Comparative analysis of concrete constitutive models in flexural beams using digital image correlation

Calibrated DEM models to simulate mechanical behavior of masonry structures under quasi-static lateral loads

Numerical approaches based on the Discrete Element Method (DEM) have proven effective in reproducing complex cracking and failure mechanisms of masonry structures. However, when intending to use them for virtual testing, an important constraint is that their predictive capability strongly depends on the appropriate calibration of material and contact parameters. This study presents the calibration of three-dimensional DEM models developed in 3DEC to simulate in-plane response of full-scale masonry wall with opening, subjected to quasi-static monotonic lateral loading. The experimental results, including the lateral force–displacement relationship, crack patterns and damage mechanisms, are used as benchmark data for the numerical model with exact geometry, boundary condition and loading scenario. Two models were calibrated, composed of rigid blocks and elastic deformable blocks. In both cases the blocks were connected through contact interfaces governed by Mohr–Coulomb joint model. To capture results of the experimental test, a tailored joint-displacement-based softening model is introduced on subcontact scale, representing main novelty of the study. Calibration using the proposed joint model successfully captures the main features of experimental behavior, including initial elastic part, stiffness degradation, peak lateral load, and post-peak softening (including an abrupt decrease in lateral load bearing of the wall at proper displacement), together with experimentally found damage mechanisms. The results demonstrate the capability of DEM-based simulations to reproduce nonlinear in-plane behavior of masonry wall without need for fracture energy parameters and highlight the importance of accurate joint softening models for reliable structural assessment of masonry structures.

Three-point bend test analysis using digital image correlation: from elasticity to damage

Three-point bend tests give access to analytical solutions for identifying mechanical parameters of constitutive models, making it a widely used method for analyzing the behavior of cementitious materials. However, a lack of knowledge regarding the kinematics, such as the Dirichlet boundary conditions, may bias the parameter identification. This paper proposes a methodology to analyze the kinematics of a three-point bend test, from elasticity to damage, and to explicitly compute the mechanical parameters without any kinematic assumptions. The kinematic fields are measured using Global Digital Image Correlation, employing a kinematic basis derived from Timoshenko–Ehrenfest beam theory for the elastic stage, and T3 shape functions for the post-peak stage. Using such bases allows for the direct calculation of the Young’s modulus, tensile strength, and fracture energy. The identified material parameters are close to those obtained through Finite Element Model Updating (FEMU) using a simple elastodamage model.

Investigating Fracture Behavior of Lattice Structures Using the XFEM and Equivalent Solid Material Model Techniques

This study aims to numerically investigate the mode I, II, and III fracture behaviors of additively manufactured degradable, bioplastic polylactic acid (PLA) lattice specimens. Numerical simulations were performed using the eXtended Finite Element Method (XFEM) based on the extracted PLA's mechanical and fracture material properties. The maximum principal stress and fracture energy power‐law criteria were utilized to simulate damage initiation and evolution in three‐dimensional (3D) numerical analyses. To consider the effects of build orientation, the transversely isotropic elasticity model (TIEM) was implemented. To facilitate the XFEM analyses, the equivalent solid material model (ESMM) technique was also utilized. The experimental load‐displacement responses of single‐edge notched bending specimens under the symmetric and asymmetric four‐point bending and mode III transverse shear cracked plate tests were conducted for comparison with the XFEM analyses in mode I, II, and III fracture, respectively. A common calibration factor, as well as the simultaneous utilization of the TIEM model, as well as the XFEM and ESMM techniques, reflected numerical results of acceptable accuracy compared to the experimental results; 5.3% (3.4%), 4.4% (5.8%), and 9.6% (5.4%) differences for the stiffness (peak load) of mode I, II, and III specimens, respectively.

