Charpy Impact Test Data Research Articles

Estimation of fracture toughness of 16MnDR steel using Master Curve method and Charpy V-notch impact energy

16MnDR steel is widely used as a low temperature pressure vessel steel in China. However, the fracture toughness of this steel significantly decreases with the decrease of temperature in the ductile to brittle transition region. To prevent the occurrence of brittle fracture, the methods which can precisely estimate the fracture toughness of 16MnDR steel are of great practical significance. In this paper, the Master Curve method, and empirical formulas between Charpy V-notch impact energy and fracture toughness are applied to estimate the fracture toughness of 16MnDR steel in the transition region. The reference temperature T0 values are determined using both single-temperature and multi-temperature method from fracture toughness test data and Charpy impact test data. The T0 values determined from different combinations of test temperatures are compared. It is found that the fracture toughness of 16MnDR steel can be well estimated using the Master Curve method in the transition region and lower shelf region. The predicted fracture toughness values obtained by empirical formulas cannot be directly used in structural integrity assessment of 16MnDR steel. The effective methods to accurately estimate fracture toughness in the transition region under the differenttestconditions are proposed for 16MnDR steel.

A simple intrinsic measure for rapid crack propagation in bimodal polyethylene pipe grades validated by elastic–plastic fracture mechanics analysis of data from instrumented Charpy impact test

Conventional test procedures, such as the S4 test to analyze the resistance against rapid crack propagation (RCP) of plastic pipe materials are characterized by usage of a lot of material, are far from saving of time and they are‐in need of special experimental set‐ups. Therefore, in the last decade, small‐scale accelerated reliable tests (SMART) are developed ‐ worldwide to overcome the disadvantage of such conventional tests. In this article, fracture mechanics based analysis of instrumented Charpy impact test data for a set of bimodal high‐density polyethylene pipe grades are compared with data of the conventional Charpy impact test. From this comparison the Charpy impact strength at −30°C comes forth as a robust reproducible measure of the resistance to RCP and it is therefore proposed as a SMART method to rank materials with respect to RCP resistance. POLYM. ENG. SCI., 57:13–21, 2017. © 2016 Society of Plastics Engineers

Estimation of fracture toughness KIC from Charpy impact test data in T-welded connections repaired by grinding and wet welding

This work presents, for the first time, and estimation of fracture toughness KIC correlations from Charpy V-notch (CVN) impact test data extracted from T-welded connections repaired with rectangular grinding and filled by wet welding. To obtain KIC values, equations based on the yield stress (σYS) of the wet welding beads were used. The estimated KIC data decreased with increasing water depth. These two characteristics (porosity and microstructures for low carbon steels) did not improve the mechanical properties, such as Charpy impact and KIC values.

Towards optimisation of load-time conditions for producing viscoelastically prestressed polymeric matrix composites

A viscoelastically prestressed polymeric matrix composite (VPPMC) is produced by applying a tensile creep load to polymeric fibres, the load being released before the fibres are moulded into a polymeric matrix. The viscoelastically recovering fibres induce compressive stresses within the matrix, which can improve mechanical properties by up to 50%. This study investigates the feasibility of reducing the creep loading period for VPPMC production. By using nylon 6,6 fibres, we have demonstrated that the previously adopted viscoelastic creep strain, requiring 330 MPa for 24 h, can be achieved over a shorter duration, tn, using increased creep stress. Thus tn was 92 min at 460 MPa and 37 min at 590 MPa. Subject to avoiding fibre damage however, it may be possible to reduce tn further. From the three creep settings, elapsed recovery strain values were similar, as were the Charpy impact test data from corresponding VPPMC samples; i.e. there were no significant differences in impact energy absorption, these being ∼56% greater than their control (unstressed) counterparts.

