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

The present paper deals with the use of the Theory of Critical Distances to model the detrimental effect of cracks and manufacturing defects in 3D-printed concrete subjected to static loading. The robustness of the proposed approach was assessed against a number of experimental results that were generated by testing, under three-point bending, 3D-printed rectangular section specimens weakened by saw-cut crack-like sharp notches, surface roughness (due to the extrusion filaments) and manufacturing defects. The sound agreement between experiments and predictive model allowed us to demonstrate that the Theory of Critical Distances is not only a reliable design approach, but also a powerful tool suitable for guiding and informing effectively the additive manufacturing process

The Theory of Critical Distances to perform the static assessment of 3D-printed concrete weakened by manufacturing defects and cracks

The Theory of Critical Distances groups together a number of approaches postulating that, in cracked/notched materials subjected to static loading, breakage takes place as soon as a critical length-dependent effective stress exceeds the material tensile strength. The characteristic length used by the Theory of Critical Distances is a material property that can directly be estimated from the ultimate tensile strength and the plane strain fracture toughness. In the present investigation, based on a large number of bespoke experimental results, it is demonstrated that the Theory of Critical Distances is successful also in quantifying the detrimental effect of cracks and manufacturing defects in 3D-printed concrete subjected to Mode I static loading

Geometric quality assurance for 3D concrete printing and hybrid construction manufacturing using a standardised test part for benchmarking capability

The need for quality control and assurance in 3D Concrete Printing (3DCP) is widely recognised. Achieving geometric accuracy to a specified tolerance is a cornerstone of component-based production and assembly. Although published work within the field recognises such issues, these fall short of proposing systematic methods to evaluate, diagnose, improve, monitor and compare system performance. This work takes inspiration from the test geometry approach readily deployed in Additive Manufacturing and develops a full-scale test part to establish a reproducible benchmark for evaluating and assuring part geometric quality of 3DCP systems. The approach is used to evaluate the benefits of a new fabrication approach that combines subtractive milling on green cement mortar in combination with 3DCP. It was demonstrated to yield useful information for direct comparison of different processes and diagnosing problems for performance improvement. The test part and measurement approach offer the 3DCP community a means of cross-platform benchmarking of 3DCP system performance