Bioceramics 20

Vols. 361-363

Vols. 361-363

Advances in Grinding and Abrasive Technology XIV

Vols. 359-360

Vols. 359-360

Progresses in Fracture and Strength of Materials and Structures

Vols. 353-358

Vols. 353-358

Innovation in Ceramic Science and Engineering

Vol. 352

Vol. 352

Composite Materials V

Vol. 351

Vol. 351

Electroceramics in Japan X

Vol. 350

Vol. 350

Advances in Fracture and Damage Mechanics VI

Vols. 348-349

Vols. 348-349

Damage Assessment of Structures VII

Vol. 347

Vol. 347

The Mechanical Behavior of Materials X

Vols. 345-346

Vols. 345-346

Sheet Metal 2007

Vol. 344

Vol. 344

Advanced Biomaterials VII

Vols. 342-343

Vols. 342-343

Engineering Plasticity and Its Applications

Vols. 340-341

Vols. 340-341

Progress of Precision Engineering and Nano Technology

Vol. 339

Vol. 339

# Advances in Fracture and Damage Mechanics VI

Volumes 348-349

doi: 10.4028/www.scientific.net/KEM.348-349

Paper Title Page

Abstract: Cyclic loading of metallic engineering components at constant elevated or fluctuating
temperature causes a complex evolution of damage which be can hardly be described in a unique
and straightforward manner. Often the thermal behaviour of the base metals is to weak, so thermal
barrier coatings were needed. Nickel is generally used for such thermal barrier coatings. Therefore
it is necessary to study the thermo-mechanical fatigue (TMF) of this material. The lifetime of these
coatings is very strong affected by the temperature loading in general, both described by nodal
temperatures and their local gradient. The thermal cyclic loading takes place as thermo-mechanical
and low cycle fatigue (LCF) damage regime. To classify the thermo-mechanical failure mechanism
of pure nickel, OP (out of phase) and IP-TMF (in phase) test series were examined. The use of
damage parameters like the unified energy approach make sense, a more detailed life time
calculation for pure Nickel can be done by using the Neu-Sehitoglu model. Summary, thermomechanical
loadings activate multiple damage mechanism. Surface embrittlement by oxidation is
the major distinctive mechanism in addition to pure fatigue damage. Different lifetime approaches
were tested and analysed to fulfil the requirements for the fatigue analysis of nickel made
components.

793

Abstract: Finite element method (FEM) is used widely for various structural problems. However, in
general, it is difficult to guarantee the accuracy of results obtained by commercial software of FEM. In
this paper, a practical finite element technique for calculating the stress concentration factors with
high accuracy is proposed in consideration of physical meaning of stress concentration, and applied to
a 2-dimentional stress problem.

797

Abstract: The nanoindentation test in the dislocation free crystal of copper is simulated by finite
element calculations coupled with ab initio calculation of ideal shear strength. The onset of
microplasticity, associated with the pop-in effect identified in experimental nanoindentation tests
(creation of first dislocations), is assumed to be related to the moment of achieving the value of the
ideal shear strength for the copper crystal. This value also depends on the normal stress in the
critical shear system in an approximately linear way, as follows from recently published first
principle calculations. The calculated values of the critical shear stress (related to the ideal shear
strength) lie exactly at the lower limit of the range of experimentally observed pop-ins in the copper
crystal.

801

Abstract: The power law hardening constitutive relations for porous material were established by the
material yield function. An idealized interface fracture model was established in which the indenter as
rigidity was embedded in the porous material. Under the condition of plane strain, through the
analysis of the singularity of the stress and strain and combining the motion and compatibility
equations, the governing equation of the wedge-tip was deduced. With the help of numerical
calculations and boundary conditions, the asymptotic solutions of the stress and strain near the
wedge-tip were obtained. Finally, the influence of the material constants α (pressure sensitive
coefficient), the angle of the indenter and the interfacial friction on the fracture of the porous material
was discussed.

