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A numerical model used to predict the behavior of 3D printed concrete in the early age phase up until the point of collapse is presented. An incremental creep model for the material including aging and temperature effects is suggested. Furthermore, kinematic nonlinear effects are included in order to predict instability. The input parameters to the numerical model are determined through an optimization process where the displacement error between a finite element method (FEM) model and digital image correlation (DIC) measurements from an actual 3D print are minimized. A simplified (current state) version of the suggested numerical model was used to predict at how many layers a specific 3D print collapsed, with an error of 58%. This was concluded to be expected, since the numerical model is not fully implemented yet.

The oil industry relies on the use of cement as a primary barrier, to isolate the steel casing from the surrounding formations and provide overall stability on the bored structure. There has been extensive technological development on the physical and mechanical properties of the materials from the cement and cementing industry, in order to produce and install effective cement barriers, capable of withstanding both physical and chemical loads under extreme wellbore conditions. In particular, the formation of cracks and interfacial damage at the primary cement sheath is a largely discussed issue. However, there is still a limited understanding about the crack formation and propagation processes in well-cements, due to the particular geometric and boundary conditions of the structural system, such as: pressure, temperature, and confinement conditions. This paper is focused on the crack formation and propagation processes on cement systems under wellbore-like geometrical conditions, and proposes a test-setup to evaluate cracking and localized damage at the casing-cement interface.

The characterization of the tensile behavior of cementitious materials has been a long-standing researchtopic and a general consensus on how to accomplish this task has not yet been reached. Many standardized tests are available but each with different test set-up and prescriptions on the definition ofmeasured and derived parameters, including toughness, elastic properties and strength. This paperdiscusses a number of test procedures for selected material properties including tension and flexure. Acomparative experimental study was carried out using two distinct fiber reinforced cementitious composites with strain hardening and strain softening behavior. Digital Image Correlation was utilized in the experimental program to detect and quantify the formation of cracks. Results show that the different test methodologies valuate specific aspects of material performance. The outcome of these evaluation procedures is compared and critically analyzed.

Knowledge of the mechanisms controlling crack formation, propagation and failure of FRCC under shear loading is currently limited. This paper presents a study that utilized photogrammetry to monitor the shear deformations of two FRCC materials and ordinary concrete (OC). Multiple shear cracks and strain hardening of both FRCC materials was observed under shear loading. The influence of fibers, fiber type, including polyvinyl alcohol (PVA) and polypropylene (PP) fibers, and shear crack angle were investigated. Based upon photogrammetric results, fundamental descriptions of shear crack opening/sliding and subsequent failure are presented.

The invention relates to a method of reinforcing a 3D printed structure (110) by interweaving reinforcement (136) with 3D printed substrate layers (122) as the substrate layers are being printed. The method comprising the steps of printing substrate layers (122), supplying reinforcement (136), and interweaving the reinforcement with the printed substrate layers to create a reinforcement grid around, and optionally in between, the printed substrate layers. The reinforcement is connected at nodes (150). The invention also relates to an apparatus (100) comprising a 3D printer (120) and a reinforcement tool (130). The reinforcement tool comprises at least one weaving tool (132) with at least one needle (134) for interweaving the reinforcement (136). It also has at least one arrangement means (138) for moving the reinforcement tool (130) to the position where the reinforcement (136) is to be interwoven with the printed layers (122). By use of the invention, a reinforced 3D printed structure (110) can be designed and manufactured to take into account the local internal forces expected to arise during use of the structure.

This paper describes an investigation of fiber reinforced cementitious composites in terms of their behavior under tensile and flexural loading. Flexural testing and subsequent derivation of the tensile stress-deformation responsefrom the flexural test data are preferred in the assessment of the tensile properties of Fiber Reinforced Cement Composites (FRCC) over the direct measurement of the tensile behavior because of the more convenient test setup and ease of specimen preparation. Three and four-point bending tests and round determinate panel test were carried out to evaluate the flexural response of FRCC. The assumptions made in the inverse analysis on the formation of cracking suggested in many standardized evaluation methods and established correlation methods have a strong influence on the results of the conversion from flexure to tension... In this paper, the formation of cracking and crack development has been quantitatively documented using a digital image correlation (DIC) system to investigate the validity of the commonly made assumptions.