International Journal of Fracture最新文献

Cooling techniques following thermal treatments and related microcracking are a hot spot in rock mechanics and must be precisely studied. Hence, this research performed systematic experiments on the influences of rapid cooling on the behavior of thermally treated granodiorite at different temperatures. Furthermore, using the optical microscope, a comparison between rapid and slow cooling methods was studied to investigate how the cooling process affected the microstructure of the Egyptian granodiorite. The granodiorite samples were heated to 200, 400, 600, and 800 °C and then cooled slowly by air and rapidly by the water. According to the experimental results, the changes in examined properties occurred in three distinct temperature stages: zone I (25–200 °C), zone II (200–400 °C), and zone III (400–800 °C). Zone II was a conspicuous transition region for the rapid cooling approach, distinguished by a significant increase in porosity, thermal damage, crack density, and a substantial decrease in wave velocities, uniaxial compressive strength, and elastic modulus. Microcrack densities and widths increased with temperature for both cooling methods. According to microscopic analyses of granodiorite samples, boundary cracks were formed at the boundaries of quartz and feldspar first due to their minimal lattice energy, followed by biotite of high lattice energy. However, due to the thermal shock induced, the intragranular microcracks of the rapid cooling technique began to form at lower temperatures (200 °C). The physical and mechanical properties of rapidly cooled granodiorite significantly dropped between 200 and 400 °C, and the failure mode altered from axial splitting to shear modes. Consequently, over 600 °C, longitudinal waves could not penetrate rock samples due to the thermal fusion of inter and transgranular fissures, which turned into macrocracks. Hence, the elastic modulus measurements and wave velocity at 800 °C were challenging with an extremely low UCS and complex failure mode.

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.

Recent experiments in bonded PMMA layers have shown dramatic changes in dynamic crack growth characteristics depending on the interface location and its toughness. We present a peridynamic (PD) analysis of the problem and identify three necessary elements in a model aimed at reproducing the observed dynamic fracture behavior at an interface in PMMA: (1) softening near the crack tip to account for changes in PMMA properties due to heat-generation induced by the high strain rates reached around the crack tip in dynamic fracture, (2) independence of extension (mode I) and shear (mode II) modes of fracture, and (3) a two-parameter bond-failure model, that can match both strength and fracture toughness for any horizon size. The PD model with these elements captures the experimentally observed dynamic fracture characteristics in bi-layer PMMA: the presence/absence of crack branching at the interface, depending on the interface location; cracks running along the interface for a while before punching through the second PMMA layer; slight crack path oscillations as the cracks approach the free surface. The computed crack speed profiles are close to those measured experimentally. The simulations help explain the observed behavior of dynamic crack growth through an interface. The model shows an enlargement of the fracture process zone when the cracks running along the interface penetrate into the second PMMA layer, as observed experimentally. This is where nonlocality of the PD model becomes relevant and critical.

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.

This paper presents the results of axi-symmetric extension tests on a Rock Analogue Material that showed a continuous transition from extension fracture to shear fracture with an increase in compressive stress. The analysis used non destructive full-field experimental methods—digital image correlation (DIC), as well as the post-mortem specimens observation. When the mean stress was small, the fractures formed through the mode I cracking at tensile equal to the material tensile strength with smooth surfaces. These surfaces became rougher or delicate plumose patterns as the mean stress increased. Fracture angles also increased progressively from extension fractures to shear fractures. Hybrid fractures formed under mixed tensile and compressive stress states and presented plumose patterns on the rupture surface. DIC results showed the localisation of tensile deformation and the acceleration of deformation at the zone that induced the fracture. The fracture caused a reduction of deformation in the surrounding areas, which showed a release of elastic energy stored in the material during the propagation of fracture.

In this article, the nonclassical transient heat propagation process in a cracked strip is investigated by Guyer–Krumhansl (G–K) model, which incorporates both the time lagging behavior and the spatially nonlocal effect. The impulsive thermal loading as well as cyclic loading exerted on the top bounding surface are examined to explore the non-Fourier thermal characteristics. By means of the Laplace transform and Fourier transform, the governing partial differential equations subjected to mixed boundary conditions are converted to a group of singular integral equations. With the aid of numerical Laplace inversion, the transient temperatures are calculated to make comparisons of thermal responses determined by Fourier’s law, Cattaneo–Vernotte (C–V) equation, and G–K model. The numerical results display the specific thermal behaviors of G–K model in the cracked medium and demonstrate the G–K model’s capabilities in eliminating the unrealistic phenomena accompanied by C–V equation. Our research would contribute to achieving a better understanding of the transient heat conduction in small-sized systems or composites at the macroscopic scale.