Determination Of Dynamic Fracture Toughness Research Articles

A comparison of different experimental approaches in the determination of dynamic fracture toughness (J1d) behavior for RHA steel cost sustainable MMAW weldments

In the present investigation, the low hydrogen ferrite consumable weldment (weldment-1) and austenitic stainless steel consumable weldment (weldment-2) of rolled and homogenous armor steel (RHA) have been prepared with manual metal arc welding (MMAW). Further, the influence of weldments (weldment-1 and weldment-2) microstructure on the dynamic fracture toughness (J1d), strength, ductility and hardness has been evaluated and compared. The three different approaches have been utilized to estimate J1d for RHA weldments. Further, all three approaches’ outcomes have been compared with the elastic-plastic fracture mechanics (EPFM) approach through Jp-R curve. The results revealed that weldment-1 (yield strength 504.24 MPa and ultimate tensile strength 763.03 MPa) exhibited 26.93 and 25.07% more yield and tensile strength respectively than weldment-2 (yield strength 384.55 MPa and ultimate tensile strength 593.05 MPa). Further, the elongation of weldment-2 (elongation 42%) is 26.72% more than weldment-1 (elongation 32.10%). The joint efficiency and fusion zone hardness of weldment-1 are 5.85 and 57.56%, respectively more than weldment-2. The EPFM approach has good agreement with the correction factor approach (approach 2) and the compliance change rate approach (approach 3) with less than 7% difference in the estimation of dynamic fracture toughness of base metal and weldments (weldment-1 and weldment-2). Further, the percentage difference between maximum load point approach (approach 1) and the EPFM approach is more than 15% difference. The fractographic investigation confirms the ductile fracture in all under-investigated materials.

Simultaneous determination of dynamic fracture toughness and tensile strength through a single three-point bending test

Simultaneous determination of dynamic fracture toughness and tensile strength through a single three-point bending test

Dynamic notched semi-circle bend (NSCB) method for measuring fracture properties of rocks: Fundamentals and applications

Abstract Rocks are increasingly used in extreme environments characterised by high loading rates and high confining pressures. Thus the fracture properties of rocks under dynamic loading and confinements are critical in various rock mechanics and rock engineering problems. Due to the transient nature of dynamic loading, the dynamic fracture tests of rocks are much more challenging than their static counterparts. Understanding the dynamic fracture behaviour of geomaterials relies significantly on suitable and reliable dynamic fracture testing methods. One of such methods is the notched semi-circle bend (NSCB) test combined with the advanced split Hopkinson pressure bar (SHPB) system, which has been recommended by the International Society for Rock Mechanics and Rock Engineering (ISRM) as the standard method for the determination of dynamic fracture toughness. The dynamic NSCB-SHPB method can provide detailed insights into dynamic fracture properties including initiation fracture toughness, fracture energy, propagation fracture toughness and fracture velocity. This review aims to fully describe the detailed principles and state-of-the-art applications of dynamic NSCB-SHPB techniques. The history and principles of dynamic NSCB-SHPB tests for rocks are outlined, and then the applications of dynamic NSCB-SHPB method (including the measurements of initiation and propagation fracture toughnesses and the limiting fracture velocity, the size effect and the digital image correlation (DIC) experiments) are discussed. Further, other applications of dynamic NSCB-SHPB techniques (i.e. the thermal, moisture and anisotropy effects on the dynamic fracture properties of geomaterials, and dynamic fracture toughness of geomaterials under pre-loading and hydrostatic pressures) are presented.

Rock Dynamic Fracture Characteristics Based on NSCB Impact Method

In 2012, the International Society for Rock Mechanics (ISRM) recommended a new Notched Semicircular Bend (NSCB) method for the determination of dynamic fracture toughness of rock materials, but it did not consider the effect of some uncontrollable factors in the course of the experiment on the test result. This thesis firstly carried out dynamic fracture toughness experiments on several typical rock materials such as sandstone using the modified Split‐Hopkinson Pressure Bar (SHPB) experimental system with high‐speed photography, directly compared the dynamic fracture failure characteristics of several rock materials, and examined the loading rate dependency of the dynamic fracture toughness of rock materials. Based on the numerical analysis method of Discrete Lattice Spring Model (DLSM), it focused on the effect of bullet impact loading rate, loading area of incident bar, support restraints of clamping specimen, and other uncontrollable factors in the course of SHPB experiment on test results. The findings can be referenced for the improvement of NSCB method.

