Key Engineering Materials Vols. 577-578

Abstract: The problem of crack deflection from the interface between two orthotropic materials is analyzed using the concept of Finite fracture mechanics and matched asymptotic procedure. A fracture criterion based on the energy approach is introduced for this problem. The main input for such criterion is the complex stress intensity factor calculated e.g. using the two-state integral. However for more precise predictions of the crack propagation also higher order terms of the asymptotic expansion are advisable to involve in the fracture criterion. To this end a T-stress term will be calculated and considered as the second input parameter. The matched asymptotic procedure together with FEM is used to derive the change of the potential energy induced by the incremental crack growth.

Abstract: Most important macroscopic inelastic phenomena of filled elastomers are due to microscopic damage processes inside the rubber network. For example, the Mullins effect can be explained by debonding of polymer chains from the carbon black aggregates. In turn, the damage and following recovery of aggregates are responsible for the hysteresis. All these effects also induce anisotropy of an initially isotropic material. In the present contribution, we show how these effects can be quantified experimentally and simulated by a micro-mechanical model. The model is based on the decomposition of the rubber matrix into a purely elastic polymer, a polymer-filler and a filler cell network. The polymer-filler network model takes into account the debonding of polymer chains from filler aggregates and is thus able to predict the strain induced damage and the permanent set. The filler cell network model describes breakage and recovery of filler aggregates and is responsible for the hysteresis. The presented model is in accord with a broad range of experimental observations.

Abstract: The fatigue damage of FRP-concrete interface is a major problem in strengthened structures subjected to fatigue loading. The available FRP-concrete interface models published in the literature usually deal with fracture mechanism approach, which is unsuitable for high cycle fatigue damage. In this study, a constitutive micro model is developed for FRP-concrete interface for high cycle fatigue and incorporated into a three dimensional finite-element program. Numerical analysis of a double lap joint is carried out, and the results show that the proposed model is reasonably accurate.

Abstract: In this paper a methodology for assessment of residual stress effects on crack behaviour in the polymer pipe is developed. For simplicitys sake, a linear distribution of residual stresses across the pipe wall is assumed. Linear elastic fracture mechanics is used for the fracture mechanics analysis of the cracked pipe. An approximate relation for the stress intensity factor estimation for a crack in a polymer pipe, with residual stress taken into account is suggested and discussed. The methodology presented can be helpful for a rapid lifetime estimation of polyolefin pipelines.

Abstract: This paper presents a 3D unit-cell approach which enables the estimation of bending, inplaneand coupling stiffness properties in the sense of the classical laminated plate theory for arbitrarilyheterogeneous plates. Periodic boundary conditions which simultaneously allow for in-plane as wellas for bending and twist deformation modes are introduced. Additionally, bending experiments of glassfibre/epoxy cross-ply laminates with cracked outer layer at the tension side are conducted and the stiffnessdegradation due to these transverse cracks is compared to numerical results.

Abstract: Evaluating fracture and fatigue life properties of structural components involves tests that are costly and time consuming. To estimate total life of engineering parts, high cycle fatigue data (S-N) for the material under study is needed. In many cases the S-N data is not available to the analyst and both the time and budget required for testing prevent engineers to meet the deadline imposed on the program. An analytical combined Progressive Damage and Fracture Mechanics based approach is proposed that estimates the S-N data for components that have stress concentrations. The proposed methodology starts from a full engineering tensile stress-strain curve of the material under study and ends up with the estimation of fracture toughness, fatigue crack growth and fatigue S-N curves.

Abstract: nterlaminar toughness of glass-epoxy laminates subjected to Mode I quasi static loading was investigated. The influence of reinforcement geometry on G_Ic was focused. Six different laminates reinforced with INTERGLAS 2/2 twill fabrics of three different areal densities and two strand orientations, θ, were tested. The considered fabric areal densities were 390g/m², 280g/m² and 163g/m², and strand orientations θ=0°/90° and θ=±45°. For laminates with θ=±45° strand orientation a statistically significant difference in the means of the interlaminar toughness G_Ic was noticed for all three laminates i.e. reinforced with the fabrics of areal densities 163 g/m² and 280 g/m², and 390 g/m². For laminates with strand orientation θ=0°/90° a significant difference in Gic means was noticed for laminates with fabrics of areal densities 163 g/m² and 280 g/m², and 280 g/m² and 390 g/m²_, only. For groups of laminates reinforced with a particular fabric type a statistically significant difference in the means of G_Ic was found each time when laminates differed in the strand arrangement θ regardless the way the G_Ic values were calculated. Fracture analysis done with the help of a SEM did not explained the observed differences in G_Ic values.

Abstract: A series of critical fracture toughness of two kinds of rock materials under different temperature which varied from-50°C to 240°C are measured by I-II-III mixed mode fracture experiments adopting atypical three point bending specimens. Relative stress intensity factors of crack initiation are calculated by finite element method. Combining with calculated values, the experiment results show that, the mixed mode fracture toughness of the rocks decreases with the increase of temperature. The experimental and calculated results can be used in the design of deep underground engineering or disaster prevention and mitigation engineering.

Abstract: For a finite deformation body, there are large strains and displacements on the crack tip. So it is necessary to study-integral based on finite deformation theory. Base forces theory is a new theory for describing finite deformation. In this paper, -integral based on base forces theory are presented. This work provides a new theoretical foundation for studying dynamic crack propagation.

Abstract: Experimental investigation about the grain boundary fracture behavior and segregation behavior of phosphorus under low tensile stresses in steel 2.25Cr1Mo and 12Cr1MoV was carried out in this paper. AES (Auger electron spectroscopy) experiments and dynamic analyses on the non-equilibrium grain-boundary segregation (NGS) of phosphorus and the SEM photos of grain boundary fracture in Auger specimens of both steels were obtained. The variation of phosphorus segregation level in grain boundary at different aging time was studied. Results show that the non-equilibrium segregation of phosphorus occurred at the grain boundaries in the two steels while subjected to a tensile stress of 30MPa and held at 500°C. The corresponding critical time was about 1 hour for steel 2.25Cr1Mo and 3.5hour for steel 12Cr1MoV respectively. SEM photos of grain boundary fracture in Auger specimens of the test steels show that the grain boundary fracture rate increased with increasing concentration of phosphorus, and that the fracture toughness of steel 12Cr1MoV is much lower than the one of steel 2.25Cr1Mo.