Analysis On Toughening Of Carbon Fiber Reinforced Polymer With Non-woven Fabric Interlayer

Delamination, which appears in the interface primarily, is the most dangerous failure modes in laminated composites. Therefore, how to inhibit the delamination damage and improve the fracture toughness of the composites are the hot research in designing and analysing the carbon fiber reinforced polymer (CFRP). It is proved that porous polyamide non-woven fabric (PNF) can achieve an excellent toughness of the composites while keeping a good processibility. However, there is less research about the interlaminar toughening mechanism of PNF up to now. It has the important theoretical significance to establish a constitutive model to accurately describe the damage mechanisms of PNF, and successfully model the delaminaton process of CFRP being financed by Nation Major Fundamental Research Program of China (973Project). Further, it also has important application value to guide practical application by studying the influence law of different materials and their parameters on the fracture toughness of CFRP.The finite element model based on cohesive zone model (CZM), which can represent the PNF, is constructed to predict the delamination onset and propagation of CFRP. The effects of the property of PNF and the geometric parameters of laminate on the mechanical response of CFRP are studied mainly.In the double cantilever beams test, which is used to calculate the mode I interlaminar fracture toughness (One) of composite, the main conclusions are as follows:(ⅰ) The peak load and CIC of CFRP increase with the increase of the cohesive normal strength. If PNF’s GIC<0.7N/mm, it is not obvious to toughen the CFRP; If PNF’s GIC>0.7N/mm, GIC of CFRP is improved, while once PNF’s GIC is greater than0.9N/mm, only part of PNF’s GIC can been converted to GIC of CFRP.(ⅱ) There is little effect of modulus and thickness of PNF on the mode I delamination of CFRP, but the resistance of propagation increase when modulus is more than2000MPa, and thickness is equal to20μm.(ⅲ) With the increase of the thickness of laminates, the peak load and extension resistance increase. The optimal laminate thickness is4mm in order to catch the obvious delamination propagation and the plastic yielding of PNF;(iv) GIC of composite increases with the increase of pre-crack length slowly, and it tends to be stable when pre-crack length is greater than45mm.(v) For a specific ply-orientation composite, once delamination begins to propagate, the figure of delamination front is consistent. It is thumbnail-shaped figure for [012/012], while straight line for [012/9012]. For the other three, they have different morphologies, and it is warped most for [012/6012]. With the increase of the ply angle, the propagation distance and peak load are reduced correspondingly.In the end notch flexure test, which is used to calculate the mode Ⅱ interlaminar fracture toughness (GⅡC) of composites, the results are obtained as follows:(ⅰ) The peak load and GⅡC of CFRP increase with the increase of the cohesive shear strength, but the increasing amplitudes are gradually reduced. Once the delamination propagates steadily, GⅡC of PNF plays a leading role. The greater GⅡC of PNF is, the greater GⅡC of CFRP and peak load are.(ⅱ) There is little effect of modulus and thickness of PNF on mode Ⅱ delamination of CFRP.(ⅲ) With the increase of the thickness of laminates, the peak load, extension resistance and GⅡC of CFRP in mode II delamination increase marketedly, but GⅡC of CFRP tends to a stable value when the thickness is higher than5mm.(iv) With the increase of the pre-crack length, the peak load is falling and GⅡC of CFRP keeps increasing, while both amplitudes of variation decrease. The30mm-long pre-crack is a spinodal, the load deflection corresponding to the peak load decreases first, and then increases,(v) Once delamination begins to propagate, the distribution of shear stress along the propagation direction is consistent, and the propagation velocity decreases. The shape of the delamination front depends on the ply angles, while it doesn’t delaminate for [9012/012] composite. When the ply changes from [012/012] to [6012/012], the propagation distance is decreased unnder the same load deflection, but GⅡC of CFRP is increased correspondingly.