The Influence of Wedge Shape on the Determination of Dynamic Fracture Toughness in SHPB Test

The SHPB loading three-point bending specimen is a popular way for measuring the dynamic fracture toughness of the material. The wedge shapes on the loading end of the incident bar have necessary effects on the propagation of the stress wave. The dynamic mechanical response and the fracture toughness of the aluminum alloy were measured by SHPB with different wedge shapes, and the influences of wedge shape on determination of dynamic fracture toughness was analyzed in this study. The investigation result can be used to provide reference for the design of a new Hopkinson apparatus for dynamic fracture testing.

A novel method in determination of dynamic fracture toughness under mixed mode I/II impact loading

The objective of this paper is to propose a novel methodology for determining dynamic fracture toughness (DFT) of materials under mixed mode I/II impact loading. Previous experimental investigations on mixed mode fracture have been largely limited to qusi-static conditions, due to difficulties in the generation of mixed mode dynamic loading and the precise control of mode mixity at crack tip, in absence of sophisticated experimental techniques. In this study, a hybrid experimental–numerical approach is employed to measure mixed mode DFT of 40Cr high strength steel, with the aid of the split Hopkinson tension bar (SHTB) apparatus and finite element analysis (FEA). A fixture device and a series of tensile specimens with an inclined center crack are designed for the tests to generate the components of mode I and mode II dynamic stress intensity factors (DSIF). Through the change of the crack inclination angle β (=90°, 60°, 45°, and 30°), the K II/ K I ratio is successfully controlled in the range from 0 to 1.14. A mixed mode I/II dynamic fracture plane, which can also exhibit the information of crack inclination angle and loading rate at the same time, is obtained based on the experimental results. A safety zone is determined in this plane according to the characteristic line. Through observation of the fracture surfaces, different fracture mechanisms are found for pure mode I and mixed mode fractures.

Analysis of dynamic conditions during thermal transient events for the structural assessment of a nuclear vessel

The possibility of dynamic loading conditions in a reactor pressure vessel (RPV) has been investigated in this paper. For this purpose, finite element (FE) numerical simulations of several thermal transients were performed including a normal shut down and two accidental thermal shocks, namely a loss of coolant accident (LOCA) and an extreme postulated pressurised thermal shock (PTS). The aim of the present contribution is to evaluate the influence of the loading rate on the fracture properties of the vessel steel of the Santa María de Garoña Spanish nuclear power plant (NPP) in the ductile to brittle transition (DBT) region. To describe the fracture behaviour of the steel in the DBT region, the master curve (MC) reference temperature, T 0 , was used. This temperature is normally used for quasi-static conditions; however, it has been recently extended to the determination of dynamic fracture toughness by means of a phenomenological model proposed by Wallin. The dynamic reference temperature, T 0,dyn , was obtained for the loading rates corresponding to the three studied situations numerically simulated and compared with the quasi-static reference temperature, T 0,sta . From these results, conclusions about the importance of loading rates in nuclear vessels were established.

Fracture characterisation of a nuclear vessel steel under dynamic conditions in the transition region

The Master Curve (MC) methodology, originally proposed by Kim Wallin, is a standardised engineering tool for analysing the fracture toughness of ferritic steels in the ductile to brittle transition (DBT) region by means of the reference temperature T 0 . This temperature is normally estimated from quasi-static fracture toughness tests, nevertheless, it has been recently extended to the determination of dynamic fracture toughness. The aim of the present contribution is to characterise the fracture resistance in the DBT region under high strain rate conditions by applying the MC methodology to the steel of the Santa María de Garoña Spanish nuclear power plant (NPP). In this sense, 15 Charpy instrumented tests were performed on pre-cracked specimens from the surveillance program of the plant. The dynamic reference temperature, T 0,dyn , was obtained and compared with the quasi-static reference temperature, T 0,sta . The reliability of a semi-empirical formula proposed by Wallin to obtain T 0,dyn from T 0,sta has been analysed for this material.

The effect of the testing conditions on the fracture mechanics characteristics of short glass fibre reinforced polyamide

The aim of the work was to investigate the influence of the testing conditions (i.e., loading rate, crack length, mechanical damping) on the fracture mechanics characteristics of a short glass fibre reinforced polyamide. Instrumented Charpy impact experiments were carried out on pre-cracked specimens of PA6.6 polyamide material containing a different quantity of short glass fibre reinforcement. In the case of 1m/s loading rate, the evaluation procedure for static tests could be applied for determination of dynamic fracture toughness (KId) and strain energy release rate (GId). In the case of 3.7m/s loading rate, the dynamic key-curve method was used to determine KId, and the time to fracture was obtained by electric-emission measurement.