Analysis and Prediction of Meso Shrinkage of Lightweight Aggregate Concrete Based on Digital Image Correlation

Existing shrinkage models are based on macroscopic linear strain measurements and have not been extended to the mesoscale. In lightweight aggregate concrete (LWAC), nonuniform deformation between aggregate and mortar phases governs early-age cracking risk, making mesoscale prediction essential. To address this gap, this study uses three-dimensional digital image correlation to measure full-field deformation on cross sections of LWAC specimens with water-to-cement ratios of 0.35, 0.40, and 0.45 over 21 days. The mesoscale shrinkage is characterized by the minimum principal strain. Four classical models (B3, ACI209, GL2000, and CEB-FIP) are reformulated in terms of the minimum principal strain and compared with experimental data. Results show that the shrinkage of LWAC develops in distinct phases governed by moisture transport from prewetted lightweight aggregates, and the B3 model best fits the measured data among the original models. The GL2000 and CEB-FIP models are then revised by introducing time-function correction coefficients and a strength discount factor, respectively. Evaluated against the unmodified models using root mean squared error and a cumulative absolute-error loss function, the revised GL2000 model is more accurate for water-to-cement ratios of 0.35 and 0.40, whereas the revised CEB-FIP model performs better for 0.45.

Numerical Simulation of Crack Propagation in Concrete with Prefabricated Array Fractures Based on the Discrete Element Method

Concrete readily develops cracks under service loads, which poses severe risks to the overall safety of engineering structures. In this work, the discrete element method (DEM) integrated with PFC2D 5.0 numerical software is adopted to construct a mesoscale concrete numerical model containing pre-existing internal fractures, and uniaxial compressive loading simulations are subsequently carried out. Unlike previous studies that predominantly examined isolated fracture parameters, this work systematically investigates the coupled effects of fracture inclination angle, length, and quantity on crack propagation mechanisms at the mesoscale, and for the first time establishes a quantitative relationship between microcrack spatial distribution patterns and macroscopic mechanical degradation. Parametric analyses are performed to quantify the influences of fracture geometric characteristics, including fracture inclination angle (30°, 45°, 60°), fracture length (short, long and extra-long), fracture quantity (4, 8 and 16), as well as the comparison between intact and fractured concrete specimens. The fracture quantities of 4, 8, and 16 are selected to represent low, medium, and high levels of initial defect density within the concrete matrix, corresponding to approximately 1%, 2%, and 4% of the total specimen area, respectively, thereby enabling a systematic investigation into the progressive deterioration of mechanical performance with increasing internal damage severity. The whole evolution process of crack initiation, crack propagation and ultimate failure patterns of concrete is systematically explored. Numerical results reveal that specimens with larger fracture angles exhibit higher compressive strength yet generate abundant newly formed microcracks, whereas low-angle prefabricated fractures are prone to triggering abrupt brittle failure. Specimens embedded with shorter fractures achieve superior mechanical strength and develop denser, more intensive microcrack distributions; in contrast, long pre-existing fractures drastically degrade compressive strength while limiting the generation of secondary cracks. Reducing the number of internal defects simultaneously improves compressive strength and expands the coverage range of the induced fracture network. Specimens with 16 prefabricated fractures deliver the weakest mechanical performance, owing to the excessively high initial defect density inside the matrix. In comparison with fractured samples, intact concrete without pre-set fractures achieves better comprehensive performance in terms of compressive strength, deformation compatibility and uniform microcrack development. A core conclusion drawn from this study is that the total quantity of microcracks cannot serve as a direct indicator to evaluate the damage degradation degree of concrete; instead, the spatial distribution pattern of microcracks dominates the deterioration level. Evenly scattered microcrack populations maintain relatively high residual strength, whereas the concentrated coalescence of microcracks into continuous penetrating macrocracks leads to an abrupt decline in structural load-carrying capacity. The findings of this research can provide theoretical references for stability evaluation and safety diagnosis of defective concrete structures in practical engineering.

Effect of delamination damage and sensitivity behaviour on stress and deformation characteristics of sandwich structure