The Theory of Critical Distances to assess the effect of cracks/manufacturing defects on the static strength of 3D-printed concrete

The application of the Theory of Critical Distances to nonhomogeneous materials

“…Turning to the defects/cracks that can be found in 3D printed concrete, Figure 12B–D shows the possible scenarios that were considered 42 to assess the accuracy of the TCD in addressing this problem. The specimens of 3D printed concrete being used in this investigation had width, W , in the range of 44–53 mm and thickness, B , in the range of 34–56 mm (Figure 12).…”

“…Finally, a number of specimens were additively manufactured by setting the technological parameters so that voids were created intentionally in between adjacent filaments/layers (Figure 12C). In terms of structural strength modeling, the defects at the fracture section were assumed to be interlinked, resulting in an equivalent crack having length a , defined as shown in Figure 12 42 …”

“…This L value was estimated by taking K Ic equal to 1.2 MPa√m and σ UTS to 13.7 MPa. In particular, the ultimate tensile strength in Equation (1) was set equal to the static flexural strength of the AM concrete being tested 42 …”

“…In light of the unique features of 3D printed materials, over the last decade, the Sheffield Structural Integrity Research Group has run a number of experimental/ theoretical projects to assess whether the TCD is successful in assessing the static [38][39][40][41][42][43] and fatigue [44][45][46] strength of notched/flawed 3D printed materials. In what follows, some specific outcomes from this body of systematic research work will be reviewed and revisited by focusing attention specifically on polymers and concrete.…”

“…In terms of structural strength modeling, the defects at the fracture section were assumed to be interlinked, resulting in an equivalent crack having length a, defined as shown in Figure 12. 42 Taking as a starting point the definitions for the crack depth, a, shown in Figure 12B-D, the finite element method was employed to determine the corresponding LEFM shape factors, α, where samples were schematized as SENB beams with notch tip radius equal to zero.…”