Fracture characteristics and the damage constitutive model of 3D printing undulating joint samples based on DIC
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摘要: 受地質構造的影響,巖體工程中經常賦存起伏結構面(如扭轉皺褶),由于形態復雜,目前起伏節理巖體的破裂及損傷本構研究仍不充分. 采用3D打印技術制作不同傾角的起伏節理模型,通過單軸壓縮試驗和數字圖像相關技術(DIC)對起伏節理試樣的力學及破裂特性進行研究,并基于斷裂力學原理,首次提出采用DIC位移場求解節理尖端應力強度因子(SIF:一型SIF,KI;二型SIF,KII)進而探究損傷本構特性的思路. 結果表明:通過分析最小強度確定了起伏節理對試樣的損傷上限為46.6%,起伏節理試樣單軸強度對傾角的敏感性大于平直節理試樣;起裂發生在峰值應力附近,破裂過程可分為破裂路徑上微裂隙的產生和同步貫通,破裂模式表現為多條裂隙張剪組合模式;峰前SIF隨荷載增加而增加,峰后同一荷載下KII>KI,節理左右兩端均勻以剪切裂隙形式擴展;起伏節理對試樣的損傷與傾角呈正弦關系,節理和荷載對試樣的總損傷與應變均大致呈“S”型曲線.
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關鍵詞:
- 起伏節理 /
- 數字圖像相關技術(DIC) /
- 應力強度因子 /
- 破裂特性 /
- 損傷本構
Abstract: Due to the influence of geological structures, various forms of joint structural planes are present in rock mass engineering. The undulating structural planes, such as a torsional fold surface, are unique geological structures. These structures affect the stability of rock masses and cause potential hazards to rock mass engineering. Because of their shape complexity, the research on the fracture and damage constitutive law of rock mass with undulating joints is not thoroughly conducted. Undulating joints with various dip angles were fabricated using three-dimensional printing technology. The uniaxial compression test and digital image correlation (DIC) technology were used to study the mechanical and fracture characteristics of undulating joint specimens. Based on the principle of fracture mechanics, an idea was proposed to use the DIC displacement field for solving the stress intensity factor (SIF: type one KI and type two KII) at the joint tips and to study the damage constitutive law. The results show that the upper limit of undulating joint damage to specimens is determined with 46.6% through the minimum strength analysis. The sensitivity of uniaxial strength to a joint dip angle of undulating joint specimen is greater than that of a straight joint specimen. The fracture initiation occurs near peak stress. The fracture process can be divided into the initiation and synchronous penetration of microcracks on the fracture path. Additionally, the fracture mode shows a combination of multiple tension and shear fractures. The SIF increases with loading at the prepeak stage, and the cracks propagate in shear fracture at the joint left and right tips in the postpeak stage because KII>KI under the same stress. The undulating joint damage to the specimen with the dip angle is in a sinusoidal curve form. The relationships between the total damage coupled by joint and load with strain are all “S” curves.-
Key words:
- undulating joint /
- DIC /
- stress intensity factor /
- fracture characteristics /
- damage constitutive model
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表 1 不同變形階段節理尖端SIF
Table 1. SIF of joint tips at various deformation stages
SIF/(MPa·m0.5) Deformation stages Joint angle, α/(°) 0 30 45 60 90 KI_l Compaction 0.26 0.23 0.35 0.38 0.30 Elasticity 0.27 0.35 0.51 0.77 0.45 Yield 0.36 0.35 0.70 1.00 0.52 Peak 0.52 0.43 0.91 1.10 0.58 Post peak 0.32 0.57 1.25 1.53 0.64 KII_l Compaction 0.35 0.26 0.31 0.42 0.34 Elasticity 0.37 0.41 0.71 0.83 0.53 Yield 0.43 0.41 0.83 1.10 0.62 Peak 0.41 0.49 0.85 1.18 0.69 Post peak 0.36 0.66 1.34 1.62 0.77 KI_r Compaction 0.10 0.06 0.03 0.04 0.07 Elasticity 0.11 0.09 0.06 0.09 0.10 Yield 0.13 0.10 0.07 0.11 0.11 Peak 0.12 0.10 0.08 0.12 0.13 Post peak 0.11 0.14 0.16 0.16 0.12 KII_r Compaction 1.36 0.22 0.09 0.11 0.24 Elasticity 1.42 0.32 0.16 0.21 0.33 Yield 1.74 0.32 0.18 0.26 0.37 Peak 1.56 0.37 0.19 0.28 0.42 Post peak 1.48 0.52 0.21 0.35 0.40 表 2 擬合曲線對應公式系數
Table 2. Corresponding formula coefficient of a fitting curve
SIFP/σmax a0 a1 b1 w KI_r/σmax ?0.02906 0.03421 0.3566 0.007055 KII_r/σmax 6.444 ?6.374 0.8606 ?0.1331 KI_l/σmax 0.03958 ?0.02441 ?0.01834 3.365 KII_l/σmax 0.04643 ?0.02781 ?0.01712 3.31 www.77susu.com -
參考文獻
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