1. The pre-cracking of wide plate specimensVladimir Gliha, Danilo Rojko, 2003, izvirni znanstveni članek Opis: The behaviour of uniformly thick small- and large-scale fracture-toughness specimens was analysed during fatigue-crack progression. Because of the increasing crack length, the stiffness of the specimens decreases. If cyclic loading is applied in the load-control mode, the stress-intensity factor range, ▫$Delta$▫K, and crack growth per cycle, da/dN, increase, which is not appropriate for controlling the size of the crack. The increase in ▫$Delta$▫K for the wide plate (WP) specimens discussed is three times lower than for single edge notch bend (SENB) and compact tension (CT) specimens. The loading range decreases if cyclic loading is applied in the displacement-control mode. The values of ▫$Delta$▫K and da/dN for SENB and CT specimens then decrease, which is helpful for controlling the crack size; however, they increase for the WP specimens in spite of lowering the loading range. This increase is one third lower than for the load-control mode, which means that it is somewhat easier to control the size of crack. Ključne besede: fracture toughness, specimen, pre-cracking, fatigue crak, crack size, stress intensity factor Objavljeno: 01.06.2012; Ogledov: 1243; Prenosov: 72 Povezava na celotno besedilo |
2. Evaluation of stress intensity factors using finite elementsBoštjan Zafošnik, Zoran Ren, Miran Ulbin, Jože Flašker, 2002, objavljeni znanstveni prispevek na konferenci Opis: The paper describes a suitability of Virtual Crack Extension (VCE) method for numerical simulation of crack propagation under mixed mode loading. The suitability of VCE method was determined using The Compact-Tension-Shear (CTS), which is subjected to fracture Mode I, Mode II or mixed mode (Mode I + Mode II) loading. In mixed mode the crack kinks when fracture crack growth occurs. Kink angle is determined with VCE method, which is an energy method, maximum tangential stress (MTS) criterion, strain energy density (SED) criterion and experimental results. Determination of crack propagation angle using MTS and SED criterion is based in regard to the stress intensity factors KI and KII. Stress intensity factors are determined using the maximum energy release rate theory using complex J integral, crack opening displacement method and method of stresses extrapolation. Bigger is the rate between KII and KI, crack path, determined with VCE method, propagates more slowly to the kink angle, determined with experiment. The computational results show that the VCE method is suitable for crack propagation, when KI around the crack tip is dominant. In case where KII is dominant, crack does not kink immediately as in other two criteria. When KII dominates around a crack tip, MTS criterion is the most appropriate for determination of kink angle. Ključne besede: fracture mechanics, stress intensity factors, CTS specimen, crack propagation, virtual crack extension method, strain energy density criterion, maximum tangential stress criterion Objavljeno: 01.06.2012; Ogledov: 1628; Prenosov: 23 Povezava na celotno besedilo |
3. Fracture behaviour of thin sheet stainless steelNenad Gubeljak, Darko Jagarinec, Jožef Predan, John Landes, 2012, objavljeni znanstveni prispevek na konferenci Opis: The differences in fracture behavior between the compact tension C(T) and the middle tensile M(T) specimens make structure integrity assessment uncertain. Two different types of specimens C(T) and M(T) specimens made from stainless steel have been used for fracture toughness testing at the room temperature by the principles of the ASTM 1820-05 standard procedure. Stable crack initiation and crack propagation occurred for the C(T) specimens at lower values of crack driving force than for the M(T) specimens. Crack tip opening displacement-CTOD has been directly measured on the surface of specimens by using a stereo-optical grading method. The critical crack tip opening displacement at crack initiation CTODi has been measured as a plastic Stretch Zone Width (SZW) during a post test fractographic inspection. Comparison between the CTOD-R curves of both types of specimens shows some difference between the C(T) and the M(T) specimens, but a more significant difference appeared in the crack driving force, as consequence of different constraint (triaxiality) of the C(T) versus the M(T) specimens. Therefore, the result obtained by test on laboratory C(T) specimens cannot be directly used as fracture toughness material properties in a structure integrity assessment, except as a conservative lower bound estimate. Ključne besede: stainless steel, compact tension specimen, middle tension specimen, CTOD-R curves Objavljeno: 10.07.2015; Ogledov: 594; Prenosov: 58 Povezava na celotno besedilo |