Numerical Study On Cutting And Drilling Damages Of Fiber Reinforced Composite

Fiber reinforced composites are widely used in aerospace?military?energy?construction and other industry fields due to their excellent properties such as high strength-to-weight ratios,high modulus-to-weight ratios,corrosion resistance,etc.Composite products generally machined by cutting and cutting will introduce damage in cutting face.Riveting and bolting connections also will adopted in assembling composite structures.In these connecting methods hole-marking quality is one of the critical factors which directly affect the joint strength and fatigue life of composite structures.The damages introduced in processes of mechanical cutting and drilling are studied in this dissertation.The main research contents and results are as follows:(1)Based on the secondary development of finite element software ABAQUS,a two-dimensional microscale simulation model of fiber composite cutting is established.The removal process of material,formation of chip and the morphology of cutting surface for a unidirectional composite are studied with different cutting angles.Cutting tests are conducted and the microscopic appearances of the cutting faces are observed by using digital microscopy.The simulations are found well representing the experimental observations.(2)A three-dimensional finite element model of hole-making for composite material is established.The initiation and extension of delamination damage around hole during the drilling are simulated.The results show that: the delamination damage in the exit is larger than in the entrance of hole;the main damage mode inside laminar is resin tensile failure;the delamination damage area of multi-directional laminated composite is smaller than unidirectional composite.(3)The drilling test of composite material is carried out.The delamination damage areas obtained by ultrasonic C scan agree with the simulation results.The finite element model established above is employed in the investigations of influences of the feed rate and main axle rotating speed on the axial force of twist bit and delamination damage of composite.Result show that: the higher of feed rate the bigger for axial force and delamination area;the higher of main axle rotating speed the smaller for axial force and delamination degree;the greater of axial force the severer for delamination damage.Thus,the axial force is provn the main cause of delamination damage around drilling hole.