含孔试样孔周破坏的应变局部化特征

Strain localization characteristics of perforation failure of perforated speci-mens

  • 摘要: 抽采钻孔孔周裂纹漏气是瓦斯抽采浓度低的原因之一,裂纹是由应变局部化带演变形成。为探究应变局部化带特征与宏观裂纹之间的关系,开展含孔试样单轴压缩破坏试验,利用数字散斑相关测量方法获取试样表面破坏图像序列及其破坏过程中的全场应变,分析不同阶段应变局部化带的分布特征,应力变化及能量演化过程。结果表明:根据受力与分布特征,应变局部化带分为主拉伸(T1),法向剪切(NS),第二主拉伸(T2)及倾斜剪切(IS),宏观主裂纹是由T2,NS和IS应变局部化带贯通所形成。形成T1和T2应变局部化带的主导因素是拉应力,NS应变局部化带是由拉应力与压应力共同作用形成,IS应变局部化带的主导因素为压应力。T2,NS和IS应变局部化带的能量积累分别是T1应变局部化带的2.2,1.8和1.6倍,加载至应变的73.6%时,T1应变局部化带率先释放能量,产生微破裂,应力峰值后,T1应变局部化带持续释放能量,T2应变局部化带的能量变化呈下降、上升和下降趋势,NS与IS应变局部化带的能量变化为上升和下降,说明试样破坏过程为局部化带之间的能量调整,能量的调整与局部化带演化相关联。结果表明了含孔试样破坏过程中孔周应变局部化带的特征规律,揭示了钻孔应变集中带区域易发生斜交裂隙的本质。

     

    Abstract: The leakage of peri-hole crack in drilling hole is one of the reasons for low gas drainage concentration,and the crack is formed by strain localization zone.In order to explore the relationship between strain localized zone characteristics and macroscopic cracks,the uniaxial compression failure test of the pore-containing specimens was carried out,and the digital speckle correlation measurement method was used to obtain the surface damage image sequence of the specimen and the full field strain during the failure process.The distribution characteristics,stress changes and energy evolution processes of strain localized zones at different stages were analyzed.The results show that the strain localized zone is divided into main tensile (T1),normal shear (NS),second main tensile (T2) and oblique shear (IS),macroscopic main crack according to the force and distribution characteristics.It is formed by T2,NS and IS strain localized zone penetration.The dominant factor for forming the T1 and T2 strain localization zone is tensile stress.The NS strain localization zone is formed by the combination of tensile stress and compressive stress,and IS strain localization.The dominant factor of the belt is compressive stress.The energy accumulation of the T2,NS and IS strain localized zones is 2.2,1.8 and 1.6 times of the T1 strain localized zone,respectively.When loading to 73.6% of the strain,the T1 strain localized zone releases the energy first,resulting in micro-fracture and stress peaks.Afterwards,the T1 strain localization zone continuously releases energy,and the energy change of the T2 strain localization zone decreases,increases and decreases,and the energy change of the localized zone of NS and IS strains increases and decreases,indicating that the nature of the damage process is the whole energy adjustment of the sample,the energy adjustment is related to the evolution of the localized bands.The results show the characteristics of the strain localization zone around hole during the failure process of the sample containing hole,and reveal the nature of the inclined fracture in the strain concentration zone of hole.

     

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