simplex-P bone cement also showed superior fracture toughness compared to Zimmer LVC cement after storage in water for 60 days at 37° C.

Regression Analysis of Single Specimen Fracture Toughness Data with Serially Correlated Errors

Abstract The statistical properties of errors associated with J-integral estimates and crack growth measurements obtained by single specimen fracture toughness test methods are examined. It is shown that the errors in the J estimates can be serially correlated. Slope and intercept estimates and their standard errors are derived for the fitted line on the basis of a regression model, suggested by Mandel, which makes allowance for the serial correlation of errors in J. A theoretical model is developed to compare the scatter apparent on a J/Δa plot with the true error inherent in the data.

Chevron-Notched Specimens for Fracture Toughness Measurements Independent of R-Curve Effects

Abstract A relatively new plane-strain fracture toughness test method based on chevron-notched test specimens has created a keen interest in comparing toughness measurements by the new method against measurements by the conventional method (ASTM E 399). Tests of various aluminum alloys by the two methods have shown a divergence in test results at the higher toughness levels. The rising R-curve effect in tough aluminums has been cited as one of the factors contributing to the observed discrepancy. This paper shows why the chevron-notched test results are independent of rising R-curve effects, whereas ASTM E 399 tests often are not. The E 399 test dependence on the rising R-curve constitutes a specimen size effect, and this dependence is partly responsible for the divergence between chevron-notched and E 399 tests of tougher aluminums. The chevron-notched method produces the toughness values which would be obtained from E 399 measurements if sufficiently large E 399 specimens could be tested.

Short-rod elastic-plastic fracture toughness test using miniature specimens

The standard ASTM-E399 plane-strain fracture toughness (K IC) test requires (1) the test specimen dimensions to be greater than a minimum size and, (2) fatigue precracking of the specimen. These criteria render many materials impractical to test. The short-rod elastic-plastic plane-strain fracture toughness test proposed by Barker offers a method of testing not requiring fatigue precracking and furthermore, it appears that test specimens smaller than that stipulated by ASTM can be used to obtain validK IC values. In this study, the use of a modified miniature short-rod fracture toughness test specimen was investigated. Our miniature short-rod specimen is approximately 7 mm long and 4 mm diameter. These mini specimens are well suited for the purpose of testing biomaterials. The value of the minimum stress intensity factor coefficient (Y m * ) for the mini short-rod specimens was determined experimentally using specimens machined from extruded acrylic rod stock. An elastic-plastic fracture toughness analysis using the mini specimens gave values ofK IC for extruded acrylic (nominally PMMA) equal to 0.67 ± 0.06 MPa m1/2. The problem of testing non-flat crack growth resistance curve materials (such as PMMA) using the short-rod fracture toughness test method is discussed. A modification to the test procedure involving the use of aY * value corresponding to a short crack length is suggested as a method of overcoming this difficulty.