Hirshikesh

In this work, we employed the phase-field fracture (PFF) model for dynamic brittle fracture in quasicrystals (QCs). The dynamic PFF formulation is derived using both elastodynamics and elasto-hydrodynamic theory. The temporal discretization is achieved using an implicit generalized-α method, which is unconditionally stable for a particular choice of constants. The model incorporates two distinct crack driving forces: (a) the contribution of elastic strain energy from both phonon and phason fields and (b) the contribution solely from the elastic energy associated with the phonon field. To validate the implementation of QCs, we have conducted benchmarking against recent results in the literature, particularly in the context of quasi-static loading. We addressed various paradigmatic case studies to demonstrate the dynamic crack nucleation and propagation in planar 2D decagonal QCs, with a primary emphasis on understanding the interplay between phonon and phason fields. Phason walls, representing low-energy crack paths resulting from atomic rearrangements, play a significant role in crack propagation by introducing an additional energy component. Notably, increasing the phonon–phason coupling constant expedites both crack initiation and propagation. Furthermore, variations in the phonon–phason coupling parameter result in different crack trajectories, observed in both uniaxial and biaxial loading scenarios. The developed code can be downloaded from https://github.com/Hirshikesh/Quasicrystal.git.

Fatigue fracture is one of the main causes of structural failure under cyclic loading, so accurate evaluation of fatigue fracture is very important for the design of structures subjected to cyclic loading. In this work, we propose an adaptive fatigue phase-field model within the framework of multi-patch isogeometric analysis to simulate crack nucleation and propagation in brittle materials under cyclic loading. Multiple non-uniform rational B-splines (NURBS) patches are used to exactly represent complex structures, and the Nitsche's method is adopted to enforce the compatibility of the displacements, stresses and phase-field variables between two patches. The coupled governing equations of fatigue phase-field model are established based on the Nitsche's method, and the selection of Nitsche's parameters are determined from numerical experiments. A refinement-correction adaptive approach based on locally refined non-uniform rational B-splines (LR NURBS) structured mesh refinement strategy is developed to alleviate the computational burden caused by the requirement of small element size around crack surface and the large number of fatigue loading. The proposed multi-patch isogeometric phase-field model can deal with the coupling between equal/unequal length interfaces, thus the fatigue crack propagation simulation in arbitrary complex structure can be implemented. Several numerical examples are investigated to verify the practicality of the multi-patch isogeometric phase-field model and the effectiveness of the adaptive scheme.

Concrete structures in cold regions are exposed to harsh environmental conditions, including freeze–thaw cycles, which lead to frost damage and degradation. Accurate simulation of the freeze–thaw damage process is essential for assessing concrete structures’ performance and service life. This paper presents a novel approach for simulating microcracks propagation in concrete during freeze–thaw cycles based on a fatigue phase-field model, in which a fatigue degradation function is introduced in the energy functional. The commercial software COMSOL is employed to implement the proposed model using a segregated scheme. The proposed model is validated against experimental results presented in the literature. Additionally, three cases are studied to get insight into the freeze–thaw damage. The results demonstrate the effectiveness of the fatigue phase-field model in capturing crack propagation in concrete under freeze–thaw cycles. The developed model offers valuable insights for assessing and designing concrete structures in cold regions.

This work presents an adaptive phase field framework for the simulation of crack nucleation and propagation in brittle materials subject to low-cycle loading. We introduce a fatigue history strain parameter within the phase-field framework to capture the fatigue effect. The resulting coupled differential equations are solved using a staggered iteration scheme. In order to improve the computational efficiency of the phase-field model, an adaptive refinement scheme is introduced. This scheme utilizes an artificial threshold that takes into consideration of both phase-field variables and cumulative fatigue history field variables to determine the elements to be refined. The handling of the hanging nodes resulting from mesh refinement is accomplished through the application of the variable-node element technique, offering a flexible and efficient mesh integration technique. We validate our proposed numerical scheme through five representative numerical examples: single-edge cracked specimen, compact tension specimen, double-edge cracked panel, plate with a hole and plate with multi-cracks and hole. The results demonstrate that the adaptive mesh refinement scheme significantly reduces computational costs without compromising the accuracy of the numerical predictions.

This paper introduces a novel topology optimization framework by combining the phase-field method and optimality criteria approach. This novel approach allows for the automatical addition of holes in the initial shape, a capability that is not achievable with the conventional phase-field model based on boundary changes for topology optimization. The distribution of the material is changed according to the sensitivity of the optimality criteria approach to nucleate holes. After the nucleation of the new holes, they are utilized for topology optimization using the phase-field method. To demonstrate the accuracy and effectiveness of the proposed approach, we conduct several numerical examples based on the two-dimensional minimum compliance problem. The obtained numerical results show the proposed method's fast convergence compared to the conventional phase-field method.

