Determination Of Cohesive Zone Model Laws Of Short Fiber Composites In Both Macro And Micro Scale Using Experimental And Numerical Hybrid Method

Plant short fiber reinforced composites has gained a considerable ground in thehigh performance applications, such as automotive interior board or aerospacestructure parts, due to its environmental protection, light weight, and good mechanicalproperties. But because of the random fiber distribution, the interface between thefiber and the matrix and other factors, the mechanical properties of this material isreally complicated. In this paper, the digital image correlation method (DICM), theinverse extraction method, and the micromechanics method are used to study thecohesive laws of random short spruce fiber reinforced composites on both macroscaleand microscale.In DICM, Newton-Raphson iterative algorithm has the ability to take thedeformation of the subset into account, but this method is sensitive to the initial value,once the initial value is not accurate, the calculation result may not converge. In thispaper, an advanced initial value transmission mechanism of DICM is presented, and itadds two features on the base of Reliability-Guided Digital Image Correlation(RGDIC) method. One is the seed point automatically re-pick feature, the other is theconvergence identification feature. After adding the two features, every temporarilywrongly computed point has up to eight opportunities to be recalculated, so that itovercomes the convergence difficulties encountered when measuring the crack-tipdeformation of the spruce/PP composites.The fault tolerance of the inverse extraction method is investigated. By applyingthis method on a finite element numerical field, we found that its fault tolerance is low.So it is difficult to apply this method directly into the experimental fieldmeasurements. In this paper, the separation can be obtained in the experiment, so thatthe fault tolerance of this method is improved, then combined with the digital imagecorrelation method, the macroscopic cohesive law for the spruce/PP composites wasobtained.The bilinear cohesive zone model is adopted to research the fiber/matrix interface.The Mori-Tanaka method is used to link the macroscopic cohesive law to themicroscopic cohesive law for fiber/matrix interfaces. The parameters in themicroscale cohesive law are completely determined from the macroscopic fractureexperiments, the Mori–Tanaka method, and the equivalence of cohesive energy on the macroscale and microscale. The parameters obtained in this work can also be aexperimental basis for finite element analysis.