Instrumented Charpy Test Research Articles

Evaluation of Leak-Before-Break (LBB) Behavior For Axially Notched X65 and X80 Line Pipes

Leak-before-break (LBB) behavior was evaluated for two series of API 5L X65 line pipes and three series of X80 line pipes with various levels of Charpy V-notch (CVN) absorbed energy. Full-scale hydrostatic burst tests were conducted for the line pipes with an axial through-wall (TW) notch to determine LBB criteria, that is, the relationship between the axial TW notch length and hoop stress for LBB. The determined LBB criteria were verified by full-scale partial gas burst tests for line pipes with an axial part-through-wall (PTW) notch and were then compared to the estimation using the CVN energy-based equation that Kiefner et al. have proposed. The present study demonstrated that the estimation using the CVN-based equation was in good agreement with the experimental results for the pipes with a relatively low CVN energy of less than 130 J. On the contrary, the equation was not applicable to the pipes with a relatively high CVN energy of more than 130 J. The results of instrumented Charpy tests clarified that the load versus load-point displacement curves for Charpy specimens from the high CVN energy pipes were different from those from the low CVN energy pipes. Therefore, the applicability of the CVN-based equation was dependent on the load versus load-point displacement curve for a Charpy specimen.

Application of Acoustic Emission for Measuring Crack Initiation Toughness in Instrumented Charpy Impact Testing

AbstractAcoustic Emission (AE) has been used to detect onset of ductile tearing in instrumented Charpy impact tests to enable determination of dynamic ductile tearing initiation toughness using a single specimen method. An AE based method was developed whereby a conventional instrumented impact tester is instrumented with a commercial broadband acoustic emission sensor mounted on the anvil. The results obtained using the new AE based method were compared to the results obtained by other researchers using specially developed AE sensors located inside the tup. Tests using both AE and direct measurement of the load-line displacement during the instrumented Charpy testing were conducted simultaneously on a conventional ship grade steel. V-notched and fatigue precracked test pieces were tested in the temperature range +23°C to −80°C.The results obtained with AE monitoring were compared to those obtained using the optical Direct Displacement Interferometric Strip (DDIS) method developed by the authors. Good correlation was found between the initiation fracture toughness determined at 0.2 mm blunting and crack extension, J0.2, by the multispecimen Ductile-Brittle Transition (DBT) method and those derived from single specimens applying AE and the new interferometric method to detect ductile fracture initiation. Fast Fourier Transformation (FFT) was applied to analyze the AE signals. The results showed that the different phases of AE and fracture modes could be distinguished based on characteristic frequency and time variance.

Dynamic deformation and fracture properties of simulated weld heat affected zone of 9Cr-1Mo steel from instrumented impact tests

Dynamic deformation characteristics such as dynamic yield stress and dynamic strain hardening exponent along with dynamic elastic-plastic fracture toughness for the different microstructural regions of heat affected zone (HAZ) of a nuclear grade 9Cr-1Mo steel have been evaluated by instrumented Charpy tests. Isothermal heat treatment at different temperatures was used to simulate the different microstructural regions in the HAZ of this steel, namely the over tempered base metal, intercritical, fine prior austenitic grained martensitic, and coarse prior austenitic grained martensitic regions. Effects of interparticle spacing on the dynamic deformation and fracture properties have been studied. It has been observed that the dynamic yield stress and the dynamic fracture toughness follow power law relationships with the interparticle spacing whereas the strain hardening exponent follows a linear fit.

The influence of ductile tearing on fracture energy in the ductile-to-brittle transition temperature range

The aim of this study is to examine the relationship between fracture energy and the ductile area measured on the fracture surface. Instrumented Charpy tests and fracture toughness tests are performed in the transition temperature range, as well as at lower temperatures. Quantitative fractographic analyses of Charpy specimens reveal a certain proportion of ductile fracture even if the Charpy test is conducted at low temperatures, below the transition temperature. The ductile fracture area situated next to the notch is correlated to fracture energy for all temperatures. In the transition temperature range, fracture energy and the ductile area have a large scatter. Since the limiting event in the development of the ductile area is the initiation of cleavage, the maximum principal stress has been computed in different specimens using the finite element method. It has been shown that the propagating ductile crack does not increase the stress level, but does increase the probability of cleavage fracture through an expansion of the plastic volume where weak points can be found.

