Abstract: The dynamic anti-plane crack problem in a functionally graded smart structure is considered. Integral transforms are employed to reduce the problem to the solution of singular integral equations. Numerical results are presented to show the nfluences of electrical crack condition, crack position, electromechanical combination factor and material gradient parameter on the fracture behavior.
Abstract: The influence of a biasing electric field on the propagation of the lowest-order antisymmetrical a0 Lamb wave modes in a bi-layered piezoelectric plate is investigated in this paper. It is found that the velocity shifts for the a0 mode due to presence of the bias field on the 10- µm LiNbO3 film structure are comparable with those observed in surface acoustic waves and Lamb waves in LiNbO3 plates. The fractional change in phase velocity of the layered piezoelectric structure is a linear function of the biasing electric field and can be used in voltage sensors.
Abstract: To describe the high-rate behaviour of metals, a revised form of the classic Johnson-Cook strength model with unknown material constants has been used. The 1D stress-strain relations as well as the effects of strain, strain rate and temperature are examined by Split Hopkinson Pressure Bar (SHPB) test. The undetermined material constants are solved using a variable-dissociation method. The element failure criterion based on maximum equivalent strain is also introduced to estimate the material failure behavior under high strain rate. A corresponding user-defined material subroutine (UMAT) has been developed for revised Johnson-Cook model, which is implemented into ABAQUS. Using this implicit scheme, several groups of finite element simulations under different strain rates are completed in ABAQUS/Standard. The results agree well with the test data and other results by explicit code.
Abstract: The present paper introduces the experimental study on soft rock (analogized with mortar)under dynamic uniaxial compression at the strain rates from 10
-5 to 101s-1. It is indicated that thecompressive strength of the soft rock increase with the increasing strain rate and the rising rates are
higher than that of hard rock. The Young's moduli and Poisson's ratio of the soft rock increase with the increasing strain rate, but the rising rates are less than that of compressive strength. In addition, the mechanism of the strain rate effect of the soft rock is primarily analyzed based on the SEM results.
Abstract: Low-velocity impact on composite sandwich panels has been investigated. The contact force is computed from a proposed modified Hertzian contact law. In the proposed contact law, the exponent is adjusted and the through-the-thickness elastic constant of honeycomb core is reduced properly to approximately predict the measured contact force-time history during the impact. The equivalent transverse elastic constant is calculated from the rule of mixture. Nonlinear equation to calculate the contact force is solved by the Newton-Raphson method and time integration is done by the Newmark-beta method. A finite element program for the low-velocity impact analysis is coded by implementing these techniques and an 18-node assumed strain solid element. Behaviors of composite sandwich panels subjected to low-velocity impact are analyzed for various cases with different geometry and lay-ups. It has been found that the present code with the proposed contact law can predict measured contact forces and contact times for most cases within reasonable error bounds, especially for thick sandwich plates.
Abstract: To evaluate the damage of composite laminate structures which are consist of maraging steel, rubber and carbon fiber reinforced composite subjected to low velocity impact, the drop weight was used to impact the specimens and nondestructive evaluation using the C-scan was performed. After experiments, impact damages were compared with respect to various temperatures and impact
energies. In case of circular plate, the damage characteristics such as delamination, matrix cracking, and fiber breakage were observed at the interface of rubber and carbon fiber reinforced composite. These results were found to be correlated with the deflection of specimen.
Abstract: Carbon fiber reinforced aluminum layer laminate (CARALL), which were consisted of various numbers of CFRP prepregs, adhesive films and aluminum sheets, were fabricated by an autoclave. Impact damage behaviors of carbon fiber reinforced plastic (CFRP) and CARALL were investigated. The impact damage resistance of CARALL was significantly higher than that of CFRP. Compression after impact (CAI) tests was conducted to investigate the effect of impact damage on the compression strength of CARALL and CFRP specimens. The CAI strength of CFRP and CARALL decreased with increase of impact energy. However, CAI strength of CARALL is higher than that of CFRP, which can be attributed to the excellent impact damage absorbability of aluminum sheet in CARALL.
Abstract: In transonic interfacial crack propagating fracture problem, the generation-phase simulations were done using the moving finite element method based on Delaunay automatic mesh generation. And the contact function based on the penalty method was newly developed to consider the crack face contact near the propagating interfacial crack tip.
It was succeeded to visualize in 3-dimensions the Mach shock wave emanated from the propagating crack tip. And it was tried for the transonically propagating crack problem that solving the energy flows through the contact zone or along the Mach shock wave line emitted from the crack tip. The energy flow patterns into the crack tip were also visualized. Furthermore, from the values of the separated dynamic J integrals, it was found that the dynamic J integral is non-zero even for transonic fracture region and the most of the energy release rate is provided from the more
compliant material epoxy.
Abstract: To understand fundamentals of kidney stone™s fragmentation by shock wave impingement, experimental approach was carried out. Air gun system was used to transfer a well-controlled stress wave into a thin disk specimen. The specimen was fabricated with plaster and its dimensions are 10 mm in diameter and 1.2 mm in thickness. The obtained results are summarized as follows: As the stress pulse duration is decreased from 12 microseconds to 5 microseconds, the critical stress for fracture increased tremendously. The critical fracture stress for a specimen with a small hole in the specimen center is about one fifth of that for the plain specimen. The fracture takes place along the diameter perpendicular to the stress wave incident direction. Numerical stress analysis suggests that the principal stress criterion can explain the fracture mode.
Abstract: By contrast with static fracture toughness determination, the methodology for dynamic fracture toughness characterization is not yet standardized and appropriate approaches must be devised. The accurate determination of the dynamic stress intensity factors must take into account inertial effects. Most methods for dynamic fracture toughness measurement are experimentally complex.
However, dynamic fracture toughness determination using strain measurement is extremely attractive in terms of experimental simplicity.
In this study, dynamic fracture toughness tests using strain measurement are performed. High rate tension and charpy impact tests are carried out for titanium alloy, maraging steel and Al alloys. In the case of evaluating the dynamic fracture toughness using high rate tension and charpy impact tests, load or energy methods are used commonly. The consideration about inertial effects is essential, because load or energy methods are influenced by inertia. In contrast, if the position for
optimum response of strain is provided, dynamic fracture toughness evaluation using strain near crack tip is more accurate. To obtain the position for optimum response of strain, a number of gages were attached at angles of 60°. Reliability for experimental results is evaluated by Weibull analysis. The method presented in this paper is easy to implement in a laboratory and it provides accurate results compared to results from load or energy methods influenced by inertia.