Iskanje po katalogu digitalne knjižnice

Opis: The heterogeneity of welded joints’ microstructure affects their mechanical properties, which can vary significantly in relation to specific weld zones. Given the dimensional limitations of the available test volumes of such material zones, the determination of mechanical properties presents a certain challenge. The paper investigates X welded joint of S690QL1 grade high strength steel (HSS), welded with slightly overmatching filler metal. The experimental work is focused on tensile testing to obtain stress-strain properties, as well as fracture mechanics testing. Considering the aforementioned limitations of the material test volume, tensile testing is carried out with mini tensile specimens (MTS), determining stress-strain curves for each characteristic weld zone. Fracture mechanical testing is carried out to determine the fracture toughness using the characteristic parameters. The experimental investigation is carried out using the single edge notch bend (SENB) specimens located in several characteristic welded joint zones: base metal (BM), heat affected zone (HAZ), and weld metal (WM). Fractographic analysis provides deeper insight into crack behavior in relation to specific weld zones. The numerical simulations are carried out in order to describe the fracture behavior of SENB specimens. Damage initiation and evolution is simulated using the ductile damage material behavior. This paper demonstrates the possibility of experimental and numerical determination of fracture mechanics behavior of characteristic heterogeneous welded joint zones and their influence on crack path growth.
Ključne besede: heterogeneous welded joint, high strength steel, mechanical testing, damage, fracture, mechanical properties, finite element analysis
Objavljeno v DKUM: 30.11.2023; Ogledov: 405; Prenosov: 34
Celotno besedilo (11,25 MB)
Gradivo ima več datotek! Več...

Opis: A two-dimensional computational model for simulation of contact fatigue of gear teeth flanks is presented. In the model, it is assumed that the initial crack of length 0.015 mm is initiated at the surface due to previous mechanical or heat treatment of the material as well as a consequence of the running in process. The discretized model with the initial crack is then subjected to normal contact pressure, which takes into account the elasto-hydro-dynamic (EHD) lubrication conditions, and tangential loading due to friction between contacting surfaces. The model also considers the moving contact of gear flanks, fluid trapped in the crack and residual stresses due to heat treatment of the material on crack propagation. The virtual crack extension (VCE) method, implemented in the finite element method, is then usedfor simulating the fatigue crack growth from the initial crack up to the formation of the surface pit. The computational results show that the initial surface crack of length 15 m and the considered boundary conditions lead to the appearance of very small surface pits, which can be termed as micro-pitting on gear teeth flanks. The numerical results correspond well withavailable experimental data.
Ključne besede: machine elements, gearing, fracture mechanics, numerical analysis, micro pitting, pitting simulation, matematical model, fatigue, contact mechanics, crack propagation
Objavljeno v DKUM: 01.06.2012; Ogledov: 2660; Prenosov: 0

Opis: The re-characterisation of complex defects with re-entrant sectors has been addressed for cracks extending by fatigue, ductile tearing and cleavage. In Part I crack extension by fatigue and ductile tearing was discussed. In Part II cleavage data are presented for a family of complex defects with re-entrantsectors. Experimental tests on complex and re-characterised profilesare analysed using deterministic and probabilistic approaches. The work addresses the conservatism of re-characterisation procedures when appliedto cleavage failure on the lower shelf and in the ductile-brittle transition.
Ključne besede: fracture mechanics, structural elements, complex defects, recharacterisation, line-spring analysis, cleavage failure, constraint, statistical fracture mechanics, numerical analysis
Objavljeno v DKUM: 01.06.2012; Ogledov: 1461; Prenosov: 102
Povezava na celotno besedilo

Opis: The paper describes modelling approach to computational simulation of surface crack growth subjected to lubricated rolling-sliding contact conditions. The model considers the size and orientation of the initial crack, normal and tangential loading due to rolling-sliding contact and the influence of fluid trapped inside the crack by a hydraulic pressure mechanism. The motion of the contact sliding load is simulated with different load cases. The strain energy density (SED) and maximum tangential stress (MTS) crack propagation criteria are modified to account for the influence of internal pressure along the crack surfaces due to trapped fluid. The developed model is used to simulate surface crack growth on a gear tooth flank, which has been also experimentally tested. It is shown that the crack growth path, determined with modified crack propagation criteria, is more accurately predicted than by using the criteria in its classical form.
Ključne besede: fracture mechanics, numerical methods, contact loading, finite element analysis, internal pressure, maximum tangential stress, strain energy density, surface crack growth
Objavljeno v DKUM: 01.06.2012; Ogledov: 2689; Prenosov: 98
Povezava na celotno besedilo

Opis: The paper deals with the research on the crack growth in a bolt connection of a lug for crane counter weight bars. Counter weight bars are structural elements subjected to very heavy loads and therefore need special attention. The main purpose of this research is to determine the number of load cycles required for a crack to propagate from initial to criticakl crack length, whenthe final failure can be expected to occur. All required material parameters and experimental results were determined in our previous research. The influence of the initial crack siye upon the remaining life of the lug is reserched numericallu by means of FE analysis and analytically by use of the corrected analystical model.
Ključne besede: fracture mechanics, cyclic loading, fatigue crack growth, service life prediction, numerical analysis, bolt connection
Objavljeno v DKUM: 31.05.2012; Ogledov: 2502; Prenosov: 127
Povezava na celotno besedilo