Hybrid Experimental And Numerical Investigation On The Fracture Behavior And Toughening Mechanism Of Short Plant Fiber Reinforced Composites

The natural plant short fiber reinforced composite is one kind of thermoplasticbio-composite with lightweight and high toughness, degradability and recyclability. Ithas gained a considerable ground in the high performance applications, such asautomobile interior board or aerospace structure parts. However, as high load-bearingstructure materials, precise evaluation of fracture toughness is very important, whichrequires the measurement of displacement and strain fields on the material surface. Alarge amount of research work has been conducted on the tensile mechanical behaviorof natural fiber reinforced composites, but for the research of fracture behavior of thismaterial is still in the stage of development.In this paper, the quasi-static compact tension (CT) fracture tests of random shortspruce fiber reinforced composites were performed. Based on a double CCDsynchronous image acquisition system, the deformed images of spra yed and naturaltextile surfaces of the composite were recorded. The consecutive macro fracturemorphologies from crack initiation and propagation, tearing to eventually completefailure, were monitored during the fracture tension process. The digital imagecorrelation method (DICM) was applied to compute the displacement and strain fieldsincrementally under different load states. The results show that a “stress-whitened”zone would be appeared around the crack tip due to the plastic deformation anddamage.Based on the fracture experiments of spruce/PP composite, an experimental andnumerical hybrid method was used to describe the fracture behavior. The CT elementmodel was created according to the size of tested specimen. The experimentaldisplacement fields calculated by DICM as the boundary conditions were importedinto the finite element model at the mesh nodes. Considering to the stress vs. strainrelationship of the composites obtained from the experiment, the fracture toughnesssuch as J integral was calculated by the finite element program. The results from thehybrid method were compared to the homogeneous isotropic model by the directnumerical simulation and shows a good agreement, which illustrates that the proposedhybrid method can be used for the calculation of fracture parameters of spruce/PPcomposites. The experiment results show that the anisotropy and random distribution ofspruce fibers in the mesoscopic scale result in the local inhomogeneity and anisotropyof the composite in the meso-scale, which complex the macro-scopic toughness anddamage mechanism. The comparison of fracture energy and the stress intensity factorin the linear elastic stage between spruce/PP and other two long fiber reinforcedcomposites show that spruce/PP have a better fracture toughness.