Abstract: In the present paper, the relation between fatigue crack growth threshold and material’s
cyclic saturation behavior is investigated. The dislocation-free zone (DFZ) model is used to
determine the dislocation distribution ahead of the crack tip. A cohesive zone model is developed to
determine the stress field of the DFZ under cyclic loading. The effect of cyclic loading makes the
plastic zone hardening (or softening), which raises the stress level in DFZ, and may lead to fracture.
It is found that the near threshold characteristics are mostly determined by the cyclic deformation
behavior of the material, and might be theoretically determinable from the standard cyclic loading
Abstract: The stress field of an interfacial crack in non-homogeneous materials is computed using
the semi-analytical method of arbitrary lines (MAL). Then, the eigen-functions of stress, strain and
displacement, i.e. the angular distribution functions near a crack tip, are analyzed based on our
wedge-shape non-homogeneous model. Finally, the growing direction of the interfacial crack is
determined according to the relevant maximum normal stress criterion accurately. Therefore, the
effective approach is provided for solving the complicated crack growing directions of an interfacial
crack in non-homogeneous materials.
Abstract: A two-dimensional cellular automaton (CA) model is developed to simulate damage and
fracture morphology evolution on the mesoscale in materials. The plastic convection of damage is
mapped onto the CA lattice, and initiation, propagation and coalescence of damage are simulated
with a local rule-based scheme of a probability cellular automaton. The model includes known
physical distinctions of fracture behavior between microcracks and microvoids, and they are
characterized by modifying the probability rule of the cellular automaton. The simulations provide
visual insight to understand how those physical processes dynamically progress and they affect the
damage evolution in materials. The modeling can be used to link micromechanical models to
continuum damage models.
Abstract: The combustor chamber, diffuser and nozzle are the main components of the ramjet
engine. In this study, the thermal strength of the combustion chamber of the ramjet engine was
evaluated. The combustion chamber consists of an Inconel alloy 718 liner and a 17-4Ph stainless
steel housing. The liner is rapidly heated to a high temperature. The heated liner is cooled with a
film cooling method that forms a cold boundary layer to separate the hot gas from the surface of the
liner. The thermo-structural analysis is evaluated the thermal strength of super alloy structure with
various thermal insulation performances by finite element method with code MSC/Nastran. The
result of the analysis is compared with accelerated stress rupture test. The experiment is performed
to get safety design and estimate actually life-time for combustor chamber under high temperature.
In general, the work in this paper is helpful to further improve the understanding and evaluation of
thermal strength of the super alloy structure with various thermal insulation performances.
Abstract: According to laboratory accelerated test data, stress corrosion cracking (SCC) in structural
metal materials occurs by initiation and coalescence of micro cracks, subcritical crack propagation
and multiple large crack formation or final failure under the combination of materials, stress and
corrosive environment. In this paper, a Monte Carlo simulation for the process of SCC has been
proposed based on the stochastic properties of micro crack initiation and fracture mechanics concept
for crack coalescence and propagation. The emphasis in the model is put on the influence of the
semi-elliptical surface cracks. The numerical examples for a sensitized stainless steel type 304
indicate the applicability of the present model to the prediction of the SCC behavior in real structures.
Abstract: A method of damage detection and fault diagnosis for gears is presented based on the
theory of elastomeric dynamics according to the theory of cracked beam. It takes an advantage of
accurate fault diagnosis of gear body using the change of dynamic features and has some
advantages for dynamic design of gear systems.The dynamics characteristics, i.e., natural frequency,
vibration shape,dynamic response and so on, due to crack of gear tooth are studied, and the gear
dynamics characteristics caused by the position and size of crack are deeply investigated by
comparison with FEM. The theoretical analysis results are contrasted with numerical simulation
results and shows good agreement with the result by FEM. The proposed method can be used to
detect damage and diagnose fault for gear structures and also can be applied to designing dynamic
characteristics for gear systems.
Abstract: The use of weight function technique in fatigue crack growth subjected to external cyclic
loading and residual stress field has been questioned by several researchers in that the technique is
unable to account for the residual stress redistribution during the crack growth. In this paper a
center cracked tension specimen containing residual stresses was analyzed by finite element
method. The crack growth was simulated by releasing the nodes ahead of crack tip in stepwise and
the stress intensity factors induced by residual stresses at different crack lengths were estimated.
The results from the numerical analysis are identical to the weight function solution, which
demonstrates that the weight function technique can be used for the fatigue crack growth analysis in
residual stress field, unless the residual stress distribution is disturbed by the plastic yield.
Abstract: In this paper, we present an efficient method for conducting a finite element analysis of a
structure with cyclic symmetry and apply the method to analyze the natural vibration and linear and
non-linear static characteristics of a blower impeller. A blower impeller is composed of
circumferentially repeated substructures. The whole structure is partitioned into substructures, and the
finite element analysis can thus be performed with one representative substructure by using the
transformed equations for each number of nodal diameters, which are derived from a discrete Fourier
transform. We calculated the natural vibration and linear and non-linear static characteristics of a
blower impeller without a stiffening ring, and with small as well as large stiffening rings, respectively.
The accuracy and efficiency of the presented method are verified by comparison of the results
obtained from the analysis using a substructure to those obtained using the whole structure.
Abstract: Strengths of multilayered structures have been investigated using three-dimensional
discrete dislocation dynamics (DDD) simulation. The multilayered structure was modeled as a stack
of misfit dislocation networks which must exist at an interface between adjoining crystals having
different lattice constants. Passages of a single mobile dislocation through several kinds of network
stacks were simulated. The critical stress required for the dislocation passage depended on the
dislocation spacing of the network, the number of network sheet and the spacing between network
Abstract: Fatigue strength data of metals are picked up from literature and rearranged on the basis
of the equivalent stress ratio which has previously been proposed by the author. The characteristics
of fatigue strength are especially investigated for metals containing nonmetallic inclusions and
phase in-homogeneity. As a result, it is found that σ
w2 -type fatigue strength is often exhibited even
in a specimen without a notch and it leads to a wide range of scattering of fatigue strength of