Mohammad Javad Mahmoodi

Piezoelectric polymer nanocomposites reinforced with conductive particles, such as carbon black (CB), have gained significant attention for their unique combination of mechanical strength and tunable electrical properties. However, accurately predicting the overall electrical conductivity of these materials remains challenging due to the complex interactions between the polymer matrix and conductive nanoparticles, as well as the critical role of interphase regions and tunneling effects. In this study, a modified unit cell model is developed to incorporate interphase conductivity and tunneling resistance, enhancing the accuracy of conductivity predictions. A hierarchical modeling strategy is introduced to capture the synergistic effects of nano- and micro-scale fillers, providing a comprehensive framework for complex composite analysis. The model is validated using CB–KNN–epoxy nanocomposite films, demonstrating strong agreement between numerical predictions and experimental measurements. This work provides valuable insights into the design and optimization of high-performance piezoelectric composites for advanced energy harvesting and flexible electronics.

The complex three-dimensional (3D) state of interlaminar stresses in the vicinity of a free corner in composite laminates brings about delamination, matrix cracking, and overall failure. This study focuses on devising a straightforward and efficient computational framework for analyzing the free-corner-induced failures in mechanically and thermally-loaded thick angle-ply composite laminates based on an innovative global-local finite element model. In so doing, the global region is dealt with by the first-order shear deformation theory, and the local sub-model region near the free corner is scrutinized using the 3D layer-wise theory. Distinctive risk parameters associated with the meso-level damage modes, including ply failure, delamination, and transverse matrix cracking are well-defined under the corresponding criteria. The precision of the model is ensured through verifications in which satisfactory alignment between the current outcomes and those of other available works in the literature substantiates the efficacy of the proposed approach. Furthermore, the impacts of the configuration parameters such as fiber orientation and thickness of plies upon the risk parameters are fully examined. It is found that, generally, by increasing the angle of fibers between two adjacent layers and diminishing the ply thickness, the composite laminate becomes more critical. The matrix cracking mode is dominated regarding the delamination and is in close agreement with the ply failure analysis. The proposed computational infrastructure, occasioning time and financial savings is valuable and enlightening for designing and manufacturing composite structures.

In this paper, a constitutive model for the stress-strain response of municipal solid waste (MSW) is presented, considering the effects of temperature and aging. Our goal is to provide a model for predicting the behavior of these materials. The models used to predict the behavior of waste have used the theory of soils, and in this research, the theory of composite materials has been used for the first time. Cylindrical sample is modeled and loaded under triaxial loading conditions as observed in the experimental specimens. Fresh MSW, as a waste sample with a specific composition, was investigated. By using the optimization method, the constants of the given equation were obtained and the basic stress-strain model was presented based on the composite theory. The obtained results are compared with previous models' experimental data and results to verify the proposed model. At the strains of less than 30%, a good agreement can be reported between the numerical and experimental results. The root means square percentage of the relative error between the present model and the model of other researchers has shown acceptable results. It is also revealed that, as the temperature of the MSW increases, the stress on the waste is increased.