Residual Stresses and Interfacial Properties of SiCf/TC17 Composite
Continuous SiC fiber reinforced titanium matrix(SiCf/Ti)composites have important applications in the aerospace field due to their excellent mechanical properties,including high stiffness,specific strength,fatigue resistance,and creep resistance.The difference in thermal expansion coefficient between SiC fiber and the titanium alloy matrix leads to the generation of thermal residual stress during the cooling process.The magnitude and distribution of residual stress play a crucial role in influencing the mechanical properties and failure behavior of the composite.Additionally,the interface properties of SiC/Ti composite significantly affect the mac-roscopic mechanical properties of the material.To investigate the distribution of thermal residual stress and the factors affecting the in-terface mechanical behavior of SiCf/Ti composite,this study employed the single fiber push-out test method and finite element simula-tion.The objective was to characterize the stress distribution characteristics of the composite,identify the primary factors influencing the interface mechanical behavior,and elucidate the interface debonding mechanism in the push-out test.SiC fibers in SiCf/Ti compos-ite,prepared using the matrix coating method,were approximately hexagonal and evenly distributed in the titanium alloy matrix.These fibers were coated with C coating with a thickness of about 2 μm,and an outer reaction layer outside C coating measured be-tween 1 to 2 μm.The load-displacement curve of the single-fiber push-out test comprised four stages:elastic deformation,fiber debonding,interfacial friction,and pressing into the matrix.The average interfacial shear strength and friction stress of SiCf/Ti compos-ite were measured as 49 MPa and 34 MPa,respectively.After cooling,SiCf/Ti composites exhibited thermal residual stress.The axial,radial,and hoop thermal residual stress in the fiber was negative,while in the titanium alloy,the radial residual stress was negative,and the axial and hoop thermal residual stress was positive.The distribution of thermal residual shear stress at the interface was sym-metrical concerning the center height of the sample,peaking near the two free faces of the sample.The shear stress symbols at these faces were opposite.An increase in the stress-free temperature led to an increase in thermal residual stress.Moreover,an increase in radial residual stress resulted in elevated interface contact pressure,leading to increased friction in the push-out load-displacement curve.While an increase in radial residual stress enhanced the average interfacial shear strength,an increase in thermal residual shear stress reduced it.Consequently,when the stress-free temperature increased,these two factors interact,resulting in a slight decrease followed by a slight increase in the maximum value of the load-displacement curve.With an increase in the friction coefficient,both the average interfacial shear strength and friction stress increased.Based on the experimental value of the friction force of the compos-ite material,the friction coefficient was determined to be 0.17.Furthermore,an increase in the intrinsic interfacial shear strength led to an increase in the maximum value of the load-displacement curve,while the friction force remains unchanged.According to the ex-perimental value of the average interfacial shear strength,the intrinsic interfacial shear strength of the material was determined to be 390 MPa.Due to the intact C coating during the preparation process and a low degree of interface reaction,debonding occurred be-tween C coating and the reaction layer in SiCf/Ti composite.Following single-fiber push-out,the surface of C coating remained smooth without any breakage,thereby reducing interface friction stress and resulting in a rapid decline in the push-out load after debonding.The shear stress generated by the push-out load at the interface aligns with the thermal residual shear stress at the support end.Conse-quently,the interface near the support end of the sample initially reached the intrinsic shear strength and debonds,followed by the ex-pansion of the debonding area along the fiber/matrix interface from the support end to the loading end.Upon reaching the maximum val-ue of the load-displacement curve,the interface was completely deboned.
SiC fiberTi based compositeresidual stressinterfacial shear strengthfinite element analysis
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