CFRP-钢层状复合结构的表面划痕损伤容限

王斌华; 康思思

doi:10.13801/j.cnki.fhclxb.20210820.004

CFRP-钢层状复合结构的表面划痕损伤容限

doi: 10.13801/j.cnki.fhclxb.20210820.004

王斌华^,,
康思思

长安大学　道路施工技术与装备教育部重点试验室，西安 710064

基金项目: 陕西省自然科学基金(2021JM-148)

详细信息

通讯作者:
王斌华，博士，教授，博士生导师，研究方向为结构/材料的变形、损伤与断裂　E-mail：wangbh@chd.edu.cn

中图分类号: TB332
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- 被引次数: 0
出版历程
- 收稿日期: 2021-06-09
- 修回日期: 2021-07-12
- 录用日期: 2021-07-26
- 网络出版日期: 2021-08-20
- 刊出日期: 2022-07-30

Scratch damage tolerance at the surface of CFRP-steel laminated composite structure

WANG Binhua^,,
KANG Sisi

Key Laboratory of Road Construction Technology and Equipment, Chang'an University, Xi'an 710064, China

摘要

摘要: 碳纤维增强树脂复合材料(CFRP)-钢层状结构在实际运营过程中，脆性碳纤维层容易出现划痕等表面损伤，因此为了保障损伤后复合结构的安全运行，需要对其进行损伤容限研究。基于边界效应理论模型(Boundary effect model，BEM)，建立了表面划痕损伤后的CFRP-钢层状结构三点弯曲断裂强度解析模型，并在CFRP表面分别预制了0.2 mm和0.4 mm深度的表面初始划痕缺陷，通过三点弯曲梁的成组试验验证了理论模型的可行性。研究结果表明：(1)利用金相显微镜观测了CFRP-钢层状结构三点弯曲极限荷载时的断裂特征，确定了表面划痕损伤后CFRP的结构特征参数C_ch，代入解析模型获得了CFRP层的拉伸强度，并与CFRP直接拉伸试验测试的拉伸强度对比，两者偏差小于10%；(2)该解析模型为“断裂荷载=拉伸强度×等效面积”的线性方程形式，“等效面积”仅与CFRP-钢层状结构和表面裂纹的几何参数有关，因此，通过CFRP的直接拉伸强度可以预测表面损伤后CFRP-钢层状结构的断裂强度，实现损伤容限设计。
- CFRP-钢层状结构 /
- 表面划痕 /
- 损伤容限 /
- 断裂强度 /
- 解析模型
Abstract: In the actual operation process, the surface of brittle carbon fiber layer of carbon fiber reinforced polymer (CFRP)-steel layered structure suffered from scratch and other damage. Therefore, it is necessary to study the damage tolerance to ensure the safe operation of the damaged composite structure. An analytical model of fracture strength at the three-point bending (3-p-b) test for CFRP-steel laminated structure with surface scratch damage was established based on the boundary effect model (BEM). And the initial scratch defects of 0.2 mm and 0.4 mm depth were prefabricated on the surface of CFRP, respectively. The feasibility of this theoretical model was verified at the 3-p-b tests. The results indicate that: (1) The fracture characteristics of CFRP-steel laminated structure at the 3-p-b tests were observed by metallographic microscope, and the structural characteristic parameter C_ch of CFRP after scratch damage was determined. The tensile strength of CFRP layer was carried out according to this analytical model, and the deviation is less than 10% compared with the tensile strength measured by CFRP direct tensile test. (2) The analytical model is a linear equation of “fracture load = tensile strength × equivalent area”. The “equivalent area” is only related to CFRP-steel laminated structure and the geometric parameters of surface crack. Therefore, the fracture strength of CFRP-steel laminated structure with surface damage can be predicted by the direct tensile strength of CFRP, and the damage tolerance design can be realized.
- CFRP-steel laminated composite structure /
- surface scratch /
- damage tolerance /
- fracture strength /
- analytic model

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图 1 碳纤维增强树脂复合材料 (CFRP)-钢复合结构的几何模型

Figure 1. Geometric model of carbon fiber reinforc-ed polymer (CFRP)-steel composite structure

CFRP—Carbon fiber reinforced polymer; S—Span length; L—Sample length; B—Sample width; P_max—Maximum fracture load

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图 2 CFRP裂纹处截面的应力-应变图

Figure 2. Stress-strain diagram of CFRP crack section

h₁—Thickness of steel plate; h₂—Thickness of CFRP plate; Δa_fic—Crack tip damage zone/fictitious crack growth; σ_n—Nominal stress at crack tip damage zone; ε_n—Nominal stress at crack tip damage zone; σ_s—Stress at upper surface of steel plate; ε_s—Strain at upper surface of steel plate; E_s—Elastic modulus of steel plate; σ’_s—Stress at the interface between steel and CFRP on steel plate; ε’_s—Strain at the interface between steel and CFRP; E_n—Equivalent elastic modulus of CFRP; a₀—Initial crack depth; x—Distance from the neutral axis of CFRP/steel layered structure to the bonding interface between CFRP and steel; M—Moment in CFRP/steel layered structure

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图 3 CFRP拉伸试件

Figure 3. Tensile specimen of CFRP

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图 4 CFRP板拉伸试件断裂照片

Figure 4. Fracture pictures of CFRP tensile specimens

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图 5 CFRP-钢复合结构的位移-载荷曲线

Figure 5. Displacement-load curves of CFRP-steel composite structure

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图 6 a₀=0.2 mm的CFRP-钢层状复合结构P_max时刻对应的裂纹扩展

Figure 6. Crack growth of CFRP-steel layered composite structure at P_max(a₀=0.2 mm)

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图 7 a₀=0.4 mm的CFRP-钢层状复合结构P_max时刻对应的裂纹扩展

