Fracture toughness

About: Fracture toughness is a research topic. Over the lifetime, 39642 publications have been published within this topic receiving 854338 citations.

The interaction of propagating opening mode fractures with preexisting discontinuities in shale

Abstract: Field observations show that hydraulic fracture growth in naturally fractured formations like shale is complex. Preexisting discontinuities in shale, including natural fractures and bedding, act as planes of weakness that divert fracture propagation. To investigate the influence of weak planes on hydraulic fracture propagation, we performed Semicircular Bend tests on Marcellus Shale core samples containing calcite-filled natural fractures (veins). The approach angle of the induced fracture to the veins and the thickness of the veins have a strong influence on propagation. As the approach angle becomes more oblique to the induced fracture plane, and as the vein gets thicker, the induced fracture is more likely to divert into the vein. Microstructural analysis of tested samples shows that the induced fracture propagates in the middle of the vein but not at the interface between the vein and the rock matrix. Cleavage planes and fluid inclusion trails in the vein cements exert some control on the fracture path. Combining the experimental results with theoretical fracture mechanics arguments, the fracture toughness of the calcite veins was estimated to range from 0.24 MPa m1/2 to 0.83 MPa m1/2, depending on the value used for the Young's modulus of the calcite vein material. Measured fracture toughness of unfractured Marcellus Shale was 0.47 MPa m1/2.

The effect of specific β‐nucleation on morphology and mechanical behavior of isotactic polypropylene

Abstract: The commercial grade of isotactic polypropylene was modified by a specific β-nucleating agent in a broad concentration range. The supermolecular structure of the specimens prepared by injection molding was characterized by X-ray scattering and correlated with mechanical behavior. It was found that at a critical nucleant concentration of 0.03 wt % the content of the β-modification virtually reaches a saturation level. With further addition of the nucleant, the β-phase content increases only slightly. The long period passes through a distinct maximum at the same nucleant concentration. This singularity in structure remarkably correlates with a minimum of the yield stress and maxima of strain at break and fracture toughness. Such general behavior is also reflected in the correlation between the β-phase concentration and fracture toughness profiles along the injection-molded bars. It is suggested that in the critically nucleated material an optimum thickness of the amorphous interlayer with connecting chains between the β-crystallites is established, rendering the material the highest possible ductility and toughness. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1174–1184, 2002

Discrete element method for modelling solid and particulate materials

Abstract: The discrete element method (DEM) is developed in this study as a general and robust technique for unified two-dimensional modelling of the mechanical behaviour of solid and particulate materials, including the transition from solid phase to particulate phase Inter-element parameters (contact stiffnesses and failure criteria) are theoretically established as functions of element size and commonly accepted material parameters including Young's modulus, Poisson's ratio, ultimate tensile strength, and fracture toughness A main feature of such an approach is that it promises to provide convergence with refinement of a DEM discretization Regarding contact failure, an energy criterion based on the material's ultimate tensile strength and fracture toughness is developed to limit the maximum contact forces and inter-element relative displacement This paper also addresses the issue of numerical stability in DEM computations and provides a theoretical method for the determination of a stable time-step The method developed herein is validated by modelling several test problems having analytic solutions and results show that indeed convergence is obtained Moreover, a very good agreement with the theoretical results is obtained in both elastic behaviour and fracture An example application of the method to high-speed penetration of a concrete beam is also given Copyright © 2006 John Wiley & Sons, Ltd

Densification and Mechanical Properties of B4C with Al2O3 as a Sintering Aid

Abstract: The densification behavior and mechanical properties of B4C hot-pressed at 2000°C for 1 h with additions of Al2O3 up to 10 vol% were investigated. Sinterability was greatly improved by the addition of a small amount of Al2O3. The improvement was attributed to the enhanced mobility of elements through the Al2O3 near the melting temperature or a reaction product formed at the grain boundaries. As a result of this improvement in the density, mechanical properties, such as hardness, elastic modulus, strength, and fracture toughness, increased remarkably. However, when the amount of Al2O3 exceeded 5 vol%, the level of improvement in the mechanical properties, except for fracture toughness, was reduced presumably because of the high thermal mismatch between B4C and Al2O3.