Abstract: Widespread Fatigue Damage (WFD) is a technical expression used in the certification of
aircraft. The paper presents a set of issues which may influence the probability that a structural item
exhibits WFD. The paper mainly follows the line of a stochastic approach to these subjects, and
includes the influence of realistic parameters - like manufacturing - and tries to assess what may be
the impact of new technologies.
Abstract: In this paper, intergranular microfracture evolution in polycrystalline brittle materials
is simulated using a cohesive grain boundary integral formulation. A linear cohesive law is used for
modelling multiple microcracking initiation and propagation under mixed mode failure conditions,
encountering the stochastic e=ects of the grain location, morphology and orientation. Furthermore,
in cases where crack surfaces come into contact, slide or separate, fully frictional contact analysis is
Abstract: As part of the requirement to demonstrate safe operation of the steel reactor pressure
vessels for the UK Magnox fleet, surveillance samples were installed at the time of construction.
These were representative of the steels and weld metals used for the manufacture of the vessels.
The history of sample removal and mechanical property testing is briefly reviewed. The factors
leading to changes in the fracture resistance and tensile properties will be discussed. The link is
described between the mechanisms leading to changes in mechanical properties and the statistically
based approach adopted to predict values of fracture toughness for the neutron dose and
temperatures at key vessel locations. Predictions are compared with test results obtained from
samples removed from a decommissioned reactor and also surveillance and accelerated radiation
samples removed towards the end of reactor life.
Abstract: Under the assumption that the artificial viscosity coefficient at the propagating crack tip
is in inverse proportion to power law of the plastic strain rate, a rate-sensitive constitutive
relationship is derived for perfect elastic-plastic material. With the adoption of the rate-sensitive
constitutive relationship, it is asymptotically investigated the propagating tip fields of plane strain
mode I. And the quasi-static equations are obtained separately governing the stress and strain fields
at the crack-tip by means of Airy stress function. Numerical calculations of governing equations are
carried out by double parameters shooting, with selections of appropriate values of each
characteristic parameter by combinations of boundary, and the fully continuous stress-strain fields
are obtained at the crack-tip. The analytical and computational results indicate that viscosity effect
is an important factor in crack-tip fields.
Abstract: In the petroleum engineering, the nonlinear bulk strain or bulk strain rate must be
considered in rock deformation, adopting the viscous-elastic theory, a constitutive equation of the
pressure-sensitive dilatant materials was established. The governing eqations were deducted in
crack-tip field of quasi-static growing crack in pressure-sensitive dilatant materials. And for the
mechanical model of a rigid-viscoelastic material interfacial crack, through numerical calculate, the
asymptotic solution of the continuous separate variable formal of stress, strain and displacement.
The significance of the material parameter in the crack-tip field is discussed. The study of the paper
will provide theoretical references for preventing the glide of the mud rock and reducing the arises
of the failure of casings of well.
Abstract: In this paper, the conception of natural fracture stress in rocks is given according to
mesomechanics analysis. The quantitative analysis about wellbore collapse and stratum fracture is
made and the density range of drilling fluid is determined. The result is the same as the conclusion
which was given by the traditional Mohr-Coulomb criterion in petroleum engineering. The new
method of combining mesomechanics with fracture mechanics is used to study the wellbore
stability in petroleum engineering, which can reveal the nature of the rock deformation mechanism
and provide theoretical reference to design of the drilling engineering.
Abstract: In this paper, the dynamic interaction is investigated theoretically between a crack and a
circular cavity in an infinite piezoelectric medium under time-harmonic incident anti-plane shearing.
The formulations are based on the method of complex variable and Green’s function. The resulting
dynamic stress intensity factors at the crack’s tip and dynamic stress concentration factors at the
cavity’s edge are obtained with crack-division technique. Numerical results are plotted to show how
the frequencies of incident wave, the piezoelectric characteristic parameters of the material and the
geometry of the crack and the circular cavity influence upon the dynamic stress intensity factors and
dynamic stress concentration factors.
Abstract: The non-equilibrium grain-boundary segregation (NGS) isotherms and its kinetics serve
to provide a more complete understanding of inter-granular segregation behavior in relation to
mechanical properties, not only for the engineering steels but also for a wide range of structural
alloys. The NGS of phosphorus and temper embrittlement dynamics on the same heat treatment
condition at the same isothermal holding time in two Cr-Mo steels, 12Cr1MoV and 2.25Cr1Mo,
was experimentally studied. The fracture behaviour was also observed by tensile tests in situ in a
scanning electron microscope (SEM). Results show that both the concentration of phosphorus
atoms in grain boundaries and the degree of embrittlement reaches a maximum at the critical time.
It can be satisfactorily elucidated by the temper embrittlement mechanism of NGS caused by
cooling from solution temperature to isothermal holding temperature.
Abstract: For most of the experiments and the practical problems about the non-equilibrium
grain-boundary segregation (NGS), segregation will always occur during continuous cooling. The
effective-time-method assumed that any continuous cooling curve for a sample can be replaced by a
corresponding stepped curve. In this paper, the non-equilibrium grain-boundary segregation of
phosphorus in step cooling process in an industrial steel12Cr1MoVis studied based on the
effective-time-method and compared with that in isothermal holding process. Results show that the
calculated result is in good accordance with the experimental observation. It provides a direct
support for the effective-time-method of NGS. The step cooling process can speed-up the
embrittlement of the steel. Based on the step cooling technique, a control method of grain-boundary
brittleness is proposed.
Abstract: When stress is high, delaminate damage can be induced by transverse cracks. A complete
parabolic shear-lag damage model containing delamination induced by transverse cracks is
therefore proposed and applied to predict the stiffness reduction by transverse cracking in cross-ply
laminated composite materials. The predictions of the complete parabolic shear-lag analysis
model, the incomplete parabolic shear-lag analysis model, and the complete parabolic shear-lag
damage model containing delamination proposed in this paper have been compared. Results show
that the young’s modulus reduction values obtained by our analysis model are better agreement with
the experimental ones than other models.