基于磁特性参数的细观尺度下物理短裂纹扩展表征

Characterization of Physical Short Crack Growth at the Meso-scale Based on Magnetic Property Parameters

细观尺度下,物理短裂纹扩展阶段占整个疲劳寿命的比例通常很高,扩展速率相对于长裂纹更快,对材料已经构成潜在危险。传统的无损检测技术不能有效地检测物理短裂纹等早期隐性损伤,因此,引入能够检测早期隐性损伤和应力异常集中的金属磁记忆技术对物理短裂纹扩展进行表征探索。针对细观尺度下物理短裂纹扩展特异性带来的参数表征难题,在细观实验基础上研究基于磁特性参数的物理短裂纹扩展表征规律与表征模型。以Q235钢三点弯曲试件为试验材料,采用TSC–5M–32金属磁记忆检测仪并配合LWD–1000长距离显微镜,原位观测并记录裂纹扩展演化过程及磁特性参数,获得在细观尺度下磁特性参数对物理短裂纹扩展的表征规律。结果表明:当长度为0~100μm时,短裂纹相互竞争,其扩展速率不断增加并出现峰值,磁场强度法向分量Hp(y)由–26.875 A/m变成7.250 A/m,出现极性跳变;切向分量Hp(x)由–17.24 A/m变成–68.78 A/m,绝对值大幅增加。当长度为100μm时,短裂纹汇聚形成主裂纹,裂纹扩展速率放缓,Hp(x)和Hp(y)剧烈跳变,合成ΔHp出现峰值。当长度为100~1 000μm时,主裂纹扩展速率再次变大且不断增加,Hp(y)与Hp(x)再次出现极性跳变与绝对值大幅增加,合成ΔHp呈上升趋势。进一步地,在实验数据基础上,基于磁特性参数分别建立细观尺度下短裂纹扩展速率、剩余寿命的表征模型,验证结果表明,模型中短裂纹扩展速率、剩余寿命的最大相对误差分别为6%、4%,为工程实际中早期隐性损伤的表征与评价提供了思路。

In the mesoscale, the proportion of the physical short crack stage in the whole fatigue life is usually high. And the expansion rate of the physical short crack is faster than that of the long crack. This phenomenon has caused potential damage to the material. The early hidden damage such as physical short cracks cannot be effectively detected by traditional nondestructive testing technology. Therefore, metal magnetic memory technology, which can detect early hidden damage and abnormal stress concentration, is introduced to explore physical short crack propagation.Aiming at the difficult parameter characterization problem caused by the specificity of physical short crack growth at the mesoscale, the characterization laws and model of physical short crack growth based on magnetic property parameters(MPPs) were conceived based on micro-experiment. The experiment material is Q235 steel. LWD–1000 long-distance microscope and TSC–5M–32 Tester of Stress Concentration were carried out to observe in-situ the evolution process of crack growth and MPPs, respectively. The characterization laws of MPPs were obtained for physical short crack growth at the mesoscale. The experimental results show that when the length is 0~100 μm, the growth rate increases continuously and peaks occur. The normal component Hp(y) changed from –26.875 A/m to 7.25 A/m with a polar jump. The tangential component Hp(x)changed from –17.24 A/m to –68.78 A/m with a significant increase in absolute value. When the length is 100 μm, the short cracks converge to form the main crack, the crack growth rate slows down, Hp(x) and Hp(y) jump sharply and ΔHp peak appears. When the length is 100~1 000μm, the growth rate of the main crack increases again and increases continuously. The polarity of Hp(y) changes, the absolute value of Hp(x) increases greatly again, and the ΔHp shows an increasing trend. Furthermore, based on the MPPs, the characterization models of short crack growth rate and remaining life at the mesoscale were established, respectively. The verification results show that the maximum relative errors in the model are 6% and 4%, respectively, which provides a new idea for the characterization and evaluation of early hidden damage in engineering practice.