International Journal of Fracture最新文献

Environmental aging induces a slow and irreversible alteration of the rubber material’s macromolecular network. This alteration is triggered by two mechanisms which act at the microscale: crosslinking and chain scission. While crosslinking induces an early hardening of the material, chain scission leads to the occurrence of dangling chains responsible of the damage at the macromolecular scale. Consequently, the mechanical behavior as well as the fracture properties are affected. In this work, the effect of aging on the mechanical behavior up to fracture of elastomeric materials and the evolution of their fracture properties are first experimentally investigated. Further, a modeling attempt using an approach based upon a micro-mechanical but physical description of the aging mechanisms is proposed to predict the mechanical and fracture properties evolution of aged elastomeric materials. The proposed micro-mechanical model incorporates the concepts of residual stretch associated with the crosslinking mechanism and a so-called “healthy” elastic active chain (EAC) density associated with chain scission mechanism. The validity of the proposed approach is assessed using a wide set of experimental data either generated by the authors or available in the literature.

Corrosion in reinforced concrete is an important feature which can lead to increased deformation and cracking, as well as to premature failure. In the present work, macro-mechanical modelling of corrosion is performed, namely the degradation of bond–slip between concrete and steel. A mixed-mode damage model is adopted, in which the interaction between the bond–slip law and the stress acting in the neighbourhood of the concrete–steel bar interface is taken into account. Bond–slip degradation is modelled using an evolutionary bond–slip relationship, which depends on the level of corrosion. Different relevant loading cases are studied. Special attention is given to the evolution of corrosion in time, under constant load. This is done by adopting a Total Iterative Approach, in which the structure is reevaluated each time step, upon damage increase due to corrosion. Pullout tests are presented to illustrate the performance of the model. Bending tests are also performed to evaluate the influence of corrosion at structural level.

In this study, the Johnson–Cook constitutive and failure model parameters of A508-III steel are determined through quasi-static and dynamic tensile and fracture tests. The reliability of model parameters is then verified by dynamic fracture tests at different loading rates. Using the Johnson–Cook model, the dynamic fracture behavior of the SEB specimen of A508-III steel under various loading rates and geometric configurations has been simulated. The effect of loading rate and specimen geometric configuration on the dynamic fracture toughness of A508-III steel is investigated. The results reveal that the critical fracture force and impact absorbed energy increase with the increase of loading rate. The dynamic fracture behavior of deep-cracked specimens is more sensitive to the loading rate than that of shallow-cracked specimens. Moreover, the critical fracture force and impact absorbed energy increase linearly with increasing specimen thickness while the initial crack size remains constant.

High temperature hydrogen attack (HTHA) is degradation of steels exposed to hydrogen gas at high temperatures and pressures. Hydrogen in steels reacts with carbon from carbides to produce methane gas bubbles typically on grain boundaries which grow and coalesce, leading to loss of strength and fracture toughness. Current design practice against HTHA is based on the Nelson curves which define the conditions for safe operation in a temperature/hydrogen-partial-pressure diagram. Nelson curves are phenomenological in nature and do not account for the underlying failure mechanism(s), material microstructure, carbide stability, and applied stresses. In light of experimental evidence of predominant cavitation ahead of cracks reported by Martin et al. (Acta Mater 140:300–304, 2017), it is expected that void growth is accelerated by the triaxial stresses associated with microstructural flaws. To this end, we propose a three-dimensional, axisymmetric, constraint-based void-growth model extending the “one-dimensional” model of Dadfarnia et al. (Int J Fract 219:1–17, 2019). The present model is shown to yield satisfactory agreement with the available experimental data from hydrogen attack of 2¼Cr–1Mo steel at temperatures ranging from 500 to 600 °C. In addition, the model is used to construct Nelson type curves in the temperature/hydrogen-partial-pressure diagram. These curves represent failure times for given applied stresses and triaxiality. The proposed methodology can be viewed as providing a step toward improving the current design practice against HTHA while maintaining the simplicity of the original Nelson curve approach.

Ground-surface accelerations warn of incipient natural hazards—but threshold criteria remain indistinct. We use a model of localizing deformation within a encapsulating compliant halo to accurately project time-to-failure and to discriminate between ultimate stable and unstable rupture. A heterogeneous distribution of displacement histories and relative polarities demark composite zones of local failure. These composite zones accommodate strain accumulation in the localizing core and strain-relaxation in the surround. Balanced rates of strain accumulation and complementary shedding project both a time-to-rupture and anticipated energetics—quiescent of dynamic. This analysis is applied to follow the evolution of both local discrete ruptures and their coalescence into macroscale failure—with equal resolution and success. Apparent is a typical deformation response characterized by creep, relaxation and reload at different positions.

Many structural components and devices in combustion and automotive engineering undergo highly intensive cyclic thermal and mechanical loading during their operation, which leads to low cycle (LCF) or thermomechanical (TMF) fatigue crack growth. This behavior is often characterized by large scale plastic deformations and creep around the crack, so that concepts of linear-elastic fracture mechanics fail. The finite element software ProCrackPlast has been developed at TU Bergakademie Freiberg for the automated simulation of fatigue crack growth in arbitrarily loaded three-dimensional components with large scale plastic deformations, in particular under cyclic thermomechanical loading. ProCrackPlast consists of a bundle of Python routines, which manage finite element pre-processing, crack analysis, and post-processing in combination with the commercial software Abaqus . ProCrackPlast is based on a crack growth procedure which adaptively updates the crack size in finite increments. Crack growth is controlled by the cyclic crack tip opening displacement (varDelta )CTOD, which is considered as the appropriate fracture-mechanical parameter in case of large scale yielding. The three-dimensional (varDelta )CTOD concept and its effective numerical calculation by means of special crack-tip elements are introduced at first. Next, the program structure, the underlying numerical algorithms and calculation schemes of ProCrackPlast are outlined in detail, which capture the plastic deformation history along with the moving crack. In all simulations, a viscoplastic cyclic material law is used within a large strain setting. The numerical performance of this software is studied for a single edge notch tension (SENT) specimen under isothermal cyclic loading and compared to common finite element techniques for fatigue crack simulation. The capability of this software is featured in two application examples showing crack growth under mixed-mode LCF and TMF in a typical austenite cast steel, Ni-Resist. In combination with a crack growth law identified in terms of (varDelta )CTOD for a specific material, the tool ProCrackPlast is able to predict the crack evolution in a 3D component for a given thermomechanical loading scenario.