|
|
Recent Approaches to Brittle Fracture Characteristics of Steels
Dlouhý, Ivo ; Hadraba, Hynek ; Kozák, Vladislav ; Chlup, Zdeněk ; Holzmann, Miloslav
A brief overview of the current approaches for evaluating selected brittle fracture properties of steels relating to fracture resistance of welded joints. A critical analysis of the existing solutions to a singleparameter description of a crack tip stress field, linear-elastic and elastic-plastic fracture mechanics. Two-parameter fracture mechanics as the next development stage of fracture mechanics and impacts of its knowledge on fracture toughness measurement. Master curve for fracture toughness description of steels in the transition region. Local approach as the next fracture mechanics concept enabling prediction of global brittle fracture properties. Application of micromechanical crack tip fracture models (toughness scaling models) for correction of fracture mechanics data in their transfer from a specimen of one geometry to a specimen of another geometry and size (transferability). Evaluation of fracture properties of heterogeneous materials according to the SINTAP procedure.
|
|
|
Evaluation of KQ toughness and Kefc fracture toughness of hypoeutectoid steel R7T
Holzmann, Miloslav ; Jurášek, L.
Interpretation of the characteristic KQ using linear-elastic fracture mechanics coupled with Irwin´s concept of the effective crack length. The effective yield stress Ref as a basic parameter controlling the level of KQ and its scatter. The use of Irwin´s concept of effective crack length for determining fracture toughness Kefc. Validity of Irwin´s concept up to certain ratio of Fmax/FGY. The scatter of the fracture toughness Kefc, i. e. probability distribution of fracture toughness Kefc diagram. This diagram can be used in the case of application of probabilistic fracture mechanics for determining cumulative fracture probability of the given crack.
|
|
|
The fracture behaviour of welded joints pearlitic and bainitic rail steel
Hadraba, Hynek ; Dlouhý, Ivo ; Holzmann, Miloslav ; Zbořil, J.
The contribution is focused on analysis of welded joint made from pearlitic rail steel of type UIC 900A and newly developed cast bainitic Lo8CrNiMo steel. The lowest dynamic fracture toughness and consequently the higher risk of brittle fracture possessed the pearlitic steel and its heat affected zone (HAZ). At application temperature range the fracture toughness of this steel was on lower shelf of ductile to brittle transition, the tempering in HAZ didn't affect the toughness substantially. The dynamic fracture toughness of cast bainitic steel in joint was two times highest comparing to pearlitic one and, in addition HAZ toughness increase was found. The weld joint itself was characterised by high scatter of toughness data, nevertheless, all the values were above the scatter band characterising the more brittle pearlitic steel.
|
|
|
Evaluation of Strain Rate Effects on Transition Behaviour Applying the Master Curve Methodology
Dlouhý, Ivo ; Kohout, J. ; Jurášek, Ladislav ; Holzmann, Miloslav
Master curve methodology has been used for an evaluation of strain rate effects on transition behaviour of wrought CrMo and cast ferritic C Mn steel.The physical aspects of strain rate effect on reference temperature has been analysed as a base for the prediction of this dependence.Statistical aspects of the strain rate effects on the master curve have been discussed showing capability of the method for the prediction of strain rate susceptibility of steel fracture behaviour. It has been experimentally proved that the master curve shape does not depend on the loading rate.The relationship between reference temperature T0 (or the shift of T0 with respect to quasi-static loading rate)and loading rate can be described with linear dependence if logarithmic scale of temporal change of stress intensity factor is considered.For experimental establishing of the dependence of reference temperature on loading rates only two T0 values as determined at different loading rates are sufficient.However,it is useful to achieve the comparable accuracy of both T0 determinations that may demand larger number of specimens for the measurement of T0 at the higher loading rate.Standard quasistatic fracture toughness has been predicted from small pre-cracked Charpy type specimens tested dynamically applying the reference temperature shift obtained experimentally.The predicted fracture toughness temperature diagram has been proved experimentally.
|
|
|
Bainitic steel for frogs of rail switches - development and properties
Dlouhý, Ivo ; Zbořil, J. ; Holzmann, Miloslav
Mechanical properties and fracture behaviour of newly developed cast bainitic steel Lo8CrNiMo, predetermined for the frogs of rail switches, has been investigated. Properties of rail steel of the type UIC 900A has been followed for comparison. According to characteristics obtained steel Lo8CrNiMo displays much better fracture resistance when compared to standard rail steel. Dynamic fracture toughness is the same as static fracture toughness. This finding has great practical importance with respect to dynamic loading to frog.
|
|
| |
|
|
Master curve evaluation at static and dynamic conditions of loading (for cast ferritic steel and pressure vessel steels)
Dlouhý, Ivo ; Chlup, Zdeněk ; Holzmann, Miloslav
Various aspects of the master curve methodology have been investigated experimentally based on data obtained with different pressure vessel and container steel. A manganese cast steel has been utilised being considered for storage containers of spent nuclear fuel. Two locations of a segment of container cask, surface and midthickness, have been followed. Some results obtained with the RPV steel of VVER 1000 type and CrMo pressure vessel steel used in petrochemical applications have also been exploited. The applied mechanical testing procedures included: Standard fracture toughness tests at different temperatures using 1T bend specimen in order to determine fracture toughness - temperature diagrams, dynamic fracture toughness has been tested by using hydraulic test machine and drop weight tower. Pre-cracked Charpy specimens have also been tested. For each test technique larger sets of data have been generated in order to follow the statistical aspects. The investigations included procedures of reference temperature determination, both by the one and multitemperature methods, and the evaluation of the scale and constraint effects and the effect of loading rate. For static loading the multi- and single temperature methods of reference temperature determination have been tested with the same family of data. The transferability of results received on the small pre-cracked Charpy specimens was analysed and applied with good results.
|
|
|
Complex assessment of fracture properties of cast ferritic steel
Dlouhý, Ivo ; Chlup, Zdeněk ; Kozák, Vladislav ; Holzmann, Miloslav
Complex analysis of fracture behaviour for low carbon manganese steel intended for fabrication of large containers of spent nuclear fuel (SKODA) has been carried out. Two locations, surface layer and central part, of the thick-walled plate have been followed in order to evaluate the material fracture resistance of full-scale cask segment. Fracture toughness data were determined for two different loading rates. Two specimen geometries, standard ones and subsized Charpy type specimens have been applied for the investigation. For dynamic loading two calculation procedures of dynamic fracture toughness determination have been applied, the first one arising from quasistatic approach and the other based on concept of dynamic key curve method. The transferability of results received on the small pre-cracked Charpy specimens was analysed and applied with good results.
|
|
|
Toughness scaling models application
Dlouhý, Ivo ; Kozák, Vladislav ; Holzmann, Miloslav
Toughness scaling model arising from basic definition of Dodds and Anderson has been applied for data adjustment in constraint dependent regime in transition region and data from subsized pre-cracked specimens. Similar model has been developed based on local parameters - Weibull stress and location parameter. The fracture toughness temperature diagram has been predicted by using data from the pre-cracked Charpy type specimen corrected applying the toughness scaling model. Introducing the statistical scale effects corrections good correlation of predicted data to those measured with 1T specimens has been obtained.
|
|
| |
guest ::
