Fracture toughness of wet and dry particulate materials comprised of colloidal sized particles: role of plastic deformation

Abstract

This work demonstrates a method of measuring the fracture toughness of particulate materials comprised of colloidal sized particles over a wide range of saturation. Diametral compression of cylinders containing flaws of controlled length was used to measure the mode I fracture toughness. The effect of degree of saturation on the fracture toughness of slip cast ceramic grade alumina (d = 0.7 μm) was investigated. Dry powder compacts have significantly lower fracture toughness than when the powder compact is nearly fully saturated. All observations are consistent with the fracture mechanism being predominantly brittle for the dry samples but predominantly ductile in the nearly saturated samples. The additional dissipation that occurs during the ductile fracture of the nearly saturated samples is due to plastic deformation in front of the crack tip. This well-known mechanism for toughening in metals has been quantified for the first time in soft matter. Analysis of the results indicates that the size of the plastic dissipation zone is more than an order of magnitude larger in the nearly saturated materials compared to the dry material. Understanding the fracture mechanisms that control the propagation of cracks through saturated, partially saturated and dry particulate materials comprised of colloidal sized particles provides additional insight into understanding drying cracks in paint, other coatings, ceramics and water treatment sludge.

Toughening Nanoparticle Films via Polymer Infiltration and Confinement

“…We observe up to a ∼146× increase of contact area in the PINF relative to the neat film, which demonstrates why the infiltration of small amount of polymer can significantly enhance fracture toughness of PINFs. This polymer capillary bridge formation is analogous to water in a wet granular material, whereby the capillary condensation of water leads to mechanical reinforcement of granular packings. − Thus, the PINF toughness can be enhanced significantly via small amount of infiltrated polymer, while still maintaining high porosity.…”

“…The crack type is known to be directly related to the plasticity , and fracture toughness . We observe complete fracture of the pure NP pillar (Figure a), indicative of a catastrophic, brittle fracture, and low toughness, whereas in the case of the PINF pillar (Figure b), the indenter pillar conformed to the indenter tip geometry and appeared to undergo a more homogeneous deformation, a signature of plasticity in the PINF structure. , The increased plastic deformation (correspondingly, decreased brittle failure) is also observed through lower load drops during unstable crack propagation in micropillars with increasing PS volume fraction in the force–displacement curves (Figure ).…”

Elastic plastic fracture mechanics investigation of toughness of wet colloidal particulate materials: Influence of saturation

“…Fracture of particulate materials is important in a range of natural and industrial drying phenomena including mud cracking as well as drying of paint, coatings, ceramics and sewage sludges. [1][2][3][4][5][6] Although drying cracking has been studied extensively [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] there is little information about the fracture toughness of wet particulate materials [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] and even less about the role of the degree of saturation on the fracture toughness. The previous work has assumed linear elastic fracture mechanics although plasticity at the crack tip has been considered.…”

“…The previous work has assumed linear elastic fracture mechanics although plasticity at the crack tip has been considered. [16,23,38] Table 1 presents a timeline of the advances in understanding the role of plasticity and saturation on the fracture of wet particulate materials. The current paper builds on this previous work and advances our previous work [38] where we investigated the critical stress intensity factor (KIC, fracture toughness) via a linear elastic fracture mechanics (LEFM) approach on dry and nearly saturated particulate bodies.…”

“…[16,23,38] Table 1 presents a timeline of the advances in understanding the role of plasticity and saturation on the fracture of wet particulate materials. The current paper builds on this previous work and advances our previous work [38] where we investigated the critical stress intensity factor (KIC, fracture toughness) via a linear elastic fracture mechanics (LEFM) approach on dry and nearly saturated particulate bodies. Although the LEFM approach would normally apply to brittle materials only, we applied a modification of the model to account for non-linearities by assuming a process zone is present and implementing an iteration procedure to determine its size.…”