Elastic and plastic deformation behaviour of UD Natural fibre composites under compression loading
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Arefe MENGSTU ASHEBRE (BELGIUM), Aart Willem VAN VUUREAbstract :
Unidirectional composite materials experience various fracture mechanisms such as micro buckling, fibre kinking, fibre breaking, and longitudinal cracking, under uniaxial compressive loading. In all these deformation cases, there is a shear deformation due to the isotropic polymer matrix which dominantly appears after the elastic limit of the composite structure due to the initial crack formation that exists at the boundary of a misaligned fibre or due to preexisting micro-voids. This study elucidates the elastoplastic deformation behaviour of enset fibre-epoxy composites under compression loading. Digital image correlation was employed to accurately measure the strain and the elastic modulus. The elastic and plastic deformation regions were investigated, and the transition strain and the offset strain were determined.
The study further examines the incipient kinking (initial crack formation) and the steady-state plastic deformation denoted as the plastic deformation points. The elastic and plastic strains were calculated with the help of Hook’s elastic equation and the corresponding gradients were figured out by differentiating the strains with time. The analysis reveals two significant intersection points: the intersection of elastic and plastic strains time curves, and the intersection of gradient sections. The convergence of gradient curves accurately pinpoints the incipient point, while the intersection of elastic and plastic strains precisely defines the plastic point.
An in-situ compression test was conducted to examine the physical behaviour of the composite at these distinct stages: incipient, transition, and plastic points. An in-house Deben setup was mounted to a computer tomography system, UniTOM HR of TeScan-xCT, to perform the compression loading and image acquisition. After reconstruction and image segmentation, parameters such as fibre misalignment, degree of anisotropy, and the orientation and volume fraction of voids were examined at these points and compared against the corresponding undeformed state. Variations in these parameters serve as crucial indicators of the predicted physical deformations hypothesized by the intersection points of elastic and plastic strains and their gradients.
In general, enset fibre composites experienced significant plastic deformation, 88%, and the remaining being elastic deformation. The composite introduces 0.10% ± 0.02% offset strain at 0.42% ± 0.06% transition strain. Damage analysis further underscores that the composite structure reaches the plastic deformation point when the secant modulus is reduced by half.
The study further examines the incipient kinking (initial crack formation) and the steady-state plastic deformation denoted as the plastic deformation points. The elastic and plastic strains were calculated with the help of Hook’s elastic equation and the corresponding gradients were figured out by differentiating the strains with time. The analysis reveals two significant intersection points: the intersection of elastic and plastic strains time curves, and the intersection of gradient sections. The convergence of gradient curves accurately pinpoints the incipient point, while the intersection of elastic and plastic strains precisely defines the plastic point.
An in-situ compression test was conducted to examine the physical behaviour of the composite at these distinct stages: incipient, transition, and plastic points. An in-house Deben setup was mounted to a computer tomography system, UniTOM HR of TeScan-xCT, to perform the compression loading and image acquisition. After reconstruction and image segmentation, parameters such as fibre misalignment, degree of anisotropy, and the orientation and volume fraction of voids were examined at these points and compared against the corresponding undeformed state. Variations in these parameters serve as crucial indicators of the predicted physical deformations hypothesized by the intersection points of elastic and plastic strains and their gradients.
In general, enset fibre composites experienced significant plastic deformation, 88%, and the remaining being elastic deformation. The composite introduces 0.10% ± 0.02% offset strain at 0.42% ± 0.06% transition strain. Damage analysis further underscores that the composite structure reaches the plastic deformation point when the secant modulus is reduced by half.