Many achievements for soft grippers are made in the structure design and grasping of target objects. However, there are limited studies on grasping objects with different attributes by soft grippers with omnidirectional bending capabilities within environments containing obstacles. In this paper, drawing inspiration from the multi-segment structure of the biological finger, a 3D-multi-segment soft pneumatic actuator (3D-MSSPA) with a strong envelope and omnidirectional independent bending is designed and manufactured. Additionally, we developed a novel prototype for a soft gripper prototype. A quasi-static model is proposed to effectively describe the bending deformation of 3D-MSSPA. The experimental results show that, for an applied pressure of 40 kPa, the single segment SPA achieves a maximum bending angle of 175.2°, aligning closely with the theoretical prediction. Furthermore, the omnidirectional bending ability of multi-segments is analyzed through the finite element method, and a position compensation method for gravity deviation is presented. Through experiments, the pressure fore and lifting force of the soft gripper are investigated, yielding maximum values of 11 N and 4.08 N, respectively. These results serve as a benchmark for the mass grasping range of the target objects. Finally, the experiments are conducted to demonstrate the soft gripper's adaptive and flexible grasping capabilities for objects with varying attributes, in both free space and complex space with obstacles. These experiments showcase their ability to avoid obstacles, adaptively grasp objects, and their good envelope ability. The proposed 3D-MSSPA can provide good inspiration and reference for flexible applications, particularly in fields such as post-disaster rescue and rehabilitation medicine.

Within the isogeometric analysis framework, industrial products or complex shapes are represented using multiple NURBS patches, resulting in non-matching interfaces and introducing additional numerical challenges, particularly in scenarios involving nonlinear behavior. This paper introduces the application of Nitsche's method to address interface coupling challenges presented in non-matching multi-patch configurations. A detailed formulation addressing geometric non-linearity in multiple Reissner–Mindlin plates is developed, and the resulting nonlinear equations are solved using the Newton–Raphson approach. The proposed formulation's effectiveness is demonstrated by a series of numerical examples involving complex geometries represented by multi-patches with non-matching interfaces. These examples are validated against the analytical solutions and results obtained using the commercial finite element package, Abaqus.

Functionally graded materials provide versatility in adjusting the volume fractions of constituent materials to meet specific design requirements. However, this customization often introduces mode-mixity at the crack tip, posing challenges in predicting fracture under cyclic loading with discrete approaches and computationally expensive with conventional phase-field fracture models. To address these issues, this paper introduces an adaptive phase-field fracture formulation with cycle jump scheme to elegantly predict fatigue crack nucleation and growth in functionally graded materials. Within this framework, the effective properties at a point are estimated using the Mori–Tanaka homogenization scheme, while the crack growth due to cyclic load is captured by incorporating an additional fatigue degradation parameter. Moreover, the computational efficiency of the proposed framework is improved through an adaptive mesh refinement and explicit cycle jump scheme. The adaptive refinement scheme utilizes an error indicator derived from both the displacement solution and phase-field variable. The adaptive refinement scheme is integrated with efficient quadtree decomposition, which generates a hierarchical mesh structure. Hanging nodes resulting from the quadtree decomposition are efficiently handled using a polygonal finite element method. The proposed framework is validated against experimental and numerical results reported in the literature. Furthermore, we investigate the fatigue crack growth resistance across a broad range of material gradation directions, gaining valuable insights and identifying functionally graded materials with high fatigue resistance.

This work presents an adaptive phase-field cohesive zone model (PF-CZM) for simulating mixed-mode crack nucleation and growth in isotropic rock-like materials subjected to thermo-mechanical interactions. The proposed approach combines an adaptive multi-patch isogeometric analysis (MP-IGA) and length-scale insensitive PF-CZM. The formulation captures the distinct critical energy release rates for Mode-I and Mode-II fractures, which is crucial for predicting mixed-mode thermo-mechanical fracture behavior in isotropic rock-like materials. The PF-CZM governing equations are solved with isogeometric analysis based on locally refined non-uniform rational B-splines (LR NURBS), and the complex structural geometry is exactly described with multiple LR NURBS patches. The field variables, such as displacement, phase-field, and temperature at the interface of adjacent patches, are coupled using Nitsche's method. To enhance the computational efficiency while maintaining accuracy, a refinement-correction adaptive scheme combined with the structured mesh refinement strategy is developed. The proposed framework is validated against recent numerical and experimental results in the literature, particularly in the context of capturing complex behavior of mixed-mode crack propagation in isotropic rock-like materials subjected to thermo-mechanical loading.

The damage mechanics challenge (DMC) represents a critical step in predicting the damage evolution and failure in rock-like materials displaying brittle/quasi-brittle characteristics. The phase-field fracture (PFF) model is a type of damage mechanics model that is thermodynamically consistent and is well suited for capturing complex crack patterns and interactions in 3D. However, there are two main shortcomings: (1) the definition of the crack driving force function and calibration of model parameters give rise to uncertainty in predictions of load–displacement curves; and (2) the finite element implementation of the PFF model generally necessitates the use of fine meshes, leading to higher computational costs. This study presents a novel numerical methodology that employs h-adaptive algorithms in combination with the stress-based PFF model, and demonstrates its validity against experimental data, as required by the DMC. The core strength of our methodology lies in its computational efficiency derived from dynamically-adaptive local mesh refinement. The potential of our methodology is further demonstrated through calibration, verification, and validation studies. Our 2D and 3D simulation results show good agreement with the benchmark laboratory data from three-point bending experiments, within the bounds of data uncertainty. Our blind prediction of the 3D crack geometry for the final challenge shows good agreement with the corresponding experimental data. We find that the stress-based PFF model simplifies the parameter calibration process to a single critical stress parameter, which reduces uncertainty.