Study On The Damage Evolution Of Three-dimensional Four-directional Braided Composite Material Under Multiple Impacts

Composite materials have shown a good development trend in recent decades due to their high specific strength,high specific stiffness,light weight and other great mechanical properties.Due to their structural particularity,braided composite materials effectively avoid many shortcomings of traditional laminated composite materials,such as weak interlayer performance,easy delamination and debonding,poor impact resistance and low damage tolerance.Braided composite materials will be frequently impacted by different objects during use and maintenance,such as tools falling during structural maintenance and stones splashing.The strength of the structures will gradually decrease after the impact of foreign objects.At present,there are many studies on single impact of three-dimensional braided composite materials in the industry,and there are few studies on the multiple impacts of three-dimensional braided composite materials.Therefore,it is necessary to conduct in-depth research multiple impacts on carbon fiber reinforced epoxy resin-based three-dimensional four-directional braided composite materials.In this paper,multiple impact tests of three kinds of punches were designed to study the impact response of the specimens when they were impacted by cylindrical punches,tapered punches and spherical punches.The internal damage area was detected by ultrasonic C-scan,and the damage propagation process of the specimens under multiple impact loads was studied.Then axial compression tests were carried out on the specimens after impact to study the effect of the number of impacts on the remaining load-bearing capacity and failure process of the specimens.The finite element software ABAQUS was used to model microstructure of the three-dimensional four-directional braided composite materials.Based on the material characteristics,the three-dimensional Hashin damage criterion was used for fiber bundle,and the maximum stress criterion was used for matrix to judge the material damage.And combine the experimental and simulation results to study failure modes and damage evolution process of the specimens under multiple impact loads.The results showed that the destruction process of the specimens was affected by the shape of the punch.Cylindrical punch caused slight damage to the specimens but the internal damage area was large.The response process of the specimens being impacted by a tapered punch was similar to that of a spherical punch,but the damage caused by a spherical punch to the specimens was more serious.Impact resistance of three-dimensional four-directional braided composite materials was affected by braid angle.The larger the braid angle,the better the impact resistance.The damaged area of the specimens with a larger braid angle expanded to surrounding area,and the damaged area of the specimens with a smaller braid angle mainly expanded in longitudinal direction.Failure modes of the specimens during impact tests were mainly longitudinal tensile failure of fiber bundle,the transverse tensile failure and the transverse compression failure of the fiber bundle and the matrix.Axial load-bearing capacity was affected by braid angle and magnitude of impact damage.When the braid angle was small and the impact damage was slight,the axial residual load-bearing capacity was strong.Remaining compressive strength of the specimens with equal braid angle was basically the same when the specimens were penetrated.Failure modes of small braid angle specimens under compressive load were mainly local buckling and collapse of fiber bundle,and failure mode of the large braid angle specimens was mainly shear failure of fiber bundle and matrix.