Effect of Off-Axis Ply on Tensile Properties of [0/θ]ns Thin Ply Laminates by Experiments and Numerical Method

The effect of off-axis ply on the tensile properties of unbalanced symmetric [0/θ]ns laminates was explored through experimental and numerical analysis. Six CFRP [0/θ]2s plies with different off-axis angles θ were fabricated for tensile tests. In situ observations of the damage to the laminates were conducted to investigate the initiation and progressive growth of the laminates during the tension tests. The fiber fractures, crack initiation, and progressive propagation were analyzed by observing the free edge of the laminates, and the difference in damage behavior caused by different off-axis angles was investigated. All the six [0/θ]2s plies with off-axis angles θ ranging from 15° to 90° showed approximate linear stress–strain responses in the tensile tests. Matrix cracks were not observed prior to the final catastrophic failure in the off-axis layers of the [0/θ]2s laminates with a θ in the range of 15–60°. Finite element analysis (FEA) of the [0/θ]s plies was conducted using a 3D micromechanical model, in which matrix cracking and fiber-matrix debonding in the off-axis layer were simulated using a cohesive interface element. Three micromechanical crack-free, cohesive interface, and initial crack models were analyzed to predict the influence of the matrix cracks inside the off-axis layer on the damage behavior of the [0/θ]s laminates. The numerical results from the initial crack micromechanical model show a lower bound of the tensile strength of the [0/θ]s plies. A high stress concentration is observed adjacent to the cracked off-axis layer, inducing a tensile strength loss of about 20%.

Simulation of Quasi-Isotropic E-Glass Composite Laminate at Low Velocity Impact with Cohesive Interface Elements

This paper examines the expediency of interface elements in modeling of impact damage analysis for Eglass composite laminate under low velocity impact test. Numerical modelsare built adopting cohesive interface behavior to authenticate the cross-ply damage response; and successively used the strategy to model the impact response of quasi-isotropic composite laminate. Impact test are performed to characterize the induced-damage behavior in quasi-isotropic composite laminate at different impact energy test in terms of impact force, displacement and damage size as well as the stress failure trajectory. Numerical result shows reliability of the model for structural impact analysisin damage initiation and progression in laminated composite plates. The simulation result though reveals large deformation, yet, did not yield in total fracture. This development shows the importance of adopting interface elements in structural impact damage criterion to trigger constraints effect on initiation phase.The study also reveals that the bottom most surface suffers huge deformation compare to the impact surface. It divulges that the extent of damage area in each ply of the composite laminate orients in the fiber direction in ‘star-shaped contour. The main novelty is the capability of using this model for structural impact analysis on both cross-ply and quasi-isotropic composite laminate.

Failure Analysis of Ultra High-Performance Fiber-Reinforced Concrete Structures Enhanced with Nanomaterials by Using a Diffuse Cohesive Interface Approach

Recent progresses in nanotechnology have clearly shown that the incorporation of nanomaterials within concrete elements leads to a sensible increase in strength and toughness, especially if used in combination with randomly distributed short fiber reinforcements, as for ultra high-performance fiber-reinforced concrete (UHPFRC). Current damage models often are not able to accurately predict the development of diffuse micro/macro-crack patterns which are typical for such concrete structures. In this work, a diffuse cohesive interface approach is proposed to predict the structural response of UHPFRC structures enhanced with embedded nanomaterials. According to this approach, all the internal mesh boundaries are regarded as potential crack segments, modeled as cohesive interfaces equipped with a mixed-mode traction-separation law suitably calibrated to account for the toughening effect of nano-reinforcements. The proposed fracture model has been firstly validated by comparing the failure simulation results of UHPFRC specimens containing different fractions of graphite nanoplatelets with the available experimental data. Subsequently, such a model, combined with an embedded truss model to simulate the concrete/steel rebars interaction, has been used for predicting the load-carrying capacity of steel bar-reinforced UHPFRC elements enhanced with nanoplatelets. The numerical outcomes have shown the reliability of the proposed model, also highlighting the role of the nano-reinforcement in the crack width control.