Mechanisms of toughness improvement in Charpy impact and fracture toughness tests of non-heat-treating cold-drawn steel bar

In this study, toughness properties of a non-heat-treating cold-drawn bar were examined by Charpy impact test and fracture toughness test, and the toughness enhancement mechanisms were clarified in relation with microstructure. As the thickness of pearlite bands decreased after the cold drawing, the Charpy impact energy of the cold-drawn bar was higher than that of the as-rolled bar, which could be reasonably explained by the thin sheet toughening. On the other hand, thin pearlite bands negatively affected the fracture toughness because of the decreased spacing between crack or void initiation sites inside the fracture process zone in front of the pre-fatigued crack tip. The Charpy impact test data could also be correlated with the absorbed energy of the dynamic compressive test specimen whose orientation was matched with the hammer impact direction of the Charpy impact test, although the Charpy impact and dynamic compressive test specimens had a notched body and a smooth body, respectively.

Impact properties of irradiated HT9 from the fuel duct of FFTF

This paper reports Charpy impact test data for the ACO-3 duct material (HT9) from the Fast Flux Test Facility (FFTF) and its archive material. Irradiation doses for the specimens were in the range of 3–148 dpa and irradiation temperatures in the range of 378–504 °C. The impact tests were performed for the small V-notched Charpy specimens with dimensions of 3 × 4 × 27 mm at an impact speed of 3.2 m/s in a 25 J capacity machine. Irradiation lowered the upper-shelf energy (USE) and increased the transition temperatures significantly. The shift of ductile–brittle transition temperatures (ΔDBTT) was greater after relatively low temperature irradiation. The USE values were in the range of 5.5–6.7 J before irradiation and decreased to the range of 2–5 J after irradiation. Lower USEs were measured for lower irradiation temperatures and specimens with T-L orientation. The dose dependences of transition temperature and USE were not significant because of the radiation effect on impact behavior nearly saturated at the lowest dose of about 3 dpa. A comparison showed that the lateral expansion of specimens showed a linear correlation with absorbed impact energy, but with large scatter in the results. Size effect was also discussed to clarify the differences in the impact property data from subsize and standard specimens as well as to provide a basis for comparison of data from different specimens. The USE and ΔDBTT data from different studies were compared.

New Methodologies for Developing Radiation Embrittlement Models and Trend Curves of the Charpy Impact Test Data

Abstract A new methodology is developed for the prediction of RPV embrittlement that utilizes a combination of domain models and nonlinear estimators including neural networks and nearest neighbor regressions. The Power Reactor Embrittlement Database is used in this study. The results from newly developed nearest neighbor projective fuser indicate that the combined embrittlement predictor achieved about 67.3% and 52.4% reductions in the uncertainties for General Electric Boiling Water Reactor plate and weld data compared to Regulatory Guide 1.99, Revision 2, respectively. The implications of irradiation temperature effects to the development of radiation embrittlement models are then discussed. A new methodology that incorporates the chemical compositions into the Charpy trend curve is also developed. The purpose of this new fitting procedure is to generate a new multi-space topography that can properly reflect the inhomogeneity of the surveillance materials and utilize this multi-space trend surface to link and project the surveillance test results to that of reactor pressure vessel steels.

Analysis of abnormal fracture occurring during drop-weight tear test of high-toughness line-pipe steel

Abstract In this study, various types of drop-weight tear test (DWTT) were conducted on a high-toughness line-pipe steel in order to analyze abnormal fracture appearance occurring in the region impacted by a hammer. A pressed notch or a chevron notch was introduced into DWTT specimens, some of which had a back slot designed to decrease the inverse fracture area. After the DWTT, percent shear area, area of inverse fracture surface, and hardness and work hardening exponent of the hammer-impacted region were measured. The results indicated that the shear area of the pressed-notch DWTT specimens was larger than that of chevron-notch DWTT specimens. In the hammer-impacted region of all the DWTT specimens, abnormal inverse fracture having a cleavage fracture mode appeared, and its fracture area was correlated well with hardness and work hardening exponent measured by an indentation test. The formation of this inverse cleavage fracture raised the fracture propagation transition temperature (FPTT) by decreasing the shear area measured in accordance of the API 5L3 specification, which was confirmed by relating to the Charpy impact test data of pre-strained steel specimens. Thus, it was desirable to exclude the inverse fracture formed in the hammer-impacted region when calculating percent shear area of DWTT because compressive pre-strain induced by work hardening did not exist in actual applications of line-pipe steels.

