Abstract
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%.
Highlights
Carbon fiber reinforced polymer (CFRP) laminates have been attracting much attention due to their outstanding mechanical properties in the fiber orientation direction.Multidirectional laminates consisting of two or more angles of off-axis layers are able to improve mechanical properties in multiple directions
The present study focused on the effect of off-axis layer on tensile properties, i ing the strength and microscopic damage propagation of unbalanced symmetric laminates using an in situ observation experiment and 3D micromechanical model observat sis
In all the [0/θ]2s laminates, the final fracture of each specimen always occurred along the corresponding off-axis angle of the [0/θ]2s laminate, indicating that the initiation, accumulation, and propagation of matrix cracks in the off-axis layer have significant influence on the failure mechanism the final failure is dominated by the 0◦ layer of the [0/θ]2s laminate
Summary
Carbon fiber reinforced polymer (CFRP) laminates have been attracting much attention due to their outstanding mechanical properties in the fiber orientation direction. Multidirectional laminates consisting of two or more angles of off-axis layers are able to improve mechanical properties in multiple directions. The initiation and growth of matrix cracks parallel to the fiber orientation in off-axis plies are always observed. The investigation of the effect of the microscopic damage in the off-axis layers on the mechanical properties of multidirectional laminates is necessary for accurately predicting the mechanical properties of multidirectional laminates subjected to an external load. Many experimental and numerical efforts have been made to analyze the effect of matrix cracks on the mechanical properties of various multidirectional laminates [1,2,3,4,5,6]
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