Dynamic fracture toughness measurements in composites by instrumented Charpy testing: influence of aging

The dynamic behavior of three different fiber fabric composite laminates was studied by testing notched specimens in an instrumented Charpy machine. The registered impact force and displacement at the specimen hammer contact point were used to evaluate Mode-I fracture energy and dynamic fracture toughness. The changes in fracture toughness due to impact velocity, crack size and stacking sequence of the specimen were investigated with different degrees of aging conditions. Aging was found to significantly affect the dynamic fracture toughness, but had less effect on the static fracture toughness.

Measurement of fracture initiation toughness and crack resistance in instrumented Charpy impact testing

A new method has been developed involving direct measurement of the load-line displacement during instrumented Charpy testing. The method uses a laser interferometer to measure displacement in addition to the load-line displacement derived from the load signal. Tests were conducted using fatigue precracked and V-notched test pieces in the temperature range +23°C to −80°C on a conventional ship grade steel, a pressure vessel steel and two welded joints. Good correlation was found between the J 0.2 initiation fracture toughness determined by the multi-specimen method and the J i fracture toughness determined from single specimens using the new method to detect ductile fracture initiation.

A FRACTURE MECHANICS STUDY OF POLYPROPYLENE–WOOD FLOURS BLENDS

Polypropylene/wood blends were prepared from various resins and wood flours through extrusion compounding and injection molding. It was observed that the notched Izod strength of the blends with a relatively brittle resin matrix exceeded that of the neat resin at higher filler loading when the compounds contained the maleic-anhydride-polypropylene (MAPP) copolymer. The Izod strength of the blends with a tough matrix increased with the content of the interfacial modifier MAPP and is higher in blends with coarser fillers. The fracture mechanics analyses of the instrumented drop-weight Charpy test results were then performed to sudy the nature of these increases in impact fracture resistance. It was found that both the fracture toughness Kc and the critical strain release energy Gc increase with filler content in blends containing MAPP. In blends without MAPP, however, Gc decreases slightly with filler content while Kc increases less significantly. The increases of Gc with MAPP and with increasing filler particle size were also observed for the blends with a tougher PP as matrix. It is thus the reinforcing role of cellulosic fibers of the wood flours that contribute positively to the impact resistance of the PP/wood blends. It was thus proposed that higher wood filler aspect ratio, stronger interface, and tough copolymer matrix is the better choice in designing the PP/wood compounds.

Determination of Tensile Properties at Increased Strain Rates and Various Temperatures

Abstract This paper reports on the development and first application of a low-cost dynamic tension testing method which makes testing at strain rates in the range of 100/s to 500/s and various temperatures as simple as an instrumented Charpy test. The kinematical and kinetic analysis of the newly introduced, reusable clamping device allows the determination of the stress-strain curve from the measured force history during the tearing process. The first results show that the new technique is very promising to determine the influence of loading rate and temperature on the mechanical properties of structural materials, since the measured dynamic tensile properties compare well in absolute value as well as accuracy and reproducibility with those obtained using conventional high-speed tension testing facilities.

Microstructures relevant to brittle fracture initiation at the heat-affected zone of weldment of a low carbon steel

Charpy toughness of the heat-affected zone (HAZ) of weldment of a low carbon steel has been investigated by means of an instrumented Charpy test and fractographic analysis. Microstructures were varied with thermal cycles simulating double-pass welding. The ductile-brittle transition temperature is the most deteriorated at an intermediate second-cycle heating temperature. The origin of the difference in the transition temperatures has been analyzed to exist in the brittle fracture initiation stage. Fractographic examination correlating with microstructural features has revealed that the brittle fracture initiation site is associated with the intersection of bainitic ferrite areas with different orientations rather than the martensite-austenite constituents. The role of the constraint of plastic deformation on the brittle fracture initiation is discussed.

