Search results for "brittleness"
showing 10 items of 93 documents
Preliminary analysis of mastication dynamics and fragmentation during chewing of brittle cereal foods
2013
We studied the masticatory behaviour of five commercial brittle cereal foods, with different formulations, shapes and mechanical properties, chewed by an individual. The investigation of oral behaviour consisted in a simultaneous recording of jaw kinematics and muscle activity by electromyography (EMG) and we also determined the food size distribution at the swallowing point by image analysis. Similar behaviour was found for the evolution of all criteria, and especially the predominance of compression, which could be attributed to the brittle behaviour of the foods. The amplitude of the jaw motion decreased with the number of chewing cycles, or sequence duration, whereas the maximum mastica…
Micro-cracking of brittle polycrystalline materials with initial damage
2016
In this paper, the effect of pre-existing damage on brittle micro-cracking of polycrystalline materials is explored. The behaviour of single and multiple cracks randomly distributed within a grain scale polycrystalline aggregate is investigated using a recently developed grain boundary 3D computational framework. Each grain is modelled as a single crystal anisotropic domain. Opening, sliding and/or contact at grain boundaries are modelled using nonlinear cohesive-frictional laws. The polycrystalline micro-morphologies are generated using Voronoi tessellation algorithms in combination with a regularisation scheme to avoid the presence of unnecessary small geometrical entities (edges and face…
Ultimate Shear of RC Beams with Corroded Stirrups and Strengthened with FRP
2019
Transverse reinforcement plays a key role in the response behavior of reinforced concrete beams. Therefore, corrosion of steel stirrups may change the failure mode of elements from bending to shear, leading to a brittle and catastrophic crisis. It is important to strengthen reinforced concrete beams with corroded stirrups to enhance the shear resistance. This paper presents a formulation, based on the modified compression field theory, to estimate the ultimate shear of reinforced concrete beams strengthened with FRP, because of stirrup corrosion. The detrimental effect of corrosion on steel stirrup yield strength was taken into account by introducing an empirical decay law. The effective st…
Hydrogen Formation on Phase Boundaries of Sn/Al
2002
The present paper continues our earlier study of the embrittlement of Sn-Al eutectic alloy in water vapor and hydrogen emission from it, Atomically clean interfaces of solid phase joints of Sn with Al served as simple phase boundary models for this system. It was found by SIMS, X-ray and SEM techniques that the brittleness is caused by chemical adsorption of hydrogen on phase boundaries. This process is facilitated by structural defects. The reaction of hydrogen with phase boundary occurs first in regions of micro-and submicrocracks. The effect is irreversible one and it is associated with the formation of SnH4 that is instable and decomposes at the room temperature. The phase boundary of S…
Universal Dynamic Fragmentation inDDimensions
2004
A generic model is introduced for brittle fragmentation in $D$ dimensions, and this model is shown to lead to a fragment-size distribution with two distinct components. In the small fragment-size limit a scale-invariant size distribution results from a crack branching-merging process. At larger sizes the distribution becomes exponential as a result of a Poisson process, which introduces a large-scale cutoff. Numerical simulations are used to demonstrate the validity of the distribution for $D=2$. Data from laboratory-scale experiments and large-scale quarry blastings of granitic gneiss confirm its validity for $D=3$. In the experiments the nonzero grain size of rock causes deviation from th…
Exponential and power-law mass distributions in brittle fragmentation
2004
Generic arguments, a minimal numerical model, and fragmentation experiments with gypsum disk are used to investigate the fragment-size distribution that results from dynamic brittle fragmentation. Fragmentation is initiated by random nucleation of cracks due to material inhomogeneities, and its dynamics are pictured as a process of propagating cracks that are unstable against side-branch formation. The initial cracks and side branches both merge mutually to form fragments. The side branches have a finite penetration depth as a result of inherent damping. Generic arguments imply that close to the minimum strain (or impact energy) required for fragmentation, the number of fragments of size $s…
Dimensional effects in dynamic fragmentation of brittle materials.
2005
It has been shown previously that dynamic fragmentation of brittle $D$-dimensional objects in a $D$-dimensional space gives rise to a power-law contribution to the fragment-size distribution with a universal scaling exponent $2\ensuremath{-}1∕D$. We demonstrate that in fragmentation of two-dimensional brittle objects in three-dimensional space, an additional fragmentation mechanism appears, which causes scale-invariant secondary breaking of existing fragments. Due to this mechanism, the power law in the fragment-size distribution has now a scaling exponent of $\ensuremath{\sim}1.17$.
Glass physics: still not transparent
1999
Glass is a commonplace word. One immediately thinks of windows or bottles and of properties like brittleness or transparency. However, for a glass blower another feature is more important: glass does not melt abruptly, as a crystal does, but gradually over a range of temperatures. This means that he or she can alter the temperature at which glass solidifies or becomes a liquid by changing the rate at which it is cooled or heated. This is in stark contrast to the behaviour observed when the crystalline form of a material is heated: it will always melt at the same temperature.
Universality in Fragmentation
1999
Fragmentation of a two-dimensional brittle solid by impact and ``explosion,'' and a fluid by ``explosion'' are all shown to become critical. The critical points appear at a nonzero impact velocity, and at infinite explosion duration, respectively. Within the critical regimes, the fragment-size distributions satisfy a scaling form qualitatively similar to that of the cluster-size distribution of percolation, but they belong to another universality class. Energy balance arguments give a correlation length exponent that is exactly one-half of its percolation value. A single crack dominates fragmentation in the slow-fracture limit, as expected.
Dynamic fragmentation of a two-dimensional brittle material with quenched disorder
1997
Fragmentation of a two-dimensional brittle material caused by a rapid impact has been analyzed. Computer simulations together with simple arguments are used to obtain a qualitative understanding of crack formation, which is then used to derive an exponential fragment size distribution valid in the large fragment size limit. In the limit of small fragments this distribution is solved numerically, and it is found to obey a scaling law with the exponent {minus}1.5. These results suggest that two different mechanisms are operative in the fragmentation process: branching of propagating cracks determines the small fragment size limit, and merging of the nucleated cracks determines the large size …