R. Lacalle

Use of Small Punch Notched Specimens in the Determination of Fracture Toughness

In recent years an increasing interest has been shown in materials characterisation techniques based on the use of reduced dimension samples. One of these techniques, first developed in the early 80’s, is Small Punch testing, in which a punch acts over a plane small specimen deforming it until fracture. So far, this test has been used as a tool for the estimation of mechanical properties, for characterising ductilebrittle transition or for knowing the evolution of these properties with ageing phenomena as neutron irradiation. The Small Punch Test has even been used in the determination of fracture toughness by means of indirect correlations or complex methodologies based on damage models and Finite Element simulations. In this paper, a direct methodology for the determination of fracture toughness from Small Punch tests is proposed. The approach is based on the use of simply modified Small Punch specimens in which a lateral notch was machined. Attending to energy considerations, the J-Δa curve for a ship-building Grade A steel, as well as for a structural steel, E690, has been obtained using this type of samples and the results have been compared with the calculated results from conventional fracture tests.Copyright

Transition Region of Nuclear Vessel Steels: Master Curve Approach Using Small Punch Notched Specimens

The behaviour of the materials in ductile-brittle transition region must be known when performing structural integrity assessments of nuclear reactor vessels working under the effects of neutron irradiation. The characterisation of this region has been usually carried out by means of Charpy impact tests. Just during last few years new approaches based on direct fracture mechanics tests have begun to be used. In most of these cases, the Master Curve methodology, which allows the transition region to be characterised using only one parameter (T0 reference temperature), has been employed. In this paper the transition region of two materials –one vessel steel and one common structural steel-has been characterised by means of Small Punch Tests. First of all, this zone has been characterised using conventional specimens and the results were compared with those of Charpy impact tests. Finally a new approach based on the use of notched Small Punch samples together with Master Curve methodology has been proposed.

Using Small Punch tests in environment under static load for fracture toughness estimation in hydrogen embrittlement

In this paper, the response of three medium and high-strength steels to hydrogen embrittlement is analyzed by means of the quasi-non-destructive test known as the Small Punch Test (SPT). SPT tests on notched specimens under static load are carried out, applying Lacaclles methodology to estimate the fracture toughness for crack initiation, comparing the results to KIEAC fracture toughness obtained from C(T) precracked specimens tested in the same environment; SPT showed good correlation to standard tests. A novel expression was proposed to define the parameter KIEAC-SP as the suitable one to estimate the fracture toughness for crack initiation in hydrogen embrittlement conditions by Small Punch means, obtaining good accuracy in its estimations. Finally, Slow Rate Small Punch Tests (SRSPT) are proposed as a more efficient alternative, introducing an order of magnitude for the adequate rate to be employed.

Structural Integrity of a NPP Using the Master Curve Approach

In this paper it is described the work performed on the steel coming from a Spanish BWR Nuclear Power Plant (NPP) vessel currently operating in order to analyse its structural integrity assessment from different procedures. The classical procedures for the characterization of the cuasistatic fracture behaviour in the ductile to brittle transition region [1] are based on conservative correlations obtained from Charpy impact tests. In this work, on the contrary, direct measurements of cuasistatic KJC fracture toughness were performed. The results were analysed according to the recent Master Curve methodology [2] in order to obtain the Reference Temperature, T0, describing fairly the response of the material in such a region.