Evaluation Of Dynamic Fracture Toughness Research Articles

Evaluation of dynamic fracture toughness of a bonded bi-material interface subject to high-strain-rate shearing using digital image correlation

The fracture toughness at the bi-material interface of layered test pieces is determined using digital image correlation (DIC) as part of dynamic shear tests. High-strain-rate shear tests are conducted on a three-layered bonded test piece comprising a central aluminum layer with PMMA resin layers. When the crack is sufficiently shorter than the bonding interface length, mode II fracture appears at the aluminum–PMMA interface; otherwise, mode I and mode II fractures appear. As the obtained stress intensity factor is consistent with the literature values, a reasonable interface fracture toughness can be evaluated using the DIC.

Evaluation of Dynamic Fracture Toughness in Ductile Steel by Means of a Split Hopkinson Pressure Bar 3PB Technique

The objective of this work is the tune of a methodology for the determination of the fracture toughness in ductile materials at high strain-rate by means of dynamic 3 Point Bending (3PB) tests. The specimens made in high strength steel have been pre-cracked in fatigue with a single edge notch. The dynamic loading conditions have been reached by means of a modified Split Hopkinson pressure Bar setup, in which two small diameter bars are used as transmitted bars instead of the standard single one. In order to obtain the maximum amount of information from each test, different measuring systems have been adopted, in addition to the strain measurements on the bars performed using semiconductor strain-gages. On the specimen surface, one or two crack-gages (one for each side for specimens) have been bonded for obtaining data about the crack propagation and the crack tip position vs. time curve. Moreover, a high speed camera has been used for obtaining the measurements of the Crack Opening Displacement (COD) and the opening velocity: digital images have been processed using tracking techniques following some points on the specimen notch and input bar tip. Starting from the experimental measurements in term of force, displacement and crack-gage data, a protocol for fracture toughness calculation at the initiation stage of the crack growth in dynamic condition has been defined and a hybrid experimental – numerical methodology has been used. One of the key variables for the determination of dynamic initiation fracture toughness is the crack time to initiation. Many efforts have been done in order to better determine a precise method to experimentally measure this entity: this datum has been obtained from the analysis of both the force and crack-gage vs. time signals and the COD measurement on high speed video. Good agreement has been found between the two methodologies. At this stage, a 3D model, which simulates the SE(B) specimens during the Hopkinson 3PB test, has been done in order to determine the toughness (J integral) as a function of time. Knowing the initiation time, the fracture toughness at crack initiation can directly be determined.

607 くさび衝撃試験による接着接合部の動的破壊じん性の同定

607 くさび衝撃試験による接着接合部の動的破壊じん性の同定

Evaluation of dynamic fracture toughness based reference temperature ( [formula omitted]) of modified 9Cr–1Mo steel in phosphorus embrittled and cold-worked condition

In the present study, the DBTT of a high phosphorus bearing modified 9Cr–1Mo steel in normalized and tempered (N&T) condition and also after 5% and 10% cold work, has been evaluated by extending the reference temperature ( T 0) based Master Curve approach to dynamic loading conditions. The reference temperature in dynamic loading condition ( T 0 dy ) thus determined is found to be significantly high for the N&T Mod.9Cr–1Mo steel as compared to plain 9Cr–1Mo steel. Cold-work effect was not found to be significant in T 0 dy evaluation of Mod.9Cr–1Mo steel. The high T 0 dy of the present Mod.9Cr–1Mo steel is attributed to a fracture initiation mechanism predominated by decohesion of prior austenitic grain boundaries at the fatigue pre-crack front. This is attributed to segregation of phosphorus along the prior austenitic grain boundaries causing embrittlement, supported by SEM and Secondary Ion Mass Spectrometry (SIMS) observations.

Evaluation of dynamic fracture toughness of cold worked 9Cr–1Mo steel

Dynamic J– R curves for cold worked 9Cr–1Mo steel have been estimated from instrumented impact test data at ambient temperature on pre-cracked Charpy specimens using three methods of analysis, namely those by Ray et al., Schindler, and Sreenivasan and Mannan. It is concluded that of these three, Schindler's method is the best suited for the purpose since it gives consistent variations with cold work of dynamic J– R curves and dynamic fracture toughness. Cold work results in substantial degradation in dynamic fracture toughness of 9Cr–1Mo steel.

Determination of Dynamic Fracture Toughness Using Strain Measurement

By contrast with static fracture toughness determination, the methodology for dynamic fracture toughness characterization is not yet standardized and appropriate approaches must be devised. The accurate determination of the dynamic stress intensity factors must take into account inertial effects. Most methods for dynamic fracture toughness measurement are experimentally complex. However, dynamic fracture toughness determination using strain measurement is extremely attractive in terms of experimental simplicity. In this study, dynamic fracture toughness tests using strain measurement are performed. High rate tension and charpy impact tests are carried out for titanium alloy, maraging steel and Al alloys. In the case of evaluating the dynamic fracture toughness using high rate tension and charpy impact tests, load or energy methods are used commonly. The consideration about inertial effects is essential, because load or energy methods are influenced by inertia. In contrast, if the position for optimum response of strain is provided, dynamic fracture toughness evaluation using strain near crack tip is more accurate. To obtain the position for optimum response of strain, a number of gages were attached at angles of 60°. Reliability for experimental results is evaluated by Weibull analysis. The method presented in this paper is easy to implement in a laboratory and it provides accurate results compared to results from load or energy methods influenced by inertia.