Two degrees of freedom modeling of precracked beams under impact

Impact loading of three point bend is modeled as a lumped mass-spring system with two degrees of freedom. The model gives all the forces involved in the impact process, viz. load measured by the tup instrumentation, contact force and experienced by the specimen. With a simplifying assumption of applicability of static crack-tip field solutions, the dynamic stress intensity factor (SIF) is computed from the beam force. Dynamic fracture toughness is obtained from the SIF at fracture initiation. The model explains the typical features of tup load and beam response records observed in instrumented Charpy testing. The model predictions are compared with results of experiments conducted on aluminum 6061 T6 and polymethylmethacrylate (PMMA).

Instrumentierter Kerbschlagbiegeversuch

The German DVM-group on Instrumented Impact Testing has recently finished a round-robin test. Seventeen participants performed about 400 instrumented Charpy tests with a German reactor pressure vessel steel at four different temperatures. The specimens were prepared with standardized V-notches, spark-eroded crack-similar slits or fatigued cracks. Besides standardized material data, like e.g. the Charpy energy, especially characteristic forces and partial energies were determined and thereon based evaluations of fracture mechanical quantities were performed. The results of the participants showed an excellent agreement. A high accuracy of the force measurement was observed. Therefore, these results support current international activities to standardize the instrumented Charpy test.

Fracture process of a low carbon low alloy steel relevant to charpy toughness at ductile-brittle fracture transition region

The fracture process that determines the Charpy energy at the ductile-brittle transition region was investigated by means of the instrumented Charpy test and fractographic analysis with a low carbon low alloy steel subjected to different control-rolling conditions. The decomposition of a Charpy energy into the energies dissipated in the course of the notch-tip blunting, stable crack growth, and brittle crack propagation is unique irrespective of the testing temperatures and specimen series. Toughness level can be divided into four regions according to the pre-dominating fracture process. The temperature dependence of toughness and effects of the an-isotropy of a specimen originates in the brittle fracture initiation stage rather than the resistance against the notch-tip blunting or stable crack growth. From fractographic examination referring to the stress analyses, it is discussed that the brittle fracture initiation is controlled by the local deformation microstructures in the plastic zone together with the stress field ahead of the notch or the stable crack front.

Evaluation of fracture toughness based on results of instrumented Charpy tests

The modified Gurson model is used to determine micromechanical toughness parameters of a weld material from the irradiation surveillance of a reactor pressure vessel. These parameters were used to numerically simulate static and dynamic fracture mechanics tests for the determination of J- resistance curves. The results were confirmed by means of experiments with irradiated subsized specimens of the original material. The essential steps of the analysis—the consideration of rate-dependent stress-strain curves and the determination of the material parameters, as well as the numerical modelling of the boundary conditions at the supports of the Charpy specimen—were validated by comparing analyses and experiments with a representative unirradiated submerged are weld material. The initiation values of the J- resistance curves converted into pseudo-plane strain fracture toughness values K Ic allowed the conservative adjustment of the ASME reference fracture toughness curve.

Analysis of the Hopkinson Pressure Bar loaded Instrumented Charpy Test using an inertial modelling technique

A one-dimensional mass spring model of the Hopkinson Pressure Bar loaded Instrumented Charpy Test is developed and validated for the lower shelf behaviour of an alloy steel, En24 (817M40). The assessment of component stiffnesses and masses, in the inertial model, is discussed. It is shown that the linear elastic components of contact stiffness values do not vary markedly with strain rate and temperature. It is also shown that plastic components of contact stiffnesses become important at intermediate force values. The developed inertial model is then used to derive values of dynamic initiation fracture toughness, K Id .

Investigation on Instrumented Impact Test and Loading Rate Dependency of Brittle Polymers.

