SiC_(f)/TC17复合材料残余应力及界面力学性能研究

Residual Stresses and Interfacial Properties of SiC_(f)/TC17 Composite

采用基体涂层法制备出SiC连续纤维增强钛基(SiC_(f)/Ti)复合材料,通过纤维顶出试验和有限元模拟研究复合材料的热残余应力分布特征与界面力学性能的影响因素。SiC_(f)/TC17复合材料中SiC纤维呈近似六方排布,均匀分布在钛合金基体中。根据单纤维顶出试验的载荷-位移曲线计算出SiC_(f)/TC17复合材料的平均界面剪切强度和摩擦应力分别为49 MPa和34 MPa。有限元模拟结果表明,随SiC_(f)/TC17复合材料中热残余应力的增加,顶出试验的摩擦力显著增加,而界面脱粘力先降后升;随摩擦系数的增加,脱粘力和摩擦力都增加;随本征界面剪切强度增加,脱粘力增加而摩擦力不变。结合顶出试验和有限元模拟结果,确定SiC_(f)/TC17复合材料的界面摩擦系数和本征界面剪切强度分别为0.17和390 MPa。单纤维顶出试验中,SiC_(f)/TC17复合材料在C涂层和反应层之间脱粘,顶出载荷在界面产生的剪切应力与支撑端的剪切残余应力方向一致,导致界面脱粘首先发生在支撑端,而后脱粘区域沿着纤维/基体界面向加载端扩展,当载荷-位移曲线达到最大值时界面完全脱粘。

Continuous SiC fiber reinforced titanium matrix(SiC_(f)/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_(f)/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 SiC_(f)/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 SiC_(f)/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 2μm,and an outer reaction layer outside C coating measured be⁃tween 1 to 2μm.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 SiC_(f)/Ti compos⁃ite were measured as 49 MPa and 34 MPa,respectively.After cooling,SiC_(f)/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 SiC_(f)/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.