Experimental And Failure Mechanism Analyses Of The Bearing Behavior Of Two-dimensional Braided Ceramic Matrix Composites

Two-dimensional braided ceramic matrix composites have excellent mechanical properties and heat resistance,and their structural components have good integrity.They are widely used in aeroengines and spacecraft.The bolted joints between two-dimensional braided ceramic matrix composites and metal are widely used in aircraft structures.Bearing failure is one of the main failure modes of these joints.Therefore,the experimental and failure mechanism analyses of bearing behavior of two-dimensional braided ceramic matrix composites are of great significance to the structural design of ceramic matrix composites.In order to study the bearing mechanical properties of two-dimensional braided ceramic matrix composites,firstly the bearing experiments of two-dimensional braided ceramic matrix composites and metal single countersunk bolted joints with different sink depths and angles were carried out.By analyzing the load-displacement curves,DIC strain contour and 3D microscope images under different sink parameters,the relationship between the ultimate load,bearing strength,strain distribution and local failure and sink parameters was obtained.Prediction of elastic constants of two-dimensional braided ceramic matrix composites was studied.Based on the periodic braided structures,a finite element unit-cell model was established with periodic boundary conditions.The elastic constants of the material were predicted under homogenization theory,which provided conditions for the analyses of progressive bearing failure mechanism of two-dimensional braided ceramic matrix composites.The modified strain-based three-dimensional Chang-Chang failure criterion and energy-based continuous linear material degradation scheme were adopted.The VUMAT material subroutine of the common finite element software ABAQUS was written in Fotran language,and the progressive bearing failure analyses method and process of braided composites were established.The bearing failure mechanism of two-dimensional braided ceramic matrix composite was studied.The finite element model of two-dimensional braided ceramic matrix composites and metal bolted joint structure was established.The results of stress,strain and displacement were obtained.The load-displacement curves and damage changes of each layer of the composites were obtained.The bearing failure mechanism of two-dimensional braided ceramic matrix composites was analyzed.The relationship between bearing mechanical properties and sink parameters of two-dimensional braided ceramic matrix composites bolted joint structure was obtained by experiment,theoretical analyses and numerical simulation.It has important reference significance for the design of two-dimensional braided ceramic matrix composite connection structure.