In the present study, the effect of the specimen size on the vibrational wave superimposed on the load-deflection curve of polymers is first investigated. Next, in the instrumented Charpy test, a shock-absorbing material is used in order to prevent the generation of the vibrational wave superimposed on the load-deflection curve, and its validity is discussed. Further, differences of the impact response curves obtained by an instrumented Charpy test and the one-point bend test are compared and discussed. The results of this study are summarized as follows. (1) The vibrational wave can be prevented by using a small specimen which shortens the period of the vibrational wave. (2) The load value is lowered by using shock-absorbing material. (3) The differences in the impact response curves and the fracture times obtained from the instrumented Charpy impact test and the one-point bend test are rather large in the lower impact velocity of 3.10m/s; however, the obtained KId values are nearly coincidental.

Comparison between dynamic fracture toughness k1dand impact strength as criteria for evaluating the mechanical properties of steels

Abstract A comparison between the Charpy-V (CV) test, widely used in steel characterisation, and the dynamic fracture toughness K1d found on precracked Charpy testpieces, is carried out. The experimental procedure, not yet standardised, used to determine the dynamic fracture toughness K1d (instrumented precracked charpy test or IPC test) is first described. The experimental procedure, not yet standardised, used to determine the dynamic fracture toughness K1d (instrumented precracked charpy test or IPC test) is first described. The conceptual differences between dynamic fracture toughness K1d and CV impact strength, the limits of CV testing in evaluating the toughness of steels, and finally the advantages of adopting the IPC test and its possible applications in the field of welding are then successively discussed.

Impact strength of notched specimen for sintered W-Ni-Fe alloy.

Instrumented Charpy tests were carried out for sintered W-Ni-Fe alloys in order to clarify the effects of notch radius on impact strength. Sintered 93.0W-4.9Ni-2.1Fe and 97.2W-2.0Ni-0.8Fe (in wt%)heavy alloy specimens were prepared. Notch radii of the specimens used were 1.0, 0.2 and 0.08 mm. The maximum load and the absorbed energy decreased with reducing notch radius. SEM fractography of impact specimens revealed a large amount of cleavage failure of tungsten grains. However, the absorbed energy corresponded well with the fraction of ductile fracture surface formed by the failure of matrix. Plastic strains near the fracture surface were measured by a grid method. The results indicated that the plastic zone size induced by an impact test was reduced as the notch radius decreased. On the basis of the observed plastic zone and the Rice-Rosengren-Hutchinson model, the estimated plastic works for the impact test specimens were close to the experimental absorbed energies.

Compliance calibration during instrumented Charpy impact testing

Abstract Any dynamic model dealing with the instrumented Charpy test has to take into account the respective compliances of both specimen and experimental set up. Comparison between the specimen compliances derived from computation or experimental measurement shows significant differences. They must be attributed to additional compliances related to both the testing device and its interaction with the specimen. Making use of a dynamic analysis allows the compliance value to be determined and taken into account for the assessment of the dynamic stress intensity factor K ID : the discussion of the related compliance values shows the model's consistency and its usefulness, for instance in determining the times at fracture initiation and crack growth resistance curves.

Fracture Properties of Fiber Reinforced Concrete Subjected to Impulsive Loading

AbstractThe need to accurately predict the response of structures under impact loadings has led to an interest in the mechanical properties of component materials at high rates of loading. The mechanism of cracking and its propagation play an important role in evaluation of the response of fiber reinforced concrete structures subjected to impulsive loading. In the present study, single–edge notched beams were tested under high velocity impact loads. A computer assisted instrumented Charpy test system was employed in performing the impact tests. Development and testing of a new fiber optic sensor, for the determination of internal Crack Opening Displacements (COD) in fiber reinforced concrete is described.

Study on instrumented charpy test. (2nd report. Procedure to determine the modified J-R curve and its application to ductile fracture temperature).

Instrumented Charpy tests and static JIC tests were conducted on fatigue-cracked and V-notched specimens of A508 Cl.3 steel at 100°C· A proposed key-curve method to compare the P-S curves of the two types of specimens and a partially loaded instrumented Charpy test using a newly designed stopper proved to be applicable not only at the transition temperature, but also at the ductile fracture temperature region, regardless of testing speed. Also, a simple formula to evaluate the Ernst's Modified J-integral was derived, and showed to have a sufficient accuracy well beyond the J-control led crack growth regime.