On indentation and initiation of fracture in glass

Abstract

The influence of indenter elasticity on Hertzian fracture initiation at frictional dissimilar elastic contact has been examined experimentally and numerically. In flat float glass specimens initiation of cone cracks has been observed and fracture loads measured with steel and tungsten carbide indenters at monotonically increasing loading and during a load cycle. The observed effect of indenter elasticity on fracture loads was found to be qualitatively different from the one predicted by the Hertz contact theory. This discrepancy may be explained by the presence of interfacial friction. The friction coefficient between the indenters and the specimen was measured and a contact cycle at finite Coulomb friction has been analyzed numerically. The influence of the indenter elasticity and the friction coefficient on the surface maximum tensile stress has been investigated and the results concerning the influence of these parameters on the fracture loads as given based on a critical stress fracture criterion. The obtained computational results were found to be in better agreement with experimental findings as compared to the predictions based on the frictionless contact theory. A remaining quantitative discrepancy was attributed to the well-known fact that a Hertzian macro-crack initiates from pre-existing defects on the specimen's surface. In order to account for the influence of the random distribution of these defects a Weibull statistics was introduced. The predicted critical loads corresponding to the 50% failure probability were found to be in close agreement with experimentally observed ones.

Performance of Dental Ceramics: Challenges for Improvements

“…Hertzian contact theory, widely used in most modeling, disregards the effect of friction during indentation (Jelagin and Larsson, 2008). Experimentally verified modeling/theory shows that: (1) difference in friction between the specimen and the indenter can significantly alter the load to initiate cone cracks; (2) the effect of friction has profound influence on the maximum surface tensile stress, and critical loads to initiate fracture were more than doubled compared with glass-to-glass contact when friction was taken into account; (3) tensile stress distribution changes dramatically, and the location of maximum stress shifts farther from the indenter contact area when friction is included; (4) friction results closely agree with experimental observations; (5) both the magnitude and shape distribution of tensile stress change when friction is integrated into the model; and (6) cone cracks with characteristic shape routinely form at unloading.…”

An Assessment of the Effectiveness of the Hertzian Indentation Technique for Determining the Fracture Toughness of Brittle Materials

“…They also did not explicitly account for the effects of these parameters on the stress intensity factor at the crack front. Recently, Jelagin and Larsson 15 considered partial stick‐slip contact and formulated the stress‐intensity factor, K I . However, their formulation was also based on the surface radial stress alone, and did not consider the steep stress gradients (drop‐off) beneath the surface.…”

Experimental characterization of non-linear behavior of monolithic glass

“…Research on structural glass commenced with a focus on glass as brittle material, which is an area that is still active [8,10,[13][14][15][16][17]. Then, research focused on laminated glass [8,11,12,[18][19][20][21][22][23][24][25], impacts and damage [10,14,15,17,20,[25][26][27][28][29][30][31][32], blast [20,27,33], manufactures and processes [9,11,24,26,30,32,34,35] and interlayers [12,17,18,24,36,37]. Research also included design and applications of glass in civil engineering and architecture [5]…”