805

Abstract: In the present study the damage mechanism of Alkali-Silica-Reaction (ASR) in concrete
bearing reactive volcanic rock is investigated. A combined numerical and experimental research is
presented. The mechanism of ASR is investigated on a concrete microbar specimen by using various
microscopy techniques. A meso mechanical model based on lattice theories is used as a starting point.
Variables in the model are the properties of the concrete components on the meso-level, like
mechanical properties of cement paste, aggregates, dissolved aggregate, bond properties and finally
the properties of the gel. It is found that current numerical model is able to simulate ASR cracks
similar to the experimental observations.

809

Abstract: The parametric variational principle adopts the extreme variational idea in the modern
control theory and uses state equations deduced from the constitutive law to control the functional
variation, which is an effective solution to the nonlinear equations. Based on the fundamental
equations of elasto-plasticity coupled damage problem, the potential functional of elasto-plasticity
is constructed. Also the state equations with approximation of damage evolution equation and load
functions are constructed in the paper. The solution of elasto-plasticity damage problem can be
deduced to solve problem of the minimum potential energy function under the restriction of state
equations. Thus the parametric variational principle for coupled damage is proposed. The
variational principle has the virtue of definite physical meaning and the finite element equations are
presented in the article to facilitate the application of parametric variatioal principle, which is easy
to program on computer. Using the method mentioned in the article, a numerical calculation is
carried out and the calculation result shows that the method is efficient for solving elasto-plasticity
damage problem.

813

Abstract: The viscosity of material is considered at propagating crack-tip. Under the assumption
that the artificial viscosity coefficient is in inverse proportion to the power law of the plastic strain
rate, an elastic-viscoplastic asymptotic analysis is carried out for moving crack-tip fields in
power-hardening materials under plane-strain condition. A continuous solution is obtained
containing no discontinuities. The variations of the numerical solution are discussed for mode I
crack according to each parameter. It is shown that stress and strain both possess exponential
singularity. The elasticity, plasticity and viscosity of material at the crack-tip only can be matched
reasonably under linear-hardening condition. The tip field contains no elastic unloading zone for
mode I crack.

817

Abstract: A crack in an infinite plate of functionally graded materials (FGMs) under anti-plane
shear impact loading is analyzed by making use of non-local theory. The shear modulus and mass
density of FGMs are assumed to be of exponential form and the Poisson’s ratio is assumed to be
constant. The mixed boundary value problem is reduced to a pair dual integral equations through
the use of Laplace and Fourier integral transform method. In solving the dual integral equations, the
crack surface displacement is expanded in a series using Jacobi’s polynomials and Schmidt’s
method is used. The numerical results show that no stress singularity is present at the crack tip. The
stress near the crack tip tends to increase with time at first and then decreases in amplitude and the
peak values of stress decreases with increasing the graded parameters.

821

Abstract: An R-curve formula for ultra high performance cementitious composites is derived in this
paper. The fracture mechanics based on R-curve is used to predict the load-deflection relation of
ultra high performance cementitious composites. The reductions of stress intensity factor and
CTOD by steel fiber reinforcement are assumed as conforming linear distribution along crack
propagation. The effective numbers of steel fiber on unit area based uniform distribution is used
here. Results of the theoretical predictions show a good agreement with test results of three point
bending beam of UHPCC. The modified R-curve formula for UHPCC can be a reference for future
study of fracture performances of UHPCC.

825

Abstract: Direct uniaxial tension test of ultra high performance cementitious composites I shape
specimens have been investigated in this paper. A nonlinear analytical model based on continuum
damage mechanics is developed to characterize tensile stress-strain constitutive response of UHPCC.
Basic governing equations of damage evolution and material constitutive relation are established
considering random damage which conforms to a modified Weibull type distribution proposed in
this paper. Calculation suggests that Weibull distribution can describe damage evolution of UHPCC
and predict the constitutive relation and damage evolution equation.

829