Abstract: In this paper, the local approach was used to analyze the geometry dependence of coating
specimens for interface brittle fracture initiation, and a definition of the fracture process zone was
proposed in the paper. The results showed that the interface fracture behavior of two types of
specimens with notch had been predicted from the test results of pre-crack specimens based on the
local approach for interface brittle fracture, and the predicted distribution of the critical load for the
notched specimens gave a good agreement with the test results. It indicated that the local approach not
only can be used to describe the interface fracture behavior, but also can be used in the integrity
evaluation for interface between different materials.
Abstract: A steady-state subsonic interface crack propagating between an elastic solid and a rigid
substrate with crack face contact is studied. Two cases with respective to the contact length are
considered, i.e., semi-infinite and finite crack face contact. Different from a stationary or an open
subsonic interface crack, stress singularity at the crack tip in the present paper is found to be
non-oscillatory. Furthermore, in the semi-infinite contact case, the singularity of the stress field near
the crack tip is less than 1/2. In the finite contact case, no singularity exists near the crack tip, but less
than 1/2 singularity does at the end of the contact zone. In both cases, the singularity depends on the
linear contact coefficient and the crack speed. Asymptotic solutions near the crack tip are given and
analyzed. In order to satisfy the contact conditions, reasonable region of the linear contact coefficient
is found. In addition, the solution predicts a non-zero-energy dissipation rate due to crack face
Abstract: Interfacial stress distribution of bonded quarter-planes subjected to a concentrated force
was re-investigated based on Bogy’s solution. The characteristic length of the singular interface end,
δ, was defined, and found varying in a very large size scale with the index of stress singularity from
millimeter to nanometer or even smaller scale. The influences the characteristic length scale on the
initial debonding of the interface end is a new question worth to pay attention. Photoelasticity
experiment was employed to verify whether the initial debonding is always located at interface end
with stress singularity. The test results show that the initial debonding does not start from singular
interface end if the index of stress singularity is small enough.
Abstract: Nonlinear finite element model analysis of the casing plug joints of steel tubular has been
realized by ANSYS software. The law of load-carrying capability and stiffness of joint are separately
gained by changing the ratio of length and diameter (R/L) and the ratio of the casing length and the
main tube length (l/L). The influence of the casing thickness on the load-carrying capability and
stiffness are also discussed. The results indicated that the load-carrying capability and stiffness of the
joints both increase with the ratio(R/L) increment and the ratio of the casing length and main tube
length (l/L). When the main tube thickness is equal to casing thickness, the load-carrying capacity of
joints achieves the most.
Abstract: The failure in an adhesive-bonded structure starts at the interface, and the interfacial
fracture is of interest whenever adhesion between different materials is concerned. One of primary
factors limiting the application of adhesive-bonded joints to structural design is the lack of a good
evaluation tool for adhesion strength to predict the load-bearing capacity of boned joints. The
adhesion strength of composite/steel bonding has been evaluated using interfacial fracture mechanics
characterization. The energy release rate of a composite/steel interfacial crack was compared with the
fracture toughness of the interface, which was measured from bi-material end notched flexure (ENF)
specimens, to predict the failure loads of bi-material lap joints. Fracture toughness, IIc G , was regarded
as a property of the interface rather than a property of the adhesive. The results show that interfacial
fracture mechanics characterization of adhesion strength can be a practical engineering tool for
predicting the load-bearing capacities of adhesive-bonded joints.
Abstract: An axisymmetric problem of interaction of a rigid rotating flat ended punch with a
transversely isotropic linear piezoelectric half-space is considered. The contact zone consists of an
inner circular adhesion region surrounded by an outer annular slip region with Coulomb friction.
Beyond the contact region, the surface of the piezoelectric half-space is free from load. With the aid
of the Hankel integral transform, this mixed boundary value problem is formulated as a system of
dual integral equations. By solving the dual integral equations, analytical expressions for the
tangential stress and displacement, and normal electric displacement on the surface of the
piezoelectric half-space are obtained. An explicit relationship between the radius of the adhesion
region, the angle of the rotation of the punch, material parameters, and the applied loads is presented.
The obtained results are useful for characterization of piezoelectric materials by micro-indentation
and micro-friction techniques.
Abstract: Adhesives are widely used in our life and industrial world. However, it is difficult to
characterize their mechanical properties because those strongly depend on environmental and
mechanical conditions such as temperature, humidity or strain rate. In this paper, we focus on the
strain rate dependence of the interfacial strength and investigate the interfacial strength by peel tests
under several peel rates. The results show that, in lower rate region (under 1.0 mm/s), the interfacial
strength is constant and, in transition region (1.0 to 10 mm/s) the interface strength increased with the
peel rate. In middle rate region (10 to 103 mm/s), the interfacial strength is constant again. Over 103
mm/s region, the interfacial strength drops and became lower than those in middle rate cases. From
the observation of peeling front by a high speed video camera, the deformation behavior of adhesives
changes with the peel rate.Finite element analysis by using cohesive zone model is also conducted,
and influence of the rate dependency of adhesive and base material is discussed.
Abstract: Alumina have been investigated for its distinguished characteristics to be widely used in
armor application. One-stage light gas gun were utilized to study the dynamic mechanical properties
of alumina subjected to shock loading. Manganin gauges were employed to obtain the stress-time
histories at the different Lagrange locations in alumina target. The Hugoniot curves of stress and
pressure versus specific volume were fitted based on the experimental data. The compressive
behaviors for AD90 alumina are shown to be from elastic to “plastic” below 12GPa and under more
higher pressure it will be transferred to similar-fluid state. Adopting LS-DYNA finite element
code the dynamic failure of alumina ceramic armor are simulated. It is concluded that nucleation
and growth of great number of radial and axial cracks and lateral cracks play dominant role in
fractured ceramic target under impact loading.
Abstract: The Mode I and Mode II dynamic fracture toughness (DFT) values, KId and KIId for high
strength steels 40Cr and 30CrMnSiNi2A were evaluated using a combined experimental-numerical
method. The tests were performed on three point bend (3PB) and shear specimens with Hopkinson
pressure bar. The time of crack initiation was determined by a strain gauge. With the assistance of
3-D transient finite element analysis, the temporal evolution of the dynamic stress intensity factor
under different loading rates was obtained, and the DFT was determined by the fracture initiation
time. In Mode I tests, a brittle transgranular fracture was found in 40Cr, while evidence for ductile
fracture was observed on the failure surface of 30CrMnSiNi2A. In Mode II tests, both tensile cracks
and adiabatic shear bands were found for the two steels. The effect of ligament size on fracture
toughness was discussed. The correlations of KId and KIId with loading rate were also investigated.
The micromechanisms of loading rate effect on the DFT were discussed for both modes.
Abstract: The dynamic fracture experiments were conducted on the heat treated magnesium alloys;
AZ31B-O, AZ31B-200 °C, and AZ31B-430 °C. Cross shaped specimens with the crack on their
center were used for the experiments. Dynamic fracture behavior near a crack tip under equal and
unequal biaxial stress was observed by the caustics method. From the observation, the stress intensity
factor and the fracture toughness value were calculated. As a result, the effect of heat treatment was
found. However, no clear relation such as correlation between dynamic stress intensity factor and heat
treatment temperature was deduced.