Figure 7. Crack growth of CFRP-steel layered composite structure at P_max(a₀=0.4 mm)

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图 8 CFRP抛磨断面示意图

Figure 8. Polishing location for CFRP

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图 9 金相显微镜下观察CFRP-钢复合结构的裂纹扩展长度(Δa_fic)

Figure 9. Crack growth length of CFRP-steel composite structure at metallographic microscope (Δa_fic)

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图 10 CFRP-钢复合结构的P_max-A_e 曲线

Figure 10. P_max-A_e curves of CFRP-steel composite structure

μ—Average; σ—Standard deviation; f_t—Tensile strength of CFRP plate; A_e—Equivalent area

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图 11 CFRP-钢复合结构的σ_n-a_e曲线

Figure 11. σ_n-a_e curves of CFRP-steel composite structure

σ_n—Nominal stress; a_e—Equivalent crack length; K_IC—Fracture toughness of CFRP plate; $a_{{\rm{ch}}}^*$—Length of characteristic crack; C_ch—Characteristic composite microstructure

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图 12 CFRP-钢复合结构的P_max-A_e曲线预测

Figure 12. P_max-A_e curves prediction of CFRP-steel composite structure

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图 13 CFRP-钢复合结构的${\rm{\sigma}}_{\rm{n}}$-$ a_{\rm{e}} $曲线预测

Figure 13. ${\rm{\sigma}}_{\rm{n}}$-$ a_{\rm{e}} $ curves prediction of CFRP-steel composite structure

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表 1 A-38/3K碳纤维丝材料性能

Table 1. Material properties of A-38/3K carbon fiber

Type	Elastic modulus/GPa	Yield strength/MPa	Elongation/%
A-38/3K	240	3800	1.6

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表 2 环氧树脂胶粘剂材料性能

Table 2. Material properties of epoxy adhesive

Type	Viscosity/(mPa·s)	Hardness/shoreD	Tensile strength/MPa	Bending strength/MPa
YT-CC302S	200-300	90	320	230

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表 3 钢板的力学性能

Table 3. Mechanical properties of steel plate

Type	Elastic modulus/GPa	Yield strength/MPa	Tensile strength/MPa
Q235	206	235	420

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表 4 CFRP板直接拉伸试验结果

Table 4. Direct tensile test results of CFRP plate

Specimen number	Maximum tension/N	Elastic modulus/GPa	Tensile strength/MPa
CFRP-1	24225.4	43	402.86
CFRP-2	24657.5	40	374.22
CFRP-3	26330.7	39	387.20
CFRP-4	29312.6	40	478.96
CFRP-5	30215.4	40	523.39
CFRP-6	22608.1	42	379.23

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表 5 CFRP-钢层状复合结构三点弯曲试验数据

Table 5. Three point bending test datas of CFRP-steel laminated composite structure

Specimen type (2D-CFRP-steel)	a₀/mm	h₁/mm	h₂/mm	P_max/N	f_t/MPa	K_IC/(MPa·m^0.5)
0.2 mm-1	0.190	2.98	1.50	1919.9	412.85	9.91
0.2 mm-2	0.285	3.00	1.51	1959.1	457.04	10.97
0.2 mm-3	0.205	2.99	1.50	1824.3	398.56	9.57
0.2 mm-4	0.194	2.99	1.51	1906.8	409.92	9.84
0.2 mm-5	0.183	2.99	1.52	1963.1	414.96	9.96
0.2 mm-6	0.196	2.99	1.52	1824.3	396.25	9.51
0.2 mm-7	0.249	3.00	1.52	1840.8	419.31	10.06
0.2 mm-8	0.285	2.99	1.53	1818.5	426.80	10.24
0.4 mm-1	0.427	3.01	1.45	1728.2	437.50	10.50
0.4 mm-2	0.418	3.01	1.48	1853.5	469.37	11.26
0.4 mm-3	0.434	3.00	1.51	1769.5	455.93	10.94
0.4 mm-4	0.418	3.01	1.49	1688.2	427.90	10.27
0.4 mm-5	0.372	3.01	1.50	1794.5	442.24	10.61
0.4 mm-6	0.392	2.99	1.51	1733.5	437.09	10.49
0.4 mm-7	0.394	2.99	1.52	1731.8	437.28	10.49
0.4 mm-8	0.432	3.00	1.50	1720.2	440.27	10.57
Notes: a₀—Initial crack depth; h₁—Steel thickness; h₂—CFRP thickness; P_max—Limit load; f_t—Tensile strength; K_IC—Fracture toughness.

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表 6 不同表面裂纹深度的CFRP-钢复合结构极限承载力P_max预测值

Table 6. P_max prediction of CFRP-steel composite structures with different surface crack depths

${a_0}$/mm	Upper limit of ultimate load/N	Lower limit of ultimate load /N	Average of limit load/N	Average decline/%
0	3274.11	2711.28	2992.74	−
0.001	3272.94	2710.31	2991.67	0.04
0.01	3163.20	2619.43	2891.36	3.39
0.1	2532.80	2097.40	2315.14	22.64
0.2	2017.21	1976.75	1996.98	33.27
0.4	1719.44	1678.98	1699.21	43.22

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表 7 不同C_ch值对CFRP-钢复合结构断裂性能的影响

Table 7. Effects of various C_ch values on fracture properties of CFRP-steel composite structures

	f_t/MPa			K_IC/(MPa·m^0.5)
C_ch/μm	33.6	48	62.4	33.6	48	62.4
Average µ	487.24	430.20	395.41	9.78	10.32	10.82
Standard deviation σ	26.96	20.23	16.20	0.54	0.49	0.44
Error/%	13.26	0	−8.08	−5.23	0	4.84

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