Size Effect Law and Critical Distance Theories to Predict the Nominal Strength of Quasibrittle Structures

Abstract

The design of structures with a nonuniform stress field is of great industrial interest. The ability of the size effect law and critical distance theories to predict the nominal strength of notched and open hole specimens is analyzed in the present paper. The results obtained with these methods are compared with the solution of the problem computed, taking into account the material cohesive law. A conclusion of this paper is that the role of the critical fracture energy in determining the structural strength is negligible, except in large cracked structures. For unnotched structures of any size and for small cracked structures, the key parameter is the initial part of the softening cohesive law. This allows us to define design charts that relate the structural strength to a specimen size normalized with respect to a material characteristic length.

Deducing the R-curve for trans-laminar fracture from a virtual Over-height Compact Tension (OCT) test

“…in coupon tests [2][3][4][5][6][7] and observed in full-scale composite structural tests [8]. On the other hand, many existing approaches for modelling Mode I trans-laminar fracture [9][10][11][12] do not directly address R-curves and assume a constant Mode I trans-laminar fracture toughness value during fracture propagation.…”

The effect of a circular hole on the tensile strength of neat and filled rigid PUR foams

“…As an alternative approach to evaluating the notch effect, the critical-distance theories are being considered [8][9][10][11][12]6]. Among them, the finite fracture mechanics (FFM) models appear to be particularly promising, because they provide an estimate of strength in the presence of stress concentrations by using just the strength and toughness characteristics of the (plain) material, thus avoiding the need for model calibration against experimental notched-strength data.…”

Finite Fracture Mechanics crack initiation from a circular hole

“…The poorness of FFM results was observed also by Leguillon et al On the other hand, in order to improve theoretical predictions, both the material properties of PMMA (i.e., σ u and K Ic ) were fitted by Hebel et al: it was however concluded that the implemented values were “unrealistic” from a physical point of view. Maimi et al performed a very accurate analysis, implementing also some cohesive zone models, mentioning but not implementing the data presented by Li and Zhang…”