Brittle-to-Ductile Transition (brittle-to-ductile + transition)

Distribution by Scientific Domains

Selected Abstracts

Nanostructure Fracturing: Brittle-to-Ductile Transition in Uniaxial Compression of Silicon Pillars at Room Temperature (Adv. Funct.

On page 2439, F. Östlund et al. report on an interesting effect observed during the compression of sub-micrometer silicon pillars; a critical diameter separates pillars that are observed to crack from pillars that exhibit metal-like ductility. This observation allows for the development of a quantitative method for measuring the fracture toughness of such structures, which can be used to predict and explain small-volume fracture behavior. [source]

Brittle-to-Ductile Transition in Uniaxial Compression of Silicon Pillars at Room Temperature

Fredrik Östlund
Abstract Robust nanostructures for future devices will depend increasingly on their reliability. While great strides have been achieved for precisely evaluating electronic, magnetic, photonic, elasticity and strength properties, the same levels for fracture resistance have been lacking. Additionally, one of the self-limiting features of materials by computational design is the knowledge that the atomistic potential is an appropriate one. A key property in establishing both of these goals is an experimentally-determined effective surface energy or the work per unit fracture area. The difficulty with this property, which depends on extended defects such as dislocations, is measuring it accurately at the sub-micrometer scale. In this Full Paper the discovery of an interesting size effect in compression tests on silicon pillars with sub-micrometer diameters is presented: in uniaxial compression tests, pillars having a diameter exceeding a critical value develop cracks, whereas smaller pillars show ductility comparable to that of metals. The critical diameter is between 310 and 400,nm. To explain this transition a model based on dislocation shielding is proposed. For the first time, a quantitative method for evaluating the fracture toughness of such nanostructures is developed. This leads to the ability to propose plausible mechanisms for dislocation-mediated fracture behavior in such small volumes. [source]

An application of the J-Q model for estimating cleavage stress in the brittle-to-ductile transition

C. A. J. Miranda
A recent model was proposed by the authors to predict cleavage failure for steels based on a weak link mechanism and a crack tip stress field modified for planar constraint by the J,Q theory. The model uses the distribution of toughness results at a single temperature to predict a toughness distribution at a different temperature and/or geometry. In this model a material cleavage stress is needed to predict when the weak link fracture is triggered. This cleavage stress is a key input for the application of the model but it is not a property that is routinely measured and it is hence not available for most steel alloys. In this paper, a method to estimate the average value of the cleavage stress is presented, based on a characteristic of the model to predict cleavage failure. Examples of cleavage stress are given for several steels and these results are used to predict the toughness distributions for structural component models. [source]

Damage-viscoplastic consistency model for rock fracture in heterogeneous rocks under dynamic loading

Timo Saksala
Abstract This paper presents a damage-viscoplastic consistency model for numerical simulation of brittle fracture in heterogeneous rocks. The model is based on a combination of the recent viscoplastic consistency model by Wang and the isotropic damage concept with separate damage variables in tension and compression. This approach does not suffer from ill-posedness, caused by strain softening, of the underlying boundary/initial value problem since viscoplasticity provides the regularization by introducing a length scale effect under dynamic loading conditions. The model uses the Mohr,Coulomb yield criterion with the Rankine criterion as a tensile cut-off. The damage law in compression is calibrated via the degradation index concept of Fang and Harrison. Thereby, the model is able to capture the brittle-to-ductile transition occurring in confined compression at a certain level of confinement. The heterogeneity of rock is accounted for by the statistical approach based on the Weibull distribution. Numerical simulations of confined compression test in plane strain conditions demonstrate a good agreement with the experiments at both the material point and structural levels as the fracture modes are realistically predicted. Copyright © 2009 John Wiley & Sons, Ltd. [source]