Abstract: Toughening of thermosets by creation of residual compressive stresses around microspheres is studied. Expandable hollow micro-spheres containing liquefied gas were used for the creation of residual compressive stresses. Microscopic compressive residual stresses around the micro-spheres in the vicinity of the crack tip were graphically analysed and related to macroscopic mechanical behaviour for mode I fracture. It was confirmed that toughening was due to residual compressive stresses rather post-cure effect.
Abstract: An advanced finite-element model for the complete failure process of a double notched specimen with crack tip blunting caused by yielding and subsequent crack propagation is used for the simulation of realistic specimens. Cracks in a homogeneous material and bimaterial cracks are studied. The calculated load-displacement curves show generally the shape known from experiments and theoretical considerations. The simulation allows determination of a working range
of set up parameters like geometry, test speed or clamping conditions.
The numerical model simulates crack propagation on the basis of a criterion which is similar to the energy release rate. The essential work of interfacial fracture method provides a method to determine the fracture toughness from load-displacement curves. This method is well suited to check the numerical simulation because both use an energy based failure criterion. If applied to simulated load-displacement curves the resulting essential work of interfacial fracture should
directly match the fracture criterion used as input for the simulation.
In fact, the data reduction of the simulated curves results in values for the fracture toughness that almost perfectly match the input values of the simulation. This agreement is a strong argument for the consistency of the simulation and the data reduction scheme.
Abstract: The microstructure, mechanical, impact and fracture properties of Australian bamboo
have been investigated. The graded composition and property has been confirmed by depth-profiles obtained by synchrotron radiation diffraction and Vickers indentation. The mechanical performance of bamboo is stronly dependent on age. Results showed that young bamboo has higher strength, elastic stiffness and fracture toughness than its old counterpart. Both crack-deflection and crackbridging
are the major energy dissipative processes for imparting a high toughness in bamboo.
Abstract: In this paper, a thermodynamic approach is presented to model coupled fluid transport, heat transfer, long-term deformation and damage in polymeric materials. The well-known Gibbs free energy is expressed as a functional of stress, temperature and fluid concentration with damage being introduced as an internal state variable. Constitutive equations for nonlinear viscoelastic
materials in hygrothermal environments are derived in memory functional forms. The kinetics of damage evolution induced by stress, temperature and fluid is described by a damage function with thermodynamic driving force. Governing equations for mass and heat transfer are obtained from transport laws relating fluid and heat fluxes to gradients of chemical potential difference and temperature. A superposition principle of time, temperature, fluid concentration, stress, and aging is
proposed so that long-term property functions may be derived from momentary master curves by horizontal and vertical shifting. The approach provides a theoretical framework for evaluating longterm behavior of polymeric materials in hygrothermal environments from short-term experiments.
Abstract: The historical developments of the fracture mechanics from planar theory to threedimensional (3D) theory are reviewed. The two-dimensional (2D) theories of fracture mechanics have been developed perfectly in the past 80 years, and are suitable for some specific cases of engineering applications. However, in the complicated 3D world, the limitation of the 2D fracture theory has become evident with development of the structure toward complication and micromation.
In the 1990’s, Guo has proposed the 3D fracture theory with a 3D constraint factor based on the deformation theory and energy theory. The proposed 3D theory can predict accurately the fracture problems for practical and complicated engineering structures with defects, by integrating the 3D theory of fatigue, which has been developed to unify fatigue and fracture. Our efforts to develop the 3D fracture mechanics and the unified theory of 3D fatigue and fracture are summarized, and
perspectives for future efforts are outlined.
Abstract: It is still an open problem how the thermal effect influences the fracture behavior of
piezoelectric materials especially under cycling electrical loading. Experimental observations have found that the fracture toughness of piezoelectric solids under electric loading may be greatly different from that under mechanical loading. A pronounced rise of temperature may be caused either by mechanical or by electric loading. In this paper, the thermal effects and energy dissipation mechanism in cracked piezoelectric materials under cyclic-electric-loading have been studied. The
temperature rise is derived under the assumption of decoupling between thermal and
electromechanical fields and the influences of frequency and the shape of electric wave on the temperature rise are quantitatively analyzed.
Abstract: This paper solves the penny-shaped crack configuration in transversely isotropic solids with coupled magneto-electro-elastic properties. The crack plane is coincident with the plane of symmetry such that the resulting elastic, electric and magnetic fields are axially symmetric. The mechanical, electrical and magnetical loads are considered separately. Closed-form expressions for the stresses, electric displacements, and magnetic inductions near the crack frontier are given.
Abstract: A periodic array of cracks in a functionally graded material under transient mechanical loading is investigated. Anti-plane shear loading condition is considered. A singular integral equation is derived, in which the crack surface displacement is the unknown function. Numerical results are obtained to illustrate the variations of the stress intensity factors as a function of the crack periodicity for different values of the material nonhomogeneity, either at the transient state or at the steady state. The material non-homogeneity can increase or reduce the stress intensity factors.
Comparing with the single crack solution, it can be shown that multiple cracking can reduce the stress intensity factor significantly.
Abstract: Two-dimensional crack problems in a three-layered material are analysed numerically
under the conditions of plane strain. An image method is proposed to obtain a fundamental solution for dislocation dipoles in trilayered media. The governing equations can be constructed by distributed dislocation technique and the solutions are sought in terms of the displacement discontinuity method. Comparisons are made between existing results in the literature and numerical results for different cases and good agreements are found.
Abstract: The deformation and failure behavior of an AM60 magnesium alloy was investigated
using tensile test on circumferentially notched specimens with different notch radii. The strain and stress triaxiality corresponding to the failure point were evaluated using both analytical and finite element analyses. Combining with systematical observations of the fracture surfaces, it is concluded that deformation and failure of AM60 magnesium alloy are notch (constraint) sensitive. The failure mechanisms change from ductile tearing to quasi cleavage with the increase of constraint.