Toughness Assessment of a Variety of Materials: Similarities and Discrepancies

To determine the toughness of materials, Charpy V notch test has been widely utilized over the world. This method is easy to conduct, but obtained values are some what qualitative. Instrumented test has also a long history and gives us a loading history during impact. However this method is also still remaining in the range of a screening test. The author has successfully developed CAI (Computer Aided Instrumented Impact Testing) System for the evaluation of dynamic fracture toughness. In this CAI system, dynamic fracture toughness parameters such as Kd, Jd, Tmat and various absorbed energies can be obtained from the load-deflection curve of a single precracked specimen for both ductile and brittle materials

Progress in the Instrumented Charpy Impact Test

It has passed one century since French G. Charpy proposed the Charpy impact test in 1901. Instrumented impact test recording load history during fracture has been attempted since 1920's. It has become possible to obtain various information from this method. However, succeeding development of fracture mechanics has made it also as a qualitative screening test. To obtain quantitative fracture toughness parameters from this method, therefore, has been desired eagerly. The author developed successfully a computer aided dynamic fracture toughness evaluation system, called CAI system already in 1980's. This paper reviews development and progress in the Charpy test, especially focusing on problems of evaluation of dynamic fracture toughness by the instrumented impact test and on accuracy of measurement in the test.

Evaluation of Dynamic Fracture Toughness of Unidirectional CFRP Laminates.

In the present paper, dynamic interlaminar fracture toughness of carbon fiber reinforced plastics (CFRP) is estimated by split Hopkinson's pressure bar test using end notched flexure (ENF) specimens. The dynamic deformation of the specimen is approximated by classical beam theory with Laplace transform. The Mode II fracture toughness of unidirectional CFRP is computed by the analyzed deflection of the specimen employing the scheme of J-integral with the measured impulsive load and reactions at the supported points. Through some numerical calculations, the validity of the J-integral for the dynamic ENF test is confirmed. The experimental results for carbon/epoxy laminates show that dynamic interlaminar fracture toughness of the unidirectional specimen has dependency on a deflection rate.

Evaluation of dynamic fracture toughness of welding heat-affected zone of structural steel

Due to the influence of welding thermal cycle toughness of structural steel degenerates. Recently, the intercritically reheated coarse grained zone (IC CG HAZ) was found display the worst toughness in welded joint, which was associated with its fracture mechanism. In this work, two IC CG HAZs of a structural steel were prepared by welding thermal-cycle simulation techniques. For the two IC CG HAZs the dynamic fracture toughness and the fracture mechanism were studied, and the correlation between fracture toughness and fracture mechanism was also discussed. Under both static and rapidly loading, cracks in the IC CG HAZ were found to initiate at the intersection of αB0 packets with different orientations, followed by propagating in cleavage. In some places of crack propagation, adjacent cleavage facets are connected by shear, producing dimple zones. Though the brittle fracture initiation mechanism remains unchanged, the cleavage facet size and the proportion of the dimple zones between facets vary with loading speed. These changes are shown being associated with the effect of strain rate on fracture toughness. In this work, the fracture behavior of IC CG HAZ was also compared with that of base metal and prestrained steel.

Dynamic Fracture Toughness Evaluation of Structural Steels Based on the Local Approach

Dynamic Fracture Toughness Evaluation of Structural Steels Based on the Local Approach

Evaluation of Dynamic Fracture Toughness of Unidirectional CFRP Laminates.

In the present paper, dynamic inter-laminar fracture toughness are estimated for carbon fiber reinforced plastics (CFRP). In the experiments, split Hopkinson's bar test was applied to dynamic end notched flexure (ENF) test. The dynamic deformation of the specimen is approximated by beam theory with Laplace transform. The mode II fracture toughness of unidirectional CFRP was estimated by the analyzed deflection of the specimen employing the scheme of J-integral with the measured impulsive load and reactions at the supported points. Through some numerical calculations, validity of the J-integral for the dynamic ENF test is confirmed. In addition, as a experimental result, dynamic inter-laminar fracture toughness of CF/EPOXY unidirectional specimens are estimated and it indicates dependency on deflection rate.

