碳纤维/环氧树脂复合材料L型接头拉伸失效机制

张琪; 蔡登安; 余章杰; 戴征征; 吴大可; 周光明

doi:10.13801/j.cnki.fhclxb.20220317.003

碳纤维/环氧树脂复合材料L型接头拉伸失效机制

doi: 10.13801/j.cnki.fhclxb.20220317.003

南京航空航天大学　机械结构力学及控制国家重点实验室，南京 210016

基金项目: 国家自然科学基金(52005256)；江苏省基础研究计划(自然科学基金)资助项目(BK20190394)；江苏省博士后科研资助计划项目(2020Z437)；中央高校基本科研业务费专项资金资助(NS2019001)；江苏高校优势学科建设工程资助项目(PAPD)

详细信息

通讯作者:
周光明，博士，教授，博士生导师，研究方向为先进复合材料结构设计及工程问题的计算机建模　E-mail: zhougm@nuaa.edu.cn

中图分类号: TB332
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出版历程
- 收稿日期: 2021-12-31
- 修回日期: 2022-02-23
- 录用日期: 2022-03-05
- 网络出版日期: 2022-03-18
- 刊出日期: 2023-01-15

Tensile failure mechanism of carbon fiber/epoxy composite L-joints

State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

Funds: National Natural Science Foundation of China (52005256); Natural Science Foundation of Jiangsu Province (BK20190394); Jiangsu Post-doctoral Research Funding Program (2020Z437); Fundamental Research Funds for the Central Universities (NS2019001); Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)

摘要

摘要: 设计了单L型(LS)及双L型(LD)两种重量相近的L型接头。采用试验与数值模拟相结合的方式对两种接头的拉伸失效机制进行了研究。通过自行设计的试验夹具在伺服液压试验机上将两种L型接头准静态加载至破坏，分析其破坏机制及应变分布。研究发现，两种L型接头存在不同的失效机制，在破坏阶段单L型接头表现出更好的延展性。单L型接头加载至峰值载荷时，在靠近加载侧的内侧螺栓孔附近首先出现破坏，随后损伤向外侧螺栓孔附近扩展，直至完全失效。双L型接头加载至峰值载荷的50%左右时，L型框体和L型片之间的胶膜首先发生破坏，随后载荷继续增加至峰值载荷时，L型框螺栓孔附近发生破坏，损伤向框体边缘扩展，载荷大幅下降。此外，两种接头的应变随载荷的增加存在不同的变化趋势。采用一种新型复合材料初始失效准则及刚度折减方法，编写用户自定义子程序(UMAT)，结合内聚区模型建立复合材料L型接头的渐进损伤模型。基于ABAQUS软件进行计算，得到接头的预测失效载荷及破坏形式。结果表明：有限元分析所得复合材料L型接头的损伤位置及失效模式与试验吻合，预测载荷与试验值相差较小，证明了有限元模型的适用性。
- 复合材料 /
- L型接头 /
- 失效机制 /
- 有限元分析 /
- 内聚区模型
Abstract: Single-L and double-L composite joints were designed with similar weights. A combination of experiment and numerical simulation was used to study the tensile failure mechanism of the two joints. Two kinds of L-joints were quasi-statically loaded to failure on the servo hydraulic testing machine through a self-designed test fixture, and the failure mechanism and strain distribution were analyzed. It’s found that the two L-joints have different failure mechanisms, and the single L-joint exhibits better ductility in the failure stage. When the single L-joints are loaded to the peak load, the damage first occurs near the inner bolt hole in the loading side, and then the damage spreads to the outer bolt hole until failing completely. When the double L-joints are loaded to about 50% of the peak load, the adhesive film between the L-shaped frame and the L-shaped sheet is first damaged, and then when the load continues to increase to the peak load, damage occurs near the bolt holes of the L-shaped frame, extending to the edge of the frame, the load drops significantly. In addition, the strains of the two joints have different trends with the increase of load. Based on a new type of composite material initial failure criterion and stiffness reduction method, a user-defined material subroutine (UMAT) was written. Combined with the cohesive zone model, the progressive damage model of the composite material L-joint was established. Based on ABAQUS software for calculation, the predicted failure load and failure mode of composite single L-joint and double L-joint were obtained. The results show that the damage position and failure mode of the composite L-joint obtained by the finite element analysis are consistent with the test, and the predicted load is slightly different from the test value, which proves the applicability of the finite element model.
- composite /
- L-joint /
- failure mechanism /
- finite element analysis /
- cohesive zone model