Estimation of fracture toughness transition curves of RPV steels from Charpy impact test data

The major concern for reactor pressure vessels (RPVs) in terms of integrity is the reduction in fracture toughness of materials due to radiation embrittlement. In order to ensure the structural integrity of RPVs, a very conservative approach has been employed since the first commercial operation of a nuclear power plant (NPP). RT NDT has been used as a principal parameter to indicate the degree of irradiated degradation in RPV material, which is determined using Charpy impact and drop weight tests based on the ASME code requirements. Charpy test is very practical and easy, but it does not provide the fracture toughness itself. Therefore, the Master Curve method, as a direct method to determine the fracture toughness of RPV, was investigated by a number of researchers during the last decade. An alternative approach is proposed in this paper to estimate the reference transition temperature, T 0, in the Master Curve method using Charpy impact test data, which are abundant for old NPPs. Two well-known correlations between Charpy absorbed energy and K Ic were used to estimate the fracture toughness transition curves.

A direct fracture toughness model for irradiated reactor vessel weld material based on reference temperature

The master curve method has opened a new means to acquire a directly measured material-specific fracture toughness curve based on testing a small number of replicate specimens. This process enables, for the first time, the construction of a material-specific fracture toughness curve for an irradiated material directly from fracture tests. Currently, only an inferred fracture model is available through a combination of the ASME Boiler and Pressure Vessel Code and a regulatory guide from the U.S. Nuclear Regulatory Commission. This approach uses the fracture toughness curve of a generic, unirradiated reactor vessel steel that is shifted by a reference temperature ( RT NDT) based on Charpy impact test data. The master curve method yields a key material parameter called reference temperature, T 0, which indicates the location of the transition range fracture toughness curve on the temperature axis. When a small number of pre-cracked Charpy specimens were tested at several different fluence levels, the material specific reference temperatures can be shown as a function of fluence. One such model for the WF-70 weld material is presented in this paper. The irradiated specimen data and analyses from Oak Ridge National Laboratory (ORNL) and the B&W Owners Group (B&WOG) are utilized for this model. This model is based on fracture toughness data, independent of Charpy impact energy levels, percent shear, and most importantly, material properties of unirradiated condition.

Unambiguous curve fitting and error estimation for charpy impact test data of reactor pressure vessel steels, suitable for a small number of samples

On the basis of the requests of a reliability consideration a new concept for curve fitting is derived. Starting from an investigation of the distribution of the content of information about the free parameters of the analytical model (tanh), an iterative curve fitting procedure has been developed. This new approach may also be applied for any other functional description of a stochastic process. By means of the Monte Carlo method, error distributions for the parameters determined are calculated and demonstrate the unambiguity of the method developed. A series of calculations for a model curve with six measuring points with various distributions of temperatures and different initial errors is performed. A proposal for planing experiments with a small number of samples is derived.

Failures of 108‐Inch Steel Pipe Water Main

The paper describes the analysis of failures of a 108‐in. (2.74 m) diameter steel pipe water main. Total pipe separations occurred because of large unrelieved thermal stresses and stress amplification caused by the eccentricity of the welded bell‐and‐spigot joints. The pipeline designer ignored these aspects in his design, thus grossly underestimating the stresses in the pipe. This could easily have been recognized by performing an elementary longhand calculation. The failure analysis described in this paper demonstrates that the asdesigned pipeline was incapable of safely withstanding even the incorrectly defined design conditions. The designer attributed the failures to low toughness of the bell steel. Conversions of Charpy impact test data and J‐integral analysis of compact tension test data are used to demonstrate that the steel had normal fracture toughness. Nonlinear finite element stress analysis and elasticplastic fracture mechanics demonstrate that for the measured range of fracture toughness the failures were inevitable.