A novel method for measuring plane stress dynamic fracture toughness

By using the self-designed Rotating Circular Disk direct tensile impact apparatus, a novel test method has been developed for studying the fracture properties of materials under impact loading. A double edge notch specimen under a plane stress state is used in fracture test conditions; the material exhibits elastic-plastic behavior at the crack tip. The SHPB technique is used to measure the dynamic loads and the displacements of the specimen; crack opening displacement is measured by applying the self-designed photoelectric transformation setup. For the evaluation of dynamic fracture toughness, the extended J-integral with the inertial effect is calculated by Rice's formula using the average load-displacement curve. The time to crack initiation is determined by the compliance changing rate method. The fracture toughness of LY12cz aluminum alloy at a loading rate K ID greater than 10 6 MPa √m/sec is obtained.

Application of the advanced instrumented impact testing facility for the irradiation damage assessment

A new test method suitable for the dynamic fracture toughness evaluation of irradiated specimens has been developed. The method is based on the application of the new pendulum type impact tester equipped with a self-adjusting IR-laser extensometer and fully computerized data acquisition and processing. The testing system contains several unique features, which make the impact testing more appropriate from the fracture mechanics point of view. These features include, for example, the inversion of the test geometry to reduce inertia and specimen oscillation effects, the utilization of larger than normal Charpy-size specimens, and the application of the IR-extensometer to evaluate ductile fracture initiation enabling the determination of the energy-based fracture toughness parameters. In this paper the testing procedure will be described and its application on the characterization of the unirradiated and irradiated IAEA phase III correlation monitor material for surveillance programmes will be presented.

Measurement of dynamic elastic-plastic fracture toughness parameters using various methods

Two improved impact testing facilities are used for the dynamic fracture toughness evaluation of precracked Charpy V- notch specimens. The methods of single specimen acoustic emission and crack mouth opening displacement testing are assumed to indicate the initiation points of stable crack growth. Thus, the dynamic ductile initiation J integral J Id can be derived. It was shown that the toughness J Id of the heat-resistant steel 10CrMo9.10 cannot be approximated by the J value at the maximum of the load deflection curve.

衝撃応答曲線法 (I.R.C.法) による球状黒鉛鋳鉄の動的破壊靭性の評価

衝撃応答曲線法 (I.R.C.法) による球状黒鉛鋳鉄の動的破壊靭性の評価

Evaluation of Dynamic Fracture Toughness of Heavy-Wall Nodular Iron Castings for Containers

Evaluation of Dynamic Fracture Toughness of Heavy-Wall Nodular Iron Castings for Containers

Evaluation of dynamic fracture toughness on heavy wall ductile cast iron for container

Dynamic fracture toughness of heavy wall ductile cast iron for container of spent nuclear fuel is evaluated mainly by the developed evaluation system, that is to say, CAI system (Computer Aided Instrumented Charpy Impact Testing System). The dynamic elastic-plastic fracture toughness value ( J d ) and the stable crack growth toughness value ( T mat ) are able to be estimated reasonably by this system. Furthermore, the β IC and impact response curve methods have been applied in transition temperature region and lower temperature one, respectively. As a result, it is clarified that these methods evaluate lower bound of dynamic fracture toughness in comparison with one obtained from conventional test method. By the way, elastic-plastic fracture toughness is generally affected by the specimen size. The valid condition for the specimen size determined under dynamic loading condition appears severer than that of ASTM E813. Constant J Id value is obtained by the specimen thickness of 20 mm (net specimen thickness 16 mm) in the side grooved Charpy type specimen.

Advanced instrumented impact testing facility for characterization of dynamic fracture behavior

The convenient and cheap instrumented Charpy impact test used for the evaluation of dynamic fracture toughness suffers many disadvantages and limitations. As an effort to enhance the reliability and accuracy of the instrumented impact testing, a new pendulum type of test apparatus has been designed and constructed at the Technical Research Centre of Finland (VTT). The new tester contains several novel features which help to avoid the drawbacks of the normal designs and which make the impact testing more reliable and appropriate from the fracture mechanics point of view. For that purpose the tester is equipped with a fully computerized data acquisition system and an optical COD measuring device. The latter has been developed and constructed through the co-operation between Materialprüfungsanstalt (MPA) and VTT. In the new testing facility the determination of fracture toughness is based on the application of the optical COD measuring device. In this paper testing equipment and procedures are described and discussed.

Dynamic fracture mechanics with electromagnetic force and its application to fracture toughness testing

This study is concerned with the application of the electromagnetic force to the determination of the dynamic fracture toughness of materials. Taken is an edge-cracked specimen which carries a transient electric current I and is simply supported in a uniform and steady magnetic field B. As a result of their interaction, the dynamic electromagnetic force occurs in the whole body of the specimen, which is then deformed to fracture in the opening mode of cracking. For the evaluation of dynamic fracture toughness, the extended J integral with the effects of the electromagnetic force and inertia is calculated using the dynamic finite-element method. To determine the dynamic crack-initiation point in the experiment, the electric potential method is used in the case of brittle fracture, and the electric potential and the J-R curve methods in the case of ductile fracture, respectively. Using these techniques, the dynamic fracture toughness values of nuclear pressure vessel steel A508 class 3 are evaluated over a wide temperature range.