Dynamic fracture mechanics assessments by simultaneous magnetic emission and potential drop techniques

Modern structural integrity assessment procedures incorporate fracture mechanical concepts most of which rely on dynamic fracture mechanics parameter determination from experiments. In the case of dynamic loading conditions, various experimental methods have evolved for determining the loading parameters and load-displacement behaviour. Ductile structural steel has many applications and its properties are interesting for designing experiments that simulate ductile, brittle and mixed fracture behaviour. In this study are presented the results of fracture mechanics investigations of a ductile ferromagnetic low-alloy high strength steel, performed under dynamic loading conditions. Standard Charpy specimens are tested by simultaneous coupled magnetic emission (ME) and potential drop (PD) techniques for determining critical crack initiation properties and resistance curve determination of a ductile steel behaviour. Equivalent brittle, ductile, and mixed mode fracture behaviour may be simulated by choice of test temperature and impact velocity. Analysis of integrated ME and PD signal data, employed in deriving critical J integral, has been successful in interpreting unstable or stable crack initiation and propagation. Experimental results are discussed with respect to the characteristics and the physical interpretations of both of the independent experimental techniques. Some specific experimental difficulties in the reliable assessment of dynamic crack initiation parameters are outlined

Dynamic fracture mechanics assessments by simultaneous magnetic emission and potential drop techniques

Modern structural integrity assessment procedures incorporate fracture mechanical concepts most of which rely on dynamic fracture mechanics parameter determination from experiments. In the case of dynamic loading conditions, various experimental methods have evolved for determining the loading parameters and load-displacement behaviour. Ductile structural steel has many applications and its properties are interesting for designing experiments that simulate ductile, brittle and mixed fracture behaviour. In this study are presented the results of fracture mechanics investigations of a ductile ferromagnetic low-alloy high strength steel, performed under dynamic loading conditions. Standard Charpy specimens are tested by simultaneous coupled magnetic emission (ME) and potential drop (PD) techniques for determining critical crack initiation properties and resistance curve determination of a ductile steel behaviour. Equivalent brittle, ductile, and mixed mode fracture behaviour may be simulated by choice of test temperature and impact velocity. Analysis of integrated ME and PD signal data, employed in deriving critical J integral, has been successful in interpreting unstable or stable crack initiation and propagation. Experimental results are discussed with respect to the characteristics and the physical interpretations of both of the independent experimental techniques. Some specific experimental difficulties in the reliable assessment of dynamic crack initiation parameters are outlined

Magnetic emission technique in assessing dynamic fracture mechanics parameters of ductile steel

Novi izazovi u proceni integriteta konstrukcija, uključujući identifikaciju opuštanja i produžetak radnog veka konstrukcionih čelika putem kvalitativnog i kvantitativnog određivanja dinamičkih parametara mehanike loma, imaju veliki značaj. Problematika eksperimentalnih istraživanja u vezi je sa preciznim određivanjem otpornosti na lom u uslovima dinamički opterećenih konstrukcija, gde još uvek nisu definisane standardne procedure u slučaju šarpi epruveta sa zamornom prslinom. Izvedeno je instrumentirano šarpi ispitivanje upotrebom tehnike magnetne emisije (ME) radi određivanja osobina kritične inicijacije prsline kod čelika sa izrazitim duktilnim svojstvima. Ekvivalentno krto, duktilno i mešovito ponašanje loma dobijeno je izborom temperature ispitivanja i brzine udara. Uspešno je sprovedena analiza i odgovarajuća interpretacija snimljenih ME signala i integrisanih ME signala, koji su upotrebljeni za izračunavanje kritičnog dinamičkog J integrala u slučaju nestabilnog ili stabilnog razvoja prsline.Concerning new challenges in structural integrity assessment, the identification of relaxation and service life extension of structural steels by qualitative and quantitative determination of dynamic fracture mechanics parameters is highly significant. Problems in experimental research are in connection with precise determination of resistance to fracture in conditions of dynamic loading of structures, where standard procedures in the case of precracked Charpy specimens are yet to be defined. Instrumented Charpy testing is performed by magnetic emission (ME) technique for determining critical crack initiation properties in a steel of dominant ductile properties. The equivalent brittle, ductile, and mixed fracture behaviour is simulated by the choice of test temperature and impact velocity. Analysis of acquired ME and integrated ME signals, both employed in deriving the critical J integral, has been successful in interpreting the results for unstable or stable crack propagation

Magnetic emission technique in assessing dynamic fracture mechanics parameters of ductile steel