Determination of dynamic fracture toughness of heat affected zone of 9Cr–1Mo steel from instrumented drop weight tests

The dynamic fracture toughness (K1d) of the heat affected zone (HAZ) of 9Cr–1Mo steel at and below the nil ductility transition temperature has been estimated from instrumented drop weight test results. The presence of a significant microstructural gradient in the HAZ, comprising coarse, fine, and intercritical regions with sharp toughness differences, is reflected in the presence of distinctive load peaks in the load–time traces; the K1d estimates for the coarse, fine, and intercritical regions are 53, 85, and 128 MPa m1/2 respectively. The results from the 9Cr–1Mo steel were compared with those for AISI grade 403 martensitic stainless steel. The lack of distinctive multiple load peaks in the load–time traces for the latter is attributed to the absence of a steep toughness gradient, owing to a more or less uniform martensitic microstructure in the HAZ.

Determination of dynamic fracture toughness for PMMA

A dynamic FEM (finite element method) and a strain gage method are applied to analyze the dynamic fracture toughness and SIF (stress intensity factor) for PMMA (polymethyl methacrylate). The analyses are carried out for plates with an edge crack subjected to one-point bending in a plane of the plate. A simple procedure that the present author has proposed is applied to the problem of using a triangular element of assumed constant strain on finite element analysis. The numerical simulation by FEM provides values for the applied forces as measured with the strain gages. Also, a crack initiation time is measured with the strain gage mounted around the crack tip. The dynamic fracture toughness is determined by adapting the crack initiation time to the simulation curve of the dynamic SIF calculated by the FEM. In this study, the usefulness of the method to determine the dynamic fracture toughness is investigated by comparing predictions with the experimental results for dynamic stresses and SIFs.

Determination of dynamic fracture toughness of nuclear pressure vessel steel using electromagnetic force.

This paper is concerned with the application of electromagnetic force to the determination of dynamic fracture toughness. We take an edge-cracked specimen which carries a transient current I and is simply supported in a uniform and steady magnetic field B. In fracture analysis, the extended J-integral with the effect of the electromagnetic force and the inertia force is calculated. Also the R-curve technique is utilized in upper shelf temperature ranges and the electric potential method below the transition ones in order to detect the crack initiation. Using these techniques, we evaluate the dynamic fracture toughness of A508 cl. 3 steel and discuss about the loading rate effect on fracture toughness.

The determination of dynamic fracture toughness of AISI 4340 steel by the shadow spot method

Dynamic crack propagation experiments have been performed using wedge loaded double cantilever beam specimens of an austenitized, quenched and tempered 4340 steel. Measurements of the dynamic stress intensity factor have been made by means of the optical method of caustics. The interpretation of experimental data, obtained from the shadow spot patterns photographed with a Cranz-Schardin high speed camera, is based on an elastodynamic analysis. The instantaneous value of the dynamic stress intensity factor K d I is obtained as a function of crack tip velocity. Finally, the interaction of reflected shear and Rayleigh waves with the moving crack tip stress field is considered.

Application of instrumented impact testing for studying dynamic fracture behaviour of rotor steels

The viability of the instrumented Charpy impact testing for studying dynamic fracture behaviour of rotor steels is investigated. This encompasses determination of dynamic fracture toughness ( K Id ) and dynamic J-integral ( J Id ), establishing correlation between oscilloscope profiles and fracture morphology of the ruptured samples and identifying fracture mechanisms involved. The predicted oscilloscope profiles for common fracture modes, their experimental counterparts, and the inferences drawn from these concerning operating fracture mechanisms are in good accord with the fractographic observations made on broken samples. Thus, the respective oscillographs vividly manifest the observed variations in the fracture processes. Fracture mechanics analysis of load-time and energy-time records of pre-cracked Charpy samples gave dynamic fracture toughness ( K Id ) values of 43, 74 and 124 MN/m 3 2 , and dynamic J-integral ( J Id ) values of 0.008, 0.03 and 0.06 MJ/ m 2 at −180°, 26° and 96°C respectively. It is possible that the deduced J Id values correspond to a small but finite amount of crack extension instead of Zero Crack extension, in line with the emerging trends of J Id estimation. Apart from increasing with temperature, both parameters recorded a true transition around 35°C which is attributed to the combined influence of a change in the fracture mode and relaxation of crack tip constraint. Another significant outcome of this investigation concerns about the existence of a minimum crack depth ratio for valid J Id determination which, based on a detailed fractographic study, is interpreted in terms of the collective influence of crack tip plasticity and notch constraint.