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图 1 单L型接头(LS)几何尺寸

Figure 1. Geometry configuration of single L-joint (LS)

R—Radius; $\phi $—Diameter

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图 2 双L型接头(LD)几何尺寸

Figure 2. Geometry configuration of double L-joint (LD)

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图 3 碳纤维/环氧树脂复合材料单L型及双L型接头试件加载示意图

Figure 3. Loading schematic diagram of carbon fiber/epoxy composite single L-joint and double L-joint

F—Force

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图 4 L型接头试验机加载图

Figure 4. L-joints on test machine

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图 5 单L型及双L型接头应变花位置示意图

Figure 5. Schematic of strain rosette positions of single L-joint and double L-joint

A—Surface A; B—Surface B; C—Surface C; D—Surface D; 1-23—Strain rosettes number

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图 6 单L型(LS1~LS3)及双L型(LD1~LD3)接头载荷-位移曲线

Figure 6. Load-displacement curves of single L-joints (LS1-LS3) and double L-joints (LD1-LD3)

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图 7 L型框螺栓附近破坏情况

Figure 7. Damage near the bolts of the L-frame

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图 8 L型框侧面拐角位置破坏情况

Figure 8. Damage of the side corners of the L-frame

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图 9 LS1和LD1的应变-载荷曲线：(a) L型框正面：面A；(b) LS1中L型框背面和LD1中L型片表面：面B；(c) L型框底面：面C；(d) L型框侧面：面D

Figure 9. Strain-load curves of LS1 and LD1: (a) Front of L frame: Surface A; (b) Back of the L frame of LS1 and surface of the L frame of LD1: Surface B; (c) Bottom of the L frame: Surface C; (d) Side of the L frame: Surface D

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图 10 双L型接头11~18号测点各方向载荷-应变曲线：(a) L型片底部：11号、12号测点；(b) L型片螺栓附近：13号、14号、15号；(c) L型框螺栓附近：16号、17号、18号

Figure 10. Load-strain curves in each direction at measuring points 11-18 for double L-joint: (a) Bottom of L-piece: No.11 and No.12; (b) Near bolts of the L-piece: No.13, No.14 and No.15 ; (C) Near bolts of the L-frame: No.16, No.17 and No.18

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图 11 碳纤维/环氧树脂复合材料L型接头有限元模型约束加载示意图

Figure 11. Schematic of constraint and load for finite element model of carbon fiber/epoxy composite L-joint

RP-1, RP-2—Reference point; U1, U2, U3—Displacement; UR1, UR2, UR3—Rotation

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图 12 单L型接头仿真损伤云图

Figure 12. Simulated damage diagram of a single L-joint

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图 13 双L型接头仿真损伤云图

Figure 13. Simulated damage diagram of a double L-joint

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图 14 各载荷阶段双L型接头胶层损伤云图

Figure 14. Simulated diagram of adhesive layer damage of double L-joints in each load stage

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表 1 碳纤维/环氧树脂复合材料的性能参数

Table 1. Material properties of carbon fiber/epoxy composite

Parameter	Material properties	Value
Parameters	E_x= E_y/GPa	57.7
	E_z/GPa	15^*
	υ_xy	0.07
	υ_xz=υ_yz	0.27^*
	G_xy/GPa	9.7
	G_xz=G_yz/GPa	6^*
Fracture parameters	X_t= Y_t/MPa	609.7
	Z_t/MPa	50^*
	X_c= Y_c/MPa	533.6
	Z_c/MPa	150^*
	S_xy/MPa	141.7
	S_xz= S_yz/MPa	70^*
Notes: E_x, E_y, E_z—Elastic modulus in direction of x, y, z; X_t, Y_t, Z_t—Tensile strength in the three directions above; X_c, Y_c, Z_c—Compress strength in the three directions above; υ_ij, G_ij, S_ij (i, j = x, y, z)—Poisson’s ratio, shear modulus and shear strength for x-y, x-z, y-z plane; *Material data were provided by the manufacture, Avic Aviation High-tech CO., LTD.. The rest data were measured by experiment on the laminates.

