Modeling Crack Behavior around Holes in Glulam Beams Using the WoodST Constitutive Model Based on Continuum Damage Mechanics

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.

Application of the Specified Stress Method to Crack Propagation Analysis in Reinforced Concrete Members

Reinforced concrete (RC) structures are susceptible to crack initiation and propagation during service, making accurate numerical simulation of crack behavior essential for assessing structural durability and safety. Current numerical approaches for simulating concrete cracking include smeared/continuum approaches, extended finite element method (XFEM), phase-field methods, and meso-mechanical models. In particular, smeared/continuum approaches (e.g., smeared crack and plastic-damage models such as CDP) indirectly reflect cracking through diffusive damage fields without providing explicit geometric information on crack locations and propagation paths. The XFEM module in commercial software is further restricted to first-order elements and encounters difficulties in simulating multi-crack propagation. These limitations indicate that further development of complementary crack-simulation frameworks is warranted. To this end, this paper presents a cracking simulation framework for RC members within the theoretical framework of the Specified Stress Method, adopting an adaptive degree-of-freedom strategy to balance computational accuracy and efficiency. The method introduces inelastic strain as an additional unknown and establishes a variational principle and the corresponding virtual work equation. Concrete cracking is described by specifying the stress on the crack plane to zero, so that the crack-surface stress remains zero after cracking, thereby avoiding the issue of damage reversibility and improving computational convergence. The method requires neither a predefined crack path nor remeshing after cracking. Unlike smeared/continuum approaches that rely on diffusive damage fields, the crack propagation paths, distribution characteristics, and evolution of multiple cracks are characterized through the spatial distribution of cracked integration points within the finite element mesh. In the present implementation, crack initiation is governed by the maximum tensile stress criterion, and a linear elastic constitutive model is adopted for concrete as a deliberate simplification to establish and verify the core computational mechanism of the framework. The proposed method was examined through three numerical examples. First, comparison with theoretical solutions confirmed the algorithm’s correctness in simulating cracking in heterogeneous RC tension members. Second, comparison with experimental results demonstrated qualitatively consistent crack propagation trends and load–displacement responses for RC beams under mixed-mode cracking; the calculated ultimate load of the plain concrete beam is lower than the experimental value, which is attributable to the use of the maximum tensile stress criterion without fracture energy considerations, and certain crack morphology deviations are observed due to the neglect of reinforcement–concrete bond-slip. Third, a multi-crack simulation of an under-reinforced RC beam showed that, whereas the XFEM module in ABAQUS captures only a single dominant crack near the mid-span, the proposed algorithm predicts multiple distributed cracking zones on both sides of the mid-span, qualitatively consistent with the typical flexural cracking behavior of under-reinforced RC beams; the algorithm also supports second-order elements (e.g., C3D20R) unavailable in the ABAQUS XFEM implementation. While the method is still in an exploratory stage, these results confirm the feasibility and potential of the Specified Stress Method as a complementary framework for RC cracking simulation, providing a basis for further development.

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.

Damage Mechanism of Braid Hole Composite Bolt Joints Under Quasi–Static Tension

Delamination Prediction in Multiangular Composite Laminates Using Cohesive Zone Surface Based Modelling & XFEM

Carbon Fiber Reinforced Polymer (CFRP) composites have become indispensable in the aerospace industry due to their superior mechanical properties. Delamination, often initiated by impact events, manufacturing defects or fatigue loading, reduces the stiffness and structural integrity of the structure. In actual structures delamination can propagate through multiple plies, causing both interlaminar and intralaminar fractures. Conventional finite element approaches, such as virtual crack closure technique (VCCT) and cohesive zone modelling (CZM), are inadequate for modelling both interlaminar and intralaminar failures. The purpose of this paper is to explain how to overcome these limitations by integrating the Extended Finite Element Method (XFEM) with cohesive zone surface‐based modelling. A comprehensive numerical model capable of accurately predicting both interlaminar and intralaminar crack propagation in multiangular CFRP composites under Mode‐1 loading is presented. Details of numerical modelling of various delamination interfaces and its comparison with experimental data are presented.

Concurrent Multi‐Scale Simulation of Progressive Damage in Laminated Composites Using Shell Finite Elements

This paper presents a study on multi‐scale modelling of progressive damage model in laminated composites using shell finite elements, with considerations for the effects of manufacturing defects. The approach utilises second‐order homogenisation with 5‐parameter shell formulation to capture the effects of complex sub‐structural geometry and damage mechanisms in a smeared, equivalent single layer manner. During analysis, the shell constitutive tensors are continually updated and derived from high‐fidelity unit cell simulations. The key benefits are two‐fold. First, manufacturing defects can be directly introduced to targeted regions by assigning unit cells containing said defects. Second, the effects of progressive damage, including delamination, are accounted for in a smeared fashion without requiring complex mesh‐stacking nor discontinuous kinematic enhancements. A series of numerical benchmarks are presented to demonstrate the model's ability to accurately predict damage/defect induced stiffness degradation, failure loads and damage morphology in laminated composites under loading conditions, including bending, shear, buckling and static indentation. Overall, the findings in this paper presents a proof‐of‐concept for a multi‐scale framework that enables defect assessment and damage modelling in shell‐based simulations of composite structures, and lays the groundwork for future computational acceleration via surrogate modelling.