Novi izazovi u proceni integriteta konstrukcija, uključujući identifikaciju opuštanja i produžetak radnog veka konstrukcionih čelika putem kvalitativnog i kvantitativnog određivanja dinamičkih parametara mehanike loma, imaju veliki značaj. Problematika eksperimentalnih istraživanja u vezi je sa preciznim određivanjem otpornosti na lom u uslovima dinamički opterećenih konstrukcija, gde još uvek nisu definisane standardne procedure u slučaju šarpi epruveta sa zamornom prslinom. Izvedeno je instrumentirano šarpi ispitivanje upotrebom tehnike magnetne emisije (ME) radi određivanja osobina kritične inicijacije prsline kod čelika sa izrazitim duktilnim svojstvima. Ekvivalentno krto, duktilno i mešovito ponašanje loma dobijeno je izborom temperature ispitivanja i brzine udara. Uspešno je sprovedena analiza i odgovarajuća interpretacija snimljenih ME signala i integrisanih ME signala, koji su upotrebljeni za izračunavanje kritičnog dinamičkog J integrala u slučaju nestabilnog ili stabilnog razvoja prsline.Concerning new challenges in structural integrity assessment, the identification of relaxation and service life extension of structural steels by qualitative and quantitative determination of dynamic fracture mechanics parameters is highly significant. Problems in experimental research are in connection with precise determination of resistance to fracture in conditions of dynamic loading of structures, where standard procedures in the case of precracked Charpy specimens are yet to be defined. Instrumented Charpy testing is performed by magnetic emission (ME) technique for determining critical crack initiation properties in a steel of dominant ductile properties. The equivalent brittle, ductile, and mixed fracture behaviour is simulated by the choice of test temperature and impact velocity. Analysis of acquired ME and integrated ME signals, both employed in deriving the critical J integral, has been successful in interpreting the results for unstable or stable crack propagation

Analytical solution of elastic-plastic stresses in thin rotating disc made up of piezoelectric material

This paper presents an analytic solution of transitional and plastic stresses in a thin rotating disc made up of piezoelectric material under internal pressure. The stresses in the rotating disc are calculated by applying the transition theory. The transitional and fully plastic stresses are derived with the help of stress strain relations. A nonlinear differential equation is obtained by substituting the resultant relations into the equilibrium equation. The solution of the differential equation with applied boundary conditions gives stresses, pressure and electric displacement. The results obtained are presented graphically and analysed numerically. It has been concluded on the basis of the study that isotropic material is better than piezoelectric material

Analytical solution of elastic-plastic stresses in thin rotating disc made up of piezoelectric material

This paper presents an analytic solution of transitional and plastic stresses in a thin rotating disc made up of piezoelectric material under internal pressure. The stresses in the rotating disc are calculated by applying the transition theory. The transitional and fully plastic stresses are derived with the help of stress strain relations. A nonlinear differential equation is obtained by substituting the resultant relations into the equilibrium equation. The solution of the differential equation with applied boundary conditions gives stresses, pressure and electric displacement. The results obtained are presented graphically and analysed numerically. It has been concluded on the basis of the study that isotropic material is better than piezoelectric material

Finite creep deformation in thick-walled circular cylinder with varying compressibility under external pressure

Creep stresses have been obtained for thick-walled circular cylinder of compressibility varying radially under external pressure with the help of transition theory using the concept of generalized principal strain measure. This theory simplifies the constitutive equations by prescribing a priory the order of the measure of deformation. Results have been analysed and discussed numerically as well as graphically. From the numerical results, it has been observed that homogeneous material is on the safer side of the design and also highly compressible cylinder made of either homogeneous or non-homogeneous material is also on the safer side of the design

Numerical aspects for efficient welding computational mechanics

The effect of the residual stresses and strains is one of the most important parameter in the structure integrity assessment. A finite element model is constructed in order to simulate the multi passes mismatched submerged arc welding SAW which used in the welded tensile test specimen. Sequentially coupled thermal mechanical analysis is done by using ABAQUS software for calculating the residual stresses and distortion due to welding. In this work, three main issues were studied in order to reduce the time consuming during welding simulation which is the major problem in the computational welding mechanics (CWM). The first issue is dimensionality of the problem. Both two- and three-dimensional models are constructed for the same analysis type, shell element for two dimension simulation shows good performance comparing with brick element. The conventional method to calculate residual stress is by using implicit scheme that because of the welding and cooling time is relatively high. In this work, the author shows that it could use the explicit scheme with the mass scaling technique, and time consuming during the analysis will be reduced very efficiently. By using this new technique, it will be possible to simulate relatively large three dimensional structures