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表 2 碳纤维/环氧树脂复合材料L型接头拉伸试验结果

Table 2. Tensile load test results of carbon fiber/epoxy composite L-joint

Specimen number	Failure load/ kN	Average load/ kN	Coefficient of variation/%
LS1	14.225	14.109	4.296
LS2	13.316
LS3	14.787
LD1	14.305	14.215	1.095
LD2	14.344
LD3	13.996

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表 3 碳纤维/环氧树脂复合材料接头性能退化方式

Table 3. Degradation modes of carbon fiber/epoxy composite joint

Direction	Criterion	Material constants to degrade	Stiffness degradation ratio
x	Eq. (1)	$\begin{gathered} {E_x},{\upsilon_{xy}},{\upsilon_{x{\textit{z}}}}, \\ {G_{xy}},{G_{x{\textit{z}}}} \\ \end{gathered} $	0.4407
x	Eqs. (2) and (3)		0.001
y	Eq. (4)	$\begin{gathered} {E_y},{\upsilon _{xy}},{\upsilon _{y{\textit{z}}}}, \\ {G_{xy}},{G_{y{\textit{z}}}} \\ \end{gathered} $	0.4407
y	Eqs. (5) and (6)		0.001
z	Eqs. (7) and (8)	$\begin{gathered} {E_{\textit{z}}},{\upsilon_{x{\textit{z}}}},{\upsilon_{y{\textit{z}}}}, \\ {G_{x{\textit{z}}}},{G_{y{\textit{z}}}} \\ \end{gathered} $	0.001

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表 4 J-116B结构胶材料属性^[25]

Table 4. Material properties of J-116B adhesive^[25]

Parameter	Stiffness		Normal strength $t_{\text{n}}^{\text{o}}$/ MPa	Shear strength $t_{\text{s}}^{\text{o}} = t_{\text{t}}^{\text{o}}$/ MPa	Fracture energy ${G^{\text{C}}}$/${\text{(J}} \cdot {{\text{m}}^{{{ - 2}}}})$
Parameter	$E/{E_{{\text{nn}}}}$/${\text{(MPa}} \cdot {\text{m}}{{\text{m}}^{{{ - 1}}}})$	${G_1}/{E_{{\text{ss}}}} = {G_2}/{E_{{\text{tt}}}}$/${\text{(MPa}} \cdot {\text{m}}{{\text{m}}^{{{ - 1}}}})$	Normal strength $t_{\text{n}}^{\text{o}}$/ MPa
Value	1000	300	20	30	2
Notes：$E/{E_{{\text{nn}}}}$，${G_1}/{E_{{\text{ss}}}}$，${G_2}/{E_{{\text{tt}}}}$—Interface stiffness for three directions, respectively; $t_{\text{n}}^{\text{o}}$，$t_{\text{s}}^{\text{o}}$，$t_{\text{t}}^{\text{o}}$—Interface strength for three directions, respectively.

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表 5 碳纤维/环氧树脂复合材料L型接头部分测点应变仿真值与试验值对比

Table 5. Comparison of simulation and test values of some strain gauges on carbon fiber/epoxy composite L-joint

Strain gauge number	Single L-joint strain at 12 kN		Double L-joint strain at 6 kN
Strain gauge number	Simulation value/10⁻⁶	Test value/10⁻⁶	Simulation value/10⁻⁶	Test value/10⁻⁶
5	1321	1675	53	110
6	1321	1143	53	30
11	−1270	−1446	387	476
12	−1270	−1173	387	393
13	3110	4471	2822	2810
14	3915	331	3300	3703
15	3110	1308	2822	3175

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