Effect of fit conditions on mechanical properties of C/SiC online riveting unit
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摘要: 针对化学气相沉积(CVI)工艺2D C/SiC材料制备热结构中大量采用的在线铆钉连接形式及地面试验中表现出的特点，研究了铆钉与平板开孔之间采用间隙或过盈配合不同形式对力学性能的影响。制备了典型含铆钉单元试件并进行了细观形貌观测，通过铆钉顶出试验得到了不同配合条件下顶出静强度及疲劳规律；通过不同配合条件下含铆钉试件与开孔试件的拉伸静强度试验，获得了C/SiC在线铆接导致的面内连接强度性能下降的规律；描述了纤维束变形和材料局部区域破坏的特点，并依据形貌观测开展了数值计算验证；在此基础上，针对C/SiC过盈配合铆接形式提出了考虑孔边应力集中影响的改进点应力失效准则。结果表明，过盈配合可以改善铆钉与平板之间的连接可靠性，显著提高铆钉顶出静强度和疲劳强度，但过盈配合铆接的工艺过程使得孔边局部碳布纤维产生挤压偏折变形并导致了孔边预应力。Abstract: According to the on-line rivet connection forms widely used in Chemical vapor infiltration (CVI) process 2D-C/SiC thermal structures and characteristics shown in ground tests, the effects of different forms of clearance or interference fit between rivets and flat openings on mechanical properties were studied. A typical test piece with rivets was prepared and the microscopic morphology was observed. Through rivet push-out test, the push-out static strength and fatigue rules under different matching conditions were obtained. By comparing the tensile static strength of the specimens with rivets and the specimens with holes under different matching conditions, the rule of in-plane strength performance degradation caused by C/SiC online riveting was obtained. The characteristics of fiber bundle deformation, hole edge pre-stress and local area damage of materials were analyzed, and numerical modeling calculation was carried out according to morphology observation. Then, an improved point stress failure criterion (PSC) considering the effect of stress concentration at the hole edge was proposed for C/SiC interference fit riveting. Research shows that interference fit can improve the connection reliability between rivet and hole, significantly improve the push-out static strength and fatigue strength of rivet. But the interference fit riveting process makes the local carbon fiber at the hole edge extrude and deform, which leads to the prestress at the hole edge.
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Key words:
- C/SiC /
- online rivet connection /
- strength character /
- fatigue test /
- fitting condition
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图 2 C/SiC在线铆接部位在振动和强度试验中的破坏现象
Figure 2. Failure phenomenon of C/SiC online rivet connection part in vibration and strength test
图 3 典型铆钉单元试件的设计及实物图
Figure 3. Design and physical drawings of typical unit specimen with rivets
图 5 C/SiC铆钉顶出强度试验的设计及现场情况
Figure 5. Design and field situation of C/SiC rivet push-out strength test
图 6 C/SiC试件的铆钉顶出静强度载荷-位移曲线对比
Figure 6. Comparison of static strength load-displacement curves of rivet push-out test pieces of C/SiC
图 7 C/SiC铆钉单元试件的顶出静强度破坏形貌对比
Figure 7. Comparison of push-out tensile strength and failure morphology of C/SiC test units with rivets
图 8 C/SiC铆钉顶出疲劳强度试验测试结果及拟合曲线
Figure 8. Test results and fitting curve of rivet push-out fatigue strength test of C/SiC
图 9 C/SiC开孔试样的试验状态和拉伸破坏形态
Figure 9. Experimental state and tensile failure morphology of C/SiC specimen with opening-hole
图 10 C/SiC单独开孔及铆钉单元试件的拉伸测试性能比较
Figure 10. Comparison of tensile test performance between opening-hole and rivet-test units of C/SiC
图 11 C/SiC铆钉单元试件拉伸破坏形貌
Figure 11. Tensile failure morphology of C/SiC test units with rivets
图 12 C/SiC单独开孔与铆钉过盈装配试件的拉伸应力-应变曲线
Figure 12. Tensile stress-strain curves of samples with opening-hole and interference fitting test units with rivets of C/SiC
图 13 过盈装配C/SiC铆钉在静载荷顶出试验时的破坏局部特征
Figure 13. Local failure characteristics of interference-fitting C/SiC rivet in static push-out test
图 14 铆钉过盈装配的几何关系以及纤维偏折/材料破坏的绕中心轴分布示意图
Figure 14. Geometry relation of rivet interference fit and fiber deflection/material failure distribution around central axis
图 15 不同厚度位置孔边纤维偏折计算及与实测对比
Figure 15. Calculation of fiber deflection at different thickness positions and comparison of measured results
图 16 采用虚拟纤维的铆钉装配数值建模
Figure 16. Numerical simulation of rivet assembly using virtual fibre
图 17 采用虚拟碳纤维和SiC实体建模的铆钉装配模型
Figure 17. Rivet assembly model based on virtual carbon fiber and SiC solid
图 18 仅考虑虚拟纤维不同几何状态的C/SiC铆钉顶出计算结果
Figure 18. Comparison of C/SiC rivet push-out calculation results only considering different geometric states of virtual fiber
图 19 铆钉过盈装配的C/SiC孔边预应力数值模拟结果
Figure 19. Numerical simulation results of pre-stress around hole in C/SiC rivet interference fitting model
图 20 C/SiC开孔和含铆钉试样的孔边拉伸应力分布
Figure 20. Tensile stress distribution near hole edge of opening-hole and rivet fitting C/SiC specimen
表 1 C/SiC材料及组分材料力学性能
Table 1. Mechanical properties of the C/SiC and component materials
Property Value Elastic modulus Ex(Ey) of C/SiC /GPa 115 Elastic modulus Ez of C/SiC /GPa 35 Poisson's ratio νxy of C/SiC 0.05 Poisson's ratio νxz(νyz) of C/SiC 0.01 Shear modulus Gxy of C/SiC /GPa 35 Shear modulus Gxz(Gyz) of C/SiC /GPa 32 Elastic modulus E1 of carbon fibre /GPa 124 Elastic modulus E2(E3) of carbon fibre /GPa 14 Shear modulus G23 of carbon fibre /GPa 18 Shear modulus G12(G13) of carbon fibre /GPa 20 Poisson's ratio ν12(ν13) of carbon fibre 0.17 Poisson's ratio ν23 of carbon fibre 0.01 Elastic modulus E of SiC matrix with voids /GPa 150 Shear modulus G of SiC matrix with voids /GPa 70 Poisson's ratio ν of SiC matrix with voids 0.08 
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表 2 C/SiC单独开孔状态下的强度特征长度
Table 2. Strength characteristic length of C/SiC under the condition of opening
Hole radius
ra/mmTensile strength
σN/mmσN/σ0 Characteristic
length da/mm0 212.0 1 / 1.0 186.0 0.877 1.38 1.75 159.3 0.751 1.32 2.0 152.0 0.717 1.32 2.75 136.1 0.642 1.39
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