Evaluation of Mechanical Properties of Silk Fiber Reinforced Biodegradable Plastic Composites (Part 2, Analytical Prediction for Stress-Strain Relationships of Silk/PBS Laminates)

Abstract

In the recent years, natural fiber reinforced composites are expected as alternative materials for traditional fiber reinforced composites. Though many experimental studies on mechanical properties of biodegradable composites have been presented in literature, analytical investigations are rarely reported. In this regard, mechanical properties of silk fiber reinforced poly(butylene succinate) (PBS) biodegradable composite (SF/PBS) laminates are investigated in the present study. In order to investigate the effects of surface treatment of the silk fiber on the mechanical properties of the SF/PBS laminates, four types of surface treatment has been applied to the silk fiber. Tensile tests are conducted on cross-ply laminates and angle-ply laminates. When the silk fibers without sericin are used, tensile strengths and Young's modulus are the highest in all laminate configurations. Stress-strain relations of both cross-ply and angle-ply laminates are predicted by combining the three-parameter plasticity model and the classical laminated plate theory. In the analysis, the properties in unidirectional composite from the generalized method of cells (GMC) micromechanics or experimental results are used. It has been found that it is possible to predict the stress-strain relations for both laminates when the experimentally-obtained properties of unidirectional laminates are used. This implies that nonlinearity caused by damages such as debondings in the unidirectional laminates under off-axis loading should be incorporated in the analysis. It has been also found that it is necessary to consider changes in fiber orientation angle due to deformation of the plates in predicting the stress-strain relation for the angle-ply laminates.