Abstract: Stress intensity factor K is analyzed by measuring distribution of sum of the principal
stresses around slit tip by an infrared stress measuring device. Under the biaxial tensile stress, both
K-values of the isotropic materials with slit angle 0° and 45° show there is no influence of the slit
angle at Mode I. The tolerance of the measured K-values of the test specimens which are compared
with measured K-values by photoelastic method are around 10-20and these increase as applied
cyclic load increases. These tolerance can be reduced up to about 8% by modifying measurements.
The effectiveness of the thermoelastic stress measurement method to KI value analyzing under
biaxial tensile stress was confirmed.
Abstract: In this paper the rather complex 3D fatigue crack growth behaviour in a SEN-specimen
under anti-plane shear loading is investigated by the aid of the programme ADAPCRACK3D and
by application of a recently developed 3D fracture criterion. It will be shown that the
computationally simulated results of fatigue crack growth in the FE-model of the specimen are in
good agreement with experimental findings for the development of two anti-symmetric cracks,
which originate from the two crack front corner points, that is where the crack front intersects the
two free side surfaces of the laboratory SEN test-specimens. Consequently, also for this case with a
rather complex 3D crack growth of two anti-symmetric cracks, the functionality of the
ADAPCRACK3D-programme and the validity of the proposed 3D fracture criterion can be stated.
Abstract: Very-High-Cycle Fatigue (VHCF) is the phenomenon of fatigue damage and failure of
metallic materials or structures subjected to 108 cycles of fatigue loading and beyond. This paper
attempts to investigate the VHCF behavior and mechanism of a high strength low alloy steel (main
composition: C-1% and Cr-1.5%; quenched at 1108K and tempered at 453K). The fractography of
fatigue failure was observed by optical microscopy and scanning electron microscopy. The
observations reveal that, for the number of cycles to fatigue failure between 106 and 4×108 cycles,
fatigue cracks almost initiated in the interior of specimen and originated at non-metallic inclusions.
An “optical dark area” (ODA) around initiation site is observed when fatigue initiation from
interior. ODA size increases with the decrease of fatigue stress, and becomes more roundness.
Fracture mechanics analysis gives the stress intensity factor of ODA, which is nearly equivalent to
the corresponding fatigue threshold of the test material. The results indicate that the fatigue life of
specimens with crack origin at the interior of specimen is longer than that with crack origin at
specimen surface. The experimental results and the fatigue mechanism were further analyzed in
terms of fracture mechanics and fracture physics, suggesting that the primary propagation of fatigue
crack within the fish-eye local region is the main characteristics of VHCF.
Abstract: Two phase metals during cyclic loading can suffer from non-uniform load or strain
sharing between the phases due to elastic/plastic anisotropy. This can strongly influence the fatigue
damage and crack initiation behavior. In this study, the fatigue damage and crack initiation behavior
of an austenitic-ferritic duplex stainless steel with anneal/quenched and aged conditions has been
studied by both experimental investigations and simulation using multi-scale material modeling. It
was found, both experimentally and via simulations, that the material damage and crack initiation
start in the ferrite phase in the material with the anneal/quenched condition and in either the ferrite
or austenite phase in the material with the aged condition, mainly in the weakest phase if the
deformation hardening is considered.
Abstract: A special specimen was created cutting a rectangular notched area from the surrounding
of the upper left corner of a wide body aircraft door. This part of the aircraft skin is made of
different layers with variable thickness and material (titanium or aluminum). Then a fatigue traction
load was applied and some notches were cut in the different layers in order to speed up the crack
initiation and reproduce a realistic crack scenario. Such through cracks were monitored during their
propagation along the specimen width, in order to have available for the simulation a realistic initial
scenario and experimental propagation data useful for the correlation with the simulated crack path
and growth rates. In particular an innovative DBEM modelling approach was devised, using a
commercial code (BEASY), capable of explicitly modelling the different test article layers with
their rivet connections even in a two-dimensional approach. The results of the simulation show a
satisfactory correlation with the experimental crack path and growth rates even for such a complex
problem: three different panels (one skin with two doublers), made of different materials, each one
with a variable thickness and connected through numerous rivets (whose shear stiffness is taken into
account for the simulation).
Abstract: In this paper, the problem of torsional buckling of a thin-walled edge cracked column,
under pure bending, is studied. To the authors’ knowledge, this subject has not been widely
investigated in the literature. A cracked member can buckle in the plane orthogonal to the crack and
out of plane triggering the Mode-III crack opening. Analytical expressions for the characteristic
equation are derived for an I-beam. The influence of the crack length and position on the buckling
load is investigated.
Abstract: In this study, it was made clear that the non-linear notch mechanics is useful not only in
the case of uniaxial tension but also in the case of biaxial tension. The difference of both cases is as
follows. In the former the plastic strain field near a notch root is determined by εp
strain at a notch root) and ρ (notch root radius) alone, but in the latter case it is determined by
y0,FEM, ρ and stress ratio k=σxn/σyn.
Abstract: The present paper describes a numerical method which is able to calculate the stress
intensity factor in two dimensional heterogeneous materials under mechanical and thermal loads.
The proposed method uses two hybrid element formulations to model the second phase
heterogeneities of the material and the crack tips. The method was used to analyse alumina-zirconia
ceramic materials, and the effects due to the zirconia t→m phase transformation and the thermal
stresses, which develop during the cooling stage of sintering, were taken into account in calculating
the stress intensity factor.
Abstract: The purpose of this study is to investigate the wear characteristics of yttria-stabilized
zirconia coating as a function of effect on post-spray heat treatment. We concerned that the residual
stress is due to during cooling from a high deposition temperature. We will focus on the tribological
wear performance as a magnitude of residual stress. The effect of residual stress as post-spay heat
treatment temperature will be discussed. The plasma-sprayed 8%Y2O3-Zirconia coating is studied
to know the relationship between phase transformations and wear properties after post-spray heat
treatment. Wear tests is carried out with ball on disk type on 50 N, 70 N, 90 N under room
temperature. The transformation of phase and magnitude of residual stress are measured by x-ray
diffraction method (XRD). Tribological characteristics and wear mechanism for post-spray heat
treatment is observed by SEM.
Abstract: The problem of an edge-bridged crack terminating perpendicular to a bimaterial interface
in a half- space is analyzed for a general case of elastic anisotropy bimaterials and specialized for
the case of orthotropic bimaterials. The edge crack lies in the surface layer of thickness h bonded to
semi-infinite substrate. It is assumed that long fibres bridge the crack. Bridging model follows from
the assumption of “large” slip lengths adjacent to the crack faces and neglect of initial stresses. The
crack is modelled by means of continuous distribution of dislocations, which is assumed to be
singular at the crack tip. With respect to the bridged crack problems in finite dissimilar bodies, the
reciprocal theorem (ψ - integral) is discussed as to compute, in the present context, the generalized
stress intensity factor through the remote stress and displacement field for a particular specimen
geometry and boundary conditions using FEM.