基于SEM、分形理论分析谷子籽粒内部裂纹产生与扩展机理

Analysis of the mechanism of internal crack generation and propagation in millet grain based on SEM and fractal theory

[目的]谷子籽粒在收获、贮藏及加工过程中由于内力或外力会产生裂纹,籽粒内部裂纹严重影响其贮藏期、降低发芽率,内部裂纹的形成主要由热湿内应力和机械作用引起,为了探明谷子籽粒内部裂纹的产生与扩展机理。[方法]采用SEM(扫描电镜)技术对谷子籽粒内部裂纹及淀粉颗粒拍照,结合分形理论、能量平衡理论分析计算谷子籽粒内部裂纹在不同扩展模型下的分形维数、临界扩展力(Gc)及扩展速率。[结果]谷子籽粒形成新的表面积的大小与输入能量的大小有关。当谷子籽粒内部局部应力大于等于8γG ky-1dg-1/2时,籽粒内部形成微裂纹。沿淀粉颗粒断裂、穿淀粉颗粒断裂、沿淀粉颗粒与穿淀粉颗粒耦合形式断裂的分形维数分别为:1.262、1.365、1.255,而分叉扩展的分形维数与分叉角呈正相关。对于同一γ值,沿淀粉颗粒与穿淀粉颗粒耦合扩展的Gc为6.85γ,沿淀粉颗粒扩展的Gc为7.086γ,穿淀粉颗粒扩展的Gc为11.652γ,分叉扩展的Gc为250γ,所以,耦合扩展的微观裂纹最容易发生,穿淀粉颗粒和分叉扩展的微观裂纹较难发生。同一种扩展模型,谷子籽粒内部淀粉颗粒的直径越大,微观裂纹的扩展速率越快;同一直径的淀粉颗粒,耦合扩展的速率最快(0.095 V0~0.309 V0),沿淀粉颗粒扩展的速率次之(0.09 V0~0.299 V0),分叉扩展的速率最小(0.0001 V0~0.01 V0)。[结论]研究分析了谷子籽粒内部裂纹产生与扩展机理,其研究成果可以为谷子贮藏、加工、种子发芽率等方面研究提供参考依据。

[Objective]During harves,storage and processing of millet grains,internal or external forces will cause cracks.The internal cracks of the grains seriously affect the storage period and reduce the germination rate.The formation of internal crack is mainly caused by thermal and humid internal stress and mechanical action.Present study was aimed to investigate the mechanism of crack generation and propagation in millet grain.[Methods]The fractal dimension(D),critical propagation force(Gc)and propagation rate(V)of internal cracks of millet grain were calculated by using SEM(scanning electron microscope)to photograph the internal cracks and starch particles of millet grain,combined with fractal theory and energy balance theory.[Results]The size of the new surface area formed by the millet grain was related to the input energy.When the internal local stress of the millet grain was greater than or equal to 8γG ky-1 dg-1/2,microcracks are formed inside the grain.The fractal dimensions of breaking along starch particles,breaking through starch particles,and the form of two breaking ways coupling were1.262,1.365 and 1.255,respectively.The fractal dimension of bifurcation extension was positively correlated with bifurcation angle.For the sameγvalue,the Gc for extending along the starch granule coupled with the penetrating starch granule,extending along the starch granule,penetrate starch particles,and bifurcation extension were 6.85γ,7.086γ,11.652γ,and250γ,respectively.Therefore,the microcracks of coupling propagation were most likely to occur,while microcracks of penetrating starch particles and bifurcation propagation were more difficult to occur.In the same expansion model,the larger the diameter of starch particles inside the millet grain,the faster the expansion rate of microcracks.The starch particles of the same diameter had the fastest coupling expansion rate(0.095 V0~0.309 V0),followed by the expansion rate along the starch granules(0.09 V0~0.299 V0);the rate of bifurcation expansion was the smallest(0.0001 V0~0.01 V0).[Conclusion]The mechanism of crack generation and propagation in grain of millet was studied and analyzed.The results can provide reference for grain storage,processing and seed germination rate studies.