Mode Ⅰ interlaminar mechanical behavior of needled/stitched multi-scale interlocking composites
Objective Non-felt needled/stitched multi-scale interlocking composites is a new type of fabric structure which enhances interlamainar strength,and it is excepted to meet the working requirements in complex environments such as hypersonic vehicles.However,the effect of stitching process on the mechanical properties of mode Ⅰ interlaminar property of non-felt needled composites is still unclear.In order to explore the influence of different stitching processes on the interlaminar properties of multi-scale interlocking composites and predict the mode Ⅰ fracture behavior,multi-scale interlocking fabrics and composites are prepared,and a finite element model of mode Ⅰ fracture behavior of multi-scale interlocking composite is established.Method In this research,quartz yarn and quartz fabrics are used as raw materials for the preparation of the multi-scale interlocking fabrics and composite.According to ASTM D5528 experimental standard,mode Ⅰ fracture behavior was tested with the prepared samples.Micro-CT and scaming electron microswpe(SEM)were used to observe and analyze the fabric structure and fracture morphology of the samples.A finite element model of mode Ⅰfracture behavior of multi-scale interlocked composites is established by using the 3 cohesive model.Results The results showed that the introduction of stitching yarns significantly improved the interlaminar property of needled composites.The maximum interlaminar fracture load of the needled composite reached 81.56N.The interlaminar fracture load values of multi-scale interlocking composites with different stitching matrices and fiber volume contents were 97.31 N,107.84 N,and 119.57 N,respectively.Compared with the needled composite,the interlaminar fracture strength was improved by 19.31％-46.61％.The critical energy release rate of needled composite was 1.80 J/m2,and the critical energy release rates of multi-scale interlocking composites with different preparation processes were 1.96 J/m2,2.24 J/m2 and 2.80 J/m2,respectivey.Compared with the needled composite,this was improved by 8.9％-55.55％.With the same stitching matrix,when the implantation amount of a single stitching yarn was increased from 100 to 200 tex,the maximum interlaminar failure load was increased by 12.91％and the critical energy release rate was increased by 17.8％.The implantation amount of the single stitiching yarn remained unchanged.With the increase of the stitching matrix,the total implantation volume was increased from 800 tex to 1 600 tex,the maximum interlaminar failure load was increased by 22.9％and the critical energy release rate was increased by 47.3％.Micro-CT observation of multi-scale interlocking fabrics revealed that the introduction of stitched and needle punched fiber bundles squeezed the fibers in the substrate,and that stitching yarns through the thickness direction of the fabric worked to achieve effective interlaminar connection.The needled fiber bundle showed T-shape and the interlaminar connection was weaker than that of stitching yarn.The fracture morphology of multi-scale interlocking composite was analyzed.The failure behavior included matrix cracking,fiber pulling out and fiber fracture.The finite element model was used to simulate the mode Ⅰ fracture behavior of multi-scale interlocking composite,and the simulation results were consistent with the sample results,with a maximum error of only 3.10％.Conclusion The study showed that compared to the needled composite,the interlaminar fracture performance of multi-scale interlocking composite is significantly improved.The maximum interlayer fracture load was increased by 19.31％-46.61％,and the critical energy release rate was increased by 8.9％-55.55％.The implantation amount of single yarn and the stitching matrix are the main factors affecting the interlaminar performance of multi-scale interlocking composite.The larger the implantation amount of a single bundle of yarn and the larger the stitching matrix,the better the interlaminar performance.The failure modes of multi-scale interlocking composite include matrix cracking,fiber pull-out,and fiber fracture.The error between the finite element simulation results of multi-scale interlocking composite and the actual results is only 3.10％,indicating that the finite element model can accurately predict the mode Ⅰ interlaminar fracture behavior of multi-scale interlocking composite.
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